INTRODUCTION:

American Academy of Orofacial Pain defined temporomandibular disorder as a musculoskeletal disorder that affects the masticatory musculature and the temporomandibular joint (TMJ) and associated structure.¹

“Triad of dysfunction” is the division of the temporomandibular disorder (TMD) system into three main categories which explains the majority of the patients’ complaints.² In this case, myofascial pain and dysfunction, internal derangement of TMJ and cervical spine dysfunction are also included. Biphenyls (2015) proclaimed that TMD is the second most common musculoskeletal condition which will result in pain and disability. A study reviewed physiotherapy treatment is an effective treatment modality to alter TMD pain subjectively.³Individuals with TMD symptoms exist over a broad range of age especially for 20 to 40 years of age. With this, TMD can be seen more common among young adults. A study reviewed that a high prevalence of TMD that was found in University students in India with a result showing that 45.16% of the students reported some levels of TMD.⁴

Presence of chronic TMD-related pain might lead to referred or radiating pain to adjacent oral, cranial facial and cervical regions due to poor localization of pain towards the TMJ and masticatory muscles.⁵ With this, parafunctional activities such as bruxism or teeth clenching act as an important precipitating factor that cause the overloading of TMJ and pathophysiological changes in the joint. TMD is also classified as a subgroup of orofacial pain disorders which consists of two types. The two types include muscle pain and pain originated from the jaw joint.⁶ A study proclaimed that the severity of TMD is classified as mild, moderate and severe TMD through Fonseca’s questionnaire scoring system.⁷ Furthermore, a study suggested that biomechanical, neuromuscular, bio-psychosocial and biological factors also responsible for the development of TMD.⁸ TMD also occurs predominantly in women as the female-to-male ratio of patients are reported ranging from 3:1 to as high as 9:1 (Scrivani, Keith, and Kaban, 2008). Besides, psychological factors also play an important role as the pain threshold of female tend to be lower and are more prone to stress.⁹ Para functional habit behaviours will be harmful towards muscles and joints around the TMJ when the frequency or forces produced exceed the tolerance of physiologic system.¹⁰

close functional connection that exists between the neck and masticatory muscles coordinate the static and dynamic physical motor activity (Giannakopoulos et al., 2013). They revealed that presence of co-activation of sternocleidomastoid and trapezius muscles during jaw movement. A study proclaimed that there is significant relationship between TMD and cervical pain.¹¹ With this, Pedroni, de Oliveira, and Bérzin (2006) reviewed that the presence of pain characteristics in TMD patients with cervical spine dysfunction often complaint cervical spine as common painful site. Hence, any changes that occur in the head posture will affect the movement of the TMJ by altering the activation of masticatory muscles.¹² This study is a preliminary attempt to seek the effect of cervical muscles strengthening exercise on the severity of temporomandibular joint disorder among UTAR students in a four-week period. TMJ is the most used joint in our human body, so the prevalence rate of TMD population is also high in nature. Therefore, it is essential to introduce new treatment protocols for a better outcome of TMD. Most of the previous studies were only focused on effects of cervical flexors strengthening towards TMD. Therefore, the need of further studies to evaluate the importance of cervical extensors strengthening among TMD population is essential.

Malaysian university students have high significant level of anxiety and stress. In this case, secondary factors like stress increases the rate of parafunctional activities like bruxism and clenching of teeth. Eventually, those activities will increase the rate of TMD. Further study suggested that stressful life events which affect psychology caused significant impairment of TMJ and quality of life.¹³ As TMD has a correlation with anxiety and stress level, further investigation should be conducted. Besides, there is a worth to evaluate the roles of cervical extensors strengthening on forward head posture which are often present among students due to prolonged usage of laptops and mobile phones. The study focuses on implementing cervical extensor strengthening in the training program which will affect the severity of temporomandibular joint disorders among students in UTAR. In addition, this study will also compare the training effects between cervical extensors strengthening and goldfish exercises. Objectives of the current study, to determine the effect of cervical extensor strengthening exercise along with goldfish exercises on the severity of temporomandibular joint disorder and maximal mouth opening among university students, and to determine the effect of goldfish exercises alone on the severity of temporomandibular joint disorder and maximal mouth opening among university students.

