Effects of low-level laser photobiomodulation on the masticatory function and mandibular movements in adults with temporomandibular disorder: a systematic review with meta-analysis

Máximo, Camila Fonsêca Guedes Pereira; Coêlho, Julyane Feitoza; Benevides, Silvia Damasceno; Alves, Giorvan Ânderson dos Santos

doi:10.1590/2317-1782/20212021138

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Systematic Review • CoDAS 34 (3) • 2022 • https://doi.org/10.1590/2317-1782/20212021138 linkcopy

Effects of low-level laser photobiomodulation on the masticatory function and mandibular movements in adults with temporomandibular disorder: a systematic review with meta-analysis

Authorship SCIMAGO INSTITUTIONS RANKINGS

Purpose To review the effects of low-level laser photobiomodulation on masticatory function and mandibular movements in adults with temporomandibular disorder.

Research strategies Search in PubMed, Web of Science, Scopus, EMBASE, Cochrane, LILACS, ScienceDirect, and Google Scholar, using the following descriptors: “temporomandibular joint disorders”, “low-level light therapy”, “low-level laser therapy”, “mastication”, and “mandible”.

Selection criteria Randomized clinical trials in adults with temporomandibular disorder, using low-level laser and assessing the mastication and mandibular movements.

Data analysis Firstly, the titles and abstracts of all retrieved studies were read. Then, only the studies selected in the first stage were read in full and assessed regarding eligibility. After the selection, the characteristics, methodological quality, and quality of evidence of the studies included in the review were analyzed. In the meta-analysis, the mean amplitude of mouth opening was considered as a measure of intervention effect.

Results The 10 articles included in the review had quite different results one from the other, especially regarding the amplitude of mouth opening, while the mastication was assessed in only one of them. Most studies had a high risk of bias, demonstrating a low methodological quality. Significantly higher results for photobiomodulation were identified in the six studies included in the meta-analysis.

Conclusion Due to the scarcity in the literature, there is not enough evidence of the effects of low-level laser photobiomodulation on mastication. As for the mandibular movements, this intervention presented significant results, particularly in the amplitude of mouth opening.

Keywords
Low-Level Light Therapy,; Temporomandibular Joint Dysfunction Syndrome,; Mastication,; Mandible,; Systematic Review

Strategy	Database
Search: ((“temporomandibular joint disorders”) AND (“low-level light therapy”)) AND (mastication) (“temporomandibular joint disorders”[All Fields] AND “low-level light therapy”[All Fields]) AND (((((((“masticated”[All Fields] OR “masticates”[All Fields]) OR “masticating”[All Fields]) OR “mastication”[MeSH Terms]) OR “mastication”[All Fields]) OR “masticate”[All Fields]) OR “mastication”[All Fields]) OR “masticator”[All Fields]) OR (((“mandible”[MeSH Terms] OR “mandible”[All Fields]) OR “mandibles”[All Fields]) OR “mandible s”[All Fields])	PubMed
((“temporomandibular joint disorders”) AND “low-level light therapy”) AND “mastication” OR “mandible” “([Quick search])- Quick Search	EMBASE
(tw:(“temporomandibular joint disorders”)) AND (tw:(“low-level light therapy”)) AND (tw:(mastication)) OR (tw:(mandible)) ([Title, abstract, and topic])	LILACS
“temporomandibular joint disorder” AND “Low-level light therapy” AND mastication OR mandible OR mastication*) ([All fields])	Cochrane Library
ALL= (Temporomandibular Joint disorder* AND Low-level laser therapy* AND mastication* OR mandible*) ([All fields])	Web of Science
ALL (“temporomandibular joint disorders”) AND ALL (“low-level light therapy”) AND ALL (mastication) OR ALL (mandible)) ([All fields])	Scopus
“temporomandibular joint disorders” AND “low-level light therapy” OR “low-level laser therapy” AND “mastication” OR “mandible” AND “Randomized Controlled Trial”	Google Scholar
“temporomandibular joint disorders” AND “low-level light therapy” OR “low-level laser therapy” AND “mastication” OR “mandible” AND “Randomized Controlled Trial”	ScienceDirect

