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ISSN: 2637-6679

Research and Reviews on Healthcare: Open Access Journal

Research Article(ISSN: 2637-6679)

Low level laser therapy and its effect on pain during orthodontic treatment: A systematic review and meta-analysis Volume 6 - Issue 2

Fazal Shahid1, Norma Ab Rahman2, Mohd Fadhli Khamis3, Adam Husein4, Mohammad Khursheed Alam5, Shifat A Nowrin6

  • 1,2,6Orthodontic Unit, School of Dental Science, Universiti Sains Malaysia, Kubang Kerian, Kelantan, Malaysia
  • 3Forensic Dentistry/Oral Biology Unit, School of Dental Science, Universiti Sains Malaysia, Kubang Kerian, Kelantan, Malaysia
  • 4Prosthodontics Unit, School of Dental Science, Universiti Sains Malaysia, Kubang Kerian, Kelantan, Malaysia
  • 5Orthodontic Department, College of Dentistry, Jouf University, Sakaka, KSA

Received: February 04, 2021   Published: March 09, 2021

Corresponding author: Norma Ab Rehman, Orthodontic Unit, School of Dental Science, Universiti Sains Malaysia, Kubang Kerian, Kelantan, Malaysia.

DOI: 10.32474/RRHOAJ.2021.06.000231

Abstract PDF


Introduction: Application of low-level laser therapy (LLLT) in reducing the pain associated with orthodontic treatment is still debated. Hence, the aim of this systematic review is to reconnoiter the effect of LLLT in pain allied with different orthodontic procedure.

Methods: Literature search in Scopus, PubMed and Science direct data bases was performed by two independent reviewers. In addition, manual hand search and references were checked to fine relevant studies. Systematic review and meta-analysis were conducted using the data entered into electronic data bases until 31st August 2018.

Results: On the basis of the different data bases search, 22 studies were included for the systematic review and total 5 studies were selected for meta-analysis. Mean pain score and standard deviation were used to evaluate the effectiveness of LLLT relation with pain in orthodontic treatment. There is significant positive association with laser application in reducing pain in elastomeric separator placement in 24 hours (P value 0.01) and 72 hours (P value 0.02). However, in terms of canine retraction, LLLT does not showed significant difference in reducing pain.

Conclusion: More clinical trials in the effectiveness of low-level laser therapy in relation with pain perception of orthodontic treatment is necessary to define better specificity of conceivable interaction.

Keywords: Pain Perception; LLLT; Orthodontic Treatment


One of the most common side effects of orthodontic treatment is pain or discomfort when patients exposed to orthodontic forces [1]. More or less 90% of patients claimed of suffering pain during orthodontic treatment. However, the intensity of the pain might vary in different stages of treatment [2] . The most intense pain usually occurs 24 hours after separator or initial wire placement and its gradually decrease over a week [3]. Hence, pain associated with orthodontic treatment is one of the reasons patients feel discouraged to continue treatment. Nevertheless, orthodontic pain is generally underestimated and neglected, though it has a significant clinical value [2,4].After placing the first wire or separator, patients are sometimes prescribed anti- inflammatory and analgesics drugs to avoid the pain [5]. However, using any drugs might have potential influence on orthodontic tooth movement and its contentious due to the adverse systemic side effects [6]. Moreover, other pain management procedures for instance vibratory stimulation of the periodontal ligament [7], anesthetic gels [8], transcutaneous electrical nerve stimulations [9], xylitol chewing gums [8] yielded fluctuating results. In recent years, low level laser therapy (LLLT) has been increased in attention for reducing pain associated with orthodontic tooth movement. Moreover, it considered as a safe procedure compare to the other traditional approaches[10]. LLLT plays an important role in increasing blood supply and stimulate the regaining of dental tissue[11]. Several studies showed that LLLT reduces the pain during orthodontic treatment [12-16]. However, few studies showed no significant difference in terms of pain with laser applications [16-18].

There are different types of lasers are being used in dentistry for reducing the pain such as carbon dioxide (CO2) laser [14], helium-neon (He-Ne) laser [19] and diode laser [12, 15, 20]. However, diode laser which is also known as semi-conductive laser is widely used in dentistry due to its low cost and comparatively compact feature. Diode laser can infiltrate into deep tissues based on its wavelength (usually 600-1000 nm) which can control the pain associated with orthodontic tooth movement[21]. In orthodontic pain management, GaAlAs laser (wavelength 780- 890 nm) has been widely used [12, 15, 17, 22] though other types of diode laser InGaAlP laser (wavelength 630-700 nm) is also showing a positive result in reducing the pain[23]. Despite, a number of clinical trials observed the effect of LLLT in reducing the pain, a little attention has been given to the precise properties of the most popular diode laser. Therefore, a systematic review is mandatory for evidence based clinical practice and results. In this current systematic review, effects of LLLT in pain associated with orthodontic treatment has been evaluated based on the outcome of different clinical researches.

