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COMPARISON OF DENTAL STATUS AND ORAL FUNCTION BETWEEN THE ELDERLY WITH AND WITHOUT TEMPOROMANDIBULAR DISORDERS 122 findings of Jeon et al. [19] suggested a positive correlation between chronic periodontitis and TMD- related muscle pain, while Fabri et al. [24] found that there were clinical comorbidities between periodontal disease and craniofacial pains. All these studies support our findings indicating that periodontitis accumulated over time might be a risk factor for TMD. TMD are a group of disorders that disrupt function or cause parafunction of the masticatory system. Surprisingly, the number of oral parafunctional activities was equal across two groups; participants in both groups had a range of 4–5 parafunctional behaviours. Our study is in accordance with Leketas et al.’s study [25] indicating that the behaviours of “Lean with your hand on the jaw”, “Chew food on one side only”, and “Sleep in a position that puts pressure on the jaw” were the most common in the TMD group. Meulen et al. [26] showed that these parafunctional behaviours often had higher scores than other parafunctional items when evaluating the validity items of OBC-21 in the Dutch population. This could suggest that the frequency of parafunctional behaviours affected TMD. The current study found that 2 out of 21 items of OBC were significantly associated with TMD among the elderly. The TMD group had higher frequency of “Hold, tighten, or tense muscles without clenching”, but a lower frequency of “Eating between meals (i.e., food that requires chewing)” than the non-TMD group. These findings could be explained by muscular activity. The increase in the frequency of tensing muscles heightened the risk of TMD between 2.9 – 10.8 times [25]. Based on an electromyography study, Ohrbach et al. found [27] a high score of masseter muscular activity in subjects with tense muscles. A high activity of masseter muscle in combination with the neuromuscular change in older age would cause muscular disorders, a subgroup of TMD. This also explained why the TMD elderly group had a lower frequency of eating between meals in our study because of muscular impairment. The current study reported difficulty chewing tough and hard food in most participants, but none indicating that TMD was related to functional limitations of mastication; such findings contrast with findings of Brandini et al. [28]. In older adults, the rate of loss was often higher in the posterior than the anterior teeth; therefore, the impaired masticatory performance was prevalent in both groups in our study. There were no differences between the two groups concerning other functional limitations related to mandibular mobility and verbal/emotional expression. However, limited mouth opening could occur with increasing age. Ikebe et al. found that 7.9% of elderly Japanese exhibited this limitation [29]. Similarly, our study demonstrated that approximately 23% of examinees self-reported a reduced mouth opening capacity to perform daily activities. The age-related degeneration of the temporomandibular joints and muscle weakness could contribute to such limitation in older people. Although the prevalence of functional limitations was high in the TMD group, there were no correlations between the functional limitations of masticatory system and TMD when compared to the non-TMD group. This suggests that multiple factors could affect the function of the masticatory system in the elderly, including chronic orofacial pain, psychological disorders, and age-related reduction of the motor function of masticatory muscles [29–31]. The important finding of the current study was that determining the JFLS-20 score of older adults might enable us to predict TMD, as the prevalence of TMD is correlated with an increasing JFLS-20 score in the general population [13]. The limitation of the study was that we only studied the oral function and parafunctional behaviours based on self-rated questionnaires. There is a need for more clinical research on this aspect. 5. Conclusion Temporomandibular disorders were associated with missing teeth and periodontal diseases. There was no association between TMD and mandibular functional limitations among the elderly. The elderly suffering from TMD tended to have increased frequency of holding, tightening, or tensing muscles. Conflicts of interest The authors declare that they have no conflict of interest. Author contributions MSN searched literature, performed clinical studies, data acquisition and statistical analysis, and wrote draft of manuscript. ÜVO, TJ, and MS designed protocol, interpreted data, and edited the manuscript. All authors read and approved the final manuscript. Acknowledgements This study was supported by the Estonian Science Foundation grant ESF 9255, the Estonian Research Council IUT 20-46, and the Internationalization Programme DoRa of the European Social Fund, which is carried out by the Foundation Archimedes. The authors would like to thank the volunteer participants from the Hoa Vang, Hai Chau, Thanh Khe, and Cam Le districts of Danang City in Vietnam for their cooperation and agreement to provide data on their oral health and temporomandibular joint status. References 1. 2. 3. 4. Unell L, Johansson A, Ekbäck G, et al. Prevalence of troublesome symptoms related to temporomandibular disorders and awareness of bruxism in 65- and 75-year-old subjects. Gerodontology. 2012;29(2):e772-e779. doi:10.1111/j.1741- 2358.2011.00558.x. [Full text links] [PubMed] Google Scholar(25) Scopus(9) Nguyen MS, Jagomägi T, Nguyen T, et al. Symptoms and signs of temporomandibular disorders among elderly Vietnamese. 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