Investigation of a hydrophilic primer for orthodontic bonding: an in vitro study

A common reason for bond failure is moisture contamination. This study investigates the in vitro bond strength of brackets bonded using a new hydrophilic primer, designed to be insensitive to moisture, and compares it with a conventional primer. Using a standardized technique, the in vitro bond strength of brackets bonded with the hydrophilic primer was compared to identical brackets bonded with a conventional primer. Although designed to be moisture insensitive, the directions for use stipulate drying the teeth before bonding. Therefore, for the purposes of comparison with a conventional primer the experiment was conducted under dry conditions. The results were analysed using the Weibull distribution modelling. The median bond strength with the hydrophilic primer (6.43 MPa, 95 per cent C.I. 7.69-9.50) was significantly lower (P = 0.0001) than the conventional primer (8.71 MPa, 95 per cent C.I. 5.89-7.59). The Weibull distribution modelling showed that brackets bonded with the hydrophilic primer were 3.96 times more at risk of failure (95 per cent C.I.: 2.39-6.56; P <0.0001). The bond strength at which 5 per cent of the brackets failed was also lower for the hydrophilic primer. The bond strengths obtained with the hydrophilic primer were significantly lower than with the conventional primer. Although the median bond strength values were promising, the laboratory results for this particular hydrophilic primer were disappointing when using the Weibull analysis, where the whole distribution of bond strength is taken into account.