Temporomandibular Disorders among Dental Students in Pakistan: Assessment of Prevalence, Severity, and Associated Factors Based on Questionnaire

Objective To evaluate the prevalence, severity, and associated factors of temporomandibular disorder (TMD) among dental students. Methods This cross-sectional study was performed on undergraduate dental students from four dental colleges in Punjab, Pakistan. Fonseca's questionnaire was used to measure the prevalence and severity of the TMD among the study participants. Bivariate and multiple logistic regression analyses were performed. Results Of 364 dental students, 323 returned the completed questionnaires and the response rate of the study was 88.7%. The study included 52.6% males and 47.4% females. The prevalence of TMD was 66.9% with mild TMD in 40.90%, moderate TMD in 14.6%, and severe TMD in 11.50% of the participants. Psychological stress (29.6%), malocclusion (20%), and hypersensitivity (19.5%) were common among participants. The mean TMD score of the sample was 31.54 ± 24.86 which was significantly higher among participants with no/school-educated mothers (P=0.021) and fathers (P=0.002). The participants with arthritis (72.81 ± 32.19) and malocclusion (59.46 ± 31.09) and those who received orthodontic treatment (53.21 ± 34.21) demonstrated higher TMD. After controlling for other study variables, the participants with arthritis were 4.71 times more likely to have moderate/severe TMD (P=0.042) than those without arthritis. Similarly, the participants with malocclusion had significantly higher odds (OR = 3.57, P=0.029) of having moderate/severe TMD than those without malocclusion. Conclusion This sample of dental students demonstrated a high prevalence and severity of TMD. The participants with arthritis and malocclusion demonstrated higher TMD. The study findings underscore the importance of prevention, early diagnosis, and management of TMD among the dental students.


Introduction
According to the American Society of Temporomandibular Joint Surgeons, "temporomandibular disorder (TMD) is a collective term embracing all the problems regarding the temporomandibular joint and related musculoskeletal structures" [1]. TMD is a multifactorial condition, and several factors are involved in the initiation, progression, and aggravation of the symptoms of TMD. Clicking, sound in temporomandibular joint (TMJ), is the most common symptom of TMD, followed by headache. Te patients with TMD may demonstrate myofascial pain, morphological changes in the condyle, disc displacement, or disc derangement [2]. Te individuals with parafunctional habits and bruxism are up to 4.8 times more likely to develop TMD [3]. It was reported that female patients demonstrated TMJ pain at rest, clicking of the temporomandibular joint, grinding of teeth, and pain in the masseter muscle more frequently than male patients [3,4].
Globally, the prevalence estimates vary considerably among diferent populations. A review of 21 studies showed that the prevalence of TMD ranged from 2.6% to 11.4% [5]. In Jordan, the prevalence of TMD was 68.6% among university students [6]. TMD pain was reported by 25.9% female and 11.4% male Finnish university students [7]. A recent study showed that 49.7% of the university students complained of at least one sign or symptom of TMD in Saudi Arabia [8]. In Brazil, the prevalence of TMD was 71.9% in university students and TMD was signifcantly associated with perceived stress, mental disorders, and parafunctional habits [9]. Among dental students, previous Brazilian studies reported TMD in 53.21%-58.9% of the participants using the Fonseca questionnaire [10,11]. Moreover, a relevant previous study from India showed that 42% of the dental students had some form of TMD [12]. In Pakistan, 42.6%-62% of the undergraduate medical and dental students presented with TMD [13,14].
Epidemiological studies of TMD are important for assessing the prevalence and severity of the condition and associated factors to help develop evidence based preventive policies and programs. TMD among the dental students has been discussed in the literature before; nevertheless, there is a lack of data about the prevalence of TMD among the dental students in Pakistan. Additionally, the associations of gender, age, and dental and medical conditions with TMD have not been thoroughly investigated among the dental students. Terefore, this study aims to evaluate the prevalence, severity, and associated factors of TMD among the dental students in Punjab, Pakistan.

Study Design.
Tis cross-sectional study was designed to evaluate the prevalence and severity of TMD among dental students using Fonseca's Anamnestic Index questionnaire. Te study (FMH-03-2021-IRB-884-M) was approved by the Institutional Review Board at the FMH College of Medicine & Dentistry, Lahore, Pakistan.

