Initial dynamic viscoelasticity change of composites during light curing.
OBJECTIVE
The aim of this study was to measure the initial dynamic viscoelastic modulus change of dental composites during light curing using a custom made oscillation rheometer.


METHODS
Six commercial universal hybrid resin composites: Z100 (Z1), Z250 (Z2), Z350 (Z3), DenFil (DF), Tetric Ceram (TC), and Clearfil AP-X (CF) were examined. A custom designed oscillation rheometer was made, which consisted of three parts: (1) an oscillatory shear strain induction unit, (2) a measuring unit of parallel plates made of glass rods, and (3) a stress measurement unit. For the measurement of the initial viscoelastic modulus change of composites during light curing as a function of time, a dynamic oscillatory shear test was undertaken at a frequency of 6Hz and strain amplitude of 0.00579rad for 10s. From the strain-stress curves, the complex shear modulus (G*), storage shear modulus (G'), loss shear modulus (G'') and loss tangent (tandelta), and the time to reach a G* of 10MPa were determined. The data were analyzed with one-way ANOVA and Tukey's post hoc test (alpha=0.05).


RESULTS
There were great differences in the development of viscoelasticity among materials. At 10s, the complex modulus G* of Z1 was the highest (563.7MPa), followed by CF, Z2, Z3, TC, and finally DF being the lowest (150.3MPa). The time to reach the G* of 10MPa ranged from 2.55s (Z1) to 4.06s (DF). The tandelta of the composites decreased with time as the polymerization reaction proceeded.


CONCLUSIONS
The initial modulus development of composites during curing plays a very important role in determining the polymerization shrinkage stress. The custom made oscillation rheometer was able to measure the very initial dynamic viscoelasticity change of several commercial composites during light curing; therefore, the instrument can be used to study the initial curing kinetics of newly developed composites.
Kim
Min-Ho
MH
Department of Conservative Dentistry and Dental Research Institute, Seoul National University, Yeongeon-Dong, Jongro-Gu, South Korea.
Min
Sun-Hong
SH
Ferracane
Jack
J
Lee
In-bog
IB
D000704:Analysis of Variance; D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects*; D003799:Dental Stress Analysis; D004548:Elasticity; D055115:Light-Curing of Dental Adhesives; D008422:Materials Testing; D009991:Oscillometry; D012212:Rheology / Q000295:instrumentation; D033081:Shear Strength; D018709:Statistics, Nonparametric; D014783:Viscosity
D003188:Composite Resins