Repeated botulinum treatment of rabbit masseter causes cumulative tissue damage.

OBJECTIVE: Botulinum neurotoxins (BoNT) are used in masticatory muscles for pain relief, unloading of the mandible, and cosmetic facial contouring. Treatment is often repeated every few months as function returns. This study assessed masticatory function and musculoskeletal structure after multiple BoNT treatment of the rabbit masseter. DESIGN: Female rabbits received 3 injections of BoNT (n = 13) or saline (n = 5) into one masseter muscle at intervals of 12 weeks. The contralateral side served as control. Periodic measurements of masticatory electromyography (EMG) and stimulated anterior bite force were made. After the final 12-week recovery interval, neuromuscular connection was investigated by stimulating the masseteric nerve to elicit an evoked EMG response. Mandibular specimens were collected for microCT analysis, and masseters were collected for histomorphometry and counts of replicating cells. RESULTS: Control and saline-injected muscles maintained consistent masticatory EMG and anterior bite force throughout the study. BoNT-injected masseters showed strong declines after each injection; during the 12-week recovery period, masticatory EMG and anterior bite force improved, although only electrical activity reached normal levels. Multiple injection resulted in persistently atrophied muscle fibers with fibrosis, and notable loss of bone from the mandibular body and condyle. The uninjected masseters of the BoNT group also showed evidence of mild toxin-related changes. CONCLUSIONS: Although muscle function is mostly regained after each injection, masseters receiving multiple doses of BoNT show extensive damage. In addition, mandibular bone density is decreased on the injected side.

Botulinum toxin in the masseter muscle: Lingering effects of denervation.

Botulinum neurotoxins (BoNTs) are paralytic agents used to treat a variety of conditions in jaw muscles. Although their effect is considered temporary, there are reports of persistent functional changes. Using rabbits that received BoNT injection in one masseter muscle, the recovery of neuromuscular connection was investigated using nerve stimulation to evoke an electromyographic (EMG) response, and the recovery of muscle fibers was investigated using histological morphometry and bromodeoxyuridine (BrdU) immunohistochemistry. One month after treatment, evoked EMG was greatly reduced in both amplitude and duration, indicating that little reinnervation had taken place. Muscle fibers were atrophied and collagenous tissue was increased. Three months after treatment, evoked EMG duration was normal, indicating that at least some neuromuscular junctions were functional. Histologically, some muscle fibers were hypertrophied, some were still atrophied, and some appeared to have died. Fibrosis was still apparent amid slight increases in dividing cells and regenerating fibers. The histological effects of BoNT were evident although attenuated at a distance of about 1 cm from the injection level, but no regional differences could be discerned for the evoked EMGs. In conclusion, there were persistent muscular deficits seen 3 months after BoNT treatment that may have been caused by the failure of some affected muscle fibers to become reinnervated.

Oral Health and Oral Health-Related Quality of Life in Children With Obstructive Sleep Apnea.

STUDY OBJECTIVES: This aim of this study was to evaluate oral health and oral health-related quality of life (OHRQoL) in children with obstructive sleep apnea (OSA). METHODS: This cross-sectional study involved 31 children who had baseline polysomnography studies and in whom a diagnosis of OSA was made by a sleep physician. They were evaluated against 36 control patients who, based on parent responses to the Pediatric Sleep Questionnaire, were at very low risk for having sleep problems. The mean age of the cohort was 12.3 ± 2.7 years. The oral health status was examined clinically and recorded using caries and periodontal indices. OHRQoL was measured using the Child Oral Health Impact Profile (COHIP) questionnaires. RESULTS: Children with OSA had significantly worsened oral health compared to control patients as evidenced by more caries (15.2 and 3.2, respectively; P < .001) and more periodontitis. Periodontitis severity was measured by the presence of bleeding on probing, (87% versus 30%, P < .001) and higher number of sites with abnormally deep periodontal probing depths (2.7 versus 0.3, P < .001). The COHIP scores were significantly higher among children with OSA compared to control patients, (29.7 versus 11.8, P < .001) consistent with poorer OHRQoL. CONCLUSIONS: This study suggests that in children OSA may have a significant association with poorer oral health when compared to control patients without sleep problems, and that their oral health status may have a negative effect on their quality of life. Increased awareness regarding the oral health effects of sleep-disordered breathing in the medical and dental community is needed.