Abstract
Objective: was to evaluate the retentive force, fatigue resistance and deformity of clasps made from two materials cobalt chromium and poly ether et her ketone (PEEK). Material and Methods: sixteen models were fabricated, each one having lower 1st molar. Models were divided into two groups according to materials, group I (GI) for cobalt chromium (Co-Cr) and group II (GII) for PEEK. Each testing models and its clasps were mounted inside universal testing machine, the retention was measured by applying withdrawal force to it by this machine at 5 mm/min. The Fatigue resistance is measured by the reduction in retention through repeated insertion and removal cycles using robot a chewing simulator. Removal and insertion cycling of clasps was carried out for 360, 730, 1080, 1,440,2,116 and 2,880 cycles (corresponding to 3,6,9,12, 18 and 24 months of simulated clinical use of a RPD) to simulate the fatigue resistance test. Deformity was measured before and after each cycling using a digital micrometer. Statistical analysis was done by 2-way-ANOVA test to detect significance effects of each variable. Results: Retention and fatigue resistance, after 360,730, 1080, 1,440,2,116 and 2,880 cycles totally the difference between Co-Cr and PEEK groups was statistically non-significant (P = 0.0980>0.05) where (Co-Cr > PEEK). Deformation results, regardless to evaluation time, Co-Cr group recorded statistically significant higher deformation mean value than PEEK group (P = 0.008<0.05). Regardless to material group, deformation mean value changed non significantly by time (P = 0.2882> 0.05). Conclusion: PEEK clasps (1.0 mm in cross section diameter) engage 0.50 mm undercut provide sufficient retention nearly similar that of Co-Cr clasps.KeywordsFlexible clasps; Polyether ether ketone, PEEK; Thermoplastic resin; Partial denture.
Highlights
Removable Partial Dentuers (RPDs) are considered one of the most important way for replacement of missing natural teeth
The most common metal alloy used for construction of the direct retainers of RPDs is a cobalt chromium (Co-Cr), other alloys as gold, titanium and round wrought wire can be used for fabrication of the direct retainer [2]
Thermoplastic resins have been introduced into the market, direct retainers fabricated in a tooth-colored material and constructed from polyoxymethylene (POM), the PEEK and polyetherketonketon (PEKK) have been used to enhance the esthetic of metal direct retainer assemblies of RPD [4]
Summary
Removable Partial Dentuers (RPDs) are considered one of the most important way for replacement of missing natural teeth. RPDs must be have Sufficient retention, flexibility and esthetics which are considered as the most important factors affecting their clinical success. The retentive clasp arms of the direct retainers must be flexible and should retain the RPD satisfactorily without not unduly stress abutment teeth or be permanently deformed during service. Metallic RPD has a big esthetic problem many methods have been carried out to overcome this problem such as etching the clasp arm and coating it with a layer of tooth-color resin, and lingual retention design [3]. Thermoplastic resins have been introduced into the market, direct retainers fabricated in a tooth-colored material and constructed from polyoxymethylene (POM), the PEEK and polyetherketonketon (PEKK) have been used to enhance the esthetic of metal direct retainer assemblies of RPD [4]. PEEK can be used for patients allergic to metals, or who dislike the metallic taste, and the unpleasant metal display of the denture framework and retentive clasps [7]
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