INTRODUCTION

The alveolar bone graft (ABG) is an essential procedure in the overall management of patients with cleft bony defect. The objectives of ABG are to stabilize the upper dental arch, to give a bony support for the teeth adjacent to the cleft area, to support the lip and the nose, and to close the residual oronasal fistula.12

Although a number of treatment protocols have been established for ABG according to donor site and surgical timing,3–5 early secondary ABG with the particulate cancellous bone and marrow (PCBM) from the anterior crest of the iliac bone (ACI) is preferable because of the abundant amount of bone material and good bone induction ability,6 and it is known not to induce the iatrogenic effects on the maxillary growth.27 However, it has been reported to have various success rates, ranging from partial improvement to complete correction.127

The vertical levels of the cleft bony defect and the grafted bone at the site of ABG have been evaluated traditionally by 2-dimensional (2D) radiograph, such as periapical, occlusal, and panoramic radiographs.26–9 However, the inability to assess the volume, labiolingual morphology, density, and architecture of the grafted bone are main disadvantages inherent to this method. In addition, it is difficult to investigate change in the aforementioned variables because of limited reproducibility before and after ABG.

Recently, 3-dimensional computed tomography (3D-CT) has been used for clinical evaluation and follow-up assessment of ABG using linear measurements in various planes and volumetric analysis.2610–16 Compared with 2D conventional radiography, 3D-CT offers better accuracy and improved quality of image without superimposition of the anatomic structure. For individual treatment planning, 2-D images were not reliable in all cases. Therefore, to overcome the disadvantages of reproducibility in 2D analysis of ABG, it is essential to use 3D-CT analysis with the proper reference points, lines, and planes.

Because a number of factors are involved with the success or failure of ABG, a prospective study is needed to remove surgeon-related, surgical timing–related, donor site–related, and cleft type–related biases. Most previous studies1214–16 using 3D-CT have simply compared postoperative grafted bone volume with the preoperative alveolar bony defect. In addition, there have been few studies concerning 3-D changes of height and labiolingual thickness in the cleft bony defect and the grafted bone using 3D-CT.

The purposes of this prospective study were to evaluate the outcome and follow-up of early secondary ABG with PCBM from ACI in unilateral cleft lip and alveolus (UCLA) and unilateral cleft lip and palate (UCLP) by estimating the change of height, labiolingual thickness, and volumes using 3D-CT and to investigate the factors affecting the results of ABG.

MATERIALS AND METHODS

Inclusion and exclusion criteria of the sample in this study were as follows. Patients with UCLA or UCLP were included, but patients with bilateral cleft lip and palate (BCLP) were excluded because they had a wide range in severity of the cleft on both sides, and it was impossible to compare cleft areas with noncleft ones. None of the subjects had other known syndromes. After presurgical expansion of the upper arch had been carried out with a removable expansion appliance, the upper arch was stabilized by a 0.9-mm lingual arch of stainless steel wire 1 or 2 weeks before ABG and were removed 3 months after ABG. All of the subjects received the early secondary ABG with PCBM taken from the ACI to eliminate biases related to surgical timing and donor site. Procedures were done by one surgeon with experience in the field of cleft surgery to exclude surgeon-related biases.

The sample consisted of 10 UCLP patients and 5 UCLA patients (11 males and 4 females; mean age = 10 years) (Table 1). No patient dropped out from the treatment protocol. The upper lateral incisor in the cleft area existed in 4 patients (Table 1). The lingual process in the cleft bony defect was present all UCLA patients (Table 1, Figure 1A); However, not all UCLP patients had the lingual process (Table 1, Figure 1B).

Table 1.  Demographic data^a

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3D-CT (Sensation 10, Siemens, Munchen, Germany) was used to evaluate the height, labiolingual thickness, and volume of the cleft bony defect and the grafted bone. Scans were obtained 1 month before (T0), 3 months after (T1), and 12 months after ABG (T2) because the volume of the grafted bone tended to decrease between 3 and 12 months.12 CT scans were taken with the axial plane parallel to the maxillary occlusal plane and with a 0.75-mm slice thickness from the nasal cavity to the maxillary occlusal plane. The obtained axial data were processed and transformed into 3D views using V-Works 4.0 program (Cybermed Inc, Seoul, Korea).

Height

The height is shown in Figures 2 and 3 and Table 2. In Plane 1, the labiolingual midpoints of the alveolar bone were subsequently constructed from the right upper second molar area to the left one to make Line 1 (L1). In the panoramic view based on L1, the vertical reference line (L2) and the horizontal reference line (L3) were drawn. The lower height was measured from the lowermost point (P6) to L3 and the upper height was measured from the uppermost point (P7) to L3.

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Table 2.  Definition of reference points, lines, planes, and measurement variables

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Labiolingual Thickness

The labiolingual thickness is shown in Figure 4 and Table 2. In Plane 1, the posterior reference line (L4) and the labial side reference line (L5) were drawn. The labial and lingual thicknesses were measured from the labial point (P10) to L5 and from the lingual point (P11) to L5, respectively. The labial and lingual thicknesses in the higher axial section (Plane 2) were measured using the same method.

