Light-Curing Units

Abstract

Light-curing units are widely employed in dentistry thanks to the development and progressive affirmation of resin composites. However, to clinically achieve great results and outcomes with adhesive dentistry, it is fundamental to understand how light curing works, its effects, and its limitations. In this chapter a basic knowledge will be given to the reader, in order to understand how to clinically deal with curing protocols and maximize the outcome of polymerization. The chemical reactions during light curing of composite resins are described, also explaining the influence of volumetric shrinkage and shrinkage stress on quality of the final restoration. The different light-curing units are presented, including quartz-tungsten-halogen (QTH), argon-ion laser (AL), plasma arch (PAC), and light-emitting diode (LED). The importance of an adequate radiant emittance, the distance between the light and the tooth and the incident beam angle are important factors in order to deliver the necessary energy dose to properly cure the restorative material. The effects of different curing protocols on the shrinkage stress are explained, including the conventional and gradual curing protocols, such as pulse delay and soft start (ramp and step cycle). Important recommendations while performing adhesive luting of indirect restorations and glass fiber posts are also described. Finally, the ocular hazards of curing lights are presented, as well the necessary protective measures for the dentist, assistant, and patient.