Influence of Thermal Expansion on Shrinkage During Photopolymerization of Dental Resins Based on bis-GMA/TEGDMA

VERONICA MUCCI; ARENAS GUSTAVO F.; DUCHOWICZ RICARDO; WAYNE D. COOK; CLAUDIA I. VALLO

DENTAL MATERIALS

ELSEVIER SCI LTD

Año: 2009 vol. 25 p. 103 - 114

0109-5641

The aim of this study was to assess volume changes that occur during photopolymerization ofunfilled dental resins based on bis-GMA-TEGDMA.Methods. The resins were activated for visible light polymerization by the addition of camphorquinone (CQ)in combination with dimethylamino ethylmethacrylate (DMAEMA) or ethyl-4-dimethyl aminobenzoate(EDMAB). A fibre-optic sensing method based on a Fizeau-type interferometric scheme was employed formonitoring contraction during photopolymerization. Measurements were carried out on 10 mm diameterspecimens of different thickness (1 and 2 mm).Results. The high exothermic nature of the polymerization resulted in volume expansion during the heating,and this effect was more pronounced when the sample thickness increased. Two approaches to assessvolume changes due to thermal effects are presented. Due to the difference in thermal expansioncoefficients between the rubbery and glassy resins, the increase of volume due to thermal expansion wasgreater than the decrease in volume due to thermal contraction. As a result, the volume of the vitrifiedresins was greater than that calculated from polymerization contraction. The observed trends of shrinkageversus sample thickness are explained in terms of light attenuation across the path length duringphotopolymerization.Significance. Results obtained in this research highlight the inherent interlinking of non-isothermalphotopolymerization and volumetric changes in bulk polymerizing systems.