Distinguishing Between Acute and Chronic Temporomandibular Disorder in Adolescent Patients

doi:10.21203/rs.3.rs-5223475/v1

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Distinguishing Between Acute and Chronic Temporomandibular Disorder in Adolescent Patients

https://doi.org/10.21203/rs.3.rs-5223475/v1

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This study compared the clinical and imaging characteristics of chronic temporomandibular disorder (TMD) to those of acute TMD in adolescent patients to identify factors contributing to symptom chronicity in adolescent patients with TMD. The 158 participants were divided into the acute (symptom duration < 6 months) and chronic (symptom duration ≥ 6 months) TMD groups. Clinical reports, panoramic radiographs, and magnetic resonance images (MRIs) of the temporomandibular joint were retrospectively reviewed and compared between groups. The results showed that the overall women-to-men ratio among adolescent patients with TMD was 1.87:1 and did not differ significantly between the groups. Moreover, compared with the acute group, the chronic group showed a significantly longer treatment duration; significantly smaller anterior and posterior joint spaces; significantly greater nasomaxillary (Na-Mx) midline discrepancy; significantly more prevalent anterior disc displacement (ADD); and higher rates of bruxism, poor posture, sleep problems, headache, and irregular diet. Treatment duration ≥ 1 year was most strongly associated with chronic TMD, followed by anterior joint space narrowing, ADD on MRI, Na-Mx discrepancy, and bruxism. Therefore, as symptom chronicity progresses, treatment duration tends to increase, and patients are more likely to experience structural changes. Clinicians should consider these findings in diagnosis and treatment of adolescents with TMD.

temporomandibular disorder

adolescent

chronic pain

joint space narrowing

panoramic radiography

magnetic resonance imaging

Temporomandibular disorder (TMD), a representative musculoskeletal disease of the orofacial area, is an umbrella term for pain and dysfunction of the temporomandibular joint (TMJ) complex and masticatory muscles ¹. TMD has a multifactorial etiology, including TMJ overload, microtrauma, microtrauma due to various parafunctional oral habits and bruxism, poor body posture, malocclusion, growth abnormalities, and psychological stress ^2,3. The typical symptoms of TMD are TMJ noise, such as clicking and crepitus, and TMD pain in the TMJ and masticatory muscles, which may be accompanied by restricted mandibular movement, ear pain, tinnitus, and headaches ³. TMD is more prevalent in women than in men, with a women-to-men ratio of approximately 1.5–2.24:1 ^4,5. Moreover, TMD affects approximately one-third of young adults ⁶. While the peak prevalence worldwide is typically observed in individuals in their 20s to 40s, in South Korea, it is most prevalent in individuals in their 20s, followed by mid-to-late teenagers ⁷. A meta-analysis by Minervini et al. reported a considerably higher prevalence of TMD in children and adolescents aged 8–19 years, ranging from 20–60% ⁸. Persisting TMD, especially when symptoms begin and continue during adolescence, can lead to permanent physical or skeletal damage such as malocclusion or facial asymmetry, which may be accompanied by discrepancies in the midline alignments of the nasal bone, maxilla, and mandible ^9–11. Despite the prevalence of TMD in adolescents and the critical importance of addressing the risk of permanent physical damage associated with persistent symptoms, research on TMD in this age group remains significantly underdeveloped compared with that on TMD in adult patients.

Adolescent and adult TMD should be examined concurrently and separately. Chronic pain during adolescence may be associated with decreased academic performance, reduced concentration, psychological distress, and adverse social outcomes ¹². In addition, chronic pain originating in adolescence warrants attention, as it can lead to physical, psychological, and social impacts that persist into adulthood ¹³. Lee et al. observed TMJ noise and TMD pain in < 80% of adolescent patients with TMD; moreover, both pain intensity and degree of mandibular dysfunction increased with age within the adolescent period ¹⁴. Juvenile temporomandibular joint osteoarthritis (TMJ-OA) in children and adolescents may lead to pain, restricted jaw function, facial growth disturbances, and/or decreased quality of life. With advances in imaging technologies, TMJ-OA is no longer obscured and has become clearer with the use of panoramic radiography (PR) or magnetic resonance imaging (MRI) ^15,16. Imaging technologies have also shown that radiographic joint space narrowing occurs more frequently in patients with chronic TMD than in those with acute TMD ¹⁷. Such narrowing may be associated with OA progression and has also been associated with disc tearing, anatomical joint structure damage, and degeneration ¹⁸. However, this parameter has not been investigated with respect to prolonged symptom duration in adolescent patients with TMD.

Preventing musculoskeletal disease is fundamentally more effective than treatment. However, if treatment is necessary, early intervention with an accurate diagnosis is preferable for managing the condition in the chronic stage ¹⁹. TMD is not a singular disorder but rather an umbrella term encompassing a wide range of joint and muscular pathologies affecting the TMJ and its surrounding structures. The manifestation of TMD symptoms varies highly among individuals; is influenced by the complex interplay of biopsychosocial, environmental, and genetic factors; and can exhibit temporal complexity within the same individual ^20,21. This variability presents significant challenges for precise diagnosis and effective management of TMD. Similar to other musculoskeletal disorders, chronic TMD pain may involve neuropathic components and peripheral and central sensitization, resulting in more complex conditions that pose challenges to both patients and clinicians ²². Consequently, acute TMD has a high propensity for progression to a chronic state. However, in many cases of musculoskeletal disorders, adjusting daily parafunctional habits or body posture and appropriately managing the affected areas at an early stage can prevent symptoms from becoming chronic ²³. The clinical and radiographic characteristics distinguishing acute from chronic TMD in adolescents are yet to be clearly identified. Thus, clarification of these aspects in adolescents may facilitate the early control of these key factors or help prevent the chronicity of TMD symptoms.

