Quantitative assessment of cleft volume and evaluation of cleft’s impact on adjacent anatomical structures using CBCT imaging

Cleft lip and/or palate (CL/P) defects are the most frequent congenital abnormalities found in the craniofacial area [1]. According to a recent systematic review [2], global prevalence is 0.45 per 1000 live births. Orofacial clefts are caused by a developmental disturbance of the maxilla and palate in the first three months of gestation and have a multifactorial etiology. They can be isolated non-syndromic clefts, or a part of a syndrome [3]. The condition has physical, aesthetic, psychologic, and emotional consequences. It can affect speech and cause malocclusion, as well as become a reason for mockery in school [4]. The classification of these malformations has three main categories: cleft of the lip only, cleft of the palate only, and cleft of both lip and palate [4]. A multidisciplinary team of specialists is required for management [1], which is a long-term process [5] with the main goal of re-establishing feeding and speech capacities as well as aesthetics [6]. Alveolar bone grafting is a surgical procedure performed when the patient reaches mixed dentition [5], between 9 and 12 years of age [7]. Autogenous bone grafts are used to repair the clefts of the maxillary alveolar process with the main goal being to bond the segments of the maxilla to close the oronasal fistula [7]. The outcome of the bone transplant must be appraised before orthodontic treatment is begun [5].

Ionizing radiation presents a higher risk to children and adolescents than adults. The tissues of children and adolescents replicate at a faster rate and are thus more vulnerable to DNA damage. Furthermore, children and adolescents have a longer post-exposure life expectancy than adults, thus providing more time for tumors to develop [8]. Consequently, when deciding the necessity of radiation exposure to children and young persons, a strict consideration about the need in every case should be applied [9, 10]. Radiographic imaging plays an important role at different phases during the treatment process in children and adolescents with orofacial clefts for different diagnostic questions. Oenning A. et al. list important clinical indications in CL/P cases: location, shape, size, and volume of the defect; eruption control of adjacent teeth; nasal cavity involvement; and treatment plans for bone grafts and orthognathic surgery [10]. After treatment, radiographic imaging is used to monitor healing, follow up tooth eruption, and plan subsequent treatment of residual clefts [10]. Cone-beam computed tomography (CBCT) produces multiplanar cross-sectional and 3D reconstructions [8]. The effective dose of CBCT is lower than of computed tomography (CT), but still much higher than traditional dental radiographs [8]. In fact, a recent study has reported that CBCT could be responsible for cytotoxic and genotoxic effects on buccal mucosa cells in children and adolescents. Thus, CBCT cannot be considered a risk-free examination [11]. According to SEDENTEXCT (safety and efficacy of a new and emerging dental X-ray modality) guidelines, CBCT is preferred over multi-slice computed tomography (MSCT) for cleft assessment, with the smallest necessary volume size selected [12]. Nevertheless, like any other radiographic modality, CBCT should never be a routine examination [8]. Use of ionizing radiation should always follow the principle of ALADAIP (as low as diagnostically acceptable being indication-oriented and patient-specific) [13]. A recent study demonstrated how an ultra-low-dose CBCT protocol provided sufficient image quality in the radiographic evaluation of children and young persons with alveolar clefts, both before and after alveolar bone grafting. This was a radiation dose reduction of approximately 70% when compared to the standard-dose CBCT protocol. Structure visibility was similar in the two protocols [14]. Regardless, and when necessary, the 3D evaluation that CBCT provides is a clear advantage over other radiographic methods in cases of CL/P [15]. CBCT is able to portray thickness and height of the alveolar bone, particularly on the buccal and palatal sides. Conventional, 2D dental radiography cannot provide such information [16]. Furthermore, the previous studies have demonstrated how pre-surgical knowledge of the exact volume of bone graft needed can improve surgical results [17‐19]. Complications, such as postoperative pain, nerve injury, and pelvic instability due to the pelvis being the graft donor site, increase the risk of donor site morbidity [19]. According to de Rezende Barbosa et al., using 3D imaging to evaluate the entire cleft and determine its dimensions is more accurate than any other method [17]. Thus, several ways of calculating cleft volume by CBCT examination have been presented [19]. However, a few clinical studies have assessed cleft volume and evaluated surrounding vital anatomical landmarks in a large group of participants.

The aim of this study was to use CBCT imaging to determine pre-operative cleft volume and evaluate the impact on surrounding anatomical structures in children and adolescents with uni- and bilateral orofacial clefts. Our hypotheses were that there is a large variation in cleft volume and that clefts influence the morphological development of adjacent anatomical structures.

Fifty-four of the cleft cases were unilateral clefts, of which 40 were examined with CBCT before, and 14 after alveolar bone graft surgery. Fourteen cases were bilateral clefts, of which 13 were examined with CBCT before, and 1 after alveolar bone graft surgery.

