Restorative

The following rheological studies of restorative materials have been published recently

2010

1. Initial dynamic viscoelasticity change of composites during light curing. Kim MH, Min SH, Ferracane J, Lee IB.
Dent Mater. 2010 May;26(5):463-70. Epub 2010 Feb 18.

A custom-made oscillation rheometer with parallel plate geometry(gap=2mm, frequency 6Hz), measured the increasing viscoelasticity of six commercial restorative composites during light curing at 25C(n=5). The possibility of predicting shrinkage stress relative to the continuously changing shrinkage strain and elastic modulus is discussed. There were great differences in the development of viscoelasticity in each material and in the time taken to reach a particular reference value of complex modulus.


2. Slumping tendency and rheological properties of flowable composites.
Lee IB, Min SH, Kim SY, Ferracane J.
Dent Mater. 2010 May;26(5):443-8. Epub 2010 Feb 18.
Slumping was assessed by measurement of aspect ratios and the complex viscosity by an oscillatory shear test (angular frequency 0.1-100rad/s.

Results Flowable composites demonstrated shear thinning behaviour, resistance to slumping increased with increased complex viscosity and there was significant variation between the five flowable composites.

2009

1. Effect of heat on the flow of commercial composites.
da Costa J, McPharlin R, Hilton T, Ferracane J.
Am J Dent. 2009 Apr;22(2):92-6.
18 conventional resin composites and four flowable composites were
tested at room temperature (23C). The conventional composites were also
tested at 54C and 68C. Thickness/volume (T/V) were compared for the composites
for the three temperatures.
RESULTS: At 23C, the flowable composites T/V were significantly less
than the conventional composites (P < 0.001). The T/V of the conventional composites were not significantly different at all three temperatures (P> 0.05),



2. Rheological properties of experimental Bis-GMA/TEGDMA flowable resin composites
with various macrofiller/microfiller ratio.
Beun S, Bailly C, Dabin A, Vreven J, Devaux J, Leloup G.
Dent Mater. 2009 Feb;25(2):198-205. Epub 2008 Jul 14.

Steady state shear tests over range of 0-30 reciprocal seconds, with cone and plate geometry, diameter 35mm and angle 1 degree, measured viscosity and Newtonian behaviour of unfilled mixtures(n=3). Filled experimental composites were tested with ARES rheometer using parallel plate geometry, diameter 25mm and gap 1mm. Time sweep tests at 0.1 rad/sec followed by frequency sweep test from 100 rad/sec to 0.01 rad/sec measured complec viscosity, storage and loss modulus and tan delta.(n=3) . All tests were carried out at 23C
Results: all unfilled mixtures as well as pure Bis-GMA and pure TEGDMA are Newtonian. Viscosity and shear thinning increased with increasing filler content. These results were compared with spacial organisation of particles using TEM and suggest that modifying chemical and physical surface properties could improve flow and handling performance.

2008

1. Slumping resistance and viscoelasticity prior to setting of dental composites.
Lee I, Chang J, Ferracane J.
Dent Mater. 2008 Dec;24(12):1586-93. Epub 2008 Apr 22.

Dynamic oscillatory test using AR 2000 Rheometer, parallel plate, diameter 8mm, gap 2mm, frequency 0.1-50rad/s, temp 25C tested three commercial compositesand compared with slumping resistance
Slumping resistance index (SRI) varied significantly between the composites and was strongly related to loss modulus.

2. Rheological properties of veneer trial pastes relevant to clinical success.
Chadwick RG, McCabe JF, Carrick TE.
Br Dent J. 2008 Mar 22;204(6):E11. Epub 2008 Feb 15.
Carri-med Rheometer with cone and plate geometry, diamter 20mm, angle 2 degrees, gap 0.07mm tested three shades of three veneer pastes at 25C and 35C (n=3). In this study, the authors have chosen to use yield stress and shear rate index as the outcome measure parameters.
Results: Temperature effects were not shown to be significant for most materials. One material showed significantly greater yield stress, which could affect handling properties.


3. Rheological properties of flowable resin composites and pit and fissure sealants.
Beun S, Bailly C, Devaux J, Leloup G.
Dent Mater. 2008 Apr;24(4):548-55. Epub 2007 Jul 30.
Eight flowable resin composites were tested with ARES Rheometer , parallel plate geometry, gap 1mm, frequency 0.01-100 rad/s, at 23C. Complex viscosity, loss and storage moduli and loss tangent were recorded. Four pit and fissure sealants which are of lower viscosity were tested with cone and plate geometry diameter 50mm, angle 0.02 rad. and frequency 0.1-100 rad/s. The filler weight content was determined by thermogravimetric analysis (TGA) and the morphology of the particles was investigated by scanning-electron
microscopy (SEM).
Results: No correlation was found between the rheological properties and the
filler weight content or the particles' shape.

2007

1. Time-dependent visco-elastic creep and recovery of flowable composites.
Baroudi K, Silikas N, Watts DC.
Eur J Oral Sci. 2007 Dec;115(6):517-21.

Creep behaviour of flowable composites was evaluated in relation to their filler
fraction and the postcure period. Flowables that had the highest percentage of filler produced the lowest creep strain. The creep response decreased with 1 month of preload storage. Clinically, the finding of this study suggests that flowable composites are unsuitable for stress-bearing areas.