Assessing thickness and stiffness of superficial/deep masticatory muscles in orofacial pain: an ultrasound and shear wave elastography study

Figures & data

Figure 1. Ultrasound imaging for thickness (A) and stiffness (B) measurements of the masseter muscle. White dashed line, maximal muscle thickness.

Figure 2. Ultrasound imaging for thickness (A) and stiffness (B) measurements of the temporalis muscle. White dashed line, maximal muscle thickness.

Figure 3. Ultrasound imaging for thickness (A) and stiffness (B) measurements of the temporalis muscle. White dashed line, maximal muscle thickness; LPM, lateral pterygoid muscle; CORP, coronoid process of the mandible.

Table 1. Characteristics of the enrolled participants.

	Asymptomatic Controls (n = 48)	Unilateral Pain (n = 13)	Bilateral Pain (n = 37)	p value
Female (%)	24 (50.00%)	9 (69.23%)	26 (70.27%)	0.129
Age (years)	51.00 ± 17.16 (46.02 to 55.98)	48.62 ± 15.09 (39.50 to 57.74)	49.30 ± 16.57 (43.77 to 54.82)	0.820
Body mass index (kg/m^2)	23.11 ± 2.84 (22.29 to 23.94)	22.78 ± 2.29 (21.39 to 24.16)	23.06 ± 4.66 (21.50 to 24.61)	0.515
Maximum pain-free mouth opening (mm)	47.29 ± 5.38 (45.73 to 48.85)	42.69 ± 5.72 (39.24 to 46.15)	45.11 ± 8.52 (42.27 to 47.95)	0.069
Numeric rating scale (right facial region)	0.00 ± 0.00 (0.00 to 0.00)	1.15 ± 1.57 (0.20 to 2.10)	3.35 ± 2.00 (2.68 to 4.02)	<0.001*
Numeric rating scale (left facial region)	0.00 ± 0.00 (0.00 to 0.00)	1.38 ± 1.80 (0.29 to 2.48)	3.27 ± 1.97 (2.61 to 3.93)	<0.001*
Masseter area tenderness (n, right facial region)	0 (0.00%)	6 (46.15%)	37 (100.00%)	<0.001*
Masseter area tenderness (n, left facial region)	0 (0.00%)	7 (53.85%)	36 (97.30%)	<0.001*
Temporalis area tenderness (n, right facial region)	0 (0.00%)	0 (0.00%)	12 (32.43%)	<0.001*
Temporalis area tenderness (n, left facial region)	0 (0.00%)	2 (15.38%)	12 (32.43%)	<0.001*

*p < 0.05.

The values of continuous variables were expressed by the mean and standard deviation (95% confidence interval of mean). The values of categorical variables were expressed by the number (percentage).

Table 2. Muscle thickness/stiffness in patients with unilateral orofacial pain.

	Painful site	Non-painful site	p value
Thickness
Masseter muscle (mm)	12.04 ± 1.31 (11.25 to 12.84)	11.87 ± 1.73 (10.83 to 12.92)	0.576
Temporalis muscle (mm)	5.35 ± 0.63 (4.97 to 5.73)	5.48 ± 0.82 (4.99 to 5.98)	0.442
Lateral pterygoid muscle (mm)	14.56 ± 1.23 (13.82 to 15.31)	14.62 ± 1.32 (13.83 to 15.42)	0.285
Stiffness
Masseter muscle (kPa)	14.68 ± 5.30 (11.48 to 17.89)	11.21 ± 4.31 (8.60 to 13.81)	0.101
Temporalis muscle (kPa)	34.49 ± 15.77 (24.96 to 44.02)	26.17 ± 9.63 (20.35 to 31.99)	0.221
Lateral pterygoid muscle (kPa)	34.18 ± 9.89 (28.20 to 40.15)	31.96 ± 12.64 (24.32 to 39.60)	0.552

*p < 0.05.

The values of continuous variables were expressed by the mean and standard deviation (95% confidence interval of mean).

Table 3. Comparative muscle thickness/stiffness values of the subjects.

