Comparison of peri-implant alveolar bone height

Mansoura University Faculty of Dentistry Department of Removable Prosthodontics

Comparison of peri-implant alveolar bone height changes of two implant-retained overdentures based on implant location Thesis Submitted to the Faculty of Dentistry, Mansoura University. Partially fulfills the requirements of obtaining doctor degree in Removable Prosthodontics.

Submitted by

Mohamed abed Mohamed abo shabana B.D.S. (2004) Master degree of Prosthodontics (2011) Department of Removable Prosthodontics Faculty of Dentistry Mansoura University

2018

Supervisors Mohammed M. Fouad Professor of Removable Prosthodontics Faculty of Dentistry Mansoura University

Moustafa elsayad Associate Prof. of Removable Prosthodontics Faculty of Dentistry Mansoura University

Radwa M.K.Emera Associate Prof of Removable Prosthodontics Faculty of Dentistry Mansoura University

Wael Mohamed Safwat Lecturer of oral radiology Faculty of Dentistry Mansoura University

List of Contents

Content

Page No

List of tables

i

List of figures

ii

List of abbreviations Abstract Chapter 1: Introduction

1

Chapter 2: Review of literature

3

Implant-assisted overdentures

3

Attachments for implant assisted mandibular overdentures

7

Implant Position options for implant assisted overdentur

16

Periimplant alveolar bone loss with implant assisted overdenture Radiographic evaluation of marginal bone resorption around dental implant

22 29

Aim of the work

34

Chapter 3: Materials and methods

35

Chapter 4: Results

63

Chapter 5: Discussion

81

Conclusion and Recommendation

95

References

96

Arabic summary

١

List of Tables

No.

Item

Page

Table 1

Comparison of VBL between groups at T1.

65

Table 2


66

Table 3


67

Table 4

Comparison of HBL between groups at T1.

68

Table 5


69

Table 6


70

Table 7

Comparison of VBL between intervals for group I.

72

Table 8

Comparison of VBL between intervals for group II

73

Table 9

Comparison of HBL between intervals for group I.

74

Table 10

Comparison of HBL between intervals for group II.

75

Table 11

Comparison of VBL between sites for group I.

77

Table 12

Comparison of VBL between sites for group II.

78

Table 13

Comparison of HBL between sites for group I.

79

Table 14

Comparison of HBL between sites for group II.

80

i

List of Figures Figure

Title

No. Figure 1 Figure 2 Figure 3

Completely mandibular residual edentulous alveolar ridge covered with healthy firm mucosa. Preoperative digital panoramic radiograph. Verification of bone in the prospective sites of dental implants using CBCT (bone quantity _a & quality _b)

Page No. 37 37 38

calculation of the angle between proposed implant Figure 4

position and the metal tube in the cross-sectional

43

images of the CT. Figure 5

virsual planning for implants parralism

43

Figure 6

Stereolithographic surgical guide template.

43

Figure 7

Universal surgical kit.

44

Figure 8

Figure 9

Figure 10

Dyna surgical implantation kit. Fixation of sterolithographic surgical guide template in patient mouth Implant site exposure using tissue punch

Figure 11 Initial pilot Drilling . Figure 12 Figure 13

47

54

55 49

final drilling of the osteotomy site. The fixture was carefully removed from its vial by using finger octadriver.

ii

49 49

Figure

Title

No. Figure 14

Figure 15

Proper implant placement was verified by intra oral panoramic radiographs. (fig 15a group I&b group II ) cover screw in its position.

Figure 16 suturing over cover screw Figure 17

the healing abutments in group I (canine areas)and II (premolar areas)

Page No. 50

58 61 62

ball abutments connected to the fixure in group Figure 18

Figure 19

I(canine areas & group II(premolar areas).

preparing the fitting surface for female housing (smart gold matrix)

56

57

The dyna smart gold matrices was placed on the ball Figure 20

attachments.

57

The denture was removed and the excess acrylic Figure 21

resin was removed carefully from the intaglio and

58

outer surfaces of the denture. Figure 22

lines and points on periapical x ray

58

Figure 23

Fixation of film holder

58

Figure 24 Comparison of VBL between groups at T1

iii

58

Figure

Title

No.

Page No.

Figure 25

Comparison of VBL between groups at T2

Figure 26

Comparison of VBL between groups at T3

Figure 27

Comparison of HBL between groups at T1

Figure 28


Figure 29


76

Figure 30

Comparison of VBL between sites for group I

77

Figure 31

Comparison of VBL between sites for group II

78

Figure 32

Comparison of HBL between sites for group I.

79

Figure 33

Comparison of HBL between sites for group II.

80

iv

List of abbreviations CT CBCT 3D TMJ CD

computed tomography Cone beam computed tomography. Three dimensional Tempromandibular Joint Complete denture

VBL

Cone beam

HBL

Horizontal bone loss

OD

Over denture

v

Abstract Comparison of peri-implant alveolar bone height changes of two implant-retained overdentures based on implant location Statement of problem: The effect of location of the two implant retaining mandibular complete overdenture on peri-implant bone height has insufficient studies. Purpose: This study aimed to evaluate peri-implant alveolar bone height changes of the two implant-retained overdentures inserted in canine and second premolars bone areas. Materials and methods: Ten male completely edentulous patients received 2 implants in anterior mandible. Implants were connected to mandibular overdentures with ball and socket attachments. According to the implant location, the patients were classified into two groups: Group I received 2 ball attachments at canine regions and group II received 2 ball attachments at premolar region . Marginal bone height changes (vertical and horizontal bone height changes) were evaluated 6 months after overdenture insertion (T1), 12 months (T2) and from 6 to 12 months (T3). Results: Marginal bone resorption was measured through the evaluation period in both groups. Group I showed (0.43), (0.82) and (0,39) values regarding the vertical marginal

bone loss respectively and showed (0.25), (0.48) and

(0.23) values regarding the horizontal marginal bone loss respectively. Group II showed (0.54), (0.92) and (0.38) values regarding the vertical marginal

bone loss respectively and showed (0.26), (0.51) and (0.25)

values regarding the horizontal marginal bone loss respectively.

vi

There was statistically insignificant difference between groups regarding the bone height changes (vertical and horizontal) at all observation times after 6 months and 12 months after receiving ball attachments .

Conclusion: Within the limitations of this study (including patient number and intervals of study), it could be concluded that: Although, the insignificant difference in alveolar bone loss around canine and premolar implants the canine implants may be more advantageous in terms of periimplant alveolar bone height preservation.

Keywords: Ball and socket, implant location, overdenture.

vii

Introduction

Introduction Although most completely edentulous patients express satisfaction with their conventional maxillary complete dentures, many struggle with the comfort and function of mandibular complete dentures. The use of endosseous dental implants to assist support, stability, and retention of complete denture is considered an effective treatment modality for completely edentulous patients. Individuals wearing implant-assisted overdentures typically report improved oral comfort and function when compared with conventional, mucosa-supported prostheses. A minimal number of implants may be used to support, stabilize, and retain overdentures. This restorative approach is both practical and clinically successful, particularly in edentulous mandible. In treatment planning, the number and position of implants to support the prosthesis is the most important question to be answered. The treatment of the edentulous mandible with the 2-implant-retained overdenture is a wellaccepted treatment with long-term successful outcomes for prostheses and implants. The prosthetic and attachment system factors of successful mandibular implant overdentures have been extensively reported in the literature. As ridge resorption occurs, the mandibular anatomy may affect available implant locations. which, in turn, may affect surgical planning and treatment outcomes. Furthermore, abutment and retention location affect the treatment outcomes and biomechanical effects of prosthesis design. Missing from these discussions, however, is an analysis of the effect of implant location on these prosthetic and surgical factors (1).

