Profiling of Patients with Temporomandibular Disorders: Experience of One Tertiary Care Center.

OBJECTIVES: The aim of this study was to assess typical and most prevalent characteristics of patients suffering from temporomandibular disorders (TMD) by a retrospective assessment of their medical records.
MATERIAL AND METHODS: Demographic data and data on the characteristics of TMD were collected from the existing medical documentation of 304 TMD patients (250 females and 54 males) who had been referred to the Department of Dentistry, Clinical Hospital Center Zagreb from October 2016 to October 2020 due to temporomandibular pain. For the purpose of analysis, three age groups were formed: i) "children and adolescents" (up to 19 years of age); ii) "middle age" (from 20 to 50 years of age); iii) "older age" (>50 year- olds). A two-step cluster analysis was performed with the aim of classifying TMD patients into homogenous groups.
RESULTS: The mean age of patients whose data were included in the study was 33.8 ± 16.66, with a significantly higher age in the group of women (p<0.001). Most of the patients had chronic pain (67.4%), with the ratio in favor of chronic patients being significantly higher in women than in men (p=0.001). Data on parafunctional behavior were confirmed in 14.5% of patients. Data on the onset of symptoms during/just after orthodontic treatment were present in 14.5% of patients. Data on spontaneous pain, assessed with a visual analogue scale, were recorded in 87 patients, with a mean of 6.14 ± 1.79 and with the highest pain in the "older age" group. Physical therapy was the most common therapeutic modality (56.3%) followed by an occlusal splint (40.5%). The analysis revealed 5 different clusters in the TMD patient data set.
CONCLUSIONS: Our results are largely in line with current epidemiological knowledge on TMD. Women predominated in all age groups and most of the patients experienced chronic pain. Classifying patients into homogeneous groups using the clustering method could provide better identification of subgroups of conditions that mainly occur together in these patients, thus providing the basis for more specific management.

Introduction

In clinical practice, patients who report difficulties that can be associated with some form of temporomandibular disorders (TMD), a heterogeneous group of pathological conditions involving the temporomandibular joint (TMJ), masticatory muscles, or both are increasingly encountered (). The most common symptoms of TMD include muscle and/or TMJ pain that occurs or intensifies during functions of the mandible, sounds in the TMJ, and difficult and/or limited mouth opening, which may be accompanied by deviation from a straight line (deviation or uncorrected deviation) ().

Risk factors associated with the onset of TMD are emotional stress, trauma, oral parafunctional behavior, and deep painful stimuli (, ). Scientific research has repeatedly confirmed that occlusion, which in the past was considered one of the main causes of TMD, has no role in the development of TMD, but may pose a problem in hypervigilant patients ().

Pain and limitations of the mandibular movement are the most commonly reported signs/symptoms by patients who seek for help (). Additionally, it is very common for patients to report various comorbid conditions such as depression, anxiety and other psychological disorders along with primary ailments (). The latter may be a direct consequence of chronic orofacial pain but is also considered one of the risk factors that can affect the intensity and course of TMD (). Tension headaches, migraines, fibromyalgia, and lower back pain are comorbidities also mentioned in the literature (). Somatization and psychological problems are more often associated with chronic pain. Neuroplasticity is involved in chronic pain development (). The most important consequence of these neuroplastic changes in chronic pain is reduced filtering ability of central sensory neurons in the brain and spinal cord resulting in wrong interpretation of noxious stimuli that can be exaggerated (secondary hyperalgesia) or misinterpreted.

The exact prevalence of TMD in the general population varies greatly in the literature and ranges from 3-33%, which might be the consequence of considerable variations in diagnostic protocols (, ). Using standardized diagnostic criteria such as RDC/TMD (Research Diagnostic Criteria for TMD) and DC/TMD (Diagnostic Criteria for Temporomandibular Disorders), recent research is providing increasingly accurate data (). Today, the prevalence of TMJ pain in the general population is considered to be 4–10% and 3–17% for muscle pain. Furthermore, the incidence of TMD is highly age-dependent with prevalence being highest at 20-40 years of age ().

With respect to gender, TMD is more common in women (). The reasons for gender inequality are still not fully elucidated (). It is hypothesized that the presence of estrogen receptors may be a predisposition to TMJ dysfunction and degradation, i.e., cartilage destruction ().