MATERIAL AND METHODS:

A randomized controlled trial was adopted to determine the effect of cervical extensor strengthening on severity of temporomandibular joint disorder among university students., and maximal mouth opening and maximal isometric strength of cervical extensor among subjects. The venue of this study was Physiotherapy Centre, university as all the instruments needed for assessments and training purposes were provided. This study was reviewed and granted approval and permission from university Scientific Ethical Review Committee (SERC). Both genders, age between 18-25 years old, Subjects who’s is scoring of 20 and above from Fonseca’s questionnaire and students community in University all were the inclusion criteria. The subjects with cervical spine pathology, malignancy, subjects with external treatment for TMD (dental complications), dental braces were excluded. Convenient sampling method was used for recruitment of participants in this study due to time constraint. A total of 60 participants were recruited and 40 participants were attaining as per inclusion criteria and volunteered to participate in this research study. A simple randomization was done through lottery technique after completion of subject recruitment to prevent selection bias from the researcher. Subjects were assigned to control and experimental group depends on the lottery paper selected. This study was single blinded as the pre and post assessment tests were not performed by researcher. An examiner was selected for measurement of pre and post assessment tests. Lafayette Manual Muscle Tester, Vernier Calliper, Blue Strap Treatment table were the instruments used. Severity of Temporomandibular Joint Disorder was analyzed by using Fonseca’s questionnaire was used to exclude individuals who score lower than 20 as it indicates individual has no TMD. Maximal Isometric Cervical Extensor Strength Lafayette manual muscle tester were used to assess the maximal isometric strength of cervical extensor of the participants before and after the intervention. One repetition of cervical extension was performed as a warm up session to guarantee appropriate performance prior to testing. A total of 3 attempts were performed and the average value was taken and recorded as pre-test and post-test result. Maximal Mouth Opening, subjects were instructed to open their mouth as wide as possible and examiner will have measured the inter incisal distance by placing the inside jaws of the caliper distance between the edges of the upper and lower central incisors. Each measurement was repeated for 3 times and an average value was obtained and recorded. In this case, only the maximum active mouth opening was measured in order to prevent errors due to different applied force during passive opening.

Subjects were informed to gather after screening test to fill in the consent form and it was required to sign by another witness. Subjects were briefed by the researcher about the process of research study, objective, advantages, risks and confidentiality of this study. Subjects were allocated randomly into two groups which were group A (experimental group (EG)) and group B (control group (CG)). Group A was assigned to perform anti-gravity cervical extension strengthening along with goldfish exercises whereas group B was chosen as control group to perform only goldfish exercises. Subjects were advised to follow the dos and don’ts during intervention period. Each subjects were introduced, explained and demonstrated about the type of exercises that they performed throughout 4 weeks’ duration. Subjects were informed that each week protocol consist of 3 sessions per week which last for half an hour per session. A sheet of paper with do’s and don’ts was given to each participants to follow throughout the intervention period. The effects on cervical extensor strengthening towards severity of temporomandibular, maximal mouth opening and maximal isometric cervical extensor between two groups were compared. All data obtained was tabulated and analyzed by using Statistical Package for Social Science (SPSS) version 23.0 and Microsoft Excel 2010 to estimate the study results. Wilcoxon Signed Ranks test was used to compare the mean result value of maximal mouth opening, maximal isometric cervical extensor strength and severity of temporomandibular joint disorder within each group during pre and post intervention. Mann-Whitney Test was used to compare the mean result between two groups. The significance level was set at the level of 5% for all tests. A p value <0.05 was considered significant.

RESULTS AND DATA ANALYSIS:

Table 1: Tests of normality

Variables	EG(M±SD)	CG (M±SD)	Sig
Age	19.42±0.84	20.48±1.47	<0.01
Height	162.54±8.00	168.98±8.05	0.21
Weight	59.15±15.78	61.74±16.11	<0.01
BMI	22.44±6.09	21.54±4.82	<0.01
Pre.MMO.A	4.40±0.94	4.84±1.04	0.38
Pre.MIS.A	32.31±11.48	35.49±15.89	0.02
Pre.Q.Total	36.05±9.94	39.76±11.45	0.02
Post.MMO.A	4.80±1.06	5.23±1.03	0.24
Post.MIS.A	36.73±9.13	34.81±15.26	<0.01
Post.Q.Total	18.42±10.81	19.76±8.58	0.01

Note: *Shapiro-Wilk test was performed for normality; Pre. MMO. A= Pre-test Maximal Mouth Opening Average; Pre.MIS.A= Pre-test Maximal Isometric Strength of Cervical Extensor Average; Pre. Q. Total= Pre-test Total Scoring of Fonseca’s questionnaire; Post. MMO. A= Post-test Maximal Mouth Opening Average; Post.MIS. A= Post-test Maximal Isometric Strength of Cervical Extensor Average; Post Q.Total= Post-test Total Scoring of Fonseca’s questionnaire; EG= Experimental group; CG= Control group; level of significant at p<0.05; M= Mean; SD= Standard deviation

