Interferometer analysis of lithium disilicate bonding surface

Objectives: To compare the effect of different hydrofluoric acid (HF) gels on the surface roughness of lithium disilicate (LD, IPS e.max CAD, Ivoclar Vivadent).
Methods: Twelve rectangular sections (10x8x1mm³) were obtained from LD blocks. Specimens were fired following the recommended crystallization program. After cooling, specimens were wet polished up to 2000-grit silicon carbide paper and cleaned ultrasonically with distilled water. Specimens were divided with copper foil tape in 6 equal areas of 2X3mm² to form 6 groups (n=6): IVO=5.0% HF (IPS Ceramic Etching Gel, Ivoclar Vivadent); VIT=5.0% HF (Vita Ceramics Etch, VITA Zahnfabrik); FGM=5.0% HF (Condac Porcelana, FGM); ULT=9.0% HF (Porcelain Etch, Ultradent); PRM=9.6% HF (Premier Porcelain Etch Gel, Premier); and BIS=9.5% HF (Porcelain Etchant, Bisco). HF etching time was 20sec for all groups, as per the LD manufacturer’s instructions. Untreated LD surfaces were used as controls. Specimens were cleaned ultrasonically with distilled water for 180sec, air dried, and surface roughness was measured using an interferometer (New View 7300, Zygo Corporation). The parameters Sa (average height deviation of the surface) and Sq (maximum quadratic roughness) were evaluated. Five measurements were taken from each LD area. 3-D optical interferometry images were also analyzed. Data were computed using one-way ANOVA (p< 0.05) and Duncan post-hoc test. The mean Sa and Sq values were compared with Student's t-test (before and after HF treatment).
Results: All HF gels resulted in greater mean roughness compared to untreated areas (p<0.001). Mean roughness increased from a nanometric to a micrometric scale with HF etching. Mean Sa (μm) after HF: IVO=0.212b; VIT=0.404f; FGM=0.371e; ULT=0.193a; PRM=0.248c; and BIS=0.293d. Mean Sq (μm) after HF: IVO=0.323b; VIT=0.869f; FGM=0.839e; ULT=0.276a; PRM=0.371c; and BIS=0.431d. Groups with different letter are statistically different.
Conclusions: Specific HF gel composition may be more relevant to the final LD surface roughness that the respective HF concentration.