Hypodontia is a dental anomaly referring to less than six congenitally missing teeth (excluding the third molars) (1, 2). Other terms used to describe hypodontia are “tooth agenesis”, “oligodontia” and “anodontia”, however, tooth agenesis and hypodontia are used in this study as they refer to developmental failure of fewer teeth, while “oligodontia” and “anodontia” refer to more severe forms of tooth agenesis, typically with more than six missing teeth or complete dentition missing (3). Hypodontia is considered to have a strong genetic (4, 5) component and is often seen in patients who also present other ectodermal anomalies, as well as non-syndromic patients with cleft lip and/or palate (CLP) (6). Other environmental factors, such as trauma, infections, and toxins can also be implicated in its incidence (3, 7).
Depending on the population studied, the prevalence of hypodontia varies from 0.03 to 10.1%, making it the most prevalent dentofacial malformation in humans, with a reportedly higher incidence in the last few decades, particularly among Caucasians (2, 8). Some studies also suggest a higher prevalence of hypodontia in females than in males, particularly in permanent dentition (3, 9, 10), however, no significant difference between genders was reported (2, 11).
There is also a difference in the prevalence of hypodontia concerning primary and permanent dentition, tooth type, and ethnicity (2, 12). The total prevalence of hypodontia in permanent dentition (excluding the third molars) was 5.5% in Europeans (13).
Most hypodontia patients lack only one or two teeth, with the upper lateral incisors and second premolars being the most often missing teeth in populations of European origin (6).
Hypodontia is commonly reported in coexistence with other dental clinical features (2, 3, 6) such as taurodontism, peg-shaped incisors, teeth rotations and generalized spacing, canine-lateral incisor transposition, retained primary teeth, or abnormal dental morphologies (1). Microdontia is also highly reported in hypodontia case reports (3, 24, 25).
Hypodontia may cause alterations in the dentofacial features of the affected due to dental and functional compensation. Apart from the need for orthodontic treatment, hypodontia affects function, appearance and the overall quality of life of the patients. This emphasizes the importance of intervention.
While several studies have reported the prevalence of hypodontia and its correlation with other dental clinical features (24-28), there are no reports concerning the association of hypodontia in Kosovar adolescents. The present study aimed to evaluate the prevalence of hypodontia according to gender and its relation with different dental clinical features among Kosovar adolescents aged between 15-21 years.
Materials and methods
This is a sequential cross-sectional study which was performed between September 2010 and June 2012 in eight different schools, in different regions (Prishtine, Prizren, Podujeve, Gjilan, Ferizaj, Mitrovice, and Suhareka) of Kosovo.
A total of 3,306 students aged between 15-21 years were examined. Sample selection was carried out using a cluster sampling method. All schools from the list of Public Schools of Ministry of Education in the Republic of Kosovo were grouped by cities included in this study. In the first phase, one school was randomly selected from each group of cities except Prishtina,where two schools were selected making it in total eight schools. In the next phase, students were randomly selected from classes. Examinations of the subjects were performed by three orthodontists and eight dentists, all of them calibrated in advance. To assess the number of present teeth, examinations were performed using a dental mirror. When missing teeth were noticed and subjects gave no history of tooth extraction, panoramic and intraoral photographs were taken to diagnose hypodontia. Our examination revealed that 77 students had hypodontia, and they then represented the sample of our study. Dental impressions were taken from selected hypodontia subjects, and dental features were analyzed on the model casts.
Exclusion criteria were implemented through an examination of previous dental history. Subjects with a history of tooth loss from trauma, extractions, caries, periodontal disease, or previous orthodontic treatments were excluded. Altogether 3086 subjects were excluded from the study. In 220 subjects, panoramic and intraoral photographs were taken and another 143 subjects were excluded since no missing teeth were found. The final sample consisted of 77 subjects.
Informed consent forms were obtained from parents or their guardians before the examination of subjects under the age of 18, whereas direct approval was taken from subjects older than 18. The study was analyzed and approved by the Research Ethics Committee of the University Dentistry Clinical Center of Kosovo (University of Prishtina) and Ministry of Education, Science, and Technology of Kosovo. The authors read the Helsinki Declaration and followed the guidelines in this investigation.
Data analysis was performed using the Statistical Package for Social Sciences (version 20.0, SPSS Inc., Chicago, Illinois, USA). The normality of data distribution was assessed using the Kolmogorov-Smirnov test. Since the p-value was >.001 for each item, it was concluded that the sample data had a non-normal distribution. Therefore, non-parametric tests were used during the calculation of mean differences (i.e. Mann Whitney test).
In this study, out of the 3,306 students examined, 77 (2.3%) had hypodontia. Since the study focused on patients with hypodontia, the results were presented in terms of 77 patients identified. Out of 77 patients with hypodontia, 46 (59.7%) were females and 31 (40.3%) were males.
