At a microstructure level, previous generation veneering materials had crystalline phases with leucite crystals that possessed an average size greater than 30 μm. These large particles left microscopically rough surfaces that abraded opposing enamel, thus increasing wear rate. Leucite was added to them as a crystalline phase to strengthen the base glass and enhance esthetics by scattering or refracting light similar to enamel. It also increased the CTE of the material.15
Abrasive wear involves a soft surface in contact with a harder surface. It has been studied by measurements of related mechanical properties such as hardness.29 Vitadur N and Alpha particles were seen to be coarse when compared to the finer texture NVP-AUY922 solubility dmso Selleck SAHA HDAC of VM7
material; they also had very high microhardness values. This has been confirmed by the results of microhardness values in this study, SEM, and EDX analysis (Table 2, Fig 7). The findings of this study indirectly support some of the claims of McLaren et al15 concerning the low wear rate of VM7 material (0.8 ± mm2) compared to Vitadur Alpha (1.83 ± 0.09 mm2) simulating that of opposing enamel due to a finer two-phase glass structure with the absence of any crystal phase. McLaren et al claimed no leucite was added in this generation. Two glass phases were mixed, different in size and refractive index, creating different diffraction properties similar to materials with a crystalline phase and a glassy phase, thus reducing wear and optimizing esthetics. These recent materials were incorporated within the glass in a size of 0.7 μm, similar to enamel rods. These smaller particles reduced the VHN of the material, rendering it kinder to opposing natural enamel. They also affected the CTE of the resultant material. Amylase EDX analysis in this study shows the composition of the three veneering materials possessing alumina, but in different proportions. This implies that VM7 is not totally glass as previously
stated; however, fine texture is evident in the SEM (Fig 7). Concerning alumina core/Vitadur N disc veneer, most debondings appeared to be interfacial by complete delaminations. The surface of the core material where the disc was present appeared visually shiny and quite distinct, which is in agreement with the findings reported by Smith et al.6 At 30×, a circular pattern was evident where the disc was present, with a clear distinct circular boundary. It suggests that shearing appeared to leave a thin layer of veneering material attached to the core (Figs 1 and 2). Smith et al6 reported that failures in their study involved interfacial stresses with crack propagation occurring at or near the core/veneer interface. Most failures in their study occurred by delamination of veneering glass alone, leaving a thin layer of residual glass on the core surface. This agrees with the findings in this study.