Analysis of bone volume using computer simulation system for secondary bone graft in alveolar cleft

Abstract

The purpose of this study was to measure the bone volume necessary for secondary bone grafting in the alveolar cleft using surgical simulation software based on three-dimensional computed tomography (CT) scan data, to compare this measurement with the actual volume of the bone graft, and to evaluate consistency. The subjects were 13 patients with cleft lip and palate who underwent CT using a cone-beam CT unit (CB-CT) 1 month before surgery, followed by bone grafting with particulate cancellous bone and marrow (PCBM) to close the cleft. The bone volume necessary for grafting was measured based on the CB-CT scan data. Correlation analysis, a test of the population mean between two samples, and Wilcoxon’s signed rank test were conducted between these measurements and the actual bone volume (PCBM volume) used for grafting. SPSS was used for statistical analysis, and the level of significance was set below the 5% level. The results showed a significant correlation, with no significant differences between the two in all tests. These results suggest that measuring and preoperatively calculating the bone volume necessary for bone grafting with surgical simulation software using CB-CT scan data is beneficial.

Secondary bone grafting in the cleft area was first reported by Boyne & Sands in the 1970s. This procedure is an essential step in the overall management of patients with cleft lip and palate (CLP), and has been accepted as a means of stabilizing the segments of the maxilla, achieving continuity of the dental arch, guiding permanent teeth towards the cleft area, obliterating oronasal fistulae, and enhancing nasal base and facial appearance .

Fresh autogenous cancellous bone is ideal for secondary bone grafting due to the supply of living bone cells that integrate fully with the maxilla and are essential for osteogenesis. Donor sites for harvesting cancellous bone include the iliac crest , tibia , mandible , ribs and skull . Among these bones, the properties, the osteogenic potential and the amount that can be collected differ, so the choice of optimal donor site must consider the size and architecture of the cleft. It is important to understand the architecture of the alveolar bone defect in bone grafting the cleft area. Accurate assessment of the cleft size and calculation of the bone volume required for bone grafting based on conventional X-ray and computed tomography (CT) imaging is difficult due to individual differences and the complex three-dimensional (3D) structure. With advancements in image processing technology, surgical simulations have been performed based on CT scan data in maxillofacial surgery . With the spread of implant treatment, 3D diagnostic imaging of the jaw bone and preoperative simulation have been widely used in dental implant surgery .

This study compared the bone volume predicted using the surgical simulation software employed in implant treatment based on 3D CT scan data, and the actual bone volume used in bone grafting, and evaluated the advantages of preoperative computer simulation in bone grafts in the cleft area.

Subjects and methods

Subjects were 13 CLP patients (5 female, 8 male; mean age 22.1 years) who underwent CT using a CB MarcuRay cone-beam computed tomography unit (CB-CT; Hitachi Medico Technology Co., Tokyo, Japan) 1 month prior to surgery between 1 March 2007 and 31 March 2008, followed by secondary bone grafting in the alveolar cleft with particulate cancellous bone and marrow (PCBM) taken from the anterior iliac crest. Cleft types were 10 unilateral CLP, 2 bilateral CLP, and 1 unilateral cleft lip and alveolus ( Table 1 ). Informed consent was obtained from all patients, in accordance with the accepted ethical standards formulated in the Declaration of Helsinki of 1964.

Table 1
Subject characteristics.
Patient no. Sex Cleft type Age at bone graft
1 M UCLP 19
2 M BCLP 19
3 F UCLP 27
4 M UCLP 18
5 M UCLP 20
6 M UCLP 14
7 F UCLP 18
8 M UCLP 8
9 F UCLP 44
10 M BCLP 47
11 F UCLP 20
12 F UCLA 14
13 M UCLP 19
Mean 22 ± 11.3

UCLP: unilateral cleft lip and palate; UCLA: unilateral cleft lip and alveolus; BCLP: unilateral cleft lip and alveolus.

CB-CT scan protocol

A light beam was used to position patients with the Frankfurt plane as a reference. The position was confirmed under fluoroscopic guidance. Imaging conditions were: 100 kV tube voltage; 10 mA tube current; 192.5 mm FOV; and 0.376 mm × 0.376 mm × 0.376 mm voxel size. Projection data were collected with a device rotating 360° around patients over a total acquisition time of 9.6 s.

