Introduction
The objectives of this study were to evaluate the prevalence of dental anomalies in patients with agenesis of maxillary lateral incisors and to compare the findings with the prevalence of these anomalies in the general population.
Methods
A sample of 126 patients, aged 7 to 35 years, with agenesis of at least 1 maxillary lateral incisor was selected. Panoramic and periapical radiographs and dental casts were used to analyze other associated dental anomalies, including agenesis of other permanent teeth, ectopia of unerupted permanent teeth, microdontia of maxillary lateral incisors, and supernumerary teeth. The occurrence of these anomalies was compared with prevalence data previously reported for the general population. Statistical testing was performed with the chi-square test ( P <0.05) and the odds ratio.
Results
Patients with maxillary lateral incisor agenesis had a significantly increased prevalence rate of permanent tooth agenesis (18.2%), excluding the third molars. The occurrence of third-molar agenesis in a subgroup aged 14 years or older (n = 76) was 35.5%. The frequencies of maxillary second premolar agenesis (10.3%), mandibular second premolar agenesis (7.9%), microdontia of maxillary lateral incisors (38.8%), and distoangulation of mandibular second premolars (3.9%) were significantly increased in our sample compared with the general population. In a subgroup of patients aged 10 years or older (n = 115), the prevalence of palatally displaced canines was elevated (5.2%). The prevalences of mesioangulation of mandibular second molars and supernumerary teeth were not higher in the sample.
Conclusions
Permanent tooth agenesis, maxillary lateral incisor microdontia, palatally displaced canines, and distoangulation of mandibular second premolars are frequently associated with maxillary lateral incisor agenesis, providing additional evidence of a genetic interrelationship in the causes of these dental anomalies.
Tooth agenesis is the most common dental abnormality, and genetics play a fundamental role in its etiology. The various clinical manifestations of tooth agenesis reflect the genetically and phenotypically heterogeneity of this condition. Molecular genetics have shown mutations in MSX1, PAX9, and AXIN2 in families with multiple dental agenesis. Additionally, mutations in many other genes have been identified in syndromes and congenital abnormalities in which tooth agenesis is a regular feature.
Tooth agenesis is frequently associated with other dental anomalies such as microdontia, delayed dental development, and some discrete tooth ectopias. These dental anomalies commonly appear together in the same patient; the possible explanation is that a certain genetic mutation might cause a series of different phenotypic expressions. In other words, different dental anomalies in the same subject could be distinctive expressions of the same genetic code.
Garn et al and Garn and Lewis were the first investigators to identify a pattern of associated dental anomalies. They found that patients with third molar agenesis had an increased prevalence of agenesis of other permanent teeth, as well as a general reduction in tooth size and delayed dental development. The agenesis of second premolars was also associated with higher prevalences of agenesis of other permanent teeth, microdontia of maxillary lateral incisors, infraocclusion of mandibular deciduous molars, and some types of ectopic eruptions. Palatally displaced maxillary canines, distoangulation of mandibular second premolars, ectopic eruption of maxillary first molars, mesioangulation of mandibular second molars, and some types of tooth transpositions are dental ectopias frequently associated with second premolar agenesis.
In addition to third molars and second premolars, maxillary lateral incisors have a high prevalence rate of agenesis. Although previous studies reported an association between maxillary lateral incisor agenesis and tooth transpositions, palatally displaced canines (PDC), and premolar rotations, no study has evaluated the frequency of associated dental anomalies in a large sample of subjects with maxillary lateral incisor agenesis compared with reference values.
Therefore, in this study, we aimed to determine the prevalence of permanent tooth agenesis, discrete ectopias, microdontia, and supernumerary teeth in patients with agenesis of the maxillary lateral incisors, comparing these prevalences with those in the general population. The hypothesis was that subjects with agenesis of maxillary lateral incisors have significantly increased prevalences of other dental anomalies.
Material and methods
A sample of 126 subjects with agenesis of the maxillary lateral incisors was selected from the orthodontic patient files of the dental school of the University of São Paulo City in Brazil and some private dental offices in Brazil. The subjects ranged in age from 7 to 35 years, and there were 84 female and 42 male subjects, with a sex ratio of 2:1. Because of the widely heterogeneous backgrounds of Brazilians, a rough estimate of the ethnic makeup of the sample was derived subjectively from facial photographic records: white (80%) and black mixture (20%). No Asian subjects were included in the sample. Panoramic radiographs, periapical radiographs, and dental casts were used to investigate these dental anomalies: agenesis of permanent teeth; supernumerary teeth; microdontia of maxillary lateral incisors; and 3 types of tooth ectopia including PDC, distal angulation of mandibular second premolars, and mesial angulation of mandibular second molars.
