TROUBLESHOOTING IN FIXED PARTIAL DENTURE.pptx

FPD - Trouble shooting

1. TROUBLESHOOTING IN FIXED PARTIAL DENTURE 1

2. CONTENTS Introduction Objectives of fixed prosthodontic treatment Classification of Failures Biological Failures Mechanical Failures Porcelain Fractures Esthetic failures Maintenance failures Repair of fractured porcelain units Summary & Conclusion References 2

3. INTRODUCTION Fixed prosthodontic treatment transforms an unhealthy, unattractive dentition with poor function into a comfortable, healthy occlusion capable of giving years of further service while greatly enhancing esthetics. To achieve such success, however, requires meticulous attention to every detail from initial patient interview, through the active treatment phase, to a planned schedule of follow-up care. Failure to achieve the desired specifications of design for function and esthetics would result in failure of the prosthesis. 3

4. OBJECTIVES OF FIXED PROSTHODONTIC TREATMENT Preservation and improvement of related hard- and soft-tissue structures Preservation or improvement of oral function Improvement or restoration of esthetics Ensuring restoration retention, resistance and stability Providing restoration with mechanical or structural integrity Preserving or improving patient comfort Designing restorations for maximum longevity. 4 Manappallil JJ. Classification system for conventional crown and fixed partial denture failures. J Prosthet Dent 2008;99:293-298

5. CLASSIFICATIONS 5

6. The causes of FPD failures were summarized as early as in 1920 by Tinker as: Faulty, and in some cases, no attempt at diagnosis and prognosis. Failure to remove foci of infection in attention to treatment and care of the investing tissues and mouth sanitation. Disregard for tooth form Absence of proper embrasures Inter-proximal spaces Faulty occlusion and articulation 6 Tinker ET. Fixed bridge-work. J Natl Dent Assoc 1920;7:579-95

7. ROBERT’S CLASSIFICATION- 1970 Cementation failure Mechanical breakdown Flexion, tearing, or fracture of the gold Solder joint failure Pontic fracture Bonded porcelain failure Gingival irritation or recession Periodontal breakdown Caries Necrosis of the pulp. 7 Roberts DH. The failure of retainers in bridge prostheses. An analysis of 2,000 retainers. Br Dent J 1970;128:117-24.

8. BENNARD G. N. SMITH- 1985 Loss of retention Mechanical failure of crowns or bridge components Porcelain fracture Failure of solder joints Distortion Occlusal wear and perforation Lost facings Changes in the abutment tooth Periodontal disease Problems with the pulp 8 Smith B, Howe L. Planning and Making Crowns and Bridges. 4th ed.:CRC Press; 2013.

9. Caries Fracture of the prepared natural crown or root Movement of the tooth Design failures Under-prescribed FPDs Over-prescribed FPDs Inadequate clinical or laboratory technique Positive ledge Negative ledge Defect Poor shape and color Occlusal problems 9 Smith B, Howe L. Planning and Making Crowns and Bridges. 4th ed.:CRC Press; 2013.

10. 10 JOHN F. JOHNSTON- 1986 Dykema RW, Goodacre CJ, Phillips RW. Johnston’s Modern Practice in Fixed Prosthodontics. 4th ed. Philadelphia, London: W B Saunders Co.; 1986.

11. 11 CAUSES FOR FAILURE Discomfort Malocclusion or premature contact An oversized or poorly positioned mastication area, with retention of food by pontics or retainers. Torque produced from the seating of the bridge or from occlusion An excess of pressure on the tissue Plus or minus contact area Over protected or under protected gingival and ridge tissue. Thermal shock Dykema RW, Goodacre CJ, Phillips RW. Johnston’s Modern Practice in Fixed Prosthodontics. 4th ed. Philadelphia, London: W B Saunders Co.; 1986.

12. 12 Looseness of FPD Deformation of the metal casting on the abutment Torque Technique of cementation Solubility of cement Caries Mobility of one or more abutments Lack of full occlusal coverage Insufficient retention in the abutment preparation Poor initial fit of the casting. Dykema RW, Goodacre CJ, Phillips RW. Johnston’s Modern Practice in Fixed Prosthodontics. 4th ed. Philadelphia, London: W B Saunders Co.; 1986.

