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Page No. 1. Introduction

2-6

2. Review of Literature

7-18

3. Discussion

19-69

4. Conclusion

70

5. Bibliography

71-76

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ERRORS IN IMPRESSION MAKING INTRODUCTIONImpression techniques and materials used in dentistry have come a long way since the early times, where it was just an attempt to record the tissues without the knowledge and appreciation of the anatomy, physiology and microbiology of tissues being recorded, to a more scientific, well documented, biologic impression making that is followed today.1 Several authors and researchers have emphasized the need to understand the concept behind the number of techniques being used today. 2 It could well be said that Prosthodontics is one of the branches of dentistry where a good impression holds the key to a successful diagnosis and treatment. The fundamental requirement of retention, stability and support of any prosthesis rests in the ProsthodoQWLVW¶V DELOLW\ WR LQFRUSRUDWH these requirements through an accurate biologic impression of the tissues being involved.3 No matter how good the prosthesis is constructed, it will not function as intended if it was not made on an accurate impression. Impression materials too have gone through a tremendous phase of development. From olden day clay, to wax to the modern day elastomers, they have indeed not only improved the quality of the material but also directly influenced the technique used to manipulate these materials during impression making.4 Many times both the impression techniques as well as the material have complemented each other in producing an accurate impression incorporating all principles for an ideal impression making.5 Impression making is the first and foremost step in diagnosis and treatment planning. A good impression will produce a cast that will apprise the practitioner of the need of patient and the prognosis of the proposed treatment. 6 It is to be agreed that time

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spent in making a good impression will reduce the time required in adjusting the final prosthesis in the mouth as well as make it more comfortable for the patient in accepting the artificial prosthesis. Ideal outcome of the impression must be borne in the mind of the dentist before it is in his hand. He must literally make the impression rather than take it. The impression material is shaped and moulded into a negative likeness of the supporting area, a cast is made from this impression and the denture base is constructed on this cast.7 Good impressions are basic to the fabrication of a wellfitting denture. An impression should mean while also IXOILO00'HYDQ¶VGLFWXP³,WLV perpetual preservation of what already exists and not the meticulous replacement of ZKDWLVPLVVLQJ´8 A good impression is not only the first stage in the fabrication process but also the prerequisite for a high-quality prosthetic restoration. The precision and accuracy of details of the impression are crucial in determining the accuracy of fit and aesthetic quality of a fixed restoration. By critically analysing various impressions at different stages of this study related to impression techniques and material it is hoped to achieve the following.2 1)

A thorough understanding of the biologic principles in impression making.

2)

To understand requirements necessary to achieve a biologic impression.

3)

The manipulation of different impression materials to achieve the desired requirements in an impression.

4)

The indications, advantage and limitations of each impression technique and material

5)

As a diagnostic tool in understanding the tissues being considered and the need for further enhancement of such tissues if required.

ϰ

6)

To help determine the treatment plan.

7)

To help distinguish from a clinically compromised impression to a clinically acceptable impression.

8)

To make an impression that will maximise support, stability and retention of prosthesis.

9)

To determine a classification system of errors in impressions.

It is obligatory for the dentist to update himself with all the theories and techniques of impression making as well as impression materials that can be used.9 The endeavour should always be to choose the best material and apply the specific technique for a particular patient while making an impression after examining the condition of soft tissues and the bony ridges, so that best results can be obtained. Nevertheless the need for evaluation of impression techniques and materials for errors used in prosthodontics is necessary due to the fast changing scenario in impression making. This library dissertation has made an attempt to summarize all the errors in impression making used in modern day prosthodontics therapy

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DEFINITION¶6

1)

Impression (GPT-7)10:- A negative likeness or copy in reverse of the surface of an object; an imprint of the teeth and adjacent structures for use in dentistry.

2)

Complete denture impression (GPT- 7)

10:

- is the negative registration of entire

denture bearing, stabilizing and border seal areas, of either the maxillae/mandible in a plastic material that becomes relatively hard/ set while in contact with these tissue. 3)

Partial denture impression (GPT- 7)10

:-

A negative likeness of part or all of a

partially edentulous arch. 4)

10

Altered cast impression (GPT-7)

:- A Negative likeness of portion/portions of

the edentulous denture bearing areas made independent of and after the initial impression of the natural teeth. Thus technique utilizes an impression tray (s) attached to the RPD framework or its likeness. 5)

Preliminary impression (GPT-7) 10:- A negative likeness made for the purpose of diagnoses, treatment planning/fabrication of a tray.

6)

Master impression (GPT ± 7)

10

:- A negative likeness made for the purpose of

fabricating prosthesis. 7)

Impression material (GPT-7)

10

:- Any substance or combination of substance

used/for making an impression/ negative reproduction 8)

Impression technique (GPT-4)

11

:- Method/manner used in making a negative

likeness. 9) Impression tray (GPT 7) 10:a.

A receptacle into which suitable impression material is placed to make a negative likeness.

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b.

A device that is used to carry, confine and control impression material which making an impression.

9)

Impression Coping (GPT-7) 10:- The component of a dental implant system that is used to provide a spatial relationship of an endosteal dental implant to the alveolar ridges and adjacent dentition or other structures. Impression coping can be retained in the impression or may require a transfer from intra oral usage to the impression after attach the analog or replicas.

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REVIEW OF LITERATURE COMPLETE DENTURE IMPRESSION Arthur (1951)5 in his article on the principles of full denture impression making and their applications mentioned the specification for an adequate full denture impression. 1.

The form of the denture foundation should be recorded without distortion.

2.

The entire area to be covered by the denture should be recorded as it is determined by functional movement of border tissue.

3.

5HOLHIDQGGDPVVKRXOGEHSODFHGDWWKHRSHUDWRU¶VGLVFUHWLRQLQVWUDWHJLFDUHDV

Carl O Boucher (1951)1 critically analysed mid-century impression techniques for full denture and summarized them as follows. Impression techniques in use at the middle of the twentieth century vary not only in the plan of the technique but also with each operator as well.

Evolution can be made only by an analysis of the

resultant impression area by area in relation to part of the mouth to which that part of the impression is adapted. The supporting structures have equal importance with the limiting structures in this analysis. The value of the procedures used will depend upon the recognition of possibilities and limitations of anatomic form and structure of the mouth, and the characteristic of the impression material selected.

Arbitrary

impression techniques do not meet the requirements of an impression technique.

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Devan3 LQKLVDUWLFOHµ%DVLFSULQFLSOHVLQ LPSUHVVLRQPDNLQJ¶EURXJKW to RQH¶V attention the basic and fundamentals in making impressions for the purpose of the construction of mucosa attached artificial dentures.

Leonard S. Fletcher12 (1952) in his article µIXQGDPHQWDO SULQFLSOHV RI IXOO GHQWXUH FRQVWUXFWLRQ¶GHVFULEHG the impression technique in complete denture construction.

Tiltton13 (1956) described a minimum pressure impression technique. He said that pressure applied in impression making must be equally balanced throughout the entire area of the impression.

Klein14 (1957) described the need for basic impression procedures in the management of normal and abnormal edentulous mouths and the purpose and objectives of the complete denture impression should be:1) Retention of the complete denture. 2) Stability of the complete denture 3) Comfort of the complete denture and 4) Maintenance of the health of the supporting tissues.

Irving R. Hardy and Krishnan K, Kapr15 (1958) described the rationale and importance of posterior border seal and gave functional and semi functional technique of developing a posterior palatal seal.

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In the functional technique, the final impression was border molded in the posterior palatal seal area with soft stick modeling compound or wax by sucking and bubbling movements performed by patients. In semi functional technique the border molding was done by the dentist.

Roberts4 (1959) in his article on present day concepts in complete denture service, gave an account on impression making. Blank16 (1961) described a procedure for making the primary and final impression for maxillary immediate dentures.

Woelfell9 (1962) described two basic impression techniques. 1.

Open mouth technique

2.

Closed mouth technique These techniques are then sub classified according to the desired type of contact with the oral mucosa as positive pressure or selective pressure. The result of his study showed that no one specific type of material or technique can be claimed superior in all aspect for edentulous impressions. Hickey, Boucher and Woelfel8 (1962) wrote on the impressions for complete dentures. They said, before impression, the mouth should be studied carefully to determine all anatomic landmarks and consistency of the soft tissue. The tray that carries the final impression material should be in harmony with these attachments. The thickness of the labial flange of the tray is an esthetic factor. The posterior extension of the impression was also important. The posterior end of the upper denture passes through the hamular notches.

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Academy of Denture Prosthetics6 (1963) on principle, concepts and practice in prosthodontics restated that preliminary impressions were made as the first step in the construction of a final impression tray. Barone17 (1963) in his article ³SK\VLRORJLF FRPSOHWHGHQWXUHLPSUHVVLRQV´described technique for complete denture impression with the utilization of the neuromuscular concepts. The patient used the function of sucking to border mold the impression. The contribution of favorable nutrition, muscle and tissue tonus, and tongue position to the retention and stability of the denture and comfort of the patient had been explained. Martone18 (1963) gave the modification of the tray for zinc oxide and eugenol wash impression. Out line in pencil on the cast the extent and thickness of space needed for final impression. The relief area were outlined on the cast for the secondary stress bearing area, one layer of pink base plate wax 1 mm thick was warmed and moulded to the cast in relief areas. One thickness of green casting wax 0.5 mm was added to the wax over the retromolar pad area. These regions are easily displaced. The amount of relief space should be modified to accommodate different anatomical foundational conditions.

