Stresses Induced by Vertical OT Attachment versus Horizontal OT Cap Attachment on the Supporting Structures of Kennedy Class I Partial Dentures: (Strain-Gauge Analysis)

Abstract

This simulation study was conducted to evaluate the effect of extra coronal attachment OT-S and extracoronal attachment OT- C on the stresses induced around the abutments and supporting edentulous ridge in partial denture restoring Kennedy class I, using strain guage analysis. Two models used educational purpose were modified and duplicated into acrylic resins to represent Kennedy class I cases with the first premolars bilaterally as last standing abutments. They were also modified for installation of strain gauges and for simulation of the oral mucosa. Canines and first premolars bilaterally were prepared to receive fixed metal crowns with porcelain facings. Two removable partial dentures were constructed following the same procedures. They exhibited the same design and only differed in the retaining attachment. The partial denture retained with OT-S attachment was seated on the first model. While the partial denture retained with OT- C was seated on the second model. Strain gauges were installed in the acrylic model in specially prepared grooves. Two of the guages were installed 1mm distal to the first premolars, one on each side of the model. Other two gauges were installed on the buccal slope of the free end saddle areas, 20mm distal to the first premolar on each side. The last two strain gauges were installed buccal to the first premolars, one on each side. T shaped load applicator bar was constructed and adapted to fit bilaterally on the occlusal surface of the first molar of the denture. Load was applied unilaterally and bilaterally by the Universal Testing Machine. The applied load will start from zero up to 100 N. A four channel strain meter was used to record the micro strains. Strain gauges were installed vertically buccal and distal to the abutments and on the buccal slopes of the free end saddles. OT-S attachments induced more stresses to the supporting structures of the abutments and residual ridges than OT-C attachments. Stresses induced to the abutments more than to the residual ridges with both types OT-S and OT-C attachments.