The present study found that CBCT appears to be feasible for volumetric assessment of alveolar clefts and their impact on anatomical landmarks in the region and supported our hypothesis of large variations in cleft volume. The same software used to assess volume is also able to produce a 3D model of the clefts, which can supplement pre-surgical planning and aid in explaining treatment for the patient and legal guardians. These are further uses of pre-operative CBCT examinations, if indicated. Previous studies have found that diagnostic information on alveolar cleft volume prior to alveolar bone grafting seems to improve surgical outcomes [17, 19]. An incorrect amount of graft material can cause various problems, such as graft failure or undue resorption [18]. The systematic review of Kapila and Nervina concluded that CBCT allows accurate assessment of cleft volume, which is optimal for planning alveolar bone graft surgery, by determining the precise amount of bone necessary [23]. The present study calculated pre-operative cleft volume using the CTAn software with CBCT examinations exposed in a clinical setting. A previous study successfully tested different volumetric assessment methods, although in plastic phantoms [17]. Mean unilateral cleft volume (1.08 cm³) was significantly higher than mean bilateral cleft volume (0.76 cm³; p < 0.001). The amount of space available for each cleft in a bilateral cleft case may explain our finding. However, different orthodontic treatment approaches can also impact cleft volume due to expansion of the maxilla. Furthermore, the large variation in cleft volume that we found has clear implications for the pre-surgical planning of alveolar bone grafting with suitable radiographic modality, that is in most cases 2D radiographs. The present study also used the retrieved CBCT examinations to analyze different anatomical landmarks in the region, which can be useful for clinicians. Our hypothesis here was that clefts influence the morphological development of adjacent anatomical structures. The systematic review of De Grauwe et al. considered CBCT to be excellent for monitoring the development of teeth adjacent to the cleft area and root morphology as well as evaluating the outcome of alveolar bone graft surgery. All of the above can be achieved in a CBCT exam with a lower radiation dose and better image quality than CT [24]. The incisive canal is an anatomical structure located anteriorly in the hard palate, connecting the oral and nasal cavities. It makes space for the nasopalatine nerve and the sphenopalatine artery [22]. The incisive foramen is the buccal opening of the incisive canal [25]. Both identification and evaluation of the incisive canal before surgical interventions in the area are important for their success, and prevention of complications [25]. Thus, the incisive foramen is an important anatomical landmark for alveolar bone graft surgery. It is important for surgeons to know the exact location of this nerval opening. In the present study, the incisive foramen was not visible in the majority of cases with bilateral clefts, and the difference was significant. Caution is recommended in these cases. The cleft can in fact involve or be situated in the incisive canal [25].

Closing the cleft lip and palate negatively affects growth, and subsequently, the morphology of the nose in terms of a deviated septum and hypertrophic nasal turbinate [25]. That could be observed in the present study. A deviated septum has been known to affect normal respiration [26]. Deviation and deformity of the nasal septum are usually present in patients with CL/P [27], and some nasal airway problems will persist, even after surgical treatment [28]. Moreover, the nasal obstruction and mouth-breathing resulting from a deviated septum can cause malocclusion [29, 30]. Septum deviation can also be the reason for esthetic problems in young patients with CL/P [29]. In the present study, the nasal septum in the majority of cases with unilateral clefts was curved towards the cleft or graft side, which is in line with the previous studies [27, 29, 31]. Using CBCT, the Jiang et al.’s study reported that the degree of nasal septum deviation was significantly related to the severity of the cleft [29]. Deviation of the septum to the cleft side causes narrowing of the nasal cavity on that side, and as a result of the concavity, widening on the non-cleft side [31]. Furthermore, evaluating nasal asymmetry is important in the treatment of patients with CL/P, to improve function and aesthetics [29]. The turbinates or conchae are major anatomical structures located within the walls of the nose. Their functions include respiration, filtration, and humidification. Conditions like deviation of the nasal septum can cause obstruction of the nose and affect turbinate functioning [26]. Inferior turbinate hypertrophy (ITH) occurs in patients with CL/P defects. ITH is particularly troublesome, since it causes a reduction in healthy nasal area, and leads to nasal obstruction on both sides. Development of the maxillofacial skeleton may become disturbed [32]. The present study has shown that the mean size of the widest part of the inferior turbinate was greater on the non-cleft side when compared to the cleft or graft side, which agrees with other studies [32, 33]. ITH usually develops on the opposite side of the deviated septum due to increased airflow through the unobstructed nostril [34], which would explain our finding. Pinto et al.’s study reported finding a substantial degree of ITH and nasal airway dysfunction in patients with unilateral CL/P [32]. The present study has shown that the position of the nasal floor on the graft side of 71% of the cases with unilateral clefts was inferior to the nasal floor on the non-cleft side. Such pre-surgical information should be useful for the plastic surgeon who is planning secondary corrections of the nose.

CBCT is, when required, a useful radiographic method in cleft cases. However, for the post-surgical control, usually made 6 months after alveolar bone grafting, a recent study has shown that CBCT is not required as a complement to the 2D radiograph, if graft failure can be observed clinically, or if the 2D radiograph shows an open residual cleft [35].

When required, CBCT is a feasible method for quantitatively illustrating alveolar clefts and their impact on the morphological development of surrounding structures. Variation in cleft volume was large.