Author	Country	Sample (n)	Objective	RDC/TMD	Intervention parameters	Type of intervention	Outcomes	Results	Conclusion
Da Silva et al.⁽¹¹⁾	Brazil	45	To assess the effects of LLL on subjects with intra-articular TMD and quantify and compare the severity of the signs and symptoms before, during, and after applying the laser.	Yes	A total of 10 sessions were conducted over 5 weeks, twice a week. The device energy during the applications was 70 mW, the application time varied according to the point, and the wavelength was 780 nm. For 52.5 J/cm², the application time was 30 seconds and 60 seconds for 105.0 J/cm². The laser was applied continuously on 5 condylar points, 3 on the masseter, and 3 on the temporal.	Two different laser doses and a placebo.	Mandibular movements and painful symptoms evoked with muscle palpation.	The analysis of variance showed statistically significant differences between the groups, with a level of 1% between doses, (except for the protrusion variables: significant difference of 5%; and opening: not significant), as well as between the assessments (except for laterality – 5% statistical difference.	This study concluded that the LLL increased the amplitude of the mandibular movements.
De Carli et al.⁽¹²⁾	Brazil	15	To compare the use of LLL and botulinum toxin to treat myofascial pain and verify whether they change the mouth opening in patients with TMD.	Not informed	Seven applications were made with 48-hour intervals in-between the applications. The wavelength was 830 nm, with a dose of 80 J/cm² and a power of 100 Mw. It was applied on 2 points of the masseter and 1 on the temporal.	Laser and type A botulinum toxin.	The amplitude of mouth opening and intensity of the pain.	Regarding the amplitude of mouth opening, no statistically significant difference was found between the laser group and the toxin group, considering that neither group had a significant increase during the treatment (p = 0.272).	The two therapies did not result in statistically significant improvement in the amplitude of mouth opening.
Kato et al.⁽¹³⁾	Brazil	18	To compare the efficacy of transcutaneous electrical nerve stimulation (TENS) and LLL therapy to treat patients with chronic myogenous TMD.	Not informed	A total of 10 sessions were conducted over 4 weeks, 3 times a week, with a wavelength of 830 to 904 nm, the output of 4 J/cm², and power of 100 mW, with sweep movements, for 9 minutes on each side of the face.	Laser and TENS	The amplitude of mouth opening and intensity of the pain.	The results showed an increase in the amplitude of mouth opening in both groups (p < 0.05). There was a significant improvement in the amplitude of mouth opening (initial mean of 42.5 mm – 43 mm in the laser group and 42 mm in the TENS group – and final mean of 47.4 mm – 47.6 and 47.2 mm in the laser and TENS groups, respectively. The ANOVA showed that there was no statistically significant difference between the groups, including the immediate effect (p = 0.860 and p = 0.091, respectively). However, there was a significant difference between the sessions (p<0.0010).	Both therapies were effective in decreasing the TMD signs and symptoms, but the immediate effect was not significant, and the cumulative effect may have been responsible for this improvement.
Kogawa et al.⁽¹⁴⁾	Brazil	19	To assess the effectiveness of LLL and microelectric neurostimulation (MENS) to treat TMD patients.	Yes	The laser therapy was conducted 3 times a week, totaling 10 sessions, with a wavelength of 830 to 904 nm, the output of 4 J/cm², and power of 100 mW.	Laser and MENS	The amplitude of mouth opening, muscle and TMJ palpation, and visual analog scale.	The results showed an increase in the amplitude of mouth opening. The initial and final means of amplitude in the laser group were 46.3 mm and 49.4 mm, respectively, while in the microelectric neurostimulation (MENS) group, it was 46.3 mm and 44 mm, respectively. There was no significant difference between the groups.	The conclusion was that both therapies (laser and MENS) are effective to treat myogenous TMD, but caution in result analysis is recommended, due to the self-limiting aspect of TMD. The amplitude of mouth opening improved in both groups.
Machado et al.⁽¹⁵⁾	Brazil	82	To investigate the efficacy of combining oral myotherapy exercises and LLL, in comparison with oral myofunctional therapy protocol, with LLL therapy alone, and placebo combined with exercises. To verify the effects of each program immediately after the treatment and in long-term follow-up.	Yes	Twelve weekly sessions for 60 days, and then every 2 weeks. Continuous emission at 780 nm wavelength, 60 mW power, and energy density varying around 60 +- 1 J/cm². It was applied on 5 TMJ points and on the masseter and temporal muscles.	Laser + oral myotherapy exercises; laser alone; placebo + oral myotherapy exercises and complete oral myofunctional therapy protocol.	Self-assessment of TMD severity, pain with palpation, the subjective intensity of the pain, orofacial myofunctional status (appearance/posture, mobility, and performance of the stomatognathic functions).	The results of the orofacial myofunctional evaluation protocol with scores were lower than in the placebo group, without statistically significant results between the groups.	The LLL combined with oral myotherapy exercises was more effective than LLL alone, decreasing the TMD signs and symptoms and improving the mandibular movements.
