Secondary alveolar bone grafting has many advantages such as excellent periodontal attachment to the adjacent teeth, restoring maxillary continuity, inducing dental eruption at the cleft site, giving aesthetic improvement through gingival recovery, and minimizing the interruption of facial growth [12
]. These results can be achieved using an adequate volume of bone grafting material. An inadequate volume of grafted bone can cause graft failure, and grafting too much along with excessive compression can lead to inordinate resorption [14
]. Harvesting too much bone or repeating the procedure with a small amount can also increase donor site morbidity. For these reasons, several studies have reported on the usefulness of the preoperative estimation of the bone defect volume on the alveolar cleft using 3D CT assessment. As mentioned above, the shape and size of the bone defect of an alveolar cleft can be adjusted according to the alveolar cleft type, but the alveolar cleft type that can influence the prediction procedure has never been considered.
Therefore, this study proceeded with the hypothesis that the alveolar cleft type has a certain effect on 3D CT assessment. The results showed that the overall PEV was not statistically different from the IMV (P=0.084) in all of the groups taken together, but there was a significant difference between them in the CLP group (P<0.05). The Mann-Whitney U test with bilaterality within the CLP group showed that there was no significant difference between the UCLP and BCLP groups (P=0.197) (). The underestimated volumes by 3D CT were -0.2 cm3 in both the UCLP and BCLP groups. Considering that the overall mean value of the IMV was 1.3 cm3, -0.2 cm3 is not negligible. In several cases, after donor site repair, the iliac donor site was opened again to harvest 0.2 cm3 more bone during the operation; this can lead to donor site complications such as scarring and infection.
The size and structural disparity between the CLA and CLP group seemed to be an important factor for explaining the difference between the two groups. The mean value of the IMV (1.5±0.4 cm3
) in the CLP group was larger, by as much as about 0.6 cm3
, than that of the CLA group. This is regarded as one of the causes of the larger difference between PEV and IMV in the CLP group. The architecture of an alveolar bone defect is a pyramidal shape posteriorly bounded by an aveolus and the palate. On a reconstructed 3D image, when accompanied by a cleft palate, the bone defect was larger and extended to the hard palate (). In the past, some have advocated that strong compression and fine bony particles were necessary for a successful bone graft, but recently, several studies have reported that excessive crushing of cancellous bone can be harmful to the blood supply to the graft core and bony particles that are too tiny easily fail to revascularize and can be resorbed [14
]. Thus, we tried not to apply excessive compression in order to avoid crushing the graft, and prepared the graft with bone chips of 2×2×2 mm to induce good revascularization () [16
]. However, in the CLP group, packing the graft posteriorly tended to overpack into the soft tissue of the lingual side that had a weak support structure without strong compression (). It was thought that this phenomenon explained the significant difference between the PEV and IMV in the CLP group. Another structural disparity was the lingual process that was is a bony ridge on the lingual side of the alveolar cleft (). The process provides strong posterior support, which reduced the gap between the PEV and IMV in the CLA group. We observed the process in 13 of the 15 patients in the CLA group (87%), but only in 1 of the 32 patients in the CLP group (3%).
Sagittal view of the postoperative computed tomography scan
Preoperative computed tomography scan
There is only one study that has reported on the usefulness of 3D CT assessment for alveolar cleft in vivo
. Shirota et al. [7
] performed late secondary bone grafting in 13 patients and suggested the usefulness of preoperative CT images by using image analysis software. Their patients' mean age was 22 years and the patients were in the period of late secondary bone grafting, not the mixed dentition period. Moreover, their study did not consider the cleft type. The results of the study showed a statistically insignificant difference of -0.3 cm3
between PEV and IMV because the study only included adult patients; thus the larger margin of error could be permitted. Recently, the alveolar bone graft has been commonly performed in the mixed dentition period because the bone graft in this period never disturbs the maxillary growth, and the erupting canine gives functional stress to the graft, which increases the success rate [17
]. Our study can support future guidelines for alveolar cleft treatment because we included only the patients in the mixed dentition period with a mean age of 9.8 years and prior to canine eruption.
The 3D CT assessment is a very reliable investigation tool, but it cannot interpret the variables of soft tissue and its elasticity because it focuses on the bony structure [8
]. The purpose of this study is to demonstrate the application of 3D CT assessment clinically. As a result, the cleft type should be considered for determining the grafted volume using preoperative 3D CT assessment. Harvesting about 0.2 cm3
more bone for patients with a concomitant cleft palate is desirable based on our results.