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Introduction
Composite materials based on dimethacrylate resins are
widely used in dentistry for the restoration of teeth’s
tissues. They have excellent mechanical and esthetic
properties, as well as the ability to bond to the enamel.
However, in a humid oral environment, these composites
can absorb water based liquids, such as saliva and
beverages, which can significantly affect the degradation
of the dental composite [1] and leach unreacted
monomers [2]. Excessive fluid absorption can have a
detrimental effect on the structure and function of the
resin [2], as it can reduce the mechanical and physical
properties, leading to a shortened life of the dental
restoration, and cause the filler to separate from the
matrix [3,4]. The purpose of this study was to determine
the water sorption characteristics and wetting angle of
light-curing resins blend modified with liquid rubber.
Materials and Methods
The material used in the study was a resin mixture with a
composition of 20% wt. BisGMA, 30% wt. BisEMA, 30%
wt. UDMA and 20% wt. TEGDMA. The Hypro
2000X168LC VTB liquid rubber (Huntsman International
LLC, USA) was used as a modifier at 0%, 5%, 10%, 15%,
20% by weight in the resin mixture. Five samples of each
material were prepared for water sorption tests. The test
method was in accordance with ISO 4049. Samples were
dried to a constant weight, then incubated in distilled
water at (37±1)°C for 7 days, and daily sample weight
measurements were taken. Wetting angle measurement
was realized using water of very high quality, the liquid
was dispensed at 2μl. The samples were tested 24 hours
after polymerization (kept dry). The study was conducted
to demonstrate the effect of liquid rubber modification on
the wetting angle values.
Results and Discussion
Results of the mass change measurements (in percent)
are shown in FIG. 1. A dynamic increase in the mass of
the samples was observed during the first three days of
incubation, after which the growth rate decreased until
saturation was reached. The largest changes in mass
were observed for samples with 15 and 20 percent liquid
rubber content and for the control sample.
Modification with liquid rubber significantly increased the
water contact angle (FIG. 2). Almost all samples showed
hydrophobicity (Θ > 65). A raise in the value of the
contact angle was observed as the amount of liquid
rubber increased. The reasons for the increase in
hydrophobicity of liquid rubber modified samples were
due to changes in surface topography as well as
physicochemical factors. BisGMA resin, as the main
component of the composite matrix, has hydroxyl groups,
while liquid rubber is non-polar, which favors an increase
in the wetting angle.
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