Background: Bruxism is a common parafunctional activity that causes destructive effects on the teeth, periodontal tissue, and temporomandibular joint, leading to hypertrophy and myositis of the masseter muscle. This study aimed to evaluate the sonography findings of masseter muscle among women with bruxism and compare them with those among healthy females.Methods: The statistical population of this study consisted of 45 female volunteers, including 23 patients with bruxism and 22 healthy subjects, referring to the Prosthodontics Department. Masseter muscles were evaluated by sonography in each group bilaterally, at rest and maximum contraction positions, and in longitudinal and transverse planes in terms of thickness. It was also examined in terms of the pattern (type I, II, and III), echogenicity (hypo, intermediate, and hyper), internal structure (homogeneous and heterogeneous), and muscle fiber limits (well-defined, poorly-defined, and ill-defined).Results: In the study of three variables of echogenicity, internal structure, and boundaries of muscle in patients with bruxism, less echogenicity (P ≤ 0.011), heterogeneous structure (P ≤ 0.003), and indeterminate boundaries (P = 0.000) were predominant, and there was a significant relationship between the two groups. Moreover, the examination of the difference in muscle thickness between the two groups showed that only the thickness of the left masseter muscle in the longitudinal plane and at rest position was significant between the healthy and bruxism groups (P = 0.040).Conclusion: There were marked sonographic changes in the masseter muscle in women with bruxism, indicating that the bruxism may affect the masseter muscle.

Masseter muscle rigidity is a known complication of drugs such as succinylcholine and volatile agents. However, muscle rigidity is an uncommon complication of propofol. We report the case of a 56-year-old ASA-PS class I woman refereeing for colonoscopy due to chronic constipation under deep intravenous sedation. She suffered masseter spasm after the injection of propofol. Masseter spasm should not be considered limited to special drug groups. In any case of difficult mouth opening, masseter spasm should be kept in mind and deepening of anesthesia or complete blockade of neuromuscular junction should be considered by the use of non-depolarizing muscle relaxants.

Objective (s): Occlusal trauma is one of the most common forms of oral biting dysfunction. Long‐term occlusal trauma could weaken the stomatognathic system; especially damage one’s masticatory muscle. Through using the rat model, this study investigated the trophic effect of ciliary neurotrophic factor (CNTF) on injured masseter muscle.Materials and Methods: Male Wistar rats (n=36) were randomly divided into five experimental groups and one control group (6 rats per group). Animals in the experimental group were cemented modified crowns on their mandibular first molars to artificially induce occlusal trauma in 1, 3, 7, 14, and 28 days. Control group was sham‐treated with forced mouth‐opening for about 5 min, while no crowns were placed. After 28 days of treatment, all rats were euthanized and their masseter muscle was collected. Through immunofluorescence and real‐time quantitative PCR, the expression of desmin, CNTF, and CNTFRa was investigated in rat masseter muscle. The microstructure of masseter muscle was observed by transmission electron microscope.Results: The expression of desmin showed a time‐dependent decrease on traumatic and non‐traumatic sides masseter, until reached the nadir at the 14th day, then restored to its normal level at the 28th day; however, the expression of CNTF and CNTFRa on the traumatic and non‐traumatic sides increased from day 7, reached the peak at the 14th day, and returned to normal level on the 28th day.Conclusion: CNTF, as an important neurotrophic factor, was tightly associated to the restoring of rat injured masseter muscle, which provides new target and treatment method for clinical application.

Background: There is no general consensus in restorative dentistry about which lateral guidance should be established. Some studies have shown that canine guidance decreases the tension of masticatory muscles. Others have reported that group function might achieve a better physiologic distribution of occlusal forces. Also, some reports have shown that both guidances are equally acceptable. Despite all discussions, clinical evidence of one guidance being superior to another is limited. Thus, this study aimed to analyze the electromyographic (EMG) activity of masseter muscles in individuals with group function and canine guidance. Methods: Twenty volunteers of both genders, aged 20-25, were divided into two groups: GF (group function guidance, n = 10) and CA (canine guidance, n = 10). EMG activity of masseters was captured using surface electrodes during habitual maximum intercuspation (HMI) and right and left lateral jaw movements and recorded using EMG amplitude values (RMS –,root means square). Student’, s t-test was used to compare mean RMS values between the groups and lateral movements in each group. Results: During HMI, there was no difference in masseter EMG activity between the groups. Both masseters showed higher activity in group GF only on the right side during lateral movements, while the left masseter exhibited higher activity on the nonworking side in both groups. The activity of both masseters distributed by tooth was higher in group CA. Conclusion: During tooth restorative procedures, any guidance is acceptable considering HMI. However, group function guidance is more favorable during lateral movements due to greater dissipation of occlusal pressures.