Monomer Conversions & Microhardness of Direct, Indirect and CAD/CAM Restoratives

Objectives: This in vitro study compared the percentages of unsaturated aliphatic –C=C- bonds, monomer conversions and microhardness of the direct, indirect resin composites and a CAD/CAM resin nanoceramic which were cured with different polimerization procedures.
Methods: Direct resin composites (Gaenial Posterior, Filtek Bulkfill), indirect resin composites (Tescera Body, Ceramage Body) and a CAD/CAM resin nanoceramic block (Lava Ultimate) were used. Direct resin composites were cured with LED light-curing unit (Bluephase, Ivoclar Vivadent AG, Liechtenstein). The samples of Tescera were polymerized with light/heat/water and pressure in the laboratory, whereas only light was used for Ceramage. Meanwhile, nanoceramic blocks were already fabricated by its manufacturer.
Real time ATR-FTIR (PerkinElmer Spectrum 100) was used for determining the percentages of –C=C- bonds and measurements of monomer conversions. Additionally, microhardness was investigated with Vickers Microhardness Tester. Data obtained were analyzed statistically and a correlation study was performed.
Results: FTIR images of this study presented unsimilar characteristics. In terms of the percentages of unsaturated –C=C- bonds, there was a difference among the materials (p < 0.001). Similarly, monomer conversions of the materials were different from each other (p < 0.001). However, there was no difference between top and bottom measurements of the samples (p = 0.162).
Microhardness of the materials used were also different (p < 0.001). Additionally, the measurements obtained from top and bottom surfaces were unsimilar for BulkFill, Ceramage and Tescera (p < 0.001).
Findings of FTIR and microhardness of this study pointed out that microhardness increased depending on monomer conversion (Spearman's correlation coefficient = 0,015).
Conclusions: Within the limitation of this study, it was shown that different materials and polymerization procedures lead to various percentages of unsaturated -C=C- bonds, monomer conversions and microhardness. Additionally, there seems to be a strong correlation between monomer conversion and microhardness of dental resin composites.