# Effects of photobiomodulation on trismus in head and neck cancer patients after radiotherapy: a prospective, randomized, triple-blind, placebo-controlled clinical trial

## TL;DR

This study found that photobiomodulation therapy can help prevent trismus and reduce muscle pain in head and neck cancer patients undergoing radiotherapy.

## Contribution

The study is the first triple-blind, placebo-controlled clinical trial evaluating PBMT's effectiveness in preventing trismus in HNC patients.

## Key findings

- PBMT significantly reduced mouth opening reduction during radiotherapy compared to placebo (p = 0.005).
- PBMT lowered the prevalence of masticatory muscle pain and grade 1 trismus (p = 0.002).
- No significant differences were found in DMFT, OHIP-14, or Anderson Symptom scores between groups.

## Abstract

To evaluate the effectiveness of photobiomodulation therapy (PBMT) in the prevention of trismus in patients undergoing Intensity-Modulated Radiotherapy (IMRT) and Volumetric Modulated Arc Therapy (VMAT), through a randomized, triple-blind, placebo-controlled clinical trial. A total of 46 patients undergoing radiotherapy (RT) for head and neck cancer (HNC) were included. Patients were equally and randomly allocated to PBMT and PBMT placebo groups and were evaluated daily by measuring mouth opening, pain during mouth opening, and pain on palpation of the masticatory muscles using the Visual Analog Scale (VAS). An extraoral infrared laser (~ 808 nm), power of 0.1 W, energy of 3 J, 30 s (107 J/cm²) per point was used, applied extraorally to the anterior temporalis (AT), masseter (MM), and temporomandibular joints (TMJ), and intraorally to the medial pterygoid muscle (MP). The Food Quality Inventory (ASGP) and quality of life analysis (QoL) (OHIP-14) were also applied. Statistical analysis included Student’s t-test, Mann-Whitney test, and linear regression models (p < 0.05). Patients in the PBMT group showed a significantly smaller reduction in mouth opening during radiotherapy compared to the placebo group (p = 0.005), as well as a lower prevalence of masticatory muscle pain and grade 1 trismus (p = 0.002). No significant differences were observed between the groups regarding the decayed, missing, and filled teeth index (DMFT), the Oral Health Impact Profile-14 (OHIP-14), or the Anderson Symptom and Overall Performance scores (p > 0.05). Mouth opening did not differ between the groups at the six-month follow-up. Photobiomodulation therapy was effective in preventing trismus and masticatory muscle pain during radiotherapy.

Clinical Trial Registration

Clinical trial number: RBR-67qxnt9 (registered on 16/04/2025).

The online version contains supplementary material available at 10.1007/s10103-026-04834-3.