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.
Clifford
Stephen S
SS
School of Dentistry, University of Minnesota, 515 Delaware Street SE, Minneapolis, MN 55455, USA.
Roman-Alicea
Karla
K
Tantbirojn
Daranee
D
Versluis
Antheunis
A
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