Evaluation of Temporomandibular Disorders Among Dental Students of Saudi Arabia Using Diagnostic Criteria/temporomandibular Disorders (DC/TMD) and Its Association With Biographic, Academic, and Psychosocial Parameters – A Cross-sectional Study

Background: Temporomandibular disorders (TMD) are a board category of conditions arising from the various components of the temporomandibular joint (TMJ) complex. Bio-psychosocial model is the most accepted theory describing the etiopathogenesis of TMD. Dental students are vulnerable to psychological disorders including anxiety, depression and stress. Hence, the aim of the current study was to evaluate the TMD among dental students of various academic levels and explore the association of TMD with biographic, academic, and psychosocial parameters. Methods: A total of 246 students of a dental school in Saudi Arabia were chosen for the study. After getting consent, all students were examined as per the diagnostic criteria/Temporomandibular disorders (DC/TMD) including components from axis-I and axis-II. Results: The overall cross-sectional prevalence of TMD was found to be 36.99%. Pain arising from the jaw, temple, and peri-auricular area was the most commonly reported symptom and elicited sign during examination. Among the pain-related TMD, myalgia was the commonest diagnosed condition, whereas disc displacement with reduction was found prevalent in intra-articular disorder category. Female (OR=1.94; P=0.004), married (OR=1.74; P=0.04), and students in clinical levels (OR=1.65; P=0.03) were shown to have signicantly higher risk to develop TMD. Among the psychosocial parameters, parafunctional habits (OR=2.10; P<0.001) and anxiety (OR=1.55; P=0.04) are shown to increase risk of developing TMD. Students with any TMD reported to have signicantly higher pain intensity (OR=1.68; P=0.01) and jaw functional limitations (OR=1.45; P=0.008). Conclusion: Dental students especially in the clinical levels were shown to poses higher risk of developing TMD, hence strategies such as academic counselling and objective evaluation via rubrics should be planned to modify the administration of the curriculum, training methods and evaluation process.

The prospective study was conducted at a dental school in Saudi Arabia. In the current study, two academic parameters namely, academic level and academic performance (GPA) were considered. As per the ve-year curriculum of the dental school, the students of the 1st and 2nd year are considered "preclinical", as they remain engaged in the dental skills laboratories. However, the students of the 3rd, 4th and 5th year learn and acquire skills in clinics and hence are considered in the "clinical" category. Based on the grade point average (GPA), the student's academic performance were categorized as low GPA (< 3) and high GPA (≥ 3). Both male and female students of 18 years of age were included in the study. Subjects who had a current dental pain conditions and underwent treatment for such conditions were excluded from the study. Subjects who reported with a recognizable neurological disorder or are currently undergoing pharmacological treatment for any such conditions were also excluded from the study.

Calibration of the Examiners:
Based on the clinical experience in dealing with TMD and orofacial pain, four specialists were selected to be the examiners for the study. Irrespective of the clinical background, all examiners underwent a training session. During the session, they were provided with copies of the DC/TMD protocol of axis-I, axis-II and diagnostic decision tree. To enhance the understanding, all examiners saw instructional videos about the clinical examination available over the o cial webpage of the International Network for Orofacial pain & Related disorders Methodology (INFORM). After they were acquainted with the theoretical aspect, they underwent clinical training with patients. The clinical training was extended until they gained su cient expertise and came to an agreement about the protocol and diagnosis. The assessment of inter and intra examiner reliability was calculated by cronbac's alpha until we achieved a high level of agreement value of 0.80.

Data collection tools:
The DC/TMD axis-I and axis-II protocol is considered to have high reliability index value and so considered as the gold standard [17]. For the same reason, we considered in the present study. The axis-I protocol includes a symptom questionnaire and an international version of the clinical examination. Based on the diagnostic criteria and reference to the decision tree, the diagnosis was made.
The standard DC/TMD symptom questionnaire comprises of 14 questions which helps to reveal the history, duration and weather any functional activity can modify the complaint by either aggravating or relieving it. The major symptoms which were enquired included pain (Q1-4), headache (Q5-7), jaw joint noise (Q8), and regarding the locking of the jaw while opening (Q9-12) and closing (Q13-14). With respect to the duration of complaint in the recent history, 30 days was considered as the benchmark while questioning about the complaint and its modifying factors [3]. The responses for all questions except the description of the pain were recorded in the dichotomous nature. The second part of the axis-I involved clinical examination, location of pain/headache, incisal relationship, midline pattern, mandibular movements, TMJ noise, joint locking, and muscle tenderness. All examination ndings were performed for both sides of the jaw. As described in the diagnostic criteria, the combinations of positive responses from the history and examination components of DC/TMD axis-I, were designated a diagnosis for the particular subject [3].
The axis-II of DC/TMD is designed to assess the psychosocial parameters. In the current study, we undertook 5 standardized questionnaire namely graded chronic pain scale (GCPS), jaw limitation pain scale (JLPS), patient health questionnaire-9 (PHQ-9), generalized anxiety disorder (GAD) and oral behaviour checklist (OBC) [3]. These questionnaires are designed to assess different aspects of patient's psychosocial element.
Study protocol and data collection: All subjects were clearly explained about the objectives of the study and were not in uenced in any manner to participate in the study. Participants were asked to give written consent before starting the data collection. Initially, an educational camp was conducted at the dental school where all undergraduate students were encouraged to attend. The camp was extended for 2 weeks where students from all academic years were contacted sequentially. They were informed about the symptoms and presentation of TMD. All students who attended the camp were motivated to come for the TMD screening session. Students who attended the screening session were evaluated according the DC/TMD criteria. A total of 246 dental students participated in the study and underwent axis-I and axis-II evaluation (Fig. 1).
The participants who gave voluntary consent were involved in the study. The study involved a 3 step protocol, where the rst two steps involved the assessment of axis-I and in the last step, evaluation of axis-II was carried out. In the rst step, the participants were given a symptom questionnaire. As per the axis-I protocol, students were subjected to symptom questionnaire followed by clinical examination. Based on the responses from axis-I and with the reference of decision tree, the speci c diagnosis of TMD was made. Lastly, all students were subjected to ve structured questionnaire as a part of axis-II evaluation.