Therefore, this study investigated the clinical and radiographic features of adolescent patients aged 12–18 years with acute or chronic TMD. The radiographic features examined on PR included joint space narrowing, presence of TMJ-OA, and discrepancy between the nasal-maxilla-mandible axes indicating facial midline deviation. Both TMJ-OA and disc displacement were evaluated by MRI. Focusing on chronic TMD, this study aimed to identify, through various statistical analyses, the factors most significantly contributing to symptom chronicity in adolescent patients with TMD, as well as other clinical and radiographic parameters that show significant influence. This study also investigated the prognosis of adolescent patients with TMD, including treatment duration until completion and pain intensity at the time of treatment conclusion. This study aimed to determine whether these prognostic factors were related to the duration of symptoms from initial recognition to hospital visit and to explore changes in pain intensity in patients with chronic TMD. The hypothesis was that repetitive microtrauma, such as bruxism, or persistent poor posture contributes to the chronicity of TMD symptoms in adolescents, and that longer symptom duration may lead to an extended treatment period. This is the first comprehensive study to elucidate the factors contributing to TMD symptom chronicity in adolescents, underscoring its significance for further research and reporting.

Demographics and pain intensity

This study included a total of 158 adolescent patients with TMD (103 women and 55 men, mean age: 15.08 ± 2.23 years). The overall women-to-men ratio among adolescents with TMD was 1.87:1. According to the duration of symptoms, TMD was categorized as acute (symptom duration < 6 months) or chronic (symptom duration ≥ 6 months). The women-to-men ratio and mean age (p > 0.05) did not differ significantly between the acute (47 women, mean age: 14.92 ± 2.27 years) and chronic (56 women, mean age: 15.23 ± 2.19 years) TMD groups. The mean treatment duration differed significantly between the acute and chronic TMD groups (8.02 ± 6.22 vs. 13.95 ± 6.79 months, p < 0.001). Furthermore, the proportion of patients with a treatment duration > 1 year was significantly higher in the chronic TMD group than in the acute TMD group (68.7% vs. 22.7%, p < 0.001). The visual analog scale scores (VAS) recorded at the initial visit (VAS-I) and at the final visit when the treatment was completed (VAS-F) did not differ significantly between the groups (3.35 ± 2.12 vs. 2.89 ± 2.19, p = 0.188 and 0.43 ± 0.70 vs. 0.41 ± 0.83, p = 0.189) (Table 1).

Table 1

Demographics and clinical characteristics of adolescent patients with TMD
	Acute TMD (n = 75)	Chronic TMD (n = 83)	p-value
	mean ± SD or n (%)	mean ± SD or n (%)	p-value
Age (years)	14.92 ± 2.27	15.23 ± 2.19	0.386
Sex
Male	28 (37.3%)	27 (32.5%)	0.616
Female	47 (62.7%)	56 (67.5%)	0.616
Treatment duration (months)	8.02 ± 6.22	13.95 ± 6.79	< 0.001***
Treatment duration ≥ 1 year (months)	17 (22.7%)	57 (68.7%)	< 0.001***
VAS-I	3.35 ± 2.122	2.89 ± 2.19	0.188
VAS-F	0.43 ± 0.70	0.41 ± 0.83	0.189
A t-test was used to compare the mean values between the acute and chronic TMD groups, and the chi-square test with Bonferroni correction was used to compare the distribution of n (%). Statistical significance was set at p < 0.05. ***p < 0.001
Acute TMD: cases in which TMD symptoms persisted for < 6 months; Chronic TMD: cases where TMD symptoms persisted for ≥ 6 months
TMD, temporomandibular disorder; SD, standard deviation; VAS, visual analog scale; VAS-I, VAS score recorded at the initial visit; VAS-F, VAS score recorded at the final visit

Chief complaints and factors contributing to TMD

The chief complaints included TMJ noise, pain, muscle stiffness, locking, bruxism, and uncomfortable occlusion. TMJ noise was the most common chief complaint and was significantly more prevalent in the chronic TMD group than in the acute TMD group (61.3% vs. 79.5%, p = 0.014). Pain was the most common chief complaint in the acute TMD group; however, the prevalence did not differ significantly between groups (80.0% vs. 73.5%, p = 0.354). Bruxism differed significantly between the acute and chronic TMD groups (20% vs. 39.8%, p = 0.026). Uncomfortable occlusion was significantly more common in the chronic TMD group than in the acute TMD group (20.0% vs. 38.6%, p = 0.014). Muscle stiffness (49.3% vs. 42.2%) and locking (60.0% vs. 62.7%) did not differ significantly between the acute and chronic TMD groups (p > 0.05).

