A dental implant is a device that is capable of replacing the functions of ... period in which soft tissue healing after surgery and proper osseointegrated must take ...
BIOPHYSICAL ANALYSIS OF THERAPEUTIC ULTRASOUND RADIATION EFFECT ON OSSEOINTEGRATION OF DENTAL IMPLANT
Thesis Submitted to The Medical Research Institute Alexandria University In fulfillment of The Degree of M.Sc. in Bio-Medical Physics. By
AHMED AHMED FOUAD ELMIKATY B.D.S. Faculty of Dentistry Alexandria University
Department of Biophysics, Bio-engineering and Medical Statistics Medical Research Institute Alexandria university 2002
Supervisors Prof. Dr. M. Sherine El Attar Professor of Prosthodontics Prosthodontics department Faculty of Dentistry Alexandria University
Prof. Dr. Moustafa M. Mohamed Professor of Biophysics Biophysics and Bio-engineering Department Medical Research Institute Alexandria University
Prof. Dr. Michael Moussa Mosaad Professor of Biophysics Biophysics and Bio-engineering Department Medical Research Institute Alexandria University
Prof. Dr. Mohamed M.Fata Professor of Maxillofacial and Plastic Surgery Maxillofacial and Plastic Surgery Faculty of Dentistry Alexandria University
CONTENTS
I.Introduction.
1
II.Review of literature.
14
III.Aim of the work.
61
IV.Material & Method.
62
V. Results.
78
VI. Discussion.
94
VII.Referances.
101
VIII. Summary& conclusion. IX. Arabic Summary
ACKNOWLEDMENT
After thanking Allah, I wish to express my deepest gratitude and appreciation to my supervisors for their guidance and encouragement.
My sincere thank and deep gratitude to Prof. Dr. Moustafa M. Mohamd Professor of Biophysics, Medical Research Institute, Alex. University.For his unfailing help, kindness and expertise. I am deeply indebted to Dr. M. S. El-Attar professor of prosthodontics department, Faculty of Dentistry, Alex, University. For his helpful supervision, consecutive comment and his endless understanding and patience. Special acknowledgment must go to Dr. Mohamed Fata Professor of Maxillo-Facial, Faculty of Dentistry, Alex. University for his helpful discussion and valuable comment during preparation of the research. I express my deep,endless appreciation and gratitude to him. Also, many special thanks to Dr. Michael Moussa Professor of Biophysics, Medical Research Institute for his meticulous supervision, his uncompromising desire for perfection and his tremendous experience.
INTRODUCTION Functional
prosthodontics , for the edentulous and sometimes
Partially edentulous patients with severe residual ridge resorption and atrophic denture supporting areas, has been fraught with compromises and complications, which were frustrating for patients and prosthdontists (1)
alike . The atrophied ridges are the common cause of poorly fitting dentures as it decreases the denture bearing area and is the cause of floating mandibular denture and the dropping upper one. In addition to the reduced stability, retention and impaired masticatory efficiency, the ill fitting denture increases the resorption of the alveolar bone. Dentists have attempted to solve the problem by various methods of treatment: vestibuloplasty, ridge augmentation and implantation. Vestivuloplasty is indicated in some cases to increase the size of the denture bearing area and the height of residual alveolar ridge
(2)
.
Ridge augmentation is indicated when the alveolar ridge is very thin and liable to fracture with slight trauma
(3)
.
Researches for dental implants began so may years ago, (4)
Mandel, trace research practitioners back nearly 5.000 years to Egypt and Hesira-the great one, chief of toothers and physicians, perhaps the first (5)
physician of the mouth .
In 1952, Branemark
(6)
embarked on studies that, years later, resulted
in the introduction of his designs and treatment concepts following an intensive prospective study of cylindrical threaded endosteal implants. This technique practically resulted in a direct bone implant interference termed “osseointegration”
(7)
.
The use of dental implants has gained acceptance and popularity since its introduction. Many studies show that, implants can be very effective and have good long term success rates. Implants can be used to replace missing single teeth and partial or complete edentulism. Knowledge of dental implants may help the adult population discover an alternative for the replacement of their teeth. Patients unsatisfied with conventional prosthodontics now have an option with dental implants to improve function, comfort and esthetics. Self esteem and quality of life can be improved with dental implants
(8)
.
A dental implant is a device that is capable of replacing the functions of natural tooth or teeth. Osseo integrated implants need stable interfacial conditions for bone to develop and according to Alberktsson
(9)
any movement in the early healing stage may shift thee stimulus towards more soft tissue cells. Fibroblasts forming soft tissue and osteoblasts forming bone tissue are both dependent on the same primitive mother cells. Alberktsson
(9)
explains that, soft tissue inevitably form at the interface of
newly inserted implants irrespective of controlled surgical technique and otherwise excellent implantation condition. For proper bone integration, this soft tissue must be replaced by bone in the case of oral implants. Two stages loading with the implant resting in bone during an incorporation phase of at least 3-4 months is sufficient to ensure osseointegration in most cases. Osseointegration of dental implant is essentially a close opposition between living bone and the surface of functioning implant. Achieving such state depends upon healing period, after (unloaded) implant placement of 3-8 months before fabrication of final prosthesis. During this stage,
the
implants (10)
osseointegration
are
to
be
left
totally
unloaded
to
attain
.So, induction of soft tissue to become hard forming
bony tissue will be our subject of concern. This will minimize the period between implant insertion and fully healing of bone around it to become osseointegrated implant.
With the introduction of the biological concept of osseointegrated the use of dental implants has become a predictable and frequently used addition to comprehensive planning and treatment of partially or fully edentulous patients
(11)
.
Healing Period After reviewing the problem of edentulism, mainly in the mandibular arch, a specific seemed to exist concerning the rehabilitation of ( 12 )
these patients utilizing implant over denture
.
A period of undisturbed healing was addressed by many authors, however this problem was not solved properly yet. Healing period is the period elapsing from the first stage surgery till (13)
loading of definitive implants by final prosthesis
. This is a very critical
period in which soft tissue healing after surgery and proper osseointegrated must take place. In the advocated protocols of implant over dentures, after first stage surgery, patients were instructed for using a soft diet. One week later, the sutures were removed and after one more week the lower denture was relined with tissue conditioning material, and patients were allowed to use their dentures. The tissue conditioning material is replaced every two weeks till the end of the four moths healing period. Accordingly, these appears the problems encountered with the healing period, namely the psychological and physiological upset of the patient for using soft diet for two weeks followed by using a poorly
efficient and poorly fitting transitional denture, throughout the healing period. Moreover, soft tissue healing after first stage surgery was often accompanied by sloughing and incision line opening and implant head dehiscence. Also the transitional transmucosal prothesis stresses on the definitive implants which affects proper osseointegrated. Disappointment experienced by patients during the healing period after implant insertion created difficult prosthodontic challenges. Inspite of the efforts of oral surgeons and prosthodontisis to rehabilitate edentulous patients`, still awkward transitional period presents a problem due to lack of efficient well stabilized temporary prosthesis
(14)
.
Temporary restorations using titanium mini implants, which are loaded into immediate splinted function, had a major role to play as a multidirectional
three
dimensional
radiopaque
guidance
enhancing
accuracy of final implant placement. Prevention of micromovement during the healing period is a major factor associated with the long tem clinical success of endosseous dental implants together with other factors such as bone quality, bone quantity, the use of postoperative antibiotics, a traumatic bone preparation and experience of the surgeon.
Another consideration in planning the treatment of an edentulous arch case for implant prosthetic restoration is controlling the transmucosal load placed by the transitional denture over the tissue covered implant sites. Since the bone surrounding the implant is an active biological tissue that undergoes periodic resorption and remodeling in response to the stress of loading, the load to the bone surrounding the implants should be reduced to prevent or minimize the loss of supporting bone around the implants. This study was mainly concerned with the healing period. For decades, scientists have been using electromagnetic and sonic energy to serve medicine, but aside from electro surgery, their efforts have fox used on diagnostic imagining of internal body structure, particularly in the case of x-ray, magnetic resonance imagining (MRI) and ultrasound systems.
Lately,
researches
have
begun to
focus
acoustic
and
electromagnetic waves in a whole new light, turning their attention to therapeutic-rather than diagnostic application. Low intensity ultrasound has been shown to facilitate the healing of fresh fractures. Frankel et al
(15)
used low intensity ultrasound for the
treatment of tibia non-union. This study concluded than, treating tibia non-
union with low intensity ultrasound compare favorably with those of invasive, operative treatment. There are numerous prospective studies starting that low intensity pulsed
ultrasound
accelerates
callus
formation
in
fractures
and
16)
pseudoarthoses ( . Scaphoid fractures are very often undiagnosed and take about 10-12 (8)
weeks to heal when treated by cast. Clinical studies by Meyer et al
demonstrate the acceleration of the healing process in the tibia and distal radius fractures by low intensity ultrasound. This therapy could also accelerate the healing of fresh, stable, scaphoid fractures. Self-paired study was conducted to assess the efficacy of pulsed low intensity ultrasound for the treatment of established non-unions in Germany and Austria. Pulsed low intensity ultrasound was found to be effective in healing established non-union without any other treatment This situation has been made using rabbits’ ears
(18)
(17)
.
. Tissue was
excised from the pinnae of both ears; one side was irradiated with ultrasound while the other was treated as a control. If the ultrasound was pulsed 2ms on 8ms off at 0.5 W cm-2, the best increase in healing was seen, although 0.1Wcm-2 delivered in the continuous mode gave
similar effect
8 W cm-2 pulsed 1 ms on: 79 ms off result in a\n increase
in lesion size. All three treatment regimes had the same –averaged intensity. For pulsed ultrasound.0.5 W cm-2 (2ms:8ms) gave more rapid healing than 0.25 W cm-2 ,1.0 W cm-2 , 1.5 W cm-2 , 2.0 W cm-2 or 4.0 W cm-2 pulsed in the same fashion. (19)
Harvey et al
demonstrated that when primary diploid human
fibroblasts were irradiated with 3 MHz ultrasound at an intensity of 0.5 W / cm-2 in vitro, the amount of protein synthesized was increased. Electron microscopic examination of irradiated cells revealed that, in comparison with control cells, there were more free ribosome, more dilatation pf rough endoplasmic reticulum more auto vacuoles, and more damage to lysosomal membranes and mitochondria. Subsequent word form the same group
(20)
has shown that cavitations may involved in producing this simulation of collagen synthesis. Increased collagen synthesis has also bee shown as a result
of ultrasonic
irradiation
of
fibroblasts
in
vivo
(21)
.
.Ultrasound has been shown to simulate the formation of granulation tissue
(22)
.
Drastichova et al.
(23)
have studied the effect of ultrasound (0.85 W
/cm-2) on the strength of scares in guinea pigs. Incisions on the back were rd
irradiated on the 3 and 4th days after cutting .The breaking strength of the
scars was 189% of that in controls in one series, and 271% in another. Dyson et al
(24)
have studied the effect of ultrasound (3MHz, 0.5W cm-2 )
on the healing of cryosurgical lesions in rats. The lesions were irradiated on days 0,1,2,3,5 and 7. The ultrasonically treated scar tissue was found to have a breaking strength of 109% of mock irradiated scars at 1 month, the breaking strength pf treated scars was 42% of that of normal skin at the same site. It is disappointing that, despite the widespread use of therapy ultrasound very few large-scale clinical trails have taken place. One condition, however, for which a trial has been carried out, is that of chronic (25)
varicose ulcers on the leg
. Treated ulcers were irradiated with pulsed 3
MHz ultrasound(2ms:8ms) at a SATP intensity of 1.0 W cm-2 after twelve treatments (thrice weekly for four weeks) insonated ulcer had an average surface area of 66.4±8.8% of their area at the beginning of treatment, where as control ulcers had an area 91.6±8.9% of initial area. Temperature rises in the treated area were measured and found to be less than 1°C. Such a temperature rise, if obtained by other means, would be insufficient to account for the observe simulation of healing, and the mechanism is thus believed to be non-thermal. In a separate study it has been shown that ultrasound may increase the take of skin grafts at trophic ulcer sites
(26)
.
Ultrasound is used with some success to soften and increase the elasticity of scar tissue and contractures
(27)
. The evidence for this is again
anecdotal, but it seems to be a fairly universal finding. The mechanism by which this may occur is unclear, but may relate to the combination of mild heating. It is thought that ultrasound can be used to some benefit in reducing oedema associated with soft injuries. The treated experimentally induced oedema in rats with 0.5 W/ cm -2 pulsed ultrasound at a range of frequencies (0.75MHz, 1.5 MHz and 3.0 MHz). A frequency-dependent effect was found, 0.75 MHz being the only effective frequency. The pulsing regime (2 ms: 8 ms or 2 ms: 2 ms) was not important. The machine producing this resolution of oedema is not known. It may be due to increased blood flow, or to localized tissue changes due to acoustic streaming. Until more rigorous scientific studies of these and of other reported effect are undertaken, the mechanism by which therapeutic benefit, if any is obtained will be the subject of speculation and it will not be possible to optimize treatment using an ultrasound of interaction mechanism. The repair of soft tissue injuries and bone injuries show some similarities.
Both processes
have
inflammatory,
proliferative,
and
remodeling phase, it is this similarity, and the fact that the cells involved initially are the same type, that has prompted the investigation of the potential of ultrasound in bone healing, although little has been published on this topic. It has been found in experimental studies of fracture in rat fibulae that ultrasonic irradiation during the inflammatory and early proliferative phases accelerate and enhanced healing. Direct ossification, with little cartilage production, is seen. Treatment in the late proliferative phase, however, was found to be disadvantages, cartilage growth being simulated, with delay to bony union
(28)
In their study, it was found that 1.5 MHz was
more effective than 3.0 MHz (0.5 W cm -2 SATP, 2 ms: 8 ms, 5 min), and so a non thermal effect is suggested, although the precise mechanism still needs elucidation.
Literature Review
History of dental implants is ancient; the search for replacement of natural dentition has occupied human interest since long time. An intraosseous implant of animal teeth carved of ivory was performed on court women of the ancient Egyptian.(29) Evidence of early trials to restore lost teeth by implantation of different teeth like material had been reported.(30) Excavation of pre-Incan skills in Ecuador and discovering gold inlays in prepared cavities and performed implantation and reimplantation of teeth. Oral implantology can also trace its history to Middle-East. In 1862, Gaillardot, discovered a prosthetic appliance doting to 400 BC near the ancient city of Sidon.(31) Endosseous oral implantology, truly begin in the 19th Century, Maggilio, in 1809, inserted a gold implant into a freshly extracted tooth socket.(32) (33)
Hodosh (1960)
began a study in an attempt to find a mean of
replacing the human natural dentition by plastic tooth. Fractured upper second bicuspid was replaced by acrylic resin tooth implant; the extracted tooth was flasked and exactly duplicated in sterile heat-processed acrylic resin.(34)
The modern era of implant dentistry most definitely began in the late 1930 with the work of Venable, Strock, Dahl, Gershkoff and Goldberg(35). In 1937, Venable developed the cost Co-Cr-Mo alloy (Vitallium). An initial use of Venable’s Vitallium was screw type dental implant by Lwin and Moses, Strock beginning in 1939. Subperiosteal implant development began with Dahls report 1941 and his subsequent patent. Implantology, a rather new but acceptable term, is the study of the placement of foreign material into or onto the jaw bone to replace or support artificial dentition(36). In 1952, Branemark(37) provided an introduction of his designs and treatment concepts, following an intensive study of cylindrical threaded endosteal implants, this technique practically resulted in a direct boneimplant interface termed “Osseo integration”. The insertion of any given foreign material in a bone sites is a multi- factorial problem that involves the implant, the adjacent bone, tissue and the interface between the implant and tissue. ONeal and Edge
(38)
presented concepts of fibro-osseointegration,
osseointegration and biointegration through a variety of implant models and surgical techniques. Fibro-Osseo integration defined as the connective tissue encapsulated implant within bone. This type of
integration was an early histological finding in implant and resulted from early types of implant materials, possibly because of lack of primary stability, premature loading of implant and/or traumatic surgical procedure causing heat induced bone necrosis. Osseointegration of implants need stable interfacial condition for bone to develop.
Implant classification Dental implants may be classified according to their position into the following: 1. Sub-periosteal implants implants placed beneath the periosteum, 2. trans osteal implants implants placed through the full thickness of the lower jaw, 3. Endosseous. Implants implants placed into the bone of either jaw 4. Endodontic stabilizer implant placed into root canal of tooth, 5. Mucosal inserts implant placed intramucuosal and 6. (Temporary Implant)(39).
1. Intramucosal inserts This type is a titanium stud retained in the denture by a grooved circular base, and is projected through an incision in the mucosa that has been made to accommodate the insert. Weiss and Judy (1973)(40), showed that the tissue receptors sites heal into a keratinized collagen that
maintains the protective integrity of the oral mucosal membrane and provides a positive mechanical lock to retain the prosthesis Guaccio 1980(40)stated that the intramucosal inserts into the oral mucosa that in effect help to plug the denture, thus clasping the tissue providing immediate
added
retention,
stability
and
patient
comfort.
The
intramucosal inserts are mushroom-shaped attachments placed in the maxillary denture that, inserted into previously prepared receptor sites in the palatal mucosa(41). 2. The endodontic implant The endodontic type is totally embedded within bone and has the distinct advantage of not communicating with the oral cavity(42). An endodontic implant is a smooth and/or threaded pin implant that extends through the root canal of a tooth into a periapical bone and is used to stabilize a mobile tooth(43). They are either a biocompatible metal., or single crystal sapphire rod, that extends beyond the apex into bone and supplements the existing periodontal support. The metal is either co-cr alloy (vitullium) or titanium. The single crystal sapphire stabilizer is chemically and structurally identical to single crystal aluminum oxide. Fragiskos et al., (1981) (44) presents a new endodontic stabilizer implant device that can be used immediately after inoculation of large periapical cyst.
3. The subperiosteal implant The subperiosteal or an epiostal dental implant that is placed beneath the periosteum and overlying the long cortex(45). The framework for a subperiosteal implant is cast from a surgical grade co-cr alloys (Vitallium), sometimes be coated with hydroxyappetite and is designed to rest precisely on the mandible or the maxilla, when the periosteum and soft tissues have been reflected (46). Recently, through a computer assisted design and manufacturing a computerized tomogrophy (C.T scan),can be taken, transferred to magnetic tape placed into computer and an exact replication of both mandible, maxilla will be generated. This new technique makes the subperiosteal implant more easily and in one stage procedure(47). The double surgical technique is more accurate than one day technique which leads to improper adaptation of the metal., framework to the bone which may be the early cause of failure of this type (48). Bailey et al
(49)
(1988) stated that the subperiosteal implant has
clinical manifestations of parasthesia, incision line separation, implant framework exposure and inflammation. 4. The ramus frame implant The ramus frame type is an implant design that consists of a horizontal intra-oral supragingival abutment in the form of a bar and endosteal implant body segments that are placed in the rami and
symphysis area as one section. It has been used to support a complete mandibular denture(50). Turner in 1990 defined the ramus frame implant as one-piece implant used in the edentulous mandible. The tripodal design offers exceptional stability, being supported by symphysis anteriorly and the two ascending rami posteriorly. A frame continuous with the endosteal portion lying above the gingival supports the patients mandibular prosthesis(51). With conventional dentistry, vestibular extension or ridge augmentation can not be satisfactory
(52)
.
The ramus frame assembly system may be the treatment of choice. It is indicated in cases of moderate to sever mandibular alveolar atrophy. Insertion requires about one hour and is relatively atraumatic (53). 5. The intraosteal implant The transosteal type is an implant that penetrates both cortical plates and passes through the full thickness of alveolar bone it is used exclusively in mandible(54). Small 1986, stated that transosteal implant are an implantable orthopaedic device, designed to restore the function of the edentulous mandible that deformed as a result of aging bone or congenital deformities. There are two main types of transosteal implants, these are the mandibular staple bone implant associated with the name of Bosker, and
these implants are made of vitallium and gold respectively. Both of them need, an external incision in the submental region, and have a metal., bone plate with retentive pins that penetrate the full thickness of the mandible in the parasymphysis region to support a removable type of prosthesis. In general, it is recommended that 9-11 mm of bone height should remain for this form of implant(55). Transosteal implant is an osseointegrated implant designed for the severely atrophic mandible or for use after mandibular trauma or tumour surgery. The transmantibular implant is placed between the two mental foramen for a submental approach(56). Small 1986 summarized the indications for a mandibular staple bone plate, as followed, severe or moderate mandibular bone deficiency, mandibular bone loss due to trauma or tumour surgery, the denture patient who has great difficulty chewing with a lower denture, congenital edentulisme (extradermal dysplasia and cleidocranial dysostosis) and T.M J instability( 57). 6. An endosseous implant Endosseous implant is a device placed into the alveolar and/or basal bone of mandible or maxilla and transecting only one cortical plate.(58) It is the most common type of implant in use nowadays They are sub-classified according to their physical shape into, blade form, root form which includes spiral form, pin form, disk form and anchor form
Blade shape implant Wedge shaped implant which is narrow buccolingnally, vents are incorporated into design to allow tissue in-growth. The anchor blade implant was presented as shoulder less modification to prevent bone resorption around shoulders of blade. Haln (1990) (59) started, the blade vent implant after several years. Resorption of the alveolar crestal bone down to and beyond the implant shoulder occurred creating a direct communication between the infrastructure and the oral cavity leading to implant failure as a result of periodontal involvement. Root form Implants In many designs, some are conical, where as others are cylindrical some are screws while other is hollow perforated cylinders known as hollow baskets. There are also many combination forms where the features of the hollow cylinder and the screw thread appeared together. The metals include commercially pure titanium (C P titanium), alloys as titanium-6 Alumunium-4 Vanadium. Implant surface may be roughened or smooth, metal implants may be coated with other materials such as tri-calcium phosphate or hydroxyl-appetite. Some implants are installed in a single stage procedure in which the implant is placed in the jaw bone and immediately protrudes into mouth, while other are placed in a two stage procedure, at the first stage, the implant is buried in the bone and the overlaying mucosa is closed, and the second stage the implant is
exposed and an extension or abutment is attached. This abutment protrudes into the mouth for the construction of the prosthetic component (60) (62)
. Lew 1970(61), created the narrow, long self tapping solid threaded
screw. These types gave better seal of the apex at same time. The implant were made of Chrome-Cobalt-Molybdenum alloy (Vitallium) . Alberktsson (1986) (63) introduced the commercially pure titanium threaded screw implant and the term osseointegration was introduced to the implant field for the first time said that a reliable osseointegration of a bone implant is dependant on the simultaneous control of several parameters as material biocomptability,
implant design, Surgical
technique and loading conditions. Failure of only one of these previous stated factors will lead to either primary or secondary failure or implant loss, with no matter how well the control of others.
