Ambient light working times of visible light-cured restorative materials. Does the ISO standard reflect clinical reality?
OBJECTIVE
The aim of this study was to determine whether a custom built light box could reliably reproduce clinical conditions and whether the current ISO standard test for the working time of visible light cured (VLC) materials (ISO. Dental Resin-based Restorative Materials. ISO:4049, 1991) reflected clinical reality.


METHODS
The ISO test requires a VLC material to remain homogenous after exposure to an 8 kLux light source for 60 s. The relationship between the intensity of ambient lighting and the working times of visible light-cured (VLC) restorative materials was investigated by exposing 23 different VLC composite resin materials to a range of light intensities and measuring the working time in seconds: (a) under clinical operating conditions; (b) in a custom light box at 24 kLux; and (c) at 8 kLux in the light box. Working times were determined by placing 0.06 g samples between two glass plates and gently rotating until clefts or voids appeared.


RESULTS
Clinical lighting conditions (24 kLux) gave a mean working time of 54 s (s.d. 14 s). In the light box at 24 kLux the mean working time was 54 s (s.d. 11 s). At 8 kLux (under otherwise identical conditions) the mean working time was 162 s (s.d. 49 s).


CONCLUSIONS
A 24 kLux illuminance in the laboratory gives an optimal correspondence to operative lighting conditions. This is three times the lighting level required for ISO purposes, and gives more realistic working times.
Lane
D A
DA
University of Manchester Dental School, UK. Andrew.Lane@lanedental.demon.co.uk
Watts
D C
DC
Wilson
N H
NH
D000704:Analysis of Variance; D003188:Composite Resins / Q000737:chemistry* / Q000592:standards; D003793:Dental Restoration, Permanent / Q000379:methods*; D005069:Evaluation Studies as Topic; D008027:Light; D011108:Polymers / Q000737:chemistry; D012015:Reference Standards; D013997:Time Factors
D003188:Composite Resins; D011108:Polymers