Influence of Finish Line and CAM Unit on the Marginal Adaptation and Margin Trueness of Lithium Disilicate Glass-Ceramic and Composite Resin Onlay Restorations.

Objective To evaluate the marginal adaptation and margin trueness of lithium disilicate glass-ceramic (LDS) and glass-filler reinforced composite resin (CR) onlays fabricated using three different finish lines and two chairside CAM units (4- and 5-axis).Methods LDS (e.max CAD) and CR (Tetric CAD) onlays were fabricated on butt joint, chamfer, and bevel finish lines using 4-axis (CEREC MC XL) and 5-axis (Programill One) chairside CAM units (N = 120). Onlays were scanned for margin trueness and marginal adaptation analyses. Data were analyzed with three-way ANOVA and Tukey B post hoc test (α = 0.05).Results A significant interaction was found among finish line, material, and CAM unit for marginal adaptation and margin trueness (p < 0.001). Bevel had the highest marginal adaptation; chamfer the lowest. Butt joint showed the highest margin trueness; bevel the lowest. CR onlays had better marginal adaptation than LDS with bevel finish lines, regardless of CAM unit. Overall, 5-axis CAM units yielded better margin trueness.Conclusions Finish line design, restorative material, and CAM unit affected the marginal adaptation and margin trueness. The bevel finish line yielded the highest marginal adaptation and the chamfer the lowest, regardless of material or CAM unit. Conversely, the butt joint showed the highest margin trueness, and the bevel the lowest.Clinical Significance Finish line design, material type, and CAM unit selection may affect marginal adaptation and margin trueness of onlays. A bevel finish line may improve marginal adaptation, while a butt joint finish line may enhance margin trueness. Using a 5-axis CAM unit can improve trueness, particularly with bevel and chamfer finish lines and composite resin materials.