Weinlaender (1991)(64) defined osseointegration as a firm, direct and lasting connection between vital bone and implants of defined finish and geometry, with no interposed connective Tissue between implant fixture and bone. Alberktsson et al, (1994)(65) defined osseointegration as a process in which clinically asymptomatic rigid fixation of the implant is maintained in bone during functional loading, root form may include:
a) Spiral implant The development of spiral implant which is a simple post of titanium of which the spiral part was placed in an artificial socket. These posts were used in many number and permitted either the replacement of single tooth or the fabrication of a bridge . b) Pin implant This type of dental implant is consisting of three tantulum pins locked together with cold-cure acrylic to form a tripodal that was extremely retentive. However in many cases, the pin implants were easily removed from the mouth of patient with the diverging pins till attached to prosthesis(49). c) Disk implant Is a unique two stages design resembles an 18th century candle stick, and uses a facial or buccal placement with special osteotomes (64). d) Anchor implant Was introduced by Cranin and Dennison,1971(40). It was a shoulderless implant, to solve the problem of bone resorption around the blade vent shoulder. Its design has two basic shapes one for the maxilla and one for the mandible, each offers a choice of three lengths, the metal, and exposure occurred after several years
Implant materials
The materials used for implants includes: Polymers, carbons, ceramic and various metal, Gold, silver and lead were the metal used until 1939,when
the
discovery
of
Chrom-Cobalt-Molybdenum
alloy
(vitallium). Opened up a new area in surgical repair and prosthesis.
Hodosh et al, (1970)(32) replaced dentition by the use of acrylic resin tooth implant and formed a new bone formation in two horizontal channels drilled through the root of polymer implanted.The single crystal sapphire which is a new ceramic material and direct bone interfaces occurred at most regions of implants. Titanium was discovered in 1789 by W. Gregor(43) it is present in nature and forms 0.6 % of earth s crusts, but not in pure state always bound with other elements.
Titanium implants were chosen for its
biocomptability, lightweight, Height strength and high mechanical properties when used in loaded functional dental or orthopaedic application(67). Titanium surface is highly polished, clinically it appears to be less plaque retentive than nature teeth(68). A wide variety of materials which has been used for the implants, but he found only a few promote osseointegration and biointegration, titanium, and titanium alloy has been the most widely used.
Implant designs
A variety in implant design has been the most extensive in the area of root form device. Many concepts have been expanded to include many types: Screws, plates, roots, baskets, Cylinders and Conical. Some have holes others include serrations or micro porosities or both. Most are intended to optimize mechanical form transfer along the bone on soft tissue interface(69)(70) . In biointegrated system, the titanium body received a hydroxy appetite coating, which permits bone to biochemical bond to the implant surface( 71).
A smooth, cylindrical implant, may require an adhesive bond for satisfactory performance but a screw shape provide a form of interlocking with the bone on a microscopic scale, that allows full development of the strength of the bone in shear and compression. The screw type has been considered more appropriate than smooth type for distribution of stresses to surrounding bone(72). Branemark (1983)(37) concluded that the screw design of an implant which is made of titanium is the best design and could be used in any place in the oral cavity after experimental and clinical experience of 20 years.
The finite element technique is a reliable method for stress analysis and accordingly can be used as an aid to implant designer. The finite element analysis, indicates that stresses distribution within bone surrounding an implant when the bone is bonded to the implant many not be biomechanically beneficial when compared with bone that is only closely adapted to an implant “Osseointegration”(73). Uses of implants Implants are used to accomplish the following: Free-end saddle area to eliminate partial denture , replace the longer or sometimes un-widely removable denture , gain additional retention for a full removable denture , stabilize loose periodentally involved tooth , stabilize fixed bridge , replace terminal abutments , and provided external mechanical retention , for the facial prosthesis in oro-facial cancer. (74)(75) In restorative therapy in patient with reduced periodontal tissue support and loss of mostly their teeth, reconstruction in patient with scleroderma which developed multiple external and internal root resorption, so all teeth
had
to
be
removed,
Also
treatment
of
severe
class
edentulous patient (76). Rusmussen (1992)(77)summarized the indications for implant treatment as follow, Severe morphologic compromise of denture supporting areas that significantly undermine denture retention, poor oral mascular cooridination , low tolerance of mucosal tissues , parafunctional
habits leading to recurrent soreness and instability of prosthesis ,Unrealistic prosthodontic expectations, active or hyperactive gag reflexes, elicitaded by removable prosthesis, psychological inability to wear a removable prosthesis , even if adequate denture retention or stability is present , and unfavorable number and location of potential abutments tooth loss to avoid involving neighboring teeth as abutments. The contraindications of implants as Follow: Systemic disorders as generalized disease of heamatopoeitic system, rheumatic disease, immune deficiencies, as well as psychotic syndromes, alcohol and drug abuse, metabolic disease such as poorly controlled diabetus mellitus, after irradiation of the jaw. Bone implantation should be performed at the earliest, one year after irradiation and heavy smokers form a relative contraindication too.
Bio mechanics Biomechanics is a marriage of engineering with dental, medical fields, it concerns with the response of biological tissues to applied load. In biomechanics the tools and the methods of applied engineering mechanics are employed in search of structure – function relationship in living materials.
a) Principles of biomechanics i.
Mass
: is an intrinsic property of matter which is measure the
gravitational attraction of body of matter experiences The standard system (S I) of units for mass is kilogram (And the pound in the U S customary system of uni(78). ii.
Force : Newton′s second law states that the acceleration of an object is directly proportion to the net external Force exerted upon it and inversely proportional to its mass or
Force = mass *
acceleration(79). The force is an influence which tends to change the state of motion of an object. In the (S I) units is measured by Kg. m /sec 2 renamed (Newton) N. Force is a vector quantity, meaning both magnitude and direction that are required to specify it completely Forces may be described as Normal (compressive and tensile) and Shear. Normal forces act parallel to the surface(78). iii.
Moment : The moment of a force about a point, tend to produce rotation or bending about that point. The moment defined as a vector, M, whose magnitude equals the product of the force magnitude multiplied by the perpendicular distance (also called moment arm) from the point of interest to the line of action of force This imposed moment load is also referred to as a torque or
torsional load, and may be quite destructive with respect to implant system. iv. Force transfer: - Stress: when a force acts on a body, a resistance is developed to this external force application. Stress is the internal reaction to the external force and is equal in magnitude and opposite to direction to the applied external force; both the force and the stress are distributed over a given area, so that stress in a structure is designed as the force per unit area on
Stress = Force \ Area
The unit of stress in (S I) system is a Pascal which is one Newton (N) per square meter (m2) The unit of stress in the (U S) customary system is pound (lb) per square inch (in2) or Psi all stresses can be resolved into three basic types which are: Tension, compression and shear. Deformation or strain: A body undergoes deformation when a force is applied to it. Strain is described as the change in length occurring per unit length of the body when a stress is applied (78) or
Strain = deformation / original length
Strain is dimensionless measure of geometric change .The amount of strain will differ with each type of material subjected to stress as well as the magnitude of the stress applied. Experimental observation has also demonstrated that lateral strain also accompanies axial load within an elastic range, these two strains , are proportional to one another as described by
Poisson's ration" μ" for
tensile loading
μ = Lateral strain \ Axial strain
The material mechanical properties described provide for the determination of implant - tissue stress - strain behavior according to established relationships in solid mechanics theory (Mish C.)(80)
Young’s modulus: The stress-strain relationship of a material and its supporting tissues studied by measuring an applied load and the resultant deformation. Hooke′s low of elasticity of solid materials states that There′s a linear relation between the forces applied and the deformation of a solid object. When an elastic body is experimentally subjected to an applied load, a load-vs-deformation curve may be generated. If the load (force) values are divided by surface area over which they act and the change in
the length by the original length, a classic stress-strain curve is produced. The slope of the linear portion (elastic portion) of this curve is referred to as the modulus of elasticity, its value is indicative of the stiffness of material under study. Impact load and Impulses: When two bodies collide a very small interval of time, relatively large reaction forces develop. Such a collision as described as impact. Upon impact the two elastic bodies are compressed until their mass centers attain the same velocity, then thy move apart. To explain this further, let us define linear momentum as the product of mass and velocity. Impulse force “I” over
a time internal is
equal to the change in momentum of a body (particle) during time interval.
I = mVf – m VI
I
= implant of force,
Vf
= velocity (final),
m VI
= mass. = initial velocity.
vi. Biomechanics in implant Biomechanics is important in oral implant design
because the
teeth on Jaw perform biomechanical activities during the mastication In order to restore masticatory function any implant design must be able to:
- Survive the various loads applied during the force of mastication. - Be of a shape that will allow to be supported within the Jaw , and , transmits loading to the surrounding tissues with no delitirious effects(84). So in addition to the importance of the material used for dental implants , the design of implant is also very important .
Several studies utilized three-dimensional finite element analysis, to study, the stresses around various root form implants and they conclude that: 1- Implants with constricted necks of their prosthetic abutments transmitted high level of stress to the supporting bone. On the other hand implants with the same diameter heads and cervical portions of the implants, transmitted moderate levels of stresses the crestal alveolar bone. 2- Under lateral loading , excessive detrimental stresses were transmitted to the supporting bone in most of the implants investigated . 3- Presence or absence of threads and surface coating, which is significant for implant retention during the healing period and osseointegration had little to no effect on magnitude of stresses transmitted to the surrounding bone(81).
Role of animal models on dental implant research Animal testing plays a major role in assessing the safety and efficacy of dental implants. Animal models are indicated in three major areas
of
implant
science
research.
Toxicity
testing,
general
biocomptability assessment, and the evaluation of the final form of the implant in the site intended for use. Animal models studies have also dealt with biomechanical evaluation of implant sites. Brunski and Hipp have designed instrument attain for measuring vertical force component on bridged titanium implant in dogs. In another study of implant in dog Jaws for two years, the accuracy of a finite element model was assessed against bone load-displacement, other investigators used histological sections of the Jaw-implant site to construct finite element models. (Natiella .J.R 88) (82) Although there is no current consensus about the best animal model for dental implant research, dogs have been used as dental model in periodontal, And osseous repair studies.
Interfacial biomechanics using animal models Both interfacial shear strength and interfacial stiffness are important interfacial biomechanical properties, which are measured and analyzed to answer and solve the problem of search of the both structural and functional measures of performance with the respect to the osseo-
integration , and fibro-osseointegration concepts.
To measure them,
researchers have placed cylindrical implants (representing various candidate fixation rationals) , transcortically or intramedullarly in animal bones ,and allowed for various healing time Then samples are harvested and “ push out” test performed, each sample subjected to cyclic load using ramp-type load a curve represent the force versus displacement is obtained, the slope of the linear portion of the curve was determined and then divided by the implant-bone interface surface are (normal or measured in some ways) to express “Interfacial stiffness” ,then the samples was subjected to loading to failure, i.e necessary force parallel to the cylinder’s axis to push the cylinder out of bone. This force was then divided by the implant-bone interfacial surface area to express (83).