For e.g. spiny knife edge ridge may require additional

space, the tray was then constructed. Scheisser19 (1964) mentioned the impression procedure for complete dentures. A stock tray was adapted to the residual ridge as closely as possible and a preliminary modelling compound impression was made. The patient was asked to extend his tongue as far out as possible close to lip around the tray handle, and draw or suck in with as hard an action as possible.

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Collett et al7 (1965) described complete denture impressions, and concluded that moisture on the tissues and secretion from mucous glands can lead to inaccuracies in impression. Lott and levin20 (1966) gave an impression technique for complete dentures, called the flange technique. The denture flanges were moulded by the patient, through various functional movements. The authors claimed that the flange techniques were superior to the results of the discretionary methods of determining the tooth and tongue positions, and the arbitrary carving of the facial tongue and palatal surfaces. Rudd21 (1967) said that the defects in complete denture impression resulting from the effect of palatal mucous secretions can be countered by using antisialogogues in conjunction with mouth rinses and gauze packs. Frank22 (1969) in his study on impression pressures stated that impression pressure can be controlled by tray design and material selection. Ellinger23 (1973) said that the success of a complete denture was determined by correct clinical procedures for each given step. The making of an impression, was one of these steps. The author in this essay tried to gave some tips as to how; we can minimize problems in making a complete lower impression. Kiein24 (1973) in her article on complete denture prosthetic procedure mentioned on primary impression and final impression technique. Smith25 et al (1979) described a technique which used polyether impression material for border moulding of complete denture impressions. There was simultaneous moulding of all borders of either maxillary or mandibular impressions. The border

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moulding could be accomplished with insertion of the tray. Functional movements performed by the patient were used in border moulding. Mc Arthur31 (1980) described a technique of making individualised impression trays from existing complete dentures. With this method the patient must have existing dentures, and the border extension must be adequate. Zinner26 (1981) gave an analysis of the development of complete denture impression technique. He said that the history of impression making shows that most of the significant advances occurred before 1930. Basic principles of pressure maximum extension and equal distribution of pressure were first introduced in 18451899. During 1900-1929 accuracy of impression techniques were emphasised. A newer method of border moulding was one of the major innovations of the era. The era from 1930 to 1940 saw great advances in the knowledge of the anatomy of tissues as they affect impression making. The use of immediate denture technique and the introduction of several new materials like zinc oxide euginol paste and hydrocolloids were also noted. Klean27 LQ KHU DUWLFOH ³SK\VLRORJLF determinants of primary impressions for FRPSOHWH GHQWXUHV´ JDYH RQ DFFRXQW RI WKH SULPDU\ LPSUHVVLRn procedures in maxillary and mandibular complete dentures. she modified the periphery of the compound impression by using Kerr impression wax. Klein28 (1985) described a secondary impression technique which helps to minimise distortion of the ridge and border tissue. Clear acrylic resin tray aid in eliminating excessive displacement at the secondary impression phase. The areas of blanching can be seen through and such areas were marked and relieved.

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Shigeto Minagi et al31 (1988) described the concept and technique for making an accurate final impression for complete dentures using a thixotropic material. Aquaviva Fernandes et. al29 (2006) described µcorrective Primary Impression Technique¶ DV a simple, quick and corrective technique for making the preliminary impression. The defects, which were present in the primary impression with compound, can be corrected with the use of alginate hence this technique can be FDOOHGDV³FRUUHFWLYHSULPDU\LPSUHVVLRQWHFKQLTXH´ Anuj Chhabra et al32 (2006) described simple and rapid approach of making the preliminary impression with sufficient viscosity yet with ample working time. This may enable the operator to fashion the preliminary impression in a single operation with practice. E.G.R.Solomon2 (2011) described complete denture impressions, factors affecting the properties of impression materials, landmarks of edentulous jaws, biological considerations in complete dentures. Kerstin wegner et al33 (2011) described the influence of two functional complete denture techniques on SDWLHQW¶V satisfaction.

FIXED PARTIAL DENTURE IMPRESSION Hudson38 (1958) described the clinical use of rubber impression materials and said a combination mix of light and heavier bodied materials may be used in a disposable stock tray or a custom made acrylic resin tray for making impressions for fixed partial dentures. The special syringe was used to inject the light bodied material into the prepared cavities or about the crown preparation.

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Davis34 (1958) described the use of rubber base impression materials in the construction of inlays. Smith35 (1963) described GHQWLVW¶V responsibility in laboratory procedures and said that there were many ways to make a good impression, many impression techniques and materials were there. The merit of each had been evaluated by each dentist. Duxbery36 (1963) described use of impression trays for rubber base impression material. The study cast was covered with one layer of base plate wax which serves as a spacer. Stops were cut in the wax and a covered cold cure acrylic resin tray was made. For smaller LPSUHVVLRQ RI RQH WRIRXUWHHWK $ µ8¶VKDSHG WUD\ RI perforated metal of bicuspid or molar size was cut to the required length. A roll of cold curing acrylic resin material was made. The resin was beaded around the border of the tray. The tray was placed in the mouth and moulded. Fusayama37 (1966) described a one piece cast permanent splint for making of the impression.

He used an indirect technique using irreversible hydrocolloid and a

specially designed instrument. The material was spatulated and injected into the preparation. The tray for the anterior teeth was filled with the impression material and placed in position or the preparations while the mix was fluid. The impression was left in the mouth for two minutes after apparent gelation. Then it was removed and immersed into a 2% znSo4 fixing solution. Then the stone was poured.

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Going39 (1968) mentioned an accurate rubber base impression procedure. The gingival retraction was done in the conventional manner. While the dental assistant was mixing the light bodied material and filling the syringe, the teeth and surrounding tissues were dried. The retraction cords were removed carefully and light bodied rubber base impression material was injected into the preparation.

The dentist

injects impression material into each gingival trough, and the cavity preparation. A second injection of the light bodied material was applied to the preparation and surrounding tissues. Sheulin40 et al (1970) in their article on the accuracy of correcting a defective rubber base impression tried these impression techniques, Then the tray filled with heavy bodied impression material was seated with a slight rocking motion to force the light bodied material further into place and to express air trapped in placing the tray.

Hubert Darby43 et al (1973) gave a procedure for void free impressions.

Anthony G. Gallegos41 et al (2004 GHVFULEHG WKH XVH RI WKH WRGD\¶ LPSUHVVLRQ materials, faults in the impression materials, and how to eliminate them.

Len Boksman(2005)43 described requirements of an impression materials and eliminating variables in impression taking.

Nachum Samet et al (2005)44 described methods to assess the quality of impressions The study evaluated the quality of impressions sent to commercial laboratories for the fabrication of fixed partial dentures (FPD) by describing the frequency of clinically detectable errors and by analysing correlations between the

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various factors involved A total of 193 FPD impressions were evaluated, immediately after arrival at 11 dental laboratories, by 3 calibrated examiners. Of the impressions, 89.1% had 1 or more observable errors.

Abdul Rohman Salem45 et al (2009) studied methods to assess the quality of impressions and was sent to dental laboratories in Jordan. A sample of 136 impressions and stone casts were examined for technical errors in 35 laboratories that construct fixed partial dentures. They were sorted into these categories: unusable, unsatisfactory, acceptable or satisfactory. The quality of impressions and casts made for fixed partial denture assessed were considered unsatisfactory or unusable in 50% of cases.

Gregori M. Kurtzman47 (2012) described the potential concerns during impression capture and addressed approaches to improve the overall quality of impressions taken.

Gary jenkinson46 (2012) described how to spot distortion in an impression and the methods to avoid that.

REMOVABLE PARTIAL DENTURE IMPRESSION Mc Cracken50 (1963) on philosophy of partial denture treatment concluded that elastic impression material which had good accuracy should be used, there were some advantages to the use of individual impression trays, but since all free end partial dentures should be made from dual impressions to provide maximum support

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for the free end bases, a hydrocolloid material was usually used to make an impression of the anatomic portion. Rapuano48 (1970) gave a single tray dual impression technique for distal extension partial dentures. The denture bases were functionally loaded and the functional load was applied along the entire length of the posterior occlusion of the removable partial denture and a less bulky final impression was obtained. Fairchild49 LQKLVDUWLFOH³9HUVDWLOHXVHRI$OJinate impression materiDO´JDYH the various uses of alginate impression material which facilitates procedures common to practice of removable prosthodontics. Appleby51 (1980) described a combined reversible hydrocolloid, irreversible hydrocolloid system. Lee52 (1980) gave an elaborate description on the mucostatic impression technique and principles. He said that the mucostatic is a principle not a technique. Beanmount56 (1983) gave an impression procedure for maxillary class I removable partial dentures. Kastner53 et al (1983) described the fabrication of individualised preliminary impression trays. Mc Arthor54 (1984) described an impression procedure for fabricating a full coverage restoration for existing removable denture. Bomberg55 (1984) described that the technique of reseating two defective impression on a preparation by the addition of a controlled amount of impression

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material for correction purpose.

