Proprioceptive neuromuscular facilitation stretching exercises for treatment of temporomandibular dysfunction in patients with forward head posture: A double-blinded,randomized,controlled trial

Abstract

BACKGROUND:

Proprioceptive neuromuscular facilitation (PNF) stretching exercises have been widely advocated for the management of patients with different musculoskeletal conditions. However, its effect on the treatment of temporomandibular dysfunction (TMD) in patients with forward head posture (FHP) has not been fully investigated.

OBJECTIVE:

To investigate the effect of PNF stretching exercises on the treatment of TMD in patients with FHP.

METHODS:

A prospective, randomized, double-blinded clinical trial. Twenty-four patients with TMD and FHP aged from 18–40 years were randomly assigned to PNF or control group. The PNF group composed of 12 patients received PNF stretching exercises of masticatory muscles in addition to routine physical therapy treatment (FHP correction exercises and ultrasound for the temporomandibular joint); the control group composed of 12 patients received routine physical therapy treatment only. Interventions were conducted twice a week for six weeks. Craniovertebral angle, pain threshold, pain intensity, temporomandibular joint ROM, and temporomandibular joint function were assessed for all participants before and after the intervention. The outcomes were analyzed using Two-way mixed MANOVA. For further multiple comparisons, post-hoc tests with the Bonferroni correction were performed.

RESULTS:

There was no significant difference between both groups pre-treatment ( $p>$ 0.05). Comparison between groups post-treatment revealed statistically significant differences in all outcome measures ( $p<$ 0.05) in favor of the PNF group.

CONCLUSION:

Adding PNF stretching exercises of masticatory muscles to routine physical therapy programs is an effective method for management of TMD in patients with FHP more than routine physical therapy programs alone.

Keywords

Neck posture craniovertebral angle neuromuscular facilitation craniomandibular disorders

1. Introduction

Temporomandibular joint disorders are an umbrella term for pain and dysfunction of the temporomandibular joint (TMJ) [1]. Alteration in the function of TMJ leads to poor quality of life for the individual as this joint is involved in basic activities like talking, eating, and laughing. The symptoms of TMJ disorders include headache, limited mouth opening, muscle spasm, tinnitus, fullness in ears, cervical spine dysfunction, and altered craniovertebral angle seen as forward head posture (FHP) [2, 3].

The TMJ within its muscular and ligamentous connection to the cervical spine forms a functional complex known as the ‘cranio cervical’ mandibular system [4]. It has been observed that there is a synergistic relationship between the cervical spine and masticatory muscles with jaw and neck muscles during normal activities involving chewing, talking, and yawning [5]. Therefore, head and neck position affects TMJ kinematics and any changes in head position change the position of the mandible [6, 7, 8].

The integrated approach of dental practitioners, physical therapists, and psychologists is often required for the successful management of people with long-standing temporomandibular dysfunctions (TMDs) [9]. According to the American Academy of Craniomandibular Disorders and the Minnesota Dental Association, physical therapy modalities (electrophysical modalities, therapeutic exercises, and manual therapy techniques), are an important treatment for musculoskeletal pain relief and inflammation reduction and restoration of oral motor function [10].

Proprioceptive neuromuscular facilitation (PNF) involves manual resistance using isometric muscular contraction followed by relaxation and stretching of the tight muscle; is used for the treatment of myofascial trigger points and as well as for the relief of any pain originating in these muscles [11]. PNF achieves these objectives by making use of two physiological phenomena: post-contraction inhibition and reciprocal inhibition [12]. It has been reported by Travell and Simon [13] that PNF techniques directed to each specific jaw muscle, namely the masseter, temporalis, medial pterygoid, and lateral pterygoid muscle can release trigger point tension in the tight jaw muscles.

It was pointed out by numerous researchers that pain in the upper quarter and masticatory motor system may be caused by cervical spine disorders and vice versa [14, 15]. In FHP, flexion occurs in the lower cervical spine C3-C7 with hyperextension of upper cervical spine C1 and C2, which generates tension in the infrahyoid muscles, lower and posterior traction on the hyoid, and traction transfer to the mandible, leading to retraction and opening of mouth [16]. In addition, FHP seemed to be associated with a decreased pain threshold and the development of active trigger points in the cervical and masticatory muscles [17, 18].

Although the literature has revealed a number of studies on PNF and its efficiency in the treatment of myofascial pain and associated dysfunction [19, 20, 21, 22, 23], to date no studies have shown the effectiveness of PNF for the treatment of TMJ dysfunction in patients with FHP. Hence, this is the first double-blinded randomized controlled trial to investigate the effect of PNF stretching exercises on the treatment of TMD in patients with FHP.