Factors contributing to TMD include tinnitus, psychological stress, sleep problems, headache, orthodontic treatment, bad posture, and irregular diet. Among these factors, bad posture was most commonly observed in both groups, with a significantly higher prevalence in the chronic TMD group than in the acute TMD group (34.7% vs. 54.2%, p = 0.016). More than half of the patients with chronic TMD reported having bad posture. Sleep problems (10.7% vs. 26.5%, p = 0.014), headache (12.0% vs. 25.3%, p = 0.042), and irregular diet (12.0% vs. 30.1%, p = 0.007) were also significantly more prevalent in patients with chronic TMD than in those with acute TMD (all p < 0.05). The prevalence of tinnitus (17.3% vs. 22.9%) and psychological stress (30.7% vs. 33.7%) were higher in the chronic TMD group than in the acute TMD group, whereas orthodontic treatment (32.0% vs. 21.7%) was less prevalent in the chronic TMD group; however, none of these differences were statistically significant (all p > 0.05) (Table 2).

Table 2

**Clinical characteristics of acute and chronic TMD**
	Acute TMD (n = 75)	Chronic TMD (n = 83)	p-value
	mean ± SD or n (%)	mean ± SD or n (%)	p-value
Chief complaints
TMJ noise	46 (61.3%)	66 (79.5%)	0.014*
TMD pain	60 (80.0%)	61 (73.5%)	0.354
Muscle stiffness	37 (49.3%)	35 (42.2%)	0.425
Locking	45 (60.0%)	52 (62.7%)	0.746
Bruxism	17 (22.7%)	33 (39.8%)	0.026*
Uncomfortable occlusion	15 (20.0%)	32 (38.6%)	0.014*
Contributing factors
Tinnitus	13 (17.3%)	19 (22.9%)	0.432
Psychological stress	23 (30.7%)	28 (33.7%)	0.735
Sleep problem	8 (10.7%)	22 (26.5%)	0.014*
Headache	9 (12.0%)	21 (25.3%)	0.042*
Orthodontic treatment	24 (32.0%)	18 (21.7%)	0.154
Bad posture	26 (34.7%)	45 (54.2%)	0.016*
Irregular diet	9 (12.0%)	25 (30.1%)	0.007**
The t-test was used to compare mean values between the adolescent TMD groups, while the chi-square test with Bonferroni correction was used to compare the distribution of n (%). Statistical significance was set at p < 0.05. p < 0.05, *p < 0.01
Acute TMD: cases in which TMD symptoms persisted for < 6 months; Chronic TMD: cases in which TMD symptoms persisted for ≥ 6 months
TMD, temporomandibular disorder; SD, standard deviation; TMJ, temporomandibular joint
Statistical significance was set at p < 0.05. p < 0.05, p < 0.01, **p < 0.001

PR findings

On PR, the anterior joint space was significantly smaller in patients with chronic TMD compared with that of those with acute TMD (2.41 ± 0.67 vs. 1.83 ± 0.64 mm, p < 0.001). Similarly, the posterior joint space was also significantly smaller in patients with chronic TMD compared with that of patients with acute TMD (2.48 ± 0.73 vs. 2.19 ± 0.69 mm, p = 0.012). Thus, both the anterior and posterior joint spaces were significantly reduced when TMD symptoms persisted for > 6 months. Anterior joint space narrowing was significantly more frequent in patients with chronic TMD than in those with acute TMD (30.7% vs. 58.6%, p = 0.001). Posterior joint space narrowing was observed in > 70% of both the acute (77.3%) and chronic (72.3%) TMD groups, with no significant difference between the groups (p = 0.583).

The amount of nasomaxillary (Na-Mx) discrepancy was significantly greater in the chronic TMD group than in the acute TMD group (1.06 ± 1.11 vs. 1.41 ± 1.06 mm, p = 0.045). Similarly, the amount of maxillomandibular (Mx-Mn) discrepancy was significantly greater in the chronic TMD group than in the acute TMD group (0.63 ± 1.04 vs. 0.98 ± 1.10 mm, p = 0.042). Na-Mx discrepancy was more frequently observed in the chronic TMD group than in the acute TMD group (53.3% vs. 71.1%, p = 0.032). Likewise, Mx-Mn discrepancy was more commonly observed in chronic TMD than in acute TMD groups (26.7% vs. 50.6%, p = 0.003). Therefore, when the TMD symptom duration is > 6 months, the likelihood of facial asymmetry, specifically midline discrepancies involving the nasal bone, maxilla, and mandible, increases compared with that when the TMD symptom duration is < 6 months. However, the prevalence of TMJ-OA on PR did not differ significantly between the acute and chronic TMD groups (29.3% vs. 24.1%, p = 0.476) (Table 3).