He found out that the results were highly un

predictable. Wood ward57 (1985) concluded that irreversible hydrocolloid impression made in perforated trays were more accurate than in rim lock trays, for production of an accurate cast. Tjan58 et al (1986) in their study on the accuracy of impression materials found that the elastic impression materials when properly handled exhibited good clinical accuracy.

Elastomeric impression materials which were made with reversible

hydrocolloids as elastic impression materials were capable of producing clinically accurate dies. Zinner63 (1987) described several impression techniques for removable components of a combination fixed and removable prosthesis. Nemetz59 HW DO GHVFULEHG ³5HYHUVLEOH K\GURFROORLG ZDs the oldest elastic impression material and with appropriate methodology the advantage outweigh the disadvantage. Skill care and comprehension of the physical properties of the material ensure success. Von krammer60 (1988) described a two stage impression procedure for distal extension removable partial dentures. A technique was described where an accurate impression of the teeth and correct border extension of the ridges were obtained with the use of a single custom tray in conjunction with a single impression material or a combination of materials.

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Gunne61 et al (1990) conducted a study on the impression techniques for R.P.Ds. their results indicated that zinc oxide eugenol paste in a border molded tray produced more extended impression lingually. Rob Veis62 (2005) described indications, description, treatment procedures, and contraindications of accurate alginate impressions. Robert W. Rudd64 (2005) described a review of 243 errors possible during the fabrication of a removable partial denture. This article was helped eliminating some of the errors that can be made by those who handle the materials used during the fabrication of an RPD and perform the procedures required for that process.

DISCUSSION PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING: The basic objective of a maxillary or mandibular impression is to record all the potential denture-bearing surface available. To a large extent this surface is readily identified if the biologic considerations of impression making are correctly understood.1

+RZHYHU WKH GHQWXUH¶V UHWHQWLRQ LV HQKDQFHG FRQVLGHUDEO\ LI WKH

denture extends peripherally to harness the resiliency of most of the surrounding limiting structures. Therefore clinical techniques and above all, judgement must be reconciled so that objectives for impression making are to be fulfilled. 1 Although impression techniques, methods and materials of choice are constantly changing, they nevertheless should be selected on the basis of biologic factors. Techniques too often follow shortcuts, perhaps to satisfy the SDWLHQW¶V desire

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for immediate results, without a consideration of the future destruction that such procedures may induce.2 The objectives of an impression are to provide retention, stability, and support for the denture.3 An impression also may act as a foundation for improved aesthetics and at the same time should maintain the health of the oral tissues. 2 Retention for a denture is its resistance to removal in a direction opposite that of its insertion. It is the quality inherent in a denture that resists the force of gravity, the adhesiveness of foods, and the forces associated with opening of the jaws. Retention is the means by which dentures are held in position in the mouth. When the soft tissues over the bones are displaced under pressure, the denture bases may lose their retention because of the change in adaptation of the basal surface of the denture to its basal seat.3 Stability of a denture is its quality of being firm, steady and constant in position when forces are applied to it. Stability refers especially to resistance against horizontal movement and forces that tend to alter the relationship between the denture base and its supporting foundation in a horizontal or rotary direction. The size and form of the basal seat, the quality of the final impressions, the form of the polished surfaces and the proper location and arrangement of the artificial teeth play a major role in the stability of dentures.3 Support is the resistance of a denture to vertical components of mastication and to occlusal or other forces applied in a direction toward the basal seat. Support is provided by the maxillary and mandibular bones and their covering of mucosal tissues.3 It is enhanced by selective placement of pressures that are in harmony with the resiliency of the tissues that make up the basal seat.

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Biologic principles of tissues health must be adhered to before a final impression procedure will enhance the retention, stability, and support of a denture.5 (Which are all interrelated features): 1.

The impression extends to include entire seat within the limits of the health and functions of the supporting and limiting tissue.

2.

The borders are in harmony with the anatomic and physiologic limitations to the oral structures.

3.

A physiologic type of border-molding procedure is performed by the dentist or by the dentist under the guidance of the dentist.

4.

Proper space for the selected final impression material is provided within the impression tray.

5.

Selective pressure is placed on the basal sea during the making of the final impression.

6.

The impression can be removed from the mouth without damage to the mucous membrane of the residual ridge.

7.

A guiding mechanism is provided for correct positioning of the impression tray in the mouth.

8.

The tray and final impression are made of dimensionally stable materials.

9.

The external shape of the final impression is similar to the external form of the completed denture.

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Anatomic considerations in impression making:

Correlation of anatomical landmarks. A, Intraoral drawing of the maxillary arch; 1, labial fraenum; 2, labial vestibule; 3, buccal fraenum; 4, buccal vestibule; 5, coronoid bulge; 6, residual alveolar ridge; 7, maxillary tuberosity; 8, hamular notch; 9, posterior palatal seal region; 10, foveae palatinae: 11, median palatine raphe; 12, incisive papilla 13, rugae. B, Maxillary final impression shows the corresponding denture landmarks: 1, labial notch; 2, labial flange; 3, buccal notch; 4, buccal flange; 5, coronoid contour; 6, alveolar groove; 7, area of tuberosity, 8, pterygomaxillary seal in area of hamular notch; 9, area of posterior palatal seal; 10, foveae palatinae; 11, median palatine groove; 12, incisive fossa; 13, rugae.

Correlation of anatomical landmarks A, Intraoral drawing of the mandibular arch; 1, labial fraenum; 2, labial vestibule; 3. buccal fraenum; 4, buccal vestibule; 5, residual alveolar ridge; 6, retromolar pad; 7, pterygomandibular raphe; 8, retromylohyoid fossa, 9, alveololingual sulcus; 10, tongue; 11, lingual fraenum; 12, buccal shelf; 13, premylohyoid eminence. B, Mandibular final impression showing the corresponding denture landmarks 1, labial notch; 2, labial flange; 3, buccal notch; 4, buccal flange, 5, alveolar groove; 6, retromolar fossa; 7, pterygomandibular notch, 8, retromylohyoid eminence, 9, lingual flange; 10, inclined plane for the tongue, 11, lingual notch, 12, buccal flange that fits on the buccal shelf; 13, premylohyoid eminence.

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7+(7+5((³0V´2)68&&(66)8/'(1785(,035(66,210$.,1* Successful complete-denture impressions require an appropriate mold (tray), method (impression technique) and material (impression material). Individually, their importance relative to the outcome of the procedure is of minor importance. 6 When considered in the context of an encompassing technique, however, they are the cornerstones of obtaining optimal denture stability and retention.6 The mold, method, and materials often differ between the preliminary (primary) and master (final) impressions.

Preliminary Impressions: Selection of an appropriate impression tray begins with the preliminary impression.7 The ideal features of a preliminary impression tray include (1)

Rigidity

(2)

Ease of modification

(3)

Compatibility with the impression material

(4)

Smoothness or comfort in the oral environment

(5)

Ability to be sterilized for reuse (or disposability).

Stock metal or rigid plastic trays that represent a reasonable approximation of the size and shape of the existing anatomic structures should be selected. Identification of the edentulous ridge areas should be done.

9

Both edentulous and

dentate stock trays are available for preliminary impression procedures. Both types of stock trays can be modified by bending, shortened by grinding, or extended by adding compound or wax to cover the entire basal seat area properly, in both types of trays, the resulting preliminary impression should be overextended in all areas,

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recording all supporting tissues.

Edentulous trays are favoured for making

impressions of edentulous arches; however, the current trend toward using disposable impression trays precludes their use because disposable edentulous trays currently are not available.4 It is at the preliminary impression stage that the clinician best is able to remake questionable impressions select alternate trays, or re-evaluate the chosen method. Material The impression material of choice for preliminary impressions is irreversible hydrocolloid. It can be mixed by hand spatulation, or by mechanical spatulation with or without vacuum. Its advantages include low cost, hydrophilic nature, and the ability of the clinician to modify its setting time and viscosity by changes in the water temperature or water to powder ratio without affecting the properties of the material adversely. Its disadvantages include lack of surface detail (when compared with other impression materials) and dimensional stability.

Owing to the process of

irreversible hydrocolloid impressions should be disinfected immediately, placed in a humidor or plastic zip-lock bag, and poured within 10 to 15 minutes after removal from the mouth. Preliminary impressions should be poured in plaster; care should be taken to remove the set cast prior to the dehydration of the irreversible hydrocolloid. Failure to do so may result in damage to the surface of the retrieved cast. Plaster is advantageous when fabricating custom trays for master impressions because it allows for easy retrieval of the custom tray from the preliminary cast. The preliminary with the anatomy of the patient to verify the extension of the planned denture peripheries prior to dismissal of the patient. Direct comparison with the patient is necessary for proper construction of the custom tray used for the master impression procedures. The peripheral extent of the proposed dentures is indicated

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with indelible pencil on the impression, or with pencil on the resultant preliminary cast.14 Composition, sometimes called impression compound, is the name given to a class of thermoplastic materials containing various waxes, resins and fillers which soften in hot water and harden at or slightly above mouth temperature.

