## 4 Discussion
In cases of intense bracket oxidation, tooth staining may occur, requiring, in extreme situations, aesthetic restorations [21]. Such a color change was confirmed by the findings of our study, where tooth color change after debonding of the metal brackets was considered \"appreciable\" according to the NBS scale. The other variable investigated in our study was the type of adhesive system used to bond the ceramic brackets. Less tooth discoloration was recorded with the use of the etch and rinse adhesive compared with the self-etch adhesive, which also led to the rejection of the second null hypothesis. Both in vitro and in vivo studies have reported conflicting results regarding the effects of orthodontic adhesive systems on tooth color change [22]. The separate etching step with the use of etch and rinse adhesive results in the dissolution of the superficial enamel and allows for subsequent penetration of the adhesive. In contrast, the self-etch adhesives simultaneously demineralize and penetrate the enamel's surface [23]. When the adhesive is polymerized, the formed resin tags have been reported to be shorter with the use of self-etching primers in comparison with the use of the conventional etching technique [24,25]. The effect of the length of formed resin tags on tooth color change is unclear. [PERSON] et al. reported that the two etching techniques (E&R and SE) had no statistically significant effect on tooth color difference and that the depth of the resin tag did not influence short-term superficial discoloration [26]. In contrast, [PERSON] et al. and [PERSON] et al. reported a reduced color change using self-etching techniques and attributed this to the formation of shorter resin tags [3,23]. The results of our study do not support this finding and are more aligned with those of [PERSON] et al., who reported that the use of SEPs with orthodontic adhesives showed increased tooth color change after debonding owing to their greater stain susceptibility [4]. According to [PERSON] et al., a thin residual adhesive layer of an average thickness of 31.2 to 200.2 \(\upmu\)m remains on the enamel surface after debonding of the brackets and even after polishing [27]. This layer is susceptible to discoloration partly due to endogenous changes related to the structural properties of adhesives. The chemical composition of adhesive, the quality of polymerization, and curing time could all play a role in the color stability of the adhesive resin and hence of the color stability of the enamel surface when residual resin remains on the enamel surface after debonding [22]. In clinical situations, these factors would be heightened by exogenous factors related to the consumption of staining food and beverages [28]. When comparing the four test groups of the current study, group C, where the teeth received ceramic brackets bonded using a three step E&R adhesive system, showed the least amount of color change. In contrast, in group B, where the teeth received metal brackets bonded with self-adhesive cement, the highest color changes were found. The difference could be explained by the combined effect of the individual variables, the bracket types and adhesive systems used, as discussed earlier. The teeth in group E, which served as control without any bonding procedure, showed a color change after thermocycling that is considered appreciable according to the NBS system. Delta E values in that group were not significantly different from those in all other test groups except group C (Table 6). Tooth color change after thermocycling may be from an increase in enamel surface roughness when subjected to cyclic thermal changes in water baths, as reported by [PERSON] et al. [29]. [PERSON] et al. demonstrated that alteration of the surface roughness of natural teeth does have an effect on the lightness of the tooth color due to alteration in the surface reflectance of the enamel surface [30].