Effect of humidity and temperature changes on orthodontic direct-bonding adhesive systems

Plastic brackets were bonded to 560 extracted human teeth with use of two orthodontic adhesive systems: (1) methyl methacrylate resin bonded to a sealant that was polymerized using ultraviolet light, and (2) self-polymerizing methyl methacrylate resin bonded directly to the etched enamel. Tensile and shearlike tests were performed. Prolonged exposure to heat, moisture, and severe temperature changes decreased the shearlike strength of both adhesives. Both systems were adequately strong to withstand routine orthodontic and estimated masticatory forces.