Many

proprietary brands are obtainable with optimum working temperatures about 65°C at which temperature they should flow easily. Whichever composition is selected for this impression the PDQXIDFWXUHU¶V instructions regarding its working temperature should be observed. Composition (impression compound) with its high viscosity, is the only material suitable for this technique and by varying its degree of softness, and thereby its rate of flow, the amount of compression obtainable can be controlled within reasonable limits. A compression impression which has been thoroughly chilled, its surface heated and the impression reseated can exert far greater compression than one in which the composition is equally softened throughout its entire mass.17 Method:

a)

Preliminary impression with impression compound Impression Compound Advantages:

1.

It can be used for compressing soft tissues.

2.

It can be added to and re-adapted.

3.

It can be used for any technique requiring a close peripheral seal.

4.

It can be used in combination with other materials.

5.

It is a good space-filler and does not slump.

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6.

Pouring the impression may be delayed, as there are no appreciable dimensional changes.

7.

It is cheap.

Disadvantages: 1.

It distorts easily and should not be used where excessive undercuts exist. It may also be distorted if any pressure is applied to it out of the mouth before it has been chilled.

2.

It does not reproduce fine surface detail.

3.

As it can be re-softened and used again it tends to be unhygienic because it cannot be sterilized without destroying its properties.

4.

It can only give an accurate impression with a long and difficult technique.

Indications for use: 1.

As a preliminary impression for the construction of individual trays.

2.

To modify the fit of stock trays.

3.

To obtain peripheral seal

4.

For compression impressions.

The upper impression The composition is softened and prepared in the way already described for the lower impression. When ready it is formed into a ball and placed in the center of the palate of the warmed tray. It is then molded outwards to the periphery until the whole tray is filled, leaving a smooth, uncreased surface identified to form a trough for the ridge and slightly raised in the middle for the palatal vault.

Sufficient

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composition must be molded along the periphery to enable the depth of the buccal and labial sulci to be reached without having to force the tray upwards too far. This is because excessive pressure together with an abundance of composition in the palatal region will cause it to flow backwards so far over the soft palate that retching and vomiting may result.19 It will be seen that the palatal area receives composition from two directions, while the sulci are filled from only one. Once the composition has been adapted to the tray the surface is lightly flamed, tempered in the water bath, inserted in the mouth and centred under the ridge. Keeping the tray handle in line with the median sagittal plane of the face ensures correct centring. Firm upward pressure now seats the impression in place ready for the peripheral moulding. Alternate cheeks are gently pulled upwards and outwards, and then downwards and inwards and slightly backwards the first movements release any trapped air or folds of tissue, while the other three movements simulate the function of the cheek when drawn into aid the placing of food over the occlusal surfaces of the teeth, and to clear the sulci of debris. The labial trimming can similarly be carried out by manipulations by the operator or the patient can be asked to purse up the lips as tightly as possible, then to retract them forcibly and finally to try to push the impression down with pressure of the upper lip. During these manoeuvres the tray is firmly held in position and for a further minute before being removed, chilled and inspected

In order to avoid cross-infection

between the clinical area and the laboratory, the impressions may be immersed in a 1 in 20 aqueous solution of chlorhexidine gluconate before delivery to the laboratory.19

Ϯϴ

COMMON FAULTS IN UPPER IMPRESSIONS:1. A crevice in the mid-line of the palatal posterior third. Causes:a) Insufficient composition in the palatal area when filling the tray. b) Insufficient pressure.

2. Excess composition extending well beyond the posterior palatal border of the tray. Causes:a) Excessive pressure or too prolonged pressure when seating a tray. b) Too much composition in the palatal area when filling the tray. composition which is unsupported by the tray will fall away from the palate by its own weight dragging some of the supported composition with it and producing an accurate impression. Upward pressure on the tray should cease when the impression material is approximately 1cm beyond the posterior border of the tray.

3. An impression short in one or more regions of the sulci, especially the areas of the tuberosities or the labial sulcus. Causes:a) Insufficient material in the tray. b) Failure to mould the peripheral composition in this region when filling the tray so that it will slip up between the cheek and the tuberosity or the lip and the alveolar ridge. c) Failure to pull the upper lip outwards and upwards sufficient to allow the composition to flow into the labial sulcus. d) Insufficient pressure.

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4.) Edge of the tray showing the impression Causes:a) Incorrect centering of the tray before seating. b) Poorly selected or adapted the tray. Most deficiencies can be corrected by the addition of small amounts of composition, as described for the lower impression, but if the tray has been malpositoned or is small it is better to retake the impression than to attempt adjustments. Palatal excess should be avoided and therefore, is not considered.21

ϯϭ

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2. The lower impression The

selected

composition

is

placed

in

a

water

bath,

preferably

thermostatically controlled to maintain the recommended temperature. After a few minutes the composition is removed from the bath, folded repeatedly from the edges to the centre thus always presenting a smooth surface on one side and replaced as quickly as possible to prevent undue loss of heat. Kneading of the composition incorporates water which acts as a plasticizer and this procedure is repeated until the material has acquired a uniform softness throughout. When the composition is ready for use the metal lower tray is warmed in a Bunsen flame, the composition formed into a suitable-sized roll and placed in the tray. (If a disposable plastic stock tray is used there is no need to warm it) it is important to have sufficient bulk extending beyond the flanges so that there is no restriction in flow when pressed into position over the ridge.

a trough may be

indented in the composition with the finger to simulate the ultimate ridge impression, the surface quickly flamed so that surface detail will be recorded, and tempered by immersing momentarily in the hot water bath to avoid burning the patient. The tray is placed in the mouth and when the operator is satisfied that it is a position in relation to the ridge and correctly centred, the patient is instructed to raise and slightly protrude the tongue and as this movement begins the tray is pressed vertically downwards to seat the impression to the desired depth. Pressure in a backward direction may also be required to counter the forward thrust from the tongue when protruded. As soon as the impression is seated in position it must be held there firmly but without any increase in pressure. In other words, the maximum pressure must be

ϯϯ

exerted when the composition is nearest to the optimum working temperature as the farther it drops below that, the less readily will it flow. The impression obtained so far will reproduce, though not accurately, the denture-bearing surface, but will be over-extended round the periphery and an individual tray constructed from it would require considerable time-consuming adjustment before it could be used for making a master impression. This reduction of the individual tray can be eliminated, or at least very considerably reduced, if the muscles around the periphery are brought into play to mould the preliminary impression and this is done in the following manner. This is held firmly in position while the patient protrudes the tongue. This movement of the tongue draws forward the palatoglossal arches, raises the floor of the mouth and tenses the lingual frenum and thus moulds the composition in the lingual sulcus to the raised position of these structures. The buccal sulci and frenum are moulded by manipulating alternate cheeks downwards and outwards, to free any trapped folds of tissue and then pulling gently upwards, inwards and slightly backwards to obtain the approximate functional positon. 19 The impression is now completed and all that remains is to hold it lightly but firmly in place for a further minute, remove, chill thoroughly in cold water and inspect. COMMON FAULTS IN LOWER IMPRESSIONS:1. Insufficient depth in the posterior lingual pouch

Causes:a) Flange of the tray short in this region. b) Lack of composition in the tray. c) Too little force used in the seating the tray.

ϯϰ

d) Tongue trapped in the tray flanges because the patient fail to raise the tongue as the tray was seated.

In some cases it is necessary to push the compound into the lingual pouch area with the forefinger just before the tray is finally seated.

2. Insufficient depth in the lingual, labial and buccal sulci.

Causes:a) Lack of impression material. b) Not seating the tray with sufficient pressure.

3. The presence of a smooth hollow in the buccal distal periphery.

Causes:a) The check was not released from beneath the compositon border during functional trimming.

4. Edge of the tray showing the impression

Causes:a. Incorrect centering of the tray before seating b. In the anterior lingual region, the forward thrust of the tongue not being countered by sufficient backward pressure on the tray. c. Use of too large a tray for the mouth or failure to trim the flanges adequately.

ϯϱ

Correction to faults 1 and 2 may be made by adding small softened pieces of composition to the perfect areas and reseating and remount the impression.21 The errors due to cheek folds 3 should be corrected by reheating the impression in that area and readapting while 4 requires an entirely new impression. While adding composition to an impression the later should first be thoroughly chilled and dried and the area requiring correction flamed sufficiently to make it sticky. A piece of the softened material is then taken, lightly flamed and attached to the main impression and moulded to the approximate shape required. Its surface is again flamed and momentarily plunges into the hot water bath before being seated in the mouth.21 Once the area to be readapted should be heated, the remainder being kept as cool as possible to avoid distortion on reinsertion.23

ϯϲ

a. Edge of the tray is visible b. Insufficient depth in the labial, lingual and buccal sulci. c. Insufficient depth in the posterior lingual pouch. d. Tongue trapped in the tray flanges because the patient fail to raise the tongue as the tray is seated.

a) Edge of the tray is visible b) Too much force used in the seating of the tray. c) Incorrect centering of the tray before seating d) Borders are not uniform

a) Not seating the tray with sufficient pressure. b) Use of large tray for the mouth or failure to trim the flanges adequately. c) Not proper tongue movements. d) Borders are not uniform. e) Edge of the tray is visible.