No significant difference was noted in the prevalence of hypodontia according to gender (p>0.05). The number of missing teeth ranged from 1 to 5, with an average of 1.8 missing teeth per subject. The mean number of missing teeth was 1.91 for females and 1.89 for males. No patient had more than five missing teeth. One missing tooth was found in 41.5% of the subjects, two missing teeth in 42.8%, and three to five absent teeth were observed in 15.6% of the subjects. Higher prevalence of missing teeth was noted in subjects aged 15-18 years (59.8%), compared to those aged 19-21 years (40.2%), which is shown in Table 1.
Among patients with hypodontia, 46 (59.7%) had maxillary hypodontia and 21 (27.3%) had mandibular hypodontia, while 10 patients (13%) had missing teeth in both jaws. The most frequently missing teeth were the maxillary lateral incisors, followed by the mandibular second premolars. The distribution of missing teeth is presented in Figure 1.
68 patients (88.3%) had at least one clinical feature concurrent with hypodontia. The distribution of clinical features associated with hypodontia is presented in Table 2. Teeth rotation was the most commonly observed clinical feature (n = 35; 45.5%), while the maxillary central right incisor was the most frequently rotated tooth. Inclination was found in 36.4% (n=28) of patients, with the maxillary lateral right incisor being the most frequently inclined tooth. All observed clinical features had a higher prevalence among female patients, aged 15-18 years. The distribution and frequency of clinical features related to hypodontia are presented in Table 2, segregated by gender and age group.
Significant associations (P<0.01) were noted among different dental clinical features in hypodontia patients, which is presented in Table 3.
This study presented a condition of 2.3% of a total of 3,306 subjects examined in different schools and universities in Kosovo. All subjects included in the study had hypodontia, however, this sample has not necessarily represented those requesting orthodontic treatment. Likewise, this sample reflected only a portion of individuals with hypodontia in those group-ages. The present study provided insight and evidence on the gender-based prevalence of hypodontia and associated clinical features in a large proportion of Kosovar adolescents, previously not presented in any other studies. The findings of the present study revealed a higher prevalence of hypodontia among females compared to males, but with no statistically significant gender-based difference in its prevalence, which is in accordance with the studies of Gokkaya et. al (22) and Badrov (23).
There are many population-based and specific case reports published regarding hypodontia and its relation to other dental abnormalities. Japanese share similar prevalence of tooth agenesis with Europeans, however, the lower lateral incisor is the most commonly missing tooth, compared to the upper lateral incisor and second premolar in Europeans (6). Our study also revealed that more than 84% of the adolescents had either one or two missing teeth. When observing the age groups, 15-18 year- old subjects had a higher prevalence of missing teeth comparing to 19-21 year- old subjects. The high percentage of subjects with only one or two missing teeth may reflect the influence of appearance, such as smile esthetics, on psycho-social level, thus motivating patients to seek orthodontic treatment. Another contributing factor to this phenomenon may be the finding that approximately 60% of subjects had maxillary hypodontia, and 13% of them had missing teeth in both jaws, potentially also affecting their smile esthetics.
Slightly higher prevalence of hypodontia and missing teeth was found among females, however, no statistically significant difference was found between the genders. The literature also contains few studies that found a significant gender-based difference (2, 15, 16).
Although many studies suggest that there is a correlation of hypodontia with several dental anomalies, including peg-shaped lateral incisors, canine- lateral incisor transposition, and taurodontism (2, 14, 17-21), our study found that above 88% of the patients had at least one clinical feature apart from hypodontia. Tooth rotation was the most frequently noted clinical feature, with higher prevalence among females compared to males. In contrast, scant evidence regarding the gender predisposition of tooth rotation was found in the existing literature. Tooth inclination as a clinical feature was also observed in 36.4% of the patients, though a similar association has not been found in the recent literature.
One commonly reported feature associated with hypodontia is microdontia of one or more teeth. Our study found that only four patients (5.2%) had microdontia coexisting with hypodontia. The other most prevalent clinical features were mandibular midline shift and crossbite.
The analysis of correlations among anomalies also showed a higher prevalence of mandibular midline shift, rotation, inclination, and microdontia.
Although the sample was widely spread, this research study has the limitation of randomly leaving out regions with a higher prevalence of hypodontia. This limitation is mainly the result of the lack of national data on the prevalence of dental status of the population, including hypodontia.
No significant difference was noted in the prevalence of hypodontia according to gender. Tooth rotation was the most commonly observed clinical feature, followed by inclination. Hypodontia is regularly associated with other dental clinical features, therefore, a multidisciplinary approach is recommended to achieve maximal functional and esthetic results.