title: Efficacy of halogen photopolymerization units in private dental offices in Toronto.
abstract: OBJECTIVE
  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.
  
  
  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.
authors.affiliation: Faculty of Dentistry, University of Toronto, Toronto, Ontario. oel.mowafy@utoronto.ca
authors.forename: Omar
authors.initials: O
authors.lastname: El-Mowafy
authors.forename: Wafa
authors.initials: W
authors.lastname: El-Badrawy
authors.forename: Donald W
authors.initials: DW
authors.lastname: Lewis
authors.forename: Babak
authors.initials: B
authors.lastname: Shokati
authors.forename: Osama
authors.initials: O
authors.lastname: Soliman
authors.forename: Jaffer
authors.initials: J
authors.lastname: Kermalli
authors.forename: Avedus
authors.initials: A
authors.lastname: Encioiu
authors.forename: Fatma
authors.initials: F
authors.lastname: Rajwani
authors.forename: Rema
authors.initials: R
authors.lastname: Zawi
mesh_terms: D000704:Analysis of Variance; D003188:Composite Resins / Q000528:radiation effects*; D003748:Dental Equipment; D006219:Halogens; D006244:Hardness; D008027:Light; D016014:Linear Models; D009864:Ontario; D044367:Phase Transition; D011331:Private Practice
chemical_list: C084111:Charisma composite resin; D003188:Composite Resins; D006219:Halogens; C451741:point 4 composite resin