Effect of reduced exposure times on the microhardness of 10 resin composites cured by high-power LED and QTH curing lights.
OBJECTIVE
To compare the effect of reduced exposure times on the microhardness of resin composites cured with a "second-generation" light-emitting diode (LED) curing light and a quartz-tungsten-halogen (QTH) curing light.


METHODS
Ten composites were cured with a LED curing light for 50% of the manufacturers" recommended exposure time or a QTH light at the high power setting for 50% of the recommended time or on the medium power setting for 100% of the recommended time. The composites were packed into Class I preparations in extracted human molar teeth and cured at distances of 2 or 9 mm from the light guide. The moulds were separated, and the Knoop microhardness of the composites was measured down to 3.5 mm from the surface.


RESULTS
The LED light delivered the greatest irradiance at 0 and 2 mm, whereas the QTH light on the standard (high power) setting delivered the highest irradiance at 9 mm. According to distribution-free multiple comparisons of the hardness values, at 2 mm from the light guide the LED light (50% exposure time) was ranked better than or equivalent to the QTH light on the high power setting (50% exposure time) or on the medium power setting (100% exposure time). At 9 mm, the LED light was ranked better than or equivalent to the QTH light (both settings) to a depth of 1.5 mm, beyond which composites irradiated by the LED light were softer (p < 0.01). At both distances, the QTH light operated on the high power setting for 50% of the recommended exposure time produced composites that were as hard as when they were exposed on the medium power setting for 100% of the recommended exposure time.


CONCLUSIONS
The ability to reduce exposure times with high-power LED or QTH lights may improve clinical time management.
Felix
Corey A
CA
Dalhousie University, Halifax, Nova Scotia. rbprice@dal.ca
Price
Richard B T
RB
Andreou
Pantelis
P
D000180:Acrylic Resins / Q000528:radiation effects; D003188:Composite Resins / Q000528:radiation effects*; D003748:Dental Equipment; D006219:Halogens; D006244:Hardness / Q000528:radiation effects; D006801:Humans; D008027:Light; D008422:Materials Testing; D008963:Molar; D044367:Phase Transition; D011140:Polyurethanes / Q000528:radiation effects; D011829:Radiation Dosage; D012666:Semiconductors; D012822:Silicon Dioxide / Q000528:radiation effects; D013674:Technology, Dental / Q000295:instrumentation; D017748:Time Management; D015040:Zirconium / Q000528:radiation effects
D000180:Acrylic Resins; C029012:Composite Dental Resin; D003188:Composite Resins; C466112:Esthet-X; C474035:Filtek Supreme; D006219:Halogens; D011140:Polyurethanes; C121818:Tetric ceram; C083568:Z100 composite resin; D012822:Silicon Dioxide; D015040:Zirconium