Introduction
Temporomandibular joint (TMJ) disorders are a diverse group of disorders that cause pain and tenderness in the TMJ. Several factors lead to TMJ disorders that consist of erosion, tearing, inflammation and swelling of the joint, trauma, stress, some dental plaques and bruxism and tooth grinding. The pain associated with TMJ disorders might vary from mild to severe. Such disorders might be transient or chronic. Virtually 15% of adults in the US have experienced chronic facial pains (1-3).
Some bad oral habits result in the exertion of abnormal forces to teeth, dental arches and muscles; these habits include nail biting, chewing gums, tooth grinding and playing with the jaws. On the other hand, some studies have reported that TMJ disorders originate from malocclusion, parafunctional habits, stress and trauma (1-4). However, the contribution of each factor to TMJ disorders is still unknown (5-8) because each factor not only contributes to TMJ disorder but also affects other factors, too. For example, if stress is considered a kind of energy, when stressful conditions affect an individual, energy is produced in the body (psycho-physic logical theory) (1).
Each structure in the masticatory system can tolerate the increase in stress, resulting from increased activity of muscles, up to a certain level.
When the stresses exerted on tissues exceed this vital threshold which is referred to as structural tolerance, the process of injury and destruction begins. The first signs of destruction appear in components of the masticatory system that have the lowest level of tolerance. Therefore, the location of the emergence of injury is different from one individual to another individual (1-3).
Deleterious parafunctional habits affect the dentoalveolar structures. If these habits are diagnosed late, resulting in delayed treatment, they will give rise to severe problems which might be irreversible or associated with high costs, difficult technical problems and severe patient suffering.
Therefore, it is necessary to decrease these habits through proper intervention and correct treatment planning, which is not possible without acquiring good statistics. Therefore, the present study was undertaken to acquire data on the prevalence of parafunctional habits and determine their relationship with TMJ disorders in female high school students in Kerman, İran, as a sample of the Iranian population.
Materials and Methods
This study had received ethical approval from Ethics and Research Committee of Kerman University (IR.kmu.ac.ir.1395.34; approval no: 2016/124).
In this descriptive-analytical study, data were collected by completing a checklist in the form of a questionnaire and by carrying out clinical examinations. The questions on the checklist were designed by two pedodontists. Then the checklist was submitted to 5 pedodontists in the faculty of dentistry for evaluation. These pedodontists confirmed that the checklist was favorable. The study population consisted of first- to fourth-grade high school students in Kerman, İran. The aims of the study were explained to all the participants who took part in the study voluntarily. Subjects with severe malocclusion and toothache were excluded from the study. Cluster samples technique was used in the present study. To this end, the high school lists were obtained in Kerman with the cooperation of the city’s General Education Organization. Then 8 high schools were randomly selected from each municipal district of the city (2 high schools from each district) as a cluster. Then the questionnaires were explained to the subjects and 368 first- to fourth-grade students in each level completed the questionnaires. Then each student was examined on a conventional chair with the use of a dental mirror, an electric torch, a Vernier caliper (for the evaluation of mouth opening), and a stethoscope (for evaluations of joint sounds) and by palpating the masticatory muscles, while each subject held the questionnaire in her hand.
Before completing the questionnaires, the subjects were informed about the reasons for and the importance of the study and all the variables and factors on the questionnaire were explained to avoid any ambiguities so that the students could complete the questionnaire after completely understanding the importance of the study and the items on the questionnaire. In addition, the aim of the study was individually explained to each student and they were included in the study after they gave their informed consent. In addition, the subjects were reassured that all the data would be kept confidential and the results only would be reported.
Clinical examinations were carried out by one last-year dental student who was trained for one week by one professor in the field in the faculty of dentistry and mastered all the principals of clinical examination. In clinical examinations, first the extent of mouth opening was determined with the use of a Veriner caliper by measuring the distance from the incisal edge of maxillary incisors to the incisal edge of mandibular incisors. Then each subject was asked to open and close her mouth several times so that any joint clicking could be heard with the use of a stethoscope which was placed anterior to the tragus for the evaluation of crepitus and other joint sounds. Then the masticatory mucus was palpated for any tenderness and muscle trismus. In addition, mandibular deviation during mouth opening and closing was evaluated.