2. Materials and methods

The present study is a prospective, randomized, parallel-group, double-blinded clinical trial. The study was carried out from August 2022 to January 2023, and was approved by the Research Ethics Committee at the Faculty of physical therapy, Cairo University (P.T.REC/012/004165). All volunteers were provided with written informed consent to participate in the study after being fully informed of the study’s goals and procedures. The participants were recruited from the Outpatient Clinic at the Faculty of Physical Therapy, Misr University for Science and Technology. Every procedure was carried out in conformity with the Helsinki Declaration of 1964 and any subsequent changes. The study was registered in the ClinicalTrials.gov registry, registration number: NCT05709340.

Figure 1.

Flowchart of study participants.

2.1 Study population

Twenty-four patients of both genders were enrolled in the current study in accordance with the following eligibility criteria: (1) The patient’s ages ranged from 18 to 40 years [24]; (2) having TMD symptoms sustained for at least twelve weeks duration established by expert physician or orthopaedician; (3) having FHP with CVA $<$ 53^∘; (4) mouth opening $<$ 25 mm [25]; (5) Pain level greater than 20 mm and less than 80 mm on Numeric Rating Scale (NRS). Patients were excluded if they exhibited any of the following criteria: (1) TMJ fracture undergone any surgical procedure for TMJ; (2) Fracture surrounding TMJ; (3) Dislocation or subluxation of TMJ; (4) Systemic joint diseases including rheumatoid arthritis and osteoporosis, congenital conditions or facial paralysis; (5) recent dental work or TMJ surgery; (6) Hematological cervical disorders which may affect the jaw; (7) Neurological deficits e.g. Bell’s palsy, Trigeminal neuralgia; (8) Recent infections affecting head and neck (within the last six months) e.g. bone infections, meningitis, encephalitis, malaria, ear infection; (9) Participants who were using any functional appliances e.g. dentures, braces, bite appliances altered or fitted within the previous 12 weeks prior to the commencement of this study; (10) Patients who underwent any physical therapy treatment within the last 2 weeks before the trial. Thirty-six patients were initially screened for eligibility, 24 were ultimately accepted into the experiment, and they were randomized into two groups as shown in Fig. 1.

2.2 Randomization

Using the online randomization application “Research Randomizer” (https://www.randomizer.org), the participants were randomly assigned to one of the two groups (ratio 1:1): PNF group ( $n=$ 12) or control group ( $n=$ 12). An investigator who was not involved in the clinical aspect of the study created sequentially numbered index cards with the random group assignments on them in accordance with the randomly generated numbers to ensure allocation concealment. Folded and sealed envelopes that were hidden from the groups contained the index cards. In order to split the participants into groups, the physiotherapist administering the therapies first opened each package. At baseline and at week six, the assessments were carried out by a different physiotherapist who had no idea which groups the patients belonged to “assessor-blinded”. The patients were blinded to the group assignments.

2.3 Intervention

The same routine physical therapy program was given to each patient in both groups. This includes ultrasound therapy followed by Kendall exercises. Ultrasound therapy was applied over TMJ and masseter area with Mode 1:1, frequency of 1MHz, intensity of 1.5 W/cm², and duration of 5 minutes [25]. Then, Kendall exercises were performed as follows: (a) Strengthening the deep cervical flexors: The patient was asked to do a flat-back, chin-down position and hold this position for 2–8 seconds, (b) Stretching the cervical extensors: The patient was asked to place one hand on the occipital area and other on the chin in a seated position, then a head-down, flexed neck position to stretch the cervical extensors, (c) Strengthening shoulder retractors: This exercise was done in order to move the shoulder blades towards one another while standing, the patient was instructed to wrap red (medium) Theraband around a stable item and then draw the band back as far as they could with both hands, (d) Stretching of the pectoralis major muscle: The therapist stood behind the patient and held both elbows and performed bilateral pectoralis stretching. To stretch the costal division, the arm should be elevated to approximately 135 degrees. For sternal division, the arm abducted to 90 degrees. For clavicular division, the arm was rested at the side. Every strengthening exercise was repeated for 12 repetitions and done for 3 sets and each stretching exercise was held for 30 seconds and repeated 3 times [26].

Table 1
Comparison of subject characteristics between PNF and control groups

	PNF group	Control group	Statistics	$p$ -value
Age, mean $\pm$ SD (years)	27.92 $\pm$ 6.40	27.50 $\pm$ 5.33	( $t=$ 0.17)	0.86
Sex, $n$ (%)
Female	8 (67%)	8 (67%)
Male	4 (33%)	4 (33%)
Affected side, $n$ (%)
Right	8 (67%)	9 (75%)	( $\chi^{2}=$ 0.20)	0.65
Left	4 (33%)	3 (25%)

SD, Standard deviation; $t$ , unpaired $t$ value; $p$ value, Level of significance.

Patients in the PNF group additionally received PNF stretching exercises for masticatory muscles. The procedures for applying the PNF exercises were done following the procedures that had been previously used by Travell and Simons [13] and Gray [19], and are detailed in the Supplementary Table 1. During PNF exercises, each contraction was held for 10 seconds, and each stretch (relaxation phase) was allowed to continue as long as the muscle tension continued to give away, for 5–10 seconds. The procedure was repeated three times for each affected muscle. Twelve sessions, two times each week for six weeks, were given to each patient in both groups.

