The aim of this study was to evaluate the position of the maxillary canines and the associated displacement tendency in a population of German orthodontic patients with a non-syndromic craniofacial disorder compared to a healthy control group without any craniofacial disorder in the Department of Orthodontics at XX. This is a novel approach regarding the group of patients with craniofacial disorders like RS and CL/P in Germany. Regarding the maxillary canine position evaluated according to the sector subdivision, both patients with and without craniofacial disorder showed no displacement tendency. Regarding the assessing method of the inclination angle, there was a statistically significant higher displacement tendency in patients with craniofacial disorder of the maxillary canine. When comparing both evaluation methods they showed different results in displacement tendency, potentially due to the fact that the methods differ from each other extensively and already have been described controversially in literature. Warford et al. showed that the sector building is the reliable value of malpositioned and impacted teeth and the angulation is a robust parameter for this purpose [39]. Several groups had shown that the sector score parameter in combination with the angulation of the canine to the lateral incisor and the midline were powerful and reliable values [38, 40]. Thus, it is recommended that the linear angle measurement in PAN, like in this study, should be combined with the additional assessment of the canine sector position [28, 41]. In the present study, there were no significant connection between the two parameters. As already mentioned, only the inclination angle showed a statistically significant result between the craniofacial disorder group and the healthy ones. This could be due to the fact of the presence of a CL/P. In the current literature, the alpha angle according to Ericson and Kurol is the most commonly used parameter to determine the angulation of the canine in patients with CL/P [24, 42]. Hereman et al. set the predictive cut-off value in patients with CL/P at an angle between the canine and the midline larger than 23.8 degrees [43]. Westerlund et al. determined a value larger than 30 degrees, likewise [44]. The group of Russel and McLeod even decreased this value with an angle more than 45 degrees [45]. Rizell et al. used a modification of the angulation and sector measurements of Ericson and Kurol adapted to dental anomalies occurring in patients with CL/P [38, 46]. They have shown that cleft canines requiring surgical exposure had an increased angulation and canines on the cleft side had an increased angulation angle. These results are in accordance with our study, observing a statistically increased angulation in canines of the cleft side compared to the non-cleft side. This showed that the canines of the cleft side have a higher risk for dislocation and malposition compared to the canines of the non-cleft side.
Due to the fact that this study showed conspicuous parameters of the craniofacial disorder group were the inclination angle in combination with the assessment TAC, this relationship has been statistically evaluated. The results showed that five patients had a displacement tendency and additionally, a tooth agenesis: Five patients showed a dislocation tendency without tooth agenesis. There was a close association between tooth agenesis and a dislocation tendency. These findings are consistent with the literature. Several authors described that displacement and impaction coincides with tooth agenesis, specifically the lateral incisor [28, 45, 47]. This tooth has a crucial role in guiding the maxillary canine to its correct position according to the guidance theory. On the other hand, it is to consider, that the absence of the lateral incisor is frequently associated with the occurrence of a cleft, certainly on the cleft-side. This tooth agenesis is more a characteristic sign of a craniofacial disorder and could lead to a displacement of the canine.
In the current literature, limitations of two-dimensional radiographic images have been extensively discussed, specifically considering magnification, distortion, high radiation dose and positioning errors in the anterior maxilla an overestimation of the distance of the tooth from the midline and of the angulation of the canine in PAN is described [48]. Nonetheless, the dental PAN is a valuable evaluation tool, providing an overview of the entire dentition. Furthermore, the patient is exposed to a lower radiation dose compared to a full-mouth series of intra-oral radiographs [49]. As a part of the clinical orthodontic routine, it is recommended to assess the localization of dislocated and impacted canines [50]. However, three-dimensional radiographic techniques, e. g. cone beam computed tomography, allow a much more precise determination of the teeth’s position and its relationship to adjacent tissue with a radiation dose comparable to PAN [51].
In the current study, the location of canines was assessed using visual diagnosis of the examiners, without an exact standardized scaling of the PAN. Regarding in the present study, the kappa values of the canine inclination of angle β in the first quadrant showed a very good degree of agreement and in the second quadrant showed a good degree. The remaining radiographic assessed parameters had moderate degrees of agreement for both examiners. Compared to a study about evaluation of the tooth agenesis of patients with CL/P or RS assessed by the same two examiners, like in the current study, the kappa value showed a moderate degree of agreement, likewise [52]. This study was performed under the same conditions as the current one. The PANs were obtained by both examiners independently of each other, in separate rooms and at different times. In order to assess the exact canine position, regardless of the reliability and bias of the examiner, three-dimensional images seem to be the reliable and ideal radiographic technique. In patients with CL/P, three-dimensional images are performed routinely to evaluate the dimensions of bone in the alveolus and palatal cleft. Indications for three-dimensional radiographic imaging are the assessment of bone volume before and after bone grafting or setting skeletal bone anchorage screws for an orthodontic appliance [53]. In combination to these examinations, it is useful to assess the position and the potential agenesis of the teeth to avoid additional images, increased an extra radiation and costs. This means that an interdisciplinary therapy can be planned based on one three-dimensional image and providing benefit to the patient and therapists.
The clinical records of this study showed in six out of fifty patients with a craniofacial disorder conspicuousness’s in form of persistence of a deciduous canine or a clinical displacement of the permanent maxillary canine. Even though this was not observed with the examination parameters of the PANs. In the current literature, there is no information about persistence of deciduous canines in patients with craniofacial disorder. Regarding the dentition, this might be a sign of an ectopic or impacted canine, due to the fact that there was no resorption of the deciduous canine root. In patients with CL/P it can be helpful to preserve the deciduous canine to avoid a mesial drift of teeth of the lateral segment. However, for the treating orthodontist or dentist it is important to know the right timeframe for removing the deciduous canine to provide space to the permanent tooth and a guide rail to erupt to the occlusal plane.
Considering the study design, there are certain limitations. This is a cross-sectional retrospective study which has already limitations and a reduced informative value in the results compared to a prospective study. That was reflected by data obtained from the clinical records in evaluating of the final canine displacement and in case of a spontaneously eruption or an orthodontically adjusted maxillary. Ideally, that parameters could be evaluated in a prospective study to assess the location of the canine at the beginning of the observation period and in a final step to evaluate the eruption position and the potential occurrence of a displacement. The age of the patients included in this study could have been better delimited depending on the eruption age of the canine tooth. This was not considered in order to eliminate the bias of too small patient groups. Here, the limitation of a small sample size is shown like it often happens in comparative monocentric studies with low prevalence’s of the disease patterns, e. g. craniofacial disorders and, specifically RS. In addition, a cross-sectional design had to be used. Further shortcomings were the possible overestimation in the anterior maxilla of the distance of the tooth from the midline and of the angulation of the canine in PAN. This has to be considered in the examination of the PANs. In general, a prospective longitudinal multicenter study with adjusted sample sizes and corresponding control groups should be performed to get further and comparable results. This should demonstrate to other practitioners the difficulty in treating patients with craniofacial malformations, the importance of a multiple interdisciplinary therapy, and the sense to recognize and treat possible other dental anomalies that may occur at the right timepoint.