Conversion rate of experimental amorphous calcium phosphate/methacrylate composites

Objectives: The objective of this study was to evaluate conversion rate of six amorphous calcium phosphate (ACP)/methacrylate composites of different consistency by using Fourier transform infrared spectroscopy and compare it to conventionally used composites. Methods: Four experimental ACP composites of different matrix composition and median particle size of ACP fillers were used. Composite samples were prepared for degree of conversion measurements by using LED curing unit Bluephase (Ivoclar Vivadent, Liechtenstein) and measured by Fourier transform Perkin Elmer model 2000 spectrometer (Perkin Elmer, UK). The conversion rate was obtained from equivalent aliphatic/aromatic molar ratios of cured and uncured samples for eight consecutive measurements for each material. Results: Results obtained indicated higher conversion rate in case of BTHZ composites containing Bis-GMA, TEGDMA, higher content of HEMA and Zirconyl dimethacrylate (ZrDMA) compared to ETHM composites based on ethoxilated bisphenol A dimethacrylate (EBPADMA), TEGDMA, HEMA and methacryloyloxyethyl phtalate (MEP). Conversion rate values for BTHZ composites varied from 80.6 to 84.7 while for ETHM composites varied from 70.5 to 76.8. Results were compared to hybrid composite Tetric Ceram (Ivoclar Vivadent, Liechtenstein) which ranged from 72.8 to 77.1 and to flowable FiltekTM Flow (3M ESPE, Germany) which reached values from 69.4 to 73.2. Conclusion: ACP based composites are photo-crosslinkable resins of excellent biocompatibility which provide sustained release of calcium and phosphate ions. Their polymerization rate, as an important factor in determining physicochemical and mechanical properties of the material, showed higher values in comparison to widely used hybrid and flowable composites. However, to obtain optimal material for clinical use, additional parameters have to be tested such as polymerization shrinkage and adhesiveness of the material. This study was supported by Ministry of Science, Education and Sports, Croatia, Grant No. 0065007.