The masseters and their treatment with botulinum toxin

20 The masseters and their treatment with botulinum toxin







History


Following on from earlier experience by Jancovic & Orman in treating other facial dystonias with botulinum toxin, investigators including Lagueny et al and Van Zandijcke & Marchau turned their attention to the treatment of bruxism. Amongst the earliest use of botulinum toxin in the treatment of bruxism associated with masseteric (and temporalis) hypertrophy was by the latter group; this was an unusually severe case of a 32-year-old woman who, following a motor car accident and brain contusion, was beginning to communicate after a prolonged coma. Although she obeyed verbal commands, she had developed severe bruxism and ‘the teeth grinding was very loud and almost continuous causing damage to the teeth and annoyance to nearby patients’. In this case 25 units were injected into each temporalis and each masseter muscle, which is, somewhat surprisingly, a similar dose to an initial dosing in todays cases. The treatment of masseteric hypertrophy soon became more widespread and today is a mainstream treatment for this condition replacing surgery in many cases. In the treatment of bruxism it has a definite place alongside and in many cases replacing splints and orthodontic techniques in selected patients.


Evidence has begun to accumulate that the masseteric hypertrophy has other effects besides the bulk it directly confers because of the muscle volume. In line with theories of bone deposition and development, Wu found in 2010 that this muscle development may have effects on the underlying bone growth and volume. Bone growth and volume are under the influence and related to the activity of the muscles attached to the bone. A bone responds to the activity and strength of the muscles attached to it by thickening and the corollary is that bone will decrease when the muscular force acting on the bone is decreased, as reported by Tsai et al. Molina et al found that the masseter neuromuscular end plates are developed by 12 weeks’ fetal gestation. By restraining mouth opening, Habib and co-workers showed by the use of suturing that restricted fetal temporomandibular joint movement influences the process of endochondral bone formation of condylar cartilage. These effects on bone may explain the trimming effect that botulinum toxin has on the facial shape may be above and beyond the effects of what would be expected by a decrease in muscle bulk alone (Fig. 20.1). However, not all authors (e.g. Chang et al) believe that bony resorption occurs after botulinum toxin injection.



One of the great determinants of beauty is facial shape. In males a square facial shape is considered desirable, but this should not be a bottom- heavy face with a wider lower face than an upper face. In females this is more of an issue, with youth and beauty being related to an oval, triangular or heart-shaped face.



Anatomy





Mar 12, 2016 | Posted by in General Surgery | Comments Off on The masseters and their treatment with botulinum toxin

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