The effect of pressure changes during simulated diving on the shear bond strength of orthodontic brackets.

Introduction: This study investigated the effect of pressure variations to which divers are subjected on shear bond strength of orthodontic brackets bonded to teeth with resin modified glass ionomer cement (RMGIC) or composite resin.

Methods: Eighty extracted premolars were randomly divided into two groups. Group 1: orthodontic brackets were bonded with RMGIC. Group 2: orthodontic brackets were bonded with composite resin. Each group was further divided into two subgroups. Subgroup A: The samples were kept at sea level pressure (101 kPa). Subgroup B: The samples were pressurised once from 101 kPa to 405 kPa for five minutes, then depressurised to 101 kPa. Shear bond strength was then measured.

Results: Shear bond strength of brackets bonded with RMGIC in the simulated diving group was significantly less than that of ambient pressure group (P = 0.019), while no significant difference was found between the simulated diving group and ambient pressure group for brackets bonded with resin cement (P = 0.935). At ambient pressure, there was no significant difference between shear bond strength of brackets bonded with RMGIC and composite resin (P = 0.83). In simulated diving conditions, there was a statistically significant difference between shear bond strength of brackets bonded with the RMGIC and composite (P = 0.009).

Conclusions: Pressure changes during scuba diving may have an adverse effect on the retention of brackets bonded with RMGIC. Using composite resin for bonding brackets appears to be good strategy for patients such as divers who will be exposed to pressurised environments.