Clinical and radiotherapeutic characteristics of patients undergoing preventive PBM for trismus with low-level laser or placebo

Most participants were male (n = 19, 82.6%), and the mean age did not differ significantly between the groups (p = 0.421). The majority of patients self-identified as brown (PBMT: n = 17, 73.9%; placebo: n = 15, 65.2%; p = 0.522) and had incomplete primary education (PBMT: n = 15, 65.2%; placebo: n = 9, 39.1%; p = 0.133). Most participants reported a family income of up to one minimum wage (PBMT: n = 20, 87.0%; placebo: n = 21, 91.3%; p = 0.636) (Table 1).

Table 1 Sociodemographic and clinical-pathological profile of patients undergoing radiotherapy for head and neck cancers submitted to preventive photobiomodulation for trismus with low-power laser or placebo

He most frequent clinical stages were T3 and T4 in both groups, with no significant difference between them (PBMT: T3 n = 7, 30.4%, T4 n = 8, 34.8%; placebo: T3 n = 9, 39.1%, T4 n = 6, 26.1%; p = 0.911). Regarding lymph node status, N0 disease was more frequent in the placebo group (n = 14, 60.9%) than in the PBMT group (n = 9, 39.1%), although this difference was not statistically significant (p = 0.068) (Table 1).

Most patients received radiotherapy doses ≥ 69 Gy, delivered in 31 to 35 fractions. No significant differences were observed between the groups in terms of total radiotherapy dose (p = 0.459), treatment technique (IMRT vs. VMAT; p = 0.768), treatment interruptions, or radiotherapy-related adverse events (p = 0.437) (Table 1).

The mean duration of radiotherapy was significantly shorter in the PBMT group (47.70 ± 9.00 days) than in the placebo group (52.39 ± 8.91 days; p = 0.041). Regarding trismus severity assessed by CTCAE between days 1 and 35, higher-grade scores (grades 1 and 2) were more frequently observed in the placebo group (11.1% and 3.4%, respectively) compared with the PBMT group (7.0% and 5.7%, respectively; p = 0.002). Additionally, the frequency of CTCAE grade 0 trismus was 1.31 times higher in the PBMT group (95% CI: 1.06–1.62) (Table 1).

Photobiomodulation minimizes loss of mouth opening, pain, and trismus scores in irradiated head and neck patients

The mean initial mouth opening of patients in the PBMT group was 42.89 ± 6.10 mm, while in the placebo group, it was 46.17 ± 7.28 mm (p = 0.104) on the first day (D1). There were no statistically significant differences in mouth opening between the PBMT and placebo PBMT groups on any of the days evaluated. However, both groups showed a slight reduction in mouth opening over the days, with a significant negative correlation with time that was stronger in the placebo PBMT group (p < 0.001, r= -0.909) than in the PBMT group (p < 0.001 r=-0.777) (Table 2; Fig. 3).

Table 2 Influence of preventive photobiomodulation protocol for trismus with low-power laser or placebo on pain variation during mouth opening in patients undergoing radiotherapy for head and neck cancer treatment

The mean change in mouth opening from the start to the end of RT was significantly more significant in the PBMT group (-0.15 ± 4.51 mm; p = 0.005) compared to the placebo group (-3.75 ± 3.69 mm). The difference between the two groups was 3.50 ± 1.21 mm. Only one patient in the PBMT group showed a reduction in mouth opening, while six patients in the placebo group had negative results in terms of mouth opening reduction (Fig. 3).

Fig. 3

Influence of the preventive photobiomodulation protocol for trismus with low-level laser or placebo on the variation of mouth opening in patients undergoing radiotherapy for the treatment of head and neck cancers. (a) Variation of mouth opening (Δ Mouth Opening) in millimeters in the PBMT and Placebo PBMT groups after the treatment period. (b) Evolution of mouth opening (Mouth Opening) over time (days) in the PBMT and Placebo PBMT groups. *p < 0.05, Student’s t-test (mean ± SD) or linear regression model

During the first seven days of follow-up (D1–D7), patients in both groups reported no pain (0.00 ± 0.00). From D8 onward, mean pain scores began to fluctuate but remained low throughout treatment. The PBMT group reported higher pain scores than the placebo group at only two time points (D7, p = 0.037; D28, p = 0.033).