Calculation of bone volume for grafting based on imaging analysis

The volume function of SimPlant Pro ver. 8.1 (Materialize Dental Japan, Funabashi, Japan) was used to calculate the bone volume for grafting. Scan data from the axial cross-sectional image captured by the CB-CT device were imported into SimPlant Pro ver. 8.1. A panoramic image of the dental arch linked to the axial image and a cross-sectional image perpendicular to the panoramic arch were constructed in the alveolar cleft area. The interval between the reconstructed images was 1 mm, both in panoramic and cross-sectional images. The bone grafting range was width – alveolar bone width between adjacent teeth of the cleft, upper edge – lower margin of the anterior nasal aperture, and lower edge – alveolar edge adjacent to the cleft. The bone grafting area was traced freehand on the axial cross-sectional image while calculating the shape after bone grafting surgery in the cleft area. Alteration of the bone grafting area was arbitrarily performed in axial cross-sectional, panoramic and cross-sectional images. In tracing the bone grafting area, window level and window width were adjusted to clearly extract the border between the bone and cleft at the contacting site between the alveolar cleft and bone on the CT image. At sites with an unclear margin, where the alveolar cleft contacted the soft tissue, the grafting area was determined based on the morphology of the unaffected side and left–right symmetry. The volume was calculated based on this data ( Fig. 1 ). For calculation of the estimated value, a radiologist specializing in maxillofacial radiodiagnosis calculated estimated values in all cases three times, and the mean values were used in the study. The radiologist who performed the calculation was not involved in the surgery to avoid bias, and all information regarding analysis results was stored until the surgery was finished.

Fig. 1
Preoperative CT data showing the alveolar cleft of the maxilla. The bone grafting area is indicated in green for determining the shape after bone graft surgery in the cleft area.

Bone grafting and PCBM measurement

Secondary bone grafting was performed by two operators in charge of cleft surgery and PCBM harvesting, and these procedures were performed simultaneously with the patient in a supine position. For all 13 cases, cleft seal and the extraction of bone for grafting were performed by the same operator.

The gingiva, palatal mucosa and upper buccal sulcus were infiltrated with 1% lidocaine containing 1:200,000 epinephrine to allow for easier dissection. Following a mucoperiosteal incision along the cleft, the gingival mucoperiosteal flaps were reflected into the nasal side, and the nostril floor was restored. About 1 cm posterior to the anterior superior iliac spine, an incision was made through the displaced skin directly over the crest. An osteotome was used to elevate the cartilaginous crest while leaving it pedicled medially on its muscular attachments and perichondrium. The flap was hinged laterally, and PCBM was harvested with spoon curettes. The osteoplastic flap was replaced and secured with a 3-0 resorbable suture, and the wound was closed by layered closure. PCBM from the iliac crest was ground with blood components, and packed into an injection syringe under the same pressure as for bone grafting in the alveolar cleft ( Fig. 2 ). The value after subtracting the remaining PCBM volume after bone grafting from the harvested PCBM volume was defined as the actual graft bone volume required for bone grafting in the alveolar cleft. After PCBM was packed firmly in the alveolar cleft, the mucoperiosteal flap was replaced to cover the bone graft, and a watertight closure of the surgical site was performed.

Fig. 2
(A) PCBM from the iliac crest. (B) PCBM was placed into an injection syringe under the same pressure as for bone grafting in the alveolar cleft to evaluate actual bone graft volume.

Statistical analysis

To evaluate the consistency between the predicted bone volume obtained by the surgical simulation software and the actual bone volume used in bone grafting, the following statistical analyses were carried out with the aid of the computer software package SPSS ver. 16: hypothesis test for Pearson’s correlation coefficient; paired Student’s t -test; and Wilcoxon’s signed rank test. All analyses were treated as two-tailed tests with a significance level of 0.05.

Feb 8, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Analysis of bone volume using computer simulation system for secondary bone graft in alveolar cleft
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