The Effect Of Long Time Wearing Clear Aligners On Masticatory And Neck Muscles And Mandibular Position

Objective:This study is to evaluate the effect of clear aligners on the masticatory and neck muscles and mandibular position.Methods:13 female subjects ranging from 20 to 28 years old were selected from the patients in Stomatology Hospital of Shandong University according to the inclusion and exclusion criteria. The subjective and objective evaluation were conducted in TO stage (before wearing the CA), T1 stage (the third month) and T2 stage (the sixth month) respectively. The Oral Behavior Checklist (OBC) and the subjective symptoms questionnaire were implemented and the surface eletromyography of anterior funicle of temporal muscle (TA), masseter muscle (MM) and sternocleidomastoid muscle (SCM) were collected in every stage. Limited cone-beam CT (LCBCT) was carried out in TO and T1 stage respectively. The scores of each stage were compared and the teeth and skeletal characteristics were compared between groups with different subjective symptoms scores.Results:1. OBC score of T1 stage was significantly reduced compared with TO stage (P<0.05), which was similar with that of the T2 stage.2. The scores of four parameters including A (TMJ click), B (pain of TMJ region), C (muscle fatigue) and G increased from TO to T1 stage, and then reduced from T1 to T2 stage. The scores of five parameters including D、E、F、H and I gradually reduced from TO to T2 stage. The total angle of Jarabak analysis was significantly larger in unfavorable change group (M) than another group.3. In MPP, the electromyographic activity of TA in T1 stage was significantly larger compared with TO (P<0.05). Although the electromyographic activity of TA had the reduced trend, the value was still larger than that of TO stage. In MPP, the electromyographic activity of MM and SCM had no significant changes (P>0.05). In MPP, the electromyographic activity of TA and SCM in T1 was significantly larger compared with TO stage (P<0.05) and had the reduced trend in T2, which was still larger than those of the TO stage. The muscles asymmetry index of TA, MM, SCM had no significant change from TO to T2 stage.4.Temporomandibular space including SS、AS、PS、MS、LS had no significant change from TO to T1(P>0.05).Conclusion:1. Long time wearing of clear aligners could reduce the frequency of oral parafunction behaviors, which were favorable for the orofacial system.2. Long time wearing of clear aligner was an adaptable process, which required the close clinical examination, especially for the patients with vertical growth patterns.3. The orofacial and neck muscles could be influenced by wearing clear aligners.4. Three months wearing of clear aligners had no effect on the mandibular position, which may be compensated by the adaption of the orofacial muscles.5. Long time wearing of clear aligners had the pros and cons, and we should make full use of the favorable effect and avoid the unfavorable influence.