Correction of Malocclusion by Botulinum Neurotoxin Injection into Masticatory Muscles

Prediction of jaw opening function after mandibular reconstruction using subject-specific musculoskeletal modelling

BACKGROUND

Mandibular reconstruction patients often suffer abnormalities in the mandibular kinematics. In silico simulations, such as musculoskeletal modelling, can be used to predict post-operative mandibular kinematics. It is important to validate the mandibular musculoskeletal model and analyse the factors influencing its accuracy.

OBJECTIVES

To investigate the jaw opening-closing movements after mandibular reconstruction, as predicted by the subject-specific musculoskeletal model, and the factors influencing its accuracy.

METHODS

Ten mandibular reconstruction patients were enrolled in this study. Cone-beam computed tomography images, mandibular movements, and surface electromyogram signals were recorded preoperatively. A subject-specific mandibular musculoskeletal model was established to predict surgical outcomes using patient-averaged muscle parameter changes as model inputs. Jaw bone geometry was replaced by surgical planning results, and the muscle insertion sites were registered based on the non-rigid iterative closest point method. The predicted jaw kinematic data were validated based on 6-month post-operative measurements. Correlations between the prediction accuracy and patient characteristics (age, pathology and surgical scope) were further analysed.

RESULTS

The root mean square error (RMSE) for lower incisor displacement was 31.4%, and the error for peak magnitude of jaw opening was 4.9 mm. Age, post-operative infection and radiotherapy influenced the prediction accuracy. The amount of masseter detachment showed little correlation with jaw opening.

CONCLUSION

The mandibular musculoskeletal model successfully predicted short-range jaw opening functions after mandibular reconstruction. It provides a novel surgical planning method to predict the risk of developing trismus.

Skeletal Class II Malocclusion: From Clinical Treatment Strategies to the Roadmap in Identifying the Genetic Bases of Development in Humans with the Support of the Collaborative Cross Mouse Population

Depending on how severe it is, malocclusion, which may involve misaligned teeth, jaws, or a combination of the two, can hurt a person's overall facial aesthetics. The maxillary molar develops before the mandibular molar in class II malocclusion, which affects 15% of the population in the United States. With a retrusive mandible, patients typically have a convex profile. The goal of this study is to classify the skeletal and dental variability present in class II malocclusion, to reduce heterogeneity, present the current clinical treatment strategies, to summarize the previously published findings of genetic analysis, discuss these findings and their constraints, and finally, propose a comprehensive roadmap to facilitate investigations aimed at determining the genetic bases of malocclusion development using a variety of genomic approaches. To further comprehend the hereditary components involved in the onset and progression of class II malocclusion, a novel animal model for class II malocclusion should be developed while considering the variety of the human population. To overcome the constraints of the previous studies, here, we propose to conduct novel research on humans with the support of mouse models to produce contentious findings. We believe that carrying out a genome-wide association study (GWAS) on a large human cohort to search for significant genes and their modifiers; an epigenetics-wide association study (EWAS); RNA-seq analysis; integrating GWAS and the expression of quantitative trait loci (eQTL); and the testing of microRNAs, small RNAs, and long noncoding RNAs in tissues related to the skeletal class II malocclusion (SCIIMO) phenotype, such as mandibular bone, gum, and jaw in humans and the collaborative cross (CC) mouse model, will identify novel genes and genetic factors affecting this phenotype. We anticipate discovering novel genetic elements to advance our knowledge of how this malocclusion phenotype develops and open the venue for the early identification of patients carrying the susceptible genetic factors so that we can offer early prevention treatment strategies.

Can Botulinum Toxin-A Contribute to Reconstructing the Physiological Homeostasis of the Masticatory Complex in Short-Faced Patients during Occlusal Therapy? A Prospective Pilot Study

The physiological homeostasis of the masticatory complex in short-faced patients is too robust to be disintegrated and reconstructed due to the powerful masseter muscle. This study innovatively introduced the botulinum toxin-A (BTX-A) into the field of dental occlusal treatment, providing a novel and minimally invasive therapy perspective for the two major clinical problems in these patients (low treatment efficiency and high rates of complications). In total, 10 adult patients with skeletal low angle seeking occlusal treatment (age: 27.0 ± 6.1 years; 4 males and 6 females) were administered 30−50 U of BTX-A in each masseter muscle and evaluated before and 3 months after injection based on cone-beam computed tomography (CBCT). We found a significant reduction in the thickness of the masseter muscle (MMT) (p < 0.0001). With regards to occlusion, we found a significant increase in the height of the maxillary second molar (U7-PP) (p < 0.05) with significantly flattened occlusal curves (the curve of Spee [COS] (p < 0.01), and the curve of Wilson [COW] (p < 0.05)). Furthermore, the variations in the temporomandibular joint exhibited a significant reduction in the anterior joint space (AJS) (p < 0.05) and superior joint space (SJS) (p < 0.05). In addition, the correlation analysis of the masticatory complex provided the basis for the following multiple regression equation: MMT = 10.08 − 0.11 COW + 2.73 AJS. The findings from our pilot study indicate that BTX-A, as a new adjuvant treatment attempt of occlusal therapy for short-faced patients, can provide a more favorable muscular environment for subsequent occlusal therapy through the adjustment of the biting force and may contribute to the reconstruction of healthier homeostasis of the masticatory complex. However, further research is required to establish the reliability and validity of these findings.