Table 2: Comparison of Median for Maximal Mouth Opening of Pre and Post Test

		EG	CG	Z	Asymp
		(n=19)	(n=21)		Sig
		(M±IQR)	(M±IQR)		(P -value)
MMO	Pre	4.53±1.43	4.89±1.76	-1.23	0.22
	Post	5.20±1.59	5.12±1.77	-1.21	0.23
	Sig	<0.01	0.02
	(P-Value)

Note: n=Number of participants; EG=Experimental group; CG=Control group; MMO= Maximal mouth opening; M=Median; IQR=Interquartile range; Asymp Sig=Significant value; p=p value <0.05 was set as statistically significant level.

Analysis of Fonseca’s Questionnaire -Severity of TMD for Pre-Test and Post- Test Groups

Figure 1: Severity of TMD in Pre-Test between Two Groups

Note: EG=Experimental; CG=Control

Figure 2: Severity of TMD in Post-Test between Two Groups

Note: EG=Experimental; CG=Control

DISCUSSION:

To the best of authors’ knowledge, this is the first study to investigate on cervical extensor strengthening on severity of TMD. The main aim of this present study was to determine the effect of anti-gravity cervical extensor strengthening exercise on the severity of TMD, maximal mouth opening and maximal isometric cervical extensor strength. Thus, the comparison between experimental and control group was analysed.

Severity of TMD: Severity of TMD vs. Cervical Extensor:

This study showed, the severity of temporomandibular disorder was assessed by scoring of Fonseca’s questionnaire. The severity of temporomandibular joint disorder was improved for both experimental (p<0.01) and control groups (p<0.01) after 4 weeks. However, the severity of temporomandibular joint disorder for post-test was not statistically significant (p=0.67). This indicates that both groups were homogenous. Overall, the major finding in this study was that 4 weeks’ duration of anti-gravity cervical extensor strengthening does not cause significant improvement of severity of temporomandibular joint disorder. In disagreement with other studies that found significant relationship between cervical extensor strength with population with TMD has been well documented(S. Armijo-Olivo and Magee, 2012). However, these findings showed similar results with studies that reviewed cervical flexor muscle strength showed low significant relationship between population with TMD and healthy subjects (S. Armijo-Olivo et al., 2011). Therefore, both of these findings are contraindicated and further research should be done for further exploration.

Severity of TMD vs. Neck Pain:

Subjects included in the present study only suffer from mild to moderate severity of TMD. The findings are consistent with prevalence of students in mild to moderate severity of TMD.¹³ A study reviewed that high levels of jaw disability has a strong interrelationship with elevated level of neck disability. As the severity of TMD of subjects were mild to moderate, therefore, low level of neck pain was found among subjects.¹⁴ In addition to this, a study suggested that subjects with mechanical neck pain undergo some alteration in the differential activation of the cervical extensor compared to those without neck pain.¹⁵ This showed consistency with the article which suggested that individuals with neck pain exhibit structural and functional changes that caused weakness of cervical extensor compared to those without neck pain which was associated with greater severity of TMD.¹⁶ What distinguishes this study from other authors were minority of the subjects suffer from neck pain. Hence, the baseline of the cervical extensor isometric strength of the subjects in this present study were compared with the previous article stated. In this case, the baseline of cervical extensor strength between both studies were compared. The value of pre-test for cervical extensor was expressed in Newton and were converted from Newton to kilogram-force through formula: Force (kgf) = Force (N) ×0.10197162129779. The results were normalized by the body mass of subjects and the value obtained was 0.06. The findings showed the subjects in our studies have lower normalized isometric strength of cervical extensors even though subjects in these studies does not suffer from mechanical neck pain. Therefore, the results obtained from this study was contradicted from other studies and further investigation should be done.

