Genetics of dental agenesis: anterior and posterior area of the arch.
Aim: The aim of this study was to evaluate whether or not dental agenesis is regulated by genes and, in those cases under genetic control, if there were differences between incisors-canines and premolars-molars in the genetic transmission of agenesis. Methods: This study was conducted on all patients who presented for a clinical evaluation in the Orthodontic Unit of the Department of Dentistry between 2001 and 2002. All patients were screened for dental agenesis. At the end of the selection process, 17 patients with dental agenesis, 6 to 20 years of age, were questioned about their family dental history for the purpose of constructing family trees and 15 family trees were constructed. The patients were questioned regarding any dental anomalies present. Panoramic radiographs, casts, and dental examinations were performed on the patients. For the patient's relatives, panoramic radiographsex and oral histories were generally collected. Results: The most often missing teeth were mandibular second premolars. On the basis of the family trees, the data allowed for the identification of two different groups: 1) 9 families had dental agenesis as a function of genetic transmission and 2) 6 families exhibited dental agenesis as a sporadic condition. In the former group of patients, agenesis primarily involved the maxillary lateral incisors. This appeared to be transmitted as an autosomal dominant characteristic, with variable expression and incomplete penetrance. In these families, both in individuals with and without agenesis, other anomalies were present, such as supernumerary teeth, microdontia, and anomalous teeth. In these cases, agenesis was one of the manifestations of an anomaly of the dental lamina, specifically mild dysplasia. In the latter group of patients, agenesis was a characteristic present only in orthodontic patients. In this group, agenesis most commonly involved the second molars and the second premolars. Conclusion: These findings indicate that agenesis of anterior teeth may depend on genes, while agenesis of posterior teeth is sporadic.
Key words: agenesis, genetics, dental anomalies
Dental agenesis is an important cause of malocclusion; if compensation does not take place, dental agenesis can cause occlusal imbalance that can result in functional changes and periodontal damage. Furthermore, the aesthetic effects can be an additional issue [Miotti, et al., 1979]. In individuals with hypodontia, the maxilla is more retrognathic due to either a shorter or more posteriorly positioned maxilla; the more upper teeth that are missing, the more often a counter clockwise rotation of the mandible occurs [Cooney, 1985]. If not treated properly, hypodontia may result in severe functional disability and cosmetic problems. In the dental management of such patients, important factors include early diagnosis of the disorder and treatment planning involving orthodontic and prosthodontic interventions. Behavioural, developmental, technical, and financial problems need to be addressed when treating these patients. Primary consideration must be given to their masticatory, aesthetic, and phonetic needs.
Because the condition presents the need for complex treatment, data on the frequency and the cause of the condition are essential for estimating costs of meeting the treatment needs [Miotti, et al., 1979]. Thus, it is important for paediatric dentists and orthodontists to ask their patients with dental anomalies about their family history. Studying family trees and clinical data can help understand the genetic basis of dental anomalies.
In the current study, family trees were constructed which showed the presence of dental agenesis, so as to examine the distribution of missing teeth, to determine if agenesis was a genetic characteristic, and to ascertain whether or not there were differences in genetic transmission in different areas of the arch and between incisor-canine and premolarmolar agenesis.
Materials and methods
Subjects. Case histories of 241 patients arriving for their first visit were evaluated in the Orthodontic Department of the Dental Clinic at Policlinic Umberto I from October 2001 to October 2002. Patients had been sent by their own dentist in order to solve orthodontic problems. Among all the patients, 27 were found to have missing teeth. Their ages ranged from 6 to 20 years; 12 patients were males (3 with a syndrome) and 15 patients were females (1 with a syndrome). Only permanent teeth agenesis was considered in this study. In the number of patients with agenesis the patients with syndromes were excluded from the study because in these cases hypodontia is one of the possible clinical manifestations of the syndrome. Christ-Siemens-Touraine syndrome, Stikle syndrome, cherubism, and ectodermal dysphasia were identified.
