The structure of dentin on three different levels, near enamel, central, and deep dentin, was examined. The solid area available for bonding was studied in a scanning electron microscope (JSM 840) connected to a computer‐assisted image analysis instrument (IBAS 2). The number of tubule openings per unit area (frequency) and the area percentages of these tubule openings were recorded. Three dentin disks were obtained from both buccally and occlusally located dentin of a single tooth (third molars were used), and the two deeper levels were each 1.25 mm deeper than the level above. The disks showed an increasing number of tubules with an increasing diameter the deeper into the dentin they were cut. Disks from the occlusal part of the tooth showed, in general, a higher number and area percentage of tubule openings than the corresponding disks from the buccal part. The variation across each disk was also larger for disks from the occlusal part than from the buccal part of the tooth. This variation increased with increasing depth of dentin. The most solid dentin with the lowest variation was found in superficial disks of buccally located dentin.

This study aimed at evaluating the early shear bond strength of enamel-composite-bracket adhesion accomplished without the use of liquid resin. Orthodontic brackets were bonded to the buccal surfaces of healthy extracted premolars in the test group by Transbond XT (n = 8) and Phase II (n = 8) composites but not the enclosed liquid resins in these products. Brackets bonded with the same materials (n = 8 for each) along with their corresponding liquid resin served as controls. The specimens were tested for shear bond strength after 24-h storage in water at 37 degrees C. The fractured surfaces were graded with Adhesive Remnant Index (ARI) under a 2x-dissection microscope. Enamel of the randomly selected test and control specimens was dissolved by 20% formic acid. Afterwards, the enamel side of the bonding materials in both groups (n = 4) was examined under the scanning electron microscope. ANOVA was used for statistical analyses. Our laboratory data suggest that the enamel adhesion produced by these two commercial materials without the use of liquid resin does not differ significantly in their early in vitro shear bond strength.

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