Relationship between Neck Pain and Cervical Spine: With this, there are theories that support neck pain which acts as a predisposing factors to pain in the masticatory muscle. First, biomechanical linkage between cervical and trigeminal sensory-motor systems hypothesized association of afferent input with neck pain. In this case, coupling of afferent input onto trigeminal motor neurons in the trigeminal cervical nucleus caused a rise in masticatory muscle hyperactivity and pain.¹ Next, a study suggested that the presence of muscular compensatory action for stability of the mandibular and cervical system explains the synergistic relationship of cervical spine and masticatory muscles (Ries and Bérzin, 2007). For instance, neck pain causes muscular imbalance and tension which eventually leads to reduction in balance for the masticatory muscle activity in TMD population. In addition, a stable cervical base is essential for mandibular functional activity as mandibular acts as a mobile bone and articulate with the skull to form TMJ. With this, the stability of head and cervical spine depend on ability of strength of cervical agonist and antagonist. Since mechanical neck pain affects the performance of cervical muscles, thus, compensatory action is needed by masticatory system to maintain stability and for refinement. Lastly, the angle between the upper part of thorax and the spine has a remarkable relationship with individual with neck pain under work posture during functional activities like speech, intake of food and yawn (Keilmann, et al., 2016). Da Costa et al., (2015) explained that as the level of neck disability elevates, the sensitivity of anterior temporalis, sternocleidomastoid and upper trapezius muscle increases. Sforza et al., (2011) reviewed a significant correlation of sternocleidomastoid and trapezius muscles towards dynamics aspects of craniomandibular system such as production of muscle co-contraction with the masticatory muscles during the clenching of teeth. These results were consistent as subjects in the study who only have mild to moderate severity of TMD does not suffer from neck disability. The mechanism of TMD is not fully understood despite several studies that were done due to the multifactorial aetiologies. In addition, clinicians should attend on the entire problem of TMD patients to maximize the potential for a desirable outcome (Bagis et al., 2012). Nevertheless, there is an insufficiency of evidences in the assessment and in supporting the needs of neck treatment in the TMD treatment protocol (Monteiro et al., 2011). Therefore, further exploration should be done to address TMJ disorder as it is often overlooked.

Severity of TMD vs. Body Mass Index (BMI):

A study reviewed that TMD and BMI are closely interrelated and often associated with each other as a decline in BMI will affect the pathological factor of TMD (Rhim et al., , 2016). In this case, females showed more significant difference compared to males in terms of abdominal obesity, lower metabolic syndrome waist circumference and lower prevalence of metabolic syndrome. LeResche et al. (2007) conducted a study to determine the risk factors for TMD and no differences of BMI were found between TMD population and control group. A study showed consistency with the previous study as association between obesity and TMD pain was rejected when gender, migraine and non-specific somatic symptoms were included (Jordani et al., 2017). The results showed by numerous studies were contradicting. On the other hand, the findings of this present study for pre-test and post-test of severity of TMD were different. Spearman correlation showed a negative but significant (P=0.05) correlation between pre severity of TMD and BMI whereas a positive but insignificant (P=0.64) correlation was found during post-test of TMD severity. Obesity is treated as a state of chronic low degree inflammation with incline of inflammatory cytokines which results in vasoconstriction of blood vessels in the white adipose tissue, disability of oxygen supply and local hypoxia (Cancello and Clément, 2006). As the association between BMI and TMD are still inconclusive, detailed discoveries should be done in order to clarify the doubts of these complex relationship between TMD and BMI.

Severity of TMD vs. Age:

As young adults age and enter society, responsibilities will be taken and complications in life will be faced. As a result of these burdens, it is found that one’s standard of living and stress level vary directly with the prevalence of TMD. Not only that, TMD population with advanced age addressed changes in perceptive of the standard of living and elevation of adaptive capacity among individual with TMD. Hence, signs and symptoms of TMD transformed from unbearable to subclinical or even undetectable which results in less pronounced severity of TMD (Barros, et al., 2009). The findings of this present study showed no significant correlation were present between age and severity of TMD for pre-test (P=0.46) and post-test (P=0.44). In agreement with this, another study showed similar results as there was no correlation found between age and severity of TMD with significant value of P=0.16.¹⁷The subjects included in this present study were university students with an age gap of 18 to 25 years old only. There was a study suggested that changes of condylar with advancing age might affect the pathophysiological alterations of the mandibular condyle.¹⁸ Therefore, further studies should evaluate on TMD population with different age gap to determine whether severity of TMD is related to difference in age.

