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

PURPOSE 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.