# Low-Level Laser Therapy for Tooth Sensitivity after Tooth Bleaching: A Systematic Review
## 3 Results  
The search strategy initially identified 2875 articles for screening. After eliminating duplicates, the total was reduced to 1532. Upon screening based on title and abstract, only  
Figure 1: The PICOS framework for inclusion and exclusion criteria. 21 articles remained for the subsequent stage of the process. Screening at the full-text level resulted in just six articles [5; 27; 28; 29; 30; 31] fulfilling all eligibility criteria. The flow diagram of the screening and selection process, according to the PRISMA guidelines, is presented in Figure 2.  
Six studies met the inclusion criteria and were included in the systematic review. All studies were written in English and were published in the last 9 years. They were all RCTs, with a total of 308 patients treated with either LLLT as a monotherapy (n = 160) or non-LLLT (n = 148) after in-office tooth bleaching. All patients had good oral health and were free from medical conditions. Cracked teeth or teeth with caries were eliminated from the test samples. The characteristics of the included studies are summarized in Table 1. Significant variability in terms of study design, population, timeline, parameters of bleaching system, LLLT, and control therapy is observed among the studies. Heterogeneity is also observed in the methodology of evaluating TS regarding the scale used (VAS, modified VAS, or VRS), the assessment periods (varying from 48 h to 21 consecutive days), and the use of any stimulation (evaporative, mechanical) to assess patients' pain (Table 2). Figure 2: PRISMA flow diagram of the literature search and selection process. The [PERSON] et al. [27] RCT investigated the effect of LLLT on TS, comparing two different wavelengths (660 and 810 nm, in the red and infrared spectrum, respectively) with each other and with a placebo group (n = 22 patients in each of the three groups), and reported that the two lasers effectively reduced pain level, but only after 24 h, with the LLLT in the infrared spectrum providing better results during the first 24 h but not differing from the red laser at 48 h. Another study [28] with five groups (n = 10 patients in each) aimed to analyze the effect of LLLT when used either before, after, or both (before and after) TB and, unlike the previous study, found no statistical differences between groups at any time point and therefore no difference in the effectiveness of LLLT in preventing TS. The study by [PERSON] et al. [29] assessed the impact of LLLT in relation to a placebo-control group, a group in which KNO\({}_{3}\) desensitizing gel was applied prior to TB, and a group in which KNO\({}_{3}\) and LLLT were combined (n = 25 in each of the four groups). LLLT was found to be capable of reducing pain sensitivity after TB, with an effect similar to that of KNO\({}_{3}\) and to the combination of these treatments. An additional study [30] correlating LLLT with an alternative desensitizing agent (specifically strontium chloride, n = 25 in each of the four groups) reached similar conclusions, illustrating that LLLT is as effective as strontium (Sr) and as the combination of the two for inhibiting TS after TB. [PERSON] et al. [31] examined LLLT, 5% NaF, and the combination of the two (n = 13 in each of the three groups) without a control group and identified that all of the desensitizing methods employed reduced post-bleaching TS with no significant differences among them. The lack of a control group in this study makes it impossible to differentiate real treatment efficacy from the natural evolution of the condition and influences the results from the Hawthorne effect [32], hence inserting bias. The most recent study [5] assessing LLLT (n = 43) for reducing TS after TB compared to a control group (n = 40) is in agreement with [PERSON] et al. [28], exhibiting no difference in the risk and intensity of TS for two pain scales. This study recruited the largest sample size (N = 83) in two groups, thus yielding the highest statistical power compared to previous studies.