THERMAL DEBONDING OF CERAMIC BRACKETS - AN IN-VITRO STUDY

Thermal debonding has been developed to overcome the problems of ename l damage and high forces when debonding ceramic orthodontic brackets. However, the temperature changes with thermal debonding have the poten tial to damage the tooth tissues. The principal aims of this study are , first, to investigate the effects of resin type, resin thickness, an d debonding force on the temperature changes in human premolars during thermal debonding of ceramic brackets and, second, to record the site s of bond failure and damage to the tooth surface. Ceramic brackets we re attached to each specimen by using one of four types of bonding res in in a controlled thick or thin resin layer. The ceramic debonding un it (Dentaurum, Pforzheim, Germany) was used to thermally debond the br ackets with either a 40 or 80 Nmm torsional force. Higher temperature changes at the pulpal wall (> 10 degrees C in some 40 Nmm torsional fo rce specimens) always occurred with Concise (3M Dental Products, St. P aul, Minn.) and Transbond (Unitek/3M Dental Products, Monrovia, Calif. ) resins, and lower temperature changes (< 5 degrees C) with Quasar (R ocky Mountain Orthodontics, Denver, Cole.) and Ortho.B.S. (Dentaurum, Pforzheim, Germany) resins. In general, resin thickness was not signif icantly associated with buccal surface or pulpal wall temperature chan ges. However, temperature changes at the pulpal wall were significantl y associated with the temperature changes at the buccal surface (r = 0 .76), with the temperature of the thermal debonder blade for thin resi n layer specimens (r = 0.50), and the time required to debond the brac ket for both thick (r = 0.74) and thin (r = 0.63) resin layer specimen s. In most specimens, the site of bond failure occurred at the bracket -resin interface. There was no evidence of enamel damage after bracket removal.