The efficacy of irradiation protocol and irradiation distance on resin-based composite performance

Abstract

The objective of the current study was to investigate the efficiency of the overlapping irradiation regime for resin-based composites (RBCs) in ISO 4049 by modifying the irradiation protocol. To exacerbate the potential for uncontrolled initiation on polymerisation and decrease the homogeneity of polymerisation along the length of the specimen, the exit window was moved by three-quarters (not half) the diameter along the top surface only so that some areas received twice the irradiation of adjacent areas. It was proposed that increasing the number of irradiations, with decreasing tip diameter from 13 to 11 and 8mm, would progressively decrease the efficiency of the polymerisation process compared with a ‘one-hit’ irradiation using a 25mm custom made fibre optic light guide. Additionally, the influence of light irradiation variables (tip diameter, irradiance, irradiation protocol and LCU) on the flexural strength, flexural modulus and the Vickers hardness were assessed. Within the limitations of the experiment tip diameter, irradiance and irradiation protocol had no influence on three-point flexural strength and modulus data. An increase in irradiance for a constant irradiation time resulted in an increase in the Vickers hardness of the bottom surfaces. The study emphasised that the relationship between the development of mechanical properties with energy density is not linear although some clinical implications were highlighted. The objective of Part II of the current study was to investigate RBC placement variables (principally irradiation distance) which has implications for strength and modulus development in clinical practice. In addition, the influence of quartz tungsten halogen LCU irradiation distance on bi-axia! flexure strength and short- and long-term in-vitro wear resistance were also