Prevalence and Pattern of Hypodontia among Croatian Orthodontic Patients

Abstract

Objective

The objective of this retrospective study was to assess the prevalence of hypodontia in the permanent dentition among Croatian orthodontic patients. The occurrence was evaluated concerning gender, specific missing teeth, the location, pattern of distribution in the maxillary and mandibular arches and sagittal and vertical skeletal pattern.

Material and Methods

The sample consisted of 194 patients (75 males and 119 females) from the Department of Orthodontics, Dental Clinic, Clinical Hospital Center Zagreb. Based on the severity of hypodontia the sample was divided into mild (1-2 missing teeth), moderate (3-5 missing teeth) and severe groups (6 or more missing teeth). The location of missing teeth was used to further divide the sample into anterior (intercanine region), posterior (premolars and molars) and anteroposterior groups. In addition, jaw localization of hypodontia was also considered.

Results

Permanent dentition hypodontia among Croatian orthodontic patients was found to be generally mild (80%), and a distribution was similar in the maxilla (39%) and the mandible (41%), as well as in the anterior and posterior segments of dental arch (44%). The number of missing teeth per person ranged from 1 to 12, with no significant difference between genders. The severity and location of hypodontia did not differ significantly between the genders, as well as in between the categories of sagittal and vertical skeletal patterns.

Conclusion

Present results suggest that the treatment plan for patients with hypodontia in permanent dentition should be individualized and adjusted for each case.

Introduction

Hypodontia is a congenital absence of one or more permanent teeth, excluding third molars (1). It represents the most common developmental anomaly of the human dentition (2). The prevalence of hypodontia in permanent dentition varies among different ethnic groups, by gender and geographical location, and ranges from 1.6% to 36.5% (3). The prevalence of hypodontia in Europe is 4.6% for males and 6.3% for females, while in Australia it is 5.5% for males and 7.6% for females (4). In North America, the prevalence among the Caucasians is lower than in Europe and Australia, with 3.2% for males and 4.6% for females (4). Regarding the gender, hypodontia affects women more often than men, precisely 1.37 times more (4). The teeth most affected with hypodontia are as follows: lower second premolar, upper lateral incisor and upper second premolar. Bilateral hypodontia is more common only when the upper lateral incisor is missing, whereas in cases where other types of teeth are missing, unilateral hypodontia is more common (4). The absence of one or two teeth is present in 83% of subjects with hypodontia (4). There is no statistically significant difference between the prevalence of hypodontia in the maxilla and mandible (4).

The aim of this retrospective study was to assess the prevalence of hypodontia in the permanent dentition among Croatian orthodontic patients. The occurrence was evaluated concerning gender, specific missing teeth, the location and pattern of distribution in the maxillary and mandibular arches and in the sagittal and vertical skeletal pattern.

Material and Methods

The sample was gained from the patients' database of the Department of Orthodontics, Dental Clinic, Clinical Hospital Center Zagreb. It consisted of 194 subjects (75 males and 119 females) between the ages of 10 and 18. After clinical examination, hypodontia was further confimed by analyzing patients' radiographic images.

Based on the severity of hypodontia, the sample was divided into mild (1-2 missing teeth), moderate (3-5 missing teeth) and severe groups (6 or more missing teeth). The location of missing teeth was used to further divide the sample into anterior (intercanine region), posterior (premolars and molars) and anteroposterior groups. Also, it was considered which jaw was affected.

The inclusion criteria for this study were permanent dentition hypodontia and Croatian ethnicity, while exclusion criteria were craniofacial syndromes, cleft lip and/or palate, history of teeth trauma and previous orthodontic treatment.

A customized cephalometric analysis was performed by DOLPHIN IMAGE software (v.11.5) on lateral cephalograms that were taken as a part of a standard procedure prior to treatment. To determine the sagittal relationships, ANB angle was observed. The values of 2.5 ± 2 were defined as a skeletal Class I, > 4.5 as Class II and < 0.5 as Class III. Vertical relationships were estimated using the Jarabak's ratio of posterior and anterior facial height (S-Go: N-Me), with a standard value of 65.5% ± 3.5%. The subjects with a ratio of less than 62% were classified as having a vertical growth pattern and and those with a ratio of more than 69% were classified as having a horizontal growth pattern.

The Chi square test with Cramer V for effect size were used for comparison of categories. The Mann-Whitney test for comparison of number of teeth between sexes was applied, while the Rosenthal formula r=Z/√N was used to calculate the effect size. Data were analysed in SPSS 16.0 software (SPSS Inc., Chicago, USA).

