abutment selection in fixed partial denture.pptx

abutment selection in fixed partial denture

1. ABUTMENT SELECTION IN FPD

2. CONTENTS: Introduction Diagnostic Casts Radiographic Examination Factors influencing Abutment selection Special Problems Pier Abutments Tilted Molars Abutments Canine replacement fixed partial denture Abutments for Cantilever FPD. 6. Questionable abutments 7. Summary & Conclusion 8. References

3.   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. INTRODUCTION

4.   A butment is defined as a tooth, a portion of a tooth, or that portion of a dental implant that serves to support and/or retain a prosthesis. (GPT 10) DEFINITION

5. Jhonston proposed 19 factors for abutment selection

6. A life size reproduction of the parts of the oral cavity and or facial structures for the purpose of study and treatment planning. Articulated diagnostic casts are essential in planning fixed prosthodontic treatment. DIAGNOSTIC CASTS

7. Periapical and bitewing films are most important in selection of abutment teeth. Radiographs provide information that cannot be determined clinically. A 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 Trauma From Occlusion RADIOGRAPHIC EVALUATION

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

9. The functional demand on the tissue of one person may be quite different from those of another. The tissue response and tolerance vary among individuals; therefore no two abutment teeth will react exactly the same under similar conditions. An understanding of the favorable indications and reasonable limitations of abutments for fixed partial dentures is essential.

10. 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, their shape, length, alignment, and 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.

11. Teeth must have adequate occlusocervical crown length to achieve sufficient retention. Teeth with short clinical crowns often do not provide satisfactory retention unless full – coverage preparations are used or additional length is achieved through periodontal surgery. CROWN LENGTH

12. CROWN FORM  Some teeth have tapered crown form, which interferes with preparation parallelism, necessitating full coverage retainers to improve their retentive and esthetic qualities. Ex: include anterior teeth with poorly developed cingulam and short proximal walls and mandibular premolars with poorly developed lingual cusps and short proximal surfaces.

13. CROWN ROOT RATIO This ratio is a measure of the length of tooth occlusal to the alveolar crest of bone compared with length of root embedded in bone. The optimum crown- root ratio for tooth to be utilized as a fixed partial denture abutment is 2:3 . A ratio of 1:1 is the minimum ratio that is acceptable for a prospective abutment under normal conditions (such as number of teeth being replaced, tooth mobility and overall periodontal health is good).

14. PDL AREA AND SURFACE AREA This is an important point in the assessment of abutment’s suitability from a periodontal standpoint. Root surface area or the area of periodontal ligament attachment of the root to the bone. Large teeth : Greater surface area Better ability to bear added stress. Diseased : Loss of supporting bone Lesser capacity to serve as abutment

15. ANTE’S LAW 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; this has been adopted and reinforced by other authors (Johnston, Dykema) in 1971 as ANTE’s LAW. This rule was based on the engineering principles used for designing bridges. ANTE’s LAW – Irwin H. Ante (Toronto, Ontario Canada) States that 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

16. AVERAGE ROOT SURFACE AREAS

17. FACTORS MODIFYING ANTE’S LAW

18. ROOT CONFIGURATION Roots that are broader labiolingually than they are mesiodistally are preferable to roots that are round in cross – section. Multirooted posterior teeth with widely separated roots will offer better periodontal support than roots that are short converge.

19. A tooth with conical roots can be used as an abutment if all other factors are optimal. • Irregularly shaped, multiple, divergent roots offer better prognosis. • A well aligned tooth will provide better support than a tilted one. Alignment can be improved with orthodontic treatment.

20. PERIODONTAL ASSESSMENT An examination of the periodontal tissues should be made. The aim is to provide a basic screening of the tissues and to obtain an indication of the treatment requirements of the patient. Mobility Recession Pocket Furcation

21. LONG AXIS RELATIONSHIP The architecture of periodontal ligament is such that forces are withstood best when they are 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 used as abutment when there is Shorter edentulous span with less occlusal force. 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 casts with a dental surveyor. Radiographs.

22. ARCH FORM When pontics lie outside the inter-abutment axis line, the pontics act as a lever arm, which can produce a torquing movement. Common problem in replacing all four maxillary incisors. Solution: The first premolars sometimes are used as secondary abutments for a maxillary four pontic canine-to-canine FPD.

23. 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 .