Functional Terms
Pain: A feeling of pain anterior to tragus at mouth opening and closing and also during palpation,
Joint sound: Sounds anterior to tragus at mouth opening and closing (crepitus),
Morning headache: Headache in the temporal area at waking up from sleep,
Pain in the ear area: Earache or pain anterior to tragus.
In addition, at the end of clinical examination, a lecture was given to the students who had problems in relation to kicking the habits, the techniques used to kick the habits and the possible future consequences if the habits are not kicked; finally, subjects with problems were referred for treatment.
Protection of human and animal subjects: the authors declare that no experiments were performed in humans and animals.
Statistical Analysis
Statistical analyses were carried out with SPSS 13.5, t-test, chi-squared and ANOVA.
Results
A total of 368 questionnaires were completed in the present study. The mean age of the subjects was
15.0±1.1 years, with an age range of 14-18 years. A total of 66 subjects did not exhibit any parafunctional habits and 78% of the subjects had at least one oral parafunctional habit; 1.2% of the subjects exhibited all the 11 parafunctional habits and 22% of the subject had only one parafunctional habit. The most frequent habits were chewing gums, chewing foods on only one side, sleeping on only one side and chewing pens or pencils (Tables 1, 2).
The prevalence of TMJ disorders in the subjects was as follows: crepitus (31%), pain in masticatory muscles (10%), pain at food mastication (24%) and pain at mouth opening (14%) (Table 3).
The following results were achieved on the relationship between each parafunctional habit and the presence of at least one of the symptoms and signs of TMJ disorders. There were significant relationships between bruxism, unilateral mastication and chewing gums, pens and pencils, tooth grinding and sleeping on one side and the symptoms and sings of TMJ disorders. In relation to nail biting, too, a relationship was detected with the symptoms and signs of TMJ disorders; however, there were no significant relationships between other habits and symptoms and signs of TMJ disorders (Table 4).
The results of this study showed the strongest relationship between bruxism and palpation tenderness of masticatory muscles (p=0.001). In addition, there were significant relationships between the signs of TMJ disorders and bruxism, unilateral mastication, chewing gums and sleeping on one side only.
The mean extent of mouth opening was 38.0±2.01 mm, with a range of 31-48 mm. The results of this study showed that of all the masticatory muscles, the most severe pain at palpation was related to masseter, followed by the temporalis muscle.
Discussion
TMJ is one of the most complex joints in the human body and is closely related to the profession of dentistry. The disorders of this joint consist of clinical problems that involve the masticatory muscles system and/or the joint itself. Based on the definition provided by the American Dental Association, the symptoms and signs of TMJ disorders consist of pain, tenderness to palpation in TMJ area or masticatory muscles, limitations in the jaw movements, mandibular deviation at mouth opening and closing, and TMJ sounds during mandibular movements (1). The etiologic factors of these disorders have not fully been elucidated and different factors have been proposed. One of the possible predisposing factors is parafunctional habits, which are described as activities of the masticatory system that do not have functional aims and do not play a role in mastication, swallowing and speaking. These habits can lead to trauma since they exert extra loads on the masticatory system. These factors include bruxism, tooth clenching, chewing of hard objects such as pencils, chewing gums, nail biting, sleeping on only one side, habitual chewing of the tongue, lips or cheeks and placing the hand under the chin (1-8).
This study showed that 66 subjects did not exhibit any parafunctional habits and 78% of the subjects had at least one oral parafunctional habit; 1.2% of the subjects exhibited all the 11 para-functional habits and 22% of the subject had only one parafunctional habit. The most frequent habits were chewing gums, chewing foods on only one side, sleeping on only one side and chewing pens or pencils, consistent with the results of other studies. In addition, in a study by Gavish et al. (2), the most important finding was the prevalence of chewing gums (58%). In a study by de Oliveira et al. (9) on 10-12-year-old subjects 47% had at least one oral parafunctional habit. In addition, Schiffman et al. (8) evaluated 269 nursing students, aged 19- 22 years, and reported that the most prevalent habit was chewing gums (87%), with a positive relationship between parafunctional habits and mandibular disorders. Gavish et al. (2) evaluated 248 girls, aged 15-16 years, and reported that the most prevalent parafunctional habit was chewing gums.
