Abstract
In this technical note we share our experience of mandibular midline distraction, a powerful tool in orthognathic surgery. The use of a tooth-borne distractor and a minimally invasive surgical procedure to perform the midline osteotomy is discussed.
In our population, retrognathism and transverse mandibular and maxillary deficiencies are not uncommon. Transverse skeletal hypoplasia is reflected in wide lateral vestibules, the so-called buccal corridors, severe anterior crowding, and tipping and impaction of the anterior teeth.
Gunbay et al. stated that in orthodontic patients, an adequate sagittal and transverse mandibular dimension with an upright tooth position centrally in the bone, are important factors to obtain a stable occlusion without an increased risk of gingival recession.
The surgical treatment of skeletal mandibular deficiency in the sagittal plane has been highly successful using conventional sagittal split procedures. In correcting transverse mandibular deficiencies, however, orthodontists have limited options. Since the mandibular symphysis fuses at the age of 1 year there is no skeletal widening. Therefore, orthodontic expansion of the mandibular arch is at high risk of relapse. The only alternatives for the orthodontist are tooth extractions and interproximal enamel reduction.
Ilizarov described distraction osteogenesis in 1954, and ever since, this technique has gained increasing popularity. It was not until the 1990s that mandibular midline distraction was offered as a treatment option for correcting mandibular transverse hypoplasia.
A novel, minimally invasive surgical approach to mandibular midline distraction in conjunction with the use of a tooth-borne distraction device is discussed.
Technique
Preoperative procedure
In order to avoid damage to the roots of the central incisors during the osteotomy, the roots of these teeth are diverged using fixed appliances on the lower dentition. Very light wires (012–014) and an open coil spring are used. In the case of severe crowding, only the two central incisors, canines, and premolars are engaged with the wire. The orthodontist starts this preparative treatment approximately 3 months prior to surgery.
At 2 weeks preoperatively, a custom-made tooth-borne appliance (Hyrax-type distractor) is fabricated and cemented to the first premolars and first molars (Multi-Cure Glass Ionomer Band Cement, Unitek – 3M, Zwijndrecht, Belgium) ( Fig. 1 ).
When the orthodontist deems the patient to be ready for surgery, a cone beam computed tomography scan (CBCT) is done, allowing the surgeon to evaluate the anatomy of the jaw, the distance between the roots of the central incisors, and the presence and position of third molars, which are usually removed during the same surgical procedure as the mandibular midline osteotomy.
Surgical intervention
For the comfort of the patient, the surgery is performed under general anaesthesia (nasotracheal intubation). The patient is placed in a supine position with the head placed in a horseshoe head rest, mounted on an operating table equipped with a trapezoidal extension plate, allowing the surgeon to sit close to the patient. Local anaesthetic is injected in the mental region (lidocaine 10 mg/ml + adrenaline 1/200,000). The facial skin is disinfected using 1% Hospital Antiseptic Concentrate and 70% ethanol. The patient is draped in a standard manner and the oral cavity is disinfected and rinsed (2% chlorhexidine digluconate solution).
The surgeon is positioned behind the head of the patient and the lower lip mucosa is exposed by the assistants using a double skin hook and two retractors. A short vertical incision is made through the lower lip frenulum, inferior to the mucogingival junction ( Fig. 2 ). A sharp incision is then made through the periosteum at the midline.
A sub-periosteal dissection is then performed between the two mental muscles and a Freer retractor is placed over the symphysis at the mandibular midline, retracting the lower lip caudally. The mandibular midline osteotomy is performed with a 0.3-mm oscillating saw, starting at the mandibular border and continuing upward as high as possible interdentally ( Fig. 3 ). The osteotomy is then finalized with a 4-mm chisel. The mobility of the mandibular halves is checked and the distractor is then activated by about 2 mm to make sure that there are no bony interferences. The distractor is then deactivated. The wound is closed in two layers: the periosteum and supra-periosteal tissues are sutured with a 4–0 resorbable monofilament suture and the mucosa is closed using a fine braided 6–0 absorbable suture ( Fig. 4 ).
