Affiliation:
1. Seungho Kang, DDS, MDS, Department of Conservative Dentistry, Seoul National University School of Dentistry and Dental Research Institute, Seoul, Korea
2. *Byeong-Hoon Cho, DDS, MSD, PhD, Department of Conservative Dentistry, Seoul National University School of Dentistry and Dental Research Institute, Seoul, Korea
Abstract
SUMMARY
The objective of this study was to evaluate the aging effects of long-term exposure to acidic beverages on the flexural strength (FS) and chemical reactions of two resin-based composites (RBCs) and one giomer. The FS of composite specimen bars (2 mm × 2 mm × 25 mm) was measured using a universal testing machine at various levels of thermocycling (TC; 0, 10,000, 50,000, and 100,000 cycles) in two beverages with different pH values (distilled water [DW], pH 7.0; Coca-Cola, pH 2.4-2.8). The FS data were analyzed using three-way analysis of variance with the post hoc Tukey test and t-test at a significance level of a=0.05. In DW, the FS of an RBC and a giomer did not decrease until 10,000 cycles. The other RBC, Z250, decreased rapidly until 50,000 cycles (p<0.05), followed by no additional decrease until 100,000 cycles. In Coca-Cola, the FS of two RBCs and a giomer decreased more rapidly than in DW from 10,000 cycles (t-test, p<0.05). In Coca-Cola, the increased porosity observed in scanning electron microscopy (SEM) images, the changes of the hydroxyl peak at 3340 cm−1 and ester peak at 1730-1700 cm−1 in Fourier-transform infrared spectroscopy in attenuated total reflectance mode (FTIR-ATR) spectra, and the continuous increase of the Si-O/Si-C peak height ratio from 10,000 cycles to 100,000 cycles in X-ray photoelectron spectroscopy (XPS) suggested an increased loss of silane-carbon bond between the matrix and fillers of the Z250 RBC, compared to those in DW. In conclusion, when TC was performed in DW, unreacted monomers and a coupling agent were washed out, which caused porosity and reduced FS. In Coca-Cola, acidic conditions accelerated the removal of the matrix through the hydrolysis reaction at the ester groups, resulting in more porosity and a faster decrease in FS than in DW.