Long term effects of Clear Aligners on the neuromuscular balance of the stomatognathic system

AIM The study aimed to investigate the long-term impact on the neuromuscular equilibrium of the stomatognathic system in adolescents and young adults treated with Clear Aligners. The null hypothesis stated that the thickness of the aligners, approximately 0.75 mm each, could interfere with the electromyographic activity of the masseter and anterior temporal muscles during maximum voluntary clenching immediately after the application of the aligners and in the subsequent months. MATERIALS AND METHODS This prospective study involved 64 healthy participants from the Orthodontics Department of the Dental School, University of Turin, between June 2022 and May 2024. Patients were subdivided into the case group treated with aligners (28 females, 16 males (mean age 18,7)) and control group treated with fixed appliance (12 females, 8 males (mean age 15,9)). For this study, the following inclusion criteria were employed: presence of all permanent teeth, except for third molar; requirement for orthodontic treatment with Clear Aligners; overjet ranging from 2 to 5 millimeters. While patients with the following criteria were excluded from the study: the presence of signs and/or symptoms consistent with temporomandibular disorders according to the Diagnostic Criteria for TMDs; presence of periodontal disease; cast restorations and cuspal coverage; history of facial and/or head trauma; syndromic subjects; presence of anterior and/or posterior crossbite; inability to wear Clear Aligners. To examine the impact of Clear Aligners on the neuromuscular equilibrium of the stomatognathic system, the Teethan EMG device was employed. Electromyographic data were gathered from case group at the following eight time points for each patient: before bonding (T0), immediately after bonding (T1), one week later (T2), one month later (T3), three months later (T4), six months later (T5), nine months later (T6) and one year later (T7); for the control group, electromyographic recordings were taken for up to 6 months (up to T5).The right and left sides of the masseter and anterior temporalis muscles were examined. The Teethan software yields five evaluation indices for assessing occlusal conditions: POC TA, POC MM, BAR, TORS and IMP. RESULTS Based on POC TA and IMP values, there is a statistically significant difference between the case and control groups. For POC MM, BAR, and TORS values, there is no statistically significant difference between the case and control groups since the p-value is > 0.05. Meanwhile, the only test group shows a statistically significant difference over time. CONCLUSION This study indicated that the use of orthodontic aligners led to alterations in the recruitment patterns of masticatory muscles, with an increase in the first month in bite force and then a reduction in bite force capacity over the twelve-month treatment period, where it nearly reaches the baseline situation. Similar outcomes were observed for tasks conducted using aligners or fixed appliances, suggesting that the alteration in muscle recruitment is driven by a functional adaptation of the muscles being studied, irrespective of the occlusal gap created by the aligners in the oral cavity. Based on the analysis conducted, it appears evident that the stomatognathic system exhibits a significant capacity for adaptation and remains unaffected by the presence of aligners. This finding should be viewed positively, as it indicates that this form of orthodontic treatment does not change the muscle activity of the masseter and temporalis muscles in patients.