Table 3

Comparison of PR and MRI findings between groups
	Acute TMD (n = 75)	Chronic TMD (n = 83)	p-value
	mean ± SD or n (%)	mean ± SD or n (%)	p-value
PR
Anterior joint space	2.41 ± 0.67	1.83 ± 0.64	< 0.001***
Posterior joint space	2.48 ± 0.73	2.19 ± 0.69	0.012*
Anterior joint space narrowing	23 (30.7%)	47 (58.6%)	0.001**
Posterior joint space narrowing	58 (77.3%)	60 (72.3%)	0.583
Na-Mx discrepancy amount	1.06 ± 1.11	1.41 ± 1.06	0.045*
Mx-Mn discrepancy amount	0.63 ± 1.04	0.98 ± 1.10	0.042*
Na-Mx discrepancy	40 (53.3%)	59 (71.1%)	0.032*
Mx-Mn discrepancy	20 (26.7%)	42 (50.6%)	0.003**
TMJ OA_PR	22 (29.3%)	20 (24.1%)	0.476
MRI
TMJ-OA_MRI	40 (53.3%)	47 (56.6%)	0.749
ADD_MRI	51 (68.0%)	72 (86.7%)	0.007**
The t-test was used to compare mean values between the adolescent TMD groups, while the chi-square test with Bonferroni correction was used to compare the distribution of n (%). Statistical significance was set at p < 0.05. p < 0.05, p < 0.01, **p < 0.001
Acute TMD: cases in which TMD symptoms persisted for < 6 months; Chronic TMD: cases in which TMD symptoms persisted for ≥ 6 months
TMD, temporomandibular disorder; SD, standard deviation; Na-Mx discrepancy, nasomaxillary midline discrepancy; Mx-Mn discrepancy, maxillomandibular midline discrepancy; TMJ, temporomandibular joint; OA, osteoarthritis; PR, panoramic radiography; MRI, magnetic resonance imaging; ADD, anterior disc displacement

MRI findings of acute and chronic TMD

Evaluation of the most common factors observed on MRI, TMJ-OA, and anterior disc displacement (ADD) revealed that TMJ-OA occurred more frequently on MRI than on PR, with > 50% of patients in both groups having this condition. The prevalence of TMJ-OA on MRI did not significantly between patients with acute and chronic TMD (53.3% vs. 56.6%, p = 0.749). In contrast, ADD on MRI was significantly more prevalent in patients with chronic TMD than in those with acute TMD (68.0% vs. 86.7%; p = 0.007). Cramer's V analysis showed that the presence of TMJ-OA on MRI was significantly associated with the presence of ADD on MRI (r = 0.233, p = 0.005) and decreased anterior joint space narrowing on PR (r = 0.117, p = 0.026). In contrast, TMJ-OA on PR was not significantly associated with anterior joint space narrowing (Table 3).

Correlations with TMD symptom duration

The results of Spearman's correlation analysis revealed the strong positive association between symptom and treatment durations (r = 0.42, p < 0.001), indicating that increased symptom duration was significantly associated with increased treatment duration. Symptom duration was also negatively correlated with anterior joint space (r=-0.30, p < 0.001), suggesting that a longer symptom duration was associated with decreased anterior joint space. Additionally, symptom duration was positively correlated with Na-Mx discrepancy (r = 0.23, p = 0.003) (Fig. 2). VAS-I and VAS-F were positively correlated, in which a higher VAS-I score was associated with a higher VAS-F score (r = 0.31, p < 0.001). However, VAS-I and VAS-F were not significantly correlated with Na-Mx or Mx-Mn discrepancies.

Considering the multiple relationships among symptom duration, treatment duration, anterior joint space, and skeletal discrepancy, increased Na-Mx discrepancy was significantly associated with both increased symptom duration and decreased anterior joint space (all p < 0.05) (Fig. 3A). The pattern of associations for Mx-Mn discrepancy with the other variables was similar to that observed for Na-Mx discrepancy; however, these relationships were not statistically significant (all p > 0.05) (Fig. 3B).

2D and 3D visualization of the relationships between chronic TMD and other factors

The factors significantly associated with the occurrence of chronic TMD (Euclidean distance ≤ 0.2), ranked in the order of proximity and strength of association with chronic TMD, were treatment duration, anterior and posterior joint spaces, ADD on MRI, poor body posture, TMJ noise, and sleep problems (Fig. 4A). This relationship diagram only represents the degree of association with chronic TMD and does not indicate positive or negative correlations. The factors more strongly associated with the development of chronic TMD than with development of acute TMD were longer or prolonged treatment duration, reduced anterior and posterior joint spaces, ADD on MRI, poor body posture, TMJ noise, and sleep problems. These factors showed complex interrelationships (Fig. 4B). Additionally, although previous studies have suggested that women are more susceptible to chronic pain than men ^31,32, the present study observed no significant correlation between sex and chronic TMD in adolescent patients with TMD. While no consistent consensus has been reached regarding the relationship between orthodontic treatment during adolescence and TMD development ^33,34, the present study observed no significant association between orthodontic treatment and TMD chronicity.

Logistic regression analysis of chronic TMD

Logistic regression analysis using both crude and adjusted models controlling for age and sex to identify the predictors of chronic TMD compared with those of acute TMD revealed that the factors associated with chronic TMD included treatment duration ≥ 1 year, anterior joint space narrowing, ADD on MRI, Na-Mx discrepancy, and bruxism. In the crude model, treatment duration > 1 year showed the strongest association with chronic TMD (odds ratio [OR]: 8.145, 95% confidence interval [CI]: 3.201–20.727, p < 0.001). The next strongest predictor was anterior joint space narrowing (OR: 6.060, 95%CI: 2.223–16.524, p < 0.001), followed by ADD on MRI (OR: 5.115, 95%CI: 1.632–16.037, p = 0.005), Na-Mx discrepancy (OR: 4.708, 95%CI: 1.630–13.595, p = 0.004), and bruxism (OR: 4.625, 95%CI: 1.579–13.548, p = 0.005). In the adjusted model, treatment duration > 1 year also showed the strongest association with chronic TMD (OR: 8.643, 95%CI: 3.285–22.738, p < 0.001). The next strongest predictor was anterior joint space narrowing (OR: 7.225, 95%CI: 2.550–20.470, p < 0.001), followed by ADD on MRI (OR: 5.448, 95%CI: 1.681–17.651, p = 0.005), Na-Mx discrepancy (OR: 5.119, 95%CI: 1.720–15.233, p = 0.003), and bruxism (OR: 4.702, 95%CI: 1.595–13.865, p = 0.005) (Table 4).

