The new method for the classification of alveolar cleft morphology presented in this study was able to cover all kinds of morphology types in clinical, and the intuitive classification pattern could be convenient for clinical application. In the past, periapical radiographs were the most frequently used 2D imaging modality to assess cleft morphology, and many radiographic scales have been developed for cleft defect description[4, 15, 20, 22, 28]. Cleft width was the most commonly used parameter of initial cleft defect in literature, though some studies assessed cleft width in different levels, but it could only reflect the characteristics of cleft defect in vertical dimension, which neglect the labial-palatal direction condition. While the importance of the cleft defect status in labial-palatal direction pre- and post-operatively has been emphasized because a high amount of resorption was normally present in the horizontal plane. Therefore, the new method for the classification of alveolar cleft morphology in this study was summarized after observing a large sample of preoperative CT images of UCLA/UCLP patients, and considering the limitations of the previous researches simultaneously. Based on the initial cleft defect reconstructed from 3D images, the morphology was divided into five types according to the different characteristics in labial–palatal and nasal–occlusal dimensions.
Significant correlation between cleft morphology and SABG outcomes suggested that the chances of a successful procedure are best when the patient has type I or IV morphology, in which the shape is like a funnel in the relatively palatal or occlusal area towards the vertical dimension. Three cases in our study showed a relatively high BFR (62.15%, 67.38%, and 80.54%), but CBCT showed that the bone bridge existed only in the apical 1/4 area and the nasal area. Although the width of the defect was reduced after SABG, there was no effective bone bridge at other levels, which explains the failure of a successful outcome in patients with a relatively high BFR. The morphology of the cleft defect of these three cases had one common feature: the minimum width was located in the middle part of the defect in both the sagittal and vertical planes, termed the funnel type morphology. Cases with the funnel type morphology resulted in increased complexity of the bone grafting procedure in the middle part of the defect, and failed formation of a successful bone bridge in the middle part prevents tooth movement. Our aim was not to derive a formula for accurate categorization of morphology but rather to identify possible outcome associations in patients who require an optimized surgical plan because of their high likelihood of failure.
Varying SABG outcomes among different cleft morphologies suggested that an individualized surgical approach based on cleft morphology was required, rather than strict adherence to a pre-established protocol. Previous studies have suggested that patients with a cleft width less than 2 mm may benefit from expansion surgery before SABG. In this study, a good/moderate outcome was seen in 57.9% of cases with type IV (n = 11) morphology, whereas a poor/failure outcome was seen in 42.1% of cases with type IV morphology. At the same time, we found that the funnel part existed at the relatively palatal, occlusal area in the moderate/good result cases, while significantly narrow defect in the relatively labial, nasal area might add up the difficulty for SABG because of the worse surgical field and surgical approach, thus lead to a poor/failure result. In 19 patients with type IV morphology, the outcome included 2 failure, 6 poor, 5 moderate and 6 good results, while all failed cases had failed construction at 7mm level. An irregular funnel type makes adequate bone grafting difficult and increases the risk of bone resorption in the funnel and adjacent areas. Orthodontic treatment before SABG in patients with type IV morphology where its funnel part existed at the relatively labial area and apical area, might improve the surgical condition for SABG afterwards. By removing the deciduous teeth adjacent to the funnel area, or moving the twisted incisor close to the cleft area towards orthodontic treatment before surgery might improve the cleft morphology and provide better surgical field and surgical approach. Types II and III were relatively rare in our study, and all such cases had a low BFR and were classified as failure/poor. Type V cases included those with extremely irregular morphology. Supernumerary, ectopic, or severely twisted teeth in the cleft site were responsible for this, and removal of these unnecessary, obstructed teeth at least 1 month before SABG (ensure the healing of extraction area) may help transform the irregular morphology to a regular type which would be beneficial for bone bridge formation.
