EVALUATION AND SELECTION OF ABUTMENTS

CONTENTS Definition Function & Ideal Abutment Types Classification Factors or Criteria for selection of an abutment Special problems ( Abutment) Reference

ABUTMENT A tooth, a portion of a tooth or that portion of a dental implant that serves to support and/or retain a prosthesis. FUNCTION OF AN ABUTMENT To Retain To Support Take up functional and parafunctional load

IDEAL ABUTMENT IDEAL CROWN ROOT RATIO ADEQUATE THICKNESS OF ENAMEL AND DENTIN ADEQUATE BONE SUPPORT ABSENCE OF PERIODONTAL DISEASE PROPER GINGIVAL CONTOUR

CLASSIFICATION OR TYPES OF ABUTMENTS PIER ABUTMENT CANTILEVER ABUTMENT ADDITIONAL ABUTMENT DISTANT ABUTMEN IMPLANT ABUTMENT

PIER ABUTMENT ADDITIONAL ABUTMENT It is the abutment which is used in addition to the primary abutments in case of a long edentulous span, or if the primary abutment is weak. PIER ABUTMENT It is a natural tooth located between terminal abutments that serve to support a fixed or removable prosthesis.

IMPLANT ABUTMENT DISTANT ABUTMENT The posterior or distal abutment which retain and support the lone pontic in anterior region.Usually used in diastema cases CANTILEVER ABUTMENT The abutments which retain and support the pontic only on one side. Can be one or more in number. IMPLANT ABUTMENT

CRITERIA (FECTORS)FOR SELECTION OF AN ABUTMENT

CROWN TO ROOT RATIO This ratio is a measure of the length of the tooth occlusal to the alveolar crest of the bone compared with the length of the root embedded in the bone. The optimum crown to root ratio is 2:3,but the minimal ratio required is 1:1. ROOT CONFIGURATION Roots that are broader labio-lingually rather than mesio-distally are preferred to roots which are round in cross section. Multirooted posterior teeth with widely seperated roots offer better support than roots that converge, fuse or have a conical configuratio

Periodontal ligament area-(Ante’s law)-combined pericemental area of all abutment teeth supporting a fixed dental prosthesis should be equal to or greater in pericemental area than the tooth or teeth to be replaced Maxillary Mandibular Tooth Area mm2 Ranking Central 139 7 103 8 Lateral 112 124 Canine 204 3 159 4 First premolar 149 5 135 6 Second Premolar 140 First molar 335 1 352 Second molar 272 2 282 Third molar 197 190 The combined root surface area of the second premolar and the second molar (A2p+A2m) is greater than that of the first molar being replaced (A1m).

LONG-SPAN FIXED PARTIAL DENTURE . Two tooth pontic span will bend 8-times A three tooth pontic span bends 27-times as much as a single pontic Short spans are rigid. Thick pontic Thin pontic

SPECIAL PROBLEMS ARCH CURVATURE There is a common problem in replacing all four maxillary incisors occurs because the pontics lie outside the interabutment axis line and thus acts as a lever arm, which can produce a torquing movement. In order to offset the torque, additional retention is obtained in the opposite direction of the lever arm and at a distance from the interabutment axis equal to the length of the lever arm.

Tilted molar abutment Some possible solutions to these problems are: Preparation modifications: Tilting is slight – recontouring of mesial surface of 2nd molar Tilting is severe – orthodontic correction Proximal half crown A telescopic crown Non rigid connector

Fixed partial dentures replacing canines can be difficult because the Canine replacement Fixed partial dentures replacing canines can be difficult because the canine often lies outside the interabutment axis. Mandibular On the mandibular canine, the forces are directed inward (lingually), against the outside of the curve (its strongest point).. Maxillary forces are transmitted outward (labially) on the maxillary arch, against the inside of the curve (its weakest point).

PIER ABUTMENT . CANTILEVER ABUTMENT

Badly mutilated Abutment RCT & restore with post & core build –up. post Cast post Pre – fabricated posts core crown

REFERENCES SHILLINGBURG- Fundamentals of Fixed Prosthodontics(3RD ED.) ROSENSTEIL-Contemporary Fixed Prosthodontics(3RD ED.)