Mass loss in urethane/TEGDMA- and Bis-GMA/TEGDMA-based resin composites during post-cure heating.

OBJECTIVES

This research examined weight loss of commercial UDMA/TEGDMA- and Bis-GMA/TEGDMA-based resin composites at a variety of post-cure temperatures. Weight loss profiles of individual monomer components were also tested at elevated temperature: Bis-GMA, ethoxylated Bis-GMA (EBis-GMA), urethane dimethacrylate (UDMA), and triethyleneglycol dimethacrylate (TEGDMA).

METHODS

Disc-shaped composite specimens (1 x 5 mm, approximately 50 mg) were light-cured and then isothermally post-cure heated in a thermogravimetric analysis (TGA) unit at either 50 degrees, 75 degrees, 100 degrees, 125 degrees or 150 degrees C. A single specimen was made for each post-cure temperature for each product (a total of 10 discs). Individual monomer components were heated to 800 degrees C. Filler and organic phase weight percentages were determined by ashing cured composite in the TGA. Weight loss differences between resin systems at various post-cure temperatures were analyzed using linear regression.

RESULTS

For each type of composite, loss of volatile component increased with both elevated post-cure temperature as well as duration of heat exposure. Using recommended post-cure temperature and time (125 degrees C for 7.5 minutes), there was no difference in weight loss profile between the two products: both exhibited 1.3% loss of resin component. After 10 min of heating, the Bis-GMA-based product always demonstrated a greater weight loss than the UDMA material. Weight loss could not be attributed to any specific monomer.

SIGNIFICANCE

Specimen weight loss during post-cure heating may result in a depletion of leachable, unreacted material at the restoration surface, possibly enhancing material properties at that location. This decrease would also potentially reduce the biological impact of leachable materials. Loss of volatile components from post-cure heating would affect the accuracy of infrared spectroscopic techniques in determining monomer conversion values.