Stress Analysis of Abutments with Reduced Periodontal support of RPDs.

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Prosthodontic cases involving periodontally compromised teeth will increase with a rapidly aging population. The need for an understanding of biomechanical considerations is especially great when designing treatment for periodontally compromised distal extension cases. An examination of load transfer characteristics of abutments and supporting structures in mandibular situations with a variety of periodontal defects was planned. The purpose of this study was to attain information vital to developing new guidelines for partial denture designs with an emphasis on preserving the abutment tceth as long as possible.In this study, 1) a new stress-analysis system was developed by adding to and improving on observation and recording techniques used in conventional Quasi-Three Dimensional Photoelastic methods of examining stress distribution characteristics in complex situations, and 2) photoclastic models were made to simulate various condition and stresses in the teeth and supporting structur … More es were analyzed. Specifically, models of i) unilateral distal extension cases (432 remaining) with various vertical and horizontal resorption (crater and trough defects for vertical resorption, and horizontal resorption rates of 20% and 35% were used), as well as ii) bilateral distal extension situations with vertical resorption in the first premolar abutment were fabricated. These models were tested against chromatic fringe patterns observed in models of a normal mandibular situation for their load transfer characteristics as load (quantity and direction), splinting, and retention device conditions were changed.The results showed that, 1) under the same load conditions, the highest stresses over the largest area developed in the model with the largest osseous defect, 2) stress distribution patterns were fundamentally different in models with vertical versus those with horizontal periodontal resorption, 3) two splints were most effective in redistributing loads incurred by periodontally compromised abutment teeth, and 4) the lbar clasp was the most effective in reducing the overall stress at the abutment tooth and producing an uniform stress redistribution. Less