Enamel loss due to orthodontic bonding with filled and unfilled resins using various clean-up techniques

An in vitro study using steel reference markers in the enamel of 100 premolars was carried out in order to determine the enamel loss resulting from each step in the placement and removal of bonded orthodontic attachments. Measurements were made by means of the optical system of a profile projector for orientation and positioning and a micrometer for quantification. Accuracy to within +/- 1 micron was achieved. The 10.7 micron of enamel lost during initial prophylaxis with bristle brush was greater than the 5.0 micron lost when a rubber cup was used, and the difference was statistically significant. A 90-second etch with phosphoric acid resulted in a mean loss of 6.9 micron, with no significant difference between liquid and gel forms. It was possible to clean up the unfilled resin with hand instruments only; this resulted in a mean enamel loss of 7.7 micron. Rotary instruments, however, were required for cleaning up filled resin. Within this group, more enamel was lost when the high-speed 7902 bur (19.2 micron) and green rubber wheel (18.4 micron) were used than when the low-speed 7111 bur (11.3 micron) was used. Total enamel loss ranged from 26.1 to 31.8 micron for unfilled resin and from 29.5 to 41.2 micron for filled resin, depending on the instrument used for prophylaxis and debonding. Twenty-seven of the teeth showed evidence of a perikymata-like structure after as much as 29 micron of enamel had been removed, questioning the reliability of anatomic landmarks as reference points in the study of enamel loss.