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Failures in Fixed Partial Denture

Failures in FPD (Fixed partial denture) and ways to manage it

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Failures in Fixed Partial Denture

  1. 1. Presented by: Dr. Jehan Dordi 2nd Yr. MDS Failures in Fixed Partial Denture 1
  2. 2. Contents 2  Introduction  Classification  Biologic Failure  Mechanical Failure  Esthetic Failure  Psychogenic Failure  Methods of Removing a Failed FPD  Review of Literature  References
  4. 4. 4  Fixed prosthodontic treatment can offer exceptional satisfaction for both patient and dentist.  It can transform 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.
  5. 5. 5  It is important to analyze failure so that the reasons can be evaluated and prevention is imparted.  A fixed partial denture (FPD) can fail as a result of:  Poor patient care  Defective design  Inadequate execution of clinical procedures  Inadequate execution of lab procedures
  6. 6. 6  The causes of FPD failures were summarized as early as in 1920 when Tinker wrote - “ Chief among the causes for such disappointing results have been:  First : Faulty, and in some cases, no attempt at diagnosis and prognosis.  Second: Failure to remove foci of infection in attention to treatment and care of the investing tissues and mouth sanitation.  Third: Disregard for tooth form  Fourth: Absence of proper embrasures  Fifth: Inter-proximal spaces  Sixth: Faulty occlusion and articulation
  8. 8. 8 Bennard G. N. Smith 1. Loss of retention 2. Mechanical failure of crowns or bridge components  Porcelain fracture  Failure of solder joints  Distortion  Occlusal wear and perforation  Lost facings
  9. 9. 9 3. Changes in the abutment tooth  Periodontal disease  Problems with the pulp  Caries  Fracture of the prepared natural crown or root  Movement of the tooth 4. Design failures  Under-prescribed FPDs  Over-prescribed FPDs
  10. 10. 5. Inadequate clinical or laboratory technique  Positive ledge  Negative ledge  Defect  Poor shape and color 6. Occlusal problems
  11. 11. John F. Johnston 1. 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  Improperly protected gingival and ridge tissue  Thermal shock
  12. 12. 2. 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
  13. 13. 3. Recurrence of caries  Improper 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
  14. 14. 4. Recession of supporting structure  Length of the span  Size of the occlusal table  Embrasure form  Improper extensions of the cervical margins  Improper impression technique can also stimulate recession of the gingiva 5. Degeneration of Pulp 6. 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
  15. 15. 7. Loss of veneers  Little retention  Badly designed metal protection  Deformation of the protecting metal  Malocclusion  Improper fusing or technique 8. 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
  16. 16. 9. 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 10.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
  17. 17. 17 Failures in FPDs can be simply classified as: 1. Biologic 2. Mechanical 3. Aesthetic 4. Psychogenic
  18. 18. 18 Biologic Mechanical Esthetic Psychogenic Caries Loss of Retention Immediate Lack of Counselling Pulpal Degeneration Connecter Failure Delayed Endodontic Occlusal Wear Periodontal Tooth Fracture Tooth Perforation Porcelain Fracture Subpontic Inflammation Occlusal Problems General Pathosis Maintenance Failure
  20. 20. Caries 20  Caries is the most common cause of biologic failure. This can be of the following types. 1. Secondary Caries:  This can happen under the margins of the retainers. Cause:  Marginal leakage due to poor margins (open margins) or poor maintenance by patient.
  21. 21. 21 Symptoms  Perceived by the patient as pain or sensitivity to hot, cold and sweet food/liquids  Bad taste  Bad breath  Loose restorations  Fractured teeth  Discoloured teeth Detection  Visually (if present on labial surface)  By probing (Tactile)  Radiographs (if present interproximally)
  22. 22. 22 Treatment  If the caries is minor and restricted to the facial surface  restore without removing the prosthesis  Material used for such restoration in order of preference is silver amalgam, composite resins and glass ionomers, depending on location on anterior or posterior teeth.  Extensive lesions may require  Removal of prosthesis and restoration  Endodontic treatment  Extraction followed by fabrication of a new prosthesis Prevention  Ensuring adequate marginal adaptation during try-in of restoration  Educating the patient in maintaining oral hygiene  Reviewing the same during recall appointments
  23. 23. 23 2. Caries of Tooth Adjacent to Retainer:  The main cause for this is lack of proximal contact at the time of cementation.