2.4 Outcome measures

For all patients, measures were taken twice: at baseline and after 6 weeks of treatment (the day after the last session). The assessment procedures include the following items:

Assessment of CVA using the photographic posture analysis method:

Surgimap software (http://www.surgimape.com) was used to determine the CVA which is proved to be valid and reliable for measuring CVA (excellent degree of reliability, with ICC $>$ 0.9) [27], 64-mega pixel camera (Samsung A71) was positioned on a tripod stand to capture side view photos of subjects [28]. The distance between the camera and the participant was 50 cm. The base of the camera was leveled to the participants’ shoulder level. After the camera was positioned, the patients were asked to stand in a relaxed position, with their feet slightly apart and arms by their sides, and look forward at a point at eye level. The right ear tragus and C7 spinous process were marked with a marker made of paper roll fixed on the skin and a side view was captured.

Assessment of pain pressure threshold of masticatory muscles:

The pain pressure threshold (PPT) over the temporalis and masseter muscles was assessed using an algometer with a 1 cm² probe tip (FDIX Digital Force Gage; Wagner Instruments). The algometer has a good degree of reliability (ICC $>$ 0.87) in the assessment of PPT [29]. Before the algometer was used for measurement, the most tender area of pain over masseter and temporalis trigger points were detected by the patient’s determination of the location as “his or her point of maximum pain” during a prior examination. This measurement site was marked by using a grease pencil to make sure that the same point was measured during the procedure. Furthermore, the sites were photographed after their marking to improve the reliability of PPT measurements at the post-treatment assessment. The tip of the algometer was placed over that area with pressure until the patient felt pain. Patients were instructed before the test to respond by “raising hands” as soon as they felt the pain. Every 30 seconds, three measurements were collected using the kg/cm² unit of measurement. The final number was determined by averaging the results of the three consecutive measurements.

Assessment of temporomandibular joint ROM:

Mandibular depression, protrusion, and lateral deviation were all measured with a caliper. The external auditory canals of both ears were covered with the fingers of both hands, and patients were instructed to open and close their mouths before moving their mandibular protrusion. The mandibular depression ranges between 34 and 44 mm. Up to 10 mm of active mandibular protrusion is considered normal. Equal distances from the midline should separate the mandibular lateral deviations. The usual range should be 10 mm when patients are requested to move their jaw to both sides without completely losing contact between their upper and lower jaw teeth.

Assessment of the function of temporomandibular joints:

Temporomandibular Disorder Disability Questionnaire was used for evaluating the temporomandibular joint function. It includes the following subsections: the Temporomandibular Disorder Disability Index, Temporomandibular Disorder symptom intensity scale, and Temporomandibular Disorder symptom frequency scale.

The Temporomandibular Disorder Disability Index (TMDDI) provides scores and information on many of the disabilities and symptoms with which patients with TMJ disorders can present. It consists of 10 questions, each with five possible answers with a score ranging from 0 to 4. The points of each question are then added and divided by the total number possible, and then multiplied by 100 to give the percentage.

The Temporomandibular Disorder Symptom Intensity Scale (TMDSIS) and the Temporomandibular Disorder Symptom Frequency Scale (TMDSFS) are two visual analogue scales with seven parts each that assess the frequency and severity of a patient’s TMJ symptoms. The patient must rate the severity and frequency of their symptoms on a scale of 0 to 10 score levels. The score for each scale is added and then divided by the maximum score possible (7 sections $\times$ 10 maximum score possible $=$ 70) and then multiplied by 100 to give a percentage.

Assessment of pain intensity using the Numerical Rating Scale (NRS):

The 101 questionnaire was measured in written form, by asking the patient to mark a number between 0 and 100 on a horizontal line that best represented how much pain they felt at their worst and their least discomfort points. The patient’s average level of pain is represented as a percentage by the average of these two totals.

2.5 Sample size determination

Sample size was calculated using sample-size calculating software G $*P$ ower version 3.1.9.2 (University of Kiel, Germany). The sample size calculation indicated the need for at least twenty-four subjects when using the following parameters: [F tests-MANOVA: Repeated Measures, within-between interaction, Type I error $=$ 0.05, Type II error $=$ 0.1, effect size $=$ 0.70]. The effect size (0.70) was calculated on the primary outcome (CVA) from a pilot study on 10 subjects (5 in each group).

2.6 Data analysis

Descriptive statistics and unpaired t-test were conducted for the comparison of subject characteristics between groups. Chi-squared test was used for the comparison of affected side distribution between groups. The Shapiro-Wilk test was used to ensure that the data followed a normal distribution. To ensure group consistency, we used Levene’s test for homogeneity of variances. CVA, NPR, PPT, TMJ ROM, and TMJ function were examined using Two-way mixed MANOVA. For further multiple comparisons, post-hoc tests with the Bonferroni correction were performed. All statistical analyses were performed with a p-value of less than 0.05 considered significant. All statistical analysis was performed using SPSS version 22 for Windows (IBM Corp., Armonk, IL, USA).