It is interesting to note that in clinical practice, more and more children and adolescents are reporting symptoms of TMD, and very often patients in the middle of the active phase of removable and fixed orthodontic therapy. An increasing number of patients, who are looking for a solution for acute and chronic forms of TMD, point to the need for better profiling in order to provide them with an individualized approach to treatment and the most precise therapy possible.

The aim of this study was to assess typical and most prevalent characteristics of patients suffering from TMD by a retrospective assessment of their medical records and to classify patients into homogeneous groups, by means of cluster analysis, based on their demographics, primary diagnosis, chronicity and risk factors.

Material and Methods

This study was a retrospective assessment of medical records of 304 TMD patients (250 females and 54 males) treated at the Department of Dentistry, Clinical Hospital Center Zagreb from October 2016 to October 2020.

The conducted research was approved by the Ethics Committee of the School of Dental Medicine, University of Zagreb (05-PA-30-VIII-6/2019) and performed following the ethical standards of the Helsinki Declaration. This study has been supported by the Croatian Science Foundation Project “Genetic polymorphisms and their association with temporomandibular disorders” (No. IP-2019-04-6211).

Description of the clinical examination protocol and therapy

Patients' examinations were conducted by two calibrated experts in TMD diagnostics (IA and EV) ().

While medical histories were taken from patients, examiners collected data about their reasons for seeking help, pain characterization (intensity, spontaneous pain, reported pain duration - TMD chronicity), limitation of the lower jaw (mouth opening, pain, and difficulties while eating, etc.), the existence of systemic diseases and previous pharmacotherapy use, awareness of oral parafunctional habits and data on previous orthodontic treatment. The clinical examination consisted of the evaluation of full dental status, analysis of panoramic imaging, palpation of the masticatory muscles, the lateral pole of TMJ, submandibular and retromandibular region. Measurements of pain-free mouth opening and unassisted mouth opening (MCO, MMO, respectively) were obtained, as well as the information about the existence of deflection and sounds in the joint. Methods for evaluation of spontaneous pain and measuring of MCO and MMO were described in our previous studies (). All patients were clinically diagnosed according to DC/TMD diagnostic tree (). If applicable, the diagnosis was confirmed by radiographic imaging.

After the clinical diagnosis had been established, it was decided which therapeutic option would be used. Physical therapy consisted of a set of recommended exercises that were performed by a patient (muscle massage, passive and active stretching, application of warm compresses) (). The production and manufacturing of stabilization splint was described in our previous research (). Pharmacotherapy mainly included analgesics, nonsteroidal anti-inflammatory drugs (NSAID) or a combination of NSAIDs/analgesics with benzodiazepines (, ). All patients received a thorough oral explanation of their condition with an emphasis on education about the nature of the present pain and various ways to deal with it.

Collected data

All data were extracted from the patient's medical records. Patients whose data were included in the study ranged between 8 to 83 years of age. For analysis purposes, three age groups were formed: i) “children and adolescents” (up to 19 years of age); ii) “middle age” (from 20 to 50 years of age); iii) “older age” (>50 year olds).

TMD was considered acute if participants were experiencing symptoms for no more than 3 months prior to the first examination, or participants experienced new, previously non-existent, symptoms (i.e. pain or limited mouth opening) in the past 3 months, regardless of existing TMD history. The division into acute and chronic pain was based on the International Association for the Study of Pain (IASP) which defines acute pain as the pain that occurs within 3 months, while chronic primary pain is the pain in one or more anatomical regions that persists or recurs for longer than 3 months and is associated with significant psychological stress and/or functional disability with symptoms that cannot be accounted for by another diagnosis ().

A history of possible orthodontic therapy had been recorded. The data about the development of new symptoms during orthodontic therapy or immediately after the end of orthodontic therapy were taken into analysis. The presence of parafunctional behavior was recorded and included into analysis if data regarding daytime grinding and/or clenching were reported by the patient himself/herself or if data on nocturnal clenching were confirmed by another person (ie. parent, spouse, partner, sibling, roommate).

Conventional radiographs were of diagnostic value only when degenerative changes were obvious. Magnetic resonance imaging (MRI) of the TMJ was requested for a limited number of patients that were unresponsive to therapy or had severely limited mouth opening (<30mm) considered to be of joint origin. Cone-beam computed tomography scans were analyzed only if previously performed.

