Objectives:
Dental-composites undergo post-cure dimensional changes after intra-oral placement. Most effects occur immediately, where post-cure polymerization, leaching of substances and water sorption are the most prominent. The purpose of this study was to study the dynamics of post-cure polymerization shrinkage and water uptake, during the first 60 minutes following light-cure of a highly-filled composite, and to understand the dimensional response of typical composites, stored wet or dry, when heated to 37°C.
Materials and methods:
Samples of Grandio (VOCO Cuxhaven, n=12) 1mm thick, 15mm diameter were light cured and either immersed in water for 1h or placed in ambient air for 5min, 1h or 3d. Following storage, samples were placed on a precision Peltier thermal-stage and heated to 37°C. Surface deformations were monitored at 4sec intervals by non-contact electronic speckle pattern interferometry (ESPI), repeatedly determining displacement-difference maps for up to 30min. Statistical significance of shrinkage was assessed by two-way ANOVA.
Results:
Table 1 depicts the cumulative deformation[%] exhibited in three groups, expansion for the first 2 minutes of heating and shrinkage at 15 and 30 minutes thereafter. All samples firstly expanded. The 1h water immersed samples exhibited similar shrinkage as the 5min samples, higher than the 1h dry samples. The highest expansion and the lowest shrinkage were observed for the 3d dry samples. The differences were statistically significant.
| 2min | 13min | 15min |
1h wet | 0,0273% | -0,0366% | -0,0121% |
5 min | 0,0200% | -0,0367% | -0,0120% |
1h dry | 0,0286% | -0,0285% | -0,0069% |
3d dry | 0,0682% | -0,0111% | -0,0052% |
Conclusion:
Substantial shrinkage takes place following curing of dental restorative-composites due to post-cure polymerization. Interferometry measurements of deformation revealed markedly different dynamics of the rate/extent of shrinkage. Placement of freshly-cured composites in water influences the post-polymerization dynamics, suggesting the need for more studies to better understanding the dynamics of interaction between water and dental-composites.