engleski

Photopolymerization - light sources and clinical aims

Photopolymerization is considered to be an extremely important step during a restorative treatment. Dentist has to select a light source from a wide variety of units, each based on different philosophy. The use of various photopolymerization methods promotes different curing effects which affect degree of conversion, temperature and volumetric changes and polymerization stress. Despite the popularity of conventional halogen curing units, serious disadvantages such as limited effective lifetime, reflector and filter degradation, due to the high operative temperature and innapropriately low and high wavelengths compromise its use. Since curing procedures are considered time consuming, high energy light sources were brought on the market. Even though high intensity lights provide higher values for degree of conversion, they also produce higher polymerization stress. Sudden stiffening in combination with the unavoidable curing contraction causes stress to the restored tooth with consequential adhesive or cohesive failures. Because of the following, the trend of using high power curing lights switched to a more gentle light sources – blue superbright light emitting diodes. Blue diodes are based on doped semicinductors for generation of light and are characterised by narrow spectral output and long lifetime expectancy. They are small, portable, ergonomic, quiet, dazzle-free and operated by batteries. Experiments conducted with low intensity LED revealed similar conversion, but significantly lower temperature rise and polymerization contraction compared to a conventional halogen light of average intensity. However, high output intensity second generation LED units enable better conversion of the material and deeper polymerization in shorter time, followed by higher temperature that could be damaging for vulnerable pulp tissue. A slower curing process, regardless whether halogen or LED, permits composite flow and may allow for stress relaxation during polymerization. Clinical aims for curing are optimal conversion to achieve optimal mechanical properties and avoid possible pulp response to uncured monomers while, at the same time, minimising polymerization stress to enable preservation of marginal integrity.

photopolymerization; light sources

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