Orthodontic resin under water immersion.

The absorption and desorption of water by a polymer matrix of composite orthodontic resin could cause debonding of the filler-matrix or hydrolytic degradation of fillers and loss of bond strength. In this study, the bond strength of brackets directly bonded with orthodontic composite to the enamel surface of premolars was measured with an Instron machine; the debonding interface distribution was analyzed by scanning electron microscope and energy dispersive x-ray spectrometry following water immersion for 1, 2, and 3 days, and 1, 2, 4, 8, 16, 24, and 32 weeks, respectively. The results show that, under water immersion, bond strength may gradually weaken over time. The greatest loss occurs initially, followed by a period of relative stabilization, and then a weaker reduction after 24 weeks. The greater the time in water immersion, the less the bond strength and the greater the destruction of the composite resin. The debonding interface occurs between bracket and resin.