Abstract
Traditional polymerisation shrinkage (PS) measurement systems measure average PS of dental composites, but the true local PS varies along the length and breadth of the composite. The PS depends on the curing light intensity distribution, resultant degree of conversion (DOC) and the curing rate. In this paper, optical fibre Bragg grating (FBG) sensing based technology is used to measure the linear post-gel PS at multiple locations within dental composite specimens, and is correlated with DOC and curing rate. A commercial dental composite is used, and its post-gel PS and DOC are mapped using embedded fibre Bragg grating sensors at different curing conditions. The distance between the curing lamp and the composite specimen is varied which resulted in different intensity distribution across the specimen. The effect of curing light intensity distribution on PS, curing rate and DOC are investigated for demonstrating a relationship among them. It is demonstrated that FBG sensing method is an effective method to accurately profiling post-gel PS across the specimen.
Highlights
Focus on aesthetics, toxicity concerns and ease of application has led methacrylate based dental composites to be the preferred restorative material by practitioners around the world[1]
fibre Bragg grating (FBG) sensing based technology is demonstrated as viable technique to measure dental polymerisation kinetics
The measured difference in degree of conversion (DOC) between specimens cured at 2 mm and 10 mm away from the curing lamp was only approximately 2.5%
Summary
Toxicity concerns and ease of application has led methacrylate based dental composites to be the preferred restorative material by practitioners around the world[1]. Mechanical and physical performance of dental resin composites are directly dependent on the extent of DOC during polymerisation; higher the conversion, higher are the longevity, mechanical and physical properties. The van der Waals distance between the atoms of monomers are reduced from to ~104 Å ~1.0 Å, resulting in bulk contraction in cured resin, i.e., volumetric polymerisation shrinkage[10,11,12]. During the initial 24 hrs after photo-polymerisation, conversion degree is not significantly affected, but the concentration of free radicals is largely reduced, leading to post-cure shrinkage[13]. A direct correlation exists between DOC and PS, higher the conversion of C=C bonds to C-C bonds, lower is the volumetric contraction during polymerisation[9]
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