The possible diagnoses, mainly based on clinical findings, were: myalgia, arthralgia, disc displacement with reduction (DDwR), disc displacement without reduction (DDwoR), degenerative joint disease (DJD) and subluxation (). The primary diagnosis was established according to a set of symptoms that patients themselves noticed and for which they primarily sought treatment, while the secondary diagnosis represented a series of additional signs or pathologies observed during clinical assessment. Finally, the pooling of diagnoses was done according to the DC/TMD diagnostic criteria into i) pain disorders (TMD-P) (myalgia and arthralgia), ii) joint disorders (TMD-J) (DDwR, DDwoR, DJD and subluxation) ().

The following data were used for analysis: demographic data including age and gender, chief complaint, presence of oral parafunctional behavior, data on the onset of symptoms during/after orthodontic treatment, spontaneous pain intensity assessed using a visual analogue scale (VAS), pain location, MCO and MMO, pain on palpation, existence of deflection while opening, primary and secondary diagnosis (if applicable), TMD chronicity, and finally, applied therapeutic modalities (physical therapy/ pharmacotherapy/stabilization splint).

Statistical analysis

Statistical analysis was performed using IBM SPSS Statistics for Windows, Version 26.0 (Armonk, NY: IBM Corp). The student (KD) collected and organized the data in an Excel table as a part of a graduate thesis.

Analyses consisted of descriptive statistics and appropriate tests (t-test for independent/dependent samples, ANOVA and Chi-square) that were used to present significant differences between variables. A value of p < 0.05 was considered statistically significant.

The two-step cluster analysis was used as an exploratory tool intended to reveal natural groupings within the data set with selected variables. After having tested other combinations of variables, based on our clinical experience, we decided to present the grouping according to the following variables: gender, age group, presence of parafunctions, data on the onset of symptoms during/after orthodontic treatment, TMD character (acute/chronic) and primary diagnosis.

Results

The mean age was 33.88 ± 16.66, with a significant difference between men (27.13 ± 12.39) and women (35.34 ± 17.12) (p <0.001). The distribution and mean age in each age group was as follows: i) “children and adolescents” (n=62 (20.4%); 17.21 ± 2.14 years), ii) “middle age” (n=183 (60.2%); 30.52 ± 9.06 years), iii) older age (n=59 (19.4%); 61.8 ± 7.89 years). Even though there was no significant difference in the representation of women vs. men between groups (p = 0.08), the most obvious difference was present in the “older age” group - from the total number of patients in the group (n=59), 89.8% were women and 10.2% were men. In the “middle age” group 82.5% were women and 17.5% men while the “children and adolescents” group consisted of 74.2% women and 25.8% men.

Regarding the reported duration of symptoms (TMD chronicity), out of 304 patients, 99 (32.6%) were considered to be experiencing acute TMD pain and 205 (67.4%) chronic TMD pain. A significant difference was present in acute/chronic TMD ratios between men and women (χ2=11.12, p=0.001). Women experienced chronic pain in 179 out of 250 cases (71.6%), while the ratio for men between acute vs. chronic cases was more even (51.9% vs. 48.1%, respectively).

In 75.3% of cases (n = 229) patients reported that the pain was unilateral, while bilateral pain was reported by 75 patients (24.7%). When asked to point a finger at the painful area (data obtained from n=262 patients) the majority of patients pointed solely to the area around the lateral pole of the TMJ as the primary pain location (n=218, 83.2%). The distribution of reported pain areas is shown in Figure 1.

Figure 1

Distribution of reported areas that patients pointed out as painful during clinical examination* (out of n=262 patients) *Bodychart retrieved from DC/TMD Assessment Instruments

According to the data collected, the distribution of diagnoses was as follows: i) disc displacement with reduction (n=118); ii) disc displacement without reduction (n=14); iii) myalgia (n=79); iv) arthralgia (n=67); v) degenerative joint disease (n=19), and vi) subluxation (n=7). Figure 2 shows the frequency of TMD diagnoses. Following the new DC/TMD classification of TMD, the distribution of diagnoses into TMD-P and TMD-J groups was as follows: TMD-P 48% and TMD-J 52%. A significant difference between the number of patients with TMD-P or TMD-J concerning TMD chronicity was found (χ2=4.29, p=0.038). In both groups, there were more chronic than acute patients with significantly more chronic patients in the TMD-J group when compared to the TMD-P group (72.8% vs. 61.6%).

Figure 2

The frequency of TMD diagnoses. DDwR – disc displacement with reduction, DdwoR – disc displacement without reduction, DJD – degenerative joint disease

In 55 patients, a secondary diagnosis was identified. The most common secondary diagnosis was myalgia (41%) followed by arthralgia (28.2%), disc displacement with reduction (9%), degenerative joint disease (9%), subluxation (11%), and disc displacement without reduction (1.8%).

