Evaluation of contraction stress, conversion degree, and cross-link density in low-shrinkage composites.
OBJECTIVE
The contraction stress, degree of conversion, and cross-link density (CLD) of the Venus Diamond (low-shrinkage), Filtek P90 (low-shrinkage) and Filtek Z350 XT composites were evaluated after photopolymerization by quartz tungsten halogen or light-emitting diode light curing units.


METHODS
Contraction stress measurements were performed on 60 samples fabricated in rings of photoelastic resin. The adhesive was applied and photoactivated, followed by insertion and photoactivation of the composites. The contraction stress (MPa) was measured using a polariscope. The measurements of degree of conversion (%DC) were determined from Fourier transform infrared (FTIR) spectra of the top and bottom surfaces on 60 specimens. Cross-link density was estimated from hardness measurements performed at the top and bottom surfaces on 60 specimens. The Knoop hardness number was measured, and the specimens were placed in absolute ethanol for 24 h. The hardness was again determined and the CLD was estimated from the percentage decrease in hardness (PD) occurring during ethanol exposure for each surface. The contraction stress and PD data were subjected to ANOVA and Tukey's test (5%). The DC data were subjected to one way analysis of variance on ranks followed by pairwise multiple comparisons using Tukey's test (5%).


RESULTS
The Venus Diamond composite exhibited lower contraction stress than other composites, with degrees of conversion similar to those of Filtek Z350 XT at both surfaces, and independent of the light curing unit. The PD value of Venus Diamond was also lower than that for the other composites.


CONCLUSIONS
The low-shrinkage Venus Diamond composite may potentially reduce stress at the restoration/tooth interface.
1 Department of Restorative Dentistry, School of Dentistry, University of North Parana , Londrina, PR, Brazil .
Anderson Rafael
AR
Aleixo
Ricardo Danil
RD
Guiraldo
Ana Paula Piovezan
AP
Fugolin
Sandrine Bittencourt
SB
Berger
Rafael Leonardo Xediek
RL
Consani
Américo Bortolazzo
AB
Correr
Alcides
A
Gonini-Júnior
Murilo Baena
MB
Lopes
D003188:Composite Resins; D008027:Light; D058105:Polymerization; D013314:Stress, Mechanical
D003188:Composite Resins