SEM evaluation of surface roughness variations in milled ceramic laminate veneers exposed to glazing and thermocycling

Abstract

CAD/CAM technologies represent one of the most rapidly advancing areas in digital restorative dentistry. This in vitro study aimed to investigate the effects of glazing and thermocycling on the surface roughness characteristics of four distinct milled CAD/CAM ceramic materials. Aim —to assess the effects of glazing and thermocycling on the surface roughness of four different types of CAD/CAM ceramic laminate veneers. The null hypothesis was that a statistically significant difference would exist in surface roughness between glazed and unglazed specimens across all four ceramic materials tested.
Materials and methods.
As part of the investigation, 80 CAD/CAM ceramic veneer samples were milled using CAD/CAM system. The processing occurred after scanning of the first right typodont incisor of the upper jaw model prepared with the palatal chamfer preparation design without approximal involvement (KaVo, Germany) via an Omnicam scanner. Four different CAD/CAM ceramic materials were evaluated in this study: lithium disilicate IPS E.max CAD (Ivoclar, Germany), leucite-reinforced ceramic IPS Empress CAD (Ivoclar), feldspathic ceramic Cerec (Dentsply Sirona, Germany), and hybrid ceramic Cerasmart (GC, Japan). The 80 samples were categorized into four groups (20 in each); each group was further subdivided into glazed and nonglazed subgroups, with 10 samples in each subgroup. All specimens underwent 10,000 thermal cycles. The surface roughness values were evaluated at three stages: post-milling, post-glazing, and post-thermocycling. Scanning electron microscope images (magnifications of 100x, 250x, 500x, and 1000x) were captured for each material before glazing and after thermocycling.
Results.
Significant differences in surface roughness values were observed among materials after glazing and thermocycling. Surface roughness notably decreased following glazing. Significantly higher surface roughness values were observed in the Cerec group compared to Cerasmart, Empress, and E.max groups (p<0.05). Analysis of the glazed surfaces after thermocycling also revealed significant differences among the groups (p<0.05). Tamhane‘s T2 post-hoc test revealed that the Cerec group exhibited significantly higher surface roughness values compared to Cerasmart, Empress, and E.max after thermocycling (p<0.05). For non-glazed samples, thermocycling similarly led to higher surface roughness values in the Cerec group compared to the other three groups (p<0.05). These findings highlight the effects of glazing and thermocycling on the surface roughness of CAD/CAM ceramic materials, reflecting their clinical behavior.
Conclusion.
There were statistically significant differences in surface roughness between glazed and non-glazed CAD/CAM materials. Among the tested materials, the Cerec group consistently showed higher roughness values compared to Cerasmart, Empress, and E.max (p<0.05). Glazing and thermocycling significantly influenced the surface roughness of all groups.