RESUMEN
These days dental composites are very popular because they look good and are similar to human teeth regarding color. Hygroscopic expansion is one of the physical properties of dental composites. A dental composite may lose its efficiency as a restoration material because of water absorption. The objective of this study was to compare the hygroscopic expansion of three dental composites. In this experimental study, to assess the effective factors of hygroscopic expansion, we used three different dental composites [Kalore, P90 and Z250]. The length of these composites in water and saliva were measured eighteen times in a three-month period. We used the marginal modeling technique, in which the correlation between response data can be included for analysis. The results of marginal modeling showed that the type of composite is significantly related to hygroscopic expansion [P<0.05]; demonstrating the highest hygroscopic expansion for P90 and the lowest for Z250. In addition, time as an independent variable had a statistically significant effect on hygroscopic expansion [P<0.05]. However, we found no significant difference between the hygroscopic expansion of saliva and water [P>0.05]. Overall, our findings showed that hygroscopic expansion is significantly related to the type of composite and time. Therefore, we should utilize the composites with lower hygroscopic expansion [such as Z250] for filling the patients' teeth