  24. 24. 24 3. Root Caries:  This is a problem associated in the elderly patients with FPDs.  It can occur even in the absence of gingival recession and pockets.  As the elderly patients may also have reduced salivary flow due to medications and sometimes radiation, the problem is accentuated.  The cause has been identified as Actinomyces viscosus commonly present in the filiform papillae of the tongue.  Advising meticulous oral hygiene measure along with cleaning of tongue for such patients may reduce the risk of developing this problem.
  25. 25. Pulpal Degeneration of Abutment 25 Causes:  Tooth preparation without sufficient cooling or an improperly directed water spray.  An abutment with an old restoration with secondary caries or unrestored carious lesion.  Cements like zinc phosphate, glass ionomers and resin cements can cause pulpal irritation, especially if the preparation is close to the pulp leading to degeneration.  Presence of interfering occlusal contacts.
  26. 26. 26 Symptoms:  Perceived by patient as pain which could be spontaneous or related to hot/cold/sweet food or accentuated by lying down/exercising. Detection:  Usually based on symptoms as vitality testing is difficult because of the presence of retainer.  Radiograph may be useful only if periapical lesions are present. Treatment:  Access is made through the retainer and endodontic treatment is performed.  The access opening can then be restored with a post and/or a core.  If occlusion is the problem, it should be corrected.
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  28. 28. 28 Prevention:  The water spray of the high speed handpiece should be cleaned regularly and checked before tooth preparation.  All carious lesions on abutment teeth should be restored prior to preparation.  Even old restorations may be removed and new restorations made.  Occlusion should be corrected before cementing the prosthesis and the same should be verified in recall appointments.
  29. 29. Endodontic Failure of Abutment 29 Causes:  The endodontic treatment of the abutment was improper or inadequate.  A root perforation or crack of the tooth during the old endodontic treatment may manifest much later. Symptom:  Perceived by patient as pain on biting or swelling. Detection:  With the help of symptoms and radiographs.
  30. 30. 30 Treatment:  Extraction must be postponed if possible.  Endodontic retreatment and apicoectomy may be attempted through the retainer or after removing the prosthesis.  Karlsson (1986) demonstrated that 10% of 641 bridge abutments exhibited periapical lesions after 10 years, 19.8% of 303 root filled abutments exhibited non-healed periapical lesions.  This conveys that just the presence of lesions on radiographs may not necessitate any treatment.  Patient symptoms need to be assessed.
  31. 31. 31 Prevention:  Endodontically treated teeth must be used as abutments only after thorough evaluation.  If endodontic treatment is found inadequate, retreatment may be performed.  When in doubt, the design of the prosthesis should be altered to exclude the tooth as abutment.
  32. 32. Periodontal Failure 32 Causes: 1. Faulty prosthesis which hinders maintenance of oral hygiene is due to:  Poor marginal adaptation  Overcontouring of retainer axial surfaces  Large connectors  Pontic contact a large tissue area  Prostheses with rough surfaces 2. Poor maintenance by patient 3. Patient with existing periodontal disease 4. Lack of abutment support due to improper treatment planning
  33. 33. 33 Treatment:  Severe bone loss  loss of abutment teeth and attached prosthesis.  In less severe breakdown  periodontal surgery but may produce an unacceptable relationship between the prosthesis and soft tissue.  If the problem is localized and related to a prosthesis that hinders effective oral hygiene, prosthesis may be recontoured or remade to correct the defect. Prevention:  Any existing periodontal disease must be eliminated and tissues should return to optimal health before commencing fixed prosthodontics treatment.  The prosthesis should be supported adequately by sufficient number of abutments to function on a long term basis.  Patient should be instructed on proper oral hygiene measures and implementation must be verified through recall appointments.