Data on parafunctional behavior were confirmed in 44 patients (14.5%). In the rest of the patients (85.5%), the data on the existence of parafunctional behavior could not be supported by sufficient information regarding grinding, clenching, or other parafunctional oral behavioral habits. Of the total 44 of patients who reported the existence of parafunctional behavior, 29.5% of them experienced activities during waking hours, 41% activities during sleep, and 29.5% both.

In medical history, orthodontic therapy had been recorded in 71 patients. Data on the onset of symptoms during/just after orthodontic treatment was found in the medical history of 44 patients, 14.5% out of all patients (n=304), and 61.97% out of patients with orthodontic treatment in their medical history (n=71). Out of those 44 patients, 77.3% had chronic and 22.7% had acute TMD. In the group “children and adolescents” a significantly higher number of patients (χ2=10.54; p =0.001) with the onset of symptoms during/just after orthodontic treatment was found when compared to adult patients (pooled “middle age” and “older age”) (27.4% vs. 11.2%).

The data regarding quantification of spontaneous pain, assessed with VAS, was present in 87 patients with a mean of 6.14 ± 1.79 with no significant difference with respect to gender (p=0.32), however, VAS was observed to be lower in men (5.38 ± 1.71) than in women (6.27 ± 1.79). When VAS was evaluated according to age groups, the highest values were observed in the “older age” group (7.43 (95% CI 6.65-8.20)), followed by 6.19 (95% CI 5.55-6.83) in the “children and adolescence” group, and the lowest in the “middle age” group (5.77 (95% CI 5.24-6.30)). No significant difference in pain intensity between acute and chronic TMD patients was found (mean VAS for acute TMD: 5.84 ± 1.55, mean VAS for chronic TMD: 6.30 ± 1.91; p=0.1).

The data regarding the confirmation of familiar pain on muscle palpation were present in medical records of 104 patients (34.2%), while in medical records of 140 patients (41.6%) the data regarding the confirmation of familiar pain during TMJ palpation existed. Data regarding the presence of uncorrected deviation (deflection) during the opening were recorded in 76 patients (25%). In 179 patients (58.9%), a limited mouth opening was noted during the clinical examination, while the report of pain during opening was present in 166 patients (54.6%). Limited mouth opening was present in all participants with disc displacement without reduction (100%), 76.1% participants with arthralgia, 44.9% participants with disc displacement with reduction, 58.2% participants with myalgia, and 57.9% participants with degenerative joint disease. The frequency of limited mouth opening in the TMD-P and TMD-J groups was 66.4% vs. 51.9% (χ2=6.63, p=0.01).

The mean MCO was 35.14 ± 10 mm (data obtained from 296 patients), while the mean MMO was 39.51 ± 8.63 mm (data obtained from 166 patients).

As a therapeutic modality, physical therapy was prescribed in 171 cases (56.3%), occlusal splint in 123 cases (40.5%), and pharmacotherapy in 59 cases (19.4%) (Note: one patient might have more than one therapeutic modality). Pharmacotherapy and occlusal splints were predominantly prescribed for patients with TMD-P when compared to TMD-J (pharmacotherapy: 61% vs. 39%, χ2=5.09, p=0.02; occlusal splint: 56.1% vs. 43.9%, χ2=5.39, p=0.02).

The data on MRI imaging were recorded in 7 patients, out of which the anterior disc displacement without reduction was confirmed in 4 patients, in 2 patients the diagnosis was subluxation, while in 1 patient joint hypomobility was present.

Grouping of the patients

Two-step cluster analysis with selected variables revealed 5 clusters (Table 1).

