Biomedical Engineering Reference
In-Depth Information
mechanical properties of the composite materials
[14]
. Water sorption also results in increased overall
weight.
Solubility, leaching, and hydrolytic degradation is a result of either the breaking of chemical
bonds in the resin or softening through the plasticizing action of water
[15]
. When resin samples are
immersed in water, some of the components, such as unreacted monomers or fillers, dissolve and
leach out of the sample. The release of these components may influence the initial dimensional
changes of the composite, the clinical performance, the aesthetic aspect of the restoration, or the bio-
compatibility of the material
[15]
. Solubility therefore results in weight reduction.
Water sorption and solubility measurements were performed as described by Oysaed and Ruyter
[16]
. Ten disk specimens were used for each material. The diameter and the thickness of the speci-
mens were measured and the volume (
v
) was calculated. The disks were conditioned in a desiccator
for 3 days, containing calcium sulfate at 37°C until a constant weight had been achieved (
w
0
). The
disks were placed in a glass vial containing 100 ml of distilled water. The vials were wrapped by
aluminum foil to protect from light and placed in an incubator at 37°C and at intervals removed, blot
dried, and weighed. This was continued until the weight change/week was less than 0.32 μg (constant
weight—
w
1
). The disks were removed from the water and replaced in a desiccator for 24 h and then
reweighed for the last time (
w
2
). These steps were carried out to evaluate water sorption (WS) and
water solubility (WSL), in μg/cm
3
.
WS
w
w V
/
1
2
WSL
w
w
V
0
2
where
w
0
is the sample weight before immersion
w
1
is the sample weight after immersion
w
2
is the sample weight after immersion and desiccation
For water sorption and solubility, statistical differences were recorded when nanofilled compos-
ites were compared. The exclusive nanofilled composite, Supreme XT, was more susceptible to water
uptake. This can be explained by the higher contact surface of nanosized fillers. Samples cured with
halogen device were less sensitive in water (
Figures 4.5 and 4.6
).
4.8
MECHANICAL BEHAVIOR
In 1983, the composite resin materials were classified according to the average size of inorganic filler
that became a standard. Based on the size, composite resin is classified as macroparticulated or tradi-
tional (up to 50 μm), hybrid (8-30 μm), microhybrid (0.7-3.6 μm), and microparticulated or minifilled
(0.04-0.2 μm)
[8]
. Due to many differences between materials classified in the same group, other
methods for classification were suggested based on mechanical properties
[7,17]
.
Compressive strength, diametral tensile strength, flexural strength, and hardness have also been
evaluated
[18,19]
, due to a direct influence of composition in the mechanical behavior
[20]
. However,
different composites are available in the market and are classified just by inorganic filler size, sug-
gesting that resins of the same group would have similar mechanical behavior. Therefore, the follow-
ing described mechanical properties and results will show a dissimilar behavior.