1

Introduction

Various types of implant attachment systems have been proposed and can be classified as the ball, o ring, locator (zest anchors), OT Equator, bars and clips, magnets, resilient liners and other types. Single attachments offer the easiest and least expensive way to provide the patient with an implant-supported overdenture as the ball attachment needs only chair side work. The main advantage of ball attachments is the versatility and applicability in various situations with no need for fabrication of new dentures when put into function (2). The impact of the location of implants and attachment systems on the retention and stability of overdentures has been alluded to in several studies

(3)

. Information regarding implant position and its effect on the

retention and stability of mandibular implant overdentures is limited in currently available studies. Although many studies assumed a 2 implant model that approximated the location of the mandibular canines, there was no in vivo evaluation of 2 implants outside the areas of mandibular canines used for assisting the mandibular complete overdenture. Accordingly, the aim of this study was to evaluate the effect of location of the two implant retaining mandibular complete overdenture on peri-implant alveolar bone height changes.

2

Review of literature

Implant-assisted overdentures Edentulism is considered a poor health outcome and may compromise quality of life. The classical treatment plan for edentulous patient is the conventional complete denture.(4)

(1)

Although many

edentulous patients are satisfied with their conventional mandibular complete dentures, some problems, such as insufficient retention and stability of the prosthesis, decreased chewing efficiency, and discomfort during mastication, continue to remain. Previous clinical studies have noticed, however, that these issues can be addressed effectively by using a dental prosthesis in combination with dental implants (5, 6). According to The Glossary of prosthodontics terms 2005

(7)

Overdenture can be defined as “a removable partial or complete denture that covers and rests on one or more remaining natural teeth, roots, and/or dental implants; a prosthesis that covers and is partially supported by natural teeth, tooth roots, and/or dental implants”.

Types of implant overdenture Implant overdentures are divided according to the attachments used and the support amount obtained from the implants and tissues into: The all implant-supported overdentures: The entire support of these overdentures is obtained from dental implants (rigid anchorage systems similar to fixed and hybrid prostheses in mechanism) e.g.: telescope and milled bar. The implant and tissue-supported overdentures: The retention is obtained from dental implants (with resilient anchorage systems) eg: locator and ball. The support is obtained from a combination of tissues and

3


implants as while the denture base properly contacts the mucosa, the simultaneous interlocking of attachment components provides the retentive quality for these systems (8) Implant-retained prosthesis term does not show the difference between implant restoration whether removable or fixed, or directly retained by dental implants, therefore, Simon and Yanase suggested a terminology for implant prostheses describing the method to connect the implant abutments whether it is screwed or luted to differentiate them from other types of prostheses Simon and Yanase (9)

Advantages of implant overdenture (10)

Kyung ,et al stated that; implant-supported prostheses provide

greater occlusal awareness, sensory functions and decrease thickness perception threshold between occlusal surfaces than conventional complete denture due to the lack of periodontal ligament of implantsupported prostheses is partly compensated by another mechanism through the phenomenon of osseointegration, namely neurointegration Overdenture therapy has been proven to be advantageous that can be summarized to improved retention and esthetics, reduced residual ridge resorption and psychological benefitsShinde and Wadkar (11) Regarding the bone loss, mandibular overdentures showed lesser bone resorption compared with conventional complete dentures due to the implant functional stimulation to the bone and bone apposition. (12) Stabilization of the overdenture by means of osseo-integrated implants has been shown to improve oral function (13-15), provide a regular chewing pattern with higher electrical activity of the masseter muscles, and improve mandibular border movements compared with conventional 4


complete dentures

(16-20)

. Moreover, implant stabilized overdentures

increase maximum bite force and masticatory performance, improve patient satisfaction and minimize pain during mastication (21, 22). The decision on the number of implants that suits a particular clinical situation is to some extent subjective and depends on the clinician’s knowledge and experience, as well as on many other factors. However, two consensus statements on the number of implants to be used with removable implant supported overdentures were published in 2002 and 2009, respectively. Both consensus statements recommended that removable implant supported overdentures with two implants should be considered as the first-choice standard of care for an edentulous mandible (23-25) A more recent survey was carried out by an expert panel of 16 representatives of academic prosthodontists to investigate if there was agreement on the gold standard for an edentulous mandible between the two-implant-supported mandibular overdentures and a conventional mandibular complete denture

(26)

. The survey results concurred with the

two consensus statements of 2002 and 2009. Two dental implant retained mandibular overdentures are considered the gold standard in the oral rehabilitation of edentulous mandible to provide support and stability for the prosthesis. Relative simplicity, minimal invasiveness, good performance and affordability make them an alternative effective treatment solution(27) Two implants overdenture is a better substitute than four implants overdenture regarding cost effectiveness. However, when two implants only are used for support, loosening or detaching attachments problems are more common, and the retention and stability are lesser than when using more implants.(28)

5


Multiple implants with cantilevered bar are indicated for support of an overdenture in cases which suffer from knife edged ridge, superficial mental foramen or sensitive supporting mucosa. However, the need for retention and protection of such problematic tissue condition can be satisfied by the use of only two implants with cantilevered bar design for supporting the overdenture. This design has the advantage of conservative surgical approach and economic treatment(29): The use of three or four implants is indicated in ridges with decreased height where the required implant length is less than 8mm and in ridges with decreased width where the required implant diameter is 3.3 mm. It’s also indicated in v shaped mandibular anterior ridges to avoid decreasing the tongue space and thick denture with inaccurate bar design. (30) Elsyad and khirallah 2014

(31)

studied three implant supported

overdenture designs (two implants and a single bar, two implants and ball attachments and four implants and a quadrilateral bar). They compared their effect on the chewing efficiency. The four implant overdentures produces higher chewing efficiency than the two implant overdentures regardless the used attachment.

6


Attachments for implant assisted mandibular overdentures An attachment is defined as “a mechanical device for the fixation, retention, and stabilization of a prosthesis ,a retainer consisting of a metal receptacle and a closely fitting part; the former (the female matrix component) is usually contained within the normal or expanded contours of the crown of the abutment tooth and the latter (the male patrix component), is attached to a pontic or the denture framework”

(7)

.

Attachments used in conjunction with implants were found to enhance the retention, the stability and support of over dentures together with the implants, thus extending their longevity. (32) The implant-supported removable denture can be attached to the edentulous jaw with splinted attachments (bars) or unsplinted attachments such as locators, ball anchors, double crowns and magnets(33). Owing to the smaller space requirements within prostheses, easy cleaning, more economical incentives and lower sensitivity to techniques, unsplinted anchorage attachments have been used with implant overdentures(34,

35)

. Compared to splinted attachments, unsplinted

attachments provide easier hygiene(36), are cost effective, have fewer technical complications(34, 35), can be used with pointed jaw which leaves insufficient tongue space for bar constructions(37) and also suggested when the implants are located very distally or in a diagonal arrangement. It is important to consider space requirement during attachment selection. The height of attachment should be estimated to minimize space required inside the denture (in order to decrease potential fracture caused by inadequate acrylic thickness) and housings with replaceable matrices(38)

7


Attachment selection depends on the anatomical state of the mandible. An advanced degree of atrophy may favor a connector which offers a considerable amount of horizontal stability as given by barconstructions or parallel-walled telescopic connectors (39). Bar constructions may provide sufficient horizontal stability if the bar is long enough(40), even when alveolar atrophy is pronounced. In situations where there is sufficient alveolar ridge height, magnet connectors offer an alternative solution, although their ease of use is in some ways offset by many patients’ desire for more retention (41).

Splinted attachments: Bar attachments: Bar attachments are classified into two groups: bar joint and bar unit(42). Bar joint allows some degree of movements around the bar during mastication. There are two types of bar joint which are single sleeve bar joint and multiple sleeve bar joint. Dolder bar joint is an example for single sleeve bar joint(43). In multiple sleeves bar joints; the retaining sleeves are relatively short. Frederick and Caputo (44)stated that, spaced oval or round bars allow both vertical and rotational movements (stress breaking retention mechanism), while parallel-sided bars may transmit more loads to the implants and less to the posterior residual ridge (rigid retention mechanism). The advantages of bar include the better transmission of force between the implants and better retention.