Botulinum toxin A in dentistry and orofacial surgery: an evidence-based review - part 1: therapeutic applications

Objective An evidence-based review on the safety and efficacy of botulinum toxin type-A (BoNTA) in orofacial conditions, focusing on the therapeutic applications and role of BoNTA as an adjuvant treatment.Data source and selection Data was collected using PubMed (Medline), Cochrane Library of Systematic Reviews and Cochrane Central Register of Controlled Trials electronic databases. Having satisfied the search parameters, 32 studies for therapeutic applications and 26 for BoNTA as an adjunctive treatment were included. The quality of relevant studies was assessed using the Best Evidence Topics (BETs) Critical Appraisal Tool.Data extraction The highest level of evidence (LOE) behind BoNTA safety and efficacy was for wound healing and scar management in the orofacial surgery context, where BoNTA was presented as an adjunctive modality. Level-I evidence was controversial for temporomandibular disorders and bruxism. However, it showed promising results for painful temporomandibular disorders of myogenic origin refractory to conservative therapies, and to decrease muscle contraction intensity in sleeping bruxism. There was only one level-II study for persistent recurrent aphthous stomatitis. Data showed limited level-III evidence for orofacial pain conditions (temporomandibular joint recurrent dislocation and pain, burning mouth syndrome or atypical odontalgia), oral cancer complications, or as an adjuvant to maxillofacial and orthognathic surgeries. Benefits of BoNTA in prosthodontics had weak level-IV evidence. No evidence was found among the periodontology field.Conclusion There is growing evidence to support the safety and efficacy of BoNTA in the investigated orofacial pathological conditions, with high levels of satisfaction from the patient and clinician perspective. However, there are some inconsistencies and limited high-quality evidence available. Well-designed controlled clinical trials are necessary to evaluate long-term safety, efficacy and cost-effectiveness before BoNTA is widely adopted with irrefutable evidence-based clinical guidelines.

Comparative Evaluation of Occlusion before and after Soft Tissue Mobilization in Patients with Temporomandibular Disorder-Myofascial Pain with Referral

The aim of the study was to evaluate occlusal parameters in patients with myofascial pain with referral before and after soft tissue mobilization. The study group consisted of 50 people (37 females and 13 males, average age 23.36 ± 2.14 years) diagnosed with myofascial pain with referral. All patients underwent triplicate soft tissue mobilization. Occlusal parameters were evaluated six times, before and after each treatment, using T-scan III. A decreasing tendency of the occlusion time was observed after the first, second, and third therapy. After the third treatment, the mean occlusion time in the entire study group was 0.119 s. The 1st soft tissue mobilization shortened both right and left disclusion times to 0.181 s and 0.185 s, respectively. After the third treatment, these parameters amounted to 0.159 s and 0.165 s, respectively. The Friedman test for the entire study group indicated that soft tissue mobilization altered the occlusion time and both disclusion times (p < 0.05). In conclusion, soft tissue mobilization affects biotensegrity of the masticatory system, thus modifying occlusal parameters. The occlusion time and both disclusion times cannot be considered as cofactors of the existing temporomandibular disorders-myofascial pain with referral.

Obvious morphologic changes in the mandible and condylar cartilage after triple botulinum toxin injections into the bilateral masseter

INTRODUCTION

Nonsurgical treatments that can prevent or reduce the extent of the mandibular excess at an early stage are desirable. A single botulinum toxin (BTX) injection into the unilateral and bilateral masseter can regulate mandibular contour and condylar cartilage. However, BTX injection is frequency dependent when used in facelifts. This study aimed to evaluate the effect of BTX injection into the bilateral masseter at different frequencies on the mandibular contour and condylar cartilage.

METHODS

In the present study, 24 female Sprague Dawley rats (4 weeks old) were divided into 3 groups: control, single injection, and triple injection. Contour measurement of the mandible was carried out by radiographic imaging. Microcomputerized tomography was performed to determine the change in bone volume in the subchondral bone. Hematoxylin and eosin staining was used to observe the morphologic changes of condylar cartilage. Immunohistochemistry was performed to detect the expression level of biomechanically sensitive factors, including transforming growth factor-β1, parathyroid hormone-related protein, SRY-box 9, and type II collagen.