Severity of TMD vs. Genders:

As stated in previous chapter before, the prevalence of TMD is higher among females due to reproductive hormones. However, the findings showed that there was no correlation between genders and severity of TMD with P value of 0.85 in pre-test and P=0.96 in post-test. This showed inconsistent results with numerous studies which found significant association of TMD with genders.¹⁹ However, a recent study reviewed no statistic significant was found between men and women in the occurrence of signs and symptoms of TMJ dysfunction. These results that showed predominance of female towards TMD probably due to factors such as women are reported to have higher psychophysiological disease. In this case suggested that a role for female sex hormones such as serum estrogen in the pathogenesis of TMD¹⁹, while on the other hand proposed that modification in adaptive capacity of neuromuscular exists in population with signs and symptoms of TMD.²⁰ However, no conclusive explanation for the high prevalence of female in TMD has been established. Hence, further additional research should explore on this issue specifically for longitudinal type of study. In addition, exploration of studies should be done towards male population with TMD as well.

Maximal Mouth Opening:

There was a significant difference in the mean difference value for maximal mouth opening in both groups: E (p<0.01) and C (p=0.02). Maximal mouth opening is defined as when the mouth of an individual is opened in widest and the greatest distance between incisal edges of maxillary central incisor to the incisal edge of mandibular central incisor were measured. In this study, the median of maximal mouth opening was shown to be from 4.53 cm for pre-test and 5.20 cm for post-test in EG group whereas it was 4.89 cm for pre-test and 5.12 cm for post-test in CG group. The mean values of this study showed similar results with another study as the maximal mouth opening for subjects were ranged from 4.43 cm to 5.13 cm (Khare et al., 2012). However, the mouth opening should not be applied as the only criteria for the presence of TMD as the range of mouth opening in the study could be considered as functional (Kitsoulis et al., 2011). On the other hand, the maximal mouth opening was not statistically significant for post-test (p=0.21). These findings indicated that cervical extensor strengthening does not cause significant improvement in maximal mouth opening. Nevertheless, the results were diverse with studies that reviewed correlation between mouth opening and changes in thickness of cervical flexors (Jun et al., 2015).

Maximal Isometric Cervical Extensor Strength:

There was a significant difference in the mean difference value for maximal isometric cervical extensor strength of the experimental group E (M= -4.42, SD= 8.50, p=0.04) whereas there was no significant difference in the mean difference value of the control group (M=2.10, SD=6.96, p=0.18). Clinically, this indicates that the 4 weeks’ duration of anti-gravity cervical extensor strengthening showed effects on maximal isometric cervical extensor strength. The results showed consistency with an article that reviewed cervical muscle strength was increased statistically after 4 weeks of anti-gravity exercise of cervical extensor (Fiebert et al., 2004). In addition, another study reviewed that an effective strengthening exercise program should maintain 2 to 3 sessions per week with 2 to 4 sets of 8 to 12 repetitions in order to address clinical benefits (Bartholdy et al., 2017). Another study proclaimed similar protocol of strengthening exercises which only required 1 set of resistance exercise with 8 to 12 repetitions to cause volitional fatigue from larger muscle groups to smaller muscle groups (Westcott et al., 2009).

Goldfish Exercise:

Although there were no significant differences between both groups, the positive outcomes of both groups after the 4-week period highlight the importance of physical therapy in treating TMD. In this case, goldfish exercise showed positive results towards both experimental and control groups. In agreement with this, a study concluded that goldfish exercise shows statistical improvement in mouth opening and reduction in disability of TMJ.⁹ The principles behind goldfish exercise mimic the pulsatile motion of goldfish to stretch fibrous band and cause reduction of TMJ stiffness. This finding revealed similar results as articles in literature review stated that jaw exercises are considered as one of the best exercise in the treatment of TMD. However, since the consistency of goldfish and jaw exercises is questionable with comparison, the explanation is not suitable to be generalised across the population.

Fonseca’s questionnaire:

The Fonseca’s questionnaire which consists of 10 questions was used to evaluate the severity of TMD in this present study.

Difficulty in mouth opening:

The first question of the questionnaire is related to the difficulty in mouth opening. In this paper, 10.5% of the subjects in the experimental group and 9.5% of the subjects in the control group chose “Yes” whereas 52.6% of subjects in the experimental group and 57.1% of subjects in the control group attempted “Sometimes” in pre-test. In this case, functional activities like consumption of foods, speech or yawn will be affected and might be accompanied with pain. For instance, myofascial pain may cause a deviation of the interincisal mouth opening to the affected side and lead to limitation of mouth opening (Benoliel et al., 2011). Mouth opening less than 30mm will be consider as limited (Bagis et al., 2012). Therefore, maximal mouth opening of the subjects were measured as an outcome measure for this study. During post-test, 0% of the subjects in both groups attempted answer “Yes” and percentages of subjects attempted “No” increased for both experimental and control groups, which are 84.2% and 76.2% respectively. In agreement with this, a study that reviewed effectiveness of goldfish exercises in improving mouth opening has been well documented in the literature review.⁹