Table 1

Percentages for each category within variables in each cluster

Variables/ Varijable	Categories/ Kategorije (%)	Clusters/ Klasteri
		1(n=67)	2(n=91)	3(n=42)	4(n=45)	5(n=59)
Gender/ Spol	Men/ Muškarci	22.4	11	23.8	2.2	30.5
	Women/ Žene	77.6	89	76.2	97.8	69.5
Age group/ Dobna skupina	Children and adolescents/ Djeca i adolescenti	59.7	0	8	0	26.8
	Middle age/ Srednja životna dob	38.3	98	59.5	0	71.2
	Older age/ Starija životna dob	2	2	32.5	100	2
Parafunctional behavior/ Parafunkcijske navike	Yes/ Da	3	0	100	0	0
	No/ Ne	97	100	0	100	100
Occurrence of symptoms during/after orthodontic therapy/Pojava simptoma tijekom/nakon ortodontske terapije	Yes/ Da	65.7	0	0	0	0
	No/ Ne	34.3	100	100	100	100
TMD duration/ Trajanje TMP-a	Acute/ Akutno	14.9	0	40.5	28.9	100
	Chronic/ Kronično	85.1	100	59.5	71.1	0
Primary diagnosis/ Primarna dijagnoza	DDwR/ PDsR	49.3	47.3	38.1	13.4	32.2
	DDwoR/ PDbR	4.4	5.5	0	2.2	5.1
	Myalgia/ Mialgija	25.4	19.8	38.1	24.4	33.9
	Arthralgia/ Artralgija	16.4	22	19	26.7	27.1
	DJD/ DBZ	1.5	2.1	0	33.3	1.7
	Subluxation/ Subluksacija	3	3.3	4.8	0	0

n - number of participants in each cluster; DDwR - Disc displacement with reduction; DDwoR - Disc displacement without reduction/ n-broj ispitanika u pojedinom klasteru; PDsR - pomak diska s redukcijom; PDbR - pomak diska bez redukcije; DBZ - degenerativna bolest zgloba

Data presented in Table 1 revealed the natural groupings of participants. Cluster No. 1 is characterized by a high prevalence of children/adolescents, chronic TMD, mainly DDwR and a high prevalence of the onset of symptoms during/just after orthodontic treatment. Cluster No. 2 consisted mainly of chronic middle-aged patients with no parafunctional behavior, no orthodontic treatment in patient’s history and DDwR as the most common primary diagnosis. Cluster No. 3 mainly included middle-aged and older patients with the presence of parafunctional behavior, with almost equal representation of acute and chronic cases, as well as the equal representation of two diagnoses, DDwR and myalgia. Cluster No. 4 was mainly composed of older women with chronic TMD and the highest prevalence of DJD. Middle-aged patients with a high prevalence of acute TMD and myalgia mostly comprised cluster No. 5.

Discussion

Signs and symptoms of TMD are present in all age groups. However, the peak incidence is considered to be between the ages of 20 and 40, which is in line with the data obtained in this study (). Although it is traditionally believed that TMD in women most commonly occurs in their reproductive years (–), recent studies have shown that the incidence of TMD in women is more common between the ages of 45 and 65 which could explain our results with men being significantly younger than women (, ). Such data can be supported by the fact that more women reported TMD than men in the “older age” group ().

The significant difference in the incidence and progression of TMD with respect to gender probably stems from the interaction of various behavioral, hormonal, anatomical, and psychosocial factors (). The prevalence of TMD in our clinical setting of 4.6:1, in favor of women, is consistent with current epidemiological information on the presence of TMD recorded in clinical studies (). Such a disparity is often explained, not only as a physiological difference between the sexes but also as a consequence of women’s greater concern for their own health and their more frequent demand for health care (). There were significantly more women with chronic TMD than acute, compared to men where the ratio between acute and chronic forms was approximately 1:1, which is in line with a study by Carlsson et al. where the signs and symptoms of TMD were more intense and prolonged in women ().

The two most common diagnoses were disc displacement with reduction and myalgia, a result that is commonly obtained in other studies (, ). In patients with disc displacement with reduction, the presence of "clicking" during function can create discomfort and occasional worry. Such patients, in a large number of cases, have no other symptoms, and their condition is generally not an indication for therapy. Their concerns are most often relieved through conversation and education about the condition affecting the temporomandibular joint. Diagnoses, which follow in frequency, were mostly painful diagnoses. This result was not surprising since pain impedes the normal functioning of patients. A great number of patients consider pain the most limiting symptom and alarm for seeking professional help ().

The association between orthodontic therapy and the occurrence of signs and symptoms of TMD during or after therapy is still the subject of debate in dental community (). Nevertheless, the results of studies have confirmed for years that orthodontics is not the primary cause of TMD (). At our clinic, we noticed a frequent occurrence of TMD symptoms during orthodontic therapy, especially during the use of an intermaxillary rubber train or bimaxillary removable appliances. As occlusion and oral parafunctional habits are considered a risk factor in hypervigilant patients, it is possible that changing the position of the lower jaw over time may cause painful problems in sensitive (hypervigilant) patients. Nowadays, orthodontic therapy is equally present in children and adults, and consequently, the average age of patients with orthodontic therapy has changed. Middle age is a higher risk factor for TMD, which may consequently affect the frequent overlap of TMD symptoms and the implementation of active orthodontic therapy. This may lead the clinician to think that a cause-and-effect relationship between TMD and orthodontic therapy exists when in fact there is a chance that there is no connection between the two (, ).