Materials and Methods

This systematic review followed the PRISMA (Preferred Reporting Items for systematic reviews and Meta-Analysis) guideline to select all the studies (Figure 1). Moreover, a distinct review question was established following population, intervention, comparison, outcome and study design (PICOS) strategy (Table 1).

Table 1. PICOS strategy.


RCT: Randomized Clinical Trial, CCT: Controlled Clinical Trial

Formulating review question

Current study intent to answer the following question: In patients undergoing orthodontic treatment, can LLLT alter the pain perception in humans when compared to the control group?

Formulating review question

Current study intent to answer the following question: In patients undergoing orthodontic treatment, can LLLT alter the pain perception in humans when compared to the control group?

Inclusion and exclusion criteria

All the articles should meet the following prerequisite criteria to include in this systematic review.

Inclusion criteria were as follows:

a) Patients are undergoing orthodontic treatment
b) RCT, CCT or quasi RCT conducted to diminish acute pain with using LLLT
c) Control group was used either with placebo or no use of laser
d) Pain scores were measured using visual analog scale (VAS), numeric rating score (NRS) or any questionnaire.

Exclusion criteria were as follows:

a) Case reports, review articles or conference proceeding
b) Animal studies
c) Incomplete information about laser

Literature search strategy

Literature search was conducted on Science Direct, PubMed and Scopus databases till 31st August 2018. For searching literatures, following key words were used: “LLLT or low-level laser therapy or laser” + “orthodontic treatment or orthodontic or fixed appliances” + “pain or discomfort”. No restrictions were levied on language, populations, treatment stage or sample size. Selected literatures were thoroughly checked, and their references were re-checked for any literature not found in selected databases. All the articles were inspected by two independent reviewers (FS and SAN) and included in current review which meet the eligible criteria.

Quality assessment of specific studies

Each selected articles were evaluated based on methodological quality assessments .24. Methodological quality scores were calculated and ranged from 0 to 15. All studies were divided into 3 categories: low, moderate and high from score 0 to 8, 9 to12 and 13 to 15, respectively.

Meta analysis

A meta-analysis was conducted based on pain score in similar days with laser applications. Study 10, 15 and 19 (Table 2) for separator placement and study 7 and 12 (Table 2) for canine retraction were chosen for meta-analysis.

Table 2. List of selected studies in the current systematic review.


Statistical analysis

All statistical analysis was conducted using IBM SPSS statistics for Windows, version 22.0 (IBM Co., Armonk, NY, USA) and Comprehensive Meta-Analysis (CMA) software version 3 (Biostat, Englewood, NJ, USA). The statistical significance (P value) set <0.05 for hypothesis test. Cohen’s kappa analysis was performed to assess the inter-observer agreement for the quality assessments. Kappa scores are graded as near perfect (0.81-1), substantial (0.61- 0.80), moderate (0.41-0.60), fair (0.21-.040) and poor (<0.20). For pain score, mean and standard deviation (SD) were adopted. Heterogeneity was verified using I2 and Q statistics. I2 <50% and P value of Q statistics >0.10 determined no heterogeneity across the studies. Funnel plots were used to check the publication bias using egger’s and Begg’s test. A P value >0.05 was indicated no bias among the studies.


Search result

Through the electronic search, initially we identified 86 studies: 60 from Scopus, 20 from Science Direct and 6 from PubMed. Furthermore, all the references were manually checked for other relevant studies and 5 more studies were included. PRISMA guideline was followed to scrutinize all the studies into current systematic review (Figure 1). After removing the duplicates and exclusion criteria 22 studies were included. Finally, total 22 studies were selected for this review (Table 2). Two independent reviewers were inspected all the studies properly to avoid any bias in selection procedure.

Analysis of selected studies

Quality analysis was performed among the selected studies following criteria described by Almeida et al (2016) [24]. Among 22 studies, total 7, 13 and 2 studies were classified as high quality (13-15 points), moderate quality (9-12 points) and low quality (0-8 points) study, respectively (Table 3). For quality assessment Cohen’s kappa score was 0.840 which is near perfect level of inter examiner agreement. Types of laser, specifications and frequency of applying laser were checked thoroughly from the selected articles which showed in (Table 4). Most of the studies used Al-Ga-As laser in the range of 640 to 940 wavelength. Laser application mostly seen after elastomeric separator placement followed by canine retraction, arch wire and molar band placement. VAS, NRS and selfdesigned questionnaire were used to assess the pain perception. However, different studies checked the pain score in different days. The analysis of the association of pain with LLLT in separator placement showed that there is significant positive association with laser application in reducing the pain (Figure 2, 3 and Table 5). However, in terms of canine retraction, LLLT does not showed significant difference in reducing pain (Figure 4). Both statistical and clinical heterogeneity were inspected among these studies in LLLT application of separator placement and canine retraction stage. A forest plot revealed that, pain subsided significantly in LLLT group compared to control in both times (24 and 72 hours) with insignificant heterogeneity in 72 hours (Table 6). Moreover, sensitivity test was also conducted after omitting one study to check the influence on pooled result nevertheless it persists same. Begg’s and Egger’s test showed no publication bias among the studies in separator placement (Table 7 and Figure 5). However, these tests couldn’t be performed for canine retraction as only 2 studies were included while minimum 3 studies need to include to perform Begg’s and Egger’s test.

