DENTAL MATERIALS
Polymerisation kinetics in a fibre reinforced resin-based composite
Nicoleta Ilie 1a*
Department of Operative Dentistry and Periodontology, University Hospital, Ludwig-Maximilians-Universität München, DE-80336 Munich, Germany
1
Dipl. Eng, PhD, Professor
a
Received: July 14, 2017
Revised: July 28, 2017
Accepted: August 24, 2017
Published: August 25, 2017
Academic Editor: Jean-François Roulet, DDS, PhD, Dr hc, Prof hc, Professor, University of Florida, Gainesville, FL, USA
Cite this article:
Ilie N. Polymerisation kinetics in a fibre reinforced resin-based composite. Stoma Edu J. 2017;4(3):164-170.
Abstract
DOI: 10.25241/stomaeduj.2017.4(3).art.1
Objective: The study aimed to evaluate the potential of a commercial fiber reinforced resin composite
(FRC) to be cured adequately also in increments larger than 2-mm.
Material and methods: One FRC (EverX Posterior, GC) was investigated by assessing in real-time the
degree of conversion (DC) and polymerisation kinetic at increasing depths (100-µm, 2-mm 4-mm
and 6-mm). In addition, a battery of mechanical properties - flexural strength, flexural modulus,
Vickers hardness, indentation modulus, creep – and the characteristics of the used curing light were
determined.
Results: One-way ANOVA revealed no significant difference in DC measured 300 s post-irradiation
in a depth of 100-µm and 2-mm (p = 0.281). Similarly, no significant difference was identified
between DC measured at 2-mm and 4-mm (p = 0.724), while the DC measured at 6-mm depth was
significantly lowest (p<0.001). The polymerisation kinetic was well described (R²>0.95) by a double
exponential sum function, distinguishing between the gel and the glass phase of the polymerisation
process. It allowed identifying a slower start of polymerization in depth, associated with a lower
maximal rate of C-C double bond conversion. The mechanical properties amounted (128.30±8.38)
MPa (flexural strength), (8.38±0.87) GPa (flexural modulus), (92.00±15.86) N/mm² (Vickers hardness),
(17.82±1.82) GPa (indentation modulus) and (3.35±0.84) % for creep.
Conclusions: While DC recorded in 2-mm and 4-mm depths were statistically similar, there is
evidence that the quality of curing in a depth of 4-mm is lower compared to the top of the specimen.
The mechanical properties were within the range of high viscosity bulk-fill resin-composites.
Keywords: fiber reinforced resin-based composite, degree of cure, polymerisation kinetics, bulk-fill,
mechanical properties.
1. Introduction
Fiber-reinforced resin-based dental composites
(FRC) are advanced restoratives, particularly
designed to be placed in load bearing areas. The
denomination FRC implies that the material is
composed of dissimilar constituents, involving a
homogeneous polymer matrix that is reinforced by
a stronger and stiffer fibrous constituent. The shape,
dimension, orientation and volume amount of fibers
are used to modulate the mechanical properties of
the FRC.
The shape of fibers is usually described by its
aspect ratio R, and is defined as the proportional
relationship between their length and width. To
achieve a high material strength, a high aspect
ratio is sought. In dental materials, an optimum
was estimated at ca. 5.2, 1 thus a fiber must be 5.2
time longer as it is wide. In addition to the aspect
ratio, the strength of a FRC is directly related to the
length of the reinforcing fibers. The critical fiber
length in dental FRC was shown to lie between 0.5
mm and 1.6 mm, 2 while fibers below these values
are inducing a lower reinforcement effect and
are considered to act similarly to fillers present in
particulate micro hybrid resin-composites. 3 A third
aspect influencing the strength of a FRC is the fiber
orientation that can be unidirectional or randomly
distributed. In continuous, unidirectional fiber
composites, high strength and stiffness is found in
the fiber longitudinal axis with very minor changes
from the matrix properties in the transverse direction.
In contrast, the material behaves macroscopically
homogenous and isotropic in randomly orientated,
discontinuous FRC. 4 It must however be considered
that, as demonstrated by Karbhari and Strassler, a
dental FRC having the highest strength does not
necessarily have the highest flexural stiffness or
the greatest capacity for energy absorption, 5 thus
the mechanical behavior of this particular material
category requires a battery of different tests to be
understood.
Beside improvements in mechanical properties
*Corresponding author:
Prof. Dr. Dipl. Eng. Nicoleta Ilie, Department of Operative Dentistry and Periodontology, University Hospital, Ludwig-Maximilians-Universität München, Goethestr. 70, DE-80336 Munich, Germany
Phone: +49-89-44005-9412, Fax: