Orthodontic Bracket Tensile Bond Strength of Recycled Bovine Enamel

Objectives: The purpose of this project was to determine if the tensile bond strength of orthodontic brackets on reused bovine tooth specimens is different from those bonded to new teeth.  If there is no difference, specimen recycling would produce considerable savings in costs and time.

Methods: Bovine incisor crowns were securely embedded in CPVC tubes with their labial surfaces slightly proud of the rim.  The enamel was flattened with sandpaper and cleaned with pumice.  The bracket (3M Unitek 0.022’’ stainless steel Victory series) bases were flattened with ~200 N load on an MTS Bionix 858 testing machine.  According to the manufacturer’s (3M Unitek) instructions, Transbond Plus Self Etching Primer was applied and the brackets were bonded with 0.152mm thick Transbond XT Adhesive Paste with a custom-made jig in a controlled temperature and humidity environment.  After incubation for eight days under controlled conditions, the brackets were de-bonded with the MTS Bionix 858.  The enamel was resurfaced and the above procedures were repeated.

Results:  Tensile bond strength decreased significantly (p = 0.0023) after resurfacing.

Bond Strength	n	Min (N)	Max (N)	Median (N)	Mean (N)	SD (N)
Initial	31	40	107	93	85.5	19.1
Resurfaced	31	38	105	71	71.5	22.2

Conclusions:  The results indicate that bovine enamel specimens should not be recycled when tested in tension.  The decrease in re-bonded strength may be due to changes in enamel rod anatomy as the DEJ is approached and/or bonding agent residue.

Supported, in part, by the Indiana University School of Dentistry Dental Student Research Fund.