13. 13 Recurrence of caries Over extension of margins Short castings Open margins Wear A retainer becoming loose Pontic form that fills the embrasure Poor oral hygiene Use of wrong type of retainer, which will promote caries susceptibility Permanent displacement of the gingiva due to temporary protection Dykema RW, Goodacre CJ, Phillips RW. Johnston’s Modern Practice in Fixed Prosthodontics. 4th ed. Philadelphia, London: W B Saunders Co.; 1986.

14. 14 Recession of supporting structure Length of the span Size of the occlusal table Embrasure form Few extensions of the cervical margins Impression technique can also stimulate recession of the gingiva. Degeneration of Pulp Fractures of bridge components A faulty solder joint Incorrect casting technique Overwork of the metal due to length of the span or parts that are too small. Dykema RW, Goodacre CJ, Phillips RW. Johnston’s Modern Practice in Fixed Prosthodontics. 4th ed. Philadelphia, London: W B Saunders Co.; 1986.

15. 15 Loss of veneers Little retention Badly designed metal protection Deformation of the protecting metal Malocclusion Improper fusing or technique Loss of function They don’t function in occlusion They have no contact with opposing teeth They have permanent contact Over carved or under carved occlusal surface may impair efficiency Loss of opposing or approximating teeth Dykema RW, Goodacre CJ, Phillips RW. Johnston’s Modern Practice in Fixed Prosthodontics. 4th ed. Philadelphia, London: W B Saunders Co.; 1986.

16. 16 Loss of teeth tone or form Pontic design Position and size of the joints Embrasure form Over contouring or under contouring of retainers Oral hygiene practiced by the patient Failure to seat The abutment preparations may not be near parallel Soldering assembly may have been incorrect, or relationship of the retainers may have been altered during soldering. Dykema RW, Goodacre CJ, Phillips RW. Johnston’s Modern Practice in Fixed Prosthodontics. 4th ed. Philadelphia, London: W B Saunders Co.; 1986.

17. 17 LOMBARDI CLASSIFICATION OF ESTHETIC ERRORS Lombardi RE. A method for the classification of errors in dental esthetics. J Prosthet Dent 1974;32:501-13.

18. 18 Lombardi RE. A method for the classification of errors in dental esthetics. J Prosthet Dent 1974;32:501-13.

19. 19 BARRETO CLASSIFICATION – 1984 Barreto MT. Failures in ceramometal fixed restorations. J Prosthet Dent 1984;51:186-9.

20. 20 THAYER CLASSIFICATION – 1984 Thayer KE. Textbook of Fixed Prosthodontics. 2nd ed. Chicago, Year Book Medical Publishers, Inc. 1984

21. 21 SELBY CLASSIFICATION – 1984 Selby A. Fixed prosthodontic failure. A review and discussion of important aspects. Aust Dent J 1994;39:150-6.

22. 22 1.General pathosis 2. Periodontal problems 3. Caries 4. Pulpal changes 5. Erosion 6. Cracked teeth 7. Subpontic inflammation 8. Temporomandibular joint disorders 9. Occlusal problems. WISE CLASSIFICATION – 1999 Wise MD. Failure in the restored dentition; management and Treatment. Quintessence: London. 1995;397-412.

23. HOW TO HANDLE FAILURES - MANAPPALLIL Class I Cause Of Failure Is Correctable Without Replacing Restoration High spots First time dislodgement Small perforations Small facing repairs Manappallil JJ. Classification system for conventional crown and fixed partial denture failures. J Prosthet Dent 2008;99:293-298.

24. Class II Cause Of Failure Is Correctable Without Replacing Restoration; However, Supporting Tooth Structure Or Foundation Requires Repair Or Reconstruction Marginal caries Minor periodontal treatment Need for endodontic treatment Manappallil JJ. Classification system for conventional crown and fixed partial denture failures. J Prosthet Dent 2008;99:293-298.

