FRACTURE INCIDENCE ON DEBONDING OF ORTHODONTIC BRACKETS FROM PORCELAIN VENEER LAMINATES

The bonding force and the incidence of porcelain fracture for two porcelain systems, on removal of orthodontic brackets bonded to porcelain veneer laminates after thermocycling, were determined. A factorial design with a total sample size of 256 was used. The factors tested were (1) porcelain type (feldspathic [porcelain CE] or high alumina [porcelain VI]), (2) surface treatment (glazed or roughened), (3) priming agent (silane or alcohol), (4) bonding resin (macrofilled or microfilled), and (5) debonding time (30 minutes or 24 hours). An analysis of variance revealed that surface treatment, primer, resin type, and debonding time each contributed significantly to the debonding force. The probability. of porcelain fracture was dependent on the porcelain type and the debonding force, with porcelain VI exhibiting a significantly higher probability of fracture than porcelain CE at the same debonding force. The etched surface of porcelain CE exhibited a more retentive microstructure than porcelain VI. The success of using bonded orthodontic brackets on porcelain veneer laminates depends on both the bond of resin to porcelain and the resistance of porcelain to fracture during debonding. For a given porcelain veneer, factors that provide a higher debonding force result in a higher probability of porcelain veneer fracture.