Table 4

Results of the logistic regression analysis to predict chronic TMD
	Crude model				Adjusted model
Parameter	OR	Wald 95% CI_Lower	Wald 95% CI_Upper	p-value	OR	Wald 95% CI_Lower	Wald 95% CI_Upper	p-value
TMJ noise	1.637	0.595	4.499	0.340	1.635	0.574	4.657	0.358
Bruxism	4.625	1.579	13.548	0.005*	4.702	1.595	13.865	.005**
Uncomfortable occlusion	1.167	0.413	3.300	0.771	1.301	0.453	3.739	0.625
Sleep problem	1.480	0.438	5.005	0.528	1.361	0.392	4.721	0.627
Headache	1.888	0.534	6.680	0.324	1.870	0.522	6.703	0.337
Bad posture	2.333	0.883	6.162	0.087	2.236	0.827	6.047	0.113
Irregular diet	2.531	0.731	8.764	0.143	2.711	0.789	9.313	0.113
Anterior joint space narrowing	6.060	2.223	16.524	< 0.001***	7.225	2.550	20.470	< 0.001***
Posterior joint space narrowing	0.396	0.137	1.146	0.088	0.433	0.144	1.307	0.138
Na-Mx discrepancy	4.708	1.630	13.595	0.004**	5.119	1.720	15.233	0.003**
Mx-Mn discrepancy	1.742	0.658	4.615	0.264	1.840	0.673	5.031	0.235
ADD on MRI	5.115	1.632	16.037	0.005**	5.448	1.681	17.651	0.005**
Treatment duration ≥ 1 year	8.145	3.201	20.727	< 0.001***	8.643	3.285	22.738	< 0.001***
Constant	0.009			0.000	0.000			0.000
The results were obtained using multiple logistic regression analysis. TMD, temporomandibular disorder; TMJ, temporomandibular joint; OR, odds ratio; CI, confidence interval; Na-Mx, nasomaxillary midline discrepancy; Mx-Mn, maxillomandibular midline discrepancy; ADD, anterior disc displacement; MRI, magnetic resonance imaging
Statistical significance was set at p < 0.05. p < 0.05, p < 0.01, **p < 0.001

This study investigated the factors influencing TMD symptom chronicity in adolescents by comparing the clinical and radiographic characteristics of patients with chronic TMD with those with acute TMD. The results of the logistic regression analysis revealed that treatment duration ≥ 1 year showed the strongest association with chronic TMD (OR: 8.643). The next strongest predictor was anterior joint space narrowing (OR: 7.225), followed by ADD on MRI (OR: 5.448), Na-Mx discrepancy (OR: 5.119), and bruxism (OR: 4.702). Owing to the potential risk of TMD in adolescents, with a negative long-term impact on their physical, psychological, and social well-being, researchers and clinicians should focus more on TMD in adolescents and actively work to prevent its progression to a chronic state.

Musculoskeletal pain can be effectively treated during the acute phase of TMD through localized inflammation and regional pain control ³⁵. However, once symptoms persist for > 6 months and enter the chronic phase, pain management becomes more complex, and treatment becomes more challenging ¹⁹. One key finding in the chronic TMD group in the present study was that the treatment duration was significantly longer (13.95 ± 6.79 months) than that in the acute TMD group (8.02 ± 6.22 months). Moreover, the proportion of patients with a treatment duration of ≥ 1 year was significantly higher in the chronic TMD group than in the acute TMD group, and a treatment duration of ≥ 1 year was a strong factor associated with an 8.643-fold increased likelihood of chronic TMD. In other words, as the symptom duration increases in adolescent patients with TMD, particularly beyond 6 months into the chronic phase, the treatment duration is likely to extend beyond 1 year. This supports our initial hypothesis of the association between a longer symptom duration and a prolonged time to achieve full recovery.

Another important finding was the significantly smaller anterior joint space on PR in patients with chronic TMD than in patients with acute TMD. Moreover, anterior joint space narrowing was also a key predictor of progression to chronic TMD. This narrowing generally owing to degeneration of the articular cartilage, leading to reduced space between adjacent bones that can impede normal joint movement, resulting in pain, stiffness, and restricted range of motion ³⁶. In chronic mechanical low back pain, narrowing of the lumbar space is associated with the presence of anterior osteophytes and increased disability ³⁷. In the present study, anterior joint space narrowing of the TMJ observed on PR was associated with disc displacement on MRI. These anatomical changes may lead to prolonged and recurrent TMD. In the knee or hip joints, joint space narrowing typically increases with age in the context of degenerative joint disease ^38,39. However, the prevalence of TMD does not increase with age in the same way as other joint diseases ⁶. TMD prevalence peaks in young adults aged 20–40 years ⁴⁰. The nature of TMD may vary across age groups ^7,41. In other words, TMD in adolescents, young adults aged 20–40 years, and older adults aged ≥ 60 years may each exhibit distinct characteristics. In the present study, increased age among adolescents did not correspond to a further reduction in TMJ joint space. The anterior joint space is significantly smaller in patients with chronic TMD than in those with acute TMD, even in adults ¹⁷. Although age may also be an important factor in the joint space and anatomical joint structural deterioration, it is likely to be more closely related to symptom chronicity in patients with TMD.