Öz et al.⁽¹⁶⁾	Turkey	40	To assess the efficiency of the laser and compare it with occlusal splints to treat myofascial pain.	Yes	A total of 10 sessions were conducted, twice a week. The wavelength was infrared (820 nm), with a dose of 3 J/cm², an output power of 300 mW, lasting 10 s on each point. The laser was precisely and continuously applied to the trigger points.	Laser and interocclusal splints.	Functional examination, finding the pressure pain threshold and amplitude of mouth opening.	Both groups had statistically significant improvements in the vertical mandibular movements after the treatment, and no significant differences were identified between the groups.	The laser was as effective as the interocclusal splints, and it can be an alternative treatment, as it is noninvasive and non-pharmacological.
Seifi et al.⁽¹⁷⁾	Iran	40	To assess the effect of LLL therapy and TENS on TMD.	Yes	Four half-hour sessions were conducted per week. The wavelength was 810 nm, with a continuous power of 0.5 W, for 60 s.	Laser, laser placebo, TENS, and TENS placebo.	Sensitivity of the masticatory muscles and amplitude of mouth opening.	The amplitude of mouth opening improved with time. However, it did not remain after 1 month in relation to the baseline (p=0.192). There were no significant differences between the LLL and TENS groups (p=0.820) in any of the stages. No statistically significant differences were found between the placebos (p=0.738). Mouth opening was significant in the laser and TENS groups and greater than in the placebo groups (p=0.002), though not in the 1-month follow-up (p=0.692).	The effects of laser and TENS can improve the TMD signs and symptoms in the short run and can be physical modalities of complementary and supplemental alternatives in TMD.
Gökçen-Röhlig et al.⁽¹⁸⁾	Turkey	40	To investigate the efficacy of LLL with 820 nm, 3 J/cm², 300 Mw output power to treat myogenous TMD.	Yes	A total of 10 laser sessions were conducted daily for 3 weeks. The wavelength was infrared (820 nm), with a dose of 8 J/cm² and power of 300 mW, for 10 s. It was continuously applied on 3 points of the masseter, 1 on the temporal, and 1 on the sternocleidomastoid muscle.	Laser and placebo	pressure pain threshold, visual analog scale, and mandibular mobility.	The laser group had statistically significant improvements in the vertical mandibular movements and lateral excursions.	The effects of laser are better than the results of the placebo group.
Madani et al.⁽¹⁹⁾	Iran	45	To investigate the efficacy of LLL to treat osteoarthritis and TMD.	Yes	A total of 12 sessions were conducted 3 times a week, for 4 weeks. The laser was applied with contact, with a power of 50 mW, 6 J per point, 3.4 J/cm² on 4 points of the TMJ, 3 on the masseter, 3 on the temporal, and on the attachment of the internal pterygoid muscle.	Laser, laser acupuncture, and placebo	Degree of pain, the amplitude of mouth opening, and joint noises.	After 12 sessions of laser application, the mean amplitude of mouth opening increased from 29.2 mm to 31.7 mm (an 8% increase) in the laser group. In the placebo treatment, it increased from 23.5 mm to 24.7 mm (a 5% increase). The analysis did not show a statistically significant difference between the groups of study or between the different assessment times in each group.	The laser and placebo group did not significantly improve the amplitude of mouth opening.
Sancakli et al.⁽²⁰⁾	Turkey	30	To assess the effect of applying LLL in the main pain points in patients with chronic masticatory muscle pain (myofascial pain).	Yes	A total of 12 sessions were conducted 3 times a week, for 1 month. The wavelength was infrared (820 nm), with a dose of 3 J/cm² and output power of 300 mW for 10 s. It was applied on the main pain points and 3 points of the masseter and temporal muscles.	Laser on the main pain points and preestablished points.	Mandibular mobility (amplitude, lateral excursions, protrusion), pressure pain threshold, pressure measure, and subjective measure of the pain.	The vertical mandibular movements, lateral excursions, and protrusion improved significantly in the LLL groups.	The LLL had positive effects on the mandibular movements due to its analgesic and myorelaxant effects. There was no difference between the application on the pain and preestablished points.