25. Class III: Failure Requiring Restoration Replacement Only. Supporting Tooth Structure And/Or Foundation Acceptable Esthetically poor Fractured, perforated Improper fit Poor margins and contacts Manappallil JJ. Classification system for conventional crown and fixed partial denture failures. J Prosthet Dent 2008;99:293-298.

26. Class IV: Failure Requiring Restoration Replacement In Addition To Repair Or Reconstruction Of Supporting Tooth Structure And/Or Foundation . Faulty restoration Repeated dislodgement Large caries lesion Need for endodontic treatment Need for periodontal treatment Manappallil JJ. Classification system for conventional crown and fixed partial denture failures. J Prosthet Dent 2008;99:293-298.

27. 27 Class V : Severe Failure With Loss Of Supporting Tooth Or Inability To Reconstruct Using Original Tooth Support. Fixed Prosthodontic Replacement Remains Possible Through Use Of Other Or Additional Support For Redesigned Restoration Repeated dislodgement Loss of supporting tooth Manappallil JJ. Classification system for conventional crown and fixed partial denture failures. J Prosthet Dent 2008;99:293-298.

28. Class VI: Severe Failure With Loss Of Supporting Tooth Or Inability To Reconstruct Using Original Tooth Support. Conventional Fixed Prosthodontic Replacement Is Not Possible. Loss of critical abutment tooth/teeth making it long span, distal extension Manappallil JJ. Classification system for conventional crown and fixed partial denture failures. J Prosthet Dent 2008;99:293-298.

29. PHILIPS AND DYKEMA A) Biological Failures Diagnosis and treatment planning. Abutment selection. Caries. Pulpal degeneration. Periodontal breakdown. Occlusal problems. Changes in vertical dimension. Tooth perforation. Subpontic inflammation. Temporomandibular disorders. 29 Dykema RW, Goodacre CJ, Phillips RW, Johnston JF. Johnston's modern practice in fixed prosthodontics. Saunders; 1986.

30. B) Mechanical Failures Loss of retention Connector failure Occlusal failure Tooth fracture Root fracture C) Porcelain Fractures Metal ceramic porcelain failures Occlusion Metal handling procedures Metal with porcelain incompatibility 30 Dykema RW, Goodacre CJ, Phillips RW, Johnston JF. Johnston's modern practice in fixed prosthodontics. Saunders; 1986.

31. Preparation, impression and insertion. Porcelain jacket crown failures Vertical fracture. Facial cervical fracture. Lingual fracture. D) Esthetics E) Maintenance Failure 31 Dykema RW, Goodacre CJ, Phillips RW, Johnston JF. Johnston's modern practice in fixed prosthodontics. Saunders; 1986.

32. 32 BIOLOGIC FAILURES Caries : One of the most common biologic failures. Early detection possible mainly through comprehensive probing of the margins of the prosthesis and tooth surfaces with a sharp explorer. Radiographs are helpful to detect caries on proximal surfaces.

33. 33 Management Small lesions : Gold foil – filling material of choice for restoring marginal caries. Amalgam – best alterative to gold foil filling. Composite – indicated for restoration of caries in esthetic zone. – Less desirable Glass ionomer cement.

34. 34 Proximal lesions : Removal of prosthesis is required to obtain access to caries. If the lesion is small, the tooth preparation can be extended to eliminate the caries and a new prosthesis can be fabricated. When the lesion is large, a restoration is often required. The abutment preparation is extended to cover the filling, and a new restoration is fabricated. An extensive lesion may require endodontic treatment when pulp has been encroached. A grossly destroyed teeth by caries that cannot be restored must be extracted.

35. 35 Pulp degeneration : Causes : Extensive preparation Excess heat generation during preparation Post-insertion pulpal sensitivity. May manifest as  sensitivity which does not subside with time Intense pain Periapical pathology Management : Endodontic intervention through the prosthesis

36. 36 The access cavity is restored with Gold foil Amalgam Cast metal inlay If the retainer becomes loose during access opening or if the porcelain fractures, then remaking of the prosthesis may be necessary. A post and core restoration should be considered if little sound tooth structure is remaining.

