Shear bond strength of metal brackets on enamel.
OBJECTIVE
To compare the shear bond strength of different metal orthodontic brackets.


METHODS
Five types of orthodontic metal brackets were selected (S1, Victory Series, 3M Unitek, Monrovia, Calif; S2, Mini Dyna-Lock, 3M Unitek; S3, Mini Sprint, Forestadent, Pforzheim, Germany; S4, Topic, Dentaurum, Inspringen, Germany; and S5, equilibrium 2, Dentaurum). Brackets were bonded on enamel surfaces of bovine incisors (Transbond XT, 3M Unitek) and were tested for shear bond strength with an Instron universal testing machine (Instron Corp, Canton, Mass). Data obtained in newtons and megapascals were analyzed with descriptive statistics and with analysis of variance and Tukey honestly significant difference (HSD) tests. The adhesive fracture site was classified with the adhesive remnant index (ARI).


RESULTS
All the specimens tested had shear bond strength adequate to resist orthodontic forces. S5 showed significantly greater bond strength when compared with the other samples, except for S1. S1, S3, and S5 showed a significantly greater bonding force. The ARI index demonstrated a large variability. Retentive structure of S1, S3, and S5 had equal validity. The enlargement of the retentive surface enhances adhesion but affects the adaptability to surface irregularity of the enamel, increasing the risk of fracture at the interface with the bracket.


CONCLUSIONS
The results of this study suggest that probably the retentive base extension can be lower than 7 mm2 proposed in previous studies as the minimal area.
Cozza
Paola
P
Department of Orthodontics, University of Rome, Italy. p.cozza@flashnet.it
Martucci
Leonardo
L
De Toffol
Laura
L
Penco
Santiago Isaza
SI
D000134:Acid Etching, Dental; D000268:Adhesiveness; D000818:Animals; D002417:Cattle; D003722:Dental Alloys / Q000737:chemistry*; D001840:Dental Bonding; D003743:Dental Enamel / Q000648:ultrastructure*; D003799:Dental Stress Analysis / Q000295:instrumentation; D004868:Equipment Failure; D007180:Incisor; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D016382:Orthodontic Appliance Design; D016910:Orthodontic Brackets; D019279:Resin Cements / Q000737:chemistry; D033081:Shear Strength; D013314:Stress, Mechanical; D013499:Surface Properties
D003722:Dental Alloys; D019279:Resin Cements; C477790:Transbond XT