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Volume

Volume is shown in Figures 5 and 6 and Table 2. The areas with different density could be displayed with different colors using V-Works 4.0 program (Cybermed Inc, Seoul, Korea). At T0, the cleft bony defect area could be demarcated according to difference in density and consideration of the alveolar bone outline of the noncleft site. At T1 and T2, the grafted bone area could be defined according to different density.15 The volume was calculated by V-works 4.0 program after demarcation of the area in the axial (Figure 6A), coronal (Figure 6B), and sagittal planes (Figure 6C) in 3D data. Axial planes were parallel to the maxillary occlusal plane and measured with 0.75-mm slice thickness from the nasal cavity to the maxillary occlusal plane. The total volume (Figure 6D) was divided into the upper and lower sections relative to L3.

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Initial mesio-distal width

The initial mesio-distal width is shown in Figure 7 and Table 2. At T0, the initial mesio-distal width of the cleft bony defect was measured as the shortest distance between lines of the greater (L6) and lesser (L7) segments at plane 1 (Mean = 3.24 mm; SD = 1.80 mm).

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Measurements were taken by a single operator. All of the variables of the 5 patients were reassessed again after 4 weeks by the same operator to evaluate intraoperator variability and by another operator to evaluate interoperator variability. Wilcoxon signed rank test demonstrated that there was no statistically significant difference in intraoperator and interoperator measures, respectively (both P > .05). For statistical analyses, the Mann-Whitney test, Wilcoxon signed rank test, and linear regression analysis were used.

RESULTS

Vertical Height

There was no significant difference in upper and lower heights at T1 and T2 and at resorption amount (RA) between UCLA and UCLP patients, respectively (Table 3). However, the upper height of the grafted bone was significantly decreased from T1 to T2 compared with the lower height in UCLP patients and the total sample (P < .01, Table 3).

Table 3.  Comparison of the grafted bone height between UCLA and UCLP patients and between upper part and lower parts^a

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The presence or absence of the upper lateral incisor (ULI) in the cleft area did not affect the height or RA of the upper and lower parts (Table 4). However, in the patients who did not have ULI, the upper height of the grafted bone was significantly decreased from T1 to T2 compared with the lower height (P < .01, Table 4).

Table 4.  Comparison of the grafted bond height according to pres ence or absence of the upper lateral incisor in the cleft area^a

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Labiolingual Thickness

The labiolingual thickness (LLT) of the grafted bone tended to decrease in both labial and lingual sides during T1–T2. Although the grafted amount in the labial side was not different between UCLA and UCLP patients, there was more resorption of the labial side of UCLA patients than UCLP ones in plane 2 (P < .01, Table 5). However, in the lingual side, the grafted amount and the resorption amount showed an opposite tendency even though there was no significant difference between UCLA and UCLP patients.

Table 5.  Comparison of change in the labiolingual thickness of the grafted bone between UCLA and UCLP patients and between planes 1 and 2^a

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During T0–T1, in the total sample, changes of the lingual thickness were more in plane 2 than in plane 1 (P < .05, Table 5). However, there was no statistically significant difference in changes of the labial and the lingual thickness during T1–T2 between planes 1 and 2. These findings mean that the PCBM was grafted more in the higher level (plane 2) than the lower level (plane 1) during T0–T1 and remained relatively stable at both levels during T1–T2.

In patients in whom ULI was missing, the grafted bone amount of the lingual side in the cleft bony defect was significantly larger in plane 2 than plane 1 (P < .01, Table 6). Although there was no significant difference in changes of the LLT between the presence and absence of ULI in Planes 1 and 2, changes of LLT during T0–T1 and T1–T2 tended to be more in patients in whom ULI was missing (Table 6).

Table 6.  Comparison of change in the labiolingual thickness of the grafted bone according to the presence or absence of the upper lateral incisor in the cleft area^a

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Volume

There was no significant difference in the amount (RA) and rate of resorption (RR) of the upper and lower parts of the grafted bone volume between UCLA and UCLP patients (Table 7). However, there was an opposite tendency in RA and RR between the upper and lower parts of the grafted bone volume. The absolute value, RA, was significantly larger in the lower part than in the upper (P < .05, Table 7) while the relative value, RR, was larger in the upper part than in the lower (P < .01, Table 7). And in UCLP patients, RR was significantly larger in the upper part than in the lower (P < .01, Table 7).

Table 7.  Comparison of change in the grafted bone volume between UCLA and UCLP patients and between upper and lower parts^a

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Presence of the ULI in the cleft area did not affect RA and RR of the upper, lower, and total volume of the grafted bone (Table 8). However, in the patients with missing ULI, RA was significantly larger in the lower part than the upper (P < .05, Table 8) and RR was significantly smaller in the lower part than the upper (P < .01, Table 8).

