Surgical management of masseteric hypertrophy and mandibular retrognathism.

Masseter hypertrophy is a rare condition. It is mostly idiopathic with no known cause. It is recognized as an enlargement of one or both masseter muscles. Most patients complain of facial asymmetry; however, symptoms such as trismus, protrusion, and bruxism may also occur. This article reports a case of bilateral masseter hypertrophy with retrognathic mandible in which comprehensive treatment was rendered to the patient by using a combination approach.

INTRODUCTION

Masseter hypertrophy is recognized as an asymptomatic enlargement of one or both masseter muscles. In majority of the cases the etiological factor is unknown therefore it is considered to be idiopathic. Although numerous factors such as malocclusion, bruxism, clenching, or temporomandibular joint disorders, have been cited, they have not been proven conclusively.

The differential diagnosis includes parotiditis, parotid tumor, lipoma, benign or malignant muscle tumors, vascular tumors, benign, and malignant mandibular tumors; thus correct diagnosis is more difficult in unilateral cases.[1] Idiopathic masseter muscle hypertrophy (IMMH) was first described by Legg in 1880.[23] The highest incidence for this condition is in the second and third decades of life with no gender predilection.[3] A congenital variety also exists, but acquired masseter hypertrophy is more common. In most cases of masseter hypertrophy it is bilateral and symmetric, but asymmetry is not unusual. Unilateral occurrence can also be seen when patients chew or clench primarily on one side.[42] The masseter muscle is essential for adequate mastication and is located laterally to the mandibular ramus, and thus plays an important role in facial esthetics. A hypertrophied masseter will alter facial lines, generating discomfort, and negative cosmetic impacts in many patients. Muscle function may also be impaired, thus introducing conditions such as trismus, protrusion, and bruxism.[2] Masseter hypertrophy leads to the prominent mandibular angle which is considered to be aesthetically unacceptable.[5]

CASE REPORT

A patient aged 23 years reported to the Department of Oral and Maxillofacial Surgery at Darshan Dental College and Hospital complaining of bilateral increase in the size of the mandibular angle region with onset 2 years prior to the visit. The patient claimed that the area was growing slowly and steadily, but there was no pain. Clinical examination revealed a soft tissue mass over the right and left body, near the angle of the mandible, which became more prominent when the patient clenched the jaws. Mandibular movements were in the normal range. There was no history of facial trauma, dental abnormalities or temporomandibular joint clicking, and family history of masseter hyper-trophy. The patient had no history of systemic diseases. Physical examination revealed that the patient had bilateral masseter muscle bulging giving a squarish facial appearance with a prominent mandibular angle at the lower border with increased lower facial width and a deep mentolabial sulcus [Figure 1 and 2]. Intraoral examination revealed angles class 2 div 1 malocclusion [Figure 3] With increased overjet and overbite, spacing in the maxillary anterior teeth and buccally placed 44. Mandibular third molarswere missing. OPG showed a prominent mandibular angle [Figure 4]. The AP view revealed broadening of the mandibular angle. Lateral cephalogram analysis revealed an anteroposterior deficiency of mandible. Data from clinical and radiographic exami-nation led to the diagnosis of bilateral idiopathic masseter muscle hypertrophy with retrognathic mandible. Surgery was offered for cosmetic reasons. Bilateral reduction of bone at the mandibular angle and an anterior repositioning of mandible by 8 mm were planned.

Figure 1

Preoperative frontal view

Figure 2

Preoperative occlusion

Figure 3

Preoperative OPG

Figure 4

Postoperative lateral profile

Technique

The operation was performed under general anesthesia with nasotracheal intubation. Xylocaine 2% with adrenalin was infiltrated and using a standard protocol the area was exposed. Sagittal split osteotomy was performed. The neurovascular bundle was carefully dissected and deviated to the distal fragment. Distal fragment is pulled and lower border osteotomy done by using surgical bur. Excess bone was removed [Figure 5] and sharp margin was trimmed with a bone file. A similar procedure was carried out on the contralateral side. Debulking of the masseter muscle was not performed as the removal of bone alone is sufficient to produce atrophy in the muscle, due to reduction of the area available for attachment. With 8 mm of mandibular advancement fragments are fixed with stainless steel miniplate in both sides. Mandibular movements were checked manually. Primary closure was done with 3-0 black silk. A pressure bandage and ice pack were applied. The patient was under regular follow-up for the next 6 months and there were no associated complications.[Figures 6–9]

Figure 5

Postoperative occlusion

Figure 6

Postoperative OPG

Figure 9

Postoperative frontal view

Intraoperative

Preoperative lateral view

DISCUSSION

There are various treatment modalities for the management of masseteric hypertrophy. This can be categorized into nonsurgical and surgical. Management of the idiopathic masseter hypertrophy is based on psychological coun-seling, use of mou-th guards, – muscle relaxant, and anxiolytic drugs, analgesics, physical therapy, dental restorations, and occlusal adjustments to correct premature contacts. A good result can be achieved in the patients with mild hypertrophy but there is no reliable report on the literature on the success rates of isolated clinical therapy.[2] Injection of botulinum toxin type A into the masseter muscle was first introduced by Smyth, Moore, and Wood in 1994 and considered a less invasive modality for the treatment of muscle hypertrophy.[4] Local injection of very small doses of the toxin into a muscle produces local paralysis and therefore, individual muscles can be selectively weakened and atrophy of the muscle occurs.[3] Perhaps the biggest disadvantage of botulinum toxin therapy is that the treatment effect wears away and reverts to the original condition in 6 months. Unlike surgical excision of muscle tissue that reduces the actual number of muscle cells, botulinum toxin type A only reduces muscle volume temporarily.[1]

Surgical treatment was proposed for the first time by Gurney in 1947. The procedure consists of a submandibular incision and the removal of 3/4 to 2/3 of all muscle mass.[2] Mandibular angle osteotomy was suggested by Adams in 1950. Removal of the masseter muscle insertion by means of a triangular incision was done by Martensson in 1950 in a patient with history of bruxism and unilateral masseter muscle hypertrophy.[2] Beckers in 1977 surgically treated 17 patients using the intraoral approach in which internal muscle band was removed from the hypertrophied mas-seter. Wood in 1982 proposed a surgical technique in which he removed the bony protuberance of the mandibular angle without removing any parts of the masseter muscle.[6] Da Cruz et al. (1994) believe that the intraoral approach offers lower risk of infection and better cosmetic results.[2]

In the beginning, the extraoral approach was widely indicated, because it offered better visualization. However, with the development of new surgical materials and techniques (rotation instruments, surgical saws, specific retractors, and, more recently, intraoral endoscopy), the intraoral approach has become a good option. Since the chief complaint reported by the patients is the facial appearance, the scar produced with the extraoral approach is undesirable. The intraoral approach has a number of advantages, such as the avoidance of a visible scar in a mainly esthetic procedure, incision in a field of surgery at a safe distance from the marginal branch of the facial nerve, and bony resection without cutting the masseter-pterygoid sling.[6]

In our case report the patient has reported with the complaint of a bilateral increase in the size of the mandibular angle. Based on the clinical, radio graphical, and model analysis we concluded the diagnosis of bilateral messeteric hypertrophy and mandibular retrognathism. In this case combination surgery has been employed. This obviates the need of second surgery for the correction of mandibular retrognathism. With a single surgery treatment of masseteric hypertrophy and mandibular advancement have been carried out which is probably the first of its kind.