37. 37 Periodontal breakdown : It can be localized around the prosthesis, as a result of inadequate instruction in prosthesis hygiene or a restoration that hinders good oral hygiene. Aspects of the prosthesis that interfere with effective plaque removal include Poor marginal adaptation Over contouring of the axial surfaces of the retainers Excessively large connectors that restrict cervical embrasure space

38. 38 A pontic that contacts too large an area on the edentulous ridge. A prosthesis with rough surfaces which promote plaque accumulation. Management : Recontour to eliminate the defects Remake to correct the defects

39. 39 OCCLUSAL PROBLEMS Interfering centric and eccentric occlusal contacts can cause Excessive tooth mobility Irreversible pulpal damage

40. 40 Management : When detected early occlusal adjustment should be done to eliminate these interferences without permanent damage. Occasionally, a combination of excessive mobility and reduced bone support require extraction of abutment teeth Irreversible pulpal damage requires endodontic treatment .

41. 41 Tooth perforation : Improperly located pinholes or pins used in conjunction with pin-retained restorations may perforate the tooth laterally. Management : depends on the location of the perforation. Occlusal to periodontal ligament Extend the preparation to cover the defect. Extends into periodontal ligament Perform periodontal surgery Smoothening of the projecting pin Place a restoration into perforated area

42. 42 Furcation region Surgically inaccessible Severe periodontal problems may ultimately lead to extraction of the tooth.

43. 43 MECHANICAL FAILURES Loss of retention : A prosthesis can become loose from an abutment tooth and if this occurrence is not detected early, extensive caries often develops. The loss of retention can be detected by several ways Patients awareness of looseness or sensitivity to temperature or sweets. He may experience bad taste or odor. Periodic clinical examinations that includes attempts to unseat existing prosthesis by lifting the retainers up and down ( occluso cervically) while they are held between the fingers and a curved explorer placed under the connector .

44. 44 If a casting is loose, the occlusal motion causes fluids to be drawn under the casting and when it is reseated with a cervical force the fluid is expressed, producing bubbles as the air and liquid are simultaneously displaced.

45. 45 Management : Removal of the prosthesis Evaluation of the abutment Caries  restoration Preparation form  modify the preparation Fabricate new restoration If the span length is excessive or occlusal forces heavy then a removable partial denture may be the only satisfactory solution.

46. 46 CONNECTOR FAILURE A connector failure between an abutment retainer and a pontic or between two pontics can occur. Under occlusal forces Internal porosity is the cast or soldered connectors When fracture occurs, pontics are placed in a cantilevered relationship with the retainer casting and this can allow excessive forces to be developed on the abutment tooth.

47. 47 Management : Prosthesis should be removed and remade as soon as possible. An inlay like dovetailed preparation can be developed in the metal to span the fracture site and a casting can be cemented to stabilize the prosthesis. Pontics can be removed by cutting through the intact connectors and a temporary removable partial denture can then be inserted to maintain the existing space and satisfy esthetic requirements

48. 48 OCCLUSAL WEAR An accelerated occlusal wear of a prosthesis can be produced due to Heavy chewing forces Clenching or bruxing After several years, a casting perforation may develop, thus allowing leakage and caries to occur, which ultimately lead to prosthesis failure.

49. 49 If the perforation is detected early, a gold or amalgam restoration can be placed to seal the area and provides additional years of service. If the metal surrounding the perforation is extremely thin, a new prosthesis should be fabricated When porcelain occlusal surfaces opposes a natural tooth, dramatic wear of enamel may occur with eventual perforation into the dentin. This problem is exacerbated by heavy chewing forces, clenching or bruxing and often requires the restoration of the abraded teeth.

