Efficacy of halogen photopolymerization units in private dental offices in Toronto.
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.
El-Mowafy
Omar
O
Faculty of Dentistry, University of Toronto, Toronto, Ontario. oel.mowafy@utoronto.ca
El-Badrawy
Wafa
W
Lewis
Donald W
DW
Shokati
Babak
B
Soliman
Osama
O
Kermalli
Jaffer
J
Encioiu
Avedus
A
Rajwani
Fatma
F
Zawi
Rema
R
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
C084111:Charisma composite resin; D003188:Composite Resins; D006219:Halogens; C451741:point 4 composite resin