Influence of environmental humidity during bonding on the bond strength of self-etch adhesives

Various adhesive systems are available for direct resin-composite restorations. However, few studies have evaluated the relationship between environmental factors and the bond strength of universal adhesives (8th generation). This study evaluated the influence of the bonding environment on the bond strength to bovine teeth by comparing four universal adhesives with two two-step self-etch adhesives (2-SEA). Bonding was performed under simulated laboratory, rubber-dam, and intraoral conditions with temperature and relative humidity of 23°C and 50%; 30°C and 50%; and 30°C and 95%, respectively. The micro-tensile bond strengths of the adhesives were not significantly different between the rubber-dam and laboratory conditions. However, the bond strength values for three universal adhesives were significantly lower under intraoral conditions. This study suggested that high-humidity conditions, such as in the oral cavity, may affect the bonding performance of universal adhesives. However, the influence of humidity might be limited when using 2-SEA or under rubber-dam isolation.