“Interfacial shear strength” At this point, it is apparent that the biophysiology, biomaterial, and the biomechanics, as well as the design of the implant are very important for the long term success of all dental implants.
Role of Electron microscopy: (84)
Branemark et al, (1983)
examined the interface zone of the
inorganic implants, the use of transmitted electron microscopy (T.E.M) approaches have refined descriptions of the tissue- implant interface. Budd et al, (1992) used (T, E, M) to define the structural elements involved in the process of osseointegration , and they reported that factors that enhance osseointegration include a-traumatic surgical procedures with minimal heat generated, close fit of the implant fixture to the formed socket and, low drilling speed (under 800 r p m ) and abundant effective irrigation with use of the chilled saline, precision drilling system , implant material , surface characteristics of the implant and type of recipient bone also the appropriate timing of placing the implant in function supporting a prosthesis is an essential in maintaining the osseo-integration process. (85)
Davies (1994)
stated that osteoconduction which is the
mechanism by which the implant surfaces contact bone growth, may be of two different fundamental types, one depends on migration of the osteoblast through a three dimensional connective tissue matrix to arrive at the implant surface or the migration of the osteoblast directly from bone into the implant surface. The biologic reaction inherent in osseointegration involves bone healing and bone remodeling.
Bone reaches the implant surface by one or both types of osteoconduction . In either case the bone / implant interface will be comprised of a calcified, but collagen-free-matrix analogus to the cement lines formed between old and new bone. In the absence of excessive mechanical forces this cement line matrix will be reformed whenever a bony remodeling unit comes into contact with the implant surface.
Role of radiographs
The use of radiographs is one of the methods for evaluation of dental implant success and osseointegration. The diagnostic radiographs in dental implantology as follow:
Plain film radiography The Plain film radiography types are: a) Intra oral radiography periapical and occlusal for initial
phase of case
evaluation. b) Cephalometric radiography for the pre surgical evaluation c) Inclination of maxillary and mandibular alveolar inclination postoanterior cephalometric X ray for lateral projections.
d) Panoramic radiography is unique in that the focus of the projection is in
the vertical plane and that controlling the vertical dimension is
different from that in the horizontal planes. Film tomography
Film tomography is done to obtain clear image of structures lying within the plane of interest Digital radiography: The main type used in implant is the intraoral radiography which is a digital technology allows for the rapid acquisition of intraoral images and their
post
acquisition
enhancement
their
storage,
retrieval
and
transmission to remote sites. Computed tomography C .T Computed tomography is used since 1970. It produces crosssectional versions of the jaws; it is less time consuming than film tomography with no super imposition. The presence of metal causes image degradation but not osseointegrated implants perhaps because of the smooth contours.
Magnetic Resonance Imaging Magnetic Resonance Imaging is used recently with implant, Svenson and Palmgvist in 1996(86). used the detailed narrow beam (D .N. B.) technique
with the scanner multimodel X -ray for the assessment of dental severely resorbed ridges as an alternative to conventional intraoral radiography. The marginal bone height was scored in relation to the threads on the implants
VISUAL CHARACTERISTICS The diagnostic quality of the radiograph is directly influenced by two visual characteristics of the radio- graphic image called density and contrast. RADIOGRAPHIC DENSITY Radiographic density refers to the degree or gradation of “blackness” on a radiographic film. It depends on the amount of radiation reaching a particular area on the film and the resulting mass of metallic silver per unit area. As the reader will recall, the silver halides of the emulsion
that have been sensitized by radiation are changed by the
developing agents into particles of metallic silver, which appear black because of their finely divided state. The greater the amount of x-ray energy that reaches the film, the greater the degree of blackening on that area of the film. Areas where relatively few or no x-ray photons reach the film will appear gray or translucent on the processed radiograph. After the exposed film is processed, the film is viewed by placing it in front of an illuminator or view-box. It is the variation in the amount of light
passing through the film that identifies the image seen. The heavier the deposit of black silver masses, the greater the quantity of light absorbed (and not transmitted) through the emulsion, and the darker the area appears. The darker areas on the film are regions of the anatomical part of the body that freely let the x-rays pass through to expose the film and are called radiolucencies. A high degree of radiographic density produces a dark film; a light film has a thin or low degree of radiographic density. Measuring Density Radiographic density is measured by an instrument called a densitometer. This instrument indicates the relationship between the intensity of the light beam of an illuminator as it strikes one side of a given area of a radiograph (called incident light intensity) compared with the light transmitted through the radiograph (transmitted light intensity) . Importance of Density Density is extremely important in the diagnostic quality of a radiograph because it carries information . Visible detail of the radiographic image is not possible without density. However, there a correct amount of density to a radiograph because too much density (dark) will conceal information, and not enough density (light) will destroy detail in the lighter areas.
The desirable degree of radiographic density cannot be fixed as permanent, because one dentist may prefer a certain degree of density while another may prefer a greater or lesser density for the same region. The degree of radiographic density may be considered to be largely a matter of individual preference. Of course, one does not want a film that is too dark or too light—the right amount of density is needed to visualize the anatomical structures accurately. In dental radiographs of correct density, the dentist should be able to see a faint outline of the soft tissues in edentulous spaces or distal to the molar teeth when the radiographs are examined in the manner habitually used. Implant-bone contact The extent of implant-bone contact is critical to initial stabilization of the implant and osseointegration. Factors associated with the long term clinical success of endosseous dental implants include bone quantity, bone quality, the use of pre and post operative antibiotics, atraumatic bone preparation, the experience of the surgeon, and the prevention of micro-movement during the healing period(88). The quantity and quality of the residual bone in which the implant is placed in a factor that the treating dentist can not control , yet the density of available bone in an edentulous site may be the most important
component in treatment planning , surgical approach , healing time , and progressive loading during fabrication(89). The macrogeometry of implant, i.e amount and orientation of surface area available to transmit loads , has a very strong influence of the nature of the force transfer at tissue implant interface (90).
BACKGROUND IN MEDICAL ULTRASOUND
Ultrasonic is the study of sound waves of frequencies higher than the upper limit of the human hearing (frequency region above 20 kHz). The upper frequency limit for the propagation of the ultrasonic waves is thermal lattice vibrations beyond which the material cannot follow the input sound. The smallest wavelength of sound is therefore twice the interatomic distance, and this is approximately equal to 2x10-10 m for metal. This occurs at a frequency of 1.25 x 1013 Hz, which corresponds, to the twenty-first harmonic of a 10-megacycle quartz crystal. At such high frequencies, ultrasonic wave periods become comparable with relaxation time. High-amplitude ultrasonic waves are sometimes called sonic, and hypersound refer to waves having frequencies greater than 1013 Hz (91). HISTORICAL OVERVIEW: The first effect to produce ultrasonic were made almost a hundred years ago by Rudolph Koenig
(91)
, one of the pioneers in acoustical
research, who sought to discover the highest pitched sound that humans can hear. As a result he constructed various devices. Ultrasonic, as a technology, can probably be said to have had its birth during World War I in a laboratory in Toulon, France. Their
professor Langevin P (92) was diligently searching for ways and means to combat the submarine menace which threatened France at the time. In the course of investigation he designed and built a high power ultrasonic generator which used quartz crystals as the active element. With this equipment he was able to produce vigorous cavitations in a large wooden tank of water and to perform various spectacular experiments (piezoelectric effect). He developed several techniques for enhancing it. The next significant group of experiments on ultrasonic was performed by Wood and Loomis in (1927)(92). These investigators observed agglomeration of particles, emulsification, dispersion of collides, atomization of liquids, the fragmentation of small and fragile bodies, the destruction of red blood corpuscles, and various effects due to frictional heating. They used quartz disks vibrating at resonance as sources of ultrasonic energy. The disks submerged in oil and then excited by applying about 50000 volts to them. Developments in the next decade centered on finding ways and mean to use sound waves as a supplement to X-rays in the inspection of material. Efforts were confined to using continuous waves, to learning about the transmission of sound across interfaces and through structures, and to devising satisfactory display systems. Progress was relatively slow.
The picture began to change during World War II with the practical development of what has proved to be a much superior method of detecting flows, namely, the use of the pulse-echo technique. There has been a continuing steady increase since 1964 in the amount of flow-detection work that is being done ultrasonically and it is now a well-established and accepted method of nondestructive testing. ULTRASOUND IN MEDICINE In the application of ultrasound in biology and medicine, the generation and detection of ultrasound depends on the piezoelectric effect, in which the mechanical energy is converted to electrical energy and vice versa. The device, which performs this conversion, is called the ultrasonic transducer.
BACKGROUND ON ULTRASONIC BIOPHYSICS Ultrasonic biophysics is the branch of science that attempts to seek logical and quantitative understanding for a series of observation in which exposure to ultrasound is found to lead to various specific modifications in living cells and tissues. In the following sections we present, physical phenomena which are known, or thought, to account for the various types of link between ultrasonic exposure and biological effects. Broadly speaking such links can be classified as either thermal or non-thermal.
Thermal Mechanisms(92): The energy transported by an ultrasonic beam is attenuated as it passes through any viscous medium. If the intensity of a plane travelling wave is Io at the point of origin, x= 0, it has a reduced intensity I (x) at a distance x from the origin, giving by the expression I (x) = Io e -x
(1)
where is the intensity attenuation coefficient which is made up of two components, that due to absorption, a, and scattering, s. Energy scattered out of the main beam may be absorbed elsewhere in the tissues. To obtain an estimate of the temperature rise that may occur in tissues due to the attenuation of an ultrasonic beam, let us assume that all the energy removed from the primary beam leads to local tissue heating. That is, we assume that attenuation is entirely due to absorption. The rate of heat deposition per unit volume, Q, is given by the equation. Q = I
(2)
If no heat is lost from this volume by conduction, convection or radiation then: Q = C
dT dt
Where is the density of the medium, C (dT/dt) is the rate of temperature rise.
(3) is its heat capacity, and
It is possible to estimate the effect that the thermal conductivity of the medium has on the final temperature achieved at equilibrium. The temperature difference maintained at equilibrium between the centre of a highly absorbing sphere of radius R (at a temperature To), and its surrounding ( can be given by QR 2 To – T = T = 2K
(4)
where K is the thermal conductivity. From equation (2) Q=I, then
T =
I 2K
.R 2
(5)
At a bone- tissue interface in the body, longitudinal waves propagating in the bone may be partly converted to transverse propagation and then rapidly absorbed in the soft tissue. This may lead to local heating at the periosteum-a region rich in nerve endings. If the temperature rise is sufficiently great, pain may be felt and permanent damage is possible.
Non-Thermal Mechanisms (92): 1- Cavitations: Many definitions of cavitations are to be found in the literature. Coaklay and Nyborg (1978)
(93)
define cavitations as the activities, simple
or complex, of bubbles or cavities containing gas or vapour, in liquids or
any media with liquid content. Apfel (1980)
(94)
defines cavitations as the
formation of one or more packets of gas (or cavities) in liquid. In this section, attention is concentrated on acoustic cavitations, which is defined as the formation and activity of gas – or vapour- filled cavities in a medium
exposed
to
an
ultrasonic
field. Common
terminology
distinguishes two types of bubble activity, namely stable cavitations and collapse cavitations. Stable cavities oscillate in response to the ultrasonic pressure field. The bubble radius varies about an equilibrium value, and the cavity exists for a considerable number of acoustic cycles. Acoustic streaming and high shear stresses may be associated with such stable cavitations activity. Collapse (or transient) cavities . Oscillate in an unstable manner about their equilibrium radius, grow to several times this equilibrium size, and collapse violently. This activity takes place over a few cycles of the sound field. High temperatures and pressures may be associated with collapse and may have important practical consequence of energy transfer to such forms as emission of light and formation of reactive chemical species.