In the PBMT group, increased mouth opening was significantly correlated with lower pain scores during mouth opening on specific days of radiotherapy, including D11 (p = 0.004, r = 0.576), D16 (p = 0.009, r = 0.535), D17 (p = 0.002, r = 0.600), D19 (p = 0.007, r = 0.544), D20 (p = 0.023, r = − 0.472), D22 (p = 0.031, r = 0.451), and D34 (p = 0.043, r = 0.425). No significant correlations were observed on any evaluation day in the placebo group (Table 2).

Trismus scores were predominantly grade 0 in both groups throughout the radiotherapy period, with no statistically significant differences between the PBMT and placebo PBMT groups at any evaluation time point (Supplementary Material 1).

Photobiomodulation reduces pain on palpation of masticatory muscles in irradiated head and neck patients

PBMT resulted in a reduction of pain on specific days in the masseter muscles when compared to the placebo group. For the right masseter, PBMT reduced pain scores on D7 (p = 0.039), while for the left masseter, no significant differences were found. The average scores in the PBMT group remained consistently lower throughout the evaluation days compared to the placebo group (Table 3).

Table 3 Influence of a preventive photobiomodulation protocol for trismus with a low-power laser or placebo on the variation in pain on palpation of the masseter and temporal muscles in patients undergoing radiotherapy for head and neck cancer

In the right masseter, both groups showed an increase in pain scores, but in the PBMT group this increase was 9.5% (p = 0.584) with values ​​ranging from 0.00 ± 0.00 to 0.22 ± 0.74, while in the placebo group 46.6% (p = 0.005) the scores ranged from 0.00 ± 0.00 to 0.78 ± 1.68. For the left masseter, there was a reduction of -13.5% (p = 0.439), ranging from 0.26 ± 1.25 to 0.22 ± 0.74; in the placebo group there was a significant increase in pain of 49.3% (p = 0.003) with scores ranging from 0.35 ± 1.67 to 0.74 ± 1.68 (Table 3).

There was no significant reduction in pain scores on specific days in the right and left temporal muscles. The mean daily reduction in pain scores on palpation of the right temporal muscle in the PBM group was marked − 48.1% (p = 0.003, ranging from 0.00 ± 0.00 to 0.00 ± 0.00. In the placebo group there was an increase in pain of 18.9% (p = 0.274). In the left temporal muscle there was also a reduction of -15.7% (p = 0.365) in pain scores on palpation, ranging from 0.00 ± 0.00 to 0.00 ± 0.0, while in the placebo group there was an increase in these scores of 52.1% (p = 0.001) throughout the RT treatment (Table 3).

In the medial pterygoid muscle on the right side, there was no significant reduction in pain scores on palpation on any evaluation day in the PBMT group (p > 0.05). However, in the medial pterygoid muscle on the left, there was a significant difference in pain scores on days D4 (p = 0.039), D5 (p = 0.019), D8 (p = 0.039), D9 (p = 0,039), D13 (p = 0.049), D30 (p = 0.043), D31 (p = 0.023), D32 (p = 0.023), D33 (p = 0.023), D34 (p = 0.023) and D35 (p-0.023) after PBM when compared to the placebo group (Table 4).

