Effect of light curing and dark reaction phases on the thermomechanical properties of a Bis-GMA based dental restorative material.

The effects of light curing units (LCU) and energy doses on the chemical and physical properties of a dental composite were investigated. Methods: The effects on the chemical and physical properties of a bisphenol A diglycidylether methacrylate (Bis-GMA) based dental restorative material were evaluated through photospectrometry, differential scanning calorimetry, and mechanical measurements. Results: The light curing conditions associated with direct and indirect restorations were replicated in vitro using optical investigation techniques. A slight attenuation resulted independently of the LCU and a strong attenuation was measured for the cement luting a thick inlay, as well as for the deepest layer of a composite filling increment. Calorimetric measurements indicated that the curing degree is very sensitive to the light energy dose rather than to the LCU. Mechanical testing showed a transient phase during which properties increased. The delay of the composite in reaching adequate properties is strongly dependent on the energy dose. Conclusions: It is recommended that composites subject to unfavorable light curing conditions undergo a prolonged light curing process.