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This study investigated the pattern of masticatory, neck, and trunk muscle activity in patients with posterior crossbites and associated mandibular displacement. The test group consisted of 75 patients [45 males mean age 19.5 years, SD 5.6 years, and 30 females mean age 20.4 (SD 3.2) years]. Of this group, 25 patients presented a left posterior crossbite, 25 a right posterior crossbite, and the remaining 25 patients a bilateral posterior crossbite. A control group of 25 subjects (19 males and 6 females aged 22.5 ± 5.8 years) without any crossbite were included. Surface electromyographic (sEMG) activity was recorded bilaterally, in the mandibular rest position and during maximum voluntary clenching (MVC), at the following sites: anterior and posterior temporal, masseter, sternocleidomastoid (SCM), upper and lower trapezius, and cervical muscles. In the mandibular rest position, patients with unilateral crossbites showed a significant difference (P < 0.05) in sEMG activity of the anterior temporal muscle, with the greatest activity being detected on the side to which the mandible displaced. Control subjects demonstrated significantly lower (P < 0.05) sEMG activity but only in the SCM muscle when compared with patients with bilateral posterior crossbites; no such differences were detected in relation to unilateral crossbites. During MVC, control subjects showed significantly lower (P < 0.01) sEMG activity in both the SCM and the posterior cervical muscles compared with patients demonstrating both unilateral and bilateral crossbites. The findings of the present study indicate that the presence of a crossbite can affect electromyography activity of masticatory, neck, and trunk muscles.

This study investigated the prevalence and type of pain experienced during orthodontic treatment in 30 subjects (12 males, 18 females, aged 12-18 years) with crowding. Fifteen patients were treated with conventional brackets (Victory Series) and 15 with self-ligating brackets (Damon SL II). The first archwire for all patients was a 0.014 inch nickel-titanium (NiTi) archwire with a force of approximately 100 g. Conventional brackets were ligated with elastomeric modules. A visual analogue scale (VAS) was used daily to assess the intensity of pain; the use of pain medication was also reported in a specially designed daybook for a total period of 3 months. Pearson's chi-square was used to investigate the difference between groups in the frequency of pain experience, its nature, and the use of analgesia. Non-parametric statistics (Mann-Whitney U-test) were computed to compare pain intensity between the groups. To investigate reported pain assessments, Friedman's two-way analysis of variance was used and the differences were estimated using Wilcoxon's signed-rank test. The results showed that pain was reported for a period of 9 days after archwire insertion. Patients treated with self-ligating brackets reported the highest pain intensity on the day following placement of the first archwire (VAS mean = 42.6), while those treated with conventional brackets experienced the greatest pain intensity at placement of the first archwire (VAS mean = 52) and after the second orthodontic appointment (VAS mean = 59.6). Analgesics were used by 16.5 per cent of patients treated with self-ligating brackets and by 10 per cent of those treated with conventional brackets, most often during the first 2 days after archwire placement. Patients treated with conventional brackets reported significantly more 'constant' pain than those treated with self-ligating brackets who complained of 'chewing/biting' pain. Pain appears to be common during orthodontic treatment but perhaps less intense when self-ligating brackets are used, although no difference was observed in the use of analgesics between those treated with self-ligating or conventional brackets. There were no reports of pain after 7-9 days in either group.

The aim of this study was to investigate the surface electromyographic (sEMG) activity of neck, trunk, and masticatory muscles in subjects with temporomandibular joint (TMJ) internal derangement treated with anterior mandibular repositioning splints. sEMG activities of the muscles in 34 adult subjects (22 females and 12 males; mean age 30.4 years) with TMJ internal derangement were compared with a control group of 34 untreated adults (20 females and 14 males; mean age 31.8 years). sEMG activities of seven muscles (anterior and posterior temporalis, masseter, posterior cervicals, sternocleidomastoid, and upper and lower trapezius) were studied bilaterally, with the mandible in the rest position and during maximal voluntary clenching (MVC), at the beginning of therapy (T0) and after 10 weeks of treatment (T1). Paired and Student's t-tests were undertaken to determine differences between the T0 and T1 data and in sEMG activity between the study and control groups. At T0, paired masseter, sternocleidomastoid, and cervical muscles, in addition to the left anterior temporal and right lower trapezius, showed significantly greater sEMG activity (P = 0.0001; P = 0.0001; for left cervical, P = 0.03; for right cervical, P = 0.0001; P = 0.006 and P = 0.007 muscles, respectively) compared with the control group. This decreased over the remaining study period, such that after treatment, sEMG activity revealed no statistically significant difference when compared with the control group. During MVC at T0, paired masseter and anterior and posterior temporalis muscles showed significantly lower sEMG activity (P = 0.03; P = 0.005 and P = 0.04, respectively) compared with the control group. In contrast, at T1 sEMG activity significantly increased (P = 0.02; P = 0.004 and P = 0.04, respectively), but no difference was observed in relation to the control group. Splint therapy in subjects with internal disk derangement seems to affect sEMG activity of the masticatory, neck, and trunk muscles.