Abstract:

Objective:The aims of this study are to analyze the surface stress of the periodontal supporting bone of the bilateral distol extension removable partial denture which is retained by using intra_coronal or extra_coronal semi-precision attachment, and to characterize the biomechanics of these two designs by using a strain gauge.Methods:A fresh human mandible specimen with \{76│67\} missing and six bilateral partial removable denture retained with six semi-precision attachments were made, including three attachments with intra_coronal studs and three attachments with extra_coronal vertical bars. A total of six 45° rosette strain gauges were bonded at six prepared points on the surface of the mandible to measure the surface stress, including the middle point between 76 of the buccal edentulous alveolar crest area under the denture base verge(point 1), the distal buccal cervix of 5 (point 2), the buccal apical area of 5 (point 3), the buccal middle area of 34 roots (point 4,5), the lingual middle area of 5 root (point 6). The static loads of 14N, 28N and 42N were applied vertically, buccally 45°, lingually 45° at the middle point of the \{6│6\} occlusal surface. The micro_strain was recorded, and the maximal/minimal principle stresses were calculated for each RPD and each point. The stress characteristics of these two types of attachments were compared and analyzed.Results:In most situations, the stress of these two semi_precision attachments showed significant differences. The vertical load: The stress values of these intra_coronal and extra_coronal attachments at points 1,2,3,4,6 differed significantly(P<0 05), including points 1,2,(σ\-\{intra\}<σ\-\{extra\}) and points 3,4,6(σ\-\{intra\}>σ\-\{extra\}). Buccal loads: The stress values of these intra_coronal and extra_coronal attachments at points 1,2,3,4,5 differed significantly(P<0 05), including points 1,2(σ\-\{intra\}<σ\-\{extra\}) and points 3,4,5(σ\-\{intra\}>σ\-\{extra\}). Lingual loads: The stress values of these intra_coronal and extra_coronal attachments at points 2,3,4,6 differed significantly (P<0 05,σ\-\{intra\}>σ\-\{extra\}). The intra_coronal attachment generally produced higher stress at the site of the alveolar bone around the abutment than the extra_coronal attachment, but extra_coronal attachment produced higher stress at the edentulous alveolar crest\ and\ the distal cervical alveolar bone of the distal abutment than the intra_coronal attachment.\ Conclusion:The intra_coronal attachment is suggested to be applied in some cases that the periodontal condition of distal abutment was good, and the extra_coronal attachment is suggested to be used in some cases that the condition of the edentulous alveolar crest is fairly good, while the periodontal condition of the distal abutment was relatively weak.

Key words: precision attachments, denture, stress analysis, denture design, partial removable denture