This study evaluated the wear behavior of metal restorations opposing prosthodontic hybrid composite resin restorations. Maxillary and mandibular teeth were fabricated with three commercial hybrid composite resins and five metals. Vickers hardness of each material was measured, and the wear resistance was assessed using an in vitro two-body wear-testing apparatus that simulates the chewing action. The worn surfaces were then observed using SEM. There was a correlation between the surface microhardness and wear resistance when the same material was opposite. Of the teeth opposing Estenia C&B, gold-silver-palladium alloy showed the greatest wear, and cobalt-chromium alloy the least. The wear level of Estenia C&B was correlated with the hardness of the opposing alloy. It was concluded that the wear of hybrid composite resin versus metal restorations was affected by the surface microhardness. Moreover, the size and shape of the filler in the hybrid composite resin influences the opposing metal wear.

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The aim of this study was to investigate a suitable bonding test to evaluate the bonding characteristics of resin-based luting cements as dental luting material to cp titanium. Five adhesive resin-based luting cements were bonded to polished or blasted titanium surfaces with a cylindrical titanium specimen. Tensile and shear bond tests were performed to determine tensile and shear bond strengths (TBS and SBS, respectively), and the rate of remnant cement (RRC) was also calculated by image analysis of the fractured surface. SBS was significantly higher than TBS (p<0.05). The relationship between SBS and TBS showed a linear regression at a coefficient of determination (R²) of 0.82; however, that for the blasted surface was not clear. The relationship between RRC and SBS or TBS showed an exponent regression curve; especially, TBS was related to RRC with a highly significant coefficient (R²=0.99). Tensile bonding tests using polished titanium specimens seem to be preferable to evaluate the bonding characteristics, since they could measure not only the bond strength but also the RRC easily.

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Tooth carving by students should be evaluated objectively. However, at present, tooth carving is almost exclusively evaluated subjectively and inconsistently by instructors. This study aimed to improve objective evaluation to analyze whole tooth carving using a three-dimensional image, and compare the objective with subjective evaluation. Tooth carving images generated by a three-dimensional surface scanner were evaluated objectively by quantifying the volume and gap in reference points between tooth carving and standard images. Using Spearman's rank correlation coefficient, we tested the correlation between objective and subjective evaluations. As a result, there was a significant correlation between the two evaluations: the rank correlation coefficient was +0.682(p<0.001). This indicates there is little difference between the two evaluations. Subjective evaluation is unstable, although the system in this study is able to reliably evaluate tooth carving because evaluation repeatedly yields the same result.

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