Summary of the Results
LLL photobiomodulation compared with placebo or other interventions for temporomandibular disorder
Patient or population: Temporomandibular disorder Context: Mandibular movements and masticatory function Intervention: LLL photobiomodulation Comparison: Placebo or other interventions
Outcome No. of participants (studies)	Relative effect (95% CI)	Potential absolute effects (95% CI)					Certainty	What happens
Outcome No. of participants (studies)	Relative effect (95% CI)	Without photobiomodulation with LLL	With photobiomodulation with LLL		Difference		Certainty	What happens
Mandibular movements assessed with: mouth opening No. of participants: 160 (6 RCTs)	-	The mean of the mandibular movements was 37.25 mm		The mean of the mandibular movements was 40.03 mm		DM 2.78 mm higher (1.12 higher for 4.44 higher)	⨁◯◯◯ VERY LOW ^a,b,c	The LLL photobiomodulation can increase/have little or no effect on the mandibular movements, but the evidence is very uncertain.
Masticatory function assessed with OMES protocol No. of participants: 39 (1 RCT)	The study presented only the analysis of the total scores of the stomatognathic functions, identifying that the group with LLL photobiomodulation did not have significant results after the treatment. On the other hand, the comparison between the various intervention groups identified significant results.						⨁⨁⨁⨁ HIGH	The study had a high methodological quality. However, it would be necessary to analyze the mastication, specifically, as well as the combination with other studies. Thus, there is not enough evidence of the effects of LLL photobiomodulation on the masticatory function.
Levels of evidence of the GRADE Working Group High certainty: We are very confident that the actual effect is close to the estimated effect. Moderate certainty: We are moderately confident about the estimated effect; the actual effect is probably close to the estimated effect, but it may be substantially different. Low certainty: We have limited confidence in the estimated effect; the actual effect may be substantially different from the estimated effect. Very low certainty: We are very little confident about the estimated effect; the actual effect is probably substantially different from the estimated effect.
Explanations a. The studies had many methodological limitations regarding the outcome assessed. Three of the six studies had a high risk of bias – one with an uncertain risk and two with a low risk –, which helped lower the quality of evidence. Some of the aspects identified were the lack of participant allocation concealment, lack of blinding, and lack of information on losses to follow-up. b. The comparison of the studies identified the presence of inconsistency, as various methodologies were used for the same outcome, with different intervention parameters and results. This led to considerable heterogeneity, also verified in the statistical analysis, which lowered the quality of evidence. c. Some studies were imprecise regarding the amplitude of the 95% confidence interval, decreasing the confidence in the estimated effects.

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[1] Caption: CI = confidence interval; DM = difference of means