3. Results

3.1 Baseline participant characteristics

Table 1 shows the subject characteristics of the study and control groups. There was no statistically significant difference between groups in age, sex, and affected side distributions ( $p>$ 0.05).

3.2 Effect of treatment on CVA, PPT, NPR, TMJ ROM, and TMJ function

A significant interaction between treatment and time was discovered using mixed MANOVA (F $=$ 109.53, $p=$ 0.001). The main impact of time was statistically significant (F $=$ 554.84, $p=$ 0.001). The main treatment effect was statistically significant (F $=$ 10.02, $p=$ 0.001).

Table 2
Mean CVA, NPR and PPT of masseter and temporalis muscles pre and post treatment of PNF and control groups

	PNF group	Control group
	Mean $\pm$ SD	Mean $\pm$ SD	MD (95% CI)	$p$ value	Effect size
CVA (degrees)
Pre treatment	44.21 $\pm$ 2.39	44.05 $\pm$ 2.38	0.16 ( $-$ 1.86: 2.18)	0.87
Post treatment	49.08 $\pm$ 2.46	46.74 $\pm$ 2.4	2.34 (0.28: 4.4)	0.02	0.96
MD (95% CI)	$-$ 4.87 ( $-$ 5.35: $-$ 4.39)	$-$ 2.69 ( $-$ 3.17: $-$ 2.21)
	p $=$ 0.001	p $=$ 0.001
NPR
Pre treatment	68.75 $\pm$ 12.63	67.08 $\pm$ 13.04	1.67 ( $-$ 9.21: 12.54)	0.75
Post treatment	37.08 $\pm$ 10.54	57.91 $\pm$ 12.14	$-$ 20.83 ( $-$ 30.46: $-$ 11.20)	0.001	1.83
MD (95% CI)	31.67 (29.25: 34.08)	9.17 (6.75: 11.58)
	p $=$ 0.001	p $=$ 0.001
PPT of masseter (lb)
Pre treatment	1.28 $\pm$ 0.24	1.27 $\pm$ 0.26	0.01 ( $-$ 0.2: 0.21)	0.93
Post treatment	1.97 $\pm$ 0.21	1.51 $\pm$ 0.24	0.46 (0.27: 0.65)	0.001	2.03
MD (95% CI)	$-$ 0.69 ( $-$ 0.75: $-$ 0.62)	$-$ 0.24 ( $-$ 0.30: $-$ 0.16)
	p $=$ 0.001	p $=$ 0.001
PPT of temporalis (lb)
Pre treatment	1.54 $\pm$ 0.23	1.60 $\pm$ 0.19	$-$ 0.06 ( $-$ 0.23: 0.12)	0.52
Post treatment	2.12 $\pm$ 0.24	1.71 $\pm$ 0.18	0.41 (0.24: 0.6)	0.001	1.93
MD (95% CI)	$-$ 0.58 ( $-$ 0.65: $-$ 0.51)	$-$ 0.11 ( $-$ 0.17: $-$ 0.03)
	p $=$ 0.001	p $=$ 0.007

Mean; SD, Standard deviation; MD, Mean difference; CI, Confidence interval; $p$ -value, Level of significance, CVA; Craniovertebral Angle, NPR; Numerical Pain Rating, PPT; Pain Pressure Threshold.

3.3 Within-group comparison

After treatment, the CVA, PPT of the masseter and temporalis muscles, and TMJ ROM (opening, protrusion, right and left deviation) of both groups increased significantly compared to pretreatment ( $p<$ 0.001). While NPR, TMDDI, TMDSIS, and TMDSFS of both groups decreased significantly in post-treatment compared with pre-treatment ( $p<$ 0.001), as shown in Tables 2–4.

3.4 Between-group comparison

There was a significant increase in CVA ( $p<$ 0.05), PPT of the masseter and temporalis muscles ( $p<$ 0.001), TMJ ROM ( $p<$ 0.001), and a significant decrease in NPR ( $p<$ 0.001), and TMJ function ( $p<$ 0.001) of PNF group compared with that of the control group (Tables 2–4).

