Microhardness of composite resin cured through different primary tooth thicknesses with different light intensities and curing times: In vitro study.
OBJECTIVE
The aim of this study was to evaluate the effect of increased exposure time and light intensity on microhardness of cured composite through different thicknesses of tooth structure in primary teeth.


METHODS
One hundred and seventy cylindrical resin composite specimens were prepared. All specimens were divided into 17 experimental and control groups. "Light-emitting diode" light curing unit (LCU) applied directly or through 1, 2, and 3 mm thicknesses tooth slices for experimental groups. The irradiation protocols were 25 and 50 s at 650 mW/cm(2) and 15 and 30 s at 1100 mW/cm(2). The "quartz-tungsten-halogen" LCU (400 mW/cm(2)) for 40 s was used in control group. Microhardness was measured by the Vickers hardness test.


RESULTS
Indirectly cured specimens and those cured through a 1 mm thick tooth structure, an increase in intensity caused hardness drop. In the specimens cured through 2 and 3 mm thick tooth structures, increased intensity and/or exposure time did not show any appropriate changes on microhardness.


CONCLUSIONS
Irradiation through a 1.0 mm thick tooth slice resulted in reduced microhardness although it was still within the clinically acceptable level. The hardness values of the specimens cured through 2 or 3 mm thick tooth slices fell below the clinically acceptable level even after doubling the exposure time and/or light intensity.
Dental Material Research Center, Department of Pediatric Dentistry, School of Dentistry, Mashhad University of Medical Sciences, Mashhad, Iran.
Fatemeh
F
Mazhari
Oral and Maxillofacial Diseases Research Center, Department of Pediatric Dentistry, School of Dentistry, Mashhad University of Medical Sciences, Mashhad, Iran.
Behjatolmolok
B
Ajami
Department of Operative and Esthetic Dentistry, Dental Research Center, School of Dentistry, Mashhad University of Medical Sciences, Mashhad, Iran.
Saied Mostafa
SM
Moazzami
Pediatric Dentist, Private Practice, Mashhad, Iran.
Bahareh
B
Baghaee
Dentist, NIOC Health Organization, Mashhad, Iran.
Bahareh
B
Hafez
Composite resin; curing time; light intensity; microhardness; primary tooth