RESUMO
This study analyses the damage done by three debonding procedures. Ceramic brackets (ORMCO) having a basic size of 12.3 mm2 were bonded with Concise Composite to 120 non-carious premolars extracted from adolescent patients and subsequently shorn off using a Zwick multipurpose testing device. In 90 teeth the brackets were removed once, in 60 twice, and in 30 three times. The shearing forces were measured electronically and evaluated statistically. In a separate experiment involving 30 teeth, the in-depth interlinkage (adhesive "pegs") were exposed by chemically dissolving the enamel. The enamel surfaces and adhesive matrix were analysed using scanning electron microscopy. Each repeat debonding was associated with a clear increase in the frequency and size of the enamel damage. This was, on average, 12% (in four teeth) at the first debonding, 17.4% (six teeth) at the second debonding, and 21.9% (nine teeth) at the third debonding, referred in each case to the exposed enamel surface after shearing off the bracket. The damage increasingly involved deeper regions within the enamel. The mean bonding force was 13.2 MPa at the first debonding, 16.1 MPa at the second debonding, and 15.5 MPa at the third. The differences are statistically significant (p < or = 0.05). It would appear that the increase in bonding force between the first and second bracket removal was due to a more pronounced adhesive matrix at the second bonding. The decrease in bonding force at the third debonding may be due to a structure of the enamel caused by the repeated debonding process.(ABSTRACT TRUNCATED AT 250 WORDS)