Subjects.
A calculated sample of 364 students was used in the study, and the sample calculations involved the assumptions of ±5% precision, 95% confdence level, and population size (N ≈ 4000). Te study used a convenience sample of consenting students from private and public dental colleges. Te participants were recruited from four dental colleges (de'Montmorency College of Dentistry Lahore, FMH College of Medicine & Dentistry Lahore, Lahore Medical Dental College, and University Medical Dental College, Faisalabad) of Punjab, Pakistan. Te undergraduate dental program consists of four years in Pakistan. Terefore, students from all four years were included in the study. Te participants with major systemic disease and/or those undergoing treatment for TMD were excluded from the study.

2.3.
Instrument. Data were gathered using a selfadministered questionnaire that included sociodemographic information, medical and dental history, and Fonseca's questionnaire. Sociodemographic information included age, gender, academic performance in the previous year, parental educational levels, and monthly family income. Te medical history included arthritis, psychological stress, trauma to head, musculoskeletal disease, sleep disorder, and others conditions. Te dental history included malocclusion, hypersensitivity, bruxism (grinding of teeth), bad breath (oral malodor), bleeding gums, difculty in biting, and pain in teeth or gums. Te types of dental treatment received were orthodontic treatment, crown and bridge, dentures, fllings, root canal treatment, extraction, and scaling. Fonseca's questionnaire with an anamnestic index was developed by Fonseca and is a valid and reliable instrument for measuring TMD [15]. Te literature shows that the Fonseca instrument has been used in a wide variety of studies to collect TMD related information from diferent populations and has characteristics of multidimensional evaluation [10,16,17]. Te questionnaire consists of 10 items that inquire regarding difculty in opening mouth, problem in moving jaw to sides, muscle pain or fatigue on chewing, feeling headache, having neck pain and ear pain, noise from the temporomandibular joint on chewing or opening the mouth, grinding of teeth, problems with biting teeth together, and feeling nervous. Each item of the questionnaire is answered with "yes," "no," and "sometimes" options, and only one option is marked by the study participants [15]. Te questionnaire was pilot tested among 30 dental students to make sure that there were no problems with readability and understanding of the questionnaire by the participants.

Procedure.
Students were briefed about the study (purpose, details, and benefts of the study), voluntary participation of study participants, and confdentiality and privacy of their responses. Tey received instructions about the questionnaire and were provided with explanations if they had difculty understanding the questions. Students who were willing to participate in the study received hard copies of the self-administered questionnaire in their classes and, after completion, they returned the questionnaires to the researchers.

Statistical Analysis.
Statistical Package for Social Sciences Version 22.0 (IBM SPSS Statistics for Windows, Version 22.0. Armonk, NY: IBM Corp) was used for statistical analysis. Frequency distributions, means, and standard deviations were calculated for the study variables. Te total score of the Fonseca questionnaire was calculated by summing up the responses of each item. A score of 10 was given to "Yes"; a score of 5 for "Sometimes"; and 0 for "No" options. Te total score of the Fonseca questionnaire ranges from 0 to 100 which was used to evaluate the severity of TMD according to Fonseca index classifcation (Table 1).

Scientifca
Te mean score of the Fonseca questionnaire was compared with gender, academic year, academic score, parental education, and family income using an independent samples t-test. Bivariate and multiple logistic regression analyses were performed to evaluate the association of independent variables (gender, academic year, academic score, parental education and family income, and medical and dental history) with the dependent variable (moderate/severe TMD). Te undergraduate dental program in Pakistan consists of four years with the frst and second years being preclinical years and the third and fourth years being clinical years. An academic score equal to or above 80% was categorized as a high score and below 80% as a low score. Te statistical signifcance level was set at 5%.