Compared to unsplinted

copings, bars are prone to mucositis and gingival hyperplasia(41), encroach more on the tongue, and reduce the functional deformation of the mandible(40). Moreover, bars require a certain amount of vertical space between the opposing arches to ensure adequate restorative material thickness, space for the retentive elements, esthetics, and cleansability (45). 8


The estimated interarch space required for an implant-retained overdenture measured from the implant shoulder to the incisal edge is approximately 12 to 14 mm. Two to 3 millimeters of soft tissue thickness is generally present above the implant, and 2 mm of space from the edentulous ridge mucosa to the bar is recommended for cleansability (45), 4.5 mm for the bar, 2 mm for the acrylic resin and clip housing, and 3 mm for the teeth above the denture base (46)

Non splinted attachments: Non splinted attachments consist of a patrix screwed into the implant and matrix attached to the overdenture. The retention delivered when the matrix fitted over the patrix by means of spring-action arms or an interchangeable elastic rubbers made of nylon and Teflon and presented in different colors corresponding to different retention degrees.(47)

I.

Locator attachments: Locator attachment are indicated in cases of tissue-supported

removable overdentures on two to four implants, partially edentulous overdentures with one or more implants, and limited interarch distance (48) When the interarch distance or the height of the denture is inadequate for placing ball attachments, several problems may occur, such as over contoured prosthesis, excessive occlusal vertical dimension, fractured teeth adjacent to the attachments, separation of attachments from the denture, fracture of the prosthesis, and overall patient dissatisfaction. In these situations, Locator® attachments or micro-head extracoronal resilient attachments (ERA) can be a suitable alternative to ball attachments because of their low profile. (49, 50)

9


II. Magnetic attachments: Magnets offer several advantages when compared to other unsplinted attachments. These advantages include low profile which enable them to be used with insufficient interarch space(41), reduction of horizontal stress transmission to the implants(51) and reduction of the stress generated in the peri-implant bone during overdenture dislodgement(52). Moreover magnets are less prominent, smoother and comfortable to the patients when the prostheses are absent from the mouth(53). They also do not disturb the surrounding gingiva(54) and can be used with non-parallel implants(55). However, the resistance of magnets against vertical dislodgement forces of the denture is markedly less than those of the barclip and ball attachments after 3 months of function (56). Moreover, magnets are associated with reduced prosthesis stability and decreased patient satisfaction(57). III. Telescopic attachments Telescopic (double crown) attachments consist of inner and outer copings (58). These attachments may be rigid or non-rigid (resilient). Nonrigid telescopes have no defined end position. These telescopes include crowns with tiny spaces between the primary and secondary copings (39, 59, 60)

and crowns with additional retention elements (58, 61). Compared to other

unsplinted attachments, telescopic crowns have an advantage of providing adequate prosthesis retention and stability, satisfactory mastication and improved phonetics

(62, 63)

. They also prevent dislodgment of the distal

extension base away from the ridge(62) and increase horizontal stabilization in mandibles with advanced atrophy(59, 60). The overdenture self-finding mechanism in telescopic constructions facilitates prosthesis insertion. This is important for geriatric patients with decreased manual dexterity (58, 60-62).

10


A possible disadvantage of the use of these attachments is the technically challenging and time consuming process of fabricating them, resulting in comparatively high costs for this type of treatment (59, 64). Moreover loss of retention resulting from mechanical wear of the copings has been discussed (64)

IV. Equator: Equator attachments are provided with low vertical profile and minimum diameter making them suitable in cases of limited inter-occlusal space exerting adequate retention for the mandibular overdenture.(65) Equator attachment is made of titanium alloy with a titanium nitride coating, and the metal housing is made of titanium alloy coming with elastic ring that is placed in special cylindrical form. This cylindrical container which placed below the equator is maintained in place to improve the prosthetic fixation.(66) Equator abutment is designed to accommodate the maximum denture bearing area with self-aligning design and up to 40o angle correction which available in multiple retention options and replaceable.(67) V. Ball attachments: Ball attachments are considered the simplest type of attachments for clinical application with tooth- or implant-supported overdentures (43). Ball attachments have been proven to be reliable among the available retention systems. (68) Ball attachment consists of a spherical patrix that is usually screwed into the implant assembly. The matrix fits over the patrix and provides retention by means of spring-action arms or an interchangeable elastic ring (O-ring)

(69, 70)

. Stoumpis and Kohal

(71)

stated that ball

attachment is the most common attachment design which consists of a 11


metal cap or a rubber ring embedded in the denture base to engage a ball abutment attached independently to each implant. Types The ball and socket attachments can be divided into the following types(40, 45, 72)

:

1. Dalbo attachment (Dalla-Bona): It’s the commonest use attachment. It consists of male, female and a nylon or Teflon ring. The golden male is spherical in shape and 4mm in height, the female housing is protected by a nylon or Teflon ring. The ball and socket mechanism provides the direct retention of the units, which is adjusted by gently bending the finger springs around the open end of the socket. The resiliency in vertical and rotational movements, is obtained from a spacer of 0.4mm. It’s available in two types rigid and resilient (73). 2. Rhein OT cap attachment: It’s castable resilient ball and socket type of attachment. It consists of male ball attachment of 2mm height and 4mm in diameter and a snape on a female socket of 1.5mm in height. The resilient ball type of the attachment helps to transfer the stress in a more favorable manner to the remaining structures in the oral cavity. It’s available in regular and micro sizes (40). 3. The O-ring attachments: consists of a ball head that attaches to a post or cuff, with a groove or undercut area between the two parts that hold the O-ring. The O-ring abutment, usually fabricated from titanium alloy, is secured directly to the implant by means of a screw or is cast in precious or semiprecious alloy as part of the superstructure bar. It has an elastomeric retentive attachments, usually made of silicone. They are held within metallic retaining rings with undercut grooves.

12


The retaining rings are embedded within the denture base resin during the

laboratory

processing

procedure

or

chair

side

with

autopolymerizing resin. The O-rings possess a number of advantages including; ease of use and maintenance and low cost. Another advantage of O-ring attachments is the wide range of movements, different degrees of retention and time saving. O-ring also allows movement in six different directions (45). Klemetti et al(74)showed that two free-standing implants can be used with ball attachments ,retained into the implants by using screw and a corresponding cap with an Oring incorporated into the denture base .They not only reduce shock, pressure and torque but also can be used with patient’s existing denture. However, as O-rings wear over time; they gradually lose retention and must be replaced. Also O-rings can fail due to the combined adverse effects of stress and environmental factors (friction, heat, and swelling)(75).It is also essential that O-ring abutments must be parallel. Lack of parallelism represents a weak point, with the risk of fracture around the neck of the abutment and interferes with insertion and removal of the prosthesis and cause unacceptable wear of the O-ring (40)

.

13


Advantages and disadvantages of ball attachments Ball attachments have gained popularity over bars, as they are easier to manage in limited prosthetic space, more economical, easily cleansable, and less technique sensitive(70). It has been shown that when 2 implants are used in the anterior mandible to retain an overdenture, solitary ball attachments are less costly, less technique sensitive(76), and easier to clean(77) and more accommodating of tapered arches(78) than bars. Moreover, the potential for mucosal hyperplasia reportedly is more easily reduced with solitary ball attachments.(79) Ball attachment provides varying degree of resiliency in both vertical and horizontal directions (51). While considered generally resilient, the specific design of the ball attachment may influence the amount of its free movement, thereby limiting its resiliency. (80) Naert et al.,

(76)

, reported that ball attachment are less costly, less

technique sensitive and easier to clean than bars (77)and less wear or fracture of the component than that of gold alloy bars (81). Moreover the potential for mucosal hyperplasia reportedly is more easily reduced with ball attachments (79). It was also reported that the use of the ball attachment may be advantageous for implant-supported overdentures with regard to optimizing stress and minimizing denture movement. (82) Several investigators (36, 54, 83-86) reported no difference in clinical and radiographical state of peri-implant tissues in normal patients treated with mandibular overdenture connected to the implants with either ball or bar attachments.

