Contraction Measurements of Dental Composite Material

GUSTAVO ARENAS; SERGIO NORIEGA; VERONICA MUCCI; CLAUDIA VALLO; RICARDO DUCHOWICZ

Campinas - Sao Paulo - Brasil

Conferencia; RIAO/OPTILAS 2007: 6th Ibero-American Conference on Optics (RIAO); 9th Latin-American Meeting on Optics, Lasers and Applications (OPTILAS); 2007

RIAO - OPTILAS

Shrinkage measurements of dental composite material during photo-polymerization by a fiber optic interferometric method. Photo-curing of multifunctional monomers is a well-known method applied in clinical restorative dentistry. Polymerization of dental resins is generally initiated by Camphorquinone (CQ)/amine photo-initiating system, which produces free radicals on exposure to 450-500 nm radiation. The difficulties of these materials are that they shrink during polymerization causing shrinkage strain and marginal gaps at the tooth composite interface. In order to monitor the shrinkage generated by new composites during photo-polymerization, we have implemented a fibre optic sensing method based on a Fizeau-type interferometric scheme. The ability to collect data at high acquisition rates permits the real-time measurement of extremely fast polymerization rates. This simple, compact, non-invasive and self-calibrating system competes with both conventional and other high-resolution bulk interferometric techniques. The quality of interference signal and fringes visibility was analyzed in order to characterize the resolution and application range.Systematic comparisons of the shrinkage evolution during photo-polymerization were made as a function of light intensity, sample thickness and photoinitiator concentration. The selected experimental results presented in this work, illustrate the effectiveness of the device. Several stages of the curing process were characterized from sample interferograms, including photo-polymerization inhibition, the onset and degree of sample shrinkage, as well as typical kinetic behaviour of photo-polymerization of dimethacrylates monomers. For all measurements, the onset of shrinkage appeared several seconds after illumination. The time lag at the beginning of each shrinkage pro¯le is attributed to the presence of both inhibitor of the polymerization reaction and dissolved oxygen. 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.