Shrinkage and hardness of dental composites acquired with different curing light sources.
OBJECTIVE
Curing light sources propel the photopolymerization process. The effect of 3 curing units on polymerization shrinkage and depth of cure was investigated.


METHODS
The curing lights were a conventional and a soft-start quartz-tungsten-halogen (QTH) light source and a light-emitting diode (LED) source. The soft-start QTH and LED intensity outputs were 9% and 17% less than the conventional QTH source, respectively. For a 40-second light cure, the light energy was 32% and 14% lower, respectively. The light sources were applied to 4 restorative composites (microfilled, 2 hybrids, and nanofilled). For each light unit-composite combination, the development of postgel shrinkage during polymerization was measured with strain gauges (n = 15), and the Knoop hardness was tested at 0.5-mm-depth increments to assess degree of cure 15 minutes after polymerization (n = 5). The results were statistically analyzed with 2-way ANOVA at .05 significance level, followed by pairwise comparisons.


RESULTS
Both factors, light source and composite, significantly affected postgel shrinkage and hardness (P < .05). The conventional QTH unit generally produced the highest shrinkage and hardness (at composite surface and 2-mm depth). The soft-start QTH unit generated the least shrinkage but achieved the lowest depth of cure. The resulting values for the LED unit were mostly in between the results of the other 2 units.


CONCLUSIONS
Curing lights should provide sufficient light energy to thoroughly cure composite restorations, which might be achieved without compromising shrinkage stresses if initial intensity is reduced.
School of Dentistry, University of Minnesota, 515 Delaware Street SE, Minneapolis, MN 55455, USA.
Stephen S
SS
Clifford
Karla
K
Roman-Alicea
Daranee
D
Tantbirojn
Antheunis
A
Versluis
D003188:Composite Resins / Q000737:chemistry / Q000528:radiation effects*; D055117:Curing Lights, Dental; D003799:Dental Stress Analysis; D006219:Halogens; D006244:Hardness; D055115:Light-Curing of Dental Adhesives / Q000295:instrumentation*; D008422:Materials Testing; D044367:Phase Transition; D011874:Radiometry; D012666:Semiconductors; D013314:Stress, Mechanical
D003188:Composite Resins; D006219:Halogens