E. Harrington

Light curing unit effectiveness assessed by dental radiometers.

OBJECTIVES The purpose of this investigation was to assess the effectiveness of five commercially available hand-held dental radiometers and a computer-based experimental radiometer. METHODS Light intensity of five visible light activation units was determined using the dental radiometers. The influence of curing light intensity on depth of cure of a hybrid composite material was determined using a digital penetrometer. RESULTS The radiometers evaluated varied with respect to sensor aperture diameter, scale readings (analogue or digital) and the units of measurement (arbitrary or mW cm2). The experimental computer-based radiometer allowed continuous recording of intensity against time; thus the light output could be monitored over the entire irradiation period. CONCLUSIONS When light intensity readings were normalized with regard to a standardized light sensing device aperture of 4 mm diameter, a linear relationship was found between depth of cure and the logarithm of the intensity of the light. The results of this investigation support the use of dental radiometers for periodically monitoring visible light activation units.

Effect of exposure intensity and post-cure temperature storage on hardness of contemporary photo-activated composites

OBJECTIVES The effect of variation in post-exposure storage temperature (18 vs. 37 degrees C) and light intensity (200 vs. 500mW/cm(2)) on micro-hardness of seven light-activated resin composite materials, cured with a Prismetics Mk II (Dentsply) light activation unit, were studied. METHODS Hardness values at the upper and lower surfaces of 2mm thick disc shaped specimens of seven light-cured resin composite materials (Herculite XRV and Prodigy/Kerr, Z100 and Silux Plus/3M, TPH/Dentsply, Pertac-Hybrid/Espe, and Charisma/Kulzer), which had been stored dry, were determined 24h after irradiation with a Prismetics Mk II (Dentsply) light activation unit. RESULTS Hardness values varied with product, surface, storage temperature, and curing light intensity. In no case did the hardness at the lower surface equal that of the upper surface, and the combination of 500mW/cm(2) intensity and 37 degrees C storage produced the best hardness results at the lower surface. CONCLUSIONS Material composition had a significant influence on surface hardness. Only one of the seven products (TPH) produced a mean hardness values at the lower surface >80% of the maximum mean upper surface hardness obtained for the corresponding product at 500mW/cm(2) intensity/37 degrees C storage temperature when subjected to all four test regimes. Despite optimum post-cure storage conditions, 200mW/cm(2) intensity curing for 40s will not produce acceptable hardness at the lower surface of 2mm increments of the majority of products tested.

A pilot investigation of operator variability during intra-oral light curing

Objective To test the hypothesis that operator experience influences the efficacy of light curing in a typical posterior intra-oral location. To investigate whether short cure cycles affect performance.Design A cross-sectional single-centre study designed to assess the efficacy of experienced and inexperienced operators when undertaking simulated intra-oral curing.Setting An in vitro laboratory based investigation conducted in a dental school during 2001.Materials and methods A computer-based technique was used to monitor light intensity in a clinical simulation. Dentists and student operators were tested for their ability to cure a posterior restoration effectively. Relative light intensity was assessed against time for each operator and test run.Results Experienced (qualified) operators produced more effective and consistent cure results than less experienced undergraduate students. Operator performance was not affected by variations in irradiation time.Conclusions This cross-sectional pilot investigation demonstrates that operator experience is a factor in successful clinical photo-curing of posterior restorations. Stable and accurate light guide positioning are required throughout the entire irradiation cycle to optimise intra-oral cure of light-activated restorations. Further investigations are planned to assess the potential of this novel method of assessment for use as a routine teaching aid in clinical practice.