50. Same problem occurs when porcelain opposes metallic restorations. So, in mouths in which occlusal wear is anticipated, it is better to place metal over occluding surfaces when natural teeth or metallic restorations are present in the opposing arch. 50

51. 51 TOOTH FRACTURE Causes : Coronal fractures : Excessive tooth preparation – leaving insufficient tooth structure to resist occlusal forces. Use of restorative material which was not retained in sound dentin with pins. Presence of interfering centric of eccentric occlusal contacts Heavy occlusal forces on a properly adjusted restoration. Attempting to forcefully seat on improperly fitting prosthesis. Incorrect unseating of a cemented bridge. Around inlays and partial veneer crowns, as a result of increasing brittleness, of tooth structure with age.

52. 52 Radicular fractures : Trauma Forceful seating of a post and core. Attempting to seat an improperly fitting post and core. Fractures occurring during endodontic treatment. If the surrounding tooth structure can be adequately prepared and still possess sufficient strength, then gold foil, amalgam, or resin can be used to restore the area.

53. 53 If there is question regarding the integrity of the remaining tooth structure or restoration, a new prosthesis should be fabricated so that it encompasses the fractured area. When fracture occurs under a full coverage retainers, it is usually horizontal, at the level of the finish line. This necessitates removal of prosthesis, endodontic therapy, a post and core, and a new prosthesis.

54. 54 ACRYLIC VENEER WEAR OR LOSS Abrasion can result in loss of severe amounts of acrylic on acrylic veneer crowns and pontics. Cause Functional loading or abrasive foods and habits. Tooth brush abrasion Repair Replacing lost contours with resin. Composites - More resistant to wear -Maintain function and appearance longer than acrylic resin repairs.

55. 55 PORCELAIN FRACTURE Porcelain fractures occur with both metal-ceramic and all-ceramic restorations . Metal – ceramic porcelain failures : Frame work design : Sharp angles or extremely rough and irregular areas over the veneering area serve as points of stress concentration that cause crack propagation and ceramic fracture.

56. 56 Perforations in the metal can also cause failure for the same reason. Sharp angles Rough surfaces Perforations Stress concentrations Crack propagation Ceramic fracture

57. 57 An overly thin metal casting does not adequately support porcelain, so that flexure and porcelain fracture may result 0.2 mm over large areas of the veneering surface, the potential for failure is greater. Also, when the angle between the veneering surface and the non-veneered aspect of the casting is less than 90 degrees, it allows occlusal forces to cause localized burnishing of the metal and distortion, which leads to premature porcelain fracture. With facially veered restorations, porcelain fracture results from a framework design that allows centric occlusal contact on, or immediately next to, the metal ceramic junction.

58. 58 Occlusion : The presence of heavy occlusal forces or habits such as clenching and bruxism can cause failure. Centric or centric occlusal interferences and uncorrected occlusal sides which create deflective contact of the opposing teeth can cause fracture of porcelain. Metal handling procedures : Metal contamination due to improper handling during casting, finishing or application of the porcelain can lead to formation of bubbles at the metal ceramic junction when porcelain is applied, creating stress and possibly cracks. Separation of the porcelain from the metal has been observed in cases of severe contamination. Excessive oxide formation on the alloy surface can also cause separation of porcelain from the metal.

59. 59 Preparation, impression and Insertion : A tooth preparation with a slight undercut can cause binding of the prosthesis as it is seated, which initiates a crack in the porcelain. An impression that is slightly distorted can also lead to the same problem. Teeth prepared with feather edge finish lines or impressions that donot record all of the finish line can lead to an extension of metal beyond the actual termination of tooth reduction, because the technician cannot determine from the die or impression where to terminate the wax pattern. The thin metal may bind against the tooth and initiate a crack in the overlying porcelain. Definite finish lines and impressions record detail are prerequisites to acceptable ceramics.

60. 60 Metal and Porcelain Incompatibility : In rare instances, an alloy and porcelain are found to be truly incompatible, and successful bonding without loss of the veneer or cracking is impossible. However, failure resulting from improper handling of the material is often attributed to porcelain, metal incompatibility. Repair of Fractured Metal – Ceramic Restorations : The best method of repairing a fractured metal ceramic fixed partial denture is the fabrication of a new prosthesis. some of the procedures available for repair can at least serve as the interim until a new prosthesis is fabricated. Material for repair : 1) Composite resins : Adequately good color matches can routinely be achieved.

