Hypodontia is a congenital absence of one or more teeth and is one of the most common developmental abnormalities in the permanent dentition excluding the third molars (1-3). According to the literature, the etiology of hypodontia remains unclear. It may occur due to genetic or environmental factors, or as a combination of both factors. Family and twin studies have showed that not only genetic factors but also other conditions play a role in the expression of this trait (4). Hypodontia may be present as an isolated condition or in association with syndromes (ectodermal dysplasia (5) and cleft lip and/or palate (6)). It is frequently associated with dental and skeletal malocclusions such as bimaxillary retrusion, mandibular prognathism, decreased maxillary jaw size, reduced vertical facial dimension, and peg shaped maxillary lateral incisors (7, 8). In order to achieve an esthetically pleasing dentition, patients with hypodontia often require interdisciplinary treatment, including orthodontic and restorative interventions. Tooth dimension plays a key role in decision- making about space management in the edentulous area or in managing functional occlusion. The prevalence of hypodontia in the deciduous dentition ranges from 0.1% to 0.9, whereas the prevalence of hypodontia in the permanent dentition ranges from 2.3% to 11.3% (9-12).
In the literature, the reports regarding tooth dimensions in hypodontia patients are controversial. Chung et al. (13) reported no associations between hypodontia and reduction in tooth dimensions. Yamada et al. (14) concluded that the remaining teeth were generally larger in patients with mild hypodontia, than those in the control group, except in cases when three or more teeth were missing. A significant reduction in tooth size was observed in the remaining dentition compared to the control group. Wisth et al. (15) found no difference in patients with hypodontia compared to the control group.
The aim of this study was to compare mesiodistal (MD) and buccolingual (BL) tooth sizes in hypodontia patients with a control group with complete dentition. The null hypothesis was that there was no difference in tooth sizes between hypodontia patients and the controls.
Material and methods
The sample was chosen from archives of Department of Orthodontics, Dental Clinic, Clinical Hospital Center Zagreb. The approval for this study was obtained by the Ethics Committee, School of Dental Medicine, University of Zagreb. More than a thousand of patient files were reviewed by the same examiner. Hypodontia was diagnosed by radiological and clinical examinations. The sample comprised 76 patients with hypodontia (50 female and 26 male) aged between 11 and 18 years (mean age 13 ± 2.35 years). The control group comprised 50 females and 26 males with the same age range as the study group (mean age 12.54 ± 1.95 years). The inclusion criteria for both study groups consisted of full eruption of all teeth except third molars, having dental casts and pretreatment panoramic radiographs. The patients with history of permanent tooth extraction or previous orthodontic treatment and those with caries, interproximal restorations and ectopic tooth eruption were excluded from the study.
Measurement and dental dimensions
Mesiodistal (MD) and buccolingual (BL) dimensions were measured on pretreatment dental casts with a digital caliper (Levior S.R.O., Kokory 381-CZ) to the nearest 0.01 mm. The MD dimension of each tooth was measured according to the method described by Moorrees et al. (16), from its mesial contact point to its distal contact point at its greatest interproximal distance. The BL dimension was measured as the greatest distance between vestibular and oral teeth surface perpendicular to the mesiodistal dimension. All the measurements, taken under natural light, were performed twice by the same operator (A.V.) who did not exceed the number of seven casts per day in order to avoid eye strain and to minimize the possibility of subjective error.
The data were analyzed using Statistica 7.1 (StatSoft Inc.) statistical package (descriptive statistics, test of distribution normality, parametric statistics). A test of distribution normality was performed by means of the (one way/unidirectional) Kolmogorov-Smirnov test. The results showed that the tested variables were normally distributed (p>0.01) and consequently parametric tests were used (t test).
The distribution of agenesis by tooth type in hypodontia group is presented in Table 1.The most commonly congenitally missing teeth were the lower second premolars (left 13.45% and right 13.90%) and upper lateral incisors (both left and right 12.56%), followed by the upper second premolars (right 9.40% and left 10.31%).
The paired-sample t-test was used to compare the mean values of the same dimension measured on the left and the right side of each dental arch. Since no statistically significant difference was found (p<0.05), the results were averaged for further analysis.
The differences of mesiodistal and buccolingual dimensions for hypodontia patients and the control group are presented in Table 2. The average differences in tooth size between hypodontia patients and the control group were found in MD dimension (4.02%) and in BL dimension (3.85%). The greatest differences were found in the upper lateral incisors. They amounted to 8.08% in MD and 6.40% in BL dimension. The smallest difference was found in BL dimension of the lower lateral incisor (2.37%), MD dimension of the lower second premolars and the upper first molar (2.61%) and MD dimension of the lower central incisor (2.26%).
Several authors (4, 17, 18) have reported that patients with congenitally missing teeth had smaller teeth in MD and BL dimensions than subjects in the control group, which was also confirmed in our study. In contrast to the above mentioned authors, Wisth et al. (15) found no statistical difference in the MD diameter of the teeth between the hypodontia group and the healthy controls, which is in concordance with Chung et al. (13) who concluded that hypodontia was not associated with reduced tooth size.
In this study, the percentage of reduction in the tooth dimensions of hypodontia group was 4.02% in MD and 3.85% in BL dimension. The greatest difference was found in MD (8.08%) and BL (6.40%) dimensions of the upper lateral incisor. The difference of 2.61%% in MD, and 3.81% in BL dimension was found for the lower second premolar. Brook et al. (17) reported that male hypodontia patients showed greater difference in BL dimension in anterior segment and in MD dimension in posterior segment of dental arch. Gungor et al. (19) found smaller MD and BL tooth dimensions in patients with severe hypodontia (six or more missing teeth) than those with mild hypodontia (two to five missing teeth), and the greatest difference was found to be MD dimension in maxillary and mandibular lateral incisors and second premolars in both hypodontia groups.
The age range of our subjects (hypodontia and controls) was 12 to 18 years. This young age group was chosen in accordance with the study of Doris et al. (20) to minimize the alteration of mesiodistal tooth dimensions due to attrition, restoration or caries. Consequently, these factors had a minimal effect on the actual MD tooth widths.
In this study, statistically significant differences in tooth sizes between hypodontia and control group were found in the teeth that are most commonly affected by hypodontia. However, the greatest difference was found for the upper lateral incisors. Ramazanzadeh et al. (21) found that the difference in tooth width between the two groups was more evident in the first and second premolars. Also, this difference was more evident in the first molars than in anterior segments. Brook et al. (18) found the greatest difference in the mandibular central incisor and maxillary lateral incisor in MD dimension and the mandibular central incisor in the BL dimension.
The results of our study point to the importance of dental measurements which should be performed for patients with hypodontia. Clinical observations have confirmed the fact that variation in tooth morphology is not only in size, but also in shape, which should be taken into consideration in orthodontic treatment planning in order to produce an occlusion that is functionally efficient, esthetic, and healthy.
The most commonly congenitally missing teeth in this study were the lower second premolars (left 13.45% and right 13.90%) and the upper lateral incisors (both left and right 12.56%), followed by the upper second premolars (right 9.40% and left 10.31%)
The dimensions of teeth in hypodontia groups were smaller than those in control subjects. Measurements showed that average sizes were 4.02% in mesiodistal dimension and 3.85% in buccolingual dimension. The maxillary lateral incisor showed the greatest variation in size.