Surface microhardness and depth of cure of composite resin cured with LED and Halogen units

Abstract

The aim of this study was to evaluate the surface hardness and depth of cure of
resin composites cured with a quartz tungsten halogen (QTH) lamp or a light emitting
diodes (LED) unit.
Swiss Tec (colten/whaledent AG, Switzerland) resin composite was placed in1, 2,
3, and 4 mm depth and 8 mm width metallic molds and cured using the QTH light or
the LED unit for 40s.
A total of 40 samples were made that divided into two groups according to the
type of curing light with 20 samples each. Each group was subdivided into 4 groups
according to the height of the mold with 5 samples each. Microhardness
measurements were performed using a calibrated Vickers indenter (100 g load and
30s dwell time). Measurement of depth of cure was carried out by means of hardness
ratio (bottom/top × 100).
Results were analyzed by paired student's t-tests (P < 0.05). Results showed that
LED exhibited higher microhardness values than QTH unit and the difference was
statistically significant (P = 0.03) at the top surface and highly significant (P = 0.001)
at the bottom surface.
Further more the results revealed that LED produced samples with hardness ratio
(depth of cure) higher than QTH unit and the difference was highly significant (P =
0.004) at 3 mm depth. Both curing lights inadequately cure samples at 4 mm depth.
Conclusions: Curing effectiveness of resin composite is better with LED than
QTH unit especially when the composite thickness exceed 2 mm.