The effect of atmospheric pressure on the bond strength of composites.

Background: In the current study, we investigated the effect of atmospheric pressure change on the microtensile bond strength of direct and indirect composite restorations to the teeth.

Materials and methods: A total of 16 extracted teeth were prepared after crown cutting and randomly divided into four groups. The study groups included: 1) direct restoration (Filtek™ Z250 Universal Composite Restorative System, 3M, United States) at constant pressure (control); 2) direct restoration in variable pressure; 3) indirect restoration (Z250 composite) at constant pressure (control); and 4) indirect restoration at variable pressure. Then, samples were subjected to thermal cycles. Variable pressure groups were pressurized to 0 to 5 atmospheres for 96 cycles inside the hyperbaric chamber, followed by measuring the microtensile bond strength of the specimens.

Results: The mean of microtensile bond strength in both direct and indirect variable-pressure groups was significantly lower than their counterpart control groups. There was no significant difference between direct and indirect restorations in constant and variable pressure. The failure mode of the samples in the control groups was often mixed, while in the pressure groups, it was dominated by adhesive. Also, microscopic examination of restoration interfaces showed that the number and volume of voids in variable pressure groups were much more than the control groups.

Conclusion: Regardless of the type of restoration, changing the atmospheric pressure is effective on the bond strength of the restorations to the teeth.