Deviations in the central axis of the anterior facial region (facial asymmetry) have been observed in patients with chronic TMD. The progression of unilateral or bilateral ADD and/or TMJ-OA along with changes in occlusion can accelerate facial asymmetry ^42,43. The mandibular condyle growth center is located in the condylar surface layer ⁴⁴, and friction between the condyle and the temporal bone occurs in cases of ADD and/or TMJ-OA. This friction leads to restricted condylar growth, condylar cartilage degeneration, and imbalanced bilateral muscle use, resulting in differences in the size and shape of the right and left condyles, discrepancies in the lengths of the mandibular ramus and body, and the occurrence of malocclusion ⁴⁵. The results of the present study demonstrated that the chronicity of TMD symptoms was associated with a midline discrepancy between the nasal, maxillary, and mandibular bones. The Na-Mx discrepancy was significantly greater in adolescents with chronic TMD than in those with acute TMD. Growth and the associated hormonal changes in adolescence can further complicate and serially influence the development of midline discrepancies in the facial bones ⁴⁶. In adolescent patients with TMD, these anatomical changes can persist into adulthood and have permanent or semi-permanent effects on the facial region; thus, these changes require careful attention.

Among the clinical characteristics, bruxism was a significant predictor of chronic TMD. Bruxism was observed in approximately 40% of patients with chronic TMD and was more prevalent than in the acute TMD group, where it was observed in 22.7% of patients. Bruxism is a major contributing factor to TMD persistence and exacerbation ⁴⁷. Bruxism is characterized by the repetitive clenching or grinding of teeth and/or bracing or thrusting of the mandible during wakefulness and/or sleep ⁴⁸. This condition is sometimes considered a form of rhythmic masticatory muscle activity that may help reduce psychological stress, alleviate emotional tension, and not necessarily cause pain in the TMJ or adjacent structures ⁴⁹. Furthermore, while bruxism has been associated with the occurrence of headaches, insufficient scientific evidence exists to support its clear association with orofacial or TMD pain ⁵⁰. However, sleep studies using polysomnography identified bruxism as a significant risk factor for TMD pain ^51,52. The present study investigated bruxism as a general term, without distinguishing between its occurrence during sleep or when awake. From a pathophysiological perspective, during bruxism, the maxillary and mandibular teeth come into contact, and the entire mandible moves, resulting in mechanical friction between the condylar head and temporal bone ⁵³. The reported prevalence of sleep bruxism in children and adolescents is as high as 49%, and sleep bruxism is a risk factor for TMD in this age group ⁵⁴. Therefore, a specific relationship between persistent and repetitive bruxism and symptom chronicity is highly likely. In addition, poor posture, sleep problems, headache, and irregular diet were significantly more prevalent in patients with chronic TMD than in those with acute TMD in the present study. The Orofacial Pain: Prospective Evaluation and Risk Assessment Project for Adult TMD identified greater parafunction, restricted jaw function, more frequent headaches, and a higher prevalence of neural or sensory medical conditions as risk factors for chronic TMD ²⁰. The present study aimed to predict chronic TMD in adolescents, with findings both consistent with and contrary to those reported by previous studies.

This study has several limitations. First, because it was conducted at a single institution, selection bias was possible. Therefore, a multicenter study involving more participants is needed to validate the results and findings of this study. Additionally, this study was retrospectively designed using a cross-sectional approach. Although the clinical and radiographic characteristics that distinguish chronic TMD from acute TMD as well as significant predictors of chronic TMD were identified using various statistical analyses, further prospective studies are warranted to explore the causal relationships among these parameters. Moreover, while addressing chronic TMD, due to the practical limitations of clinical trials, we could not address peripheral sensitization, central sensitization, and neuropathic or neuronal symptoms, nor did we consider the psychosocial factors of patients. Comprehensively integrating these aspects in clinical trials, animal studies, or cellular experiments is challenging. Although adolescent patients with TMD were diagnosed according to the DC/TMD criteria by TMD specialists, no analyses based on specific TMD subgroups were performed. The findings may vary depending on the classification of TMD as arthrogenous, myogenous, or mixed. However, continued research efforts focusing on the prevention of TMD and the chronicity of TMD symptoms are planned to ensure that acute TMD does not progress to chronic TMD in adolescent patients, ultimately improving their pain management and quality of life.

In conclusion, this study identified significant clinical and radiographic predictors of chronic TMD symptoms in adolescents, including prolonged treatment duration, anterior joint space narrowing, ADD, Na-Mx discrepancy, and bruxism, highlighting the importance of early intervention to prevent progression from acute to chronic TMD. Despite several limitations, such as its single-institution and retrospective design, the results of this study provide valuable insights into the distinct characteristics of chronic TMD in adolescents and emphasize the need for continued research to better understand and manage TMD and, ultimately, to improve the quality of life of adolescents by preventing symptom chronicity. This study represents the first comprehensive approach to elucidate the factors contributing to TMD symptom chronicity in adolescents, making a valuable contribution to the field.