61. 61 Lack of longevity is the main drawback because true chemical bonding does not occur between the current resins and either metal or porcelain Pinholes or groves must be made for mechanical interlocking. 2) A more permanent repair is possible when adequate metal framework thickness is available. This techniques works best with facially veneered restorations and involves the following steps. Procedure : Removal of the remaining porcelain on the fractured to expose the underlying metal. Drilling of several pinholes (4 or 5) into the framework to a depth of at least 2 mm. Making of an impression.

62. 62 Creation of a pin – retained metal casing 0.2 to 0.3 mm thick out of a metal – ceramic alloy to fit over the exposed metal framework. Fusion of porcelain to the pin – retained. Cementation of the casting in position. With full porcelain coverage prosthesis failures, the fractured area can be prepared with an incisal or occlusal path of insertion, and a staple like casting can be fabricated and veneered. The preparation should include grooves and pinholes, or both, in the underlying framework to provide retention and stability. A metal ceramic restoration is then fabricated and cemented in position.

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64. 64 Porcelain jacket crown failures : Fractures are more frequently observed when these restorations are placed on posterior teeth and on canines because of the occlusal forces on these teeth. All ceramic restorations are more likely to fail in the presence of heavy occlusal forces, clenching, or bruxism. Vertical fracture : The marginal area of jacket crowns is often more closely adapted to the prepared tooth than are other areas of restoration. If a tapered finish line (such as a chamfer) is used, the restoration may contact the tooth on a sloping surface, so that forces are produced that attempt to expand the restoration and that are not well resisted by porcelain. A vertical fracture may occur.

65. 65 Vertical fractures have been observed when a large portion of the proximal preparation form is missing and is not restored prior to the impression procedure. When occlusal forces to the marginal ridge in which the missing tooth form is located, greater leverage is developed because of the distance from the point of force application to the underlying prepared tooth. Sharp areas on the preparation such as the line angles or the incisal edge, produce areas of high stress in the restoration – causing fracture.

66. 66 The occlusal forces attempt to rotate the restoration, causing expansive forces. A round preparation form that does not provide adequate resistance to rotational forces can also cause vertical fracture. Facial cervical fracture : Fracture of the facial cervical porcelain, which often assumes a semilunar form, generally occurs, with a short preparation. The incisocervical length of the preparation should be two – thirds to three quarters that of the final restoration. When the preparation is short, forces applied at the incisal edge attempt to tip the restoration facially and cause cervical porcelain fracture.

67. 67 Lingual fracture : Semilunar lingual fractures are observed when the occlusion is located cervically to the cingulum of the preparation, where forces on the porcelain are more shear in nature and not well resisted. Other lingual fractures, not necessarily semilunar in form are the result of inadequate lingual tooth reduction in which less than 1 mm of porcelain is present. Exceptionally heavy occlusal forces also can cause lingual fractures even when adequate porcelain thickness is present.

68. 68 Dealing with failures of all ceramic crowns : There are no satisfactory methods of repairing fractures of all ceramic restorations. A new restoration must be fabricated. In early failures, in the absence of clinical or laboratory defects, occlusal forces are likely to be present that exceed the strength of the restoration. In such case, a metal – ceramic restoration should be seriously considered for the new restoration. If many years of good service occurred prior to failure and optimal esthetics is still required, a new all ceramic restoration should be considered

69. 69 ESTHETIC FAILURES Ceramic restorations more often fail esthetically than mechanically or biologically. Poor color match is the frequent reason for most of the remakes of the restorations. Causes : For unacceptable color match. Inability to match the patients natural teeth with available porcelain colors. Inadequate shade selection. Metamerism. Insufficient tooth reduction. Failure to properly apply and fire the porcelain – creating a restoration that does not match the shade guide itself or the surrounding teeth.

70. 70 6. Incorrect form or a framework design that displays metal. Age changes in the natural tooth over the years. When thin incisors are prepared, the metallic color of the partial coverage casting may be visible through the remaining tooth structure (grayness).

