Efficacy of halogen photopolymerization units in private dental offices in Toronto.

PURPOSE: Light units used for polymerization of resin composites are subject to deterioration with age, and frequent maintenance is required to maintain optimal efficacy. This study examined the efficacy of quartz-tungsten-halogen light units in private dental offices in Toronto for polymerization of resin composites. MATERIALS AND METHODS: One hundred dental offices met all selection criteria and agreed to participate in the study. The light intensity was determined for a total of 214 light units. Disk-shaped specimens, 2.5 mm thick, were made from 2 resin composites (Charisma, Heraeus Kulzer; Point 4, Kerr Corp) and were subjected to photopolymerization: Charisma for 20 seconds (99 units) and Point 4 for 20 and 40 seconds (all 214 units). Knoop hardness values for the upper and lower surfaces of each specimen were determined, and relative hardness values (hardness of lower surface/hardness of upper surface x 100) were calculated. Data were analyzed using descriptive statistics, t-tests, 1-way analysis of variance, and simple and multiple linear regression (a = 0.05). RESULTS: The light intensity of the individual units varied widely, from 120 to 1,000 mW/cm2. Surface hardness and relative hardness were significantly (p < 0.05) and positively associated with light intensity, and wide ranges in surface hardness and relative hardness values were observed. Mean relative hardness ranged from 34.8% to 57.7%. CONCLUSIONS: Light polymerization units in private dental offices displayed a wide range in light intensity, and many had below-recommended levels. Of the resin composite specimens polymerized for 40 seconds with each of the 214 light units, only 10% reached the desired relative hardness of at least 80%. A positive linear relationship was found between light intensity and relative hardness. Increased exposure time resulted in a significant increase in relative hardness. Also, relative hardness was found to be dependent on the brand of composite material used. Dentists should regularly monitor the condition of light units and replace deteriorating parts.

Intensity of quartz-tungsten-halogen light-curing units used in private practice in Toronto.

BACKGROUND: The authors conducted a study to determine light intensity and heat/glare measurements of quartztungsten-halogen (QTH) light polymerization units used in dental offices. METHODS: Research assistants visited 100 dental offices and assessed 214 QTH light units. They recorded each unit's model, age, service history, light intensity and heat/glare emissions. RESULTS: Mean light intensity was 526 milliwatts per square centimeter (120-1,000 mW/cm2), with 26 units having intensity less than 300 mW/cm2. The mean light unit age was 5.6 years. Light units older than three years had significantly lower output intensities than those that were one, two or three years old. The authors found a wide range of heat/glare measurements (3-300 mW/cm2), with 4.6 percent of the units having values greater than 50 mW/cm2, including three with values of more than 200 mW/cm2. The mean light intensity of units serviced in the preceding year was 539 mW/cm2; it was 418 mW/cm2 for units serviced from one to six years previously. CONCLUSIONS: Light intensity and heat/glare values varied among the 214 units; some units had values well outside the recommended levels. Each unit's age and service history significantly affected its intensity. An awareness campaign is needed to promote testing, repair or replacement of light polymerization units. Periodic testing of light polymerization units should be considered by regulatory bodies to ensure optimum quality of composite restorations. CLINICAL IMPLICATIONS: Light polymerization units in some private dental offices in Toronto had intensities that may result in composites restorations with inferior properties. Dentists need to regularly monitor the intensity of the light polymerization units and maintain the units to ensure quality composite restorations.