European Cells and Materials Vol. 9. Suppl. 1, 2005 (pages 33-34) ISSN 1473-2262 Contribution of the dilatometric studies on the polymerization’s kinetics of the dental composite resins C Villat 1,3 , N Pradelle-Plasse 2,3 , B Picard 2,3 & P Colon 2,3 1 Université Claude Bernard Lyon 1, UFR d’Odontologie, Rue Guillaume Paradin, 69372 – LYON, Fr 2 Université Denis Diderot Paris 7, UFR d’Odontologie, 5 Rue Garancière, 75006- PARIS, Fr 3 Laboratoire de Biomatériaux, Université Denis Diderot Paris 7, UFR d’Odontologie, 5 Rue Garancière, 75006- PARIS, Fr INTRODUCTION: Leakage involved by the polymerization shrinkage is a major drawback of composite restorations. However, the only value of the final polymerization shrinkage is not able to explain all laboratory results. A recent study using a dilatometer has described the velocity of the polymerization shrinkage of resin composites 1 . The aim of this study was to characterize the different elements of the curves of polymerization contraction of two dental composite resins regarding the light curing unit (LCU). METHODS: Polymerization shrinkage as a function of time was investigated with a mercury dilatometer 2,3 (fig.1). To complete the study, temperature rise was registered on samples of 8 mm diameter and 2 mm thick. Fig. 1: Schematic representation of mercury-filled dilatometer Two dental microhybrid composite resins (CR) (Z100 ® , Tetric Ceram ® ) were used with one conventional halogen LCU (Elipar ® Highlight) and two light emitting diodes LCU (Elipar ® Freelight 1, and Apollo GC-e Light ® ). The light curing modes used were 20 s, 40 s, and 40 s progressive. RESULTS: The analysis of the polymerization curves during the two first minutes of the setting reveals four characteristic elements (fig. 2) : the dilatation peak at the beginning of the curing procedure (table 1), the angle formed by the initial slope of shrinkage with the vertical axis, the angle formed by the secondary slope of shrinkage with the vertical axis, and the intersection point between the two slopes of shrinkage (table 2). The stastistical analysis used was the ANOVA multi range test and the Fisher’s test. Fig. 2: Example of shrinkage curve (point a : dilatation peak at the beginning of the curing procedure ; angle α : angle formed by the initial slope of shrinkage with the vertical axis ; angle β : angle formed by the secondary slope of shrinkage with the vertical axis ; point b : intersection point between the two slopes of shrinkage) CR LCU 20 s 40 s 40 s prog EHL 0,11 0,09 0 EFL1 0,04 0,04 0,02 Z100 ® AGCL 0,09 0,03 0 EHL 0,63 0,54 0,10 EFL1 0,09 0,19 0 Tétric Ceram ® AGCL 0,17 0,18 0,06 Table 1. Mean values of the dilatation peak (%) (point a). Table 2. Mean values of the angles formed by initial slope of shrinkage and the vertical axis (angle α), formed by the secondary slope of shrinkage and the vertical axis (angle β),) and the intersection point between the two slopes of shrinkage (point b).