Effect of bracket bonding on nanomechanical properties of enamel.
BACKGROUND
In this study, we investigated the nanohardness and elastic modulus of enamel after debonding metal brackets.


METHODS
The surfaces of 3 maxillary premolars were subdivided into 3 regions. Two regions were exposed to a conventional etching system (Transbond XT, 3M Unitek, Monrovia, Calif) and a self-etching system (Transbond Plus primer, 3M Unitek); the third region was not etched. Metal brackets were bonded with Transbond XT composite to the 2 etched regions. After storage for 24 hours in distilled water, the brackets and residual adhesive were removed, and the teeth were sectioned transversely. Seven nanoindentations (2 mN load) were placed 1 to 25 μm from the surface in each region. Mean nanohardness and elastic modulus were compared with analysis of variance (ANOVA) and the Scheffé test.


RESULTS
Locations 1 and 5 μm from the enamel surface had significantly (P < 0.05) lower nanohardness and elastic modulus values for the conventional system compared with the self-etching system and the unetched region. All other locations for the conventional system and all locations for the self-etching system and unetched area had no significant differences. The nanohardness was much higher than the Vickers hardness for enamel.


CONCLUSIONS
The minimal effect of the self-etching system on the nanomechanical properties of enamel arises from much lower chemical attack. The much greater effects of the conventional system require further study.
Division of Orthodontics and Dentofacial Orthopedics, Department of Oral Growth and Development, School of Dentistry, Health Sciences University of Hokkaido, Ishikari-Tobetsu, Hokkaido, Japan. iijima@hoku-iryo-u.ac.jp
Masahiro
M
Iijima
Takeshi
T
Muguruma
William A
WA
Brantley
Shuichi
S
Ito
Toshihiro
T
Yuasa
Takashi
T
Saito
Itaru
I
Mizoguchi
D000134:Acid Etching, Dental / Q000379:methods; D001641:Bicuspid / Q000648:ultrastructure; D001696:Biomechanical Phenomena; D003188:Composite Resins / Q000737:chemistry; D003722:Dental Alloys / Q000737:chemistry; D001840:Dental Bonding; D003743:Dental Enamel / Q000648:ultrastructure*; D055119:Elastic Modulus; D006244:Hardness; D006801:Humans; D008422:Materials Testing; D036103:Nanotechnology; D016910:Orthodontic Brackets; D019279:Resin Cements / Q000737:chemistry; D013314:Stress, Mechanical; D013997:Time Factors; D014867:Water / Q000737:chemistry
D003188:Composite Resins; D003722:Dental Alloys; D019279:Resin Cements; C429625:Transbond Plus Self-Etching Primer; C477790:Transbond XT; D014867:Water