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b)

Preliminary impression with Irreversible hydrocolloid: Impression for the Mandibular Arch:

1.

Select a slightly oversized perforated impression tray.

The mandibular tray

should be refined at its posterior borders with utility wax to carry the impression material to place. 2.

Mix the

irreversible

hydrocolloid

impression

material according to

the

PDQXIDFWXUHU¶V VSHFLILFDWLRQV ,Q WKLV VWHS RI WKH SURFHGXUH WLPH WHPSHUDWXUH RI water and quantity of material are critical. A time clock should be used. 3.

Just before inserting impression material instruct the patient to irrigate his mouth with astringent mouthwash to reduce viscosity of saliva.

4.

Load the tray from the side slightly over level full.

5.

Using mouth mirror, place a small amount of impression material in the right and left retromylohyoid spaces.

6.

Seat the tray in the mouth. Instruct the patient to raise his tongue and let it fall slightly forward. Vibrate the tray to place until the material flows out into the labial and buccal reflection areas.

7.

Hold the tray in place for three minutes. Remove from the mouth. Rinse under gentle stream of tap water, dry and pour immediately with dental plaster or stone.

ERRORS IN LOWER IMPRESSIONS:-

ϯϵ

a) Removing the impression before setting time- leading to tearing of thr impression b) Edge of the tray is visible c) Insufficient depth in the posterior lingual pouch. d) Tongue trapped in the tray flanges because the patient fail to raise the tongue as the tray is seated.

a) Edge of the tray is visible b) Too much force used in the seating of the tray. c) Incorrect centering of the tray before seating d) Borders are not uniform

a) Tongue trapped in the tray flanges because the patient fail to raise the tongue as the tray is seated. b) Not proper tongue movements. c) Borders are not uniform. d) Edge of the tray is visible. e) Insufficient depth in the posterior lingual pouch.

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Impression for the Maxillary Arch: 1.

Select proper sized tray and using utility wax, extend across the posterior border and the distal termination of the buccal flange area. If necessary the labial flange may be altered with utility wax. When the patient has a very high vault utility wax may be added to this area in the tray these alterations are accomplished to carry the impression material more accurately to place and insure the same bulk throughout the palate.

2.

Immediately prior to mixing to the impression material, wipe the posterior palatal seal area of the hard palate and the soft palate with gauze to remove excessive saliva.

3.

Mix impression material as above load the tray from the side.

4.

Using the mirror or index finger as a carrier placed the remaining material in the vault of the palate and the buccal vestibule.

5.

Place the tray in the mouth so that the impression material in the tray attaches itself to the impression material in the mouth.

6.

Vibrate the tray and seat until the impression material flows out into the buccal and labial reflection areas and over the posterior palatal seal area. As the tray is being seated, instruct the patient to keep his eyes open, relax, take short breaths through the nose, and flex the head forward.

7.

Hold the impression material in place for three minutes remove from the mouth, rinse with tap water, dry and pour immediately with dental plaster or stone.

ERRORS IN UPPER IMPRESSIONS

ϰϭ

a) Removing the impression before setting time- leading to tearing of the impression b) Edge of the tray is visible c) Excess composition extending well beyond the posterior palatal border of the tray d) Impression is short in one or more regions of the sulci.

a) Insufficient composition in the palatal region when filling the tray. b) An impression short in one or more regions of the sulci, especially the areas of the distobuccal flange. c) Non-homogenous material..

mix

of

the

d) Edge of the tray is visible.

a) An impression short in one or more regions of the sulci, especially the areas of the distobuccal flange. b) Incorrect centering of the tray. c) Impression borders are not on tray borders. d) Excess composition extending well beyond the posterior palatal border of the tray

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&h>dz>'/Ed/DWZ^^/KE^ ERRORS IN ALGINATE IMPRESSIONS Error 1 Using an expired irreversible hydrocolloid. This will lead to greatly reduced tear resistance and elasticity of the set material. Solution Always to code the expiration date or test a little quantity of the material according to the manufacturer's instructions.64

Error 2 Incorrect storage of the material (Heat or Cool or Freeze), this will alter the setting time of the material and it will be severely in case of high cooling and irregular in case of heat. Solution Store irreversible hydrocolloid in a controlled temperature between (4.5 - 32.2) 0C

Error 3 Unsealed container or unclosed after used , This will lead to moisture contamination and alter of the chemical and physical properties of the Alginate material. Solution Test the material before using; otherwise you have to be sure of sealing.

Error 4

ϰϯ

Using irreversible hydrocolloid that has been contaminated by particles of gypsum that this may contaminate the entire material. 64 Solution Use a separated dry spatula and rubber bowel for mixing. Error 5 Using too thin mixture of Alginate: - This may cause voids in the impression . - Alginate flow out of the tray and cause gag reflex. - The tray could not be able to provide enough pressure on the tissue. Solution Follow the manufacturer's instructions concerning theproper water/powder ratio. Error 6 Using too thick mixture of alginate: - There will be inaccurate flow of the material. - Set of the material before seating in the mouth and If that will happen there will be wrong impression and wrong cast. Solution Follow the manufacturer's instructions for mixing the material. Error 7 Attempting to control the setting time of irreversible hydrocolloid by altering the w/p ratio: This will lead to unreliable result Solution It is advisable to modify the temperature of the water to be more than the room temperature to set the mixture faster.

ϰϰ

Error 8 Using tap water to mix the powder: - It is not too bad but, But it may contain different types of chemicals like Chlorine , FDUERQIOXRULGHSRWDVVLXPFDOFLXPDQGVRRQ«Wherefore it is not, easy to know how are These compounds affect the mixture, but sure it can alter the setting time. Solution Scientifically mixing should be always by using distilled water, otherwise tap water should be used.

Error 9. Adding water to powder during mixing; this will leave some remnant of powder unmixed and lead to inaccurate mixture. Solution Always powder should be added to water in order to be sure of dissolve of powder step by step. Error 10. Inadequate mixing time of the irreversible hydrocolloid If it is not mixed enough pockets of dry or partially wetting can be caused and lead to distortion.. Solution The correct Hand mixing should be 60 sec. and 15 sec.in case of vacuum mixing. Error 11. Partially mixed irreversible hydrocolloid and remaining of unmixed powder around the top of the mixing bowl the dry or partially wetted I.H is in contact with a tooth or

ϰϱ

soft tissue therefore, the dry material will expand after removal of the impression from the mouth and washing it. Solution Just be sure that there is no dry powder during preparing of the mixture. Error 12. Using an impression tray that is too small; - This may lead to displace the soft tissues. - The resulting casts may distort also. - Impression cannot be removed from the mouth without distortion And tearing, and sometimes the tray may be separated from the impression during pulling and removing. Solution Just be certain to use a suitable size of tray or modify the tray to be suitable. Error 13 The impression tray is too large; -The irreversible hydrocolloid material may be away from the soft tissues, e.g; palatal surfaces. - It also may be difficult to seat the tray posterior e.g; ramus of mandible. Solution The selected tray should be a way from the tissue about few millimeters.

Error 14. Irreversible hydrocolloid sets under pressure this will cause a distorted impression. Solution

ϰϲ

Release the pressure required to seat the impression as soon as it is seated. Error 15. applying continuous pressure when seating an impression in a perforated tray; - It may lead to escape of impression material and lead to a thin layer cover the teeth. Solution Impression Always should be remade. Error 16. Failure in support the tray during the initial setting time of the impression about 30 sec it may cause movements of the impression due to tongue movements by the patient. Solution Always highly control the tray and the patient. Error 17. Do not allow enough time for the impression material to flow before it sets that may lead imperfect registration of anatomy of the tissue. Solution I H provide a 15 sec. for flow if you need more time you have to use cool water to increase it to 20 sec. Error 18. Making an impression with a coated layer of plaque and debris on the teeth and interproximal areas This will produce inaccurate cast due to unreliable impression. Solution Routinely scaling and polishing should be done before making impression for such cases by using lubricating prophy paste.