71. 71 FACING FAILURES a facing repair may be indicated if the prosthesis is otherwise satisfactory. It can be rebuild the desired form with a resin. Pins can be cemented or threaded into the casting if additional retention is required. Another technique is to prepare the remaining metal casting so that a new pin – retained casting can be fabricated and cemented in place.

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74. 74 Removal of a prosthesis : Many well retained restorations cannot be removed intact and to prevent abutment tooth damage, must be cut off the prepared tooth and thereby destroyed. Attempts should be made for intact removal of restorations without damaging the abutments. The forces applied for removal should be sharp and in an occlusal direction. Straight chisel and mallet technique : The chisel is kept as nearly parallel as possible to the path of withdrawal and mallet is used to tap with sharp blows, not so intense to cause tooth fracture or extreme pain.

75. 75 2) Crown removers : These can be placed around retainers or under pontics and connectors so that occlusally directed forces can be applied

76. 76 Richwil technique : If the restoration cannot be removed with a crown remover the addition of the use of an Amurol sugarless fruit drop or a Richwil crown remover can be used. It is based on the principles of adhesion and depends on equal and opposing force being applied to opposing teeth. Liebenberg WH. Methods for removing crowns and bridges: Preserving the restoration. Quintessence international. 1995 Jan 1;26(1).

77. 77 The material [Amurol sugarfree fruit drop) is tempered in water at 145 F for 1-2 min. Then the material is placed on the opposite to the restoration being removed. The patient should close into the material compressing it to 2/3 rd its original height, holding steady for about 10 seconds. The patient should then open the mouth with a quick movement. This exerts a constant negative load on the restoration in a completely vertical direction instead of the torquing action from the crown remover. Liebenberg WH. Methods for removing crowns and bridges: Preserving the restoration. Quintessence international. 1995 Jan 1;26(1).

78. 78 Advantage : Effective and highly successful in highly retentive restorations. Eliminates any marginal damage that could occur with metal instrument. Modification techniques : Typing of ligature wire around contacts. Application of a grappling hook to improve the direction of unseating forces. Ultrasonic instrumentation Liebenberg WH. Methods for removing crowns and bridges: Preserving the restoration. Quintessence international. 1995 Jan 1;26(1).

79. 79 Golden west crown remover : This uses a sized hole cut in the occlusal surface of posterior units. A hollow core tap, threaded both inside and outside is tapped into the sized opening and against tooth structure. A pin is inserted into the core of the tap, which engages tooth structure. A small bolt is threaded into the inside of the tap to engage the pin at which point a strong and effective unseating force may be exerted . This is much less traumatic than the blow imparted by the crown remover but care must be taken not to drive the pin through foundation or tooth structure into the pulp. Liebenberg WH. Methods for removing crowns and bridges: Preserving the restoration. Quintessence international. 1995 Jan 1;26(1).

80. 80 2) Sectioning and prying method : The safest but most destructive method of removing cemented units is by cutting a channel through the restoration to prepared tooth structure on the facial or lingual and occlusal or incisal aspects and gently expanding the casting with a large spoon excavator to break the cement joint. When this removal technique is used it is advantageous to use a round bur for cutting the metal. The curved cutting leaves of the round bur remain intact and sharper for a much longer time than the angular leaves of a fissure or an inverted cone bur. Liebenberg WH. Methods for removing crowns and bridges: Preserving the restoration. Quintessence international. 1995 Jan 1;26(1).

81. REVIEW OF LITERATURE 81

82. purpose of this article was to identify the incidence of complications and the most common complications associated with single crowns, fixed partial dentures, all-ceramic crowns, resin-bonded prostheses and posts and cores. Conventional fixed partial dentures had the greatest complications (27%), resin bonded prostheses (26%), single crowns (11%) posts and cores (10%), all-ceramic crowns had the lowest incidence (8%) of complications. 82 Goodacre CJ, Bernal G, Rungcharassaeng K, Kan JY. Clinical complications in fixed prosthodontics. The Journal of prosthetic dentistry. 2003 Jul 1;90(1):31-41.