The research protocol complied with the principles of the Declaration of Helsinki and was approved by the Institutional Review Board of Kyung Hee University Dental Hospital in Seoul, South Korea (IRB No-KH-DT23016). For participants < 18 years of age, informed consent for study participation was obtained from their parents or legal guardians.

Study population

The study population comprised 158 consecutive adolescent patients with TMD (103 women and 55 men; mean age 15.08 ± 2.23 years) who visited Kyung Hee University Dental Hospital between January 2018 and August 2024. A specialist with > 10 years of experience diagnosed TMD based on the criteria for TMD Axis I ²⁴. Adolescent patients with TMD were identified, and all clinical reports and PR and MRI images of their TMJs were retrospectively reviewed. The TMD symptom duration reported by patients was recorded in months, with 6 months used as the threshold to classify the patients into two groups: acute TMD (symptom duration < 6 months) and chronic TMD (symptom duration ≥ 6 months) ²⁵. This study investigated the clinical characteristics associated with chronic TMD in comparison with acute TMD as well as the factors related to increased symptom duration.

The exclusion criteria were serious previous injuries such as unstable multiple traumas to the orofacial area and maxillary and mandibular fractures; patients with systemic diseases potentially affecting the TMJ such as rheumatic diseases, systemic osteoarthritis, pregnancy, psychological problems, or psychiatric or neurological disorders; and cases in which the structure of the TMJ complex was not clearly distinguishable on PR and/or MRI ²⁶.

Sample size

The sample size was calculated using G*Power version 3.1.9.7 (Heinrich-Heine-Universität Düsseldorf, Düsseldorf, Germany). A total of 134 participants (alpha error, 0.05; actual power, 0.95) was calculated as the target sample size, and 158 adolescent patients with TMD were recruited.

Pain intensity and treatment duration

Pain intensity was assessed using the VAS. Specifically, the VAS-I and VAS-F were evaluated. The VAS score ranges from 0 to 10, with 0 indicating no pain and 10 indicating the worst imaginable pain. Treatment duration was defined as the period from the first visit to the final day of treatment and was recorded in months. The proportion of adolescent patients with TMD with a treatment duration of > 1 year was investigated according to the group.

Chief complaints and contributing factors for TMD

Six chief complaints were investigated in adolescent patients with TMD: TMJ noise, pain, muscle stiffness, locking, bruxism, and uncomfortable occlusion. The presence of each parameter was recorded based on patient reports and assessed dichotomously as either “yes” or “no.” The criteria for each chief complaint were as follows: (1) TMJ noise: sounds such as clicking and crepitus originating from the TMJ during both functional and nonfunctional movement of the mandible, (2) TMD pain: pain associated with TMD involving the TMJ structures, (3) Muscle stiffness: stiffness, heaviness, or discomfort in muscles during function or at rest, (4) Bruxism: clenching or grinding of teeth while awake or sleeping, (5) Locking: jaw locking with a mouth opening of < 35 mm, indicating limited mouth opening, as reported by the patient, and (6) Uncomfortable occlusion: abnormal or awkward sensation related to occlusion, regardless of whether an actual malocclusion is present. The contributing factors included the presence of tinnitus, psychological stress, sleep problems, headache within the last month, history of orthodontic treatment, poor habitual posture, and an irregular diet. Each contributing factor was also assessed dichotomously.

PR parameters

PRs were obtained for all participants using the same panoramic dental imaging unit (Planmeca Promax; Planmeca OY, Helsinki, Finland) according to the manufacturer’s instructions. The head was held in position using a chin rest and bite guide. The optimal image density and contrast were achieved using the following exposure settings: 84 kVp, 16 mA, and 16 s. The magnification factor was 1.20. The PR data were saved as Digital Imaging and Communications in Medicine (DICOM) files, and a Picture Archiving Communication System (PACS; Infinitt Healthcare, Seoul, Korea) was used to analyze the DICOM data to establish reference lines and generate quantitative measurements. PR (ProMax; Planmeca, Helsinki, Finland) was performed in all patients. The PR images were independently and subjectively evaluated by two experts blinded to patients’ clinical information that could bias their interpretation of alterations in the TMJ.

The TMJ spaces were measured in the anterior and posterior regions. The anterior and posterior joint spaces were measured quantitatively using PR, and the presence of joint space narrowing was assessed. The anterior joint space was assessed by drawing a perpendicular line from the center of the condyle to the Frankfort horizontal line, followed by measuring the anterior and posterior joint spaces 60° from the horizontal axis in both the anterior and posterior directions. The distance between the outermost points of the cortical lines of the condyle and temporal bone was measured in millimeters. Joint space narrowing was defined as anterior or posterior joint space of < 2 mm or < 3 mm, respectively. The values from both the right and left sides were averaged to obtain a single parameter value per individual, which was then used in the statistical analyses.

The PR images were analyzed dichotomously by the experts and defined as either “no evidence of OA” (non-OA, normal) or “TMJ–OA.” A normal condyle was defined as round or oval in shape in the axial plane and convex, round, or flat in the coronal plane.

Midline discrepancies

To evaluate the midline deviation, the alignments of the midlines of the nasal and maxillary bones were assessed on the PRs (i.e., the presence of a Na-Mx discrepancy). If they did not align, the degree of Na-Mx midline discrepancy was measured. Additionally, the alignment of the maxilla and mandible (i.e., the presence of an Mx-Mn discrepancy) was also assessed, and the extent of any discrepancy was quantified. All parameters were measured in millimeters using the PACS on PR (Fig. 1).