ϰϳ

Error 19. Failing to remove prophy pumice and paste may lead to the same problem of the plaque and debris. Solution Use strong air-water spray and scaling if necessary before impression. Error 20. Removing the impression before setting time- that may be lead to tearing of the impression (it is poor tearing resistance). Solution - Wait to exact setting time of the material; moreover give additional 2min for complete curing of the inner material. - At the same time check the remains of the mixture in the bowel to be sure that the material is set. Error 21. Leaving the impression too long time in the patient mouth; - It may lead to adhere of the material to the teeth and there will be no enough time to pour the impression with stone. Solution Always check time and follow the accurate method of manipulation. Error 22. Removing the impression slowly or with a rocking movements lead to distort the impression. Solution

ϰϴ

Twists the tray otherwise breaks the seal by insert fingers posterior and slightly snaps movements to the tray. Error 23. Failing to inspect the impression and pouring it without checking; This may lead to undetected defect then to recall the patient for another visit to repeat the impression. Solution Check the impression by light and compare it with the patient mouth and the study model, if there is any defect it is better to remake the impression immediately better than the later visit. Error 24 Failing to clean the impression before pouring with stone may interfere with produce an accurate cast. Solution Always rinse the impression with tap water to remove any debris. Error 25. Delay pouring the impression: This will lead to syneresis and shrinkage of material. Solution Impression should be poured immediately after removed from the mouth otherwise should be covered by a wetted piece of cloth but not more than 10-12 min. in order to avoid dimensional changes.

ϰϵ

&h>dz>'/Ed/DWZ^^/KE^

ϱϬ

Alginate; Advantages: 1.

It produces excellent surface detail.

2.

It is dimensionally accurate if poured within a short time of removal from the mouth.

3.

It is elastic and will spring over bulbous areas returning to its correct position when removed from the mouth; this only applies if the undercuts are not too deep.

4.

It is hygienic, as fresh material must be used for each impression.

5.

It is relatively inexpensive.

6.

It is relatively inexpensive.

7.

There is a wide range with different viscosities for different clinical situations.

Disadvantages: 1.

It does not readily flow into areas in which the tray does not extend.

2.

It cannot be used alone for compressing the tissues.

3.

It cannot be added to if faulty.

4.

Distortion may occur without it being obvious; it must be held stationary in relation to the tissues throughout its setting period and it must remain adherent to the tray during removal.

5.

It is liable to distortion in the laboratory.

6.

It is difficult to box in the laboratory. Indications for use:

1.

For preliminary impressions.

2.

For master impressions in rigid individual trays.

ϱϭ

Suggestions For The Clinical Use Of Alginates 1.

The use of perforated metal trays or rimlock metal trays is strongly suggested. resin trays can be used with success if they are perforated with many holes.

2.

Teeth should be cleaned adequately by scaling and polishing before impressions are made.

3.

The mouth should be rinsed well with slightly flavored water at body temperature, hot or cold water or very astringent mouth rinses should be avoided, as they can stimulate a body reaction to secrete saliva and mucus, with the resultant undesirable changes in the impression.

4.

Just before placing the alginate impression, the mouth should evacuated clear of saliva, and an air stream should be blown on the remaining teeth. This air drying is particularly important in any areas that are to contact with removable partial denture rests or retainers.

5.

As the alginate impression is ready to be placed in the mouth and after air has been blown on the remaining teeth, a small amount of alginate should be placed on WKHFOLQLFLDQ¶VILQJHUDQGUXEEHGLQWRDQ\DUHDWKDWPD\WUDSDLUYRLGV$PRQJVXFK locations are the following:

(1)

The palate area, especially if it is a high vault or if clefts or indentations exist:

(2)

Occlusal surfaces of all remaining teeth, which often trap numerous bubbles if not filled with alginate by finger pressure before placing the impression tray; and

ϱϮ

(3)

Any rests or areas of teeth that are to contact removable portions of the prosthesis.

6.

With any material, placement of the mandibular impression is suggested before the maxillary impression.

Apprehension of patients is higher for the maxillary

impression because of the gag reflex. Therefore, making the mandibular impression first relieves anxiety when the maxillary impression is placed. Less apprehension means decreased secretions, less gagging and better impressions. 7.

Air bubbles are often formed in the mucobuccal fold area. If the soft tissue is not pulled toward the facial to free those bubbles and to allow flow of the alginate into the tissue fold, air bubbles will result in projections on the cast.

Custom trays

fabricated on such casts will lack surface detail and intimacy of contact. 8.

A common problem with alginate impressions is their premature removal from the mouth. Alginate impressions should be left in the mouth for 2 to 3 minutes after they are firm to the touch for adequate maturation of the chemical set.

9.

Impressions should be washed with a stream of water to remove debris and should be dried with an air stream until they have only a slightly moist appearance. Impressions should be poured within 10 minutes after removal from the mouth for optimal accuracy.

10.

Use of surface tension changing liquids is desirable before pouring alginates. Placement of very slight quantity of this material is desirable to allow adequate flow of stone into the impression and to lessen bubbles. Stone should be poured directly over the slightly moistened impression.

ϱϯ

Casts should be removed from alginate impressions as soon as the stone has reached an optimal stage of rigidity. If stone casts are allowed to remain in alginate impressions until the alginate dehydrates, damaging changes take place in the surface of the stone

MASTER / FINAL / SECONDARY IMPRESSION: Mold Optimal master impressions are achieved best using a custom tray constructed of auto polymerizing acrylic resin or light-cured composite resin. Custom tray fabrication and adaptation is one of the most important aspects of completedenture impression procedures. The idea features of a custom impression tray include. (1)

Stability

(2)

Rigidity

(3)

Proper extension cover the basal seat areas of the edentulous arches (for pro stability);

(4)

A consistently relieved approximation of the vestibular tissues particularly those involved in the peripheral seal (for proper retention); and ease of modification (either by grinding or the addition of appropriate material to ensure proper extension. If the trays overextended, it distorts peripheral tissues during the impression procedure, leading to an unstable prosthesis that may cause ulceration of the peripheral tissues. If the tray is under extended, may not maximize the available denture bearing area, and result in lack retention and stability of the impression tray. The degree to which relief provided within the custom tray is based on the anatomy

ϱϰ

and condition of the existing oral structures and on the impression philosophy used in complete denture construction. The custom tray should provide the clinician with the best opportunity to provide stability and retention for the subsequent prosthesis. To be successful, the custom tray must be maintained in the mouth in a repeatedly stable position throughout the impression procedures. To achieve this, it should provide intimate contact with the oral tissues, except in the peripheral areas. These areas should allow modification of the custom tray during the process of border molding. Border molding is the shaping of the border areas of an impression tray by functional or manual manipulation of the tissue adjacent to the borders to duplicate the contour and size (width and length) of the vestibule of both dental arches.

Impression Material Selection: Numerous impression materials are available for use in the master impression procedures. These include the irreversible hydrocolloids, ZOE impression pastes, polysulfides, polyethers, condensation silicones, and vinyl polysiloxanes.

Impressions Paste (ZOE)18 Advantages 1.

It produces excellent surface detail.

2.

It is dimensionally accurate as it is only used I a thin layer.

3.

It is hygienic, as fresh material must be used for each impression.

4.

It does not lose surface detail in wet mouths.

5.

It can be added to and re-adapted if faulty.

6.

In thin washes it can be used for compressing soft tissues.

ϱϱ

7.

It reduces nausea to a minimum.

8.

It adheres well to a dried surface so that when the minimum of material is used there is little degree of flaking on removal from the mouth.

Disadvantages: 1.

It cannot be used when more than a slight undercut exists.

2.

May slump in thick layers and therefore can only be used as a wash material.

3.

Will not produce a satisfactory impression of the periphery unless supported by a very accurate or border moulded tray.

4.

Some patients find the eugenol content unpleasant.


As a final wash material when using techniques which have produced a closely adapted periphery.

2.

In cases exhibiting pronounced nausea.

ϱϲ

a) Flecks of impression material on the borders indicating improper mix. b) Too many voids and irregularities in the posterior region indicate improper flow of material while recording tissues. c) Improper impression technique

a) Voids in the posterior region b) Excess material c) Improper flow of the material while making of the impression d) Overriding of the borders previously established e) Entire denture bearing area recorded under pressure.

a) Improperly positioned tray while recording b) Labial flanges too thick c) Overextensions at posterior region d) Excess material within the special tray

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ϱϳ

a) Improper molding at buccal vestibule region b) Insufficient molding due to the tongue c) Tray placed slightly anteriorly due to which the lingual surface in the anterior region is recorded under pressure.

a) Overextended impression material b) Displacement of tray while recording of the tissues c) Improper moulding in the vestibular regions d) Pressure areas a) Excessive thickness of impression material over the borders b) Improper flow at the time of impression taking. c) Insufficient depth in the posterior lingual pouch.

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ϱϵ

IMPRESSION MATERIAL FOR FIXED PARTIAL DENTURE Elastomers Advantages 1.

Excellent surface detail.

2.

Dimensional accuracy

3.

No separator required before pouring casts.

4.

Record undercuts but polysulphides may suffer from permanent deformation on removal.

5.

Polysulphides have good tear resistance.

6.

Addition silicones have excellent dimensional stability, even in cold sterilizing solutions.

7.

Wide range of different viscosities available to match different clinical situations.

8.

Low viscosity silicones suitable for wash techniques

9.

Putty silicones are useful as space ±filling materials.

10.

Pleasant appearance and feel in the mouth. 34

Disadvantages 1.

They are hydrophobic and so tend to slip on wet, mucus-covered mucosa.