  34. 34. Tooth Perforation 34 Causes:  Tooth perforation can occur during:  Placement of pinholes/pins  Endodontic treatment  Preparation for post and core Treatment:  Endodontic treatment is performed when pinholes or pins perforate into pulp chamber.  If perforation is located occlusal to alveolar crest, preparation can be extended to cover defect.  If located below crest and is accessible, perforation can be sealed through periodontal surgery.  If perforation is inaccessible then the abutment requires extraction.
  35. 35. Sub-Pontic Inflammation 35 Causes:  Excessive pressure by pontic due to improper pontic design and pontic contacting too large an area  Improper prosthesis design  Poor maintenance by the patient
  36. 36. 36 Symptoms:  Perceived by the patient as pain, swelling, bad breath, bad taste, bleeding gums and poor aesthetics. Treatment:  If improper design is the problem, the prosthesis should be refabricated with proper design after allowing the inflammation to subside.  Patient should be educated to maintain the pontic space using aids like superfloss.
  37. 37. Occlusal Problems 37 Symptoms:  Problems in occlusion is perceived by the patient as discomfort on biting, sore teeth, loose teeth or bridges, sensitive teeth and tired or sore muscles. Causes and Treatments:  Interfering centric or eccentric contacts  tooth mobility and irreversible pulpal damage.  Tooth mobility is reversible if problem is detected early and adjusted but correction may cause prostheses failure due to perforation and loss of aesthetics.  Pulpal damage should receive endodontic treatment following occlusal correction.
  38. 38. 38  Mobility due to long term occlusal interferences on normal teeth and due to traumatic occlusion on teeth weakened by periodontal disease, are treated by removing FPD and splinting teeth with removable prosthesis.  If mobility is severe, extraction is necessary.  An altered vertical dimension also leads to occlusal problems.  This is the result of poor treatment planning and needs to be identified and corrected.  It may also lead to temporomandibular disorders.
  39. 39. General Pathosis 39  Failure to diagnose a pathological change, having a vital bearing on the patient’s life expectancy is a failure.  For example a patient with a squamous cell carcinoma being treated for missing teeth with a FPD instead of the more important condition is a failure.  Many times patients come back to the dentist after many years for restorative treatment. Patient’s current medical condition should be evaluated.  A change in a patient’s medical condition like cerebral hemorrhage alters patient’s motivation, physical ability to maintain teeth, diet and general resistance, leading to a deterioration of restorations and abutments.
  40. 40. Maintenance Failure 40  Maintenance of the prosthesis is very important for the biologic survival of the restoration.  Failure may be due to:  Failure of the dentist to prescribe a maintenance program  Failure to implement or prescribe a recall system  Inadequate motivation of patient  Inadequate motivation by dentist
  42. 42. Loss of Retention 42  For a restoration to accomplish its purpose, it must stay in place on the tooth.  No cements that are compatible with living tooth structure and the biologic environment of the oral cavity possess adequate adhesive properties to hold a restoration in place solely through adhesion.  The geometric configuration of the tooth preparation must place the cement in compression to provide the necessary retention and resistance.
  43. 43. 43 Causes:  Excessive taper  Short clinical crowns  Misfit  Misalignment  Improper cementation procedure  Poor fit of casting  Excessive span length  Heavy occlusal forces like cantilevers if designed improperly  If not detected early, a loose retainer can lead to extensive caries of the abutment.
  44. 44. Excessive taper:  As a cast metal or ceramic restoration is placed on or in the preparation after the restoration has been fabricated in its final form  the axial walls of the preparation must taper slightly to permit the restoration to seat.  Theoretically, the more nearly parallel the opposing walls of the preparation are, the greater should be the retention.  Recommendations for optimal axial wall taper of tooth preparations for cast restorations ranges from 10 to 12 degrees.  Tooth preparation taper should be kept minimal because of its adverse effect on retention, but Mock estimates that a minimum taper of 12 degrees is necessary just to insure the absence of undercuts.
  45. 45. Short clinical crown:  Cements create mechanical interlocks between the inner surface of the restoration and the axial wall of the preparation.  Greater the surface area of the preparation  greater is its retention.  Preparations on large teeth >> retentive >> preparations on small teeth.  A short, over-tapered or short clinical crown would be without retention  many paths of removal.  A shorter wall cannot afford enough resistance. The walls of short preparations should have as little taper as possible.
