Date of Award

Spring 1991

Document Type

Thesis - Restricted

Degree Name

Master of Science (MS)

Department

Dentistry

First Advisor

Dhuru, Virendra B.

Second Advisor

Ferfuson, Donald J.

Third Advisor

Kittleson, Russell

Abstract

Ceramic brackets were introduced in response to a demand for aesthetic orthodontic appliances. Early ceramic brackets possessed excessive bond strengths leading to enamel fracture upon debonding. Recently, several manufactures have modified the retentive form of their bracket bases. The most recent modification in retention involves the fusion of small particles to bracket bases. A logical question to be explored would be: is there a specific resinbracket combination that will aid in removal of these new mechanically retained ceramic brackets, yet maintain adequate bond strength? This experiment was designed to evaluate the effect of changes in adhesive filler concentration on the tensile bond strength of two mechanically retained ceramic brackets. One hundred twenty bovine incisors were assigned to one of six treatment groups. The teeth were etched for 20 seconds and bonded with 30, 55, or 80 percent filled adhesive. After bonding, the teeth were stored in 37°C distilled water for 72 hours prior to testing. A custom fabricated alignment apparatus, a tensile debonding instrument, and an lnstron testing machine were utilized to apply a tensile force. The force needed to induce bond failure was recorded and the site of bond failure evaluated under a stereo microscope. The following conclusions were obtained: 1. There was no significant difference in the tensile bond strength between Unitek Transcend 2000 and American 20/20 ceramic bracket types. 2. Testing of adhesive type revealed that the 55 percent filled adhesive displayed a significantly greater tensile bond strength than the 30 percent filled adhesive. Hence, moderately filled adhesives produce significantly higher tensile bond strengths. 3. The tensile bond strength of the Unitek Transcend 2000 bracket bonded with 55 and 80 percent filled adhesives were equal and significantly greater than when bonded with 30 percent filled adhesive. In the American 20/20 treatment groups, the moderately filled adhesive (55 percent filled) produced higher but not significantly different tensile bond strengths. 4. No significant difference exists in the site of bond failures between bracket types. Both bracket types predominantly undergo failure at the bracket-adhesive interface. 5. No significant difference exists in the site of bond failure due to changes in the adhesive filler concentration.

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