Evaluation of Fatigue Resistance of Acetal Resin and Cobalt–Chromium Removable Partial Denture Clasps. An In-vitro Study: Part 1

Abstract

Purpose: This study was aimed to evaluate the retentive forces of acetal resin clasps and Cobalt-Chrome (Co-Cr) clasps during attachment/detachment cycles on abutment teeth with two different undercuts and at different intervals. Materials and Method: Twenty models were constructed by placing either an upper 1st premolar or upper 1st molar inside an acrylic rectangular block. Models were divided according to the abutment teeth into two groups (GI for 1st premolars group and GII for 1st molars group), 10 each. Each group was divided into two subgroups according the framework material, SGA for acetal resin clasp and SGC for Co-Cr clasp. Each testing models and its framework were mounted inside universal testing machine (Lloyd instruments Ltd, England). Retention of each clasp at pre-test (0 cycle) and after cycling intervals (730 cycles, 1460 cycles, 2190 cycles, and 2920 cycles) were measured by applying withdrawal force to it using universal testing machine. The data of the retentive force magnitudes at different intervals were collected and tabulated. The data were subjected to statistical analysis using 3-way-ANOVA test, student’s t and paired t tests. Results: After 730 cycles, 1460 cycles, 2190 cycles, and 2920 cycles there were non significant difference between SGIA and SGIC, and SGIA and SGIIA at 95% confidence level (P > 0.05), however there were statistical significant difference between SGIIA and SGIIC, and SGIC and SGIIC at 95% confidence level (P ≤ 0.05). Conclusion: Acetal resin clasps (1.0 mm in cross section diameter) engage 0.25 mm provide sufficient retention nearly similar that of Co-Cr clasps, The acetal resin clasps should be thicker more than 1.0 mm (in cross-sectional diameter) when engage a deeper undercut (0.50 mm) to gain the stiffness of the cast Co-Cr clasps 1 mm in cross sectional diameter and to obtain clinically acceptable retention.