Table 8.  Comparison of change in the grafted bone volume ac cording to presence or absence of the upper lateral incisor in the cleft area^a

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Initial mesio-distal width

The initial mesio-distal width of the cleft bony defect did not show any correlation with the height, LLT, and volume of the grafted bone (Table 9).

Table 9.  Correlation between the initial mesio-distal width of the bony cleft defect and the amount and rate of resorption of the grafted bone^a

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DISCUSSION

Resorption of the grafted bone could occur because of excessive tension in the mucoperiostal flap resulting in inadequate coverage in the early stage12 and absence of physiologic stress because of congenital missing ULI in the later stage.1217 Because the alveolar bone can only exist when teeth are present, Kearns et al18 attempted to overcome the issue of missing teeth adjacent to the cleft by placing implants into the grafted area. Sufficient labiolingual thickness of the alveolar bone might be important for proper implant installation and normal eruption of the upper canine in the grafted bone areas. Arctander et al15 found that a longer interval between the bone graft and implant placement was associated with a greater likelihood of alveolar bone resorption. The eruption path of the upper canine could be influenced by the amount of bone in the labiolingual direction and the presence of the ULI, which could guide the eruption path.

In the present study, the upper height of the grafted bone was significantly decreased compared with the lower height during T1–T2 (P < .01, Table 3). However, eruption of the upper canine during T1–T2 can introduce functional stress to the lower part of grafted bone and prevent resorption of the lower height in the grafted bone or can result in increased vertical growth of the alveolar bone.12719 On the contrary, presence of ULI did not affect the upper and lower height of the grafted bone (Table 4) because ULI had a decreased bone-induction ability when it was almost erupted or already erupted at the bone graft stage.

Although Tai et al13 insisted that it was difficult to distinguish the grafted bone from the surrounding alveolar bone in volumetric analysis of cleft patients 1 year after surgery, the results of the present study indicated that it was clearly possible to discern between grafted and surrounding bone because there was a sharp difference of bone density between the grafted bone and the alveolar bone adjacent to the grafted bone until the T2 stage. Our findings were in accord with those of Arctander et al.15

There was an opposite tendency with respect to RA and RR of the grafted bone volume between the upper and lower parts of the bone graft (Table 7). The reason for these results could be an opposite direction of resorption in grafted bone between the upper and lower parts, eruption of the upper lateral incisor or canine into or adjacent to the grafted bone, and effect of gravity on the grafted bone particle (PCBM) during healing.

In this study, unilateral cleft type (UCLA vs UCLP) and presence of ULI in the cleft area did not affect the change in height and volume of the grafted bone (Tables 3, 4, 7, and 8). However, the finding that more resorption of the grafted bone occurred in the UCLA patients than in the UCLP patients during T1–T2, in spite of similar amounts of grafted bone in plane 2 (P < .05, Table 5), means unilateral cleft type might affect the change in labiolingual thickness of the grafted bone. The lingual process in UCLA patients could play a role to support packing and/or condensation of the grafted bone. Therefore, the reason why there was more resorption in the labial thickness of the grafted bone of UCLA patients seems to be overpacking and/ or excessive condensation of the grafted bone, which could result in a limited blood supply to the center area of the grafted bone.

In this study, initial cleft width did not show any significant correlation with the change of height, LLT, and volume of ABG in UCLA and UCLP patients (Table 9). It was in accord with other studies920 that reported that presurgical cleft width had little or no impact on the success of ABG. Excessively large cleft width can affect the survival of osteoprogenitor cells in the center of the grafted area because revascularization is more likely to fail.921 Therefore, proper arch expansion before ABG could guarantee an easy surgical manipulation of the flap and, eventually, would not diminish the probability of ABG success. However, in aspects of variability of the mesio-distal width through the axial levels according to height, further study considering this point will be necessary.

Abyholm et al19 explained the poor ABG results in BCLP patients because of wide and large cleft bony defect and mobile premaxilla. Therefore, the reasons why there was no significant difference in changes of the height and volume of the bone graft between the UCLA and UCLP patients in this study might be the fact that this study did not include BCLP patients and that all UCLA and UCLP patients wore a lingual arch to stabilize the maxillary arch. The reason for removing the lingual arch at the T1 stage was that conventional orthodontic treatment usually started to align the maxillary anterior teeth at that time. To prevent constriction of the bone grafted area, a widened archwire and/or open coil spring was used in the maxillary arch.

The lack of significant findings could be attributable to the small size of samples and inherent variability. Therefore, further studies of an increased number of patients with a longer follow-up period will be necessary.

CONCLUSIONS

• Unilateral cleft type and presence of ULI in the cleft area did not affect the change in height and volume of the grafted bone.

• Initial mesio-distal width of the cleft bony defect was not correlated with change in the height, labiolingual thickness, and volume of the grafted bone in unilateral cleft patients.

• Overpacking and/or excessive condensation of the grafted bone would not be necessary in UCLA patients with the lingual process because of more likelihood of resorption in the labial side of the grafted bone.