Time
Applied Acoustic Pressure
Time
Bubble Radius a- Stable cavitations Applied Acoustic Pressure
Time
Time Bubble Radius
b- collapse transient cavitations Figure (1): Radius-time curves for cavitating bubbles in an ultrasonic field.
2-Formation of cavities (92) The origin of cavities that grow and become active under the action of an externally applied acoustic field has been the subject of some controversy. Large bubble of radius R, will rise in a fluid at a velocity defined by Stokes viscous drag and the buoyant force, given by
2 o gR 2 V= 9
(6)
where is the liquid density , is the liquid viscosity and g is the specific gravity .
Smaller bubbles, on the other hand, may dissolve.
Consider a bubble of radius R, with internal pressure Pb. If the hydrostatic pressure in the liquid is P, the difference in pressure across the bubble surface is given by Pb- P=
2 R
(7)
where is the surface tension. It is seen that the excess pressure within the bubble increases with decreasing bubble radius. The cavitations formation depends on: i-Ultrasonic intensity. As the ultrasonic intensity within a sample is increased from zero, initially there is no indication of cavitations; but, as the intensity crosses a threshold level, cavitations begins. As the intensity is increased further, the transient cavitations threshold is passed, and
cavitations activity becomes stronger. The level of cavitations activity reaches a plateau and may decrease at higher intensities. Morton et al. (1982)(95) irradiated cells in suspension with 1 MHz ultrasound and the sample was monitored. It was found that, there was a clear threshold at which cell lysis was seen, membrane damage was found, and the cells began to lose their reproductive integrity. ii-Ultrasonic frequency. In general, as the ultrasonic frequency is increased, a higher intensity is required to produce cavitations. iii- Ultrasonic pulsing condition. The dynamics of the growth of bubbles and their maintenance at resonance at a resonant or near resonant size are related to ultrasonic pulse duration. iv- Ambient pressure. The peak of acoustic pressure required to induce cavitations in air-saturated water increased with increasing ambient pressure. Morton et al (1983)( 96) have demonstrated the effect of ambient pressure on cavitations- associated loss in reproductive ability in cells irradiated with 1MHz ultrasound in suspension. This study showed the way in which increasing the ambient pressure by 0.5 to 3 atmospheres affects the threshold of loss of survival. v- Sample gas content. The acoustic pressure required to produce cavitations in a liquid falls as the gas content of that fluid is increased.
vi- Ambient temperature. There is linear relationship between natural logarithm of the acoustic pressure amplitude required to produce cavitations and reciprocal temperature. vii- Medium viscosity. The threshold acoustic pressure for cavitations increases with nearly linear with increasing medium viscosity. 3- Cavitations Thresholds (92) Cavitations thresholds (upper and lower) are usually described in terms of the parameters PA (acoustic pressure amplitude), PO (ambient pressure), RO (initial bubble radius), and ω (angular frequency of the ultrasonic radiation). Two types of thresholds may be involved in acoustic cavitations, namely the stable cavitations threshold and the transient cavitations threshold. A condition of stable cavitations threshold is reached when the flow of gas during both phases of the pressure cycles is equal while collapse cavitations thresholds have been made for the upper and lower thresholds that define the range of acoustic pressure over while collapse cavitation may occur.
4- Cavitations monitoring: Several methods are available for monitoring cavitations activity in fluids. These falls into three main categories, namely the measurement of
the acoustic emission from cavitating bodies, analysis of chemical reactions produced within the medium, and direct imaging of bubbles. i-Acoustic emission.
Cavitating bubbles act as secondary sources of
sound, the emission of which can be monitored and analyzed. A hydrophone in the vicinity of cavitations activity can pick up the acoustic signals, which may then be displayed on a spectrum analyzer or fed through frequency filters to select specific frequencies. At low intensities (sub- threshold) only the drive frequency, fo, is detected. As the intensity is increased the emission spectrum from the medium becomes more complex. ii- Impedance change. As bubbles form in an irradiated fluid, the acoustic properties of that fluid are altered. The change in acoustic impedance of the medium reflects the amount of cavitations activity within it. iii- Sonoluminescence. The phenomenon of sonoluminescence is the emission of light from media irradiated with ultrasound, and is generally thought to be an indicator of transient cavitations activity. iv- Sonochemistry. One indicator of cavitations activity within an irradiated sample is the occurrence of chemical reactions typical of the presence of energy-rich species such as ionized and excited molecules, ions, and free radicals. These chemical reactions are thought to be indicative of collapse (transient) cavitations and are attributed to the
electrical and thermal effects. Although the chemistry is not understood completely, it is generally believed that, in the presence of acoustic cavitations, water undergoes the reaction: H2O H+ OH v- Direct imaging methods. Optical detection of bubbles using high speed photography is a useful method of viewing cavitations in optically transparent liquids, but is of no real use in opaque media such as biological tissues. Bubble formation in tissues can be monitored using a pulse-echo ultrasonic imaging system. Until recently, the available cavitations detection methods did not lend themselves to the study of opaque structured tissues. For this reason, much of the cavitations work reported on such tissues had either been carried out in plant tissues, in which direct observation has been possible, or has relied on circumstantial evidence from histological study of mammalian tissue which have been excised and fixed after irradiation. Non-Thermal and Non-Cavitational Mechanisms(92). Non-thermal and non-cavitational mechanisms by which ultrasound interact with tissue may be of considerable importance in determining and controlling either the therapeutic and surgical actions of ultrasound or any possible damage which it may cause. In this section we discus these mechanisms.
1- Radiation pressure:An ultrasonic field will exert forces at the boundaries of the container of the propagating medium, and also on any inhomogeneities lying within that field. These forces have two components- an oscillatory component having the same frequency as the sound beam, and with a time average of zero, and a steady component that has a non-zero time average. This steady component is known as the radiation force, and it arises from nonlinearity in the sound field. This force is periodic in half a wavelength and thus could be responsible for a phenomenon of blood cell stasis in which circulating erythrocytes in small blood vessels, when subjected to an acoustic standing wave field, are seen to clump into apparently static bands oriented normally to the field direction. In blood cell stasis, erythrocyte bands form at nodes.
2- Acoustic streaming :Acoustic streaming is the unidirectional circulation that may be set up by an acoustic field in a fluid. The velocity gradients associated with this fluid motion may be quite high, especially in the vicinity of boundaries within the field, and the shear stresses set up may be sufficient to cause changes and\or damage. Streaming may account for the increases in heat transfer, acceleration of rate processes, and stripping of cell
surfaces that can occur in biological tissues as a consequence of irradiation with ultrasound. 3- Shear stress :The development of unidirectional fluid circulation (streaming) in an ultrasonic field has been described in the previous section. Since the induced fluid velocity is spatially non-uniform, velocity gradients exist within the field. Objects within streaming fields are thus subjected to shear stress. Two types of velocity gradient are set up in a fluid. The velocity gradients due to acoustic streaming are “steady” and relatively invariant with time. The periodic nature of the ultrasonic beam means that oscillatory velocity gradient exit at boundaries within the field. The steady stress exerted on a boundary due to unidirectional streaming around a spherical vibrating obstacle of specific radius. Although the steady stress may be an order of magnitude smaller than the oscillatory stress, it acts for a longer time at the boundary, and is more significant factor in producing cellular effects. 4- Acoustic micro-streaming around bubbles The oscillations of bubbles in a sound field set up eddying motions of the fluid immediately around the bubble. Because of the small scale of the streaming, it is called micro-streaming. High velocity gradients can be set up and thus significant shear stress may act on boundaries within the
region. This can be an effective mechanism for the damage caused in a cavitations field. Biological molecules and cells situated near bubbles will be subjected to the shearing forces generated within these streaming fields.
AIM OF THE WORK The present work aims to: 1- Evaluation of the role of the ultrasound in accelerating the osseointegration around dental implant. 2- Study the effect of ultrasonic intensity in accelerating the osseointegration. 3- Study the effect of the healing period in accelerating the osseointegration. 4- Study the biomechanical properties of the interfacial layer between implant and bone at different conditions. 5- Study the ultrastructure of the interfacial area
Materiel and Methods I -Selection of experimental animals: Three dogs, weighting approximately 20 kg, each, were chosen free from any anomalies or general contraindicated conditions.
II- Titanium implant: Uncoated titanium implant used in this study (IMTEC Implant system: IMTEC CORPORATION - ARDMORE, OKLAHOMA 737401, U.S.A.). The IMTEC implant can be obtained in varying lengths (10, 13, 15, 18 and 20 mm), and various diameter ( 3.3- 3.75-4.0and 4.75 mm) The fixture can be obtained alone or premounted. The implant could be obtained coated or self-tapping. The IMTEC kit used in this study included the following: 1-
Cylinder root form, self tapping, endosseous fixtures with nominal
dimensions of each were 3.3 mm outside diameter and 10 mm overall length 2- Cover screw 3- Marking drills. 4- Internally irrigated trispade drills. 5-
Mallet: a resilient tipped seating instrument which is essential in
cylinder Internaly irrigated trispade drills. 6- The motor ( physio—despenser 3000, louvag A/C SAl Ltd, CM 9400 Roschach / Switzerland ) used, had internal irrigation, high torque. speed reduction with autoclavable hand piece.
III- Surgical step: Using standard aseptic technique, dogs were anaesthetized with (thiopental sodium) (30 mg / kg) (EIPICO PHARMACEUTICAL — EGYPT) using an intravenous solution of Ringer’s lactate. 1-The surgical areas were shaved, infiltrated locally with 2% lidocaine containing I: 10.000 epinepherine and pointed with an antiseptic solution” Povidone Iodine”. 2- Incision was done within skin, exposure of the superficial fascia, leading to the muscles of the thigh then a blunt dissection of the muscular layer reaching the femur figure (3). 3- 3 holes were drilled in the right femur of each dog and 1 hole is made on the left femur as control figure (4,5,6). Using low speed (15.000 RPM), high torque, and internal irrigated hand piece, sterile saline was used for internal and external irrigation while preparing implant sites. 4- Drill holes were made bilaterally in the medial cortex at a right angle to the long axis of the shaft with an internal distance about 5 cm between holes figure (7).
The holes were prepared so as the implants penetrated in a single cortex . This area was calculated. Using a mathematical formula =d.h where “d” was the diameter of the implant “h” was the thickness of cortex at the prepared site. Insertion of implant fixtures in the prepared sites was preformed according to the following groups according to the time and intensity of the ultrasound waves using model csl-1ultrasound therapy instrument. Irrigation with saline in site of surgery to ensure a complete cleanness of field then, tattooing over each implant was done using Talbot iodine painting. The flap was repositioned and sutured using number 2.0 silk sutures (surgisilk DW 2922 , ltd, U.K) The animals received a prophylactic intramascular injections of (Cephapirine sodium) (CEPHATREXYL - BRYSTOL MYER SQUIBB - EGYPT). 15 mg/kg for fire dogs after surgery. All animals were allowed immediate unrestricted weight- bearing and left for a healing period.
