The prevalence of tooth agenesis, excluding third molars, was observed at 4.89% among females and 4.07% for males, for a total of about 9% for both sexes together. This result showed a higher prevalence compared with the two previous Italian studies on this topic and confirms that hypodontia is a common developmental anomaly in Italian children. In the analysis of Lo Muzio et al., the prevalence was 5.17% [14], and according to the data of Polastri et al., the prevalence was 5.14% [15]. The sample studied by Polastri et al. included 700 national servicemen aged between 19 and 26, so it was much smaller and very different from our sample of patients. This research is the first of its kind in Italy analyzing the prevalence of dental agenesis in a sample of orthodontic patients. Comparing our results with those of a study of the non-orthodontic Italian sample, we found a slightly higher prevalence of dental agenesis (9% against 7.1%), perhaps because it is more likely that a patient with one or more missing teeth gets to an orthodontic visit.
According to literature review on the prevalence of agenesis, we could state that the range of prevalence values varies from 2.8% in the Malaysian population [19] to 12.6% in the German population [20].
Also, in the same population, different studies reported various values of prevalence: Celikoglu et al. determined prevalence of 4.6% in Turkish orthodontic patients [21] while Sisman et al. found a prevalence of 7.54% in another sample of the Turkish population [22].
The result of this study pointed out a higher prevalence in Italy than in most other countries. A higher prevalence rate was found in a few other studies: Chung et al. estimated a prevalence of 11.2% in Korean population [23] and Hunstadbraten of 10.1% in Norway [10]. A very high prevalence was also reported in two German studies (12.6% [20] and 11.3% [6]). The wide range of prevalence values observed in these studies has indicated that geographic, gender, races, and genetics differences as well as the big differences in the sample size and criteria of selection play a fundamental role in the varied results of studies of hypodontia. This wide range could make the comparison of the result of this study very limiting with other previous studies.
Polder examined a total of 28 studies and concluded that the prevalence of dental agenesis in females was almost 1.4 times higher than in males [10]. In this study, there was no significant difference between the prevalence of hypodontia in males (4.07%) and females (4.89%). Females presented a higher prevalence of congenital missing teeth, which is in agreement with the majority of reports by Grahnèn [24], Haavikko [25], Fekonja [6], and Endo et al. [8]. But Larmour et al. [26] found that in the primary dentition, there was no gender distribution, while in the permanent dentition, females are affected more frequently than males by a ratio of 3:2. In the study of Behr et al. on the German population [20] and of Laganà et al. on a non-orthodontic Italian sample [27], the percentage was equally distributed between males and females.
Usually, a patient’s first visit to a dental clinic for an orthodontic evaluation occurred between the ages of 9 and 12. However, patients at the same chronological age can have significant differences in mineralization stages. These major differences in mineralization can be found in the lower second premolar buds [28,29,30,31,32].
To prevent a false-positive diagnosis of agenesis, we selected 9 as the minimum age because calcification of teeth has usually not been completed by this age [1], and to prevent classification of late mineralized teeth as congenitally missing, final longitudinal panoramic views were also used to confirm a diagnosis of hypodontia.
In the present study, of the individuals identified with congenitally missing teeth, 84% had one or two missing teeth; this is in accordance with other studies by Davis [33], Fekonja [6], Gomes et al. [34], and Goya et al. [35]. Thus, most of the affected individuals suffer only a mild form of hypodontia.
We found that the most often congenital missing tooth types in patients observed in our study were mandibular second premolars, followed by maxillary lateral incisors and maxillary second premolars. Lo Muzio et al. [14] and Laganà et al. [27] had similar findings in the previous study on the Italian population, whereas Polastri [15] found that the most affected tooth was the maxillary lateral incisor followed by the mandibular second premolar.
There is some variation in the literature concerning the description of the most frequently missing tooth, excluding third molars. In the European population, the teeth that were most frequently affected by hypodontia are the following: mandibular second premolar, maxillary lateral incisor, and maxillary second premolar [10]. The mandibular second premolar is the most frequently missing tooth also reported by Polder et al. [10], Endo et al. [8], Tunc et al. [36], Goya et al. [35], and Kirzioglu et al. [37]. In Malaysian [19], Turkish [35], and American populations, the most commonly missing tooth was the maxillary lateral incisor [13]. In the Chinese population, the most frequently missing teeth are mandibular central and lateral incisors [10]. Teeth with the lowest frequency of agenesis were canines (6 males and 15 females) and the first molars (0 males and 3 females). The first molar was missing only in patients with oligodontia.
We found more missing teeth in the maxilla than in the mandible, and the difference was not significant. This result corresponds with the analysis performed by Peker et al. [38], as well as Fekonja [6] and Wong et al. [39] who found missing teeth considerably more frequently in the upper arch than in the lower arch in orthodontic patients. However, Kirzioglu [37] found more missing teeth in the mandible than in the maxilla. Gomes et al. [34] found maxillary hypodontia in 59.2% of patients and in the mandible of 40.8% with an overall ratio of 1.45:1 in orthodontic patients.
Bilateral agenesis manifested a frequency of 4.4%. The most common bilaterally missing teeth were the mandibular second premolar and the maxillary lateral incisor. Goya et al. [35] found that symmetry of congenitally missing teeth was predominant (74.6%), and Kirzioglu et al. [37] observed that bilaterally missing teeth was 73.2%. Moreover, symmetrical hypodontia was predominant, being found in both the contralateral and antagonistic quadrant, possibly suggesting a strong genetic pattern of hypodontia. It was demonstrated also that permanent tooth agenesis, maxillary lateral incisor microdontia, palatally displaced canines, and distoangulation of mandibular second premolars were frequently associated with maxillary lateral incisor agenesis, providing additional evidence of a genetic interrelationship in the causes of hypodontia [40]. Moreover, a significant decrease in maxillary transversal and sagittal size was demonstrated in patients with dental agenesis [41].