  46. 46. Clinical conditions with excessive taper and short clinical crowns should be treated with :- 1. In case of excessive taper:  Incorporation of proximal grooves  Additional retentive grooves (should be along with the path of insertion)  Additional pins 2. In case of short crowns:  Crown lengthening procedure  Modification of supra-gingival margin  sub-gingival margin  Additional retentive grooves and proximal box  Incorporation of pins  Addition of extra abutments
  47. 47. Misfit :  The misfit can occur at different locations : 1. Internal gap 2. Marginal gap 3. Vertical marginal discrepancy 4. Horizontal marginal discrepancy 5. Over-extended margin 6. Under-extended margin
  48. 48. Causes for misfit:  Distortion of the metal substructure  Distortion of the margins (towards the tooth surface)  Improper water/powder ratio  Improper mixing time  Improper burnout temperature  Metal bubbles in occlusal or marginal regions  Inadequate vacuum during investing  No surfactant  Porcelain flowed inside the retainer  Excessive oxide layer formation in inner side of the retainer (due to contaminated metal or repeated firing of porcelain)  Tight contact points  Thick cement space  Insufficient pressure during cementation procedure
  49. 49. Misalignment:  In case of the cemented FPD, it is more difficult to differentiate whether an FPD is not seating because of a faulty fit, or the alignment of the retainers relative to each other is incorrect.  The only difference which may sometimes be apparent is that, in the case of misalignment, the FPD will have some ‘spring’ in it and tend to seat further on pressure due to the abutment teeth moving slightly, whereas in the case of a defective fit, the resistance felt will be solid.
  50. 50. Causes for misalignment:  Abutment displacement due to improper temporization  Distortion of wax pattern while sprueing and investing  Casting defects  Distortion of metal frameworks in porcelain firing  Porcelain flow inside the retainers  Misalignment of soldering points  Insufficient pressure in cementation  Thick cement film  Excessive metal or porcelain in tissue surface (ridge lap) of pontic prevents the proper seating of FPD and open margin (can be detected by observing the blanching of the tissue or patient may complain of pressure on the pontic region).
  51. 51. 51 Symptoms:  Patient may perceive a loose retainer as sensitivity to temperature or sweets and bad taste or odour. Detection:  A curved explorer is placed under the connector and an occlusal force is applied.  The retainer is then pressed cervically with a finger.  If retainer is loose, the occlusal force causes fluids to be drawn under, the casting is reseated with a cervical force, the fluid is expressed in the form of bubbles as air and liquid are simultaneously displaced.
  52. 52. 52 Treatment:  Prosthesis must be removed. It can be recemented if the reason was a cementation problem and it is intact.  If loss of retention is due to preparation design, the teeth should be modified to improve retention and resistance form and new prosthesis fabricated.  If excessive span length is the problem, a removable partial denture may be the only option.
  53. 53. Connector Failure 53 Causes:  Inadequate connector width if posterior - occlusocervical, if anterior - buccolingual.  This is usually due to supraeruption of opposing tooth  leaving no space for pontic in height  Internal porosity, incomplete casting or soldering which has weakened the metal can also cause connector failure.
  54. 54. 54 Treatment:  If the cause is supraeruption  offending tooth may be contoured to provide adequate clearance.  If severe, intentional endodontics may be required, following which a new prosthesis is made.  If casting defect was the problem  most often a new prosthesis is made.
  55. 55. Occlusal Wear 55 Causes:  Insufficient thickness of restoration due to inadequate preparation of occlusal surface or lack of functional cusp bevel.  Heavy chewing forces/bruxism  Rough porcelain occlusal surfaces cause wear of opposing natural teeth
  56. 56. 56 Treatment:  If wear is due to inadequate preparation  a new prosthesis is made after providing adequate clearance  Any rough porcelain surface should be polished or glazed.  For bruxers, a night guard may be a solution.  When occlusal wear is anticipated  it is better to plan metal occlusal surfaces opposing natural teeth or metallic restorations.
