Efficacy and Safety of a Novel Botulinum Toxin A for Masseter Reduction: A Randomized, Double-Blind, Placebo-Controlled, Optimal Dose-Finding Study

Efficacy and Safety of PrabotulinumtoxinA in Subjects With Benign Masseteric Hypertrophy: A Double-Blind, Randomized, Placebo-Controlled, Multicenter, Phase 3 Trial and Open-Label Extension Study

BACKGROUND

Despite the widespread use of botulinum toxin (BTX) injection for the treatment of masseter muscle hypertrophy (MMH), there is no standard treatment option.

OBJECTIVE

We report the efficacy and safety for BTX in MMH over a period of 48 weeks.

METHODS

In double-blinded, placebo-controlled phase 3 trials, 180 patients (randomized 1:1) received treatment with placebo (normal saline) or prabotulinumtoxinA (48 units). Masseter muscle thickness (at maximal clenching and resting positions), 3D imaging analysis, and masseter muscle hypertrophy scale grades were analyzed at each time point. After the 24-week CORE study, all patients who met the same criteria of the CORE study at week 24 ( n = 114) received only prabotulinumtoxinA, regardless of previous treatment, for an additional 24 weeks (48 weeks in total) for the open-label extension study.

RESULTS

The largest differences in mean and percent changes from baseline in masseter muscle thickness were observed at 12 weeks, and there were significant differences between the 2 groups at all time points (all p < .001). The effect was independent of the number of injections. No serious adverse event was observed.

CONCLUSION

PrabotulinumtoxinA could effectively ameliorate MMH without major complications.

A Multicenter Phase II Study Evaluating the Safety and Efficacy of Botulax in Asian Patients with Benign Masseteric Hypertrophy

BACKGROUND

Benign masseteric hypertrophy (BMH) is a condition in which the thickness of the masseter muscle is increased, resulting in jawline prominence with an undesirable cosmetic appearance. Botulinum toxin type A (BTA) injection is a promising treatment option, but its effective dose remains debated.

METHODS

Adults older than 19 diagnosed with BMH through visual examination and palpation related to a masseter muscle prominence were selected, and 80 patients were randomly assigned into five groups (placebo group and four groups with different doses of BTA: 24 U, 48 U, 72 U, or 96 U, on both sides of the jaw) and treated with placebo or BTA once at their baseline visit. During each follow-up, the treatment efficacy was evaluated with ultrasound examination of the masseter muscle, three-dimensional facial contour analysis, visual evaluation by the investigator, and patient satisfaction evaluation.

RESULTS

The mean age of the 80 patients was 42.7 ± 9.98 years; 68.75% were women. The mean change in masseter muscle thickness during the maximum clenching state after 12 weeks of drug administration compared with baseline in the 24-U, 48-U, 72-U, and 96-U groups were -2.33 ± 0.41 mm, -3.35 ± 0.42 mm, -2.86 ± 0.42 mm, and -3.79 ± 0.42 mm, respectively. All treatment groups showed a statistically significant decrease compared with placebo. Regarding subjective satisfaction, all treatment groups, except the 24-U group at 4 weeks, showed higher satisfaction than the placebo group during all visits. No significant adverse events were noted.

CONCLUSION

BTA administration of at least 48 U for BMH is more cost-effective than high-dose units and has a low risk of side effects.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, II.

Neurectomy of the Masseteric Nerve Using an Extra-Oral Approach to Treat Masseter Hypertrophy: Case Report and Literature Review

Masticatory muscle hypertrophy is a benign clinical anomaly which leads to facial asymmetry or a squared face appearance. We report a case of masticatory muscle hypertrophy, particularly on the right side, that was successfully treated by neurectomy of the right masseteric nerve through an extra-oral approach. Clinical examination showed significant aesthetic improvement of the facial symmetry with complete paralysis and atrophy of the right masseter muscle. The impaired postoperative function of the frontal branch of the right facial nerve was fully restored 10 weeks postoperatively. The patient no longer experiences headaches or discomfort with eating or sleeping on her right side.

Optimizing the results of facial animation surgery: Botulinum toxin injection into free functional gracilis flap transfer

Although neuromuscular gracilis transplantation is the best choice for facial reanimation in patients with congenital or inveterate palsy, the results are not completely satisfactory. Ancillary procedures developed to achieve better symmetry of the smile and reduce the hypercontractility of the transplanted muscle have been reported. However, the intramuscular injection of botulinum toxin has not been described for this purpose. Patients undergoing gracilis injections of botulinum toxin after facial reanimation surgery between September 1, 2020, and June 1, 2022, were retrospectively enrolled in this study. We collected photographs taken before and 20-30 days after injection and compared the symmetry of the face using software. Nine patients with a mean age of 23.56 years (range, 7-56 years) were enrolled. Reinnervation of the muscle was provided by the contralateral healthy facial nerve via a sural cross-graft (four patients), by the ipsilateral masseteric nerve (three cases), and by the contralateral masseteric and facial nerve (two). Using Emotrics software, we identified differences in the commissure excursion discrepancy of 3.82 mm, the smile angle discrepancy of 0.084°, and the dental show discrepancy of 1.49 mm; the average difference in the commissure height deviation was 2.26 mm (P = 0.02), and those in the upper- and lower-lip height deviation were 1.05 mm and 1.49 mm, respectively. Gracilis injection of botulinum toxin after gracilis transplantation is a safe and feasible procedure that could be applicable to all patients with asymmetric smiles related to excessive transplant contraction. It yields good esthetic results with little to no related morbidity.