RESULTS

Bone volume and/or total volume, trabecular number, and trabecular thickness of the mineralized cartilage and subchondral bone significantly decreased in the triple injection group when compared with the single injection group. Mandibular contour also diminished after increased BTX injection frequencies. Chondrocyte proliferation ability and the expression levels of transforming growth factor-β1, parathyroid hormone-related protein, SRY-box 9, and type II collagen significantly decreased in all BTX injection groups and more in the triple injection group.

CONCLUSIONS

Morphologic changes of the mandible and condylar cartilage become more obvious after increased BTX injection frequencies, suggesting that multiple BTX injections into the masseter of patients may relieve the severity of mandibular deformity at an early stage.

Botulinum toxin A injection into the anterior belly of the digastric muscle increased the posterior width of the maxillary arch in developing rats

Background

The purpose of this study was to evaluate the effects of botulinum toxin A (BTX) injection into the anterior belly of the digastric muscle on a growing rat.

Methods

Ten Sprague Dawley rats were used in this study. When the rats were 13 days old, 0.5 units of BTX was injected into the anterior belly of the digastric muscle for the experimental group (n = 5). For the control, the same volume of normal saline was injected (n = 5). The rats were sacrificed at 60 days old, and the skulls were harvested for micro-computed tomography (μCT) analysis.

Results

In anthropometric analysis, the zygomatic arch and mandibular bi-condylar width were significantly lower in the experimental group than those in the control group (P = 0.025 and 0.027, respectively). The maxillary point width was significantly higher in the experimental group than that in the control group (P = 0.020).

Conclusion

BTX injection into the anterior belly of the digastric muscle had effects on the maxillofacial bony width in growing rats.

Micro-CT Analysis of Morphological Changes in Mandibles of Growing Rats with Unilateral Occlusal Elevation

Objectives:

This study investigated the effect of unilateral occlusal elevation in the molar region on facial and mandibular development in growing rats.

Materials and Methods:

Thirty 5-week-old male Wistar rats were randomly allocated to three groups (n = 10). The control group was allowed to develop naturally until 9 weeks of age. A device fitted on the caused unilateral occlusal elevation at 5 weeks in the removal group. The device was removed at 7 weeks and the rats were observed until 9 weeks. In the continuation group, the same device fitted on the left-side molars caused unilateral occlusal elevation continuously for 9 weeks. All groups underwent craniofacial scanning with three-dimensional micro-computed tomography at 5, 7, and 9 weeks.

Results:

In the removal and continuation groups, the mandible was displaced to the unelevated side. At 7 weeks, both these groups showed greater skeletal growth and molar extrusion on the elevated side, with significant differences between the elevated and unelevated sides. At 9 weeks, there were significant differences in both skeletal and alveolar growth between these groups; the asymmetry ameliorated in the removal group.

Limitations:

We evaluated three-dimensional morphometry by fitting a device to rat molars for a short observation period; thus, future studies are warranted to acquire data following long-term observation.

Conclusion:

Unilateral occlusal elevation during the growth period suppressed molar eruption and extrusion on the elevated and unelevated sides, respectively. The height of the mandibular ramus increased on the elevated side, resulting in asymmetric growth.

Challenges and opportunities facing contemporary orthognathic surgery

Here, we provide a brief overview of the challenges, innovations and potential opportunities facing contemporary management of individuals requiring orthognathic care.

The effect of botulinum toxin-A injection into the masseter muscles on prevention of plate fracture and post-operative relapse in patients receiving orthognathic surgery

Background

Botulinum toxin-A (BTX-A) injection into muscle reduces muscular power and may prevent post-operative complication after orthognathic surgery. The purpose of this study was (1) to evaluate BTX-A injection into the masseter muscle on the prevention of plate fracture and (2) to compare post-operative relapse between the BTX-A injection group and the no injection group.

Methods

Sixteen patients were included in this study. Eight patients received BTX-A injection bilaterally, and eight patients served as control. All patients received bilateral sagittal split ramus osteotomy for the mandibular setback and additional surgery, such as LeFort I osteotomy or genioplasty. Post-operative plate fracture was recorded. SNB angle, mandibular plane angle, and gonial angle were used for post-operative relapse.

Results

Total number of fractured plates in patients was 2 out of 16 plates in the BTX-A injection group and that was 8 out of 16 plates in the no treatment group (P = 0.031). However, there were no significant differences in post-operative changes in SNB angle, mandibular plane angle, and gonial angle between groups (P > 0.05).

Conclusions

BTX-A injection into the masseter muscle could reduce the incidence of plate fracture.