# Low-Level Laser Therapy for Tooth Sensitivity after Tooth Bleaching: A Systematic Review
## 4 Discussion  
This systematic review summarizes the best available evidence regarding the effectiveness of low-level laser therapy (LLLT) for managing tooth sensitivity (TS) following tooth bleaching (TB). Although the outcomes do not represent a consensus, it appears that laser application after TB is an effective and safe option for controlling tooth sensitivity. Six RCTs were included in this systematic review, which evaluated the efficacy of LLLT in the prevention of TS after in-office TB compared to a control group [5; 27; 28; 29; 30] or other desensitizing agents [29; 30; 31]. The majority of these studies [27; 29; 30; 31] demonstrated positive  
Figure 3: Quality assessment of all studies included per domain according to the revised Cochrane assessment tool RoB 2. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & & & & & & & \\ \hline [PERSON] et al., 2016 [27] & + & – & + & + & + & – \\ \hline [PERSON] et al., 2017 [28] & + & – & + & – & + & – \\ \hline [PERSON] et al., 2018 [29] & + & – & + & + & + & – \\ \hline [PERSON] et al., 2021 [30] & + & – & + & + & + & – \\ \hline [PERSON] et al., 2021 [31] & + & – & + &? & + & – \\ \hline [PERSON] et al., 2022 [5] & + & – & + & + & + & – \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Risk of bias of included studies according to the revised Cochrane assessment tool RoB 2. [(+): low risk of bias; (–): high risk of bias; (? ): some concerns)]. results with LLLT for addressing post-bleaching TS, whereas two studies [5; 28] found that the parameters tested were not effective in preventing TS. Heterogeneity is evident across the studies included. Four out of six of the studies [5; 28; 29; 30] were conducted in Brazil, one in Iran, and one in Saudi Arabia. Two of the papers received funding (grant or scholarships), while two were supplied with the whitening kit or the laser device. The number of participants ranged from 39 to 83, with differences in the recall period and the follow-ups after TB. In addition, various adjunct products, such as KNO\({}_{3}\), NaF, and strontium chloride (SrCl\({}_{2}\)), were combined with the main therapy in certain subgroups. The HP used had a concentration of either 35% or 40%, and one, two, or even three bleaching sessions were applied in the different studies. The parameters of LLLT were also non-homogenous across the studies, with wavelengths varying between 660 nm and 900 nm, output power falling between 40 and 200 mW, and energy ranging from 12 to 100 J/cm\({}^{2}\) (refer to Table 2); it does not appear that any specific parameters are more effective for the treatment of tooth sensitivity. Furthermore, the study design varied, with four of the studies having a parallel design [5; 27; 28; 31], while the other two employed a split-mouth design [29; 30]. The latter, although beneficial for reducing the number of patients recruited and minimizing inter-subject variability (as each participant serves as their own test and control), has some limitations that should be taken into consideration. In particular, these include the 'carry-across effect', which refers to the potential leakage of effects from one treatment site to another, and the influence of combining different treatment approaches at separate sites, which may affect the patient's assessment of pain for each treatment independently [34; 35]. Five of the studies included had a placebo-control group; only [PERSON] et al. [31] did not. The inclusion of a placebo group offers the advantage of maintaining patient blinding, especially when the two treatments cannot be made identical. This approach enhances the study's statistical power and internal validity while reducing the risk of ascertainment bias [36]. Two studies [5; 27] evaluated color change following bleaching as well. Both showed a significant whitening effect on teeth measured thirty days after TB for all groups, with no difference between them. This suggests that patients undergoing TB can potentially benefit from the adjunctive use of LLLT without compromising the final whitening result.