## 4 Discussion  
The aesthetic appearance of teeth after debonding of the orthodontic appliances is a primary concern for both the patient and the orthodontist. However, orthodontic treatment may present a risk factor for tooth discoloration. This study evaluated the effect of orthodontic bracket type and adhesive system on tooth color change. Metal and ceramic brackets along with etch and rinse and self-etch adhesives were investigated. Considering that the sensitivity of the human eye in detecting small color differences is both restricted and subjective, a spectrophotometer was used in the study to provide a consistent and objective assessment of the tooth color changes in response to the different procedures tested. Tooth shades were measured before the placement of the brackets and after debonding. Before debonding, the teeth were subjected to 7500 thermal cycles, simulating more than 7 months of clinical use [15]. Thermocycling simulated the temperature changes that occur in the oral cavity and is a substitute for time-consuming and costly clinical studies [16]. The study results revealed that the ceramic brackets were associated with significantly less tooth discoloration compared with metal brackets. Therefore, the first null hypothesis was rejected. To our knowledge, no previous studies have compared the effect of the bracket type, whether metal or ceramic, on tooth discoloration after debonding. [PERSON] et al. [17] evaluated the tooth color change of bonded metal and ceramic brackets after they were subjected to different beverages. Consistent with our results, teeth with metal brackets showed a greater color change than those with ceramic brackets. They attributed their results to the possible corrosion of the metallic orthodontic appliances when subjected \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Groups**} & \multicolumn{2}{c}{**Mean**} & \multicolumn{2}{c}{**95\% CI of the Difference**} & \multirow{2}{*}{\(p\)\({}^{*}\)} \\  & & **Difference** & & **Lower** & & **Upper** \\ \hline \multirow{4}{*}{Group A} & Group B & \(-\)3.39 & \(-\)6.81 & 0.04 & 1.000 \\  & Group C & 3.03 & \(-\)0.40 & 6.45 & 0.121 \\  & Group D & \(-\)0.50 & \(-\)3.93 & 2.92 & 1.000 \\  & Group E & \(-\)0.54 & \(-\)3.97 & 2.89 & 1.000 \\  & Group C & 6.41 & 2.98 & 9.84 & 0.003 \\ Group B & Group D & 2.88 & \(-\)0.55 & 6.31 & 1.000 \\  & Group E & 2.84 & \(-\)0.58 & 6.27 & 1.000 \\  & Group D & \(-\)3.53 & \(-\)6.96 & \(-\)0.10 & 0.121 \\  & Group E & \(-\)3.57 & \(-\)7.00 & \(-\)0.14 & 0.091 \\ Group D & Group E & \(-\)0.04 & \(-\)3.46 & 3.39 & 1.000 \\ \hline \hline \end{tabular} \({}^{*}\)Dunnett test for nonparametric multiple comparison; Significance values have been adjusted by the Bonferroni correction for multiple tests.  
\end{table} 
Table 6: Multiple comparison between the different groups tested. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Delta** & **Group A** & **Group B** & **Group C** & **Group D** & **Group E** & \(p\)\({}^{*}\) \\ \hline Mean & 5.03 & 8.42 & 2.00 & 5.54 & 5.57 \\ SD & 2.61 & 5.66 & 0.89 & 4.43 & 3.63 & 0.006 \({}^{*}\) \\ \hline \hline \end{tabular} \({}^{*}\)Statistically significant at \(p\) value \(<\) 0.05.  
\end{table} 
Table 5: Comparison of means and SDs of \(\Delta\)E among the different groups tested using Kruskal-Willis nonparametric test. to staining beverages with low pH. In our study, no staining beverages were used, but the teeth were subjected to thermocycling. In addition to the environmental conditions present in the oral cavity, thermocycling has been reported to affect the structural stability of the brackets, resulting in the release of metal ions and the decrease of their corrosion resistance [18,19]. According to [PERSON] et al. [20], metal ions (mainly chromium and nickel) released by corrosion of the orthodontic brackets may diffuse through the adhesive system and even penetrate into the tooth enamel in a process known as metallosis.