Diapositive 1

1
Rheology of Flowable Resin Composites and Pits
and Fissures Sealants
Sébastien BEUN1-2, Christian BAILLY2, Jacques
DEVAUX2 Gaëtane LELOUP1 1School of Dentistry
and Stomatology, Université catholique de
Louvain, Brussels, Belgium 2High Polymers
Laboratory, Université catholique de Louvain,
Louvain-la-Neuve, Belgium
Sebastien.Beun_at_patd.ucl.ac.be
Introduction
Results
FLOWABLE COMPOSITES
FLOWABLE COMPOSITES

• A dental resin composite is a mixture of
  monomers in which an important amount of
  inorganic filler particles are included.

All the flowable resin composites used in this
study showed a NON-NEWTONIAN, SHEAR-THINNING
behaviour their complex viscosity decreased
dramatically as the frequency increased.
THIXOTROPY is demonstrated by monitoring the
evolution of the complex viscosity after having
performed a pre-shear simulating the flow of the
materials through syringes tips.

• Flowable resin composites are HIGHLY STRUCTURED,
  SHEAR-THINNING FLUIDS showing an ELASTIC
  BEHAVIOUR. Although they all belong to the same
  class of restorative materials, their was a huge
  difference between the viscosity of the most
  flowable one and the viscosity of the less
  flowable one (almost two decades).

ORGANIC MATRIX Newtonian
COMPLEX RHEOLOGICAL PROPERTIES

• Non-Newtonian shear-thinning
• Yield stress
• Thixotropy

COMPLEX RHEOLOGICAL PROPERTIES ARE DUE TO THE
PRESENCE OF INORGANIC FILLERS
Left recovery of the initial viscosity of the
materials after pre-shear. Right example of the
Point 4 Flowables recovery of initial viscosity
after transformation and curve fitting.
Complex viscosity of the flowable composites in
relation with the frequency of deformation.
The absence of Newtonian plateau at low
frequencies suggests the existence of a YIELD
STRESS under which the materials dont flow.
But no good correlation was made between the
rheological properties and the inorganic fillers
weight content
Do resin composites show complex rheological
properties?

• INORGANIC FILLER WEIGHT CONTENT

Flowable resin composites are highly filled
materials. Inorganic fraction values ranged from
45.0 for the Revolution Formula 2 to 66.2 for
the Filtek Flow.

• Today, there is very few scientific literature
  available dealing with the rheological properties
  of resin composites. The aim of this study was to
  investigate these properties in order to better
  understand and improve the clinical behaviour of
  resin composites.

The complex rheological properties of resin
composites depend probably more on

• the inorganic volume fraction
• the filler particles morphology
• the fillers surface treatments

providing the materials a strong
three-dimensional internal structure
Storage shear modulus (left) and loss tangent
(right) of the materials in relation with the
frequency of deformation.
THIXOTROPY
The storage modulus of elasticity tends to a
horizontal at low frequencies most of the time,
which is a characteristic of ELASTIC materials.
The loss tangent (the ratio between the loss
modulus and the storage modulus) confirms this
elastic behaviour since its values for most of
the materials tested are below 1.

• 7 flowable resin composites and 4 pits and
  fissures sealants were tested

COMPOSITES
SEALANTS

• Further studies are to be conducted in order to
  understand the mechanisms of the final
  rheological properties of resin composites and to
  control and improve their clinical behaviour.

• Admira Flow (Voco)
• Filtek Flow (3M-ESPE)
• FlowLine (Heraeus Kulzer)
• Point 4 Flowable (Kerr)
• Revolution Formula 2 (Kerr)
• Tetric Flow (Ivoclar/Vivadent)
• X-Flow (Dentsply)

• Clinpro (3M-ESPE)
• Delton FS (Dentsply)
• Estiseal F (Heraeus Kulzer)
• Guardian Seal (Kerr)

Inorganic fraction of the materials tested
measured with TGA.

• MORPHOLOGY OF THE FILLER PARTICLES

• Flowable composites were chosen in this study
  because of the importance of their rheological
  properties in their clinical indications but
  studies also need to be undertaken on universal
  resin composites to determine whether their
  rheological properties are comparable to those of
  the materials studied here.

PITS AND FISSURES SEALANTS

• Rheological measurements were performed at 23C
  with an ARES (TA Instruments, New Castle, DE,
  USA) dynamic oscillatory rheometer using a 25mm
  diameter parallel plates geometry and a gap of
  1mm.

PITS AND FISSURES SEALANTS

• Pits and fissures sealants have a lower filler
  content than flowable resin composites.

Most of the pits and fissures sealants studies
showed NEWTONIAN OR SLIGHTLY SHEAR-THINNING
BEHAVIOUR. Both the storage and loss moduli
continue to decrease at low frequencies,
indicating a LIQUID-LIKE BEHAVIOUR.

• INORGANIC FILLER WEIGHT CONTENT

There were high differences in the organic
fraction values for the pits and fissures
sealants tested. They ranged from 6.5 for the
Clinpro to 54.3 for the Delton FS.
PITS AND FISSURES SEALANTS ARE POORLY STRUCTURED
AND SHOW A LIQUID-LIKE BEHAVIOUR

• Pits and fissures sealants are NOT THIXOTROPIC

• But differences in the rheological properties of
  pits and fissures sealants compared to those of
  flowable resin composites can probably also be
  linked to other factors such as the organic
  fraction or different surface treatments of the
  filler particles.

• Parameters measured were

Complex viscosity in relation with the frequency
of the pits and fissures sealants tested.
Inorganic fraction of the materials tested
measured with TGA.

• MORPHOLOGY OF THE FILLER PARTICLES

• The inorganic filler weight content was measured
  using Thermogravimetric Analysis (TGA/SDTA861e,
  Mettler-Toledo, Greinfensee, Switzerland)

The authors would like to thank the manufacturers
for supplying the materials used in this
study. They also would like to express their
gratitude to Thérèse Glorieux for manipulating
the TGA and SEM.
Storage shear modulus (left) and loss tangent
(right) of the materials tested.

• The morphology of the filler particles was
  examined using Scanning-Electron Microscopy
  (Leica Stereoscan S-260, Cambridge, UK)

Again, the liquid-like behaviour as described
with the moduli is confirmed by the loss tangent,
which values are highly above 1.
It is to be noted that it was impossible to get
an image of the Clinpros filler particles due to
its very low inorganic fraction.