Adhesive
interface between bracket and enamel is based on adhesion of resin-based
material to enamel and to bracket, the latter being typically reinforced by
mechanical retention of the bracket bonding surface. Bonding results are
influenced by brackets, adhesive systems and by composite resin between bracket
and enamel. The adhesion strength is also influenced by use of possible
reinforcing materials at the interface. The main objective of this study was to
study the behavior of resin composites at the bracket-tooth interface under different
loading conditions with or without use of intermediate layers of reinforcing
glass fibers. The orthodontic brackets were bonded using flowable composites
with different visco-elastic properties and the values of
debonding load and displacement were determined at the point of debonding. The degree of cure (DC %) of
the glass fiber reinforced adhesive layer underneath the bracket and irradiance
power of the light curing tip underneath the bracket was determined.
Furthermore, the creep behavior of the interface adhesive materials was studied
using orthodontic
bracket-tooth and three-point bending test models. The adhesive interface was
subjected to constant interfacial loading. To characterize the properties of
the adhesive interface materials used, nanomechanical (nanohardness and elastic
modulus) properties was evaluated. The
outcome of the experimental study demonstrated that the
incorporation of a glass-fiber reinforced composite (FRC) with a low elastic
modulus at the adhesive interface between the orthodontic bracket and enamel
increased the debonding force and strain compared to adhesive systems with
higher elastic modulus. An enhanced degree of cure of the photopolymerizable adhesive reinforced
with glass FRC was observed under the metal brackets. The creep test
demonstrated that the incorporation of
continuous glass fibers at the interface between orthodontic bracket and enamel
increased the creeping and debonding time of the bracket and that the orientation of the fibers and
the resin matrix type significantly affected the creep behavior of the adhesive
materials. From the above outcome, it
can be concluded that incorporation of glass FRC at the adhesive interface
could be beneficial considering the long duration of orthodontic brackets remaining in the oral cavity.