Progression of Grafted Bone Density in Cleft Alveolus

Patient Information and Data Collection Patients who had nonsyndromic unilateral or bilateral cleft lip and alveolus with or without cleft palate and received ABG at our center between 2016 and 2018 were enrolled. All patients underwent at least 2 CBCT scans after operation. Postoperative image acquisition was performed at two time points, namely 6 months (T1) and 2 years (T2) after ABG. The ABG procedures for all patients were performed by the same senior surgeon per the protocol of our center, which comprises an iliac cancellous bone graft and the sealing of the Scarpa fascia to the defect before the bone graft is packed.2,12 Patient who had syndromic cleft alveolus, who underwent two-stage ABG (performed for bilateral cases), or who exhibited failed grafted tissue were excluded. In total, 40 patients were enrolled in the present study. The demographic and clinical variables for ABG were retrospectively collected through a review of medical charts. All CBCT images were obtained using an i-CAT CBCT scanner (Imaging Sciences International, Hatfield, PA, USA); the parameters for the images are as follows: 120 kVp, voxel size of 0.4 × 0.4 × 0.4 mm3, 40-s scan time, and 22 × 16-cm field of view.

BMD Measurement The Picture Archiving and Communication System (PACS) was applied for image analysis. In addition, areas of interest were checked in the axial view slice by slice to locate the grafted tissue. Three methods (A, B, and C), which differed by the size of the selected area, were designed to measure Hounsfield units (HU). For all methods, we first identified the most superior and inferior planes transecting the grafted tissue. Subsequently, the middle plane of the grafted tissue was identified. For the selected plane, the distance between two teeth had to be larger than 2.5 mm in diameter; this was required for all three methods. On each plane, the selected circular area is defined as being located at the midpoint of the line between the centers of the two adjacent teeth. The HU of the selected area could be obtained using PACS.

For Method A, the circular zone located 1 mm from the adjacent teeth was selected. For Method B, the largest circular zone that exactly transected the two adjacent teeth or was tangent to the surrounding cortical bone was selected. For Method C, a circle was drawn with a diameter of 2 mm. Furthermore, an area of 2 × 0.5 mm2 in the pogonion was selected to obtain its HU at T1 and T2; this was the reference for calibration (Figure, Supplemental Digital Content 1). HU was the reference for BMD13 and represented the average density of the three planes. Calibrated BMD (BMDc, %) was defined using the following formula:

〖BMD〗_c (%)=〖HU〗_(selected zone)/〖HU〗_pogonion ×100.

Density enhancement rate (%) was calculated using the following formula:

Density enhancing rate (%)= (〖BMD〗_cT2-〖BMD〗_cT1)/〖BMD〗_cT1 ×100, where BMDcT2 is BMDc measured at T2, and BMDcT1 is the BMDc at T1. All the BMD and pogonion density data were measured by one examiner and repeated twice on different dates that were separated by a 3-month interval; the second round of measurements was conducted without reference to the first-round measurements. The average of the six sets of data (two measurements for each of the three planes) was used for the final statistical analysis.

Statistical Analysis In the descriptive analysis, continuous variables were summarized by means ± standard deviations. All variables were examined for normal distribution using the Shapiro-Wilk test. Student's t-test was performed to compare the means of continuous variables with normal distribution, and a chi-squared test or Fisher's exact test was used for categorical data. Furthermore, we performed analysis of variance with repeated measures to compare the differences between the three methods with respect to BMDc measurements and density enhancement rates in normally distributed data; for data that were not normally distributed, Friedman test was used. To compare the differences in BMDc at T1 and T2, we performed a paired t-test and a Wilcoxon signed-rank test for bilateral cleft due to small sample size. Bland-Altman plots were used to evaluate the agreement of each method. Intrarater reliability for the three methods was calculated using intraclass correlation coefficients (ICCs). All statistical tests were two-tailed, and a p value less than 0.05 was considered statistically significant. All data were analyzed using SPSS 24.0 (SPSS, Chicago, IL, USA).