14


In comparison to the ball-retained overdenture, a significantly higher retention values were observed with bar-retained overdentures; however, assessment of patient satisfaction did not reflect this difference.(87) In a comparative 5-year study by Gotfredsen and Holm, periimplant conditions and maintenance requirements for implantsupported overdentures were evaluated. These authors found a 100% survival rate for 2-implant ball- or bar-retained overdentures.(36) No differences in marginal bone loss or health of the periimplant mucosa were observed, but the frequency of technical complications and repairs per patient was higher for bar attachments than ball attachments. In vitro and in vivo studies by Menicucci et al(88, 89)compared the stresses on the bone surrounding 2 implants with either a bar clip or ball attachments for overdentures. They found greater stresses on the periimplant bone with a bar-clip attachment compared to ball attachments. This was consistent with a photoelastic analysis by Kenney and Richards

(90)

when their model was subjected to posterior vertical load. However, other authors, in an in vivo study on force transmission onto implants supporting overdentures, found that rigid bars contributed to load sharing.(91) However ball anchors were found to provide more postinsertion maintenance in comparison with bar anchors

(92)

. They demand re-

activation of their retentive components more frequently(93) due to gradual and continuous loss of retention associated with repeated insertion-removal cycles(94). Ball attachments have shown to need a significantly higher level of maintenance on isolated implants than attachments with resilient telescopic crowns. (95)

15


Implant Position options for implant assisted overdentur The proper positioning of dental implants and the good assessment of the distribution of strain and/or stress have great impact on the management of overload as the most common cause of failure in dental implants, and this can aid in avoiding mechanical overload, counteracting failures, and increasing the success rate of dental implants (96). When planning for an implant in a mandibular implant overdenture the clinician may be faced with a great degree of ridge resorption that alters the anatomy of the Mandible and minimizes the available locations and thus even affecting the treatment.(97)) Also one of the vital points related to implant position and which clinical researches have recorded as one of the principle worries of a patient wearing a two implant overdenture is the rotational movement. Consideration must be paid to the occlusal harmony as well as the suitable extension of the denture base to attempt to counteract excessive rotational movement. (98)) The parameters related to implant location are factors that may influence the dental implant outcome. The bone characteristics (quantity, quality and crestal width) on the implant site may impact the failure rate. (99)

To get satisfactory functional and esthetic results, it is important to accomplish proper 3-dimensional positioning of the implants.(100)) The location and the distribution of implants assume an essential part in the amount of load transmitted to the surrounding bone in addition to the types of loading, prosthesis, attachment and number of implants. ((101)

16


In the completely edentulous patient, the anterior mandible tends to have substantive residual alveolar bone, even after extraction, when most of the alveolar bone has been resorbed. Thus, the anterior mandible in the inerforaminal area is known as a generally more favorable location for implants than other areas.(102) (101)) When the amount of alveolar bone at the lateral incisor and canine positions is comparable, the lateral incisor areas could be chosen because the placement of implants in lateral incisor areas has a mechanical advantage over other areas.(103)) It was reported that if implants are set in a lateral, instead of a canine position, hinge movement will be diminished, because the anterior– posterior distance from the incisal edges of the anterior teeth to hinge axis between the laterally placed implants is decreased(104)) In a study comparing stresses in three different implant positions, it was concluded that the lateral incisor position had the lowest stress compared to canine and premolar positions.(105)) Surgical correction operations are often needed in patients with great degree of alveolar bone resorption so this positions where extensive surgical reconstruction procedures are seldom required offers a chance to avoid surgery.(106) The design of the implant supported overdenture is determined by implants position and number which can be placed with respect to anatomic limitations. The implant distribution is determined by size, shape and curvature of the ridge. Usually the mandibular implant overdenture patient needs can be achieved by two to four implants. (107)

17


The impact of the location of implants and attachment systems of overdentures has been alluded to in several studies. The authors were able to determine that retention and stability of overdentures could be improved by altering implant location and distribution. The authors determined after cyclic loading and wear analysis that wide, even distribution of attachments provided the highest level of retention and stability(108) Certain implant positions are more important from a stress management perspective. In any prostheses, the canine is an important implant position. The occlusal scheme, direction of force, and magnitude of force require a canine implant whenever this site is available(109)) If sufficient alveolar bone remains, the insertion of two implants in the canine areas is the preferred treatment option. (103)) A study performed at a mandibular implant overdenture retained by two implants in the canine areas showed the lowest resistance to oblique dislodging forces and the lowest retentive forces at that area(110) Another reason for the preference of lateral incisor areas over canine areas for the installation of the implants is that it is easier to alter the implant retained overdenture to be a fixed overdenture, that requires the use of three more implants at least, when the two implants are positioned in the lateral incisor areas .(111) A study found that when implants were separated more apart each other on the test model, the forces required to dislodge the overdenture generally increased as (inter-implant distance increased).(112) Positioning of implants in the lateral incisor sites has not been recommended in partially edentulous patients because of the lack of bone width at the implant insertion site. Instead, biomechanical studies have suggested canine and premolar locations. (105)

18


In vitro study carried out by Scherer M. et al., 2014 (1)demonstrated that implants inserted at the premolar position may be a more-viable position for an implant-retained overdenture therapy compared with implants insreted in the lateral incisor or canine positions. Even though the removable implant supported overdenture with two implants is a reliable clinical decision and is considered as the minimum standard that should be appropriate for most patients, it does not suit all patients and the abovementioned factors should be taken into account when planning for mandibular removable implant supported overdentures. As a general guide, two implants of 4mm diameter and a minimum of 8mm length are sufficient in order to obtain satisfactory retention and stability. The two implants are preferably located in the lateral incisor areas and not in the canine region. (105) This location is regarded as the best site for installation of the implants for several reasons. For instance, if a removable implant supported overdenture is supported by two implants that are placed in the canine regions, and the removable implant supported overdenture then needs to be altered into a fixed one where five implants are considered essential, placement of three additional implants between the two existing implants may not be possible as the space would be insufficient. Additionally, it has been suggested that the anterior mandibular area should be divided into five equal spaces, in which prospective implants may be positioned .(113) By this strategy, more implants may be installed if the overdenture needs to be changed from a two-implant-supported overdenture to a fourimplant-supported overdenture. Furthermore, if four implants were installed with an equal distance between each, placement of an additional implant when it is required is not possible, as there will be insufficient space to accommodate the fifth implant. (113) 19


Selection of overdenture attachment and implant position The interactions between attachment system, direction of force, and implant number and distribution were statistically significant. Resistance to vertical dislodging forces of a simulated overdenture prosthesis increased with additional widely distributed implants. Four narrowly distributed implants with Locator and Ball attachments had higher mean dislodging forces than widely spaced implants. Attachment type affects retention and stability differently by location. Ball attachments reported the highest levels of retention and stability.A single implant and ball attachment may provide adequate retention for implant overdenture treatment. Two widely spaced implants may be as effective as three narrowly spaced implants. Four parallel implants may provide the most retention and stability.Retention and stability of a simulated prosthesis is significantly affected by implant number, distribution, and position. Most studies reveals that retention increases with increasing implant number and distribution. (1) Three main factors are involved in optimal overdenture treatment: retention, support, and stability. While difficult to isolate from each other, the combination of these factors contributes to overall acceptance and satisfaction of a removable prosthesis. Retention of commercially available stud attachment systems has been the subject of many in vitro studies. Most of these studies assumed a two-implant model approximating the location of the mandibular canines, and evaluation of in vitro retention of prostheses outside of these areas is limited. Retention and stability have been measured comparing the number of implants for implant-retained and supported overdentures; however, these studies have focused their attention on evaluating retention, release, and stability between types and forms of attachments.(108) 20