IV- Ultrasound therapy application: i- Instrumentation: In the present work an ultrasonic therapy instrument (Figure 9) model CSL was used. This instrument operates at a frequency of 0.8 MHz and can be used selectively in continuous wave or pulsed wave mode operation. In the present work, ultrasonic intensity of 1,2,3 w/cm2 at
pulsed wave mode with duty ratio 1/3 was used to enhance the bone healing around the implants figure .
II - Sonocation procedures of implants: On the tattooed site responding to each implant coated with ultrasonic gel which is a combination of liquid paraffin. The probe was directed in close contact to the skin of the femur which was previously shaved. Pulsed waves were directed to the tattooed site of each implant in a gentle rotary motion. We can change the intensity of the radiation pulses as desired to each implant. In our study we used the small probe (0.5 cm2) and pulsed ultrasonic wave mode to avoid undesirable radiation effects to neighboring implant. The 12 implants were divided into three groups. Each group has 4 implants as following: Group one (first dog): Three implants were inserted on the right femur of the 1st dog (experimental group) & one implant was inserted as control at the left femur. The three implants of the experimental group was exposed to 1,2, 3 w/cm2 peak intensities , respectively, for a sonocation time of 2 min. day after day for 2 weeks. The ultrasonic prop was moved continuously during the sonocation time in a rotary motion to give a homogenous
ultrasonic exposure around the implant. The control insert was not exposed to any insonation.. This dog was sacrificed after 2 weeks. Group two (second dog): 3 fixtures were inserted on the right femur of the 2nd dog as experimental group& one fixture was inserted as control at the left femur. This experimental group is exposed to insonation for 4 weeks ranging from 1,2,3 w/cm2 in a rotary motion for 2 minutes for the first, second and third fixture, respectively. The dog was sacrificed
after 4
weeks Group Three: 3 fixtures were inserted the right femur of the 3rd dog. One fixture was inserted as control at the left femur. This experimental group was exposed to insonation for 8 weeks with 1-3watt/cm2 intensity of ultrasound in the same manner. The dogs will be sacrificed after 8 weeks.
The animals were sacrificed following a healing period of 2-8 weeks respectively according to each experimental group. The femoral bones were retrieved, followed by isolation of each inserted fixture carefully, removal of the endosteal surface on top of them, for proper seating in the push-out test machine.
V-Radiographic measures: The primary purpose of the diagnostic radiography is to transfer information from an-xray beam to eye-brain complex of the radiologist. In the present work to measure the bone density of the interfacial area around the implant, x-ray were taken for the implant in place and its surrounding bone. The degree of radiographic density (the amount of film blackening) depends entirely on the amount of radiation reaching the film and therefore on the amount of x-ray attenuated from the beam by the tissue through which they pass. The samples of each group, of each dog, were radio-graphically photocopied for further investigations. So we had radiographs
each
femur
Figure
(8).
Radiographic
films
type
cephalometric were used, to ensure the integrity of implants within bone, follow up of the osseointegration process and to measure the thickness of cortex at the point of implantation.The X-ray photographic films obtained from different group were scanned using digital scanner of a resolution 600 ppi (pixels per inch) which has the ability to convert images into electronic impulses and transfer it to a personal computer for imaging processing. As the body organs produce different gray appearance on an x-ray film, it is possible using computer techniques to measure these differences and display them in varying shades of gray. The panoramic xray films were examined with paint shop program to measure the gray
scale as a measure to identify the bone density formed in the interface area. Each pixal has an address (X-Y coordinate value) and a grayscale value which is an integer from 0 (darkest) to 255 (lightest). The gray scale data from 20 points around each implant at the interfacial zone and 20 points from bone away from implant were collected and averaged. The density of the new bone formed around each implant relative to nature bone density was calculated as the ratio of the gray scale at the two regions around and away from the implant.
VI- Mechanical testing: Mechanical testing was performed on an MTS closed loop hydraulic test machine. (MTS system, St.Paul, Minn, U.K.). Operated in stroke control at a constant displacement rate of 0.127 mm/minute, a linear variable displacement transformer (L.V.D.T.) system was utilized to measure the displacement of the implants which the loads was recorded directly from the machine load cell. (Figure 2) For each group, specimens were cycled, using the ramp-type loading from approximately 0 to 50 kg. The results were tabulated in a load displacement table, from which a load- displacement curve for each specimen was obtained. The slope values of the linear load deflection region, was noted, and divided by the previous calculated interfacial area representing “The interfacial stiffness”. This is followed by applying
load to failure .i.e. application of force on the fixture till its complete push-out from the bone specimen which was also obtained and divided by the previous calculated interfacial area representing “The interfacial shear strength”.All specimens were kept moist with saline solution during testing procedure. The results of mechanical testing were tabulated and analyzed using standard statistical methods t-test of two population means (Richard Goodman)(106).
Cross Load
Specimen
L.V.D.T.
Figure (2) Schematic diagram of MTS closed loop hydraulic test machine
v- Preparation for E.M.: Samples from each group were decalcified in 0.1 mol L-1 , EDTA, the pH of which had been adjusted to 7.0 with NaOH each of the specimens was placed in a separate glass vial with 100 ml of decalcifying solution for 10 days. 3% glutaraldehyde was added to the specimens. Glutaraldehyde is sometimes used in this way in an attempt to reduce the loss of ultrastructural detail during decalcification. (Baird et al 1967 and Vangsavan et al (107). Fixation: Small pieces of bone samples from the interfacial area of different groups were fixed in 3% glutaraldehyde phosphate buffer(PH 7.4) for 2 hours at 4oc, washed in phosphate buffer, then post fixed in 1% osmium tetraoxide for 2 hours at 4oc.
Dehydration: The specimens were dehydrated in graded series of ethyl alcohol and cleaned in acetone. Embedding : Araldite epoxy resin was used as an embedding materials. The procedure followed may be summarized as follow: 10 ml of araldite resin was added to 8 ml of D.D.S.A. The embedding mixture was mixed properly and kept at 600C in an oven for 15 minutes to eliminate air bubbles. The embedding mixture was then diluted with an equal volume of propylene oxide. Dehydrated samples were then kept over night in this diluted embedding medium (Infiltrating medium) in a
small open vials. This is to allow the slow evaporation of propylene oxide. The accelerator DMIP-30 was then added (0.4 ml) and mixed before use. The tissues were then embedded in prelabelled plastic capsules, and kept to polymerize at 600c. in an incubator for 48 hours. Trimming and sectioning: The polymerized block was trimmed under a dissecting microscope into a smooth pyramid, with a small parallel surface. Sectioning was carried out using LKB ultramicrotome. Freshly prepared glass knives were used for obtaining thin sections. Staining: Lead citrate appears to give higher contrast level, while uranium gives a better resolution. Uranium acetate usually requires at least 10-60 minutes to achieve the best results, while lead provides a surface, which make the structure in the sections appear as if they were thinner compared to the background. The mounted sections were doubly stained using the following procedures. Grids were floated on the surface of a drop of pre-filtered saturated solution of uranyl acetate in 50% ethanol for 15 minutes. The sections were immediately washed by dipping them several times in deionized water. After washing, the grids were placed on filter paper with the sections upward. After drying the sections were double stained by lead citrate according to Reynold
(108 )
.
The grids were then micrographed and the electron films were processed using D- 19 developer and fixer. Specimen were examined using transmission Electron microscopy (JEOL-JEM100CX)
Figure (3) Showing surgical
Figure (4) Showing drilled
access
bone
Figure(5) Showing implant in place.
for
for
implant
implant
insertion
positioning
Figure (6) Showing implant of control group in place
Figure (7) Showing implants
of
experimental
group
Figure (8) Showing panoramic x-ray film and implants are in place This x-rays are measured by gray scale
.
Figure (9) showing the ultrasound system,.
RESULTS Mechanical Results: For mechanical testing of interfacial areas of implants under study, the specimens were cycled and allowed to have gradual loads. Stress-strain curves at different healing period and ultrasonic intensities were obtained. From these curves the interfacial shear strength and interfacial stiffness were calculated as following. Mathematical calculation of the interfacial area: The interfacial area = π d h. Where π = 3.14 d = diameter of the implant = 3.3 mm h = Thickness of cortex at the implant site =3mm So, The interfacial area = 3.14 x 3.3 x3 The interfacial shear strength = Failure load Interfacial area
The interfacial stiffness = Slope of the curve Interfacial area The results obtained are summarized in Table I.
Interfacial shear strength: 1st dog 2 weeks of healing period: There is an increase in the mean values of interfacial shear strength between implants and bone exposed to the ultrasonic waves of different intensities comparing to that of the control implant (Figures 10-13, Table I). Generally the interfacial shear strength increases with increasing of the ultrasonic intensity from 1 to 3 w/cm2.
2nd dog (4 weeks of healing period): There is increase in the mean of interfacial shear strength in implants exposed to 1, 2 and 3w/cm2 than control group (figures 14-17, Table I).
3rd Dog (8 weeks of healing period): Also as in case of first and second dog there is increase in the mean of interfacial shear strength in case of implants exposed for ultrasonic waves of intensity 1, 2 or 3 w/cm2, for third dog (Figures 18-21).
The interfacial stiffness: 1stdog (2 weeks of healing period): The values of the interfacial stiffness are generally higher for implants exposed for ultrasonic waves comparing to that of control implant (Figures 10-13, Table I). 2nddog (4 weeks of healing period): There is increase in the mean of interfacial stiffness in group exposed to ultrasonic wave comparing to the control implant (Figure 14-17, Table I). The 3rd dog (8 weeks of healing period): The 3rd group showed increase in value of interfacial stiffness of experimental group exposed to ultrasonic wave comparing to control implant (Figure 18-21, Table I). This increase with increasing of ultrasonic intensity.
1st dog control
Load in Newton
400.00 y = 5.5612x R2 = 0.9809
300.00 200.00 100.00 0.00 0
10
20
30
40
50
60
Displacement in um
Figure ( 10 ) Typical load-displacement curve for push –out testing of implant for 2 weeks without insonation.
1st dog 1 w/cm2 350.00
y = 6.7631x R2 = 0.9913
Load in Newton
300.00 250.00 200.00 150.00 100.00 50.00 0.00 0
10
20
30
40
50
Displacement in um
Figure (11) typical load-displacement curve for push –out testing of implant exposed to 1 w/cm2 ultrasonic waves for 2 weeks.
1st dog 2 w/cm2 insonation
Load in Newton
400.00
y = 7.9129x R2 = 0.963
300.00 200.00 100.00 0.00 0
10
20
30
40
50
Displacement in um
Figure (12) Typical load-displacement curve for push –out testing of implant exposed to 2 w/cm2 ultrasonic waves for 2 weeks.
1st dog 3 w/cm2 400.00
y = 8.2116x R2 = 0.951
Load in Newton
350.00 300.00 250.00 200.00 150.00 100.00 50.00 0.00 0
10
20
30
40
50
Displacement in um
Figure (13) Typical load-displacement curve for push –out testing of implant exposed to 3 w/cm2 ultrasonic waves for 2 weeks.