4. Discussion

Table 3
Mean TMJ ROM pre and post treatment of PNF and control groups

ROM (mm)	PNF group	Control group
	Mean $\pm$ SD	Mean $\pm$ SD	MD (95% CI)	$p$ value	Effect size
Opening
Pre treatment	22.35 $\pm$ 2.22	22.52 $\pm$ 2.59	$-$ 0.17 ( $-$ 2.21: 1.88)	0.87
Post treatment	39.00 $\pm$ 3.00	26.85 $\pm$ 3.61	12.15 (9.34: 14.95)	0.001	3.66
MD (95% CI)	$-$ 16.65 ( $-$ 17.64: $-$ 15.64)	$-$ 4.33 ( $-$ 5.33: $-$ 3.33)
	p $=$ 0.001	p $=$ 0.001
Protrusion
Pre treatment	5.88 $\pm$ 0.51	5.85 $\pm$ 0.55	0.03 ( $-$ 0.42: 0.47)	0.91
Post treatment	7.60 $\pm$ 0.43	6.56 $\pm$ 0.51	1.04 (0.63: 1.43)	0.001	2.20
MD (95% CI)	$-$ 1.72 ( $-$ 1.93: $-$ 1.49)	$-$ 0.71 ( $-$ 0.93: 0.48)
	p $=$ 0.001	p $=$ 0.001
Right deviation
Pre treatment	5.55 $\pm$ 0.66	5.58 $\pm$ 0.68	$-$ 0.03 ( $-$ 0.60: 0.53)	0.90
Post treatment	9.64 $\pm$ 0.89	6.48 $\pm$ 0.91	3.16 (2.39: 3.92)	0.001	3.51
MD (95% CI)	$-$ 4.09 ( $-$ 4.44: $-$ 3.74)	$-$ 0.9 ( $-$ 1.25: $-$ 0.54)
	p $=$ 0.001	p $=$ 0.001
Left deviation
Pre treatment	5.54 $\pm$ 0.48	5.40 $\pm$ 0.38	0.14 ( $-$ 0.23: 0.50)	0.45
Post treatment	9.5 $\pm$ 0.98	6.32 $\pm$ 0.61	3.18 (2.48: 3.87)	0.001	3.89
MD (95% CI)	$-$ 3.96 ( $-$ 4.39: $-$ 3.52)	$-$ 0.92 ( $-$ 1.34: $-$ 0.47)
	p $=$ 0.001	p $=$ 0.001

Mean; SD, Standard deviation; MD, Mean difference; CI, Confidence interval; $p$ -value, Level of significance, ROM; Range of Motion.

Table 4

Mean TMJ function pre and post-treatment of PNF and control groups

	PNF group	Control group
	Mean $\pm$ SD	Mean $\pm$ SD	MD (95% CI)	$p$ value	Effect size
TMDDI
Pre treatment	83.58 $\pm$ 6.62	82.71 $\pm$ 7.18	0.87 ( $-$ 4.97: 6.72)	0.75
Post treatment	31.45 $\pm$ 10.46	61.87 $\pm$ 9.77	$-$ 30.42 ( $-$ 39: $-$ 21.84)	0.001	3.01
MD (95% CI)	52.13 (49.01: 55.23)	20.84 (17.72: 23.94)
	p $=$ 0.001	p $=$ 0.001
TMDSIS
Pre treatment	76.35 $\pm$ 10.97	74.17 $\pm$ 11.00	2.18 ( $-$ 7.13: 11.48)	0.63
Post treatment	27.09 $\pm$ 6.01	46.91 $\pm$ 7.48	$-$ 19.82 ( $-$ 25.56: $-$ 14.07)	0.001	2.92
MD (95% CI)	49.26 (45.64: 52.87)	27.26 (23.64: 30.88)
	p $=$ 0.001	p $=$ 0.001
TMDSFS
Pre treatment	74.01 $\pm$ 10.81	70.87 $\pm$ 10.96	3.14 ( $-$ 6.08: 12.35)	0.48
Post treatment	24.60 $\pm$ 5.82	42.29 $\pm$ 7.51	$-$ 17.69 ( $-$ 23.38: $-$ 12)	0.001	2.63
MD (95% CI)	49.41 (45.68: 53.13)	28.58 (24.86: 32.31)
	p $=$ 0.001	p $=$ 0.001

Mean; SD, Standard deviation; MD, Mean difference; CI, Confidence interval; $p$ -value, Level of significance, TMDDI; Temporomandibular Disorder Disability Index, TMDSIS; Temporomandibular Disorder symptom intensity scale, TMDSFS; Temporomandibular Disorder symptom frequency scale.

Conservative treatment approaches for TMD patients are currently supported by evidence. It has been reported by Armijo-Olivo et al. [30] that physical therapy is one of the top 10 treatments for reducing neck and mandible pain and increasing ROM in TMD patients. However, there is still a gap in the literature about to what extent PNF stretching exercises for masticatory muscles could be effective for the treatment of those with TMD and FHP. So, the current study was conducted to examine the effect of PNF stretching exercises on pain intensity, ROM, CVA, pain threshold, and functional abilities in TMD patients with FHP. This study exhibits that the study group who obtained PNF exercises along with the routine physical therapy program demonstrated greater improvement than the control group who received routine physical therapy alone regarding pain intensity, pain threshold, CVA, ROM, and function in TMDs patients with FHP.