Family trees. Among the selected subjects, not all family trees could be constructed; therefore 17 patients were selected based on the cooperation and availability of their close relatives. Because of the inclusion of two pairs of siblings, 15 family trees were eventually drawn up. Even if each family tree extended back to include great grandparents, our focus was on the dental status of the parents, brothers, sisters, grandparents, uncles, aunts, and cousins. The patients were asked if there were people in their family with dental anomalies, agenesis, and tooth shape and size anomalies. Wide teeth agenesis was not considered for study because of their late formation, their high incidence of agenesis, and because of the controversy about the cause of their absence.
Diagnosis. The diagnosis of dental anomalies in our patients was based on panoramic radiographs, dental casts, and clinical examinations of the oral structures. For parents, brothers, and sisters, the observation was made on panoramic radiographs and dental histories while for the grandparents and other relatives, only panoramic radiographs was available for some cases; data were based largely on clinical examinations and history.
Agenesis. Dental agenesis was present in 27 out of the 241 patients for a prevalence of 11.2%, which is somewhat higher than reported in the literature (1.6-9.6%), [ Clayton., 1956; Grahen, 1956; Pindborg, 1970]. The male-to-female ratio was 3:4, also higher than that reported in the literature, [Egermark-Erikson and Lind, 1971] however; the females were missing significantly more teeth than the males. The tooth most frequently missing was the mandibular right second premolar (14.3%). The order in which teeth were most frequently missing in the sample was as follows:
1) mandibular second premolars 27.1%,
2) maxillary lateral incisors 21.4%,
3) maxillary second premolars 17.14%,
4) maxillary second molars 11.4%,
5) mandibular second molars 11.4%.
Frequency. In previous studies, the tooth most frequently missing was the maxillary lateral incisor, [Malik, 1972; Muller et al., 1970]. In other studies, and consistent with our results, the mandibular second premolar was the most frequently missing tooth, [Grahen, 1956; Serrano, 1972]. In agreement with the literature [Stritzel et al., 1990]. when the mandibular second premolars were missing, more teeth were missing, while the same relationship did not apply to the maxillary lateral incisors. The least frequently missing teeth were the maxillary central incisors, canines, first premolars, and mandibular lateral incisors and first molars. About 50% of cases exhibited a symmetric agenesis.
Family trees. Of the 15 family trees that were drawn up and analyzed. 5, the most significant, are shown as samples: they are family 1, 2, 7, 9, and 10 (figs. 1 to 5). Under each tree, dental anomalies have been reported.
The data allowed two different groups to be distinguished, one with sporadic agenesis and one with familial agenesis. Families 3, 4, 10, 11, 12, and 13 belonged to the former group. In these families, the probands were the only individuals that had dental agenesis within their own family. The most frequently missing teeth were posterior teeth, especially the second molars (15/24). In family 11, it was the tooth 3.1 (FDI notation) that was missing. In families 3, 4, 10, and 12, all second molars were missing (except tooth 3.7 in family 12 and tooth 1.7 in family 4). In family 13, all second premolars and mandibular first premolars were missing. Furthermore, even in families with familial agenesis (1, 2, 7, 8, and 9), sporadic agenesis in the posterior segments was present, especially the second molars and second premolars. In summary, sporadic agenesis predominantly involved the posterior teeth, especially the second molars, even in families with familial agenesis.
Little data were available in the literature because the incidence of second molar agenesis is extremely low in the cases reported. Lo Muzio et al.  reported that the prevalence of second molar agenesis ranges from 0% [Bracco et al., 1986] to 2.5% [Palattella et al., 1982].
Clinical cases are very rarely reported, both with respect to familial and sporadic agenesis. Among familial agenesis cases, Tal , Ranta  and Desiate and Milano  reported clinical cases. Tal  described three sisters with agenesis involving the anterior and posterior areas, probably inherited from their mother. Ranta  described a patient with congenitally absent maxillary second premolars, and first, second, and third molars. The alveolar process in the posterior area of the maxilla was totally absent. She had a slight nasality of speech and adhesive otitis media. Both her sons lacked second premolars, and first and second molars. Only one of the sons had a slight nasality of speech. Desiate and Milano  reported a case in which an individual had all second molars and upper lateral incisors missing. The same type of agenesis (except tooth 1.2) was present in his nephew. Cases with sporadic agenesis involving the molars have been reported by Eagland .
