Preheating of new Bulk-fill composite materials: polymerization shrinkage and conversion degree

Bulk-fill composites have recently been introduced to the market and are receiving attention mainly because they can allow 4 mm increments without negative effects on polymerization, boasting very good characteristics of adaptation to cavities and a good degree of conversion (DC). Furthermore, their polymerization shrinkage appears to be lower than conventional composites, such as to reduce the post-operative problems of gap formation with consequent formation of secondary caries.
It is now known that the type of composite material and the pre-cure temperature influence the final degree of shrinkage of the composite.

Pre-heating the new bulk-fill composites during restorations prior to photoactivation appears to further decrease the polymerization induced shrinkage force without compromising the degree of conversion even more than in conventional composites.

This is discussed in an article that appeared in the Journal od Dentistry of November 2015.
The authors of this work analyzed four bulk-fill composite materials (Tetric EvoCeram Bulk Fill-TECBF, x-tra fil-XF, QuixFil-QF, SonicFill-SF) and a conventional nano-hybrid composite (Tetric EvoCeram-TCE). The test materials were either stored at room temperature or preheated to 68 ° C using a commercial heating device, before being photoactivated with an LED curing light for 20s at 1170mW / cm. Contraction force values ​​were then recorded at 1.5 mm thickness in real time for 15min inside a temperature-controlled chamber at 25 ° C (intraoral simulation temperature after rubber dam application) with a stress analyzer measures. The degree of conversion of the samples was also analyzed by infrared spectroscopy. Data were analyzed with t-test, HSD ANOVA and Tukey post-hoc test.

The authors obtained the following results:
preheating of the composite material before photopolymerization led to a significant increase in the degree of conversion of Tetric EvoCeram Bulk Fill (TECBF), but had no particular effect on the conversion of the monomers of the other materials investigated. For each of the test materials, the pre-heated composites generated significantly lower shrinkage forces than the composites used at room temperature.

Preheating composite materials before light-curing significantly reduces the shrinkage force of even the new high-viscosity bulk-fill composites in addition to conventional resin composites, but the diversity of the final conversion degree is also highly dependent on the specific composite material used.
Curated by: Lara Figini