Table 4 Influence of preventive photobiomodulation protocol for trismus with low-power laser or placebo on the variation of pain on palpation in medial pterygoid muscles and temporomandibular joints in patients undergoing radiotherapy for head and neck cancers

Over the 35 days of evaluation, there was a mean daily reduction of -62.5% (p < 0.001) in pain scores on palpation in the PBM group in the right medial pterygoid muscle, while on the left side, the mean daily reduction in the placebo group was − 14.6% (p = 0.402). In the left pterygoid muscle, there was an increase in pain scores in both groups, but in the PBMT group this increase was 18.6% (p = 0.282), while in the placebo group this increase was 51.3% (p = 0.002). However, on specific days, pain scores in the right and left medial pterygoid did not vary significantly on most days evaluated in both groups (p > 0.05), except on the specific days mentioned above (Table 4).

In the right TMJ, PBMT did not show statistically significant differences in pain scores on any of the days evaluated when compared to the placebo group (p > 0.05). However, on the left side, PBMT was significantly more effective in reducing pain on days D9 (p = 0.039), D10 (p = 0.039) and D13 (p = 0.049) compared to the placebo group. Linear regression indicated a mean daily reduction of -9.4% (p = 0.589) in the PBMT group, while in the placebo group there was a significant increase of 72.6% (p < 0.001). Pain scores in the left TMJ in the PBMT group increased in both groups, however in the BMTP group this increase was 9.8% (p = 0.574) and in the placebo group it was 19.2% (p = 0.267) over the 35 days of treatment (Table 4).

Photobiomodulation to prevent trismus has little effect on oral health profile, nutritional intake, and quality of life

The DMFT index showed no statistically significant differences either within or between groups (p > 0.05). However, the ASGP increased significantly in both the PBMT group (p = 0.002) and the PBMT placebo group (p < 0.001), but there was no significant difference between the treatments (p > 0.05) (Table 5).

Table 5 Influence of preventive photobiomodulation protocol for trismus with low-power laser or placebo on oral health profile, nutritional intake, and quality of life in patients undergoing radiotherapy for head and neck cancer treatment

Regarding body weight, both groups showed a significant reduction over time (PBMT: p = 0.002; Placebo PBMT: p < 0.001), but there was no statistically significant difference in the percentage change in weight between the groups (p = 0.537) (Table 5).

As for the impact on quality of life, measured by the OHIP-14, there was a significant increase in the final scores in both groups (PBMT: p = 0.049; Placebo PBMT: p = 0.006), indicating a worsening in the perception of the oral impact. However, there was no statistically significant difference between the groups in the final values (p > 0.05) (Table 5).

The subscales of the OHIP-14 revealed that the dimensions of functional limitation and physical pain showed significant increases within both groups (p < 0.05), while the other dimensions, such as psychological discomfort, physical disability, psychological disability, social disability, and disadvantage, showed no significant changes within or between groups (p > 0.05) (Table 5).

The OHIP-14 scores showed small changes over time, with statistically significant differences in some questions. However, no robust differences were observed between the PBMT and Placebo PBMT groups (Supplementary Material 2).

Influence of a preventive photobiomodulation protocol for trismus on mouth opening after the first six months of radiotherapy

No statistically significant differences were observed between the PBMT and PBMT placebo groups in any of the evaluated periods (M1 to M6; p > 0.05). Mouth opening showed a slight increase over time in both groups, with a positive correlation in the PBMT group (r = 0.720, 95% CI: -0.218 to 0.966; p = 0.106) and a negative, also non-significant, correlation in the PBMT placebo group (r = -0.726, 95% CI: -0.967 to 0.207; p = 0.101) (Table 6).

Table 6 Influence of preventive photobiomodulation protocol for trismus with low-power laser or placebo on the variation in mouth opening after the first six months of radiotherapy in patients with head and neck cancer tumors

Pain scores during mouth opening also showed no significant differences between the groups over the six-month follow-up (p > 0.05). Pain remained at low levels in both groups, with a weak positive correlation in the PBMT group (r = 0.383, 95% CI: -0.621 to 0.911; p = 0.453) and a moderate correlation in the PBMT placebo group (r = 0.580, 95% CI: -0.436 to 0.946; p = 0.226) (Table 6).