Biomedical Engineering Reference
In-Depth Information
incorporated into orthodontic adhesive materials to prevent bacterial adhesion and caries during
orthodontic treatment.
One of the current challenges in adhesive dentistry using hybrid materials is over-hydrophilic
bonding formulations, which facilitate water percolation through the hybrid layer resulting in unre-
liable bonded interfaces. A recent study evaluated a nanogel-modified dentin adhesive composed of
BisGMA/HEMA (2,2-bis [4(2-hydroxy-3-methacryloyloxy-propyloxy)-phenyl] propane/2-hydroxy-
ethyl methacrylate)
[19]
. The nanogel additives of 10- to 100-nm-sized particles with varied hydro-
phobicity were synthesized in solution and added to BisGMA/HEMA. Nanogel copolymers at a
70:30 molar ratio of isobornyl methacrylate (IBMA) and either urethane dimethacrylate (UDMA—
less hydrophobic) or ethoxylated bis-phenol-adimethacrylate (BisEMA—more hydrophobic) was
used. Adhesive viscosity, wet mechanical properties, short-term microtensile bond strength to acid-
etched and primed dentin were studied. All these parameters evaluated were significantly enhanced
in the nanogel-adhesive group over the control group containing just BisGMA/HEMA. These recent
studies reinforce the importance of nanoscale-modified adhesive materials with improved properties
for their use in orthodontics.
11.5
Nanoparticle delivery from orthodontic elastomeric ligatures
Fixed orthodontic appliance treatment significantly increases the risk of enamel decalcification and
white spot lesions. These are caused due to prolonged accumulation and retention of bacterial plaque
on the enamel surface adjacent to the attachments (orthodontic brackets and bands). Demineralization
of enamel has been reported to occur around orthodontic brackets within 1 month of bracket
placement in the absence of fluoride supplementation
[31,32]
. Elastomeric ligature ties have been
conventionally used to hold orthodontic wires securely in the bracket during the treatment pro-
cess. These elastomeric ligatures can serve as a carrier scaffold for delivery of nanoparticles that
can be anticariogenic, antiinflammatory, and/or antibiotic drug molecules embedded in the elasto-
meric matrix. The release of anticariogenic fluoride from elastomeric ligatures has been reported
in the literature previously
[33
35]
. The studies concluded that the fluoride release was character-
ized by an initial burst of fluoride during the first day and second day, followed by a logarithmic
decrease. For optimum clinical benefit, the fluoride ties should be replaced monthly
[33]
. These
ties gained weight intraorally with residual, leachable fluoride present in fluoride-impregnated and
non-fluoride elastomeric ligature ties after 1 month of intraoral use, due to imbibition
[34]
.
An in vivo study evaluating the efficacy of fluoride-releasing elastomers in the control of
colony forming units (CFUs) of Streptococcus mutans in the oral cavity concluded that fluoride-
releasing elastomeric ligature ties are not indicated for reducing the incidence of enamel decalcifi-
cation in orthodontic patients. The study found no significant reduction in CFUs in saliva or plaque
around the fluoride-releasing ties when compared with the conventional elastomeric ligature
ties
[35]
. There are very few published studies evaluating the release and efficacy of nanoparticle-
based anticariogenic, antiinflammatory, analgesic, or antibiotic drug delivery from orthodontic elas-
tomeric ligatures to prevent enamel decalcification, decrease the biofilm accumulation during the
orthodontic treatment, or reduce infections. Medicated wax applied to orthodontic brackets that
slowly and continuously released benzocaine was shown to be significantly more effective in
