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Abstract
The aim of this study was to develop a method for measuring the slumping resistance of resin composites and to relate it to the rheological characteristics.
Five commercial hybrid composites (Z100, Z250, DenFil, Tetric Ceram, ClearFil) and a nanofill composite (Z350) were used to make disc-shaped specimens of 2 mm thickness. An aluminum mold with square shaped cutting surface was pressed onto the composite discs to make standardized imprints. The imprints were light-cured either immediately (non-slumped) or after waiting for 3 minutes at 25℃ (slumped). White stone replicas were made and then scanned for topography using a laser 3-D profilometer. Slumping resistance index (SRI) was defined as the ratio of the groove depth of the slumped specimen to that of the non-slumped specimen. The pre-cure viscoelasticity of each composite was evaluated by an oscillatory shear test and normal stress was measured by a squeeze test using a rheometer. Flow test was also performed using a flow tester. Correlation analysis was performed to investigate the relationship between the viscoelastic properties and the SRI.
SRI varied between the six materials (Z100 < DenFil < Z250 < ClearFil < Tetric Ceram < Z350). The SRI was strongly correlated with the viscous (loss) shear modulus G' but not with the loss tangent. Also, slumping resistance was more closely related to the resistance to shear flow than to the normal stress.
Slumping tendency could be quantified using the imprint method and SRI. The index may be applicable to evaluate the clinical handling characteristics of composites.
Figures and Tables
Figure 1
(a) Dimension of the aluminum mold used to imprint on composite discs.
(b) The procedure to make an imprint on a composite disc with the aluminum mold.
Figure 2
(a) The laser 3D profilometer used to scan the surface profiles of the replica stone casts of composite discs before and after slumped.
(b) 3D profiles of before and after slumped of composite discs of Z100 at 25℃.
Figure 3
Representative line profiles of before and after slumped of composite discs of Z100 at 25℃.
(a) Initial surface topography of Z100 right after imprinted with a square shaped mold.
(b) Post slumped surface topography of Z100 after three minutes.
The slumping resistance index (SRI) was defined as 
(Hi, Li: before slumping heights of the highest and lowest point from the base line respectively; Hs, Ls: after-slumping heights of the highest and lowest point from the base line respectively).
(Hi, Li: before slumping heights of the highest and lowest point from the base line respectively; Hs, Ls: after-slumping heights of the highest and lowest point from the base line respectively).
Figure 6
Rheological characteristics of composites as a function of strain at 25℃. (a) Elastic (storage) shear modulus G" (b) Viscous (loss) shear modulus G" (c) Loss tangent, tan δ
Figure 7
Logarithmic regression curve, y=aln(x-xo), fitted on the SRI of the composites as a function of viscous (loss) shear modulus G"
Table 2
a) The elastic (storage) shear modulus G', viscous (loss) shear modulus G", loss tangent Tan δ, and complex viscosity η* of composites at the frequency of 1Hz, strain of 0.08 in the strain sweep test at 25℃
b) Normal stresses measured by squeeze test, spreaded diameter measured by flow test and SRI at 25℃
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