Families 1, 2, 5, 6, 7, 8, 9, 14, and 15 belonged to the group with sporadic agenesis, in which it showed a familial pattern. In families 1, 2, 7, and 9, familial patterns were present both in the mother's and the father's lineage. The most frequent anomalous teeth in terms of size, shape, and number were the maxillary lateral incisors (families 1, 2, 6, 7, 8, 9, and 15).
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Based on our findings, we have concluded that agenesis involving the maxillary lateral incisors could be determined by an autosomal dominant gene of incomplete penetrance and variable expressivity. For example, descendents of individuals with agenesis of teeth 1.2 and 2.2 in families 1, 2, and 7 exhibited agenesis or peg-shaped teeth (i.e., variable expressivity).
Incomplete penetrance was observed in families 5 and 6. Agenesis affects both males and females, and both males and females can carry the trait. Our data does not agree with that of Shulz [1932, 1934] and other authors, [Bella et al., 1984a,b] who suggested that agenesis inheritance is determined by an autosomal dominant sex-linked gene, and that females are more affected and only females can transmit the gene. Our data agree with the that of Alvesalo and Portin  as these authors held the view that the aetiology of peg-shaped teeth is probably such that they have only one (medial) lobe instead of three, so that the missing tooth, the existing tooth, and the peg-shaped tooth are different expressions of the same gene or genes. Their data also agree with Shinufvul et al. . In accordance with Grahen  and many others [Alvesalo and Portin, 1969; Svinhufvud et al., 1998] the gene is inherited as autosomal and dominant, and heterozygotes could show mesio-distal reduction [Vercellino et al., 1980]. From our findings, we noted that IV-4 from family 9 had maxillary second molars and mandibular first molars and IV-9 from family 14 had a maxillary first molar lacking a cusp; the condition is similar to a peg-shaped tooth.
From analysis of families 1, 2, 5, 7, and 8, a significant link between mesio-distal reduction and oligodontia was found. In these families, both anomalies were present. Microdontia is a dental anomaly that refers to teeth with reduced dimensions, but normal shape. Schalk et al. [1992, 1996] studied that link. They showed that the teeth of patients with oligodontia have smaller mesiodistal dimensions than in the control group. This condition especially pertains to the central and lateral incisors, and the second premolars. This size reduction of the teeth also occurs in relatives of patients with oligodontia. Even if this dimensional reduction cannot be properly referred to as microdontia, there is clearly a link between dimensional reduction and oligodontia. In our study, we could not thoroughly analyze the tooth dimensions of all relatives, but we nevertheless call attention to the existence of individuals with microdontia in families with familial agenesis.
A further observation that was very interesting in this group of families was that in some of these families, more than one anomaly was present. In addition to agenesis, supernumerary teeth (family 8), dimensional anomalies (microdontia in families 1, 2, 5, 7, and 8) and aberrant shapes (peg-shaped teeth and molars lacking a cusp in families 1, 2, 7, 9, and 14) existed; these observations are in agreement with some studies [Vercellino et al., 1981; Pokala and Acs, 1994; Svinhufvud et al., 1998] that have held the view that agenesis is a dysplastic expression of the ectoderm, even if mildly expressed.
Agenesis of anterior teeth may depend on genes, while agenesis of posterior teeth is sporadic. In some families, in addition to agenesis, supernumerary teeth, dimensional anomalies and aberrant shapes existed; these observations could suggest that agenesis is a dysplastic expression of the ectoderm, even if mildly expressed.
We are grateful to Professor Raffaella Elli of the Cellular Biotecnologies and Ematology Department for her valuable help in collecting and analyzing data.
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G. Galluccio, A. Pilotto
Dept. Odontostomatology, University of Rome "La Sapienza", Rome, Italy
Postal address: Dr A. Pilotto, Via Sicilia 32, 04019 Terracina (LT), Italy Email: firstname.lastname@example.org
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|Title Annotation:||CLINICAL RESEARCH|
|Author:||Galluccio, G.; Pilotto, A.|
|Publication:||European Archives of Paediatric Dentistry|
|Article Type:||Clinical report|
|Date:||Mar 1, 2008|
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