  57. 57. Tooth Fracture 57 1. Crown fracture: Causes:  Excessive tooth preparation leaving insufficient tooth structure to resist occlusal forces.  Endodontically treated abutment with excessive tooth structure loss.  Abutment with large restorations.  Interfering centric/eccentric contacts.  Attempting to forcibly seat an improperly fitting prosthesis.  Unseating a cemented bridge incorrectly.
  58. 58. 58 Treatment:  Small coronal fractures common around inlays and partial veneer crowns. These can be restored.  Large fractures around partial veneer crowns require a build-up and full veneer crown.  Fracture around partial veneer crowns with pulp exposure will require endodontic treatment with/without post and core followed by full veneer crown.  Fracture around full crowns if occurs horizontally at level of finish line, is treated by endodontics, followed by post and core and a new prosthesis.  If finish line is intact then ‘retrofit technique’ can be attempted to salvage the retainer or crown.
  59. 59. 59 Retrofit technique:  In this technique, a post and core is fabricated to fit an existing fractured abutment tooth with an intact crown or retainer. Hence, it is termed ‘retrofit’.  The procedure for fabricating a retrofit cast post and core is as follows:  A post space is prepared in the abutment tooth.  A resin pattern of the post and core is fabricated to fit the crown.  The pattern is cast and cemented along with the crown.
  60. 60. 60 2. Root Fracture: Causes:  Improperly designed or a poorly fitting post  Root fracture occurring during endodontic or post treatment, but manifests later  Trauma  Reduced neural feedback leading to increased loading in endodontically treated teeth Treatment:  Extraction followed by a new prosthesis
  61. 61. Porcelain Fracture 61 1. Metal-ceramic fracture Causes:  Improper framework design:  Sharp angles or irregular areas over coping surface  stress concentrations  cracks  Perforations in metal or overly thin metal casting  inadequate support for porcelain  With facings, occlusal contact on or adjacent to metal-to-ceramic junction causes porcelain fracture  Any unsupported porcelain can fracture.
  62. 62. 62  Occlusion:  Heavy occlusal forces like clenching, bruxism.  Centric or eccentric occlusal interferences.  Metal handling procedures:  Improper handling of alloy during casting, finishing or porcelain application can cause contamination which leads to ceramic fracture.  Excessive oxide formation in metal can also cause porcelain fracture.  This is caused by improper conditioning of base metal alloys.
  63. 63. 63  During clinical procedures:  Teeth prepared with slight undercut can cause bending of prostheses during insertion, which initiates crack propagation.  Distorted impressions can also cause prosthesis failure.  When teeth are prepared with feather-edge finish lines or if finish lines are not recorded properly in impression, the technician may extend the metal beyond finish line as finish line is vague.  The thin metal may bind against tooth and initiate crack of overlying porcelain.
  64. 64. 64  Cleaning fitting surface of prosthesis using ultrasonic scalers can initiate cracks in the porcelain.  This typically happens when the prosthesis has been fixed provisionally or when a dislodged prosthesis is recemented.  Metal and porcelain incompatibility:  This happens rarely. This can be easily prevented if manufacturer’s instructions are followed when choosing the porcelains for a particular metal.
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  66. 66. 66
  67. 67. 67
  68. 68. 68 Treatment:  The best method is to fabricate a new prosthesis.  Repairs can be attempted until a new prosthesis is fabricated.
  69. 69. 69 A. Resin Repair:  Composite resins of appropriate shade are used and repair is made directly in the mouth.  The exposed ceramic surface is etched with hydrofluoric acid for 30sec.  The exposed metal surface can either be sandblasted or roughened for mechanical retention.  A silane coupling agent is applied and allowed to remain on the surface for 1 min. It is not light cured.  A composite bonding agent is applied and light cured for 10sec.  An opaque composite paste is applied on the exposed metal surface to mask the colour of metal and light cured for 20sec.  Composite resin of appropriate shade is selected and contoured on the surface, light cured for 20sec, finished and polished.