Algometer and NRS readings both measure a participant’s pain; one is an objective measure, the other subjective. In the existing study, the experimental group showed statistically significant differences in NPR, from 68.75 $\pm$ 12.63 before treatment to 37.08 $\pm$ 10.54 after treatment, and in PPT, from 1.28 $\pm$ 0.24 to 1.97 $\pm$ 0.21 for the masseter muscle and from 1.54 $\pm$ 0.23 to 2.12 $\pm$ 0.24 for the temporalis muscle ( $p<$ 0.05). Pain relief and increased PPT are the results of the stretching effect applied using PNF techniques as they stimulate muscle and tendons receptors, improving the efficiency of nerve control in muscles, increasing blood circulation and tissue fluids, and normalizing muscle tone [21]. During PNF techniques, Golgi tendon organs are activated during the autogenic inhibition process. When the target muscle contracts to the maximum, the inhibitory pulse is sent through the afferent nerve fibers Ib to the inhibitory interneurons in the spinal cord. The same muscle’s alpha motor neuron is also suppressed by these inhibitory interneurons. This theory explains how the inhibitory muscle can relax during PNF’s contract-relax and hold-relax techniques [11].

In between-group comparison, the significant improvement in pain intensity and pain threshold in favor of the PNF group comes in accordance with the existing evidence of Gray [19], who revealed that there was a statistically significant improvement in Masseter, Temporalis algometer readings favoring the PNF group for the treatment of masticatory myofascial trigger point-induced TMJ dysfunction. In addition, the results of this study come in agreement with Trampas et al. [20] who investigated the therapeutic effects of massage and stretching PNF on pain intensity and PPT at myofascial pain trigger points and found that the group receiving massage along with stretching therapy PNF techniques experienced a substantial improvement in pain and PPT. On the contrary, Freshwater and Gosling [31] reported that PNF exercises did not significantly decrease pain in TMD patients. This contradiction in the results between the two studies may be due to a difference in the inclusion criteria of the patients between the two studies. In the study of Freshwater and Gossling, both symptomatic and asymptomatic patients with a limited set of mouth openings were recruited; while in the current study, only symptomatic patients were recruited.

Regarding TMJ ROM, there was a significant improvement in both groups but more significant in the PNF group which is consistent with the findings of Malone et al. [32] advocate that “hold-relax” techniques are similar to Muscle Energy Technique (MET) for mandibular elevators (masseter, temporalis, medial pterygoid) in improving ROM, functional mobility. Besides, Calisgan et al. [23] demonstrated that PNF, myofascial releasing, and home exercises were found to be more successful in the treatment of bruxism than traditional treatment methods. Further confirmation of the superiority of PNF to improve joint ROM is provided by the data from previous studies applied to investigate its effect on different joints in the body. In a study conducted by Gonzalez-Rave et al. [33], the ROM of 51 patients’ hip and shoulder joints after using PNF procedures was examined, and they reported that joint ROM improved significantly more in the PNF group compared to the other groups ( $p<$ 0.05). Furthermore, the current findings are in line with those of a study by Fasen et al. [34], which measured the effects of stretching therapy on 100 patients and found that active stretching therapy based on PNF was successful in increasing their joints ROM. Additionally, in a study conducted by Decicco and Fisher [35] it was found that PNF-based stretching therapy increased the ROM of overhand athletes’ shoulder joints.

Dysfunctions in the cervical paravertebral muscles have been linked to improper tension in the masticatory muscles, which has been linked to poor head position [36, 37]. So, when evaluating TMD patients, it is necessary to evaluate and treat the cervical spine and shoulder girdle in addition to the stomatognathic system in order to assist in relieving the complicated and persistent head and neck symptoms [2]. A possible explanation could be the biomechanical and neurophysiological relationships between the cervical spine and the TMJ [38]. So, the significant improvement in the CVA in the PNF group more than in the control group may be attributed to the significant improvement in the TMJ ROM, and PPT of the masseters and temporalis muscles in the study group than the control group. This explanation was confirmed by Halmova et al. [39] who investigated the causality between the myofascial pain in the head and neck and craniocervical dysfunction as well as the clinical value of physiotherapy, and they demonstrated the effectiveness of combining masticatory muscle therapy with cervical muscle relaxation and stretching exercises.

Further confirmation of the effect of PNF exercises on the alignment of the cervical spine by Lee [22] who concluded that a 4-week PNF exercise is an important component of treating the disc location at the TMJ by evaluating the correct alignment of the neck and the contraction of the upper cervical extensors. In addition, Maluf et al. [40] found that individuals with TMDs who stretched their superficial neck and masticatory muscles experienced a reduction in pain intensity and tension in their neck and craniofacial muscles. Overall the results of the current study confirm the superiority of PNF in addition to routine physical therapy programs compared to routine physical therapy programs alone regarding pain, PPT, ROM, and functionality in patients with TMDs with FHP.

There are issues in this study that need to be addressed. The first is that we don’t know how long the effects of treatment last because we haven’t done a follow-up examination after a long period after treatment was completed. Therefore, a study with a long-run follow-up period is needed. The second one is that our sample size was relatively small and the sample was restricted to patients aged 18–40 years; therefore, future studies are required for older patients with large sample sizes.