83. The most common complications associated with conventional fixed partial dentures were caries in 18% of abutments With resin bonded prostheses, the most common complications were debonding (21% of prostheses. The most common complications associated with conventional single crowns were need for endodontic treatment (3%), porcelain fracture (3%). The most common post and core complications were post loosening (5%) With all-ceramic crowns, the most common complications were crown fracture (7%) 83 Goodacre CJ, Bernal G, Rungcharassaeng K, Kan JY. Clinical complications in fixed prosthodontics. The Journal of prosthetic dentistry. 2003 Jul 1;90(1):31-41.

84. 84 Compared the flexural strengths of porcelain bonded to composite resin specimens using four organosilane materials. 3M porcelain repair kit (Scotch bond) (Dental products division / 3M) Fusion repair material (George Taub products, Jersey city NJ) Ultrafine (Sybron / Kerr) porcelain repair bonding system. Den Mat ultrabond restorative kit product. CONCLUSION: There was no significant difference in the bond strength of these materials. It is noted that the organosilane coupling agent did not bond to a metal surface as it did with the porcelain. Therefore it is advisable to create mechanical retention by using a coarse diamond when a repair involves a large surface of metal Bailey JH. Porcelain-to-composite bond strengths using four organosilane materials. The Journal of prosthetic dentistry. 1989 Feb 1;61(2):174-7.

85. To evaluate effect of ultrasonic instrumentation on the retention for both zinc phosphate and glass ionomer cemented cast crowns. A 12 minutes vibrations showed a significant decrease in retention for both the cements. CONCLUSION: When it is desirable to try removal and recementation of a cast restoration instead of refabrication, vibration used for the specified length of time can be a valuable aid, used in conjunction with other removal devices. 85 Olin PS. Effect of prolonged ultrasonic instrumentation on the retention of cemented cast crowns. The Journal of prosthetic dentistry. 1990 Nov 1;64(5):563-5.

86. A copper band is prepared by adapting it to the crown to be removed and soldering a 0.9mm metallic SS wire on the buccal and lingual sides to form a handle. Several holes are made in the band body and abraded with air borne particles on the inner surface. Band is placed on the crown and autopolymerising acrylic resins is added on the entire crown and allowed to set. Once set the crown is removed and the copper band is separated using a disk. 86 Naffah N, Chidiac JJ. Removing crowns with minimal damage. The Journal of prosthetic dentistry. 2003;5(89):522-3.

87. 87 Naffah N, Chidiac JJ. Removing crowns with minimal damage. The Journal of prosthetic dentistry. 2003;5(89):522-3.

88. 88 CONCLUSION The first consideration when confronted with any failure or repair situation is to ascertain the cause. If there is a cause that is correctable it should be taken care of first. Care should be taken not to become involved in repairs that should have been remakes. Imagination and innovation are key factors in successful repairs. Most failures are unique and present varying challenges to the dentist. Great satisfaction can be achieved in meeting a situation and solving it in an effective and economical manner .

89. References Tylman. Theory and practice of fixed prosthodonitcs Rosensteil. Contemporary fixed prosthodontics Shillinberg. Fundamentals of fixed prosthodontics Dykema R.W., Goodacre C.J. and Phillips R.W. “Johnston’s Modern Practice in Fixed Prosthodontics”. Fourth Edn, W.B. Saunders Co. Philadelphia, London. Thayer. Fixed Prosthodontics. Second edition 89

90. Removing crowns with minimal damage, JPD 2003; 89:522-27 Effect of prolonged ultrasonic instrumentation on the retention of cemented cast crowns. JPD 1990; 64; 563-65 A survey of crown and fixed partial denture failure. JPD. 1986; 56: 415-21 Longevity of fixed partial dentures J Prosthet Dent 1997; 78: 127 A rationale for comparison of plaque retaining properties of crown systems. JPD 1989; 62: 264-67 The role of coronal contour in gingival health. J Prosthet Dent 1977; 37: 280 Clinical evaluation of fixed bridges ten years after insertion. Journal oral rehabilitation 1986; 13: 423 90