There is an intuitive association between clefts including the alveolar ridge and dental agenesis or hypoplasia in that specific area. Many case–control studies evaluated the type and number of dental anomalies compared to the healthy population to show that patients with CL/P are more likely to be affected by several kinds of aberrations concerning the dental system. Two meta-analyses from 2012 and 2021 have addressed the issue and came to the same conclusion: evidence suggests that a higher number of dental anomalies is noted in individuals born with orofacial clefts [18, 19].

Various explanations are used for this correlation. On the one hand, the failed fusion of the maxillary and medial nasal prominences might lead to mesenchyme insufficient to develop into a healthy tooth [7]. The anatomic defect of the cleft might lead to insufficient calcification of the lateral incisor in the cleft area. Another factor to be considered is the early surgical interventions for reconstruction of lip and palate, that might impair the development and calcification of the anterior teeth crowns and induce teeth displacement and rotation in the posterior region [7, 20, 21]. A study by Korolenkova et al. assessed the role of external etiological factors in the development of dental anomalies and found a significant relation between their prevalence and the treatment protocol. Early orthodontic therapy to reposition the maxillary segments and reduce soft tissue tension, palatal defect after primary palatoplasty and primary periosteoplasty each had a significant effect on the prevalence of dental aplasia, hypoplasia and frontal teeth enamel defects [22]. The evaluation of prevalences of dental anomalies might therefore also allow the comparison with other collectives to rule out excessive external influences in one clinic.

On the other hand, the higher incidence of dental aplasia outside the cleft region points in the direction of underlying genetic causes. Evidence suggests that some genetic variations might induce both orofacial clefting and hypodontia, supposedly by affecting the regulation of ectodermal-mesenchymal signaling pathways [23,24,25]. Ultimately it is most likely an intricate combination of internal and external factors resulting in a high prevalence of various dental anomalies in patients with CL/P. Nonetheless, many of the studies evaluating the correlation between orofacial clefts and dental anomalies excluded cleft variations that did not affect the alveolar ridge (cleft lip only, cleft palate only) [19]. Our data showed for patients with CPO, that the prevalence of aplasia in secondary dentition was higher than in the healthy European population [26], but no patient showed supernumerary teeth. Supernumerary teeth in patients with CL + A or CLP occurred in the cleft area only. This might indicate, that while dental aplasia in patients with CL/P is at least partly caused by genetic variations, supernumerary teeth develop mainly due to the physical interruption of the alveolar ridge.

Dental aplasia of the permanent dentition was seen most often in the maxillary lateral incisors, but was also found in maxillary and mandibular premolars, maxillary medial incisors and very rarely in any other tooth (Fig. 1). In our collective the change of teeth showed no noticeable deviation from the norm, which contradicted one of our working hypotheses.

While there is a large body of literature on the causes of dental agenesis and aplasia, the therapeutic implications of dental anomalies in the treatment of patients with CL/P have been discussed rarely. Maxillary hypoplasia is a common finding in patients with CL/P and to this day, there is no consensus about its reasons. Postsurgical scarring of the palate has been found to contribute to the maxillary growth inhibition whereas the effect of lip surgery seems to be of smaller impact [13, 14], and has on the contrary been discussed to induce maxillary growth [15]. Missing lateral incisors clearly have been found to play a major role in the development of the maxilla [16, 17]. Our data shows a higher need for orthodontic treatment and also for orthognathic surgery compared to cleft patients without dental aplasia. The high prevalence of dental anomalies (> 90%) in patients in need of orthognathic surgery confirms the theory that dental agenesis correlates with maxillary hypoplasia and might even predict the need for Le Fort I advancement in cleft patients [17].

In any case one must consider that dental anomalies might correlate with the cleft width and severity, thus the higher treatment need might be partly caused by a more complex initial situation [26, 27].

For parents and caregivers of patients with orofacial clefts the question of anomalies to be expected in the permanent dentition usually arises at an early age. We could show that the occurrence of aplasia in the primary dentition in cleft patients significantly increases the probability of dental aplasia in the permanent dentition. In general, we found a higher frequency of dental aplasia in the permanent dentition compared to the primary dentition, which is in accordance with the literature [28]. This applied to all cleft entities (Table 1). The opposite relationship was observed for supernumerary teeth: while no case was observed in patients with CPO, patients with CLP or CL ± A showed a significantly higher prevalence of supernumerary teeth in the primary compared to the permanent dentition.

Patients with a left-sided or bilateral cleft of any manifestation presented with a significantly higher risk for aplasia of permanent dentition and supernumerary teeth of primary dentition than patients with other cleft entities. This is in contrast to Möller et al. whose results suggest that right-sided clefts of patients with CLP are more susceptible to supernumerary teeth [26].

In summary, the generally high frequency of dental anomalies differs significantly between patients with different cleft entities and also between primary and secondary dentition. While dental aplasia occurs mainly in the cleft area, it appears-with a reduced frequency-in the whole maxillary and mandibulary dentition. Supernumerary teeth on the other hand were documented in the cleft region only, suggesting that while orofacial clefts and dental aplasia share some underlying genetic mechanisms, the connection between orofacial clefts and supernumerary teeth is mainly mechanical. Dental anomalies, especially dental aplasia, significantly increase patients’ need for orthodontic therapy and orthognathic surgery. Physicians involved in the treatment of patients with orofacial clefts need to be aware of the high frequency of dental anomalies and the therapeutic implications in this patient population.