Although the literature states that the prevalence of pain in the temporomandibular area with respect to age is highest around middle age, the results of this study have revealed that higher values of VAS were observed in the older group of patients (). Our results can be explained by the fact that older patients are likely to have more free time to think about pain compared to younger ones. On the other hand, the prevalence of orofacial pain peaks around age 65, which coincides with the age of the subjects in this study, and it is precisely this kind of pain that can be presented as a painful diagnosis of TMD ().

Despite the lack of consensus on the efficacy and, in general, the necessity of using an occlusal splint, the treatment of TMD often begins with the development of a stabilization splint (). However, experts in the field of diagnostics and treatment of TMD recommend physical therapy, i.e. a manual musculoskeletal approach as the first choice in treatment, which was the guiding thought of our experts (). Physical therapy has been shown to be successful in treating both muscular and joint disorders, primarily in increasing mouth opening (). In addition to simplicity and cost, its advantage is the improvement of signs and symptoms of TMD after only a short period of time, which allows a quick assessment of the need for further therapy (). Additional advantages of physical therapy are that it is not limited in time and, if performed correctly, there are no harmful effects. Therefore, the patient can start and stop physical therapy whenever he/she feels the need for it. Although there is no uniform evidence and accurate knowledge of the mechanisms of action, a large number of studies indicate the existence of a significant difference between the occlusal splint and other placebo forms, with occlusal splint performing significantly better in terms of reducing pain and limitations when compared to non-occluding devices and thin foils (). In clinical practice, as the newest literature suggests, splints should be used in combination with physical and behavioral therapy since its precise contribution to pain-relief has not been fully understood (). Our results showed that splints are prescribed more to patients with chronic forms of TMD.

The efficacy of pharmacotherapy in the treatment of chronic pain in TMD has not been supported by solid scientific evidence (). Given that drugs used in TMD pharmacotherapy such as non-steroid anti-inflammatory drugs (NSAIDs) and benzodiazepines have adverse side effects, the risk-benefit ratio in each individual situation should be assessed carefully (). Although NSAIDs and benzodiazepines are recommended for short-term pain control in patients with TMD, long-term pharmacotherapy should be considered in those patients who have a poorer response to therapy (). It is important to emphasize that we used additional diagnostic methods, such as magnetic resonance imaging, in a small number of cases that did not respond to therapy, in accordance with modern guidelines for the diagnosis and treatment of TMD (). Namely, it is important to make additional imaging if the findings might affect the current or future therapeutic direction.

By performing cluster analysis, we were able to show the natural grouping of patients and create a pattern in which it is possible to easily classify new patients and align different therapeutic options with the group profile. For example, in patients constituting cluster number 5 (mostly acute and pain patients), it would be best to assess, among other things, the level of stress, given that stress is often associated with exacerbation of painful conditions and begin taking a behavioral approach (). With such acute forms, it would be best to limit the function to a comfortable opening and avoid anything that exacerbates the discomfort. In patients with severe, limiting pain, we would also implement pharmacotherapy over a shorter period of time. When the pain begins to subside, the patient should slowly start doing exercises. In such patients, it is important to start therapy as soon as possible in order to prevent progression to a chronic condition, especially if those patients exhibit anxiety and/or depressive traits in addition to high self-perceived pain (, ).

This study has certain limitations. One of them is lack of certain data (for example, data on pain intensity according to VAS was recorded in a smaller number of patients), but such a lack is not significant if we consider the number of processed medical records and a generally large number of subjects and uniform approach to diagnosis and treatment of clinicians whose patients have been taken for analysis. In addition, there might be a bias in selecting variables for cluster analysis. However, we used a two-stage cluster analysis in which finishing optimizes homogeneity within the cluster and heterogeneity between clusters and is thus less susceptible to external factors (). Also, the patient profile is related only to the specified institution and it is advisable to interpret the data with caution.

Conclusions

Our results are largely in accordance with current epidemiological knowledge on TMD. Women predominated in all age groups and most of the patients experienced chronic pain. Classification of patients into homogeneous groups using the clustering method could provide better identification of subgroups of conditions that mainly occur together in these patients, thus providing a clue for a better prognosis of TMD patients.