Botulinum neurotoxin type A in the masseter muscle: effects on incisor eruption in rabbits

Effect of local injection of injectable platelet-rich fibrin on eruption rate of teeth (Rabbit animal model)

OBJECTIVE

This study aimed to evaluate the effect of the local injection of injectable platelet-rich fibrin (i-PRF) on the eruption rate of the teeth and evaluation of the effect of i-PRF on the number of odontoblast, cementoblast, osteoblast, osteocyte, and osteoclast cells.

MATERIALS AND METHODS

The samples consisted of 20 male albino rabbits and were divided randomly into the control group (5 rabbits) and i-PRF groups (15 rabbits) sub-divided into week 1, week 2, and week 3 sub-groups. The labial surface of lower right incisors was marked by drilling a hole at the level of the free gingival margin in the mid-line of each tooth with a small round bur, and the eruption rates were measured by measuring the distance from the most apical point of the free gingival margin and the center of the hole with a digital caliper. i-PRF was prepared by centrifuging autologous blood of each rabbit at 1000 rpm for 5 minutes; then the i-PRF layer was collected. The control group received no treatment, whereas i-PRF groups received i-PRF in the following manner: For week 1 groups, a single dose was given at 0 day; for week 2 groups, double doses were given at 0 and 7 days; and for week 3 groups, three doses were given at 0, 7, and 14 days. At the end of experiments for each group, animal scarification was performed, and histological steps were performed.

RESULTS

There was a significant increase in the rate of tooth eruption in i-PRF groups when compared to the control group, and the eruption rate was increased in 107.3%, 144.7%, and 167.5% for week 1, week 2, and week 3, respectively. Concerning the histological finding, the i-PRF groups gave rise to a higher number of odontoblast, cementoblast, osteoblast, osteocyte, and osteoclast cells with a significant difference when compared to the control groups (P ≤ 0.05).

CONCLUSIONS

Applying i-PRF significantly increased the rate of teeth eruption at all-time intervals. Platelet-rich fibrin injection can be an effective method for acceleration of teeth eruption.

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.

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.

Influence of botulinum toxin A on craniofacial morphology after injection into the right masseter muscle of dystrophin deficient (mdx-) mice

BACKGROUND

Severe craniofacial and dental abnormalities, typical for patients with progressive Duchenne muscular dystrophy (DMD), are an exellcent demonstration of Melvin L. Moss "functional matrix theory", highlighting the influence of muscle tissue on craniofacial growth and morphology. However, the currently best approved animal model for investigation of this interplay is the mdx-mouse, which offers only a limited time window for research, due to the ability of muscle regeneration, in contrast to the human course of the disease. The aim of this study was to evaluate craniofacial morphology after BTX-A induced muscle paralysis in C57Bl- and mdx-mice, to prove the suitability of BTX-A intervention to inhibit muscle regeneration in mdx-mice and thus, mimicking the human course of the DMD disease.

METHODS

Paralysis of the right masseter muscle was induced in 100 days old C57Bl- and mdx-mice by a single specific intramuscular BTX-A injection. Mice skulls were obtained at 21 days and 42 days after BTX-A injection and 3D radiological evaluation was performed in order to measure various craniofacial dimensions in the sagittal, transversal and vertical plane. Statstical analysis were performed using SigmaStat®Version 3.5. In case of normal distribution, unpaired t-test and otherwise the Mann-Whitney-U test was applied. A statistical significance was given in case of p ≤ 0.05.

RESULTS

In contrast to C57Bl-mice, in mdx-mice, three weeks after BTX-A treatment a significant decrease of skull dimensions was noted in most of the measurements followed by a significant increase at the second investigation period.

CONCLUSIONS

BTX-A can induce changes in craniofacial morphology and presumably partially inhibit muscle regeneration in mdx-mice, but cannot completely intensify craniofacial effects elicited by dystrophy. Further research is necessary in order to fully understand muscle-bone interplay after BTX-A injection into dystrophic muscles.