Data analysis:
The distribution of data was done using number and percentages. For the inferential analysis, the univariate and multivariate analysis was performed for the variables, where P < 0.05 was considered as statistically signi cant. All data analysis was performed with SPSS v.21. For the purpose of diagnosis of the psychosocial parameters, pre-validated cut-off was used, as described previously [23][24][25][26][27]. While during inferential analysis of these parameters, as described previously, the scores were dichotomized as "0" absent and "1or ≥ 1" as present of psychosocial parameter [14].

Results
A total sample of 246 dental students across all academic levels from a dental school in Saudi Arabia was studied. The sample consisted majority of 20-25 years-aged subjects with male and female representing 55.69% and, 44.30% respectively. More than half of the subjects (63%) belong to the clinical oriented academic levels. Considering the GPA, about 82.92% of the sample represented ≥3 GPA, whereas only 17.07% of subjects has <3 (Table1). Based on the assessment of subjects with the criteria of DC/TMD axis-I, around 36.99% of subjects reported with at least one of the TMD. Pain arising from the areas such as jaw, temple, or in front of the ear was the most commonly (76.92%) reported symptom followed by joint noise (30.76%). On performing the clinical examination, pain/familiar pain was the most frequently recorded sign followed by alternations in the mandibular movement (64.83%) ( Table 2).  On evaluating the psychological components, subjects with TMD were found to have a signi cantly higher risk to possess parafunctional habits (P<0.001) and anxiety (P<0.04). Raised pain intensity level and altered jaw function are seen to be 1.68 times and 1.45 times higher in dental students with TMD in contrast to non-TMD students (Table 5).

Discussion
The overall prevalence of TMD observed in our sample of dental students was 36.99%. These disorders were found to occur signi cantly higher among female students in their clinical academic levels. On evaluating the axis-II, it was observed that anxiety and parafunctional habits signi cantly increase the risk of TMD.
TMD is a complex condition with a multifactorial etiology. The major clinical presentation of these disorders is pain in the orofacial region of non-odontogenic origin [12]. The present study was carried out on dental undergraduate students of Saudi Arabia. The majority of the studies had done in the past have used self-reported symptoms/questionnaires [28,29] or RDC/TMD [8,15], whereas the present study has an edge over others since we evaluated symptoms along with clinical examination using DC/TMD. Since TMD considerably affects daily functions, its early diagnosis, prevention, and therapeutic management are deemed necessary.

Overall Prevalence of TMD
In the past, studies done on the general population had observed around 25% of the population reporting symptoms of TMD, but very few were actually seeking treatment [30]. The present study reported 36.99% prevalence of TMD, whereas a different study on Indian dental undergraduates reported a relatively less prevalence (30%) [14].Similarly, in a study on medical undergraduates' prevalence (17%) was even lesser [13]. A probable reason for the increased prevalence of TMD in the current study was the complexity level of the curriculum and the demanding nature of the study patterns followed in Saudi Arabia. Furthermore, dental students being more informed about the signs and symptoms associated with TMD, could have been more forthcoming in responding to the questions. In population-based studies [9,16] the diagnostic criteria used was RDC/TMD and moreover, in a few studies [31] it was coupled with selfreported symptoms which were more subjective rather than objective.

