Prolonged application methods of self-etching primer: Effect of aging on micro-shear bond strength to lithium disilicate and zirconia-reinforced lithium silicate ceramics

Purpose: To evaluate the effect of different self-etching primer (Monobond Etch & Prime—MEP) application protocols and aging on micro shear bond strength (µSBS) and surface etching patterns of zirconia-reinforced lithium silicate (ZLS) and lithium disilicate (LD) ceramics. Materials and Methods: Twenty-eight blocks of Vita Suprinity (VS), Celtra Duo (CD), and IPS e.max CAD (EM) were cut into two sections each (n = 56 specimens per ceramic) and divided into groups: 5% hydrofluoric acid with silane (HF + S, control), and MEP scrubbing for 20, 40, and 60 s, with a 40-s reaction time (n = 14 per condition; n = 10 for µSBS and n = 4 for scanning electron microscopy [SEM]). For µSBS, resin cement was applied and light-cured; half of the resin cylinders were stored for 24 h, while the other half underwent thermocycling (TC) (10,000 cycles; dwell time of 30 s between 5°C and 55°C) before testing. Data were analyzed using three-way repeated measures analysis of variance (ANOVA) and Bonferroni post hoc tests (α = 0.05). Results: The HF + S group showed higher µSBS for EM than VS and CD (p < 0.001). MEP100 achieved comparable µSBS with HF + S for CD (p < 0.001) and improved µSBS for VS and EM (p = 0.128). TC decreased the µSBS values in most groups. The only exception was observed when the VS and CD surfaces were treated with MEP100, and when the CD surface was treated with MEP80. Adhesive fractures were predominantly seen. SEM revealed MEP100 produced etching patterns like HF, with lithium metasilicate and orthophosphate crystals present. Conclusions: Prolonged MEP application (MEP100) produced etching patterns and µSBS values comparable to HF + S, making it a viable surface treatment alternative for ZLS and LD ceramics.