Abutment selection in fpd

objectives in abutment selection in fixed dental prosthesis.the ideal requirements of abutments in selection for FDP.

1. Abutment selection in fpd Dr. Shannon Fernandes Department of Prosthodontics Third year PG

2. CONTENTS Introduction Diagnostic casts Radiographic examination Factors influencing abutment selection Crown length Crown form Crown root ratio Periodontal ligament areas Root configuratoin Root proximities

3. CONTENTS 10. Periodontal examination 11. Long axis relationship 12. Arch form 13. Span length 14. Unrestored abutments 15. Endodonticaly treated abutment 16. Rigidity of prosthesis 17. Margin location 18. Occlusal anatomy

4. 19. Pontic tissue contact 20. Available tooth structure 21. Patient age 22. Vitality testing of the pulp 23. Long term abutment prognosis

5. Special problems Pier abutment Tilted molar abutment Canine replacement fpd Abutments for cantilever fpd Questionable abutments summary

6. INTRODUCTION Fixed partial dentures transmits forces through the abutments to the periodontium . Failures are due to poor engineering, the use of improper materials, inadequate tooth preparation, and faulty fabrication. Successful selection of abutments for fixed partial dentures requires sensitive diagnostic ability. Thorough knowledge of anatomy, ceramics, the chemistry and physics of dental materials, metallurgy, Periodontics , phonetics, physiology, radiology and the mechanics of oral function is fundamental.

7. DEFINITION A tooth, a portion of a tooth, or that portion of a dental implant that serves to support and/or retain a prosthesis. ( GPT 9 )

8. DIAGNOSTIC CASTS Accurate diagnostics casts must be correctly oriented to the transverse hinge axis and plane of occlusion on an articulator to permit eccentric movements similar to those that take place in the mouth. This procedure allows a simple evaluation of occlusal relationship of dental arches and the abutment teeth. Rotated malposed teeth can be easily observed. The form and contour of abutment teeth can be visualized as well as the alignment and contacts of opposing teeth.

9. RADIOGRAPHIC EXAMINATION Periapical and bitewing films are most important in selection of abutment teeth. On occasion additional views, such as TMJ radiographs for patients with TMJ dysfunction and panoramic radiograph can also be useful.

10. An intraoral radiographic examination reveals : Remaining bone support Root number and morphology (long, short, slender, broad, bifurcated, fused, dilacerated etc.) and root proximity. Quality of supporting bone, trabecular patterns and reactions to functional changes. Width of periodontal ligament spaces and evidence of TFO.

11. Areas of vertical and horizontal osseous resorption and furcation involvement Axial inclination of teeth(degree of non parallelism if present) Continuity and integrity of lamina dura .

12. Pulpal morphology and previous endodontic treatment with or without post and cores. Presence of apical disease, root resorption or root fractures. Retained root fragments, radiolucent areas, calcifications, foreign bodies or impacted teeth.

13. Presence of carious lesions, the condition of existing restorations, and proximity of carious lesion to the pulp. Proximity of carious lesions and restorations to alveolar crest. Calculus deposits

14. Factors influencing abutment selection The choice and number of abutments are determined by a combination of load- bearing ability of the abutment teeth plus the forces and stresses to which these will be subjected. The number of roots,shape,length,alignment , bone height has a direct relation to the load- bearing capacity of teeth. The shorter, more tapered the root and lower the bone level, the less satisfactory the tooth will be as an abutment.

15. CROWN LENGTH Teeth must have sufficient occlusocervical crown length for sufficient retention. Teeth with shorter clinical crowns do not provide sufficient retention unless full- coverage preparations are used or additional crown length is achieved through periodontal surgery.

16. CROWN FORM Some crown have tapered crown forms making the parallelism during preparation difficult. Necessitating full coverage retainers is needed to improve their retentive and esthetic qualities.

