Biomedical Engineering Reference
In-Depth Information
(PCL) and their copolymers [21]. In the composites, glasses are often
added as particles or fibres.
In the treatment of bone defects around dental implants, easy applica-
tion of the filler material is desired. Glass particles are difficult to handle
and maintain in the defect site. A composite blended of particles of S53P4
glass and the thermoplastic biodegradable polymer poly(
-caprolactone-
co -DL-lactide) was discovered to be easy to inject into bone defects. It
stayed mouldable for a few minutes at body temperature after being
heated to 50 C, which is the melting point of the polymer [22]. The
composite showed improved bone response in vivo when compared to
polymer without glass particles.
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11.9 BIOACTIVE GLASSES IN GLASS IONOMER
CEMENTS
Glass ionomer cements are powdered fluoroaluminosilicate glasses
mixed with water-soluble polymers, usually poly(acrylic acid). After
mixing, the cement will harden. The glass ionomer cements are adhe-
sive, long-term fluoride-releasing materials used in dentistry as liners
and restorations. Their fluoride release improves remineralisation and
reduces the solubility of dentine and enamel. The glass ionomer cements
bond chemically to enamel and dentine. However, the poor mechanical
properties of glass ionomer cements have restricted their use as filling
materials mainly to cavities in primary teeth or areas not subjected to
high loading. Their low shrinkage has great benefits when they are used
to fill cavities.
The first in vivo results of the ability of bioactive glass-containing
glass ionomer cements to remineralise damaged dentine were reported
by Yli-Urpo et al . [23]. The mixture of two commercial glass ionomer
cements with powdered bioactive S53P4 glass (diameter
m) was
filled into cavities drilled in the teeth of dogs. The results suggested that
glass ionomer cements have the potential to mineralise dentine in vivo
[24]. However, the compressive strength and hardness of glass ionomer
cements in vitro decreased with increasing amount of bioactive glass.
Accordingly, bioactive glass-containing glass ionomer cements were
suggested only for applications where the bioactivity can be beneficial,
such as root surface fillings and liners, and where high compressive
strength is not needed. The decrease in the mechanical properties was
attributed mainly to the poor bonding between the polymer and the
glass. Modifications in the structure of the polymer have been reported
<
45
μ
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