Evaluating the effect of preheating on resin composites in pit-and-fissure caries treatments with a digital intraoral scanner.

OBJECTIVE: To evaluate the effect of preheating on the microleakage and surface hardness of resin composites in the treatment of pit-and-fissure caries with various widths, as measured by an intraoral scanner. METHODS: A total of 153 L-shaped cavities with different widths (1 mm, 1.6 mm and 2 mm) were prepared on the buccal or palatal/lingual surfaces of human molars. The cavities were measured in three dimensions by a TRIOS scanner and then filled with various resins (room temperature Z350 flowable resin and room temperature and 60 ℃ Z350 universal resin). Microleakage and gap formation at 2 sites were evaluated by stereomicroscopy and scanning electron microscope. Resin samples were prepared, and the top surface Vickers hardness (VHN(top)) of all samples was measured at 1 day and 30 days postirradiation. RESULTS: No difference were observed in the 3D scans for the cavities sizes among groups with the same width. For the 1 mm-wide cavity, the lowest microleakage was obtained with the flowable group; for the 1.6 mm-wide cavity, the nonpreheating universal group showed the highest microleakage at site 1, and the preheating group exhibited lower microleakage than that of the nonpreheating universal group at site 2; and for the 2 mm-wide cavity, the preheating group presented lower microleakage at site 2. The gap formations were consistent with the microleakage degrees. The preheating group exhibited the highest VHN(top) at 1 day and 30 days postirradiation. SIGNIFICANCE: A digital intraoral scanner could be used to scan the cavities in three dimensions. Preheating technology could reduce the microleakage of Z350 universal resin and enhance its surface hardness.