It was demonstrated by a study that implant location affects the in vitro retention and stability of an implant overdenture and showed that vertical retention increases with distal implant location up to the second premolar, with the incisor area showing the lowest mean retentive values, and the highest values were in the second premolar area. Also horizontal displacement forces increase with distal implant location up to the first premolar, and the oblique pull tests, the results varied considerably, depending on the type of attachment tested. (1) The final location of the implant in relation to the bone and the prosthetic teeth will help to decide the type of attachments used; this should be determined at the diagnosis and treatment planning phase before the placement of implants. In order for the individual attachments to provide adequate retention, all the implants need to be placed as parallel to each other as possible. If the implants cannot be placed relatively parallel to each other, then a bar design would be our next choice to be fabricated for the patient. Additionally, a bar would be considered in cases where implants cannot be placed in ideal locations due to anatomic structures; eg, presence of mental foramen or ridge crest seen in patients with severely resorbed ridges.(114, 115) The sort of attachment affects the influence of vertically applied forces. ERA and O-Ring demonstrated comparative results to one another. In these attachment types, the largest amount of power was needed to dislodge the implants located at the first and second premolar locations, and the lowest at the incisor location. In the Locator and Ball attachment systems, the highest values were located at the second premolar location, and a significant drop in retention occurred when moving implants from the canine to the first premolar location, followed by a significant rise in retention at the second premolar location. (1) 21


Periimplant alveolar bone loss with implant assisted overdenture Osseointegration is defined as a direct structural and functional connection between ordered, living bone and the surface of a load-carrying implant. Osseointegration of the implants to the bone is one of the most crucial factors for implant stability and success. (116) The long-term maintenance of bone around an osseointegrated implant is paramount to clinical success, and peri-implant bone remodeling has commonly been expressed in terms of survival rates(117, 118) . Several factors may affect peri-implant bone resorption: local, surgical, implant, post restorative and patient-related risk factors which include systemic diseases (diabetes), genetic traits, chronic drug or alcohol consumption, and smoking status. (119) Stable marginal bone levels around implants are the key determinant of a successful treatment outcome . Marginal bone loss is a major criterion in the long term implant success

(120, 121)

. As a natural biological process,

the accepted annual bone loss is less than 1.5 mm in the first year and 0.1 mm in the subsequent years or annual bone level loss of 0.2 mm at the contact area between the implant and the bone (122). This phenomenon was described as a “steady state” (123). Causes of rapid initial bone loss include; surgical periosteal elevation, surgical trauma from the preparation of the implant socket or stress concentration from over tightening of the implant (124)

. Marginal bone loss is either vertical or horizontal. It is classified as

vertical when an angle less than 60 degrees exhibit between the implant axis and the alveolar crest of the bone. If the angle greater than 60 degrees, it is a horizontal bone loss. (125)

22


Implant primary stability is a main indicator for implant success depending on bone quality, the geometry of the implant, and surgical technique. If the primary stability is compromised, micro-movements will be increased leading to bone resorption around implant. (126) The effect of time of loading on the marginal bone height changes in implant ball retained mandibular overdenture was evaluated. From this study, it was found that more marginal bone loss and more probing depths were associated with the immediately loaded implants

(127)

. In another

study, the effect of time of loading on the marginal bone height changes was evaluated in implant mandibular overdenture retained by locator attachment and found that more marginal vertical bone loss was associated with the immediately loaded implants compared to the delayed loaded implant overdenture. (31) Implant size plays an important role in marginal bone loss. It was recommended that implants should be as long and wide as possible within the anatomic limitations of the patient in order to decrease stress applied on the bone so, decreasing marginal bone loss as much as possible. (128) Overload and para-function increase marginal bone resorption around implants during function. This is attributed to the increased stresses around the implant caused by this increased forces. Nonpassively fitting implant superstructures induce forces that are transmitted to the surrounding bone. (129) Overloading of the implant has been said to be detrimental for the surrounding bone, but thresholds of loading and the extent of biologic tolerance are still unknown

(130)

. Fatigue micro damage of bone and bone

loss results from excessive mechanical forces beyond a certain limit. (131)

23


Peri-implant alveolar bone loss with implant assisted overdenture with ball attachments: In a study which assesses the influence of attachment types (ball attachment, bar attachment and bar with cantilever) on the marginal bone loss around dental implants supporting mandibular overdentures, it was found that the attachment type for overdenture support seems not to influence marginal bone loss, but cantilevering of the bars increases bone loss significantly. In the same study, it was found that implant length is an important factor in marginal bone level maintenance. Implants shorter than 10 mm engender a greater amount of marginal bone loss.(128) The design of overdenture attachments should allow optimum force distribution around supporting implants to permit bone loading within physiologic levels. In vitro experiments and numeric analysis have suggested that overdenture attachment design may influence stress/strain magnitudes around implants and that lower stresses occur around unsplinted implants.(101, 132) . An In vitro study was done to evaluate stress patterns generated within implant supported mandibular overdentures retained by two different attachment types: ball and socket and locator attachments. Unilateral masticatory compressive loads of 50, 100, and 150 N were applied vertically to the overdentures, parallel to the longitudinal axes of the implants. Loads were directed toward the central fossa in the molar region of each overdenture, that linear static analysis was carried out to find the generated stresses and deformation on each part of the studied model. It was found that the ball and socket attachment enables greater energy absorption, which reduces the amount of energy (stress) transferred to the mucosa and cortical and cancellous bone due to its smaller neck compared with wider diameter locator attachment.(133) 24


A study done to evaluate the peri-implant bone condition after ten years of application of two different overdenture attachments ( ball and socket and bar-clip attachments). The study revealed no significant difference found between two groups regarding the bone loss despite the smaller size of ball and socket compared to bar-clip attachment. However, ball attachments showed shallower probing depths around the implants.(134) A comparative study was done to evaluate stress applied on bone using three different overdenture attachments (Bar-clip, Cantilevered bar clip and Ball/O ring attachments). It was found that, Bar-clip group showed the greatest stress values followed by cantilevered bar-clip followed by Oring group enhancing the hypothesis of using small size unsplinted attachments reduce maximum and minimum principal stresses levels in both implant/prosthetic components and supporting tissues.(135) Another study was performed to compare the stress levels of four different overdenture attachments (bar, bar/ball, bar/distally placed Rk-1s and locator). Vertical loads (100N) were applied to the central fossa of the right first molar of each overdentures. Stress levels developed in in the denture bearing areas were observed photoelastically and evaluated visually. The study showed that, the greatest stress with bar/ball design was found while the lowest stress levels were observed with the locator attachments design ( the smallest design among other designs in the study).(136) Jins John et al. (2012) made an invitro study to evaluate stress applied on bone using two different implant mandibular overdenture attachments ( ball/O-ring and magnet attachments). Ball attachment was of 2.5 diameter and the magnet was of 4mm diameter. Forces of 10 N, 35 N and 70 N were applied from the horizontal, vertical and oblique directions respectively and the stress distribution was studied. The study revealed that 25


ball attachment exerted lesser stress levels on peri-implant bone compared to magnet attachment.(116) Implat-retained mandibular overdentures require sufficient space otherwise attachment separation, denture base may occur so there is a need for occlusal plane repositioning and management of overdenture attachment selection

(137)

Peri-implantitis and parafunctional habits are

important factors of implants failure that should be into the considerations of the clinicians. (138)

Periimplant alveolar bone loss with implant assisted overdenture with different positions The bone mineral content of the trabecular and cortical bone is essential for osseointegration and with advanced age, this content decreases. A study found a higher trabecular bone ratio in the mandible in the lateral incisor region than in the canine and premolar areas of edentulous patients.(139) In an in vitro study, Elsyad, et al. (2013)(140) showed that when the implants are distributed in a quadrilateral design in the dental arch, very little values of strains around the implants are developed. These strains might lead to excessive bone resorption under functional occlusal loads, especially around the implant shoulder. This could be because of the large distribution of loads over a square area, and to the excellent support produced by this design which is similar to a four-legged chair. In contrast, Krennmair, et al. (2012)(141) in an in vivo study found a 100% implant survival rate and minimal marginal bone resorption when they placed four implants in a linear design to support mandibular overdentures with rigid telescopic attachments.

