Bonding stability of universal adhesives to feldspathic ceramic with or without prior silane application

Purpose: This study aimed to assess the bonding stability of three universal adhesives to a CAD-CAM feldspathic ceramic with or without prior silane application.Materials and methods: The universal adhesives tested were Ambar Universal (FGM), Single Bond Universal (3M), and Ybond Universal (Yller). Scotchbond Multipurpose Plus (3M) was used as a control. The silane used was RelyX Ceramic Primer (3M). Microtensile bond strength (mu TBS) to Vitablocs Mark II was measured after 24 h or 6 months of water aging (n = 20). Failure modes were observed through scanning electron microscopy, and pH and degree of C=C conversion (DC) of the adhesives were measured (n = 3). Data were analyzed using one-, two-, and three-way ANOVA.Results: The pH values differed significantly among the adhesives (p < 0.001), while the DC was similar (p = 0.141). The universal adhesives showed significant differences in mu TBS, with higher immediate results when using silane and lower results after aging. Notably, a significant decrease in mu TBS was observed after 6 months when silane was applied. In contrast, the control adhesive exhibited consistent results between the 24-h and 6-month storage periods. The universal adhesives showed a decrease in mu TBS ranging from 25.5% to 40.1% after prolonged storage. Adhesive failures were predominant in all groups. The presence or absence of silane in the adhesive composition did not affect the bonding performance.Conclusions: The application of a separate silane coupling agent improved the immediate bond strength of universal adhesives to CAD-CAM feldspathic ceramic. However, this bond strength significantly decreased after 6 months of water aging. The bond strength remained stable for universal adhesives when applied without silane after 6 months of aging.