17. CROWN ROOT RATIO Defined as Physical relationship between the portion of tooth within the alveolar bone compared to the portion not within the alveolar bone, as determined by radiograph. This ratio is the measure of length of tooth occlusal to the alveolar crest of bone compared with length of root embedded in bone. Optimum crown-root ratio is 2:3. minimum 1:1

18. ANTE suggested in 1926 that it was unwise to provide a FPD when the root surface area of the abutment was less than the root surface area of the teeth being replaced ANTE’s LAW – the combined pericemental area of all abutment teeth supporting a FPD should be equal to or greater in pericemental area than the tooth or teeth being replaced.

19. Newman and Ericsson however cast a doubt on the validity of Ante’s Law by demonstrating that teeth with considerably reduced bone support can be successfully used as FPD abutments. The majority of treatments presented by these authors had an abutment root surface area less than half that of replaced teeth and there was no loss of attachment after 8-10 years. They attributed this success to meticulous root planing during the active phase of treatment, proper plaque control during the observed period and the occlusal design of the prosthesis.

20. ROOT CONFIGURATION Elongated labiolingually than mesiodistally rather than round Flared rather than fused

21. ROOT PROXIMITY There must be adequate clearance between the roots of the proposed abutment to permit the development of physiologic embrasures in completed prosthesis.

22. PERIODONTAL DISEASES Healthy periodontal tissue is prerequisite for all fixed restorations. Abutment with bone loss needs more careful assessment Conical shape of roots with 1/3 rd of root exposed; 1/2 of supporting tissue lost Lengthened clinical crowns lead to greater leverage forces

23. Successful fixed prosthesis with severely reduced periodontal support, is assured when periodontal tissues have been restored to excellent health and Long term maintenance has been assured, otherwise results may lead be disastrous.

24. PERIODONTAL ASSESSMENT Mobility Recession Pocket Furcation

25. LONG AXIS RELATIONSHIP The architecture of periodontal ligament is such that Forces are withstood best when directed along the long axis of the tooth. A severely inclined tooth will not withstand forces as well as one that is erect. Inclined tooth as abutment : Shorter edentulous span with less occlusal force.

26. Common path of insertion for all retainers : Conventional FPD: Less then 25° inclination. Resin-bonded FPD: Less then 15° inclination mesio -distally and same plane facio-lingually . Evaluation : diagnostic cast with a dental surveyor and radiograph

27. ARCH FORM When pontic lies outside the interabutment axis line, the pontics act as lever arm, which can produce a torquing movement. This is common while replacing anterior teeth. SOLUTION: the first premolar are sometimes used as secondary abutment for a maxillary four pontic canine to canine fpd .

28. SPAN LENGTH In addition to the increased load placed on the periodontal ligament by a long span fixed partial denture, longer spans are less rigid. Bending or deflection varies directly with the cube of the length and inversely with the cube of the occlusogingival thickness of the pontic . Compared with a fixed partial denture having a single tooth pontic span, a two tooth pontic span will bend 8 times as much. A three tooth pontic will bend 27 times as much as a single pontic .

29. T o minimize flexing caused by long and/or thin spans: Pontic designs with a greater occluso -gingival dimension is needed The prosthesis may also be fabricated of an alloy with higher yield strength, such as nickel-chromium Double abutment Retainers on secondary abutments must be at least as retentive as the retainers on the primary abutments. As the retainer on secondary abutments will be placed in tension when the pontic flexes, with primary abutment acting as fulcrum .

30. A secondary abutment must have at least as much root surface area and as favorable a crown-root ratio as the primary abutment . When the pontic flexes, tensile forces will be applied to the retainers on the secondary abutments. There also must be sufficient crown length and space between adjacent abutments to prevent impingement on the gingiva under the connector.

31. UNRESTORED ABUTMENTS An unrestored , caries free tooth is an ideal abutment. It can be prepared conservatively for a strong retentive restoration with optimum esthetics. In an adult patient, an unrestored tooth can be safely prepared without affecting the pulp as long as the design and technique of tooth preparation are wisely chosen.