MR image acquisition

High-resolution MRIs were obtained using a 3T MRI system (Signa™ Genesis, GE Healthcare, Chicago, IL, USA) with a 6-cm × 8-cm diameter surface coil. The MRI examinations were performed using the MR sequences and protocols of Kyung Hee University Medical Center. All scans involved sagittal oblique sections (section thickness, ≤ 3 mm; field of view, 15 cm; matrix dimensions, 256 × 224), and spin-echo sagittal MRIs were obtained on axial localizer images. T2-weighted images (T2WIs) were obtained using a 650/14 repetition time (TR)/echo time (TE) and 2650/82 TR/TE sequences. Proton density (PD) images were obtained using a 2650/82 TR/TE sequence. The MRI protocols for the TMJ evaluation were as described previously ^3,27.

ADD and TMJ-OA on MRI

The left and right sides of patients with bilateral TMJ and ADD were evaluated separately using T2WI and PD images. The MRI indicators for assessing ADD in patients with TMD were as follows ²⁸: ADD of the TMJ was defined as the posterior band of the articular disc displaced anteriorly beyond the normal range in the closed-mouth position. Non-ADD was defined as the posterior band of the articular disc located at the 12 o’clock position relative to the condylar apex in the closed-mouth position. TMJ-OA on MRI was diagnosed based on the presence of one or more of the following ²⁹: condylar flattening, subchondral sclerosis, surface irregularities, erosion, or condylar deformities associated with these features, including the presence of osteophytes. Two experts with > 10 years of experience analyzed the MRI findings with the naked eye while blinded to the patients’ clinical information. The patients were diagnosed with TMJ-OA or ADD if either (right or left) or both sides of the TMJ exhibited these conditions. Intra-class correlation coefficients (ICCs) of 0.78 and 0.84 were estimated in intra-examiner reproducibility measurements. The inter-examiner ICCs for TMJ effusion diagnosis were 0.80 and 0.83, respectively, for each measurement. Disagreements were resolved through discussion until a consensus was reached.

Statistical methods

The data were analyzed using IBM SPSS Statistics for Windows, version 26.0 (IBM Corp., Armonk, NY, USA). Descriptive statistics are presented as mean ± standard deviation or as frequencies with percentages, as appropriate. The distributions of categorical data were analyzed using the χ² test and Bonferroni correction for equality of proportions. The t-test was used to compare mean values between the two adolescent TMD groups. Spearman's correlation analysis was conducted to evaluate the strengths of the associations between variables. Cramer's V analysis was also used to assess the strength of the associations between two variables; the statistic values range from 0 to 1, with values closer to 1 indicating a stronger correlation ³⁰. Multivariate stepwise logistic regression analysis was performed to evaluate the risk factors for chronic TMD compared with those for acute TMD. Parameters that were correlated with chronic TMD were simultaneously considered to calculate the ORs for a high likelihood of SB (the dependent variable). To move beyond understanding the isolated relationships between variables, we aimed to provide a comprehensive and intuitive understanding through two- and three-dimensional visualizations of the relationships between chronic TMD and related variables. Visualization was performed using Python version 3.9.7 (Python Software Foundation, DE, USA) and R version 4.0.2 (R Foundation for Statistical Computing, Vienna, Austria). A two-tailed p < 0.05 was considered statistically significant in all analyses.

Additional Information

Conflict of interest

The authors declare that this study was conducted in the absence of any commercial or financial relationships that could be construed as conflicts of interest.

Acknowledgments

The authors extend their special thanks to Sung-Woo Lee of the Department of Oral Medicine and Oral Diagnosis at Seoul National University and to Jung-Pyo Hong of the Department of Orofacial Pain and Oral Medicine at Kyung Hee University Dental Hospital.

Informed consent

Informed consent was obtained from all patients involved in the study.

Data availability

The datasets used and/or analyzed in the current study are available from the corresponding author upon reasonable request.

Ethics statement

The research protocol complied with the principles of the Declaration of Helsinki and was approved by the Institutional Review Board of Kyung Hee University Dental Hospital in Seoul, South Korea (IRB No-KH-DT23016). For participants <18 years of age, informed consent for study participation was obtained from their parents or legal guardians.

Funding:

This work was supported by a National Research Foundation of Korea (NRF) grant funded by the Korean Government (MSIT) (No. NRF-2020R1F1A1070072, 2021M3E5D2A01019545) and Kyung Hee University in 2021 (KHU-20211863).

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No competing interests reported.

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Distinguishing Between Acute and Chronic Temporomandibular Disorder in Adolescent Patients

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Abstract

Figures

Introduction

Results

Demographics and pain intensity

Chief complaints and factors contributing to TMD

PR findings

MRI findings of acute and chronic TMD

Correlations with TMD symptom duration

2D and 3D visualization of the relationships between chronic TMD and other factors

Logistic regression analysis of chronic TMD

Discussion

Conclusion

Methods

Study population

Sample size

Pain intensity and treatment duration

Chief complaints and contributing factors for TMD

PR parameters

Midline discrepancies

MR image acquisition

ADD and TMJ-OA on MRI

Statistical methods

Declarations

References

Additional Declarations

Status:

Version 1