Date Published: June 14, 2019
Publisher: Public Library of Science
Author(s): Ya-Yi Chen, Hueng-Chuen Fan, Min-Che Tung, Yu-Kang Chang, Yi Hu.
The prevalence of temporomandibular disorder (TMD) among elderly people with Parkinson’s disease (PD) is relatively high, but a population-based study of the relationship between PD and TMD is still lacking. This study, therefore, sought to investigate the association between TMD and PD by using data for one million randomly sampled beneficiaries of Taiwan’s National Health Insurance program, including 6,185 PD patients who were matched through propensity score matching with 18,555 non-PD patients. Both the PD and non-PD cohorts were followed until death, any diagnosis of TMD, or December 31, 2013, whichever occurred first. Each diagnosis of TMD was made by a qualified physician according to the International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9-CM), using the diagnosis codes 524.60, 524.62, 524.63, and 524.69 while excluding tooth abscess, wisdom tooth eruption, herpes zoster and postherpetic neuralgia, mastoiditis, otitis externa, otitis media, parotitis, sialadenitis, and trigeminal neuralgia. We used Cox proportional hazard regression models to calculate the relative risk of TMD and found a 2.11-fold (95% CI: 1.35–3.30) increased risk of TMD overall in the PD group compared with the non-PD group. Stratified by follow-up period, there was a 4.25-fold (95% CI: 1.51–11.93) increased risk in the PD group in the first year after the initial PD diagnosis and a 3.88-fold (95% CI: 1.33–11.28) increased risk in the second year. Over the long-term (>5 years), PD was significantly associated with an increased risk of TMD. These findings suggest that it is important to closely monitor the temporomandibular joint health of PD patients.
Among the neurodegenerative disorders, Parkinson’s disease (PD) is second only to Alzheimer’s disease in terms of prevalence, affecting 0.3% of the population in general  and more than 1% and 4% of people aged at least 60 and 80 years old, respectively [2–4]. PD is a chronic, progressive central nervous system disease that results from dopamine deficiency in the brain due to the death of dopaminergic neurons in the substantia nigra . The resulting motor symptoms include postural instability, hand and facial tremors, muscular rigidity, impaired balance, and bradykinesia [6, 7]. Common postural instabilities seen among patients with PD include cervical spine flexion, thoracic hyperkinesis, scoliosis, abduction of the shoulders, and flexion of the arms .
The PD patients, 51.2% of whom were male, had a mean age of 70.2 years and a mean CCI score of 3.65, with the largest percentage of these subjects (37.9%) living in the northern geographic region of Taiwan. The matched non-PD patients, 51.6% of whom were male, had a mean age of 70.0 years and a mean CCI score of 3.58, with the largest percentage of these subjects (39.9%) also living in the northern geographic region of Taiwan. The two groups were thus, as expected, similar in terms of the baseline characteristics on which they were matched (Table 1).
In this study, we found a significantly increased risk of TMD among patients with PD as compared to non-PD patients, particularly among those patients who had lived with PD for an extended period of time. While sometimes undervalued or compartmentalized as separate from the health of the rest of the body, oral health is of critical importance given its numerous physical and psychological effects, including its impacts on how people look, speak, and socialize, among others . By causing pain suffering, and alterations in diet, oral health problems can directly affect overall health, including people’s quality of life and well-being in general . Moreover, oral health or the lack thereof can have direct effects on chronic diseases such as PD . For example, various studies have reported associations between poor oral health and chronic obstructive pulmonary diseases, cardiovascular disease mortality, and respiratory disease mortality [35, 36].
In conclusion, the results of this study demonstrated that the PD patients had an increased risk of TMD compared to the matched controls, with the difference being significant for 2 years after the diagnosis of PD. Understanding these long-term associations of PD with TMD, as well as the risk of causal motor symptoms, is of substantial value for those seeking to improve oral health policies.