5. Conclusions

PNF stretching exercises of masticatory muscles with routine physical therapy programs improved CVA, PPT, TMJ ROM, and function of TMJ, and decreased pain in patients with TMD and FHP more than routine physical therapy programs alone. Therefore, in a clinical setting, the addition of PNF stretching exercises of masticatory muscles to routine physical therapy programs for patients with TMD and FHP is recommended.

Author contributions

M.S and W.M conceived the research idea and designed the study. M.S and W.M. recruited the study participants and performed the interventions. M.S, W.M, W.H, and E.M interpreted and analyzed the data. M.S and W.M drafted the manuscript. W.H and E.M critically revised the manuscript for important intellectual content. All authors contributed to revisions of the manuscript and reviewed the final version.

Data availability

The data that supports the findings of this study are available from the corresponding author upon reasonable request.

Ethical approval

The protocol was registered and received approval from the Ethics Committee at the Faculty of Physical Therapy, Cairo University (P.T.REC/012/004165).

Funding

The authors received no financial support for the research, authorship, and/ or publication of this article.

Informed consent

All patients signed a written informed consent form.

Supplementary data

The supplementary files are available to download from http://dx.doi.org/10.3233/BMR-230358.

Footnotes

Acknowledgments

The authors would like to extend their appreciation to all patients who participated in this study.

Conflict of interest

The authors declare no potential conflicts of interest with respect to the research, authorship, and/ or publication of this article.

References

List

Jensen

. Temporomandibular disorders: Old ideas and new concepts. Cephalalgia. 2017; 37: 692-704.

De Wijer

Steenks

De Leeuw

Bosman

Helders

. Symptoms of the cervical spine in temporomandibular and cervical spine disorders. J Oral Rehabil. 1996; 23: 742-750.

Feteih

. Signs and symptoms of temporomandibular disorders and oral parafunctions in urban Saudi Arabian adolescents: a research report. Head Face Med. 2006; 2: 1-7.

Wadhokar

Patil

Phansopkar

. Efficacy of Sub Occipital Myofacial Release Technique on Functional Disability in Temporomandibular Dysfunction with Neck Pain: A Randomized Control Trial 2021.

Kraus

. Temporomandibular Disorders, Head and Orofacial Pain: Cervical Spine Considerations. Dent Clin North Am. 2007; 51: 161-193.

Higbie

Seidel-Cobb

Taylor

Cummings

. Effect of head position on vertical mandibular opening. J Orthop Sports Phys Ther. 1999; 29: 127-130.

Poacher

. The relative effectiveness of three treatment protocols in the management of temporomandibular disorder (Doctoral dissertation); 2011.

Pardehshenas

Maroufi

Sanjari

Parnianpour

Levin

. Lumbopelvic muscle activation patterns in three stances under graded loading conditions: proposing a tensegrity model for load transfer through the sacroiliac joints. J Bodyw Mov Ther. 2014; 18: 633-642.

Harrison

Thorp

Ritzline

. A proposed diagnostic classification of patients with temporomandibular disorders: implications for physical therapists. J Orthop Sports Phys Ther. 2014; 44: 182-197.

10.

Sharma

Gupta

Pal

Jurel

. Etiological factors of temporomandibular joint disorders. Natl J Maxillofac Surg. 2011; 2: 116-119.

11.

Hindle

Whitcomb

Briggs

Hong

. Proprioceptive neuromuscular facilitation (pnf) its mechanisms and effects on range of motion and muscular function. J Hum Kinet. 2012; 31: 105-113.

12.

Liebenson

Tunnell

Murphy

Gluck-Bergman

. Manual resistance techniques. In Rehabilitation of the Spine: A Practitioner’s Manual. Lippincott/Williams & Wilkins, Baltimore, 2007.

13.

Travell

Simons

. Myofascial pain and dysfunction (Vol. 1); Baltimore, MD, USA: Williams and Wilkins, 1999.

14.

Gadotti

Berzin

Biasotto-Gonzalez

. Preliminary rapport on head posture and muscle activity in subjects with class I and II. J Oral Rehabil. 2005; 32: 794-799.

15.

Wiesinger

Malker

Englund

Wänman

. Does a dose-response relation exist between spinal pain and temporomandibular disorders? BMC Musculoskelet Disord. 2009; 10: 1-8.

16.

Taucci

Bianchini

. Verification of the interference of temporomandibular disorders in speech articulation: complaints and characterization of mandibular movements. Int J Speech Lang Pathol Audiol. 2007; 12: 274-280.

17.

de Farias Neto

de Santana

de Santana-Filho

Quintans-Junior

de Lima Ferreira

Bonjardim

. Radiographic measurement of the cervical spine in patients with temporomandibular dysfunction. Arch Oral Biol. 2010; 55: 670-678.

18.

