Anatomic Occlusal Splint for Treatment of Essential Tremor: A Case Report

Characterized by involuntary, rhythmic oscillations, essential tremor (ET) is a common neurological disorder that often confers substantial disability.1, 2 Pharmacotherapy for ET primarily involves antiepileptic drugs and nonselective beta-blockers, with reported efficacy in only about half of the patients.3 While more effective, neuromodulation therapies like neurostimulation and nucleus ablation often cause significant patient anxiety regarding potential surgical risks, influencing their treatment decisions.4 As a disease of uncertain pathological and neurophysiological mechanisms, treatment of ET is an unmet clinical necessity for both clinicians and patients. The authors observed that an occlusal splint improved both mandibular and upper limb tremors in a patient with a prior diagnosis of ET during a dental procedure. A 78-year-old woman reported to the dental clinic with the chief complaint of difficulty in chewing for 1 year. She presented with a roughly 15-year history of upper limb tremor, 11-year mandibular tremor and voice tremor, which had accelerated in the past year following the placement of a full-arch zirconia fixed prosthesis due to missing and loose teeth. Previously, arotinolol hydrochloride (10 mg BID) produced limited benefit but was discontinued due to bradycardia. She has neither a family history of tremor nor symptoms of anxiety or depression. Past medical history is notable only for poorly controlled diabetes mellitus for 10 years. Examination demonstrated persistent mandibular tremor and a full-arch zirconia fixed prosthesis with unstable occlusal contacts (Video 1, part 1). Palpation revealed tenderness in the left temporomandibular joint, lateral pterygoid, medial pterygoid, and mylohyoid muscles. A chairside-fabricated Lucia Jig was placed anteriorly to facilitate neuromuscular reprogramming of the masticatory system (Video 1, part 2). This allows mandibular stabilization independent of tooth contact, devoid of muscular or temporomandibular joint discomfort (termed centric relation position in dentistry). Simultaneously, the patient's mandibular tremor subsided upon contact with the Lucia Jig. Subsequently, a maxillary anatomic occlusal splint was digitally designed and fabricated. Upon placement, the tremor resolved immediately (Video 1, part 3) with reduced tenderness. The patient was required to wear it all day long. One month after treatment, she discontinued splint wear due to complete tremor remission and significant improved chewing function. The 2-month virtual follow-up (Video 1, part 4) demonstrated a stable treatment effect. To quantify the improvement in the patient's mandibular tremor, tremor frequency was obtained via video tracking. Briefly, the connected components of the upper and lower teeth were segmented. The lowest pixel of the lower teeth segment served as a tracking marker, and a time-series signal was generated based on its y-coordinate (the y-coordinate/height of the lowest point of the lower teeth, normalized according to the patient's nasal width) across all video frames, representing the vertical movement of the mandible. Subsequently, the signal before and after treatment could indirectly signify the difference in tremor severity accordingly. Shown as Figure 1, the tremor was more severe before treatment, and the tremor nearly disappeared afterward. Mandibular stability, measured by the normalized standard deviation, improved by approximately 92.4% after treatment. The two-month follow-up video was not suitable for quantitative analysis because the mouth was not held open; however, no mandibular tremor was observed. In this case, the patient's longstanding mandibular and upper limb tremor were alleviated through the use of an occlusal splint. Although this was an incidental finding, we conducted a comprehensive review of the diagnosis and the patient's presentation before and after treatment. First, by reviewing the medical history and comparing two tremor analyses performed 8 years apart (Supplementary Fig. S1), we confirmed the diagnosis as ET, rather than Parkinsonian tremor or dystonic tremor. Second, in addition to the improvement in mandibular tremor, the patient reported significant subjective reduction in upper limb tremor (70%) and voice tremor (50%). During a two-month period without the splint, no symptom recurrence was observed. At the most recent follow up (8 months later), only mild tremor persisted. A thorough review of the literature reveals no report on the use of occlusal splints for treating ET, indicating that this potential therapeutic approach remains entirely unexplored. However, limited evidence exists regarding their application in managing Parkinson's disease, dystonia, and Tourette's syndrome.5-7 Nomoto et al reported that an occlusal splint improved grip strength and motor function in a Parkinson's patient without mandibular tremor during the OFF-medication phase.5 In cases of Tourette's syndrome, occlusal splint therapy improved motor symptoms and enhanced concentration.7 Proposed mechanisms involve proprioceptive modulation of jaw-closing muscle spindles, or trigeminal nerve influences on brainstem sensorimotor circuits.5-7 The occlusal splint is a mainstream and established treatment modality for temporomandibular disorders (TMD) in dental clinical practice. Functional neuroimaging has identified neural alterations in TMD patients, such as changes in cortical thickness, cerebral blood flow and connectivity.8 Splint therapy may function by alleviating symptoms through the induction of neuroplastic recovery in these affected regions.8 Despite their clinical differences, ET and TMD may be linked by overlapping functional changes in the brain. Reduction of salience network connectivity by the occlusal splint has been reported in TMD patients, and this network is linked to movement disorders.8 The observed phenomenon may be explained by neuroplastic changes triggered by the occlusal splint. Despite epidemiological evidence pointing to a higher prevalence of TMD in the aging Parkinson's disease population compared to non-PD population (1.53% vs. 0.6%),9 the potential relationship between TMD and ET remains unexplored. Further research is needed to explore the relationship as well as the potential underlying mechanisms of occlusal splint. Additionally, long-term follow-up for this patient is required to fully assess outcomes. (1) Research project: A. Conception, B. Organization, C. Execution; (2) Statistical analysis: A. Study design, B. Study execution, C. Review and critique; (3) Manuscript preparation: A. Writing of the first draft, B. Review and critique. P.Y.: 1A, 1B, 1C; 3A. K.Z.: 1C, 2A, 2B. J.H.: 1B, 1C. H.W.: 1A, 1C, 2A, 3B. H.D.: 1A, 1B, 3B. We thank the patient and their family for their support of this publication. Ethical Compliance Statement: We confirm that the approval of an institutional review board was not required for this work. We confirm that we have read the Journal's position on issues involved in ethical publication and affirm that this work is consistent with those guidelines. The research was conducted in conformity with the ethical principles set forth in the 1964 Declaration of Helsinki and its subsequent amendments. We obtained written informed consent from the patient to publish the details of this case report, along with all associated photographs and video recordings. Funding Sources and Conflicts of Interest: This work was supported by the National Nature Science Foundation of China (No. 82171255), Central High Level Clinical Research Special Project (No. 2022-PUMCH-B-018), Peking Union Medical College Hospital Talent Cultivation Program (Category C) (UBJ10847) and National High Level Hospital Clinical Research Funding (2022-PUMCH-C-070). The authors declare that there are no conflicts of interest relevant to this work. Financial Disclosures for the Previous 12 Months: The authors declare that there are no additional disclosures to report. The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions. Figure S1. Results of the 2018 tremor analysis. 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