## 4 Discussion
### Effects of Dental Bleaching on Composite Restorations  
In the literature, the effect of bleaching on composites has been evaluated in a few randomized controlled trials, which examined mainly microhybrid resins and nanocomposites. Composites are resin-based monomeric materials, which have now replaced metal and amalgam, in dental restoration procedures after caries removal. Composites are made up of two or more materials useful to provide more performing characteristics or to add additional functionality to the original components [69; 70; 71]. With the development of micro/nano-science and technology, other filling materials and natural minerals in various shapes and sizes have been added to the traditional composite resins made of quartz filler and strontium or barium glass, resulting in an improvement in mechanical qualities [70]. The materials used as filler in nanofilled are Zirconia/Silica and nanosilica, while hybrid composite resin is a combination of macrofilled and microfilled [72; 73].  
The randomized controlled clinical trial of [PERSON] et al. analyzed the effect of 15% CP bleaching gel for at-home use on two types of composite resin restorations, namely nanocomposite and microhybrid. The parameters evaluated when taking digital photographs are color patterns, opacity, and fluorescence. At 2 weeks, microhybrid composites show superiority in terms of color patterns. On the other hand, the mean opacity and fluorescence values show no statistically significant differences [72].  
[PERSON] et al. also evaluated the at-home bleaching procedure with 10% CP in a randomized controlled trial on anterior maxillary teeth. The parameters analyzed this time was color changes and TS, comparing decayed teeth and non-decayed teeth at week 2 after whitening. The authors concluded that there is a lower degree of whiteness in teeth that had undergone a restoration compared to healthy ones. On the other hand, regarding TS being the most frequent side effect of a bleaching procedure, they did not detect any statistically significant difference [74] (Table 8).  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Authors** & **Type of the Study** & **Aim of the Study** & **Materials** & **Results** \\ \hline \hline  & & Sixty class V cavities in maxillary & \\  & & premolars. Teeth were divided in & \\  & & & 4 groups: & \\  & & Group A (control): 15 specimens, & \\  & & light nanocomposite resin (Filtek & \\  & & Z350 XT) with no post-restoration & \\  & & bleaching procedure (control): & \\  & & Group B (experimental): & \\  & & 15 specimens, light nanocomposite & \\  & & resin (Filtek Z350 XT) with & \\  & & post-restoration bleaching & \\  & & procedure, & for color patterns. No \\  & & & differences in mean \\  & & microhybrid resins. & \\  & & & \\  & & & \\ \hline \hline  & & Forty patients divided in 2 groups. & \\  & & Group A: 20 patients with 6 & \\  & & and TS after 10\% CP & \\  & & at-home bleaching in & \\  & & sound and restored teeth. & \\  & & & \\ \hline \hline  & & & \\ \end{tabular}
\begin{tabular}{c} [PERSON] et al., 2010 [74] \\ [PERSON] et al., 2010 [74] \\ [PERSON].  
From these works, it can be assumed that it is not rational to change the type of restoration after a bleaching procedure in the absence of aesthetic problems and that it may be necessary, after bleaching, to replace the restorations to achieve better aesthetic results.