Hypodontia
Patients with craniofacial clefts are often affected by various dental anomalies, such as tooth agenesis, supernumerary teeth, microdontia, taurodontism, dilaceration, ectopic eruption, impacted teeth and late dental development [11, 19]. Among these, hypodontia is the most common one. In our investigation, 50% of the cleft patients analyzed, had congenital missing teeth. This is just a little less than the 62–73% reported in comparable studies [7, 11, 13, 20]. In contrast, one study reported an even lower prevalence of 38.6% for hypodontia [21]. These differences might be influenced by the composition of the cleft population analyzed or the relatively small sample size of the groups studied. Nevertheless, the prevalence found in our examination was still ten times of the prevalence of hypodontia calculated for the permanent dentition of a healthy European population, excluding third molars (5.5%) [10]. On the one hand, the order of the prevalence of absent teeth from highest to lowest, starting with the lateral upper incisor, followed by the upper second premolar and the lower second premolar, equates to those found in other studies [7, 11, 13, 20, 22], on the other hand, some authors calculated higher percentages for agenesis of the lower second premolars than the upper ones [5, 15, 23]. We found the upper lateral incisor to be the most commonly missing tooth in cleft patients with a prevalence of 23.2%, which is in agreement with other studies reporting percentages ranging in between 20 and 28% [7, 15]. However, in the literature, for the lateral incisor, there are also reports on a prevalence of hypodontia in cleft patients ranging in between 35% and 45% [11, 13, 20, 23]. In our study hypodontia of the upper second premolar was higher (14.2%) than values found in other studies, ranging from 5.3% to 10.4% [7, 13, 20, 23, 24]. Only one other comparable study showed higher values of 20.7% [11]. This inconsistency may be caused by small sample sizes, different composition of the cleft groups or even the time and type of cleft palate operation, as this could be an important environmental influence on hypodontia in cleft patients [8]. In the mandible in our study 5.1% of second premolars were missing, which is close to data reported for a healthy European population (2.9%–3.1%) [10] and studies on cleft patients with a comparable prevalence of 1.9%–3.5% found in their investigations [7, 13]. Otherwise, hypodontia of lower premolars has been described to be 6.6%–10.3% as well [11, 20, 23, 24]. We observed an increase of the frequency of hypodontia alongside with the extend of the cleft, which is in agreement with other investigations [6, 13] (see Fig. 1), as dental disorders in cleft patients usually increase with the severity of the cleft, thus the continuity of alveolar bone tissue harboring the tooth buds becomes more susceptible to dental alterations [27]. CLA patients of our collective were affected by hypodontia in 34.5%, UCLP patients in 51.6% and BCLP patients in 70.6%. In the CLA group, hypodontia was mainly caused by missing upper lateral incisors (17.2%), whereat in patients with an UCLP, in addition to the lateral incisors (21.8%), second premolars were missing (18.6%), too. In the BCLP group, second premolars were almost as affected by hypodontia (17.7%) as in the UCLP group, but the lateral incisors were missing 2.1 times more frequently (38.2%), explaining the high values of hypodontia found in that group. In the literature, the percentage and distribution of missing second premolars in cleft individuals showed a high variety, ranging from 0.0% [24] to 4.5% [11] for CLA, 6.2% to 33.0% for UCLP [24,25,26] and 10.8% to 28.5% for BCLP patients, respectively [11, 24,25,26]. Those differences could also be explained by different sample size and composition of the cleft population analyzed, as well as ethnical differences.
Supernumerary teeth
In our study, supernumerary teeth were observed in 33.3% of cleft individuals. This result is much higher, compared to both, the calculated prevalence of supernumerary teeth in the permanent dentition of a healthy European population (1.0–2.2%) [14], and outcomes, previously reported for CL/P samples ranging in between 4.8% and 10.9% [7, 11, 13, 20, 23], but was very similar to the findings of Stahl et al., who found a prevalence of 32.2% for supernumerary teeth in the deciduous and permanent dentition of German cleft patients [6]. Our investigation revealed that in the UCLP group, right-sided clefts were statistically significant more often affected by supernumerary teeth than left-sided clefts, which is in accordance with the findings of Stahl et al., Byloff-Clar and Droschl [6, 11]. However, other studies did not confirm that right-sided clefts showed a higher risk of supernumerary teeth [7, 20]. In our cases, all supernumerary teeth found, were located in the maxillary anterior region. This is consistent with many other studies [7, 11, 13, 20, 23]. Except this, only Stahl et al. also found a supernumerary lateral incisor in the lower jaw [6]. However, in our investigation the maxillary lateral incisor was most often affected with a prevalence of 17.6%. Although these findings are higher than reports of other investigations with values of 5.9% and 12.7%, respectively [6, 11], they illustrate that in cleft patients the lateral incisor is the most frequent supernumerary tooth, followed by the central upper incisor and mesiodentes. Reports of affected upper canines can be found in the literature as well [11], but these results could not be confirmed within our study. Concerning cleft type, statistically significant differences of the prevalence of supernumerary teeth could be found in CLA patients (51.7%) and CLP patients (26.6%) (p = 0.014) (Fig. 1), which is in line with other reports of a higher prevalence for supernumerary teeth in CLA than in CLP patients [6, 7]. This could be attributed to the extend of the cleft and its effect on the epithelium, forming the dental germs. If a smaller extension of the cleft stops the epithelium from uniting, causing a supernumerary tooth, a larger cleft could cause microdontia or an even greater lack of epithelium, hypodontia [7]. That would explain the increasing prevalence of hypodontia and decreasing the prevalence of supernumerary teeth in CLP patients (Fig. 1). Interestingly Byloff-Clar and Droschl could not find such a difference [11]. Their survey on Austrian cleft patients demonstrated an equal distribution of supernumerary teeth throughout the three cleft groups with a prevalence of 9.1% for CLA, 10.9% for UCLP and 12% for BCLP patients. On the one hand, this variety in results shows the value of local data for treatment planning by surgeons and orthodontist, those dental disciplines deciding about balanced tooth extraction or gap opening for later implantation or when and which tooth to extract in case of supernumerary, not to harm other developing tooth germs. On the other hand, studies with a greater sample size would help to gain more information and a general view on the prevalence of numerical alterations in CL/P individuals. Actual data show, that pre-surgical orthodontic treatment will strongly improve bone healing after grafting and alveolar cleft repair [28]. Therefore, prevalence and location of numerical tooth alterations is very important to raise the awareness of good time to manage local dental problems in growing cleft patients.
Despite some limitations (small sample size of cleft patients and not including a non-cleft German control group, as it is difficult to include representative healthy individuals due to x-ray regulations and ethical concerns), this study helps to fill gaps in the current literature on local data on dental anomalies of German CL/P patients. For a general prevalence of hypodontia and supernumerary teeth in German cleft patients, we recommend a multi-center study. A greater sample size will help to get a clear picture of correlations between tooth count anomalies and cleft types, which might vary in small samples sizes due to different sample compositions and regional varieties.