Three-dimensional soft tissue landmark detection with marching cube algorithm

Current method of analyzing three-dimensional soft tissue data, especially in the frontal view, is subjective and has poor reliability. To overcome this limitation, the present study aimed to introduce a new method of analyzing soft tissue data reconstructed by marching cube algorithm (Program S) and compare it with a commercially available program (Program A). Cone-beam computed tomography images of 42 patients were included. Two orthodontists digitized six landmarks (pronasale, columella, upper and lower lip, right and left cheek) twice using both programs in two-week intervals, and the reliability was compared. Furthermore, computer-calculated point (CC point) was developed to evaluate whether human error could be reduced. The results showed that the intra- and inter-examiner reliability of Program S (99.7-100% and 99.9-100%, respectively) were higher than that of Program A (64.0-99.9% and 76.1-99.9%, respectively). Moreover, the inter-examiner difference of coordinate values and distances for all six landmarks in Program S was lower than Program A. Lastly, CC point was provided as a consistent single point. Therefore, it was validated that this new methodology can increase the intra- and inter-examiner reliability of soft tissue landmark digitation and CC point can be used as a landmark to reduce human error.

Botox Therapy for Hypertrophy of the Masseter Muscle Causes a Compensatory Increase of Stiffness of Other Muscles of Masticatory Apparatus

Little is known about the nature of masseter muscle hypertrophy. We investigated the masseter muscle stiffness change after a single intra-masseteric session of Botox injections in people with benign bilateral masseter hypertrophy and the effect of the treatment on the stiffness of the temporalis muscle. Stiffness of the muscles was measured with shear-wave elastography at baseline and 3 weeks after Botox injections in 22 otherwise healthy people. Before the treatment, the stiffness of the masseter was lower than of the temporalis muscle (10.18 ± 1.67 kPa vs. 11.59 ± 1.54 kPa; p = 0.002). After the treatment, this difference increased (6.38 ± 1.34 vs. 13.10 ± 1.92; p < 0.0001). The drop in the stiffness of the masseter muscle was symmetrical (left side by 3.78 kPa; right side by 3.83 kPa). No differences between the left and right sides of the face in terms of muscle stiffness were observed. The study shows that Botox injections reduce stiffness of the masticatory muscles which, in turn, increases the stiffness of the temporalis muscles. Due to the knock-on effect of the change in the masseter function on the other masticatory muscles, simultaneous evaluation and treatment of the temporalis muscle may be required to ensure the desired functional and cosmetic effect.

Efficacy of botulinum toxin in masseter muscle hypertrophy for lower face contouring

BACKGROUND

Masseter muscle hypertrophy (MMH) usually presents with cosmetic concerns as it may lead to widening of the lower face. Apart from the traditional surgical approaches, botulinum toxin type A (BTA) injection is a non-invasive treatment option available. There are no standard guidelines for this procedure.

OBJECTIVES

To study the efficacy of botulinumtoxin A in MMH for lower face contouring.

METHODOLOGY

The Cochrane Library, PubMed/MEDLINE, Google-scholar, Science-Direct database, and ResearchGate from inception until September 2021 were searched using the keywords "botulinumtoxin type A," "masseter muscle hypertrophy," "lower face contouring," and "masseter botox." All available retrospective and prospective studies, case-series, case-reports, and expert reviews were included with an emphasis on efficacy of BTA in MMH and units injected into the muscle, points of placement, adverse events, and the duration of its effect. Reference lists of the resultant articles, as well as relevant reviews, were also searched.

RESULT

40 articles were shortlisted for the review, of which 14 studies with sample-size ≥10 in accordance with the study requirements were summarized in a tabular form for analysis and easy comparison and reference.

CONCLUSION

BTA injection is a non-invasive, safe, and effective treatment for MMH. The optimum number of BTA units could not be ascertained due to wide variability in the studies as well as ethnicity of patients and extent or some measurement of MMH. The points of placement of injection should be well within the boundaries of the masseter muscle. The maximum effect of BTA after a single injection session is usually seen in ~3 months, and the duration may last for 6-12 months. Multiple injection sessions may be required to maintain a long-term effect. Injection technique and total number of injection units of neuromodulator must be individualized for each patient.

Practical Application of Novel Test Methods to Evaluate the Potency of Botulinum Toxin: A Comparison Analysis among Widely Used Products in Korea

The safe and effective dosing of botulinum neurotoxins (BoNTs) requires accurate and reliable methods to measure their potency. Several novel methods have been introduced over the past decade; however, only few studies have compared the potency of BoNT products with that of the LD50 and other alternative assays. Therefore, the objective of this study was to comparatively evaluate widely used BoNT products using various test methods. Four types of BoNTs (prabotulinumtoxin A, onabotulinumtoxin A, neubotulinumtoxin A, and letibotulinumtoxin A) were used in this study. The estimated potency was assessed using the LD50 assay, and the total BoNT type A protein levels were measured using the enzyme-linked immunosorbent assay (ELISA). The in vitro efficacy of the BoNTs was determined using fluorescence resonance energy transfer (FRET) and surface plasmon resonance (SPR) assays. The results showed differences in the total amount of BoNT protein and the cleavage activity of SNAP-25 within all types of BoNTs. The SPR study seemed to be useful for evaluating the potency by specifically measuring intact 19S neurotoxin, and these results provide new insights for assessing different BoNT products.