Difficulty in Moving Mandibular Side by Side:

The second question of Fonseca’s questionnaire is related to difficulty in moving the mandibular side to side. 10.5% of the subjects in the experimental group and 0% of the subjects in the control group attempted answer “Yes” whereas 21.1% of subjects in the experimental group and 61.9% of subjects in the control group chose “Sometimes” during pre-test whereas 10.5% of subjects in experimental and 23.8% of subjects in control group chose “Sometimes” in pre-test. Biomechanically, weak cross-linking of collagen fibres along the Medio lateral axis in disc promote more surface defects due to excess shear stress fields during lateral movement.²¹ TMD population with the presence of restriction of jaw function due to pain often encounter limitation at the mandibular in all directions.²² For instance, these phenomena trigger a great deal of anxiety and stress towards to individual who suffers from TMD. Majority of the subjects in both experimental and control groups showed relief of symptoms as the number of subjects who chose “No” in post-test were increased, with percentages of 89.5% and 71.4% respectively.

Tiredness or muscular pain while chewing:

The third question of Fonseca’s questionnaire is related to the presence of tiredness or muscular pain while chewing. This type of muscular pain is known as myofascial pain as contraction of muscle repetitively causes tension or stress and related muscle tension addresses the problem of myofascial pain (Rodrigues et al., 2015). Myofascial muscle pain is primarily characterized by unilateral or bilateral pain in the temporomandibular region as pain is often present between the comorbid muscle and TMJ pain (Benoliel et al., 2011).During post-test, the percentage of subjects that attempted “No” in the experimental group was lower than the control group, which were 57.9% and 71.4% respectively. The findings obtained showed inconsistency with a study that reviewed that the presence of trapezius muscle weakness for population with myofascial pain syndrome. There are few possible factors that lead to these findings. Firstly, psychosocial impairment which is a challenging condition for the subjects in the study. It affects the negative prognosis in subjects with chronic myofascial pain (Manfredini et al., 2018). Not only that, studies also showed high frequency of parafunction habits which displayed strong correlation with the first episode of masticatory myofascial pain (Ohrbach and Michelotti, 2018).

Presence of headache:

The fifth question of Fonseca’s questionnaire is related to headache. 26.3% of the subjects in experimental group and 9.5% of the subjects in control group attempted answer “Yes” whereas 31.6% of subjects in experimental group and 47.6% of subjects in control group chose “Sometimes” in pre-test. Headache which can be known as cervico genic orofacial disorder are the most common type of neurological pain apart from the musculoskeletal pain for orofacial region (Gupta et al., 2018). The primary type of headaches that usually found in TMD population are migraine, Episodic Tension Type Headaches, Chronic daily headaches (Klaric, et al., 2015). Study found strong correlation between headaches and other dysfunctional symptoms in particular pain in the TMJ are during mandibular movement, anxiety or stress (Tchivileva et al., 2018). These findings can be explained by an inclined in central sensitization to pain as it is characterized by pain hypersensitivity, particular dynamic tactile allodynia, after sensations and enhanced.²³ Presence of headache is not a pathognomonic symptoms and the symptoms can be related to the ear. During post-test, percentages of subjects attempted “No” increased for both experimental and control groups, which are 52.6% and 52.4% respectively. Hence, as severity of TMD reduced, the prevalence of headache reduced. This can be explained by pain adaptation theory which stated that different types of pain might reinforce each other whereas relief from one weaken one another (Paungmali, et al., 2016). This findings showed consistency with study that reviewed strong correlation between headaches and TMD symptoms.²³

Presence of pain on the nape or stiff neck:

The fifth question of Fonseca’s questionnaire is related to presence of pain on the nape or stiff neck. In the study, 5.3% of the subjects in the experimental group and 28.6% of the subjects in the control group attempted “Yes” whereas 57.9% of subjects in the experimental group and 38.1% of subjects in the control group chose “Sometimes” in pre-test. Minority of subjects in this study suffered from chronic neck pain as the severity of the TMD was only mild to moderate. The pathological and correlation between neck pain and TMD has been discussed in the previous section.

