Effects of fl uoride release from orthodontic bonding materials on nanomechanical properties of the enamel around orthodontic brackets

Abstract

Background: The aim of the present study is to evaluate the effects of a fl uoride-releasing

composite resin bonding material on reducing enamel demineralization underneath and around

orthodontic brackets and compare that with a conventional adhesive system.

Materials and Methods: Buccal surfaces of 10 intact extracted premolar teeth were divided

into two parts with nail varnish and stainless steel brackets were randomly bonded by two resin

composite systems: (Transbond XT) and (Transbond XT plus Color Change) (3M, Unitek, Monrovia,

CA, USA) on two sides of the teeth and then samples were placed in a demineralization solution. It

is claimed that the second system has the ability of fl uoride release. Elastic modulus and hardness of

enamel were measured with nanoindentation test in 6 depths in 1-36 μm from the enamel surface

and in 7 regions: Control (intact enamel surface), underneath the brackets and also 50 and 100 μm

from the brackets edge. These nanomechanical features were evaluated in different regions and

depths using analysis of variance and paired t-test (P < 0.05).

Results: Considerable difference can be seen in different depths and regions in terms of hardness

and elastic modulus. The region under the bracket with fl uoridated adhesive shows similar results

with intact enamel, whereas these parameters in fl uoride less side show a signifi cant reduction

(P < 0.05).

Conclusion: Results show that use of resin composite bonding system with the ability of fl uoride

release for bracket bonding, may reduce demineralization of enamel around brackets during

orthodontic treatment.

Key Words: Elastic modulus, enamel demineralization, fl uoride releasing adhesive, hardness nanoindentation