26


A finite element analysis study compared the stresses in peri-implant areas in 2-implant retained mandibular overdenture with implants positioned in lateral incisor position, and 4 -implant supported mandibular overdenture with implants positioned in lateral incisor and second premolar position, this study found that stresses were around the lateral incisor position in the 2-implant retaind overdenture were greater than around the lateral incisor position in the 4-implant design (142) Celik and Uludag found that there is no significant effect on stress values around implants regarding the number of implants used. Als no difference was found in the radiographical state or clinical satisfaction of patients treated with either two or four implants. (143) In an in vitro finite element analysis study on two overdenture on two models (one model had two anterior implants and two ball attachments and the other had two anterior implants and two ball attachments with additional 2 posterior implants for support), it was found that there is high strains around the implants in the design of two implants only that can harmfully affect the surrounding bone because it exceeds the bone’s hyperphysiologic limit. Whereas the addition of posterior implants showed reduction of these harmful hyperphysiologic strains(144) Denture fracture is a very common complication with overdenture wearers due to stress concentration over the implants so, periodic follow up and denture base reinforcement or replacement are of important issues(145) Occlusal forces affect the bone surrounding an oral implant. Mechanical stress can have both positive and negative consequences for bone tissue and, thereby, also for maintaining osseointegration of an oral implant. After the ﬁrst year of function, loss of marginal bone is small 27


around most oral implants, although a considerable loss can be observed at some implants (146) Furthermore, it has been stated that the occlusal forces on an oral implant can result in loss of the marginal bone or complete loss of osseointegration even after a long time of service(147). An association between oral microbiota (plaque accumulation), peri-implant mucositis, loss of marginal bone (peri-implantitis), and subsequently loss of implants has also been described (148)

28


Radiographic evaluation of marginal bone resorption around dental implant The evaluation of radiographic bone height changes around implants is currently the only available method for evaluating success from survival. Therefore, it is important that a standardized radiographic method is used and the implants are followed up sequentially to provide reliable longitudinal data. The importance of standardizing the radiographic method has been documented extensively (149). Methods used for measuring and evaluating implant marginal bone loss Include: Panoramic radiographs, Intraoral radiographs, Multislice computed tomography (CT), Cone beam computed tomography.

1.

Panoramic Radiographs:: Panoramic radiographs are widely used for evaluation of the

condition of the bone around implants retaining mandibular overdentures (150)

. A panoramic radiograph, includes both the jaws and the implants, is a

simple examination process, offering ease of operation and a shorter working time and can be used even in patients with limited mouth opening(151). Panoramic radiographs are as reliable as conventional intraoral ones when used to assess the point of bone attachment to implant threads. (149)Because of its standardized projection in the vertical plane, it is well suited for vertical measurements (152). Distortion, magnification, relative unsharpness and superimposition of the vertebral column are the main disadvantages of panoramic radiographs. Also, they are not very reproducible in edentulous patients. (153)

29


With panoramic radiography, it is difficult to control the placement of the subject relative to the x-ray source, with small differences in placement having large effects on resulting images. For this reason, it is impossible to superimpose subsequent panoramic radiographs for performing image subtraction. Tymstra et al, (2011) (154) used proportional area measurements on panoramic radiographs to assess the effect of a mandibular-retained overdenture using two or four dental implants or a conventional completet denture on resorption of the residual ridge of the maxillary anterior and mandibular posterior areas over a period of 10 years. In a retrospective study performed using data from patients who had been restored with implant-supported cantilevered bar-retained prostheses, Semper, et al (2010) evaluated vertical changes in crestal bone level by panoramic radiographs. The quantitative evaluation of peri-implant bone resorption was performed by routinely analyzing the taken panoramic radiographs on the mesial and distal sides of each implant. A specific reference point at the level of the implant-abutment interface was used. To eliminate radiographic distortion, the original implant length was used in an equation to measure the actual vertical bone loss.(155) Panoramic radiographs were used in another study for measuring the marginal bone loss around dental implants in mandibular 2 implants overdenture. The authors used the known distance between implant threads and the number of exposed threads in the panoramic radiograph for calculating the amount of bone loss around the implants. (152)

30


2.

periapical Radiographs:: The ideal evaluation technique for the peri-implant bone loss is the

intraoral periapical radiographs when the film holder is fixed to the implant to standardize the technique

(156)

. Many authors have reported an annual

bone loss of less than 0.1 mm using the long cone technique but without an aiming device

(157)

.This technique provides the best resolution among all

imaging modalities (158). The disadvantage of this technique is that it is not as simple to perform as the panoramic radiograph and it is not always possible to depict the entire implant on the radiograph.

(159)

Film holders

are usually very painful for edentulous patients particularly when the clinical height of the residual ridge is limited; making intraoral periapical radiographs a challenge. (160) Many techniques were conducted to standardize the evaluation of peri-implant bone in the anterior mandibular area. One method used a template of autopolymerizing acrylic resin holding the film parallel to the area to be exposed and a film holder is used to connect it with the long xray tube. This procedure assured that the focus-film and implant-film distances were maintained throughout all exposures. (161) For conventional intraoral radiographs, research data indicate that a change in the vertical radiographic projection angle results in a change of the measured bone level by approximately 0.1 mm for every degree the angle is changed. A film position that is not parallel to the long axis of the implant will also give false information on the marginal bone levels.(162)On the other hand, the deviation from a perpendicular projection relative to the long axis of the fixture should not exceed 9○ (163).

31


3.

Multislice computed tomography (CT):: Multislice CT was preferred over panoramic and periapical

radiography to evaluate marginal bone changes as it provides excellent bone height and width measurements, while panoramic and periapical radiography have large information voids related to depth, and are affected by projection geometry, so their measurements are not reliable

(164)

.

Compared with cone beam CT, multislice CT has the same image quality of trabecular bone and higher image quality of cortical bone with high image accuracy. (165) Marginal bone loss around immediate and delayed loaded unsplinted implants supporting mandibular overdentures with ball attachments was evaluated using multislice CT . The authors found that immediately loaded two implants supporting a ball-retained mandibular overdenture are associated with more marginal bone resorption and increased probing depths when compared with conventionally loaded implants after 3 years. The bone resorptions at distal and labial sites are significantly higher than those at mesial and lingual sites. The authors used the coronal view of the CT image for determination of vertical and horizontal bone loss mesially and distally and used the sagittal view of it for determination of vertical and horizontal bone loss buccally and lingually.

4.

Cone beam computed tomography (CBCT):: Cone beam computed tomography (CBCT) provides cross-sectional

images in the 3 dimensions

(166)

that allow monitoring of the buccal and

lingual bone levels around implants (167). Cone beam tomography utilizes a cone-shaped x-ray beam and either an image intensifier or flat panel detector for volumetric image acquisition. (168) 32


CBCT was used in a study for measuring peri-implant vertical and horizontal bone loss for mandibular overdentures retained by splinted and nonsplinted immediately loaded implants. The authors measured both vertical and horizontal bone loss along mesial, distal, buccal and lingual sides of implants. The technique for measuring was as follows: The 3D position of each implant was determined by the program. Then, horizontal (X and Y) planes at right angle to the long axis of every implant were reconstructed to give 2 vertical cross-sectional images as follows: a mesiodistal image, formed by using a “curve tool” that bisected the alveolar ridge and the implants mesiodistally, and a buccolingual image, formed by the axis that bisected the implant buccolingually. This brought about 4 circumferential measurements: distal, buccal, mesial, and lingual. At that point, the peri-implant marginal bone levels were determined at the four sites. (169)

33

Aim of the Work

Aim of the Work This study was done to evaluate the effect of location of the two implants used to retaining mandibular complete overdenture on periimplant alveolar bone height changes Two groups were evaluated: Group I: where the two implants were inserted in the canine areas. Group II: where the two implants were inserted in the second premolar areas. Radiographic evaluation of peri-implant alveolar bone height changes were done at time of attachment pick up (To), after 6 (T1) and 12 (T2) months of denture insertion.