Figure 1: Flow chart of the PRISMA guideline for the selection of studies.


Table 3. Quality assessment of selected studies.


Figure 2: Forest plot of pain observation in separator placement at 24 hours.


Figure 3: Forest plot of pain observation in separator placement at 72 hours.


Figure 4: Forest plot of pain observation in Canine retraction stage at day 3.


Figure 3: Funnel plot for the publication bias test in separator placement.


Table 4. Laser specification of selected studies.


Table 5. Effect of LLLT on pain perception in elastomeric separator placement..


Table 6. Heterogeneity test among the studies.


Table 7. Publication bias among the studies.



In current systematic review we have selected 22 studies for quality assessment after an extensive search. Methodological quality assessment revealed only 7 out of 22 studies consist of sound methodology. Furthermore, 13 studies fall in moderate group and 2 in low group. After further screening, we found most of the clinical trials were randomly selected the voluntary subjects either from dental school or patients from hospital. No proper sample size calculation has been done. Whereas, sample size is considered to be a very important factor in any clinical trial [25, 26]. Moreover, most of the studies have flaws in selection criteria and randomization process. 10 out of 22 studies were mentioned only about inclusion criteria and ignore the exclusion criteria. In addition, only 8 studies mentioned the randomization and blinding protocol properly. Individual 2 studies discussed the limitation of the study. Therefore, definite studies may acquaint with bias owing to methodological imprecisions.

Included studies were conducted in 13 different countries with varying total number of subjects. Study designs were different. Among 22 studies, 5 studies were based on parallel design and rest were split mouth design. Split mouth study designs might have advantages over parallel study design due to the efficiency and decrease requirement of sample. However, lack of uniformity in allocation segment, carry across effects or contamination is the main disadvantages for split mouth studies. Moreover, split mouth study design should be carried out when proper sample size has been calculated [27]. As there is a lack of sample size calculation in most of the studies, methodological soundness is still questionable among most of the selected studies. Mainstream of the studies were used GaAlAs diode laser with diversified application methods and time duration. It is difficult to perform quantitative synthesis with varying of data and outcome [28]. Pain perception was mostly checked after placing elastomeric separators (10 studies) following canine retraction (7 studies), arch wire (4 studies) and molar band placement (1 study) (Table 2). The pain scores were checked in different time in different studies selected in current systematic review. However, Day 1 (24 hours) and Day 3 (72 hours) were most common selected time for checking pain status after laser application. 8 among 22 studies were used GaAlAs laser and checked the pain perception commonly at day 1 and day 3. However, 3 studies checked the median value of pain perception [16,18,29,2] studies displayed the results with graphs without any numeric result presented [30,31]. Yet only 3 studies with pain perception after placing the separator were presented with mean pain score and standard deviation which we included in metaanalysis [17,20,32]. On the other hand, in terms of laser application during canine retraction stages, 2 studies presented the detail result in pain perception for day 3 [12, 15].

Though all the studies included for quantitative synthesis showed positive outcome, both Q statistics and I2 test was performed to check the heterogeneity. Pain score at 24 hours after laser application of separator placement and 72 hours of canine retraction indicated significant heterogeneity among studies. However, 72 hours after laser application of separator placement showed insignificant Q statistics and I2. The laser application methods and dosimetry might be affecting the comparability of the studies. Therefore, future research is advisable to adopt a common model for assessing LLLT effects on orthodontic pain. Nevertheless, clinical heterogeneity is always present in meta-analysis due to study design, intervention, outcome and sample size. This metaanalysis also represents clinical heterogeneity on study background, sample size, ethnic background and outcomes.


Current systematic review and meta-analysis concluded that LLLT might have positive aspect of reducing pain in different orthodontic procedure. However, the heterogeneity and the varying protocols of laser application cannot provide sufficient evidence to judge whether LLLT is effective in reducing orthodontic pain. Further clinical trials with better study design, controlled laser dosimetry and appropriate sample size is recommended to provide more meaningful evidence for the clinical application of laser.


RU grant 1001/PPSG/812154 and Vice Chancellor Award.


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