2nd dog control 300.00
Load in Newton
y = 4.5299x 2
R = 0.9649 200.00
100.00
0.00 0
10
20
30
40
50
60
Displacement in um
Figure (14). Typical load-displacement curve for push –out testing of implant for 4 weeks without insonation.
2nd dog 1 w/cm2
Load in Newton
400.00
y = 6.174x R2 = 0.9312
300.00 200.00 100.00 0.00 0
10
20
30
40
50
60
70
Displacement in um
Figure (15) Typical load-displacement curve for push –out testing of implant exposed to 1 w/cm2 ultrasonic waves for 4 weeks.
2nd dog 2w/cm2
Load in Newton
500.00 y = 7.507x
400.00
R2 = 0.9238
300.00 200.00 100.00 0.00 0
10
20
30
40
50
60
Displacement in um
Figure (16) Typical load-displacement curve for push –out testing of implant exposed to 2 w/cm2 ultrasonic waves for 4 weeks.
2nd dog 3 w/cm2 insonation
Load in Newton
500.00 y = 7.7469x
400.00
2
R = 0.9087
300.00 200.00 100.00 0.00 0
10
20
30
40
50
60
Displacement in um
Figure (17) Typical load-displacement curve for push –out testing of implant exposed to 3 w/cm2 ultrasonic waves for 4 weeks.
3rd dog control
Load in Newton
400.00 y = 5.9738x R2 = 0.9773
300.00 200.00 100.00 0.00 0
10
20
30
40
50
60
Displacement in um
Figure (18) Typical load-displacement curve for push –out testing of implant for 8 weeks without insonation.
3rd dog 1w/cm2
Load in Newton
400.00 y = 6.2019x + 33.176 R2 = 0.9651
300.00 200.00 100.00 0.00 0
10
20
30
40
50
Displace me nt in um
Figure (19) Typical load-displacement curve for push –out testing of implant exposed to 1 w/cm2 ultrasonic waves for 8 weeks.
3rd dog 2 w/cm2 insonation
Load in Newton
400.00 y = 7.1947x R2 = 0.9823
300.00 200.00 100.00 0.00 0
10
20
30
40
50
60
Displacement in um
Figure (20) Typical load-displacement curve for push –out testing of implant exposed to 2 w/cm2 ultrasonic waves for 8 week.
3rd dog 3 W/cm2 insonation
Load in Newton
500.00 y = 7.7863x
400.00
2
R = 0.9529
300.00 200.00 100.00 0.00 0
10
20
30
40
50
60
Displacement in um
Figure (21) Typical load-displacement curve for push –out testing of implant exposed to 3 w/cm2 ultrasonic waves for 8 weeks.
Ultrasonic Intensity
Control (0 w/cm2)
1 w/cm2
2 w/cm2
3 w/cm2
2 weeks
4 weeks
8 weeks
274.4
254.8
317
9.7098
9.0162
11.21726
5.5612
4.5099
5.9738
196.786
160.293
211.3871
313.6
333.2
352
Interfacial shear strength Slope of the curve (N/mm)
104.09
11.969
12.480
6.763
6.174
6.2019
Interfacial stiffness Failure load Interfacial shear strength Slope of the curve Interfacial stiffness Failure load
239.31
218.471
219.452
313.6 11.969
352.8 12.4840
352.8 12.455
7.912
7.507
7.1947
279.97
265.64
254.589
333.6
352.8
372.4
Interfacial shear strength Slope of the curve Interfacial stiffness
119.69
124.840
124.55
8.211
7.7769
7.7863
290.57
274.129
275.523
Failure load (N) Interfacial shear strength (MPa) Slope of the curve Interfacial stiffness (GPa) Failure load
Table (1) Showing comparison of the interfacial shear strength and stiffness of the three groups
The radiographic measurements The x-rays images, stored as TIFF computer image files, were studied using paint shop computer program. Gray scale measurements around and away from the implant were collected by a Pantium IV computer These measurements show a measure for bone density taken by scanning the panoramicx-ray film for all femur legs of the 3 dogs. The program gave numeric data which is collected and tabulated the diagrams was drawn. The bone density is compared with the that of the bone away from implant giving the relative density measurements. Figures (22-27) show the gray scale reading of the interfacial area and relative bone density. Fgure 28 summarized the data obtained for the three dogs at different ultrasonic intensities. The data presenting in this figure indicate increase of bone density intensity.
with increase of ultrasound
2 weeks 120 100 80 Gray Scale Reading
60 40 20 0 Control
1 w/cm2
2 w/cm2
3 w/cm2
Ultrasonic Intensity
Figure (22) presenting gray scale reading of the first dog exposed to ultrasound for 2 weeks.
2 weeks
1 0.8 Relative 0.6 Bone Density 0.4 0.2 0 Control
1 w/cm2
2 w/cm2
3 w/cm2
Ultrasonic Intensity Figure (23)representing the relative bone density of the first dog.
4 weeks 130 125 120 115 Gray Scale 110 105 100 95 Control
1 w/cm2
2 w/cm2
3 w/cm2
Ultrasonic Intensity
Figure (24) representing grayscale reading of the second dog exposed to ultrasound for 4 weeks.
4 weeks
0.95 0.9 Relative 0.85 Bone Density 0.8 0.75 0.7 Control
1 w/cm2
2 w/cm2
Ultrasonic Intensity Figure (25) representing the relative bone density of the second dog. .
3 w/cm2
8 weeks
140 135 130 Gray Scale 125 Reading 120 115 110 Control
1 w/cm2
2 w/cm2
3 w/cm2
Ultrasonic Intensity Figure (26) representing gray scale reading of the third dog exposed to ultrasound For 8 weeks.
8 weeks
1.05 1 Relative 0.95 Bone Density 0.9 0.85 0.8 Control
1 w/cm2
2 w/cm2
Ultrasonic Intensity
Figure (27) representing the relative bone density of the third dog.
3 w/cm2
1.1
Relative Bone Density
1.05 1 0.95
2 weeks 4 weeks 8 weeks
0.9 0.85 0.8 0.75 0.7 0.65 0.6 0
1
2
3
Ultrasonic Intensity (w/cm2)
Figure (28) representing comparison of relative bone density of the three dogs.
4
Effect of pulsed Ultrasound waves (0.8 MHZ ) on ultrastructural changes: Figure (29) show normal osteoblast with normal distributed collagen for the interfacial bone of the control implant which does not exposed to ultrasonic waves. The ultastructure study of the interfacial bone around the implant exposed to ultrasonic waves for 2 weeks (Figure 30 - 31 ) show the primary changes started bydistortion of the collagen fibres. This could be due to the thermal and nonthermal effects of ultrasonic waves. When the healing period increased to 4 weeks (Figures 32,33) abnormal collagen fibres distribution appears with active osteoblast. The rearrangement of the collagen fibres could be due to the trigrring of the osteoblasts on the site of ultrasound exposure for new bone formation then stimulation of the matrix formation of the new bone. At a healing period of 8 weeks, active and very active osteoblasts surrounded with ostiod, collagen and dilated R.E.R. with large rounded nuclei appears (Figure 34,35).
Figre (29) Showing normal osteoblast with normal distributed collagen. (x, 12.000).
Figure (30) Showing distorted collagen fibres.(x 60.000)
Figure (31) Showing ostoid tissue and collagen with normal osteoblast. (x, 7.500) .
Figure (32) Abnormal collagen fibers distribution by the effect of ultrasound waves. (x10.500).
Figure (33) Showing active osteoblast surrounded by collagen fibres ready for formation of new bone .(x,10.500)
Figure(34) Active osteoblast surrounded with ostoid collagen & dialated R.E.R. + large rounded nucleus.(x, 7.500)
Figure (35) Showing very (x 12.000)
active
osteoblast
surrounded
by
collagen
deposition
DISCUSSION In this study, the three experimental dogs were selected free from any general contraindication condition demarcated by veterian doctor, because any of such condition may influence on the bone resorption process and on the osseointegration ability. Surgical procedures were done precisely and a-traumatically at implant insertion, to achieve osseointegration process (Shalman 1988) (98) stated that trauma during surgery, lead to failure of the implant due to massive bone loss caused as a complication of the trauma. All cutting instrument used in present study were well sharpened, and cooling fluid was allowed to pass to the very bottom of the site under preparation
(99)
. The drill pressure and
speed were kept low to avoid heat generation. Lundskoy (1972)(100) found that temperature above 47°c during drilling of the implant sites, lead to necrosis and resorption of the bone in these sites, also thermal trauma to bone lead to development of
un-differential smear tissue, delayed wound healing and possible failure of osseointegration process. The femoral radiographs were taken before implant placement for ensuring the diameter of the femora of the dog to insert the implant just in place at the intermedullary position. The radiographs taken after insonation and postoperatively to measure the effect of the ultrasound to the bone and take our collected data by gray scale program by the computer to use them as a measure for regarding the effect of ultrasound and its variable intensities to bone and osseointegration. During the period of healing the dogs were allowed unrestricted weight-bearing, as micro-movement during the early stage of wound healing is enough to direct the differentiation of mesenchymal cell into fibroblasts instead of osteoblasts, and so fibro-osseointegration, for this reason, dogs were in their cages postoperative and avoid movement or pressure during ultrasound application.
The healing period varied from 2, 4 and 8 weeks to give all the osseointegration period to be processed and noticed during healing. During laboratory step, the removal of the overlying cortex and spongy bone within the medulla was sawed, so that the effective interfacial area were be equal to the area of implant contact the cortex, mathematically equal to the by product of π .d .h Where d is implant diameter, h is the thickness of cortex and it is found to be 3mm (101). The method of testing was of some concern since it was desirable to obtain pure shear loading at the interface area. Pushout test arrangements in which cortical bone was supported at an appreciable distance from the interface, such loading will impose bending loads in addition to direct shear loads and thus may produce greater superposed stresses level.(100) The method used in our study enabled direct shear loading of the interface with minimal machining of specimen. The constant displacement rate of the mechanical push-out hydraulic machine was chosen to be at rate of 0.127mm/minute
and this is according to Thomas and Cook (101) (1985), while the ramp type loading was chosen to be from 0 to 5 kg and this is to be as possible to the reported normal biting force value in human(102).
Biomechanical View: Failure load: Failure load was defined as force required to dislodge the implant to produce the first movement of the implant and was apparent from the immediate fall in loaddisplacement curve. The increase in the value of failure load in study groups subjected to ultrasound may be explained by the osteoinductive properties of the heat generated, and so induction of new bone that improve both quantity and quality of function of any successful dental implant enabling the interfacial tissue to support masticatory forces for a long period of time. Slope of the curve: There was an increase in the slope of curves values in study groups gradually according to intensity of ultrasound applied which varied from 1, 2, 3 w/cm2 .The value
also increased in increasing the healing period from 2,4 and 8 weeks gradually. Interfacial shear strength:Osseointegration is the essential basis of
current dental implant. The biomechanics of dental bone interface is the mechanical performance of osseointegration and the functional basis of dental implant. Strength at dental implant bone interface as measured by push-out test represent, to a large extent, the bonding strength between implant and bone and potential failure load of dental implant. There was an increase in interfacial shear strength value compared with control groups. The explanation was clearly and followed the same sequence and behavior of failure load values. Burnski (1988)(83) stated that for micro interlock fixture, the shear strength ranged from 1-4 MPa for uncoated implants, and this is in agreement with our result generally. Interfacial stiffness: The increase in the interfacial stiffness in study group compared with control groups in agreement with Thomas and Cook(101) (1985), who stated that the rough surface stiffness exhibited no definite trend when compared to the
corresponding polished surface stiffness values. Also, the interfacial stiffness values followed the same pattern as it is mathematically the ratio between the slope of the curve value and the interfacial area, Where the interfacial area is a constant value.