  70. 70. 70
  71. 71. 71 B. Facing Repair:  This is a repair made with porcelain indirectly in the laboratory.  It is a more definitive repair but requires adequate framework thickness. It works well with facings.  The fractured porcelain is completely removed from the metal by grinding.  Four to five pinholes are made on the metal surface.  Impression is made and a thin metal with porcelain superstructure is fabricated.  This is cemented over the labial metal surface.
  72. 72. 72 2. All ceramic fracture Causes:  Vertical fracture:  Inadequate finish lines like feather edge.  Sharp areas on prepared tooth.  Large portion of proximal preparation form is missing and not restored prior to impression procedure.  Round preparation form without resistance to rotational forces.
  73. 73. 73  Facial-cervical fracture:  If tooth is over-prepared and it is less than two-third or three-fourth of final restoration in height, this fracture occurs due to poor resistance.  Opposing tooth contact located incisally to prepared tooth.  Lingual fracture:  Inadequate lingual tooth preparation.
  75. 75. Immediate Aesthetic Failure 75  Aesthetic problems at the time of cementation can be due to:  Poor shade match – reasons for this may be:  Inadequate selection and communication  Metamerism  Insufficient tooth preparation  Failure to properly apply and fire porcelain  Poor tooth contour, gingival contour, pontic ridge contour and embrasure  Poor margin placement  Framework design that displays metal  Unrealistic expectations of patient due to poor communication
  76. 76. DELAYED AESTHETIC FAILURE 76  These occur over a period of time following cementation due to:  Gingival recession due to:  Poor fit  Overcontour  Excessive trauma during tooth preparation and impression making.  Subpontic tissue shrinkage following extraction – if insufficient time for healing of tissues.  After periodontal surgery – margins will be exposed due to gingival recession if insufficient healing time.  Unglazed porcelain can cause unsightly wear of opposing natural teeth.  Poorly glazed porcelain restorations also develop black specks over time.
  78. 78. 78  When all the parameters for a successful FPD have been met with, rarely a patient may still feel uncomfortable with the restoration.  This has been attributed to the stress and behavioural changes in the individual.  The patient may require counselling to get over this problem.  A failure to recognize this problem during the diagnostic phase itself, can lead to a failure of the prosthesis.
  80. 80. 80  If a FPD fails; usually it needs to be removed for any treatment.  Most often it cannot be removed intact and must be cut off from the abutment.  It is necessary at least to attempt intact removal. The following methods can be employed with abundant caution not to damage the abutment: 1. Using a straight chisel:  By applying a sharp force in an occlusal direction using a mallet, with a sharp chisel placed under the retainer margin.  The tapping should be done parallel to the path of withdrawal of prosthesis.
  81. 81. 81 2. Using a crown remover: These are commercially available and may be of the following common types: i. Back action:  Uses a weight to deliver a force directed backward with the tip placed such that it transfers the force occlusally. ii. Spring loaded:  Uses a spring mechanism to deliver a sudden force.
  82. 82. 82 iii. Pneumatic:  Uses compressed air to deliver a controlled force to remove crowns and bridges.  They are all manufactured with different tips to engage retainers and pontics.  Other commercial examples include – Richwill, Metalift and Coronaflex, each with its own unique method of usage.
  83. 83. 83 CORONAFLEX crown remover  Air driven device that connects to standard handpiece hoses via Kavo’s Multiflex coupler.  The crown remover  controlled low amplitude impact at its tip.  Kit includes loop to thread under FPD’S connectors that is attached to a holder and an adhesive clamp to obtain a purchase on single crowns.  It delivers the impact in the long axis of the tooth.  The loop is threaded under the connector.  The tip of the crown remover is placed on the bar and the impact is activated by releasing the index finger from the air valve.  The adhesive clamp is attached with autopolymerising resin used to remove a single crown.
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  85. 85. 85 METALIFT crown and bridge removal system  Access to the metal on each abutment is provided by preparing through the porcelain around bur to create a pilot channel in each abutment  The pilot hole is followed by the special drill.  Cement should be visible through the hole  The metalift instrument is threaded into the holes and the FPD removed.  It can be recemented for further service.