34

Material and methods

Material and Methods Selection of the patients Ten healthy completely edentulous male patients (age ranging from 50 to 60 years) with mean age (55 years) were selected from outpatient clinic of the Prosthodontic Department, Faculty of Dentistry, Mansoura University according to the following criteria:

Inclusion criteria: 1. Completely edentulous Maxillary and mandibular Healthy, well formed residual alveolar ridge covered with firm, relatively even compressible mucosa as detected by visual examination and palpitation test using the handle of the mirror.(fig.1) 2. The mandibular residual alveolar ridge was without local inflammation or any remaining roots verified by digital panoramic.(Fig. 2) 3. Sufficient bone quantity and quality was verified in the prospective sites of dental implants (canine and 2nd premolar areas) by preoperative CBCT using clear acrylic resin radiographic template representing the conventional mandibular denture. ( Fig. 3 a & b) 4. Angle's class I maxilla-mandibular relations with adequate interarch space as detected by tentative jaw relations. 5. At least 6 months elapsed from last extraction

35


Exclusion criteria: 1- Patients with any systemic diseases that affect the implantation procedures as uncontrolled diabetes, hyperparathyroidism, osteoporosis, advanced renal and hepatic disorders. 2- TMJ disorders. 3- Abnormal parafunctional habits, as bruxism and clenching, etc..... 4- Smokers and alcoholics. 5- History of radiation therapy in the head and neck region. 6- Uncooperative patients.

36


Fig. (1): Completely mandibular residual edentulous alveolar ridge covered with healthy firm mucosa.

Fig. (2): Preoperative digital panoramic radiograph.

37


a

b

Fig. (3 a &b): Verification of bone in the prospective sites of dental implants using CBCT (bone quantity _a & quality _b)

38


I. Patient's Approval: After the patients were informed about the line of treatment and the need of their regular and frequent recall, they were approved their treatment plan on a written consent to follow the study protocol throughout the total period of the research.

II. Presurgical procedures Radiographic examination and implant selection: Preoperative CBCT was taken for each patient to evaluate the bone quality and quantity in the mandibular premolar areas and canine areas. Implant fixture was selected for all cases according to available bone heights. . (Fig. 4)

Evaluation of the interarch space: Maxillary and mandibular preliminary irreversible hydrocolloid

*

impressions were recorded and poured in stone. After construction of autopolymerized acrylic resin ** record bases and occlusal rims, a tentative vertical and horizontal maxillomandibular relations were recorded. The casts were arbitrary mounted on the articulator to estimate the available interarch space to select a minimum interarch distance at the canine and premolar areas.

*CA‐37 superior Pink.Cavex.Holland ** Acroston, self‐curing acrylic resin, Egypt

39


Construction of conventional complete denture:  Autopolymerized acrylic resin custom trays were constructed on the primary cast and border molded with low-fusing green compound* then final impressions were made with zinc-oxide impression material**  Final impressions were boxed and poured to obtain master casts.  Record blocks were constructed over master casts and were used to record vertical and horizontal maxillo-mandibular jaw relation.  The maxillary cast was mounted on the semi-adjustable articulator using maxillary face-bow and the mandibular cast was mounted using centric interocclusal records.  _Semi anatomic artificial acrylic resin teeth were arranged, waxed up, tried in; and processed into heat-cured acrylic resin.  Laboratory remount was done to correct any occlusal errors.  After finishing and polishing, dentures were clinically remounted to finally adjust premature occlusal interference.

Grouping of patients According to the location of the implants, all patients were equally divided randomly into two groups: Group I: where the two implants were inserted in the canine areas. Group II: where the two implants were inserted in the second premolar areas. *

SpofaDentala.s. (A Kerr Company) Markova 238 506 46 Jicin Czech Republic. ** Cavex impression paste, Holland

40


Planning of implant prospective sites and construction of Stereolithographic stent: -

The new mandibular denture was duplicated to create an acrylic resin radiographic template (gutta-percha radiopaque markers fitted to the fitting and polished surface). Patients underwent CT scans to accurately assess the quantity of bone for prosthetically driven implant placement(170)

-

Five gutta-percha radiopaque markers were attached to holes prepared in the fitting surface the duplicated denture opposite to each canine and 2nd premolar areas used to calculate the average thickness of the mucosa covering the residual alveolar ridge. In addition to radio opaque material was prepared in the labial, buccal and lingual polished surfaces of the denture (at mid line, canine and at first molar region) to estimate the thickness of the acrylic resin.

-

The patients were double-scanned (Dual scan protocol) using Cone Beam Computed Tomography (CBCT). The first scan was made with the radio graphic stent separately without the patient. The second scan was performed while the patient occluding on the radiographic stent (171)

-

The raw dicom files of the scan are imported into a specific implant analysis software (In 2 guide module of OnDemand 3D APP software, cypermed , Korea).

-

The software superimpose both scans together and the denture acrylic fitting surface act as guide for mucosal surface

41


The plane was done according to specific principles which are: 1. The two implants are placed virtually in the guide software, optimizing position, angulation and distribution 2. Two implants were placed at canine or premolar area parallel to each other and perpendicular to occlusal plane. Premolar implants were inserted in premolar area just anterior to mental foramina with safety margin from the foramina 3. All planning was performed by the same radiologist and checked by the prosthodontist(171). The plan was used to construct a mucosal supported stereolithographic surgical template with 2 sleeves positioned over proposed implant sites, and the template was constructed by rapid prototyping technology -

Virtual model planning software was used to define the sites for implant placement and anchor pins for the Stereolithographic surgical guide (fig 5,6).

-

A universal surgical kit* was supplied with the mucosal supported stereolithographic surgical template to be used during osteotomy preparation (fig7). This kit includes hand drill sleeves with successive increasing diameters that fit the template sleeves. The hand sleeves were used during drilling procedures with surgical guide to accommodate successive increasing in drill diameter.

42


Fig (4) calculation of the angle between proposed implant position and the metal tube in the cross-sectional images of the CT.

Fig (5) : virsual planning for implants parralism

Fig. (6): Stereolithographic surgical guide template.

43


Fig 7 (a & b) Universal surgical kit

44


III.

Surgical procedures: All patients were administrated 1 gm broad spectrum antibiotic * and

50 mg anti-inflammatory ** tablets one hour just before and daily for one week after surgery. They also used chlorohexidine mouth wash which started ten minutes before surgery and continued after surgery twice daily. According to Matteo Chiapasco etal,2001

(172)

,Two stage surgical

protocol was done in the following steps: 1.

Under local anesthesia, Placement of implants in the corresponding sites for the two groups will be done using the flapless technique.

2.

The surgical mandibular Stereolithographic template and upper denture were then seated over the ridge and the patient was instructed to occlude to ensuring that the surgical template is exactly seated on the underlying mucosa to resume the same position..

3.

Fixation of template by anchor pins to engage in the underlying bone then removal of upper denture prior to surgery (fig. 8).

4.

circular tissue punch was done with a tissue puncher to expose the implant site (fig. 9)..

5.

By using the initial drill (available in the universal kit* provided by the radiologist) with a maximum speed of 1400 rpm, drilling was done carefully for 11.5 mm depth (3.2 mm diameter and 11.5 mm. length) (Fig.10).