3D radiographic imaging is superior to 2D imaging for evaluating the bony support of the teeth adjacent to the cleft[7, 31, 32], and is also reliable for assessing the volume and thickness of the bone bridge[8, 32]. In the past, satisfactory outcomes (up to 95%) had been reported in literature according to 2D evaluation methods, but with the consensus of using 3D evaluation methods instead of 2D in recent years, though outcomes were much poorer, it had reflected the architecture of bone defect and unsatisfactory bone formation along the labial-palatal axis. 2D techniques can’t display the 3D morphology of the alveolar cleft pre- and post-surgery, and they tend to overestimate the success rate of SABG[35, 36].
Both categorical and continuous methods should be used for 3D radiographic assessments in patients undergoing SABG. The former provides an objective basis for further orthodontic treatment, and the latter provides 3D visualization of the direction of orthodontic movement. Based on the evaluation methods above, statistics showed that the outcome of SABG was not satisfactory in most cases. Only 21 patients (40.4%) demonstrated a good result, while 8 patients (15.4%) had no bone bridge formation at all assessment levels. One of the main objectives of SABG is the formation of a bone bridge, allowing tooth eruption and subsequent orthodontic tooth movement. Stasiak et al. found no bone bridge in 46.43% of the measurement sites on the cleft side. In this study, it was 33.2%. The results may be due to a larger sample size and the impact of different study group selection. In general, bone bridge formation exhibited better formation at the apical level (7mm and 9mm assessment level) compared with the occlusal level (3mm and 5mm assessment level). Unqualified oral hygiene maintenance after SABG or infection around the suture might add up the possibility of more bone resorption at the occlusal level. There was evidence that orthodontic tooth movement stimulates bone apposition, it was not necessary for the bone thickness to be at least the root width of the adjacent teeth, and bone resorption in the most inferior 1/4 level was acceptable. Furthermore, in 5 patients, it was found that root length of the central incisor at the cleft side was less than 9mm due to higher probability of malformation, thus bone bridge assessment at the level of 9mm was compared with the root diameter measured 0.5mm beneath the apex, though the scores at this level were all above 2, but they might face higher risk of root resorption in the orthodontic treatment after SABG procedure.
BFR results indicated a relatively great amount of bone resorption in most patients. A reconstruction of the cleft defect could be generated after segmentation for the surgeon and orthodontists to have a better understanding of the bony architecture. A comparison of the reconstructed images of the alveolar cleft defect before and after SABG allows visualization of the resorption site [25, 35, 40]. Though BFR is the most commonly used evaluation tool for SABG procedure nowadays, a completely restored alveolar cleft defect was not the indicator of success. Some degree of bone graft resorption is compatible with a successful outcome, as long as it allows tooth eruption. However, percentage ratios do not provide a spatial assessment of the bone bridge architecture, whether orthodontic movement would be available afterwards could not be decided according to BFR only.
The results of our study are similar to those of previous studies suggesting that sex, age of the patient and type, side of the cleft and volume of bone defect do not affect the SABG outcomes[7, 11, 42]. The interference from confounding factors cannot be excluded, which may make determination of the accurate correlation difficult. Though the optimal age for SABG is 9–11 years, when the canine roots are one-half to two-thirds formed. However, due to childhood diseases, presurgical orthodontic treatment, or a lack of parental cooperation, the surgeries were often performed at the later age in clinical. There was no significant correlation between patient age and SABG outcome. Age was taken into account as a confounding factor in this study, through subgroup analysis of patients aged 9-11 years, same results were found. Despite some studies have reported that younger patients may have a higher rate of graft survival, but these studies were based on 2D imaging, which is inaccurate and may lead to erroneous assessment of outcomes. The timing of SABG should take into account the patient’s age as well as the position and developmental stage of the canine root in the cleft side. If the initial cleft size is relatively large, distraction osteogenesis may be an alternative.
Compared with previous reports, this study presented a new method for the classification of alveolar cleft morphology. By combining the categorical and continuous evaluation methods together, enabled a more precise examination of the outcomes of SABG. These evaluations provide further information on the morphology and need for multi-disciplinary treatment based on the morphology of the cleft defect. Despite the possibilities of orthodontic movement after SABG in some patients, bone defects still existed in the majority of cases. Slow orthodontic movement with strict periodontal control is always suggested.