Association of TMD with biographic parameters
A widely reported fact is that TMD are more prevalent in females [14,32] and we too observed signi cant female preponderance with 1.94 times higher risk for developing TMD. However, previous study has reported a 2.3 times higher risk of TMD in female [32]. Another study with adolescent sample had found the similar gender variation [4]. The higher prevalence of TMD in females can be attributed to various gender oriented variations including hormonal, anatomical, behavioural and genetic [33]. It has been reported that the females during their reproductive period have higher levels of estrogens and progesterone. Under the in uence of estrogens, the laxity of the ligament increases during the preovulatory phase which further gets attenuated with the movement of TMJ leading to irritation [34]. Anatomically, it has been observed that the TMJ translation is more stable in males compared to females because they posses larger mandibular condylar head, deep temporal fossa and the angle of the jaw is less obtuse. Additionally, the maxillary bones in males are longer, wider and thicker compare to females. Also, genetically researchers have found that patients with TMD disorders mostly experience pain in other area which is considered as co-morbidity and it is more common in female. Lastly, the coping strategies for stress have remained different among gender [34].

Association of TMD with Academic parameters
Another interesting observation made in the current study was the higher prevalence of TMD among the students belonging to the clinical levels with 1.65 times more likely chances to develop TMD. This can be understood by acknowledging the fact that these students have acquired theoretical knowledge about the TMD as a part of their curriculum. Hence, they can relate well to the symptoms and signs of TMD and so, thus responded to the questionnaire and clinical examination in a more responsible and informed manner. Inherent challenges, demanding patient care and apprehension about the carer are some of the concerns which can be attributed to the students in the clinical levels [19][20][21].
Stress, somatic distress, and depression are seen as important etiological risk factors for pain related TMDs, thus these conditions have shown to be commonly associated with psychological distress [35]. In the present study, married students were reported with 1.74 times higher risk to develop TMD compared to their unmarried counterpart. In accordance to our results, Blanco-Hungría A et al., reported higher prevalence of TMD among separated and divorced individuals followed by married and least among the single individual [36]. Contrary to this, Han W et al., reported single females to have more TMD disorders compared to married contemporaries [37]. Although married individuals could have additional emotional support, prevailing social, economic and professional demands could challenge their threshold, and offset the balance of personal and professional life. Hence, the married individuals nd di cult to nd a balance between the personal and professional life.

Association of TMD with psychological parameters
To assess the pain intensity, graded chronic pain scale (GCPS) was used in our study. It's a tested and reliable tool used only to measure the pain intensity but also quanti es the deleterious impact of pain while performing daily, recreational and social activities in the last 30 days [3]. In the present study, it was observed that the students with raised pain intensity are 1.68 times more likely to have any TMD. Pain is a subjective feeling and its threshold varies from person to person [38]. It is also noteworthy to mention that the pain behaviour undergoes modulation during its transmission to the higher centres and nally perception of pain at the supra-spinal levels is in uenced by the psychological factors [39]. Although the pain attributed from the TMD disorders usually starts as a somatic disorder, but eventually progress towards the chronic pain, where the psychological components plays an important contributing role [40].
Likewise, in the current study the students with TMD were shown to have signi cantly higher pain intensity than with students with no TMD. Our results are in agreement with pervious study conducted with dental students of European continent [14].
The etiopathology of pain has been best described by the biopsychosocial model. According to this model, there is interplay between the biological and psychosocial component leading to the pain presentation [13]. In order to evaluate this, anxiety, depression and jaw functional limitation scale were assessed.
The students with higher anxiety score were shown to have 1.55 times higher risk for developing TMD. Our observations restate the signi cance of the psychosocial component in the development of TMD. Student population generally seen to have higher anxiety levels compared to the adult population, as they remain in constantly challenging environment [20]. Additionally, previous studies have shown dental students to have higher level of stress and anxiety [41]. As an outcome of longstanding TMD, it was expected from the sample of dental students with TMD to show higher levels in JFLS. Conversely, subjects with high levels of JFLS were reported 1.45 times more likely to develop TMD.
The intention of including the oral behaviour checklist was to evaluate the impact of parafunctional habits. The checklist comprised of 21 questions pertaining to posture, motion and activities involving the oral musculoskeletal structures including the jaws and tongue. The assessment differentiated between the activities performed during sleep and awake state in the last month [3]. The students reported with parafunctional habits were found to have 2.10 times higher risk to develop TMD. Clenching/grinding teeth and chronic chewing gum were the most popular activities indicating a state of sub-conscious anxiety. This has shown to trigger muscle contraction leading to fatigue and eventually causing TMD [42].
Availability of data and materials The datasets used and analysed during the current study are available from the corresponding author on reasonable request.

Competing interests
We declare no potential con icts of interest with respect to the authorship or publication of this manuscript.

Funding
The current study is Self-funded

Authors' contributions
All authors contributed to this article. KCS, DS and KJ Conceptualized and developed methodology. KCS and DS collected the data and drafted of the manuscript. ZAK and AK analyzed the data. MAM and MH were involved in Validation, Visualization and revising the manuscript. KCS and MKA supervised the project, resources and revised the manuscript. All authors read and agreed with the content of the submitted manuscript.