Veronica Mucci

Influence of thermal expansion on shrinkage during photopolymerization of dental resins based on bis-GMA/TEGDMA.

OBJECTIVE The aim of this study was to assess volume changes that occur during photopolymerization of unfilled 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 for monitoring contraction during photopolymerization. Measurements were carried out on 10mm diameter specimens of different thicknesses (1 and 2mm). 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 assess volume changes due to thermal effects are presented. Due to the difference in thermal expansion coefficients between the rubbery and glassy resins, the increase of volume due to thermal expansion was greater than the decrease in volume due to thermal contraction. As a result, the volume of the vitrified resins was greater than that calculated from polymerization contraction. The observed trends of shrinkage versus sample thickness are explained in terms of light attenuation across the path length during photopolymerization. SIGNIFICANCE Results obtained in this research highlight the inherent interlinking of non-isothermal photopolymerization and volumetric changes in bulk polymerizing systems.

Contraction Measurements of Dental Composite Material during Photopolymerization by a Fiber Optic Interferometric Method.

In order to monitor the shrinkage generated by new composites during photopolymerization, we have implemented a fiber optic sensing method based on a Fizeau‐type interferometric scheme. This simple, compact, non‐invasive and self‐calibrating system competes with both conventional and other high‐resolution bulk interferometric techniques. Several stages of the curing process were characterized from sample interferograms, including photopolymerization inhibition, the onset and degree of sample shrinkage, as well as typical kinetic behaviour of photopolymerization of dimethacrylates monomers. Some complementary studies (temperature and transmission measurements) were performed to complete the kinetic scheme. A simple polymerization model was generated in order to discuss the main results.