1. Volume contraction in photocured dental resins : the shrinkage - conversion relationship revisited Dewaele M.- Truffier D.- Leloup G.- Devaux J. Université catholique de Louvain The volumetric contraction: - still remains unavoidable - constitutes the main reasons for premature replacement of resin composite - the main limitation of present-day resin composites Its elimination is one of the most important research tasks in this field. Its elimination is one of the most important research tasks in this field. INTRODUCTION Literature: unfilled resins: magnitude of total volumetric “free” curing contraction: +/- 4.0 to 9.0 vol % up to about 24 hours after polymerization Monomer molecules Secondary cohesion (4 Å) Polymer network Covalent links (1,5 Å) the most important !!! (immediate) polymerization less important (during the cooling) Curing reaction is exothermic

2. Volume contraction in photocured dental resins : the shrinkage - conversion relationship revisited Dewaele M.- Truffier D.- Leloup G.- Devaux J. Université catholique de Louvain In literature: Volumetric contraction Degree of conversion :ideal In this study: Volumetric contraction C=C C-C Loshaeck, 1953: “For every mole of C=C being converted in C-C, there is an associated volume shrinkage of 23 cm 3.” MATERIALS AND METHODS Experimental resins: Experimental resins: Bis-GMA/TEGDMA: 100/0, 80/20, 70/30, 60/40, 50/50, 40/60, 30/70, 20/80 % Bis-GMA/TEGDMA: 100/0, 80/20, 70/30, 60/40, 50/50, 40/60, 30/70, 20/80 % weight + 1% CQ/amine 50/50 (initiator/activator system) weight + 1% CQ/amine 50/50 (initiator/activator system) Bis-GMA TEGDMA unpolymerizedpolymerized TEGDMA: flexible: high DC Bis-GMA: much more rigid Bis-GMA: much more rigid TEGDMA: mole C=C init./g: 2/MM= 6,9*10 -3 TEGDMA: mole C=C init./g: 2/MM= 6,9*10 -3 Bis-GMA: mole C=C init./g: 2/MM = 3,9*10 -3 Bis-GMA: mole C=C init./g: 2/MM = 3,9*10 -3 Do not permit direct correlation between DC and % contraction DC *≈2 OBJECTIVES

3. Volume contraction in photocured dental resins : the shrinkage - conversion relationship revisited Dewaele M.- Truffier D.- Leloup G.- Devaux J. Université catholique de Louvain specific gravity of uncured composite resin (d unpolymerized): pycnometre specific gravity of uncured composite resin (d unpolymerized): pycnometre specific gravity of cured specific gravity of cured composite resin (d polymerized): density column Density Column method : To determine the density of a sample, the height at which it stabilizes in a density gradient column is observed and compared with calibrated marker floats. % Volumetric contraction = 100 * (d poly. – d unpoly.) / d poly. (∆V/Vunpolymerized) RESULTS: % Volumetric contraction:

4. Volume contraction in photocured dental resins : the shrinkage - conversion relationship revisited Dewaele M.- Truffier D.- Leloup G.- Devaux J. Université catholique de Louvain RESULTS: C=C C-C: Moles C=C poly/g = Moles C=C init./g * DC Moles C=C init./g * DC Moles C=C poly/cm3 = Moles C=C poly/g * d poly Moles C=C poly/g * d poly DC unpolymerized and polymerized resins: Raman Spectroscopy Comparison between the vibration bands of the residual unpolymerized methacrylate C=C stretching mode at 1640 cm -1 and the aromatic C=C stretching mode at 1610 cm -1 (internal standard). The unpolymerized resin (+ initiator/activator system) is used as reference (DC= 0). DC (%)= 100 * (1 - (R polymerized/R unpolymerized)) R= band height at 1640 cm -1 /band height at 1610 cm -1

5. Volume contraction in photocured dental resins : the shrinkage - conversion relationship revisited Dewaele M.- Truffier D.- Leloup G.- Devaux J. Université catholique de Louvain - Univocal relationship between the volume contraction and the actual number of vinyl double bonds converted into single ones. - Level of contraction increasing with the number of double bonds converted. - Volume shrinkage of 20 cm 3 /mole of double bonds converted. A Reduction of the polymerization shrinkage due to the chemical reaction may obviously be expected from the addition of molecules allowing to decrease the number of double bond converted per unit of volume of resin matrix while maintaining the degree of conversion (of Bis-GMA and TEGDMA) and thus the mechanical properties similar. CONCLUSIONS