Marginal adaptation and hardness of resin composite restorations activated with four energies.
OBJECTIVE
The purpose of this study was to evaluate the influence of variations in light intensity versus exposure time, under the same energy density, on the marginal adaptation and hardness of resin composites restorations.


METHODS
The occlusal surfaces of 20 third molars were flattened with 180-grit SiC paper and a Class I cavity was prepared (4 mm wide, 4 mm long, and 2 mm deep). The specimens were randomly divided into four groups (n = 5 teeth). The adhesive system was applied according to the manufacturer's directions followed by one increment of Filtek Z250. The resin composite was light activated with 18 J/cm(2) according to one of the following light intensities/exposure times: group 1-100 mW/cm(2)/180 s; group 2-300 mW/cm(2)/60 s; group 3-600 mW/cm(2)/30 s; group 4-1,000 mW/cm(2)/18 s. After 24 hours, the restorations were longitudinally sectioned into two halves. Enamel, bottom, and total mean gap widths (in micrometers) were measured with a stereomicroscope (x200). After that, one of the sections was embedded in acrylic resin and polished up to 4,000-grit SiC for Knoop hardness number (KHN) measurements (100 g/15 s) at the top and bottom surfaces. The data from mean gap widths were analyzed by one-way analysis of variance (ANOVA). The KHN values (kg/mm(2)) were subjected to a two-way, repeated-measures ANOVA (a = .05). Tukey's test was used for pairwise comparisons.


RESULTS
No significant difference was observed between total and bottom mean gap widths among groups (p > .05). Group 1 showed lower enamel mean gap widths than did groups 3 and 4 (p < .05) but similar to those for group 2 (p > .05). The KHN at the top surface was higher than the bottom hardness (p < .05). For the bottom surface, all groups had similar KHN values (p > .05).


CONCLUSIONS
The variations in light intensity and exposure times allowed the achievement of adequate mechanical properties. The use of a low light intensity reduces only the enamel mean gap width but has no effect on the overall gap formation along the composite-tooth interface.


CONCLUSIONS
As long as an adequate energy density is used to produce adequate mechanical properties in the resin composite, the use of a low light intensity for an increased time does not markedly improve marginal integrity.
da Silva Segalin
Aline
A
Dental School, University of Oeste de Santa Catarina, Joaçaba, Brazil.
Fernandez
Dalexandra Manuella
DM
de Oliveria Bauer
José Roberto
JR
Loguercio
Alessandro Dourado
AD
Reis
Alessandra
A
D000704:Analysis of Variance; D003188:Composite Resins / Q000528:radiation effects*; D003748:Dental Equipment; D018772:Dental Marginal Adaptation; D003799:Dental Stress Analysis; D006219:Halogens; D006244:Hardness; D006801:Humans; D008027:Light; D044367:Phase Transition; D011874:Radiometry; D011897:Random Allocation; D018709:Statistics, Nonparametric; D013997:Time Factors
D003188:Composite Resins; C444701:Filtek Z250; D006219:Halogens