Results
Of 364 dental students, 323 returned the completed questionnaires and the response rate of the study was 88.7%. Te study included 64.1% of the participants from private and 35.9% from public colleges. Tere were 52.6% males and 47.4% females, and most participants had a high monthly family income (75.4%), and their fathers (80.8%) and mothers (75.5%) had college/university education. Te mean TMD score of the sample was 31.54 ± 24.86. A signifcantly higher mean TMD score was observed among participants whose fathers (P � 0.002) and mothers (P � 0.021) had no/school education compared with those who had college/university educated parents. Te study demonstrated no statistically signifcant diferences in TMD score between males and females (P � 0.453), participants from public and private colleges (P � 0.627), participants from preclinical and clinical years (P � 0.174), participants with low and high academic scores (P � 0.733), and those with low and middle/high monthly family income (P � 0.098) ( Table 2). Table 3 presents data on TMD and its relationship with medical and dental history, as well as dental treatment. Psychological stress (29.6%), malocclusion (20%), and hypersensitivity (19.5%) were common among participants. Regarding medical history, the participants with arthritis showed the highest mean TMD score (72.81 ± 32.19), followed by trauma to the head (41.0 ± 27.67) and musculoskeletal disease (40.50 ± 29.29). Regarding dental history, the mean TMD score was the highest among participants with malocclusion (59.46 ± 31.09) and the lowest with bleeding gums (24.46 ± 17.11). Regarding dental treatment, the participants who received orthodontic treatment showed the highest TMD severity (53.21 ± 34.21), whereas the participants with scaling demonstrated the lowest mean TMD score (24.60 ± 17.83). Figure 1 shows the distribution of study participants with diferent levels of TMD. Only 33.10% of the participants reported no TMD, whereas 66.9% of the participants demonstrated TMD with mild in 40.90%, moderate in 14.6%, and severe in 11.50%.
Te participants with no/school-educated fathers had signifcantly higher odds (OR � 2.76, P < 0.001) of developing moderate/severe TMD than those with college/ university educated fathers. Similarly, participants with no/ school-educated mothers were signifcantly more likely (OR � 2.33, P � 0.002) to have moderate/severe TMD than those with college/university educated mothers. Statistically higher odds of moderate/severe TMD were found among participants with arthritis (OR � 14.4, P < 0.001), malocclusion (OR � 6.06, P < 0.001), and those who received orthodontic treatment (OR � 3.08, P 0.001) ( Table 4).
Statistically signifcant or marginally signifcant factors were included in the fnal model. Arthritis and malocclusion were signifcantly associated with moderate/severe TMD after controlling for parental education, monthly family income, and orthodontic treatment. Te participants with arthritis were 4.71 times more likely to have moderate/severe TMD (P � 0.042) than those without arthritis. Similarly, the participants with malocclusion had signifcantly higher odds (OR � 3.57, P � 0.029) of having moderate/severe TMD than those without malocclusion (Table 5).