	Right side	Left side	p value
Asymptomatic Controls (n = 48)
Thickness
Masseter muscle (mm)	12.09 ± 2.10 (11.48 to 12.70)	12.05 ± 2.09 (11.45 to 12.66)	0.829
Temporalis muscle (mm)	5.72 ± 0.91 (5.46 to 5.99)	5.56 ± 0.68 (5.37 to 5.76)	0.261
Lateral pterygoid muscle (mm)	16.52 ± 1.17 (16.18 to 16.86)	16.24 ± 1.39 (15.84 to 16.65)	0.054
Stiffness
Masseter muscle (kPa)	9.90 ± 2.56 (9.15 to 10.64)	9.24 ± 2.48 (8.52 to 9.95)	0.074
Temporalis muscle (kPa)	34.48 ± 19.19 (28.91 to 40.05)	40.52 ± 23.99 (33.55 to 47.49)	0.115
Lateral pterygoid muscle (kPa)	33.07 ± 14.15 (28.97 to 37.18)	32.93 ± 13.59 (28.99 to 36.88)	0.894
Patients with Unilateral Oral Facial Pain (n = 13)
Thickness
Masseter muscle (mm)	12.21 ± 1.48 (11.31 to 13.10)	11.71 ± 1.55 (10.77 to 12.64)	0.087
Temporalis muscle (mm)	5.42 ± 0.83 (4.92 to 5.92)	5.42 ± 0.63 (5.04 to 5.79)	0.944
Lateral pterygoid muscle (mm)	14.63 ± 1.32 (13.83 to 15.42)	14.56 ± 1.23 (13.81 to 15.30)	0.109
Stiffness
Masseter muscle (kPa)	14.05 ± 5.62 (10.66 to 17.45)	11.84 ± 4.35 (9.21 to 14.47)	0.279
Temporalis muscle (kPa)	31.82 ± 16.55 (21.81 to 41.82)	28.85 ± 10.01 (22.80 to 34.89)	0.917
Lateral pterygoid muscle (kPa)	35.05 ± 9.88 (29.07 to 41.02)	31.09 ± 12.42 (23.59 to 38.60)	0.196
Patients with Bilateral Oral Facial Pain (n = 37)
Thickness
Masseter muscle (mm)	11.75 ± 1.74 (11.17 to 12.33)	11.49 ± 1.91 (10.85 to 12.13)	0.161
Temporalis muscle (mm)	5.36 ± 0.72 (5.12 to 5.60)	5.26 ± 0.88 (4.97 to 5.55)	0.377
Lateral pterygoid muscle (mm)	14.65 ± 1.38 (14.19 to 15.11)	14.34 ± 1.37 (13.88 to 14.79)	0.052
Stiffness
Masseter muscle (kPa)	15.64 ± 7.50 (13.13 to 18.14)	14.46 ± 7.90 (11.83 to 17.10)	0.074
Temporalis muscle (kPa)	34.45 ± 13.16 (30.06 to 38.84)	40.29 ± 25.81 (31.68 to 48.89)	0.222
Lateral pterygoid muscle (kPa)	33.82 ± 12.12 (29.78 to 37.86)	34.97 ± 10.34 (31.52 to 38.42)	0.236

*p < 0.05.

The values of continuous variables were expressed by the mean and standard deviation (95% confidence interval of mean).

Table 4. Associations between patient demographics and masticatory muscle thickness/stiffness values.

	Thickness			Stiffness
	Masseter muscle	Temporalis muscle	Lateral pterygoid muscle	Masseter muscle	Temporalis muscle	Lateral pterygoid muscle
Female	−1.018(−1.659 to −0.377)	−0.277(−0.541 to −0.014)	−0.298(−0.802 to 0.206)	0.124(−1.912 to 2.16)	−4.949(−12.321 to 2.423)	−2.398(−6.95 to 2.153)
	p = 0.002*	p = 0.039*	p = 0.247	p = 0.905	p = 0.188	p = 0.302
Age	−0.021(−0.040 to −0.003)	−0.008(−0.016 to −0.001)	0.001(−0.014 to 0.015)	−0.009(−0.069 to 0.051)	−0.141(−0.358 to 0.077)	−0.011(−0.145 to 0.124)
	p = 0.026*	p = 0.033*	p = 0.942	p = 0.764	p = 0.204	p = 0.878
BMI	0.259(0.172 to 0.346)	0.081(0.045 to 0.117)	−0.018(−0.087 to 0.050)	0.344(0.067 to 0.621)	0.505(−0.498 to 1.508)	0.634(0.015 to 1.253)
	p < 0.001*	p < 0.001*	p = 0.603	p = 0.015*	p = 0.324	p = 0.045*
Right side	0.186(−0.015 to 0.387)	0.115(−0.025 to 0.255)	0.262(0.062 to 0.462)	1.097(0.384 to 1.811)	−4.677(−8.477 to −0.878)	0.181(−2.161 to 2.523)
	p = 0.070	p = 0.107	p = 0.010*	p = 0.003*	p = 0.016*	p = 0.880
Presence of Oral Myofascial Pain	−0.267(−1.044 to 0.510)	−0.127(−0.523 to 0.269)	−1.751(−2.417 to −1.085)	1.804(−0.760 to 4.368)	−9.050(−19.970 to 1.870)	−0.372(−7.109 to 6.364)
	p = 0.501	p = 0.528	p < 0.001*	p = 0.168	p = 0.104	p = 0.914
Side of Pain	0.114(−0.417 to 0.645)	−0.147(−0.493 to 0.199)	−0.057(−0.574 to 0.46)	3.603(1.736 to 5.471)	9.055(−0.399 to 18.509)	2.252(−3.577 to 8.081)
	p = 0.674	p = 0.404	p = 0.829	p < 0.001*	p = 0.060	p = 0.449

*p < 0.05. Data are expressed by the beta coefficients and their 95% confidence intervals (analyzed by a generalized estimating equation).

BMI: body mass index.

Figure 4. Correlations between muscle thickness/stiffness and numeric rating scale for masseter (A, B), temporalis (C, D) and lateral pterygoid (E, F) muscles.

Data availability statement

The datasets generated or analyzed during the study are available from the corresponding author on reasonable request.