An-invitro comparison of Thermocycling Effect on Micro- hardness and Micro-tensil bond strength of Nano composite denture teeth

Purpose: The purpose of this study was an evaluation of the effect of thermocycling on micro-hardness and microtensile bond strength (μTBS) of the cross-linked acrylic and nanocomposite teeth to the acrylic denture base. Materials and methods: twelve teeth of the upper denture teeth were selected. Six teeth of nano-hybrid composite resin denture teeth and six cross-linkedacrylic teeth. These teeth, together with theacrylic resin bases, have been fixed to a micro- sawing machine to form 120 microbeam samples. These samples were divided into two storage regimes (dry and thermocycler), forming eight groups, each group containing 15 beams. These 8 groups were divided in equal parts to test the micro-hardness and strength of the micro-tensile bond (4 groups for each test).
Results: Paired t-test was used to analyze the effect of aging on micro- hardness and micro-tensile bond strength for both types of denture teeth. The tests were considered significant when p ≤ 0.05 and highly significant when p ≤ 0.001. Thermocycling procedure decrease the mean values in micro-tensile bond strength for both types of denture teeth brands but with statistical significant difference regarding the cross- linked acrylic one . it produces highly significant decrease in mean values for cross- linked acrylic but has nearly no effect on nanocomposit teeth regarding the micro-hardness test. Considering denture teeth brand Cross linked acrylic denture teeth showing higher mean values in micro- tensile bond strength before and after aging. Also, it was showing higher mean values in micro-hardness before thermocycling. This condition was totally reversed after aging as nano composite teeth showing higher mean values with significant difference in relation to acrylic one.
Conclusion: The newly introduced nanohybrid composite denture teethwere less markedly affected by thermocycling specially in term of hardness,but practically and from financial point of view, the cross- linked acrylic resin teeth has a comparable result to nanocompsite one as it shows higher micro-tensile bond strength (μTBS) so, it appears more applicable for patients.