Related Experiment Video
Updated: Feb 9, 2026

Determining the Mechanical Strength of Ultra-Fine-Grained Metals
Published on: November 22, 2021
Shear bond strength of metal brackets on enamel
Paola Cozza1, Leonardo Martucci, Laura De Toffol
1Department of Orthodontics, University of Rome, Italy. p.cozza@flashnet.it
Objective:
To compare the shear bond strength of different metal orthodontic brackets.
Materials And 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.
Related Concept Videos
Bonding in Metals
Metal-Ligand Bonds
In these complexes, transition metals form coordinate covalent bonds, a kind of Lewis acid-base interaction in which both of the electrons in the bond are contributed by a donor (Lewis base) to an electron acceptor (Lewis acid). The Lewis acid in...
Bonding and Strength of Aggregate
Metallic Solids
All metallic solids exhibit high thermal and electrical conductivity, metallic luster, and malleability....
Ionic Bonds
When atoms gain or lose electrons to achieve a more stable electron configuration they form ions. Ionic bonds are electrostatic attractions between ions with opposite charges. Ionic compounds are rigid and brittle when solid and may dissociate into their constituent ions in water. Covalent compounds, by contrast, remain intact unless a chemical reaction breaks them.
Opposing Charges Hold Ions Together in Ionic Compounds
Ionic bonds are reversible electrostatic interactions between ions...
Ionic Bonding and Electron Transfer

