Is SEMG recorded “hyperactivity” during mandibular rest a sign of dysfunctional jaw muscle activity and temporomandibular disorders (TMD)?

BackgroundSome authors state that above‐normal surface electromyography (SEMG) levels during mandibular rest (MR) are a general sign of temporomandibular disorders (TMD).ObjectiveThe aim was to compare SEMG levels in the masseter and anterior temporalis areas during MR between patients with disc displacement (DD) and subjects identified as healthy. The hypothesis was that average SEMG levels would be higher in the patients during MR before and after repeated clenches with maximal effort.MethodsThirty‐six healthy subjects, and 42 patients with DD, were included. SEMG levels were recorded bilaterally in the temporalis and masseter areas during MR before clenching and after repeated clenches with maximal effort. Multivariate analysis of variance (MANOVA) was used to compare the means of the log‐transformed SEMG‐values for the subject groups.ResultsThe mean MR levels in the four areas before clenching ranged from −0.19 log (µV) to 1.20 log(µV) in healthy subjects and from −0.22 log(µV) to 0.96 log(µV) in patients. The mean MR levels in the four areas after repeated clenches ranged from −0.19 log (µV) to 1.04 log(µV) in healthy subjects and from −0.27 log(µV) to 0.93 log(µV) in patients. The MANOVA test showed no significant differences in the means for MR for the four areas between the groups at the 5% significance level.ConclusionThe hypothesis that jaw muscle SEMG levels during MR are on average generally higher in TMD patients is not supported. A possible explanation for the previous findings is that activity in other muscles was mislabelled as jaw muscle activity.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/156203/2/joor13032_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/156203/1/joor13032.pd

Quantification of orthodontic loads on teeth in the correction of canine overeruption using different archwire designs

Introduction This study quantifies the effects of material, size of the continuous archwires, and level of overeruption on the loads on teeth in the correction of overerupted canines. Methods An orthodontic force test (OFT) was used to measure the 3-dimensional loads delivered by the archwires to the brackets attached to the maxillary right incisors, canine, and premolars. Dentoforms simulating canine overeruptions at the 0.5 mm and 1 mm levels were made from computerized tomography scans. Archwires with 2 types of material (stainless steel [SS] and nickel-titanium [NiTi]) and 2 sizes (0.014-in and 0.016-in) were tested, respectively, on the 0.022 × 0.028-in brackets through elastomeric ligatures. Results The forces were dominantly intrusive on the canines and extrusive on the first premolars and lateral incisors. The magnitudes of the extrusive forces were about 74% and 52% that of intrusive force on the canines, which range from −0.48 ± 0.01 N to −5.70 ± 0.14 N depending on the wire material, size, and severity of overeruption (P <0.01). The canine intrusive forces created by SS wires were about 3 times higher than that of NiTi wires with the same sizes, 0.016-in archwires were about twice higher than that of 0.014-in with the same materials, and 1 mm overeruption level doubled with respect to 0.5 mm. Significant second-order moment as coupled with the intrusive or extrusive forces. Conclusions The intrusive and extrusive forces on teeth in the correction of canine overeruption can be quantified by the in vitro orthodontic force test, and the effects of the 3 factors significantly affect the loads on the teeth