Earaches or pain in the cranio mandibular joints:

The sixth question of Fonseca’s questionnaire is related to presence of earaches or pain in cranio mandibular joints. In the research, 5.3% of subjects from the experimental group and 19% of subjects in the control group whereas 42.1% of subjects in the experimental group and 33.3% of subjects in the control group chose “Sometimes” attempted answer “Yes” in pre-test. The presence of this question in this questionnaire can be explained as otologic symptoms showed close and complex relation towards TMJ disorder. The theories behind otologic symptoms and TMJ are maybe due to closeness of development between embryonic and TMJ. Next, morphological proximity and connection of the innervation field of shared nerves such as trigeminal nerve can be relate towards the presence of earaches in TMD population (Badel et al., 2011).

Presence of TMJ clicking while chewing or mouth opening:

The seventh question of Fonseca’s questionnaire is related to presence of TMJ clicking while chewing or mouth opening. 31.6% of the subjects in the experimental group and 38.1% of the subjects in the control group attempted “Yes” whereas 36.8% of subjects in the experimental group and 42.9% of subjects in the control group chose “Sometimes” in pre-test. These findings showed consistency with an article that suggested the presence of TMJ clicking or joint sounds are common within TMD population (Ryalat, 2009). Generally, the presence of clicking sounds in joint is a common phenomenon that occurs in asymptomatic individual. TMJ clicking can be consider as a normal variant rather than a disorder (Bagis et al., 2012). Clinically, internal derangement of TMJ is the most determine factor that affects TMD clicking whereas “slipped disc” occurs when condylar head and fossa has moved out of its original position caused locking of TMJ which produces clicking sound during closing of mandible.²² During post-test, 31.6% of subjects in the experimental group and 19.0% of subjects in the control group chose “No” for pre-test whereas during post-test percentages of subjects attempted “No” increased for both experimental and control groups, which were 63.2% and 52.4% respectively. TMJ clicking showed a positive relationship towards psychological characteristics like teeth clenching or bruxism.²⁴

Parafunctional habits:

In this paper, 15.8% of the subjects in the experimental group and 0% of the subjects in the control group attempted answer “Yes” in pre-test in question 8 of Fonseca’s questionnaire which is related to the presence of teeth clenching or grinding habits. Teeth clenching acts as one of the contributing factors for TMD as the mechanism of this action causes excess loading of teeth (Watanabe, et al., 2011). In this case, the mechanical overloading increased the risk of cartilage degradation.²⁵ Research suggests that modulation of postural control mechanism during clenching is performed by jaw sensory motor system. Thus, changes occur in the posture of jaw can influence the joint position sense in the cervical region.²⁶ Another study suggested that the delivery of sensation from the mesencephalic nucleus area to trigeminal nuclei during teeth clenching due to masticatory muscle contraction and input sensation by proprioceptors within teeth, gums and TMJ serve for activation purpose.²⁷ With this, activation of excited trigeminal nuclei alters the tonic muscles equilibrium and stimulation of cervical postural maintenance muscles which are innervated by trigeminal nerve occur.

Murali, et al., (2015) reviewed that unconscious contraction of the masseter and temporalis muscles are mechanisms behind teeth clenching.²⁸ In agreement with this, several articles in the literature review proclaimed that parafunctional habits caused alterations in the masticatory muscl.²⁹ In consistent with this, involvement of teeth clenching or bruxism act as one of the factors that affects the maintenance of TMD. Therefore, the results of the study might be affected due to involuntary action done by subjects especially in the experimental group only.

Articulation of teeth:

The ninth question of Fonseca’s questionnaire is related to an articulation of teeth. 10.5% of the subjects in the experimental group and 9.5% of the subjects in the control group attempted “Yes” and 57.1% of subjects in the control group chose “Sometimes” during pre-test. In this case, structural, neurological and muscular diseases caused an impact on the articulation of teeth (Keilmann et al., 2016). Bad articulation of teeth provokes social activities such as speech and self-perception. During post-test, the percentage of subjects attempted “No” increased for both experimental and control groups, which are 84.2% and 76.2% respectively. Constant unilateral chewing or bruxism might cause abnormalities in the mandibular movement as lateral condylar movements is related to vertical jaw movements.³⁰ Hence, parafunctional activities like unilateral chewing due to pain by subjects were unavoidable.