Effect of ultrasound on ultrastructural changes: The electron microscopy shows the presence of the proliferating osteoblasts with their large prominent nuclei, rough endoplasmic reticulum that indicate an active phase of osteoblast prior to new bone formation. Although this controversy concerning the potential inductive and/or conductive mechanism of ultrasound therapy application on enhancing Osseo integration of dental implant. Ultrasound has been applied clinically and shown to be effective for the treatment of difficult to heal fractures .Data suggest that this effect stems from an increase in fluid flow and mass transport of nutrients, minerals, and hormones to and waste products from the fractured site. Based on these data the application of acoustic energy to strengthen bones and prevent bone loss in space seems logical. When designing the experimental device, researches will identify the bandwidth and optimal application regime to produce the therapeutic effect.
Cell growth in response to US was measured by John Glenn.(103) Direct cell counting showing proliferation rate after exposure to increasing doses of US, relative to the growth of the non-exposed cells used as control. The increase in dose gives non significant increase in cell count measures, where the increase in duration gives significant increase in cell count. US has previously been shown to have a potent influence on integrity and transport properties of the plasma membrane .
Ultrastructural study of the interfacial bone exposed to 0.8MHz pulsed ultrasonic waves showed various changes starting new bone formation as rearrangement of the collagen fibres giving meshwork for a newly bone matrix, then the process is developed to give the 2nd stage which is formation of the osteoid matrix by stimulation of newly formed osteoblast then formation of new bone. All of these consequences were done by the effect of ultrasound and increase
Summary & Conclusion
The present dissertation dealt with the role of ultrasound waves in enhancing the osseointegration of dental implant. To evaluate the role of biomechanical , radiographical (as a measurement of bone density) and ultrastructural evaluation of the interfacial bone around the implant in the presence and absence of ultrasonic waves were studied. Different parameters which enhance bone healing such as ultrasonic intensity and healing period were investigated. This study was carried out in three dogs. Three holes were drilled bilaterally perpendicular to the medial cortex in right femur of each dog and one hole is made on left femur. Tewelve fixtures were implanted in these holes. The first , second and third implant of the right femur were sonocated for 2 minutes day after day with 0.8 MHz ultrasonic waves at intensity of 1, 2, and 3 w/cm2, respectively and the implants in the left femurs of dogs were left without sonocation as control. The first dog was sacrificed after 2 weeks, the second after 4 weeks while the third after 8 weeks. X- Ray photographs were taken for different implants and then the implant with surrounding bone was prepared for mechanical and ultrastructure studies. The results obtained show that:
1- Interfacial shear strength of implanted fixtures is generally increases with increasing of ultrasonic intensity and bone healing while stiffness increases with ultrasonic intensity but is different for each dog. 2- Bone density of the interfacial area around the implant increases with increasing of ultrasonic intensity and healing period. 3- Ultrastructural study of interfacial area shows the presence of cellular proliferating process leading to potential induction for new bone formation. From this study, we can conclude that: 1) The ultrasonic waves show an increase in new bone formation in the interface area between the implant and the surrounding bone leading to decrease of the healing period needed for complete osseointegration. 2) Biomechanical examination showed that interfacial.bone healing increases with the increase of ultrasonic intensity and healing time. 3) The radiographic examination indicates the increase of bone density in the interfacial bone with increasing of ultrasonic intensity and healing period. 4) The ultrastructural examination of the effect of the ultrasound showed a superior osseointegration process.
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ملخص الرسالة تمهيد إن استخدام الموجات الصوتية العالجية فى تحسين التئام العظام و األنسجة يعتبر من التقنيات الحديثة والمتقدمة لتقليل مدة التئام الكسور والجروح .تعتبر طول المدة الالزمة اللتئام العظام حول غارسات األسنان من المعوقات الشديدة التي تؤدي إلى عدم التوسع فى عمليات غرس األسنان حيث أن عملية االلتئام العظمى بعد عملية الغرس تحتاج ما بين 21 – 8أسبوع حتى تتم عملية االلتئام الكامل ما بين العظم والغارس ،وخالل تلك الفترة يحدث الكثير من االلتهابات ،ويقع على الغارس عدة حركات نتيجة عمليات المضغ مما يؤدى إلى تحريك الغارس من مكانه ،األمر الذى يؤدى إلى فشل العملية وبالتالى يخرج الغارس من العظم المحيط وفشل العملية ككل.
الغرض من البحث تهدف هذذه الرسذالة إلذى اسذتخدام الموجذات فذول الصذوتية فذي تحفيذز تكذوين العظام حول غارسات األسنان وتقليل الفترة الزمنية الالزمة لاللتئام العظمى الكامل مذذا بذذين الغذذارس والعظذذم المحذذيط بالغذذارس عذذن طريذذل اسذذتخدام الموجذذات الصذذوتية العالجية بطاقات مختلفة ممذا يسذاعد علذى االلتئذام السذريع مذا بذين الغذارس والعظذم، وكذلك االلتئام السريع للجرح النذات عذن عمليذة الزراعذة فذى النسذي المذبطن للعظذم
عن طريل رفع درجة الحرارة في منطقة الغارسات مما يؤدي إلذى انذدفاع الذدم إلذى هذه المنطقة وإعادة توزيع للخاليا الموجودة بالنسي العظمى المحيط بالغارس.
طريقة الدراسة تمت هذه الدراسة على ثالثة من كذال
التجذار عذن طريذل زرع عذدد 21
غارس بالتجويف النخاعى لسال عظمة الفخذ لهذه الكال ،في كل تم غذرس ثذالث غارسات في السال اليسرى كمجموعة تجريبية وغارس في السال اليمني كمجموعة ضابطة وتعريض غارسات المجموعة التجريبية لجرعات مختلفة من الموجات فول الصوتية لمدد زمنية متفاوتة يوم بعد يوم على النحو التالى: في الكل
األولى تذذذذم تعذذذذريض الغذذذذذارس األول والثذذذذاني والثالذذذذث للمجموعذذذذذة
التجريبيذذة لموجذذات فذذول صذذوتية بشذذدة 3 ،1، 2وات /سذذم 1علذذى الترتي ذ ، وذلك لمدة أسبوعين على أن يترك الغارس فى النخاع العظمذى للسذال األخذرى للكل
لنفس المدة،علي أال يكون معرضا ألية موجذات صذوتية ليكذون مجموعذة
ضابطة. المجموعة الثانية
:وتتكون أيضا مذن 3غارسذات تتعذرض إلذى موجذات
صوتية ذات تردد مذا بذين 3 ، 2وات /سذم 1علذى الترتيذ كذذلك ،ولكذن لمذدة أربعة أسابيع مع وجود المجموعة الضابطة بالرجل األخرى للكل . المجموعة الثالثة
:وهى األخرى تتكون من 3غارسات على نفس النحو
مع وجود المجموعة الضابطة ،وذلك لمدة ثمانية أسابيع.
بعد فترة االلتئام لكل مجموعة يتم تشريح كال
التجار وعزل عظم الفخذ،
وفصل كل غرس محاط بقطعة عظمية علذى حذده وتحضذير العينذات إلذى التصذوير عذذن طريذذل األشذذعة السذذينية لكذذل عظمذذة ،وذلذذك لقيذذاس الكثافذذة العظميذذة حذذول كذذل غذذارس عذذن طريذذل الكمبيذذوتر وبعذذدها تؤخذذذ عينذذات للكشذذف عليهذذا عذذن طريذذل الميكروسذذذكو االلكترونذذذى ،ثذذذم يذذذتم تحضذذذير العينذذذات لعمليذذذة الذذذدفع الميكذذذانيكى الخارجى للغارسات عن طريل ماكينة الدفع الخارجى لتعيين قيمتىInterfacial ، “ shear strengthوهى تحذدد قيمذة القذل التفذابلى وكذذلك قيمذة ” Interfacial “ stiffnessوالتذذى تحذذدد قيمذذة الصذذالبة التقابليذذة بذذين سذذطحى الغذذرس والعظذذام المحيطة.
النتائ العملية يمكن التعبير عن النتائ العملية كما يلى: .2التحليل الكيفى لكمية العظذام المحيطذة بالغذارس عذن طريذل اسذتخدام األشذعة السذذينية باسذذتخدام برنذذام للكمبيذذوتر يحذذدد درجذذة اللذون لصذذورة العظذذام فذذى المنطقة المحيطة بالغارسات . ،حيث أن الزيادة في درجة اللذون تتناسذ مذع عملية االلتئام العظمى وقد تبين من الدراسة أن عملية تكوين النسي العظمذى حول الغارسات المعرضذة للموجذات الصذوتية تكذون أكبذر ممذا هذو عليذه فذى حالة غارسات المجموعة الضابطة الغير معرضة للموجات وفذى نفذس المذدة وقذذد تبذذين أيضذذا ازديذذاد كثافذذة العظذذام المتكونذذة حذذول الغارسذذات بزيذذادة شذذدة الموجات فول الصوتية.
.1التحليل الميكانيكى .وجذد مذن دراسذة الذدفع الميكذانيكي لغارسذات األسذنان أن قيمة شذدة القذل التقذابلى
“ ”Interfacial shear strength
تزداد بزيادة شدة الموجات الصوتية العالجية و تكون بصفة عامة اعلي عنها فى حالة عدم استخدامها فى نفس المدة .ومع حسا
قيمة شدة القل التقابلى
وج د أنها تزداد مع استخدام الموجات الصوتية العالجية عنهذا مذن الغارسذات الغير معرضة لهذه الموجات لنفس المدة. .3الدراسة الميكروسكوبية .حيث تم أيضا دراسة التركي
الدقيل لمنطقة التحام
الغارسذذذات بالعظذذذام فذذذى المجموعذذذات الثالثذذذة ومقارنتهذذذا مذذذع المجموعذذذات الضذذذابطة ،وأثبتذذذت أن عمليذذذة االلتحذذذام العظمذذذى تكذذذون أكثذذذر مذذذع اسذذذتخدام الموجات الصوتية. وقد تم مناقشة النتائ فى ضوء بعذض األبحذاث المشذابهة ومذدلوالتها والمقارنذة بينهما وتم استخالل ما يلى:
الخالصة واالستنتاج إن استخدام الموجذات الصذوتية العالجيذة بجانذ غارسذات األسذنان فذى الفذك تعمل علذى تح فيذز إنتذاج عظمذى جديذد وسذريع يسذاعد فذى تثبيذت تلذك الغارسذات ويزيد من قوة تحملها ميكانيكيا.
تقييم بيوفيزيقي لتأثير الموجات الفوق صوتية العالجية علي التالحم العظمي لغارسات األسنان رسالة مقدمة لمعهد البحوث الطبية
للحصول علي درجة الماجستير في الطبيعة الحيوية
من
احمداحمد فؤاد الميقاتي بكالوريوس طب األسنان كلية طب األسنان-جامعة اإلسكندرية
2002