32. ENDODONTICALLY TREATED ABUTMENT Teeth in which the pulpal health is doubtful should be endodontically treated before initiating fixed prosthesis. Although direct pulp caps maybe acceptable, risk for a simple amalgam or composite resin or a conventional endodontic treatment is normally preferred for cast restorations, especially where the later need for endodontic treatment would jeopardize the overall success of treatment.

33. Such endodontically treated teeth serve well as abutment with post and core foundation for retention and strength. Sometimes its better to remove badly damaged tooth rather than attempting endodontic treatment. S uch teeth Can not be selected for cantilever FPD.

34. RIGIDITY The lack of sufficient rigidity in a fixed prosthesis is a frequent cause of failure. Rigidity is obtained by use of the proper materials arranged in the correct shape form and thickness in regard to the forces acting upon them. Excessive occlusal forces cause loosening of prosthesis through flexure or can induce ceramic fracture. The force can also cause tooth mobility, particularly in presence of decreased bone support. Flexure can cause damage to the abutments and may result in eventual loosening of the retainers, and fatigue of the metal.

35. MARGIN LOCATION Sound tooth enamel cannot be improved biologically or esthetically. Therefore when conditions permit, margins of restorations should be kept away from the gingival tissues. The most accurate margin for any restorative material irritates the gingiva when it is extended beneath the free margin. In case of eroded teeth , gingival finish line is placed beyond the eroded area or restoration. T his arrests the process.

36. OCCLUSAL ANATOMY Natures own anatomy and contour should be recreated in all restorations . It has an indirect influence on the loads transmitted. Ridges and grooves increase the sharpness and shearing action of teeth and reduce friction between opposing surfaces by keeping the contacting area to minimum. Permits the most efficient mastication of food, thus reducing the load transmitted. According to Stallard Attrited teeth need more muscular power and longer and more masticatory strokes in order to chew food enough.

37. Attrition and abrasion problems encountered are:- Vertical height is less so less retention FPD may not be possible Plan out for overdenture or telescopic denture

38. Factors affecting occlusal forces : Degree of muscular activity. Habits such as bruxism . Number of teeth being replaced. Leverage on the bridge. Adequacy of bone support. Results of excessive occlusal forces : Loosening of prosthesis through flexure. Ceramic fracture. Tooth mobility (In presence of decreased bone support).

39. Replacement strategies : Buccolingual width of pontic should harmonize with buccolingual dimension of natural unmutilated teeth, and recreate the normal buccal and lingual form to the height of contour. The total meso -distal width of the cusps of abutment should be equal or exceed that of pontics .

40. PONTIC TISSUE CONTACT The tissue contacting the surfaces on the pontic should be convex, smooth and free of porosity. The area of contact should be minimal, free of pressure and thought of as having saliva contact rather than tissue contact

41. AVAILABLE TOOTH STRUCTURE The size, number and location of carious lesions or restorations in tooth affect whether full or partial coverage retainers are indicated. Extensive defective restorations or fractures require intentional endodontic therapy or post and core fabrication to provide a sufficiently retentive and resistant form. Crown lengthening maybe indicated to expose sound tooth coronal to biologic width when caries, restorations fractures are in proximity to alveolar crest.

42. Mutilation Sufficient abutment height of at least 4 mm should be present. Core build up with composite resins can be done for tooth <4 mm occluso-gingivally .

43. AGE Fixed Partial Denture is usually contraindicated in children Because: • Teeth are not fully erupted. • Excessively large pulp horns . Treatment options: Space maintainer : Holds abutment and opposing teeth in position. Minimal tooth reduction : Prosthesis considered temporary and remade when pulp size permits.