2.

Prolonged setting time, especially polysulphides.

3.

Tear resistance of silicones is low.

4.

Condensation silicones are dimensionally unstable.

5.

Silicone putty can easily distort peripheral tissues.

6.

Most expensive of all impression materials.

7.

After set, borders cannot be adjusted.

8.

Polysulphides have strong odour of rubber. 34

ϲϬ


Where there are severe undercuts.

2.

In-patients exhibiting xerostomia.

3.

In-patients with lesions of the mucosa, such as pemphigus or lichen planus.

4.

For master impressions in rigid individual trays.

Suggestions For Clinical Use Of Polysulfides 1.

Lubricate potential skin contact areas of the patient and the clinician.

2.

Obtain short setting time polysulfides (5 to 6 minutes)

3.

Use the viscosity that suits your needs most adequately

4.

Pour impressions within approximately 3 hours after removal from the mouth.

5.

Do not spill these materials on clothing. Any inadvertent spill or spot will destroy the clothing as the elastomer cannot be removed well.38

Suggestions For Clinical Use Of Polyethers 1.

/XEULFDWH ERWK WKH SDWLHQW¶V VNLQ DQG FOLQLFLDQ¶V KDQGV YHU\ ZHOO WR DYRLG KDYLQJ the material stick.

2.

Warn the patient about the poor taste of polyethers.

3.

Warn the patient that the impression will be difficult to remove from the mouth because of its rigidity.

4.

Mix the material quickly and to a homogeneous consistency. 38

ϲϭ

Suggestions For Clinical Use Of Condensation Reaction Silicones 1.

Casts should be poured very soon after making impressions. Research reports suggest pouring casts within 1 to 3 hours after removal of the impression from the mouth. The material shrinks during the first few hours.

2.

Because of poor adhesives for these materials, it is advisable to cut holes in the impression trays if they are not perforated.

3.

Purchase of more than a one-year supply of these materials in not suggested because most of them degenerate rapidly in storage.

4.

The liquid catalyst is difficult to proportion with the past exactly each time. Therefore, squeeze the container to allow counting of number of drops released. 38

Suggestions For Clinical Use Of Addition Reaction Silicones 1.

Mix the materials thoroughly to avoid inconsistencies in setting time and other properties.

2.

These materials are relatively fool proof and do not have significantly difficult clinical use characteristics. 38

ERRORS IN IMPRESSIONS FOR FIXED PARTIAL DENTURE

1. TISSUE CONTACT WITH TRAY Problem: 6L]HDQGVKDSHRIWUD\LVQRWFRUUHFW 7UD\LVQRWVHDWHGFRUUHFWO\ 1RWHQough tray or wash material used Solution: )LOOWUD\»IXOO8VHPRUHZDVKPDWHULDODURXQG preparation and adjacent teeth.

ϲϮ

8VHFXVWRPWUD\RU-step putty/wash in a stock tray. &KHFNWUD\VL]HDQGUHWDNHLPSUHVVLRQ 6HDWWUD\HYHQO\ $YRLGWRRWKFRQWDFWZLWKWUD\ZKLOHVHDWLQJ 46

2. NOT ENOUGH WASH MATERIAL & TOOTH CONTACT WITH TRAY & NOT ENOUGH TRAY MATERIAL Problem: 8QDEOHWRFDSWXUHDOOWKHGHWDLOQHHGHG :LOOQRWEHDEOHWRVXSSRUWWKHZHLJKWRIWKHGLHVWRQHZKHQSRXULQJ Solution: )LOOWUD\»IXOO 8VHPRUHZDVKPDWHULDODUound preparation and adjacent teeth. 8VHFXVWRPWUD\RU-step putty/wash in a stock tray. 46

3.) VOIDS & BUBBLES Problem: ,PSURSHUV\ULQJHWHFKQLTXH $LULQFRUSRUDWHGLQWRV\ULQJHZKLOHORDGLQJPDWHULDOLQWRV\ULQJHRUWUD\ %ORRGVDOLYDFRQWDPLQation around preparation. 47

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Solution: 7RSUHYHQW³YRLGV´DOZD\V³SXVK´WKHPDWHULDODKHDGRIWKHV\ULQJHWLSDVWKHWLSLV circled around the prep, and do not pick up the tip around the margin. Keep expressing syringe material while withdrawing syringe tip. ,IXVLQJDV\ULQJHORDGIURPWKHIURQWUDWKHUWKDQWKHEDFN (QVXUHQRH[FHVVSRROLQJRIPRLVWXUH 5LQVH UHWUDFWLRQ FRUG WKRURXJKO\ SULRU WR UHPRYDO WR HOLPLQDWH VXOIXU EDVHG contaminates from haemostatic agent or glove. 4.) INADEQUATE MARGINS Problem: ,QVXIILFLHQW7LVVXH0DQDJHPHQW ,QVXIILFLHQWZDVKPDWHULDO 7LSQRWFRQWLQXDOO\VXEPHUVHGZLWKLQLPSUHVVLRQPDWHULDODQGVXOFXV 7HDULQJRIWKHPDUJLQ ([FHHGLQJZRUNLQJWLPHRIPDWHULDO 0D\UHTXLUHDGGLWLRQDOWRRWKSUHSDUDWLRQIRr adequate sulcus width. Solution: (QVXUHJRRGWLVVXHPDQDJHPHQW$WOHDVWPPDSLFDODQGPPODWHUDOO\1R JLQJLYLWLVRU³SXPSLQJ´VXOFXV&OHDQILHOGLVFULWLFDO'RXEOHFRUGPD\DOOHYLDWH

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.HHS V\ULQJH WLS LPPHUVHG LQ PDWHULDO DQG VXOFXV DQG SXsh the material 360 degrees around sulcus. 8VHZDVKPDWHULDOWKDWKDVKLJKHUWHDUVWUHQJWKSURSHUWLHV 6HDW5HJXODU6HWPDWHULDOZLWKLQPLQXWHVHFRQGVDQG)DVW6HWPDWHULDOZLWKLQ 35 seconds. 5.) PULLS & DRAGS Problem: 7LPLQJRIZDVKDQGWUD\PDterials not synchronized. 7UD\VHDWHGWRRODWH 7UD\PRYHPHQWGXULQJLPSUHVVLRQPDWHULDOVHWWLQJUHDFWLRQ Solution: 6HHVHFWLRQRQ0DWHULDO6HOHFWLRQ3DWLHQW(GXFDWLRQDQG6HDWLQJDQG5HPRYDORI the Tray. 6.) TEARING Problem: 3RRUWHDUVWUHQJWKRf impression material. ,QDGHTXDWHVSDFHFUHDWHGGXULQJUHWUDFWLRQ 3UHPDWXUHUHPRYDOIURPPRXWK ,QDGHTXDWHEORFNLQJRIVHYHUHXQGHUFXWV

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Solution: (QVXUH ! PP RI ODWHUDO UHWUDFWLRQ FLUFXPIHUHQWLDOO\ DURXQG ILQLVK OLQH 7KH greater the bulk of impression material the more resistance to tearing. 8VH D WLPHU WR HQVXUH WKH VHWWLQJ UHDFWLRQ IURP WLPH RI PL[ LV FRPSOHWH $Q additional safeguard would be to check the set of the peripheral areas of the impression prior to removal. %ORFNVHYHUHXQGHUcuts with easily removable material such as soft wax. 7.) INADEQUATE TRAY ADHESION Problem: 7UD\DGKHVLYHQRWXVHGRUDSSOLHGSURSHUO\ 7KH LPSUHVVLRQ PDWHULDO FDQ VKULQN DZD\ IURP WKH WUD\ FDXVLQJ GLVWRUWLRQ WKDW results in a reproduction smaller than the tooth. 7KH WUD\ LV QR ORQJHU VXSSRUWLYH RI WKH LPSUHVVLRQ PDWHULDO DQG GLVWRUWLRQ FRXOG result upon pouring. Solution: 8VHWUD\DGKHVLYHUHFRPPHQGHGE\PDQXIDFWXUHU $SSO\RQHWKLQHYHQFRDWRIDGKHVLYHWRWUD\FRYHULQJDOODUHDVRIFRQWDFWEHWZeen tray and impression material. $OORZPLQXWHVWRGU\

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8.) DE-LAMINATION/LACK OF CO-ADAPTATION Problem: 7LPLQJRIZDVKDQGWUD\PDWHULDOVQRWV\QFKURQL]HG 0DWHULDOQRWVHWWLQJ /DWH[FRQWDPLQDWLRQ 3URYLVLRQDOUHVLGXDOIURPR[\JHQLQKLELWLRQ layer. %ORRGVDOLYDZDWHU FRQWDPLQDWLRQ HVSHFLDOO\ ZLWK D two-step technique when a spacer is not used. 5HOLQLQJRILPSUHVVLRQZLWKZDVKPDWHULDO Solution: 6HDW5HJXODU6HWPDWHULDOZLWKLQPLQXWHVHFRQGVDQG)DVW6HWPDWHULDOZLWKLQ 35 seconds. 8VHDVSDFHUIRU7ZR6WHSWHFKQLTXHV /DWH[JORYHVVKRXOGQRWWRXFKPDWHULDO (QVXUHSURSHULVRODWLRQ 'RQRWXse the same impression in a two-step technique for the provisional matrix and the final impression. 46

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TISSUE CONTACT WITH TRAY

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Conclusion Making impressions is an important part of every dental practice. Success of complete dentures largely depends on accuracy of impression. Some of the more common concerns include tearing, voids, bubbles, and tray contact, the more that are made, the greater the inaccuracy, and the more that are eliminated, the better the result. Complications during the impression process can be perplexing to both the dentist and laboratory technician .Based on the particular condition, dentist needs to select material and technique of impression for success of complete denture therapy. This dissertation addressed solutions for correction of some of the most prevalent impression defects that are experienced in clinical practice. By taking the necessary precautions to avoid damaged impressions, clinicians can ensure improved accuracy in communication of critical parameters as well as an overall improvement in restorative fit.