Discussion
Te present study was conducted to evaluate the distribution and severity of TMD among dental students in Pakistan. Te study showed the presence of TMD in 66.9% of our sample with 40.9% mild, 14.6% moderate, and 11.5% severe TMD. Tis fnding is supported by the results of a recent study by Khan and Zaigham who used the Fonseca questionnaire and observed TMD in 62% of the medical and dental students in Pakistan [14]. Based on the same questionnaire, Nomura et al. reported that the prevalence of TMD was 53.21% among the Brazilian undergraduate dental students with 35.78% mild, 11.93% moderate, and 5.5% severe TMD [10]. Another study from Brazil by Rocha et al. reported TMD in 58.9% of the dental students [11]. Similarly, a relevant previous study by Alfawzan (2020) showed TMD in 45% of the dental students in Saudi Arabia [18]. According to another study of female dental students, 62.8% of the participants were shown to demonstrate mild to severe TMD [19]. In India, an investigation of TMD among the dental students by Kumar and Harshitha showed TMD in 42% of the participants [12]. In addition, many previous studies used the Fonseca questionnaire among health care students and showed prevalence estimates of 30.6% in Nepal [20], 54.2% in Saudi Arabia [21], and 72.2% in Turkey [22]. Tese variations in the prevalence of TMD can be attributed to the diferences in study designs, sample size and sampling methods, and the measurement instrument or diagnostic criteria used to measure TMD.
A systematic review and meta-analysis of 21 articles on the prevalence of TMD reported that 19.1% population sufered from disk displacement and 9.8% from degenerative joint disease [23]. It is known that the dental students with TMD are at a signifcantly increased risk of developing jaw functional limitations and oral parafunctions [24]. Based on the aforementioned present study and previous relevant studies, there was a high prevalence of TMD among dental students which emphasizes the importance of preventive measures. Tis is further confrmed from the fndings of another study where authors observed a signifcantly greater distribution of TMD among the dental students (80%) than nondental students (62%) [25]. Dental students with TMD related pain diagnosis such as myalgia or arthralgia were also shown to experience signifcantly higher pain intensity than those without TMD pain [24]. Te etiology of TMD is not fully understood, and being a multifactorial disorder, multimodal treatment approaches should be used for individuals with TMD [26]. Terefore, the stakeholders in dental academia and healthcare systems should develop policies to prevent and manage temporomandibular dysfunctions among dental students to reduce the burden of this disease including improvement in the quality of life and learning experience. Approximately one-third of the dental students (29.6%) reported psychological stress in our sample of students. A  previous study of medical and dental students in Pakistan showed a lower prevalence of stress among dental students (12.2) than our estimates. On the contrary, Abbasi et al. reported that 68% of the dental students in their clinical year sufered from high stress in Pakistan [27]. Te diferences in these prevalence estimates can be attributed to the diferences in the measuring instrument, study sample, and geographic location. Over the years, research has shown that stress is common among dental students which is related to demanding curriculums, course and clinical requirements, examinations, and patient management and can adversely afect their academic performance, general health, and quality of life [11,28]. Te relationship between stress and TMD among dental students has been reported in the literature [11]. However, the present study did not fnd a signifcant relationship between psychological stress and TMD. Tis is in line with the results of a study by Lövgren et al. who found no diference in psychological factors between dental students with or without a TMD diagnosis [24]. In the presents study, 20% of the dental students had malocclusion who demonstrated the second highest score of TMD. Te study also showed a statistically signifcant association between malocclusion and moderate/severe TMD where dental students with TMD were 3.57 times more likely to have TMD than those without malocclusion. Te association between TMD and malocclusion was confrmed by Tilander et al. who found that anterior open bite, posterior crossbite, increased overjet, and Angle class III malocclusion were associated with TMD [29]. As demonstrated in the present study, dental students are at risk of developing TMD; therefore, a routine dental examination should be performed to identify malocclusion and other oral problems and referred for early investigation and intervention.
Osteoarthritis and rheumatoid arthritis are common conditions encountered in clinical practice and are associated with TMD [30,31]. With a global prevalence of 15%, osteoarthritis is characterized by chronic degeneration of joint tissues causing pain, and it afects stress-bearing as well as other joints in the body including the temporomandibular joint (TMJ). Osteoarthritis may be localized to the TMJ or can be part of a generalized form of this condition [30]. Rheumatoid arthritis (RA) is a chronic, systemic, immunemediated infammatory disease that involves symmetrical    [31]. In the present cross-sectional study, dental students with arthritis demonstrated the highest mean TMD score and participants with arthritis had signifcantly higher odds (4.71) of having moderate/severe TMD than those without arthritis.
Te following limitations of this study should be considered. Data collected from four dental colleges may not represent the dental student population in Pakistan; therefore, the generalizability of study fndings is limited. Furthermore, a convenience sample of dental students may lead to selection bias and infuence the validity of the study. Random errors can also occur in this type of research if participants do not accurately respond to each item in the questionnaire. To the best of our knowledge, this is the frst study that identifed signifcant associations of malocclusion and arthritis with TMD among dental students. However, a cross-sectional study design is limited as far as the investigation of cause and efect relationships is concerned. Additionally, the present study included self-reported data on malocclusion and arthritis and found their signifcant associations with TMD. Terefore, large cohort studies should be conducted to investigate clinically diagnosed TMD and associated factors including diferent types of malocclusion and joint diseases among dental students.

Conclusions
Tis study showed a high prevalence and severity of TMD among dental students. Psychological stress and malocclusion were also common among them. Te participants with arthritis and malocclusion demonstrated high TMD. Moreover, arthritis and malocclusion were signifcantly associated with an increased likelihood of moderate/severe TMD. Te study underscores the importance of prevention, early diagnosis, and management of TMD among the dental students.

Data Availability
Te SPSS data fle of this study is available from the corresponding author upon request.

Conflicts of Interest
Te authors declare that they have no conficts of interest.