Association Of Forceful Interference Occlusal Contacts With The Electromyographic Activity Of Jaw-closing Muscles In Temporomandibular Disorders Patients

Temporomandibular disorders(TMD) are common oral-facial disease. The aetiology of TMD is multifactorial, and occlusal factors play a vital role in TMD. The occlusal interference would evoke a periodontal-elevator muscle contraction feedback to adjust the constitution of the muscular fibers of the jaw to contract. So, it is helpful to assess the association of occlusal contact characteristics with the electromyographic activity of jaw-closing muscles in reveal the pathogenic process of TMD. The occlusion information from the T-Scan III system can be simultaneously measured along with the SEMG activity of the jaw muscles by Bio-EMG III system. The aim of the present study was to investigate whether some of the occlusion features had an association with the SEMG activity of the jaw elevator muscles by simultaneously recording the occlusal features with T-Scan III system and the SEMG activity of jaw-closing muscles in TMD patients with two kinds of occlusal contacts based on the prediction that occlusal interferences would be regularly located in the interferences area to facilitate the analysis of the elusive occlusion criteria.Firstly, the asymptomatic volunteers and the TMD patients with similar morphologically well-arranged dentition were simultaneously compared with occlusal features and the SEMG activity of jaw-closing muscles by the T-Scan III system and the Bio-EMG III system. A total of 7 tasks were randomly recorded for each subject: #1–4 involved closing of the mouth from the rest position to perform MVC as quickly as possible in ICP(#1), in protrusive edge-to-edge contact position(#2), and in left or right edge-to-edge position(#3 and #4). Tasks #5–7 were movement tasks that involved closing the mouth from the rest position to the ICP as fast as possible, then following a mandibular movement along the maxillary anterior guidance to perform a protrusive movement or along the lateral guidance to perform a right or left side lateral excursive movement, during these procedures, biting efforts were kept. The aim was to assess whether some of the occlusion features had an association with the SEMG activity of the jaw elevator muscles.Then, occlusal features and SEMG activity of jaw-closing muscles were simultaneously recorded in TMD patients with a unilateral over-erupted mandibular third molar. The present purpose was to investigate whether some of the occlusion features of the over-erupted third molar had an association with the TA and MM’s SEMG activity by comparing between the over-eruption side and the non-over-eruption side.We get the results as the following:1. Compared by the asymptomatic volunteers with morphologically well-arranged dentition, the TMD patients shown a forceful interferential contact located in the posterior arch so that when protrusive MVC was performed, the Biting-Force-Distribution in the anterior arch was decreased whereas that in the posterior arch was increased. Meanwhile, when protrusive MVC was performed on the protrusive position, the SEMG activity of the bilateral side TA and MM in TMD patients were higher than that in the asymptomatic volunteers.2. The forceful occlusal contact is found associated with SEMG differences in MM of TMD patients with over-erupted third molars. Although there are often balancing contact, i.e., the balancing contact number did not differ between the side with over-erupted third molar and the side without, a forceful interferential contact is often located on the over-erupted third molar so that when protrusive MVC was performed, the Biting-Force-Distribution on the non-over-erupted side was decreased whereas that on the over-erupted side was increased, and when performing lateral MVC on the non-over-erupted side, the Biting-Force-Distribution on the working side was lower, but that on the balancing side was higher than that when performing lateral MVC on the over-erupted side. Meanwhile, when lateral MVC was performed on the non-over-erupted side, the SEMG activity of the working side MM was higher than that when performing lateral MVC on the over-erupted side.The results indicated that1. Heavy forceful interferential contacts in the posterior arch of the TMD patients with morphologically well-arranged dentition during protrusive maximal voluntary clenching was found to be associated with an increased SEMG activity of TA and MM.,2. Heavy interferential contact of an over-erupted mandibular third molar during protrusive and lateral excursive maximal voluntary clenching was found to be associated with an alteration in SEMG activity of MM.