Psychological stress:

In respond to Fonseca’s questionnaire, 36.8% of the subjects in the experimental group and 23.8% of the subjects in the control group attempted answer “Yes” in the tenth question of Fonseca’s questionnaire. It is related to whether subjects considered themselves as a tense or nervous person. The findings revealed higher percentages of subjects in experimental group considered themselves as a tense person. In agreement with these findings, the marked increase in prevalence of anxiety and stress among Malaysia university students (Shamsuddin et al., 2013). The results also showed consistency with some articles stated that external factors related to psychosocial aspects affects TMD pathologicall.²⁹ Stress, depression, anxiety, nervous and tense are considered as psychological factors which alter pain threshold of an individual and causes pain during chewing or movement like the opening and closing of mouth (Resende et al., 2013). Moreover, presence of stress and tension among students eventually increase the incidence and rate of parafunctional habits which will cause overloading of TMJ and hyperactivity of chewing muscles (Ohlmann et al., 2018). Parafunctional activities include clenching of teeth and bruxism (Abekura et al., 2011). A study reviewed that a strong correlation between the aggravation of masticatory dysfunction and negative emotional state in generation X who encounter final stage of maturation and early adulthood. Since more subjects in the experimental group considered themselves as a tense person, this might affect the results of study as stress affects the treatment process of TMD as well as increases the rate of parafunctional habits.⁹

LIMITATIONS OF THE STUDY:

Absence of clinical diagnosis or examination of TMD, Fonseca’s questionnaire unable to identify the reliability of participant’s score due to absence of clinical examination and laboratory findings, Description of signs and symptoms in Fonseca’s questionnaire does not necessarily be a synonym of TMD, Small sample size, Researchers are unable to control confounding factors, the time frame given for this study is too time constraint as there were only 4 weeks of intervention period.

RECOMMENDATIONS:

Determination of severity of TMD through clinical diagnosis, Includes larger sample size, Researchers control confounding factors within their limits, Extension of the time frame or duration to at least 6 weeks as longer period of study allows researcher to work on the progression and effect of the intervention on the outcome measure, Incorporate evaluation of cervical in study to maximize the potential of a successful treatment outcome, Further studies can investigate effect on cervical extensor strengthening in TMD population with neck pain.

CONCLUSION:

Four weeks of anti-gravity cervical extensor strengthening exercises protocol showed no significantly difference of the severity of TMD and maximal mouth opening between both control and experimental group. Rejecting the alternate hypothesis which mentioned there will be significant difference in severity of TMD and maximal mouth opening between control and experimental group. On the other hand, goldfish exercises showed significant improvement of maximal mouth opening and reduction in severity of TMD after 4 weeks of intervention period. Clinically, the anti-gravity cervical extensor strengthening showed significant improvement in isometric cervical extensor strength in the experimental group. Further studies should examine and investigate the effects of cervical extensor strengthening on other population such as TMD population with neck pain or cervical disorders. Lastly, justification of cervical extensor strengthening in clinical use of TMD treatment should be further explore.

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Received on 25.04.2020 Modified on 11.06.2020

Research J. Pharm. and Tech. 2021; 14(4):2233-2242.

DOI: 10.52711/0974-360X.2021.00397

Variables	Age	Pre severity of TMD	Post severity of TMD
Age	Spearman Correlation P	-0.12 0.46	0.13 0.44
BMI	Spearman Correlation P	-0.31* 0.05	0.08 0.64
Gender	Chi-Square Test P	0.03 0.85	0.00 0.96

Variables

EG(M±SD)

CG (M±SD)

Sig

Age

19.42±0.84

20.48±1.47

<0.01

Height

162.54±8.00

168.98±8.05

0.21

Weight

59.15±15.78

61.74±16.11

<0.01

BMI

22.44±6.09

21.54±4.82

<0.01

Pre.MMO.A

4.40±0.94

4.84±1.04

0.38

Pre.MIS.A

32.31±11.48

35.49±15.89

0.02

Pre.Q.Total

36.05±9.94

39.76±11.45

0.02

Post.MMO.A

4.80±1.06

5.23±1.03

0.24

Post.MIS.A

36.73±9.13

34.81±15.26

<0.01

Post.Q.Total

18.42±10.81

19.76±8.58

0.01

EG

CG

Z

Asymp

(n=19)

(n=21)

Sig

(M±IQR)

(M±IQR)

(P -value)

MMO

Pre

4.53±1.43

4.89±1.76

-1.23

0.22

Post

5.20±1.59

5.12±1.77

-1.21

0.23

Sig

<0.01

0.02

(P-Value)

EG

CG

Z

Asymp

(n=19)

(n=21)

Sig

(M±IQR)

(M±IQR)

(P - value)

MMO