Polymerization and polymerization shrinkage stress: fast cure versus conventional cure
Strydom, C.
Sadj Journal of the South African Dental Association 60(6): 252-253
2005
ISSN/ISBN: 1029-4864 PMID: 16119025 Document Number: 594676
Dentists nowadays have a choice of conventional halogen lights, halogen lights with more sophisticated curing cycles (step-cure, rapid-cure, ramp-cure & pulse-cure), fast halogen lights, laser lights, plasma arc lights (PAC) and, lately, LED lights. While the manufacturers of some of the curing units try to improve on the operational reliability of their lights with a slower initial rate of cure, other manufacturers simply wish to offer as fast a curing time as possible. The conventional approach to cure accepts that sufficient light intensity of at least 400 mW/cm2 at a wavelength of 400-500 nm, and an exposure time of at least 40 seconds is needed to cure a 2-mm layer of composite. When a halogen light with higher or very high intensity is used, alternative curing strategies provide for an initial slower cure to allow flow, and after that a higher-intensity cure to improve the degree of cure. In contrast, in the fast-cure or rapid-cure approach it is suggested that a layer of composite can be cured for only 5- 10 seconds at >2000 mW/cm2. Some go so far as to say that an exposure time of 3 seconds per layer may be enough. This contradictory approach is compounded by the fact that this support for fast cure does not seem to consider the negative consequences. Therefore, to address these concerns, this review discusses the possible effects of a fast cure approach compared to a more conventional approach in polymerization and polymerization shrinkage, and the consequences there-off. Other factors that play an influencing role in polymerization shrinkage stress are also included in the discussion.