Fernández-de-Las-Peñas

Galán-del-Río

Alonso-Blanco

Jiménez-García

Arendt-Nielsen

Svensson

. Referred pain from muscle trigger points in the masticatory and neck-shoulder musculature in women with temporomandibular disorders. J Pain. 2010; 11: 1295-1304.

19.

Gray,

. The relative effectiveness of proprioceptive neuromuscular facilitation versus ultrasound therapy in the treatment of temporamandibular joint dysfunction caused by masticatory myofascial trigger points, in terms of subjective and objective clinical findings (Doctoral dissertation), 2002.

20.

Trampas

Kitsios

Sykaras

Symeonidis

Lazarou

. Clinical massage and modified proprioceptive neuromuscular facilitation stretching in males with latent myofascial trigger points. Phys Ther Sport. 2010; 11: 91-98.

21.

Lee

Park

. The effect of proprioceptive neuromuscular facilitation therapy on pain and function. J Phys Ther Sci. 2013; 25: 713-716.

22.

Lee

. Influence of proprioceptive neuromuscular facilitation therapeutic exercise on woman with temporomandibular joint disorder: a case study. J Exerc Rehabil. 2018; 14: 1074.

23.

Calisgan

Talu

Altun

Dedeoglu

Duman

. The effects of proprioceptive neuromuscular facilitation, myofascial releasing maneuvers and home exercises on pain and jaw function in patients with bruxism. Medicine. 2018; 7: 617-621.

24.

Trivedi

Bhatt

Dhanakotti

Nambi

. Comparison of muscle energy technique and myofascial release technique on pain and range of motion in patients with temporomandibular joint dysfunction: a randomized controlled study. Int J Physiother Res. 2016; 4: 1788-1792.

25.

Tuncer

Ergun

Karahan

. Temporomandibular disorders treatment: comparison of home exercise and manual therapy. Fizyoter Rehabil. 2013; 24: 09-16.

26.

Diab

Moustafa

. The efficacy of forward head correction on nerve root function and pain in cervical spondylotic radiculopathy: a randomized trial. Clin Rehabil. 2012; 26: 351-61.

27.

Helmy

El-Sayyad

Kattabei

. Intra-rater and inter-rater reliability of Surgimap Spine software for measuring spinal postural angles from digital photographs. Bull Fac Phys Ther. 2015; 20: 193.

28.

Mohankumar

Yie

. Head and Neck Posture in Young Adults with Chronic Neck Pain. IJRAMR. 2018; 4: 2946-51.

29.

Potter

McCarthy

Oldham

. Algometer reliability in measuring pain pressure threshold over normal spinal muscles to allow quantification of anti-nociceptive treatment effects. International Journal of Osteopathic Medicine. 2006; 9(4): 113-119.

30.

Armijo-Olivo

Pitance

Singh

Neto

Thie

Michelotti

. Effectiveness of manual therapy and therapeutic exercise for temporomandibular disorders: systematic review and meta-analysis. Phys Ther. 2016; 96: 9-25.

31.

Freshwater

Gossling

. The effect of specific iso metric muscle energy technique on range of opening of TMJ: A pilot study. J Osteopath Med. 2003; 6: 36.

32.

Malone

McPoil

Nitz

. Orthopedic and sports physical therapy. Mosby. 1997.

33.

González-Ravé

Sanchez-Gomez

Santos-Garcia

. Efficacy of two different stretch training programs (passive vs. proprioceptive neuromuscular facilitation) on shoulder and hip range of motion in older people. J Strength Cond Res. 2012; 26: 1045-1051.

34.

Fasen

O’Connor

Schwartz

Watson

. Plastaras

, et al., A randomized controlled trial of hamstring stretching: comparison of four techniques. J Strength Cond Res. 2009; 23: 660-667.

35.

Decicco

Fisher

. The effects of proprioceptive neuromuscular facilitation stretching on shoulder range of motion in overhand athletes. J Sports Med Phys Fitness. 2005; 45: 183.

36.

Evcik

Aksoy

. Correlation of temporomandibular joint pathologies, neck pain and postural differences. J Phys Ther Sci. 2000; 12: 97-100.

37.

Häggman-Henrikson

Lampa

Marklund

Wänman,

. Pain and disability in the jaw and neck region following whiplash trauma. J Dent Res. 2016; 95: 1155-1160.

38.

Ferreira

Waisberg

Conti

Bevilaqua-Grossi,

. Mobility of the upper cervical spine and muscle performance of the deep flexors in women with temporomandibular disorders. J Oral Rehabil. 2019; 46: 1177-1184.

39.

Halmova

Holly

Stanko

. The influence of cranio-cervical rehabilitation in patients with myofascial temporomandibular pain disorders. Bratisl Lek Listy. 2017; 118: 710-713.

40.

Maluf

Moreno

Crivello

Cabral

Bortolotti

Marques

. Global postural reeducation and static stretching exercises in the treatment of myogenic temporomandibular disorders: a randomized study. JMPT. 2010; 33: 500-507.