Abstract
In this study the authors evaluate and quantify the residual bony defect in the mandibular symphysis and its effect on the soft tissue contour a minimum of 1 year after harvesting chin bone. 59 ASA I cleft lip and palate patients, aged 8–19 years were included. In all patients an autologous bone graft from the mandibular symphysis was harvested for transplantation to the alveolar cleft. Lateral cephalograms were used to measure the donor site defects, and the effects on the soft tissue contour. An evident residual defect was measured at the donor site 1 year after harvesting chin bone. A significant relation was seen between age at time of surgery and size of the defect 1 year postoperatively. In older patients a larger defect remained. Using the current surgical technique of harvesting chin bone, complete bony repair of the defect was not achieved. This study shows postoperatively persisting defects that comprise on average 14% of the original peroperative defects. A significant increase in soft tissue thickness was seen at the mandibular symphysis at a minimum of 1 year postoperatively. These changes in the soft tissue chin contour 1 year after harvesting bone are similar to normal growth changes.
Several donor sites have been described for harvesting autologous bone grafts for the treatment of an alveolar cleft in cleft lip and palate (CLP) patients . Autologous bone harvested from the mandibular symphysis has favourable properties; its ectomesenchymal and membranous origin enables it to maintain its volume and viability due to early vascularization , it responds well to orthodontic loading of the alveolar process , and as a donor site it has low objective and subjective morbidity . This makes the mandibular symphysis the first choice donor site in many cleft centres .
After the harvesting procedure, the bony defect can be filled with a biologically resorbable gelatine sponge (Spongostan ® ) to restrict bleeding, to provide platelet rupture and to support fibrin threads . Although studies show limited and acceptable postoperative morbidity, a number of patients experience sensory loss, pulp obliteration and/or necrosis due to apical damage after the harvesting of chin bone . Lateral cephalogram analysis from 1 year postoperatively onwards, frequently shows a residual defect in the mandibular symphysis. Donor site morbidity is an inherent side effect of harvesting chin bone , thus challenging investigators to seek suitable allograft alternatives for the repair of alveolar clefts.
The aim of this study was to evaluate and quantify this residual bony defect in the mandibular symphysis, and the effect of harvesting chin bone on the soft tissue contour of the chin at a minimum of 1 year postoperatively.
Methods and materials
92 consecutive CLP patients operated on between 2001 and 2006 were examined. 33 patients were excluded because of incomplete data, earlier operations in the chin region, or severe co-morbidity, such as diabetes or a congenital syndrome. Ultimately, 59 patients with unilateral or bilateral CLP who underwent a surgical procedure to harvest chin bone for repair of the alveolar cleft were included. The study group comprised 39 males and 20 females: 24 right-sided, 17 left-sided and 18 bilateral CLP patients. The mean age of the patients was 12 years (range 8.4–19 years). All patients underwent a standardized surgical procedure to harvest the chin bone graft. Surgery was performed by four surgeons who all used the same surgical technique.
Surgical procedure
The buccal cortical surface of the mandibular symphysis was approached through a horizontal incision in the vestibule of the lower lip within the intercanine region. After dissecting a submucosal flap, an incision was made through the mental muscles on each side and down to the bone. After elevating the muco-periosteal flap the mental nerve was localized on both sides. Using the position of the apices of the incisors and the germs or roots of the permanent canines as seen on preoperative orthopantogram, the outline of the bone graft was marked with a fissure burr. The monocortical bone graft was sawn out with a reciprocal saw, irrigated with physiological saline solution 0.9%, and harvested using a chisel. To collect the maximum amount of bone, the remaining cancellous bone within the symphysis was harvested using excavators. A biologically resorbable gelatine sponge (Spongostan ® ) was used to fill the bony defect . Closure was achieved by approximating the periostium and both mental muscles to their origins with a Vicryl ® 2-0 suture (Ethicon, Johnson & Johnson Intl.); the mucosa was closed with a Vicryl ® 4-0 running mattress suture. Directly postoperatively the chin was taped with elastic tape to minimize swelling from oedema and restrict haematoma formation. The tape was removed after 72 h.
To prevent wound infection, a standard prophylactic antibiotic regime of clindamicyn (Hameln Pharmaceuticals, 31789 Hameln, Germany) 10 mg/kg per 24 h was prescribed for 48 h postoperatively. A soft diet was prescribed to prevent wound dehiscence.
Evaluative methods
Standardized digital lateral cephalograms were used to evaluate and quantify the bony defect. Adobe Photoshop 9.0 was used to adjust the radiographs for proper analysis. The mandibular and maxillary regions of each lateral cephalogram were selected, resulting in a detailed image of the mandibular symphysis with a standard image size of 6.5 cm × 8.3 cm at a resolution of 300 DPI. To measure the bony defect directly postoperatively and at a minimum of 1 year postoperatively, digital tracings were made. To achieve maximal standardization and restrict variability to a minimum, each tracing included a number of cephalometric hard-tissue landmarks ( Fig. 1 ): Menton (Me), the most inferior point of the mandibular symphysis; Gnathion (Gn), the most anterior inferior point of the bony chin in the midsagittal plane; Pogonion (Pog), the most anterior point of the bony chin in the midsagittal plane; B-Point (B), the deepest (most posterior) midline point on the bony curvature of the anterior mandible; Infradentale (Id), the most superior anterior point on the mandibular alveolar process between the central incisors .
Each tracing included the mandibular symphysis including the defect if present. The ventral outline of the defect was standardized by tracing a straight line ( Fig. 2 ) from the caudal labial border to the cranial labial border of the defect. The size of the defect area was calculated by counting the number of pixels making up the defect as well as the number of pixels depicting the whole symphysis in the same radiograph. In this way the postoperative defect ( Fig. 2 ) could be expressed as a percentage of the symphysis. Using this method it was also possible to calculate the size of the residual defect 1 year or more after surgery ( Fig. 3 ) and to compare it with the defect directly postoperatively.
To analyse the effect of harvesting chin bone on the soft tissue at a minimum of 1 year after surgery, the authors used the same detailed images of the mandibular symphysis. Digital tracings of the soft tissue contour were made preoperatively, and at a minimum of 1 year postoperatively. The thickness of the soft tissue was measured by tracing a perpendicular line on to every tangent line of four standardized hard-tissue landmarks: (1) Me; (2) Pog; (3) the centre of the defect; and (4) B-point. Each perpendicular line (soft tissue thickness) was measured digitally ( Fig. 4 ).
The study group consisted of 59 patients but because complete data were not available for all patients, the data were analysed in three groups (A, B and C) ( Table 1 ).
| Preoperative and 1 year postoperative cephalograms | Postoperative and 1 year postoperative cephalograms | 1 year postoperative cephalograms | |
|---|---|---|---|
| Group A ( n = 59) | Comparison of the residual defect with the mandibular symphysis | ||
| Group B ( n = 23) | Comparison of the postoperative defect with the residual defect after 1 year | ||
| Group C ( n = 31) | Analysis of the effect of chin bone harvesting on the soft tissue thickness after 1 year |
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