Influence of pH Variation on Physical Properties of Composite Resin

Objectives: The aim of this study is to evaluate the effects of acidity and alkalinity as found in 2 common beverages- coffee (acid free and regular) and alkaline water over micro-hybrid composite restorative material.
Methods: 42, D3 shade microhybrid composite resin discs were fabricated with diameter 10mms and thickness 2.0mms and polished using Buehler polishing discs. After initial measurements, 7 samples each were immersed in acid free, regular coffee (brewed in distilled water and alkaline water separately), distilled water and alkaline water (6 solutions) for a period of 45 days. On day 0, 1, 15, 30 & 45 color-shade change and surface roughness measurements were repeated then disks re-immersed in the respective fresh solutions. Micro-hardness measurements were made on day 0 and day 45.
Results: Data was analyzed on SPSS software using ANOVA for a P≤0.05. Changes were seen in surface roughness, color-shade stability and micro-hardness between specimens tested in different solutions owing to the pH variation, while the control specimens showed insignificant change.
Conclusions: Composite discoloration arising from stains (extrinsic or instrinsic) is one of the major reasons for composite restoration replacement world over. Coffee is considered as one of the most staining drinks with pH of regular coffee noted as 4.8 versus 5.6 for acid free coffee. The change in pH may be responsible for increased shade change with regular coffee, while alkaline water seemed to counteract the effects of increased discoloration and surface roughness caused by acidity. We may hypothesize that higher acidity can cause roughening or degrading of the resin material increasing susceptibility to staining. Further studies are being conducted to understand the process.