Curing-mode effects on flexural strength and modulus of resin cements

Methods andmaterials: Sixteen slices of eachmaterial, IPS e.max CAD (EMAX) and Vitablocs Mark II (VITA), were embedded in acrylic resin andpolished. The surface of eachblockwas randomly assigned to; E: etching with hydrofluoric acid (HF) according to manufacturer instructions, rinsing for 60 s and cleaning in ultrasonic bath (2min); E/S: HF-etching, rinsing for 60 s, cleaning in ultrasonic bath followed by silane application for 20 s, air drying for 20 s and hot drying (60 ◦C) for 20 s; E/S+: HF-etching, rinsing for 60 s and cleaning inultrasonic bath, followed by silane application for 60s, air drying for 20 s and hot air drying (60 ◦C) for 20 s, rinsing with boiling water for 15 s and hot air drying for another 20 s; S: silane application for 20 s and air drying for 20 s and hot air drying (60 ◦C) for 20 s; S+: silane application for 60 s followed by air drying, air drying for 20 s and hot air drying (60 ◦C) during 20 s, rinsing in boiling water during 15 s and hot drying (20 s). Cylinders of composite resin (n=12) (Z100) were bonded with adhesive resin (Optibond FL adhesive). SBS testing was carried out after 24h of storage in distilled water or after thermocycling (20,000cycles) for groups E; E/S and E/S+. The mode failure was assessed by macro-photography. Results: For 24h SBS the two-way ANOVA and Tukey HSD test (p<0.05) showed significantly higher mean bond strength with E/S (EMAX 21.06MPa; VITA 24.27MPa), compared to E and E/S+ (range: 15.50–20.96MPa). The use of silane alone showed significantly lower mean bond strength (EMAX 3.92–4.32MPa; VITA 5.69–5.91MPa). No significant differences were found between E/S and E/S+ for VITA. The SBS was negatively affected by simulated aging in E/S (19MPa vs. 24MPa at baseline for VITA and 16MPa vs. 21MPa at baseline for EMAX) and positively in E/S+ (25MPa vs. 19MPa at baseline for VITA and 21MPa vs. 15MPa at baseline for EMAX). While the failure mode for EMAX was always adhesive, VITA failed cohesively when etched (unless aged in E and E/S). Conclusion: The association of HF-etching and silane showed to be significant to obtain a high SBS; when considering a single treatment, HF-etching proved to be superior to the use of silane. Furthermore, the results revealed that the optimized silane application is not relevant to the immediate SBS while it enhances the performance of aged specimens.