44. Static or dynamic occlusion of teeth Abutment teeth are examined for tilting rotation, overeruption,malalignment ,wear faceting and burnished areas on restorations. The occlusion is assessed as canine protected or group function, and any non-working side contacts are noted.* Interferences are abnormal contacts that interfere with the smooth movements of the mandible and may be the cause of tooth fracture or cementation failure of a crown etc., or may lead to tooth mobility. Such deviations from the normal movements are recorded and noted.

45. VITALITY TESTING OF THE PULP Vitality of the tooth may be tested using either electrical or thermal stimulation . Electrical testing will require a charge to be applied to the tooth. The charge is generated by a machine and the patient becomes part of the circuit when the tip is applied to the tooth. Good electric contact is achieved by use of prophylactic paste

46. Thermal stimulation may be through either cold or heat, but cold stimulation is preferred. This is done using a ice stick or a pledget of cotton wool soaked in ethyl chloride, which will give a quick response. However, a more intense cold stimulus can be provided by use of dry ice. This way the prospective abutment teeth are tested for pulp vitality, if pulp in non- vital it should be endodontically treated before using as abutment for a FPD

47. LONG TERM ABUTMENT PROGNOSIS When there is some question of the ability of remaining supporting structures to accept additional occlusal forces, the bilateral bracing afforded by a removable prosthesis may be advantageous. Also a tooth with sufficient loss of periodontal support and questionable long term prognosis may be best treated with a removable prosthesis . Overloading of abutments : • The ability of abutment teeth to accept applied forces without drifting or becoming mobile must be estimated and has a direct influence on prosthodontic treatment plan. • These forces are severe during Parafunctional grinding and clenching and need to be eliminated during restoration of damaged dentition.

48. Additional complications

49. PIER ABUTMENTS/ INTERMEDIATE ABUTMENTS Definition: A natural tooth located between terminal abutments that serve to support a fixed or removable partial denture.

50. Completely rigid restoration : Contraindicated 1 Tendency for prosthesis to flex. Stress concentration increases around abutments. 2 . Forces transmitted to terminal retainers as a result of middle abutment acting as a fulcrum, causes failure of weaker retainer . 3. Differences in retentive capacity: Smaller anterior tooth < Larger posterior tooth. Dislodgement of anterior retainer

51. The use of a non-rigid connector has been recommended to reduce this hazard. It uses Broken stress mechanical union of retainer and pontic . • key way : Distal contours of pier abutment • Key : Mesial side of the distal pontic

52. Advantages: Movement prevents the transfer of stress from segment being loaded to the rest of the FPD. Transfers shear stress to supporting bone rather then concentrating it in connector. Minimize mesio -distal torquing while permitting them to move independently. Disadvantages : Not preferred in teeth with decreased periodontal attachment. Supraeruption of key and posterior unit when opposed by RPD or no teeth.

53. MESIALLY TILTED MOLARS (Loss of first molar due to caries) The mesial one- half crown preparation, the non - rigid attachment (semi- precision or stress breaker) and the telescopic prosthesis have been suggested as solution to the problem. With extreme malalignment orthodontic uprighting or space maintainer appliance maybe a logical approach, this also eliminates bony defects along mesial surface of root.

54. The non rigid attachment must not be used indiscriminately. Because of mesial component of force, the female portion of attachment is usually placed on distal surface of mesial abutment. The cantilever effect on the non- rigid design can pace additional stress on the abutment with the rigid connector, therefore rigid connector is only placed on a strong abutment, and the non rigid design is avoided altogether with long span pontics . Telescopic prosthesis requires radical tooth preparation to provide adequate space for the telescopic coping and the overcastting.

55. CANINE REPLACEMENT FIXED PARTIAL DENTURE This is a problem because often the canine lies outside the inter abutment axis. The abutments are the lateral incisor, usually the weakest in the entire arch and the first premolar, the weakest posterior tooth . A FPD replacing maxillary canine is subjected to more stress than that replacing a mandibular canine since forces are transmitted outward on the maxillary arch. So the support from secondary abutments will have to be considered . Edentulous spaces created by the loss of canine and any contiguous teeth is best restored with Implants.