  86. 86. 86 RICHWIL crown and bridge remover  Small cubes of adhesive water pliable resin softened in warm water (55 degrees) for 1-2 minutes and patient is instructed to occlude on it.  The resin is cooled with water  A sharp opening action will remove the crown. It is useful for  Removing partially uncemented crowns  Retainers which have been sectioned but still resists removal
  87. 87. 87 HIGA bridge remover  Removal of provisional bridges/cementation failures  A cavity is cut into the occlusal surfaces of crowns to expose the tooth.  The pins on the remover are adjusted to align with the cavities  0.5 mm of wire is passed beneath the proximal joints and extends out of the mouth  The wire is attached to the spindle and tightened by turning the screwdriver  Further tightening applies axial load on the tooth via the pins and an occlusal load on the bridge via the wire, and cement fracture occurs.
  88. 88. 88 3. By cutting retainer:  This is the best method to prevent any damage to the abutment. But it will destroy the prosthesis.  A thin groove is placed in the middle of the restoration with a high speed airotor handpiece using diamonds (ceramic) and carbides (metal).  This should cut through the restoration and expose the abutment.  The groove can be placed in the facial aspect but placing it lingually especially for anteriors, may allow the restoration to be used provisionally after removal.  A facial slot works best for maxillary and mandibular molars because lingual access is difficult.
  89. 89. 89  Removal is attempted with a crown remover following cutting through one surface, if not, both facial and lingual surfaces are cut dividing the retainer into two halves.  It is now easy to remove with a crown remover or a sharp instrument is used to wedge the two halves.
  91. 91. 91 Koenig V, Vanheusden A, LeGoff S and Mainjot A conducted a clinical risk factors related to failures with zirconia-based restorations: an up to 9-year retrospective study.  147 ZBR were evaluated after a mean observation period of 60 months.  Accessorily, zirconia implant abutments (n = 46) were also observed.  The technical and the biological outcomes of the ZBR were evaluated.  Occlusal risk factors were examined: occlusal relationships, parafunctional habits and the presence of occlusal nightguard. Journal of Dentistry 41 (2018) 1164 – 1174
  92. 92. 92  The results showed the survival rate of crowns and FPDs was 93.2%, the success rate was 81.63%.  The chipping rate was 15% and the framework fracture rate was 2.7%.  Most fractographic analyses revealed that veneer fractures originated from occlusal surface roughness.  Several parameters were shown to significantly influence veneer fracture: the absence of occlusal nightguard, the presence of a ceramic restoration as an antagonist, the presence of parafunctional activity and the presence of implants as support.  The results of the study confirm that chipping is the first cause of ZBR failure.
  93. 93. 93 E. G. Kontakiotis, C. G. Filippatos, S. Stefopoulos & G. N. Tzanetakis conducted a prospective study of the incidence of asymptomatic pulp necrosis following crown preparation.  A total of 120 teeth with healthy pulps scheduled to receive fixed crowns.  Teeth divided into two groups:- Intact teeth and Teeth with preoperative caries, restorations or crowns and into further four groups:- maxillary anterior and posterior teeth, mandibular anterior and posterior teeth  Experimental and control teeth  electric pulp testing on three different occasions before treatment commencement (stage 0), at the impression making session (stage 1) and just before the final cementation of the crown (stage 2). International Endodontic Journal 2017
  94. 94. 94  Teeth that were considered to contain necrotic pulps were submitted to root canal treatment.  Upon access, absence of bleeding was considered as a confirmation of pulp necrosis.  The overall incidence of pulp necrosis was 9%.  Intact teeth had a significantly lower incidence of pulp necrosis (5%) compared with preoperatively structurally compromised teeth (13%).  No significant differences were found amongst the four groups with regard to tooth type.  They concluded that the incidence of asymptomatic pulp necrosis of teeth following crown preparation is noteworthy.
  95. 95. 95 Al-Sinaidi A and Preethanath R conducted a study on the effect of fixed partial dentures on periodontal status of abutment teeth.  This study was aimed to assess the periodontal status of Saudi adult females who had received regular oral prophylaxis following the insertion of fixed partial dentures.  The effects of sub- and supra-gingivally placed crown margins were also assessed.  Sample size - 78 females who had fixed partial dentures  From each study participant, two paired eligible sites, one for the abutment and one for the matched non-abutment teeth, were selected.  The plaque index, gingival index, probing pocket depth, tooth mobility and locations of the crown margins were assessed and recorded by one calibrated examiner. The Saudi Journal for Dental Research 2018.