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BIBLOGRAPHY 1. Carl O. Boucher Mid-century impression techniques for full denture J. Prosthet Dent 1951; 1: 472 ±489. 2. E. G. R. Solomon. A Critical Analysis of Complete Denture Impression Procedures. J Indian Prosthodont Soc (July-Sept 2011) ; 11(3):172±182. 3. Devan M.M. Basic principles in impression making. J. Prosthet Dent 1952; 2: 26-35. 4. Robert AL. Present day concepts in complete denture service. J. Prosthet Dent 1959; 9: 903 ±906. 5. Arthur L.R. Principles of full denture impression making and their application. J. Prosthet Dent 1951; 1: 213 ±28. 6. Academy of Denture Prosthodontics ± Principles concepts and practice in Prosthodntics. J. Prosthet Dent 1963; 13 : 280 ±86. 7. Collet H.A. Complete denture impressions. J. Prosthet Dent 1965; 15: 603 ± 614. 8. Hicky JC., Boucher Co., Woelfel JC. Impression for complete denture. J. Prosthet Dent 1962; 12: 638 ± 649. 9. Woelfel J. Two impression technique in complete denture prosthetics J. Prosthet Dent 1962; 12: 229 ±232. 10. Glossary of Prosthodontic terms- 7 11. Glossary of Prosthodontic terms- 4 12. Leonard SF. Fundamental principles of full denture construction. J. Prosthet Dent 1952; 2: 204 ± 209. 13. Titton GG. Minimum pressure technique. J. Prosthet Dent 1956; 6: 6±28. 14. Klien IE. Basic impression procedures J. Prosthet Dent 1957; 7: 579 ± 589.

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15. Hardy, Krishnan K. Rationale and importance of posterior border seal. J. Prosthet Dent 1958; 8: 386 ±397. 16. Blank H. H. A combination impression technique. J. Prosthet Dent 1957; 7:271 ± 276. 17. Barone Physiologic complete denture impression. J. Prosthet Dent 1963; 13: 800 ±809. 18. Matrone. Modification of trays for zinc oxide euginol impression. J. Prosthet Dent 1963; 13: 18 ± 19. 19. Scheisser Impression procedure for complete denture J. Prosthet Dent 1964; 14: 858 ± 861 20. Lott. E, Levin A. An impression technique for complete dentures. J. Prosthet Dent 1966; 16: 394 ± 412 21. Rudd R. Defects in complete denture impression. J. Prosthet Dent 1967; 18: 86 ± 90. 22. Frank C. Pressure during impression making. J. Prosthet Dent 1969; 22: 410 413. 23. Ellinger C.W. Minimising problems in making complete denture impression. J. Prosthet Dent 1973; 30: 553 ± 56. 24. Klein IE. Complete Denture prosthetic procedure. J. Prosthet Dent 1973; 30: 622 ± 630. 25. Smith DE, Toolson B. One step border molding of complete denture impression using polyether impression material. J. Prosthet Dent 1979; 41: 347 ± 351. 26. Zinner Ira D. An analysis of the development of complete denture impression technique. J. Prosthet Dent 1981; 46: 242 ± 248.

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27. Klean IE. Physiologic determination of primary impression for complete dentures. J. Prosthet Dent 1984; 51: 611 ± 620. 28. Klein IE. Complete denture secondary impression technique. J. Prosthet Dent 1985; 54: 660 ± 664. 29. Fernandes A. et al Corrective Primary Impression Technique. The Open Dentistry Journal 2010 ; 4: 27-28 30. 0F¶$UWKXU,QGLYLGXDOLVHGLPSUHVVLRQWUD\-3URVWKHW'HQW ± 581. 31. Shigeto H.M. Method of dislodging impression tray. J. Prosthet Dent 1989; 16: 54 - 61. 32. Chhabra A. et al. A new approach of making preliminary impression in completely edentulous patient. The Journal of Indian Prosthodont Soc Dec 2006 ; 6(4): 192-93 33. Kerstin wegner et al. Influence of Two Functional Complete-Denture Impression Techniques on Patient Satisfaction The International Journal of Prosthodontics 2011; 1: 540-44 34. Davis Moetiner C. Use of rubber base impression material in the construction of inlays. J. Prosthet Dent 1958; 8: 124 ±156. 35. Smith J. Dentists responsibility in laboratory procedures. J. Prosthet Dent 1963; 13: 297 ± 302. 36. Duxbery M. Impression trays for rubber base impression materials. J. Prosthet Dent 1965; 13: 489 ± 490. 37. Fusayama T. One piece cast permanent splint J. Prosthet Dent 1966; 16: 572 ± 579.

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38. Hudson C. Clinical use of rubber impression material J. Prosthet Dent 1958; 8: 111 ±119. 39. Going. Accurate rubber base impression procedure. J. Prosthet Dent 1968; 20: 330 ±344. 40. Sheulin. Accuracy of correcting a defective rubber base impression. J. Prosthet Dent 1970; 23: 648 ± 652.

41. Anthony G. et al. 8VH RI WKH WRGD\¶ LPSUHVVLRQ PDWHULDOV IDXOWV LQ WKH impression materials, and how to eliminate them. Practical applications dental economics 2004; 1:1-6 42. Hubert D. Copper band gingival retraction to produce void free crown and bridge impression. J. Prosthet Dent 1973; 29: 513 ± 516 43. Len Boksman. Eliminating Variables in impression-taking. Ontario Dentist December 2005; 22-25 44. Nachum Samet. A clinical evaluation of fixed partial denture impressions. J. Prosthet Dent. Aug 2005; 94: 112-17 45. Abdul R. S. Assessment of impressions made for fixed partial denture prosthesis in Jordan. Pakistan Oral & Dental Journal June 2009; 29 :1: 167170 46. Gary J. Impressions: avoiding distortion. Private Dentistry October 2012 47. Gregori M.K. Dental impressions identification and correction of common problems. Dental practice 2012; 2(2): 18-22

48. Rapuano. Single tray dual impression technique for distal extension partial dentures. J. Prosthet Dent 1970; 24: 41 ± 45.

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49. Fairchild. Versatality of alginate impression material J. Prosthet Dent 1974; 31: 265 ± 268. 50. McCracken. Philosophy of partial denture treatment. J. Prosthet Dent 1963; 13: 893 ± 894 51. Appleby DC, Cornalis P.

A combined reversible hydrocolloid, irreversible

hydrocolloid impression system J. Prosthet Dent 1980; 14: 27- 35. 52. Lee RE. Dent Clin North Am. J. Prosthet Dent 1980; 24: 81 ± 86. 53. Kastner U. Trinkel FJ. Fabrication of individual primary impression tray. J. Prosthet Dent 1986; 50: 131 ± 135. 54. MC Arthur L. Fabrication of full coverage edentulous impression for existing removable partial denture. J. Prosthet Dent 1984; 51: 529 ± 532. 55. Bomberg TJ correction of defective impression. J. Prosthet Dent 1984; 52: 3841 56. Beanmount AJ. Sectional impression for class I RPD. J. Prosthet Dent 1983; 49: 738 ± 739. 57. Woodward J. Irreversible hydrocolloid and tray selection. J. Prosthet Dent 1985; 53: 347 ± 350. 58. Tjan AHL, Wang B. Accuracy of commonly used impression materials. J. Prosthet Dent 1986; 56: 4 - 8. 59. Nemetz H, Tjan H. L. Reversible hydrocolloid standard of excellence. J. Prosthet Dent 1988; 60; 267 ± 270. 60. Von Krammer.

Two stage impression procedure for distal extension

removable partial denture. J. Prosthet Dent 1988; 60: 199 ± 201. 61. Gunne J, Hogstorm J. Impression technique for removable partial denture. J. Prosthet Dent 1990; 14: 225 ± 31.

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62. Rob Veis. Accurate alginate impressions. The practice building bulletin 2002; 4:1-4. 63. Zinner ID. Impression procedure. Dent elin north Am J. Prosthet Dent 1987; 31: 417 ± 440. 64. Robert W. Rudd. . J. Prosthet Dent 2001; 86: 251 ± 261

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