Effect of multiple injections of botulinum toxin into painful masticatory muscles on bone density in the temporomandibular complex

Background

Adverse effects of masticatory muscle injections of Botulinum Toxin (Btx) have been noted in animal and, less dramatically, human studies.

Objective

Among women treated in multiple community‐based private practices, to compare TMJ bone density and mandibular condylar volume between patients with myofascial TMJD receiving multiple masticatory muscle Btx treatments and similarly diagnosed women not receiving such treatment.

Methods

Cohorts consisted of women whose treatment charts indicated a diagnosis of myofascial TMJD: 35 received at least 2 Btx treatment cycles; 44 received none. Bone density at pre‐specified regions of interest (ROI) was defined by grey scale values from Cone Beam CT, adjusting for a fixed density phantom included in each scan. Mean bone density and mandibular condyle volume were compared between groups. Dose‐response effects were tested within the Btx‐exposed group.

Results

The mean density of primary and secondary ROIs was similar between exposure groups, as was condylar volume. Among Btx‐exposed women, increasing dose of Btx to the temporalis muscle was inversely proportional to the density of the trabecular area of the mandible body. Many Btx‐exposed women received smaller doses of Btx to the masseter muscles than in most TMJD Btx clinical trials.

Conclusion

Masticatory muscle injections of Btx failed to produce clinically significant TMJ bone‐related changes. Should Btx receive regulatory approval for treatment of myofascial TMJD, a phase IV study is recommended to evaluate potential adverse effects of Btx on bone and muscle when administered at higher doses and/or for more treatment cycles.

[Long-term stability and relapse of deep bite correction: a systematic review]

INTRODUCTION

 Deep overbite is one of the most common malocclusions and is the most difficult to treat successfully. The real challenge remains the stability of long-term deep overbite correction. A search through the scientific literature revealed only one systematic review on this subject. Given the recent publications on the stability of deep bite correction and the development of new processes designed to avoid relapse of these treatments, this one existing systematic review needs to be updated. The purpose of the present systematic review is to evaluate the long-term stability of deep overbite correction.

MATERIALS AND METHODS

 Electronic databases were searched and nonelectronic journals were manually explored for papers on long-term stability and relapse of deep overbite correction. Articles deemed appropriate for inclusion in this review were selected and analyzed. Their scientific quality was assessed and the data they contained were extracted and summarized.

RESULTS

 The rate of deep overbite relapse was 47.27%. Patients treated with the straight wire appliance showed a 67.74% relapse rate whereas those treated with the Ricketts biological progressive segmented mechanics appliance displayed a 30.38% rate. Subjects treated towards the end of adolescence presented a 14.3% rate of deep overbite relapse whereas those treated in their early teens or in adulthood had a deep overbite relapse rate of 30% and 30.8%, respectively. Intramuscular injections of botox helped obtain 100% stability in maxillofacial surgery to correct deep bite.

CONCLUSION

 Age at initiation of treatment and treatment technique are two factors impacting the long-term stability of deep overbite correction.

Compensatory dentoalveolar supraeruption and occlusal plane cant after botulinum-induced hypotrophy of masticatory closing muscles in juvenile rats

OBJECTIVE

The purpose of this study was to investigate changes in the dentoalveolus and occlusal plane associated with the hypotrophy of unilateral masticatory muscles following botulinum toxin (BTX) treatment in the juvenile period of rats.

DESIGN

We hypothesized that the loss of functional loading of masticatory muscles and occlusal force invites compensatory dentoalveolar supraeruption, accelerating occlusal cant and skeletal asymmetry. In order to confirm this hypothesis, six-week-old male rats (N = 5) were treated with BTX simultaneously at the unilateral masseter, temporalis, and medial pterygoid muscles, with a booster injection after six weeks for the experimental group. The control group (N = 6) had saline injections on both sides at the same sites and on the same schedule.

RESULTS

After 12 weeks, masseter and medial pterygoid muscles on the BTX side showed hypotrophic change. The mandibular structure was asymmetrical, with decreased size and lateral tilting. The maxillary and mandibular molars were supraerupted from the Frankfort plane or mandibular inferior border with lateral tilt. They accompanied downward occlusal plane cant resulting from the supraerupted maxillary and mandibular molars on the BTX side. The dentoalveolar structural changes included diminished alveolar bone density, narrow periodontal ligament space, and disorganized distribution of periodontal collagen fiber.