24.  To minimize flexing caused by long and/or thin spans: Pontic designs with a greater occluso -gingival dimension. The prosthesis may also be fabricated of an alloy with higher yield strength, such as nickel-chromium. Double abutment

25. 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. UNRESTORED ABUTMENT

26. ENDODONTICALLY TREATED ABUTMENT Teeth in which the pulpal health is doubtful should be endodontically treated before initiating fixed prosthesis. • 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. • Cannot be selected for cantilever FPD.

27. FACTORS AFFECTING OCLUSAL FORCES Degree of muscular activity. Habits such as bruxism. Number of teeth being replaced. Leverage on the bridge. Adequacy of bone support. 

28. RESULTS OF EXCESSIVE OCCLUSAL FORCES Loosening of prosthesis through flexure. Ceramic fracture. Tooth mobility (In presence of decreased bone support).

29. 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 to the preparations. • Crown lengthening maybe indicated to expose sound tooth coronal to biologic width when caries, restorations fractures are in proximity to alveolar crest.

30. AGE Fixed Partial Denture should be avoided in adolescents , 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.

31. LONG TERM ABUTMENT PROGNOSIS 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.

32. SPECIAL CONSIDERATIONS PIER ABUTMENT Completely rigid restoration: Contraindicated. Physiologic tooth movement: Faciolingual 56 to 108 μ m. Intrusion 28 μ m. Independent in direction and magnitude: Tendency for prosthesis to flex. Stress concentration around abutments

33. Arch position of abutment: Forces transmitted to terminal retainers as a result of middle abutment acting as a fulcrum, causes failure of weaker retainer. Disparity in retentive capacity: Retention: Smaller anterior tooth < Larger posterior tooth. Dislodgement of anterior retainer

34. The use of a non-rigid connector has been recommended to reduce this hazard. key way : Distal contours of pier abutment Key: Mesial side of the distal pontic

35. Advantages: Movement prevents the transfer of stress 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 and anterior three unit by natural teeth.

36. TILTED MOLAR ABUTMENTS Discrepancy in long axis of molar and premolar makes it impossible to achieve common path of insertion. 3rd molar tipped with tilted 2nd molar prevents complete seating of FPD

37. ADJUSTMENT FOR TILTED MOLAR: If the encroachment is slight, the problem can be remedied by restoring or recontouring the mesial surface of the third molar with an overtapered preparation on the second molar. If the tilting is severe, other corrective measure will have to be followed. The treatment of choice is uprighting of the molar by orthodontic treatment. A proximal half crown can be used as a retainer on the distal abutment.

38. 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.

39. QUESTIONABLE ABUTMENTS: • General Disorder: Mineralization Amelogenesis Imperfecta. Dentinogenesis Imperfecta. Hypocalcification. Ectodermal Dysplasia. Internal resorption . Congenital & growth deformities: • Malformed dentition. • Malposed teeth. • Skeletal disparities of Maxillo-mandibular relationships. • Oligodontia.

40. TREATMENT STRATEGY: Abutment with generalized mineral disturbance: • Full coverage restoration. • Success depends on supporting tissue response. Congenital and growth deformities: 1st line of treatment: • Orthodontics. • Interceptive periodontics. • Restorative dentistry.

41. 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.

42. Periodontally involved teeth: • Review the reason for the condition. • Periodontal treatment before caries control. • Loss of periodontal support: Splinting may compensate. Mobility: • Due to Primary TFO: Occlusal correction. • Due to Secondary TFO: Splinting. Furcation involvement: ( Class III) • Open and closed root debridment . • Filling the furca with polymeric ZOE cement or GTR. • Root amputation and hemisection .

43. SUMMARY AND CONCLUSION In the above discussion various 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. In a concluding note the importance of selecting a suitable abutment for a fixed partial denture cannot be overemphasized. It forms the preliminary treatment planning for fixed partial dentures whose proper selection and preparation aids in long term durability of the restoration.

44. REFERENCES Shillingburg . Fundamentals of Fixed prosthodontics. 4 th ed. Rosenstiel, Land, Fujimoto. Contemporary Fixed prosthodontics. 5 th ed Tylman’s Theory and practice of fixed prosthodontics. 8 th ed. Jhonston’s modern practice in fixed prosthodontics. 4 th ed. Colin R. Cowell. Inlays, crown and bridges. A clinical handbook. 4th ed. Glossary of Prosthodontic Terms. JPD 2005;94. Crown root ratio : Its significance in restorative dentistry. JPD 1979;42. The prosthodontic concept of crown-to-root ratio: A review of the literature. JPD 2005;93.

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