## 4 Discussion
However, this decreased during further follow-up visits. Does the type of malocclusion have some effect on the development of temporomandibular disorders? In the current study, Class II malocclusions had increased odds of developing TMD, while Class I had the least odds. These results, however, were not statistically significant. Previous studies have shown weak evidence that Class II malocclusions are associated with TMD [28]. Major risk factors identified for TMD development were the presence of more than four somatic symptoms occurring at least monthly and the presence of anxiety or depression at the baseline. In thecurrent study, this tripled the odds of developing TMD during orthodontic treatment. Previous studies have shown that TMD patients have higher anxiety levels compared with normal patients, but a cause-effect relationship between anxiety or depression and TMD has yet to be established [18; 29; 30; 31; 32]. Anxiety and depressive initial symptoms, along with the somatic accompanying symptoms, may promote muscular hyperactivity and altered muscle mechanics that may lead to muscle pain [29; 33]. In the craniofacial area, muscle disorders may initiate TMJ inflammation and pain. These are related to abnormal pain processing in the trigeminal system, which involves components of the neurotransmitter system (serotonin and catecholamines) [29; 34; 35; 33]. Recently, the involvement of catecholamine O-methyl transferase (COMT), which is implicated in the regulation of pain sensitivity genes, has been also reported [36; 37]. Therefore, TMD pain may reflect the physical manifestation of depression and anxiety, even though a direct relationship has not been demonstrated. One of the limitations of this study is the lack of radiological diagnosis due to the difficulty in performing magnetic resonance imaging (MRI) during orthodontic treatment. The diagnosis of TMJ dysfunction may not be determined by clinical examination alone, but the diagnosis is carried out by a combination of clinical manifestations and diagnostic imaging confirmation. Above all, an MRI is helpful when clinical examination cannot predict disk position. Disk positional modifications have been considered one of the main risk factors related to the development of abnormal mechanical trauma and inflammatory disorders within temporomandibular disorders. However, at the end of treatment, an MRI was performed on all symptomatic patients and, in 100% of the cases, the clinical diagnosis was confirmed. Moreover, retrospective studies are susceptible to selection bias due to their design and are also associated with the deflation of treatment effects. In this research, to reduce selection bias, a precise case definition was set by several clinical and morphological variables. This process, together with the large sample size, produced a study group that reflected the exposure of the population that gave rise to the cases and minimized the selection bias. In view of the findings of the current study, the following recommendations can be made. Firstly, each patient who is being considered for orthodontic treatment must be evaluated for temporomandibular joint dysfunction, and this must be documented if present. If the patient has any modifiable risk factors, such as behavioral or somatic accompanying symptoms, an attempt must be made to improve or correct them. Prior to beginning orthodontic treatment, the risk of developing temporomandibular joint dysfunction must be explained to the patients as part of their informed consent. Finally, at each orthodontic appointment, the clinician must ascertain whether the patient has experienced symptoms of TMD and, if they have, must examine the TMJ for any dysfunction. The results of the current study show that most cases of TMD related to orthodontic treatment are temporary and resolve after the completion of the treatment. In conclusion, this study found a slight increase in TMD signs and symptoms during the course of orthodontic treatment, which were mostly resolved upon completion of treatment.