The Ethics Committee of the Zagreb School of Dental Medicine approved this study. An informed consent forms authorizing the use of patients radiograms were signed by each patient or their parent, if they were under 18.

Results

Females (61.3%) were more affected with hypodontia than males (38.7%).

The number of missing teeth per person ranged from 1 to 12 (median 2, interquartile range 1–2) and did not differ between the genders (p=0.590; Figure 1).

Figure 1.

Frequency histogram for number of persons by number of missing teeth

Hypodontia was found to be generally mild (80%), localized equally in the maxilla (39%) and the mandible (41%) and in both the anterior and posterior segments of dental arch (44%).

The severity and location of hypodontia did not differ significantly between the genders (p≥0.106; Figures 2–4).

Figure 2.

Severity of hypodontia

Figure 3.

Location of hypodontia in dental arch

Figure 4.

Jaw localization of hypodontia

The severity and location of hypodontia also did not differ between the categories of facial rotation patterns or between skeletal classes (p≥0.105; Figures 5-10)in a statistically significant manner.

Figure 5.

Distribution of hypodontia by severity and skeletal class

Figure 6.

Distribution of hypodontia by location in dental arch and skeletal class

Figure 7.

Distribution of hypodontia by jaw localization and skeletal class

Figure 8.

Distribution of hypodontia by severity and facial growth pattern

Figure 9.

Distribution of hypodontia by location in dental arch and facial growth pattern

Figure 10.

Distribution of hypodontia by jaw localization and facial growth pattern

Discussion

The differences between studies about hypodontia, regarding sampling, age range and gender, make their comparison difficult (2). For defining the incidence and distribution of hypodontia in the human population, meta-analyses have a great importance and majority of the authors are referring to them. The best examples are studies published by Polder et al. in 2004. (4) and by Khalaf et al. in 2014. (2). The latter reported of a higher prevalence of hypodontia than stated before, which might be a result of using better diagnostics and having a greater number of prevalence studies.

In the present study, hypodontia was found to be generally mild (80%), meaning that most of the subjects were missing one or two teeth. Similar findings were reported in some other studies (5-7).

The severity and location of hypodontia did not differ significantly between the genders, which was also found in previous studies (7, 10, 13, 17, 32, 33). When it comes to number of missing teeth and sexual dysmorphism, there is much more evidence that females are at greater risk of being affected with more severe hypodontia than males (13, 14, 16, 34-37).

The results as which arch is predominantly affected with hypodontia are not conclusive (8). According to some authors, there seems to be no significant difference between the prevalence of hypodontia in the maxilla and mandible (4, 5, 9, 30), which was also confirmed in our study. Many previous studies concluded that the maxilla was more frequently affected with hypodontia than mandible (6, 7, 10-14, 31). There is also a group of authors who had found a greater rate in the mandible (15-21).

Few studies have evaluated the distribution of hypodontia in the anterior and posterior segments of dental arch (10, 13, 22). Some authors reported that the anterior segment is more affected with hypodontia (10, 13, 23), while others noted that the posterior tooth agenesis increased with hypodontia severity (5, 22). Our findings suggest that hypodontia is equally localized in the anterior and posterior segments of dental arch.

No statistically significant difference was found between the categories of facial rotation patterns or between skeletal classes regarding the severity and location of hypodontia. Severe hypodontia, according to some studies, was associated with Class III malocclusion (24, 25). Hirukawa et al. (26) reported that hypodontia in the maxilla was commonly associated with Class III, while Class II was more common among subjects with hypodontia in the mandible.

It is assumed, that an anterior rotation of the mandible is attributed to a lack in occlusal support, arising from a large number of agenetic teeth (27). A tendency towards horizontal growth pattern in subjects with posterior hypodontia was reported by Bauer et al. (28). Another study published by Kreczi et al. (29) reported that in subjects with hypodontia neither a vertical nor a horizontal growth pattern is dominant.

Conclusion

Permanent dentition hypodontia among Croatian orthodontic patients was found to be generally mild, localized equally in the anterior and posterior segments in both the maxilla and the mandible. The number of missing teeth per person ranged from 1 to 12, with no difference between genders.

The severity and location of hypodontia did not differ significantly between the genders, as well as in between the categories of vertical and sagittal skeletal growth pattern.

The obtained results suggest that the treatment plan for patients with hypodontia in permanent dentition should be individualized and adjusted for each case.