CONCLUSIONS

Unilateral hypotrophy of masticatory muscles affected the growth, symmetry, and structure of the skeletal jaws and dentoalveolus. Our hypothesis about the dentoalveolar compensation, that muscular hypotrophy was closely integrated with dentoalveolar supraeruption and an inclined occlusal plane, was confirmed.

Correction of Malocclusion by Botulinum Neurotoxin Injection into Masticatory Muscles

Botulinum toxin (BTX) is a neurotoxin, and its injection in masticatory muscles induces muscle weakness and paralysis. This paralytic effect of BTX induces growth retardation of the maxillofacial bones, changes in dental eruption and occlusion state, and facial asymmetry. Using masticatory muscle paralysis and its effect via BTX, BTX can be used for the correction of malocclusion after orthognathic surgery and mandible fracture. The paralysis of specific masticatory muscles by BTX injection reduces the tensional force to the mandible and prevents relapse and changes in dental occlusion. BTX injection in the anterior belly of digastric and mylohyoid muscle prevents the open-bite and deep bite of dental occlusion and contributes to mandible stability after orthognathic surgery. The effect of BTX injection in masticatory muscles for maxillofacial bone growth and dental occlusion is reviewed in this article. The clinical application of BTX is also discussed for the correction of dental malocclusion and suppression of post-operative relapse after mandibular surgery.

S100 and p65 expression are increased in the masseter muscle after botulinum toxin-A injection

Background

The purpose of this study was to compare the expression levels of p65 and S100 in the rat masseter muscle after the injection of different concentrations of botulinum toxin-A (BTX-A).

Methods

We injected either 5 or 10 U of BTX-A into both masseter muscle of rats. As a control group, the same volume of saline was injected. After 14 days, the animals were sacrificed. Subsequently, a biopsy and immunohistochemical staining of the samples were performed using a p65 or S100 antibody.

Results

The cross-sectional area of each myofibril was significantly reduced by BTX-A injection (P < 0.001). The expression of p65 and S100 increased significantly with increasing concentrations of BTX-A (P < 0.001).

Conclusions

The injection of BTX-A into the masseter muscle induced muscle atrophy. Subsequently, p65 and S100 expression in myoblasts were increased for the protection of muscle cells.

Bone and cartilage changes in rabbit mandibular condyles after 1 injection of botulinum toxin

INTRODUCTION

Temporary paralysis of the masseter muscle caused by botulinum toxin is a common treatment for temporomandibular disorders, bruxism, and muscle hypertrophy. Loss of masseter force is associated with decreased mandibular mineral density. Our objectives were (1) to establish whether bone loss at the mandibular condyle is regionally specific and (2) to ascertain whether the treatment affects the condylar cartilage.

METHODS

Young adult female rabbits received a unilateral masseter injection of botulinum neurotoxin serotype A (BoNT/A, n = 31), saline solution (n = 19), or no injection (n = 3) and were also injected with bromodeoxyuridine (BrdU), a replication marker. The rabbits were killed at 4 or 12 weeks after treatment. The condyles were processed for paraffin histology. Cortical thickness, cartilage thickness, and trabecular bone areal density were measured, and replicating cells were counted after BrdU reaction.

RESULTS

The BoNT/A rabbits exhibited a high frequency of defects in the condylar bone surface, occurring equally on the injected and uninjected sides. Bone loss was seen only on the side of the BoNT/A injection. Cortical as well as trabecular bone was severely affected. The midcondylar region lost the most bone. Recovery at 12 weeks was insignificant. Condylar cartilage thickness showed no treatment effect but did increase with time. The numbers of proliferating cells were similar in the treatment groups, but the BoNT/A animals showed more side asymmetry associated with the condylar defects.

CONCLUSIONS

Bone loss may be a risk factor for the use of botulinum toxin in jaw muscles.