Timing for composite resin placement on mineral trioxide aggregate.

INTRODUCTION The aim of this study was to investigate the proper time to restore composite resin over mineral trioxide aggregate (MTA). METHODS Thirty-five samples of MTA blocks were divided into 7 groups with 3 different times (10 minutes, 1 day, and 7 days) selected for restoring the composite resin over MTA with and without bonding resin, and a control group was included for comparison. After 21 days, the distances between MTA and the composite resin or between MTA and the bonding agent on sectioned planes along the long axis were measured using a scanning electron microscope (×2,000 magnification). The hardness of the MTA near the composite resin was presented as the Vickers microhardness. RESULTS There were no gaps at the interface in the 10-minute groups, the 1-day group with a bonding agent, and the 7-day group with a bonding agent. The groups without a bonding agent at 1 and 7 days presented a separation or gap at the interface. The value of the Vickers microhardness in the 1-day groups was significantly decreased compared with those of the other groups regardless of the presence or absence of a bonding agent. CONCLUSIONS These findings suggest that composite resin with a bonding agent over MTA can be restored almost immediately after MTA mixing during a single visit.