56. ABUTMENT SELECTION FOR CANTILEVER FPD Cantilever FPD is one that has an abutment or abutments at one end only, with the other end of the pontic remaining unattached. This is a potentially destructive design with the lever arm created by the pontic . Abutment teeth for cantilever FPDs should be evaluated for lengthy roots with a favourable configuration, good crown root ratios and long clinical crowns . Generally, cantilever FPDs should replace only one tooth and have at least 2 abutments .

57. QUESTIONABLE ABUTMENTS CLASSIFICATION • General Disord er: Mineralization Amelogenesis Imperfecta . Dentinogenesis Imperfecta . Hypocalcification . Ectodermal Dysplasia. Discolouration due to drugs like Tetracycline . Flourosis . Internal resorption  

58. Congenital and growth deformities : Malformed dentetion Malposed teeth Local problems : Polycarious teeth Periodontally involved teeth Tilted teeth Endodontically treated teeth Occlusal plane correction

59. TREATMENT STRATEGY Abutment with generalised mineral disturbance: full coverage restorations Congenital and growth deformities orthodontics and restorative dentistry

60. Malposed teeth: Judicious tooth reduction. Orthodontics for minor tooth movement: Requires periodic occlusal adjustments. Telescopic crowns Occlusal plane correction: Supra-erupted teeth Intentional RCT. Reduction to satisfactory occlusal plane. Tooth preparation to receive retainer. Construction of opposing prosthesis.

61. Polycarious teeth: no contraindication caries control program Endodontic and periodontic treatment Cast metal restoration after amalgum restoration Strict recall visits

62. Periodontaly involved teeth: periodontal treatment is needed and splinting in case of loss of periodontal support In furcation involvement: Root debridement Filling furcation with ZOE cement or GTR Root amputation and hemisection

63. CONCLUSION V arious guides have been suggested for selection and construction of fixed partial dentures that should withstand the forces of oral function with maximum service. Abutments bear the stresses of mastication and the choice of abutment influences the prognosis of treatment. T he importance of selecting a suitable abutment forms the preliminary treatment planning for fixed partial dentures whose proper selection and preparation aids in long term durability of the restoration

64. It is advocated that when supporting bone has been lost because of periodontal disease, teeth involved may have a lessened capacity to serve as abutments. Abutment teeth are unsuitable because they can be "overstressed" from the additional forces applied to teeth supporting a fixed partial denture. This may be attributed to the resistance to the impact of occlusal forces called as " shock absorber effect " as documented by Carranza, Newman

65. On the contrary, there is evidence that teeth with compromised periodontal support can serve successfully as the fixed bridge abutments  but clinicians continue to avoid using periodontally compromised abutment teeth. The degree of periodontal compromise in abutment teeth to be utilized in a fixed partial denture is however, restricted to grade 1 or 2 mobility. Though compromised, abutments are utilized only in a status quo to prevent a further increase in mobility.

66. Splinting an additional abutment to periodontally compromised abutments is not required when primary abutments has lost 2/3 of periodontal ligament. It is beneficial by splinting additional abutment when primary abutment has lost 1/3 of periodontal ligament.

67. R eferences V Rangarajan , Textbook of Prosthodontics Reynolds JM. Abutment selection in fixed prosthodontics . J Prosthet Dent 1968;19:483-8 The glossary of Prosthodontic terms, 8 th Edition J Prosthet Dent 2005; 81:63 Resensteil SF, Land MF, Fujimoto J. Contemporary fixed prosthodontics 3 rd ed. Elsevier 2000. p.46-64 Subhashini MH, Abirami G, Jain AR. Abutment selection in fixed partial denture-A review. Drug Invention Today. 2018 Jan 1;10(1).