*

(Megamox . Julphar Egypt ) (Cataflam 50mg. Novartis Egypt)

**

45


6.

The final drill of the implant system** (3.2 diameter ) was used at low speed of 800 rpm and high torque (35 NCm) hand piece and external irrigation to avoid overheating and prepare the final osteotomy at length of 11.5 mm score line of the final drill (Fig.11).

7.

The crestal tap drill was used at speed of 15 rpm to prepare the countrsink of fixture at the top of osteotomy to preserve marginal bone.

8.

The osteotomy site was irrigated with perfuse saline to eliminate any bone chips.

9.

The finger octa driver was inserted in the fixture within the sterile vial to grip the octa hole implant carefully (Fig.12).

10. The fixture was self tapped within the osteotomy by using finger octa driver until it resists the tap in procedure to ensure implant initial stability. (Fig13) 11. The wrensh was adjusted for 35 N/cm and used to complete the final tap of the fixture provided that the mesial and distal fixture margins were in level with crest of the ridge (Fig.14). 12. Proper implant placement was verified by intra oral panoramic radiographs .(fig 15a&b)) 13. Cover screws were fixed on the two implants. (fig 16) and then suturing of the insertion sites was done. (fig 17) 14. Post-operative instructions including

46


a. Ice packs applied in the first 24 hours over the surgical area to reduce post-operative edema. b. Patients were informed to eat soft diet (eg. milkshakes, fruit juices, mashed potatoes, soups, and soft pasta) and avoid hard foods (eg. popcorn, granola, and nuts) which may become lodged in the surgical site.

Fig. 7 Dyna surgical implantation kit.

47


Fig 8 ,Fixation of sterolithographic surgical guide template in patient mouth

Fig 9 , Implant site exposure using tissue punch

48


(Fig.10) Initial pilot Drilling .

Fig 11 , final drilling of the osteotomy site

(Fig.12) The fixture was carefully removed from its vial by using finger octadriver.

49


(Fig 13 a&b) Proper implant placement was verified by intra oral panoramic radiographs. (fig 15a group I&b group II )

50


Fig14 :cover screw in its position.

Fig 15 : suturing over cover screw

51


V. Prosthetic phase: 1. The fitting surface of the mandibular denture above the implants was relieved to provide adequate pressing on the right and left side of the denture. The denture fitness was secured by relining with a soft tissue conditioning material. 2. Participants were informed to attend regular follow-up visits (twice/ week for 3 weeks and once/week for 3 months) to verify oral hygiene practice and perform adjustments of the relined dentures till osseointegration occurs. 3. The mandibular denture was relined with tissue conditioner material for 2 weeks, then the tissue conditioner was replaced with autopolymerized soft liner. 4. After the osseointegration period (3 months) , circular tissue punch was done with a tissue puncher to expose the fixture .The cover screw was unscrewed and a 2 mm height healing abutments was screwed into the fixture by a Hex Key (Fig.18). 5. Participants were instructed for oral hygiene procedures as follows: gently brush the healing abutments with soft brush, use mouth wash and meticulous clean the mucosa around implants to avoid plaque accumulation on the healing abutments. 6. After one week , healing abutments were replaced by 2mm neck height ball abutment which were screwed into the fixures by using the Hex driver.(fig 19 a&b))

52


Direct pick up of the female house (Smart Gold Matrix) The direct pick up of the female house was done according to Corinne et al., (2004 )(173) as follows: 1- The house of the processing smart matrix in the denture fitting surface was relived for 3mm. and a venting hole was drilled lingually opposite to each house. The healing abutments were unscrewed from the fixture and replaced by the ball abutments. 2- The ball abutments were screwed into the fixture and the Smart Gold matrix was placed on the ball. Interferences were disclosed between the intaglio surface of the denture and the attachment system with a low-viscosity silicone material * using acrylic resin stine bur , the fitting surface of the mandibular denture was prepared for receiving the smart gold matrix.(fig.20). 3- The Smart Gold matrix was removed and a rubber spacer was seated around each attachment to block the interference bulge of the ball. 4- The lingual portion of the denture opposite to the attachments was perforated to allow escape of the excess of the pick-up acrylic resin. 5- The Smart Gold matrix was repositioned over the ball abutments (Fig.21).. 6- The denture was inserted under firm finger pressure and then the patient was asked to occlude until centeric occlusion polymerization is completed. 7- The denture was removed and the excess acrylic resin was removed carefully from the intaglio and outer surfaces of the denture (Fig.22).

* (Pressure Spot Indicator; Coltene/ Whaledent Inc, Cuyahoga Falls, Ohio) 53


8- The elastic bands were removed and approximately 1mm of acrylic resin adjacent to the matrix was removed with a bur, to prevent impingement on the gingival peri-implant soft tissue. 9- The denture was delivered in the patient mouth and checked for convenient insertion and removal then delivered to the patient. 10- The patient was instructed for proper hygiene and home care of the denture. 11- The patients were informed about the follow up and periodical recalling for evaluation.

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(Fig 16 a & b) , the healing abutments in group I (canine areas)and II (premolar areas)

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Fig 17 a&b , ball abutments connected to the fixure in group I(canine areas & group II(premolar areas).

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(Fig.18) preparing the fitting surface for female housing (smart gold matrix)

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(Fig.19) The dyna smart gold matrices was placed on the ball attachments in group I&II.

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(Fig.20)The denture was removed and the excess acrylic resin was removed carefully from the intaglio and outer surfaces of the denture.

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Methods of evaluation: VI. Periapical radiographic assessment of peri implant alveolar bone height changes Peri-implant marginal bone height using periapical radiographs will be evaluated at time of connecting the definitive attachment and loading (TO) and after 6 months (T1) ,after 12 months (T2) . Intraoral radiograghs were produced using standardized long cone paralling technique and a film holder designed specifically for implant imaging. Walter, et al. (2000) For maintaining the same film implant distance and cone implant distance during subsequent film exposures, standardized intraoral radiograghs of the coronal parts of the implants were taken using modified plastic film holder (fig 23). The peri-apical films were scanned using a black and white translucent scanner and the radiographic images were magnified approximately *15 after digitizing the radiographs. Implant dimensions in the radiographs were compared with actual implant dimensions to detect magnification errors. The ratio between implant dimensions in the radiographs and actual implant dimensions was used to modify the apparent measurement of peri-implant bone levels in the radiographs to obtain their actual values. (174) Peri-implant crestal alveolar bone changes were determined along vertical and horizontal planes as recommended by Heckmann et al. (2004) (175)

.

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To measure the vertical bone loss (VBL), the distance between the shoulder of the implant (point A) and the first bone to implant contact (point B) was measured and referred to the vertical bone level in mm (AB line). AB line at 0 month was subtracted from AB line at 6 and 12 months to measure the VBL. To measure the horizontal alveolar bone loss (HBL), the distance between the periimplant bone level (C point) [which is the crossing point of the tangent to the horizontal bone crest (CD line) and the tangent to the crater shaped defect (CB line)] and the implant at right angle was measured and referred to the horizontal bone level. Horizontal bone level at 0 month was subtracted from horizontal bone level at 6 and 12 months to measure HBL. (Fig 24). All measurements were determined at mesial and distal surfaces of each implant.(127) To represent time of insertion of attachment (base line) T1 represent first 6 months T2 represent the 12 months of the study T3 represent second 6 months

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Fig (21) : lines and points on periapical x ray

Fig (22) : Fixation of film holder

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Statistical analysis The data were analyzed using SPSS® software version 22 (SPSS Inc., Chicago, IL, USA). One-Sample Kolmogorov-Smirnov and Shapiro Wilk tests were used to diagnose normality of data distribution of all variables. The data were parametric and presented as mean±SD. Betweengroup comparisons of VBL and HBL was performed using independent ttest. To detect significant differences between observation times paired ttest was used. Independent t-test was used to detect differences between mesial and distal site in the same group. P-values