Does preheating a dental composite degrade its post-cure properties?

Objectives: Preheating of resin-based composites (RBC) prior to placement is an approach that temporarily lowers the viscosity of the RBC. This study determines whether preheating degrades mechanical, cure and esthetic properties of an RBC.
Methods: Syringes of Filtek™ Bulk Fill Posterior were divided into two groups: 1) a room temperature control and 2) an experimental, where the syringes were cycled twenty times through heating for one hour at 60° C and cooling at room temperature for one hour. Samples for all tests were light cured at room temperature.
The following mechanical and cure tests were performed: diametral tensile strength (DTS), flexural strength and modulus, depth of cure, and polymerization shrinkage stress (aluminum block-based cusp deflection). For esthetics, color and polish retention were measured. Color was measured on an X-Rite color spectrophotometer. CIE Lab color parameters of L*, a*, b* and contrast ratio (CR) were recorded. Polish retention was determined using a tooth-brushing machine and is reported as the 60° gloss reading after 6,000 tooth brushing strokes.
Results: Results are summarized in the following tables.
The only test where one of the pair of values is statistically different (2 sample t-test, p<0.05) from the other is flexural modulus. The level of difference (0.4 GPa) is within the range shown by different, clinically accepted RBCs.
Conclusions: Consequently, we conclude that preheating of RBCs up to 60°C prior to placement does not cause a clinically relevant degradation of mechanical, cure or esthetic properties.