One of the major goals of adhesive dentistry is to improve the interaction of the already-existing adhesives with different substrates by using different application techniques. Thus, the objective of the present in vitro study was to assess the bond performance of four adhesive systems, Prime&Bond Universal (PBU), Clearfil SE Bond (CSE), OptiBond Universal (OBU), and OptiBond FL (OBFL), to dentin using various application modes: passive application (PA), active application (AA), Compo-Vibes modified application (CVM), and Compo-Vibes application (CV). Eighty extracted human molars were allocated into four groups based on the application modalities tested. The micro-tensile bond strength as well as fracture mode were tested in accordance with ISO/TS 11.405 after 24 h and 6 months of aging. Adhesive contact angle (CA) and scanning electron microscope analysis were also performed (n = 3). Statistical tests were performed with α = 0.05. After 24 h, a significant difference with a higher bond strength value was found for PBU in the AA modality and for CSE in the CVM modality (p < 0.05). However, no significant difference was shown between the techniques used among the other adhesives (OBFL and OBU). Moreover, at 24 h, only the PA demonstrated significant differences between the tested materials (p < 0.05). After 6 months, CSE, PBU, and OBU demonstrated significant differences between the techniques (p < 0.05), with a higher bond strength for CSE in AA and CVM modalities, for PBU in AA modality, and for OBU in AA and PA modalities. No significant differences were found between the techniques used among the OBFL (p > 0.05). In addition, only the CVM technique demonstrated significant differences between the tested materials after 6 months. CV and CVM showed a decreased value after aging for CSE and PBU, respectively. However, all the modalities decreased for OBU and OBFL after aging. All the adhesives showed marked resin infiltration into dentinal tubules in AA among all the modalities tested. Both universal adhesive systems (OBU and PBU) demonstrated statistically lower CA when compared to the other systems (CSE and OBFL) (p < 0.05) when applied in the PA mode. Concerning the AA mode, only CSE and OBFL were tested. The AA demonstrated lower CA values compared to the same adhesives in PA (p < 0.05). It could be concluded that the bond strength could be influenced by both materials and application techniques. It seems that the AA technique could be recommended as a gold standard for the application of an adhesive system to dentin. Plus, the CV and CVM modalities after 6 months of aging were considered stable for PBU and CSE, respectively. Consequently, the performance of these adhesive systems might vary when applied to other modalities. Future studies are needed to test this hypothesis.
Keywords: application techniques; bond strength; microtensile bond strength; resin-dentin interface; universal adhesive.