Does the fatigue loading frequency affect the lithium disilicate glass ceramic inlay-dentin bond strength?

The aim of this study was to verify the effect of loading frequency during mechanical cycling on the microtensile bond strength between tooth and ceramic inlays. Twenty-four extracted permanent maxillary molars were standardly prepared (3 mm wide × 4 mm deep) to receive lithium disilicate-based ceramic inlays. After the adhesive cementation, the restored teeth were divided into three groups (n = 8), according to different range of mechanical cycling frequency: control group – water storage, 2.0 Hz group – mechanical cycling at frequency of 2.0 Hz (0–100 N, 1.2 × 10⁶ cycles, water 37 °C), and 6.7 Hz group – mechanical cycling at frequency of 6.7 Hz (0–100 N, 1.2 × 10⁶ cycles, water 37 °C). The teeth were then cut into microbars (1 × 1 mm, non-trimming method), which were tested under microtensile (MTBS) loading. The failure mode was classified and the data were analyzed by one-way ANOVA. The mean bond strength value of the control group was the highest and the values of the cycled groups were 15% lower, however the groups were statistically similar (p = 0.58). Chi-square test showed no statistical difference among the groups regarding the pre-test failures (p = 0.17). For all groups, the most frequent failure type was mode 1 (adhesive at the interface ceramic/cement) and mode 2 (mixed failure). Loading frequencies up to 6.7 Hz had no effect on the lithium disilicate glass ceramic inlay-dentin bond strength.