  96. 96. 96  The abutment teeth scored significantly higher plaque and gingival indices and greater probing pocket depth than non-abutment teeth.  In addition, the abutment teeth scored greatest mean values of the clinical parameters in subjects who were 46 year-old or older and those who had their functioning fixed partial dentures for more than 5 years.  The teeth with supra-gingivally placed crown margins had significantly higher mean values of plaque index, gingival index and probing pocket depth than teeth with sub-gingival crown margins.  The results of this study indicated that in subjects with fixed partial dentures, the abutment teeth are more prone to periodontal inflammation than the non- abutment teeth.  Additionally, the individual’s age, duration of insertion of fixed partial dentures and location of the crown margins affect the periodontal health of the abutments.
  97. 97. CONCLUSION 97
  98. 98. 98  Fixed prosthodontic treatment does not end with the fitting of restorations.  Subsequent maintenance is an integral part of treatment. If this is not adequately prescribed, failure can occur.  The first consideration when confronted with any failure 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. Repairs are usually the second best to the original in one or more ways.  Most failures are unique and present varying challenges to the dentist. Therefore treatment plan for each situation must be individualized.
  99. 99. REFERENCES 99
  100. 100. 100  Planning and making crowns and bridges. Smith B, Howe L. 4th edition. Abingdon, Informa healthcare.  Contemporary fixed prosthodontics. Rosenstiel S, Land M, Fujimoto J. 4th edition. St Louis, Mosby Elsevier.  Shillingburg HT, Hobo S, Whitsett LD, Jacobi R, Brackett SE. Fundamentals of fixed prosthodontics. Quintessence Publishing Company.  Koenig V, Vanheusden A, LeGoff S and Mainjot A. A clinical risk factors related to failures with zirconia-based restorations: an up to 9-year retrospective study. Journal of Dentistry 2018;41:1164 – 1174.  E. G. Kontakiotis, C. G. Filippatos, S. Stefopoulos & G. N. Tzanetakis. A prospective study of the incidence of asymptomatic pulp necrosis following crown preparation. International Endodontic Journal 2017.  Seong LG, May LW. Key Indicators of success or survival for clinical performance of fixed partial denture. Annals of Dentistry University of Malaya. 2019 Dec 3;26:53-8.  Kapoor C, Vaidya S. Evaluation of Complications Associated with Fixed Partial Denture-An observational study. Journal of Advanced Medical and Dental Sciences Research. 2019 Aug 1;7(8):149-52.
  101. 101. 101  Al-Sinaidi A and Preethanath R. A study on the effect of fixed partial dentures on periodontal status of abutment teeth. The Saudi Journal for Dental Research 2018.  Triwatana P, Nagaviroj N, Tulapornchai C. Clinical performance and failures of zirconia- based fixed partial dentures: a review literature. The journal of advanced prosthodontics. 2012 May 1;4(2):76-83.  Muddugangadhar BC, Amarnath GS, Sonika R, Chheda PS, Garg A. Meta-analysis of failure and survival rate of implant-supported single crowns, fixed partial denture, and implant tooth-supported prostheses. Journal of international oral health: JIOH. 2015 Sep;7(9):11.  Swain PK. Failure Rate in Fixed Partial Denture Patients-A Clinical Study. Journal of Advanced Medical and Dental Sciences Research. 2018 Oct;6(10).  Jain JK, Sethuraman R, Chauhan S, Javiya P, Srivastava S, Patel R, Bhalani B. Retention failures in cement-and screw-retained fixed restorations on dental implants in partially edentulous arches: A systematic review with meta-analysis. The Journal of the Indian Prosthodontic Society. 2018 Jul;18(3):201.  Alraheam IA, Ngoc CN, Wiesen CA, Donovan TE. Five‐year success rate of resin‐bonded fixed partial dentures: A systematic review. Journal of Esthetic and Restorative Dentistry. 2019 Jan;31(1):40-50.
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