Effect of Intra-oral Temperature and Time on Resin-based Composites Properties

Objectives: To evaluate the effect of curing two resin-based composites-(RBC) at room or intra-oral temperatures.
Methods: Two types of RBC, Filtek-Supreme-Ultra-(FS) and Tetric-EvoCeram-Bulkfill-(TBF) were light cured for 10-s using a modified Valo LED light curing unit (Ultradent, South Jordan, UT, USA) with the light tip placed directly over each specimen. The RBC was expressed into metal rings that were 2.0 and 4.0 mm thick, with a 4-mm internal diameter directly on an Attenuated Total Reflectance FT-IR plate heated to 23° or 33°C. The Degree of Conversion-(DC) of the RBC was recorded for 10-s before light exposure and for 110 seconds after the light was turned on. The specimens were then removed and the Knoop-microhardness-(KHN) was tested within 10-minutes both at the bottom and top of the specimens. The KHN was tested again after 24-hrs storage in the dark at 37°C and 100% humidity. Five specimens were made and tested in each group. The DC and KHN results were analyzed with Fisher’s PLSD at α = 0.05.
Results: Temperature had a large and significant effect on the DC and KHN values of the RBCs. Greater conversion degree and hardness occurred when the curing temperature was increased from 23° to 33°C and the KHN was always greater 24-hrs later.
Conclusions: Small differences in temperature from room to intra-oral temperature had a large and significant effect on the DC and KHN of both RBCs. As the RBC is not cured in the tooth at 23°C and the patient does not wait 24-hrs to chew on their new restoration, the RBC should be tested at intra oral temperatures both immediately and after 24-hrs.