Lobbezoo et al. (10) and Restrepo et al. (11) reported that the most prevalent parafunctional habits were bruxism, tooth clenching, tooth grinding and nail biting.
In relation to the prevalence of parafunctional habits, tooth grinding, and chewing were reported in 9.8% and 9.5% of the subjects, respectively. In the study by Choi et al. (12), these prevalence rates were 8.4% and 9.9%, respectively, among 19-year-old Korean subjects.
Therefore, the prevalence of this parafunctional habit is different in different communities, which might be attributed to differences in the study populations in different studies. In addition, factors such as individual’s psychological status, habits and sleep status can affect these two factors.
The results of the present study showed that the most prevalent symptoms and signs of TMJ disorders in the subjects were joint sounds (crepitus) (31%), pain in masticatory muscles (10%), jaw pain during food mastication (24%) and pain at mouth opening (14%). In a study by Miyake et al. (13), the most prevalent sign of TMJ disorders was joint crepitus. This study showed significant relationships between nail biting, tooth clenching, unilateral chewing, chewing gums, pens and pencils, tooth grinding and sleeping on one side and the signs of TMJ disorders, consistent with the results of other studies (14).
In a study by Motghare et al. (15), too, there were significant relationships between nail biting, lip biting, tooth grinding and symptoms and signs of TMJ disorders. Based on the results of a study by Alamoudi on 3-7-year-old children, there was a definitive and significant relationship between tooth grinding and TMJ pain, muscle tenderness and limitations in mouth opening (7).
In a study by Sonmez (3) on 182 children aged 5-8 years, there was a definite relationship between thumb sucking and nail biting on one hand and TMJ disorders on the other hand during mixed dentition period. In addition, in a study by de Oliveira et al. (9) on 10-12-year-old subjects, there was a strong relationship between parafunctional habits and tenderness of masticatory muscles to palpation. Gavish et al. (2) showed significant relationships between chewing gums, playing with the jaws and leaning on the jaw and tenderness of masticatory muscles to palpation and TMJ disorders. However, there was no significant relationship between tenderness to palpation of masticatory muscles and TMJ disorders.
A study by Motghare et al. (15) showed the strongest relationship between clenching and tenderness to palpation in masticatory muscles. In addition, there were significant relationships between tooth clenching, unilateral food chewing, chewing gums and sleeping on one side and the symptoms and signs of TMJ disorders. In a study by Ciancaglini et al. (16), there was a strong relationship between bruxism and the symptoms and signs of TMJ disorders, especially limitation of jaw movements. However, in a study by Choi et al. (12) it was reported that bruxism was not possibly a direct risk factor for inducing TMJ disorders and tooth clenching was considered much more dangerous than bruxism. Furthermore, Pullinger et al. (17) reported a relationship between tooth clenching and pain in facial muscles. In a study by Gavish et al. (2), there was a strong and significant relationship between chewing gums and muscular tenderness and joint clicks. In the present study, too, there was a significant relationship between unilateral chewing and joint pain.
The results of the present study showed that of all the masticatory muscles, the most severe muscular pain at palpation was related to the masseter. In a study by Morrant and Taylor (18) in Glasgow University, 18% of the subjects exhibited pain and muscle tenderness in the masseter muscle during palpation. In a study by Agerberg and Inkapool (19), muscle pain was the most severe in the temporalis muscle.
Conclusion
The results of the present study showed that the highest frequency of parafunctional habits was related to chewing gums and the most frequent sign of TMJ disorder in the subjects was joint clicks. In addition, there were significant relationships between all the symptoms and signs of TMJ disorders and the parafunctional habits of bruxism, unilateral mastication and tooth clenching.
Ethics
Ethics Committee Approval: For study, approval of Ethics Committee of Kerman University of Medical science was obtained (approval no: 2016/124).
Informed Consent: Protection of human and animal subjects: The authors declare that no experiments were performed in humans and animals.
Peer-review: Internally peer-reviewed.
Authorship Contributions
Surgical and Medical Practices: M.A.H., Concept: M.A.H., Design: M.A.H., Data Collection or Processing: F.M., Analysis or Interpretation: A.M., Literature Search: F.M., Writing: M.A.H., A.M.
Conflict of Interest: No conflict of interest was declared by the authors.
Financial Disclosure: The authors declared that this study received no financial support.