[Enamel abrasion and enamel tears by porcelain brackets].
Orthodontic brackets manufactured of poly- or monocrystalline alumina ceramics are aesthetically appealing, but unfortunately show disadvantages for clinical application primarily causing (1) Abrasions of the enamel of antagonistic teeth, and (2) Tear-outs of the underlying enamel through debonding. To determine whether hardness and/or textural and structural qualities of the ceramics (as characterized by SEM investigations) are responsible for the deleterious clinical effects of abrasion, the amount of decrease of the height of human enamel-molar-cusps was measured. Enamel loss was shown to be significantly more than 100 microns at 10 min. operating time in an abrasive testing device. Also debonding of the ceramic brackets proved to be problematic. Whereas metals and polymeric brackets allow some deflection of the material in addition to the tensile stress, separating the bracket from the enamel at the bracket-to-adhesive interface, or within the adhesive composite, the lacking workability in the ceramic brackets may induce a shift of the break-line during debonding to the adhesive-enamel interface or even into the dental enamel. Development and clinical application of ceramic brackets should improve safety for the enamel. Regardless of ceramic brand the abrasiveness endangers enamel through ceramic/enamel interferences. To avoid tear-out defects, brackets should debond at the ceramic-adhesive interface.