## 4 Discussion
### Enamel Loss Following Clean-Up Procedures  
Even though with a low ARI score the debonding may have a relevant influence, adhesive removal (clean-up) is the phase that produces the highest amount of enamel damage [29]. There are many tools available on the market for the adhesive removal and, although there is no agreement on which protocol to apply in this stage, it is believed that multi-step cleaning produces less damage than single-step procedures [19; 40]. [PERSON] et al. concluded that clean-up procedures with carbide burs alone may cause excessive enamel loss and leave a large amount of composite on the surface. Conversely, when combined to the multi-step rubber polishing kits, it showed some advantages in enamel loss prevention. Even though composite remnants were not completely removed, it gave a smooth and shiny surface that was visually assessed as an accurate clean-up [5]. [PERSON] et al. compared the efficacy of tungsten carbide burs with air abrasion [28]. They reported that air-abrasion with alumina particles was shown to cause more damage than the tungsten carbide bur, and the amount of enamel removed was far less predictable. Based on this finding, they stated that alumina particles are not suited for debonding procedures. Conversely the bioactive glass air-abrasion was found to be at least as good as the tungsten carbide bur in terms of enamel preservation [28]. The inherent characteristics and the clinical technique are also important. The divergent stream cuts mainly at the center and less at the periphery, resulting in an indistinct abrasion margin, making it easier to polish. In order to obtain those properties a proper distance and technique need to be used [28]. In the attempt to find the best tool, which should be able to be selective for the adhesive without harming the sound enamel, [PERSON] et al. tested a zircon-rich glass-fiber-reinforced composite bur [34]. This bur was developed for other purposes, but various studies showed that it can be safely used for debonding [17; 41]. They concluded that this composite bur is less detrimental than the tungsten carbide bur. Moreover, after debonding of conventional metal orthodontic appliances, composite bur followed by either polishing pastes or Sof-lex discs offered the best protection for enamel. Conversely, after ceramic bracket debonding, the authors reported that Sof-lex discs resulted as the most appropriate resin removal method [32]. Although lingual appliances represent a fixed alternative to clear aligners, especially for complex cases [42], only one paper investigated them [35]. The authors, focusing on clean-up aids, did not report if buccal or lingual brackets resulted in significantly higher enamel loss.  
In order to detect and remove adhesive properly, [PERSON] et al. and [PERSON] et al. tested a fluorescence-aided identification technique (FIT), comparing it with a conventional light source [33; 35]. [PERSON] et al. reported a high sensitivity of the FIT method which allows to reveal small composite remnants in difficult to find areas, for example, in grooves or pits. This technique also tolerates water cooling, thus limiting a potential temperature increase that may harm the pulp during a dry clean-up [43]. This finding was also supported by [PERSON] et al., who reported higher clean-up efficacy when FIT was used. Conversely, lingually, the FIT methods resulted in larger enamel defects. [PERSON] et al. also reported that the FIT method reduced the operating time significantly. The time required per tooth was on average 80 s with the FIT technique, whereas it was 130 s approximately with conventional light source [33].  
Among the included studies, the enamel volume loss following debonding ranged between 0.02 \(\pm\) 0.01 mm\({}^{3}\)[34] and 0.61 \(\pm\) 0.51 mm\({}^{3}\)[33]. Those results have different clinical significance based on the considered tooth. The same volume lost on a molar surface may have different significance compared to lower incisors.