The critical age of 14 years was considered to confirm the absence of third molars. This criterion was used to restrict the sample for evaluation of third-molar agenesis to only those with diagnostic records at 14 years of age or older (n = 76). Diagnosis of palatally displaced maxillary canines followed the radiographic parameters suggested by Lindauer et al, and it was confirmed by interpretation of periapical radiographs by the tube-shift technique, a method of object localization with 2 projections with significantly different x-ray tube angulations. Taking into account the findings of Ericson and Kurol that the attempt to determine the eruption path of maxillary canines radiographically is generally of little value in children younger than 10 years, only subjects 10 years of age or older were considered in evaluating PDC (n = 115). Diagnosis of distal angulation of mandibular second premolars followed the criteria of Shalish et al, using the inferior border of the mandible as a baseline. The maxillary lateral incisor was considered as having microdontia when the maximum mesiodistal crown diameter was smaller than the same dimension of the opposing incisor in the same patient. This category also included conical and peg-shaped maxillary lateral incisors.
Statistical analysis
The diagnosis of all dental anomalies was considered as a single statistical unit even for bilateral occurrence of the anomaly in the same subject. Therefore, subjects and not single dental anomalies were considered for the analysis. This is correct due to the possible genetic background underlying the bilateral occurrence of the dental anomalies.
Two calibrated investigators (D.G.G., B.M.A.) examined the records and diagnosed the dental anomalies simultaneously. Consensus was obtained in case of divergent diagnoses. The results were analyzed with the chi-square test for goodness of fit to compare the frequency of dental anomalies in the sample with previously published reference values. The hypothesis was tested at the 5% level of significance. The odds ratio (OR) was calculated at the 95% CI to measure the strength of associations between agenesis of maxillary lateral incisors and the other dental anomalies investigated.
Results
In the sample of 126 patients with agenesis of maxillary lateral incisors, 51.6% (n = 65) had bilateral expression, and 27.7% (n = 35) had right unilateral and 20.7% (n = 26) had left unilateral expression.
The prevalence of other permanent tooth agenesis in the sample, excluding third molars, was 18.2%, a 3-fold increased prevalence (OR, 3.5) compared with reference values in the general population ( Table I ). The frequencies of maxillary second premolar (OR, 7.5), mandibular second premolar (OR, 2.7), and mandibular third molar (OR, 2.0) agenesis were significantly higher in the sample compared with the general population ( Table I ). No differences between the sample and the reference values were observed for the prevalence of supernumerary teeth ( Table I ).
| Dental anomaly | Prevalence rate in study sample | Reference values | Difference chi-square |
OR | 95% CI OR |
|
|---|---|---|---|---|---|---|
| Tooth agenesis (excluding third molars) | 18.2% 23/126 |
5.0% 53/1064 |
Grahnen, 1956 | 25.31 P <0.001 |
3.57 | (2.11-6.02) |
| Maxillary second premolar agenesis | 10.3% 13/126 |
1.5% 722/48274 |
Polder et al, 2004 | 65.40 P <0.001 |
7.58 | (4.25-13.52) |
| Mandibular second premolar agenesis | 7.9% 10/126 |
3.0% 1479/48274 |
Polder et al, 2004 | 10,01 P <0.002 |
2.73 | (1.43-5.21) |
| Third molar agenesis | 35.5% 27/76 |
20.7% 427/2061 |
Bredy et al, 1991 | 9.61 P <0.002 |
2.11 | (1.30-3.41) |
| Supernumerary teeth | 0.8% 1/126 |
3.9% 39/1000 |
Baccetti, 1998 | 3.15 P = 0.076 (NS) |
0.20 | (0.03-1.45) |
Patients with agenesis of maxillary lateral incisors showed a significantly higher prevalence of microdontia of maxillary lateral incisors (OR, 12.9), as shown in Table II . Considering only the patients with unilateral agenesis of maxillary lateral incisors (n = 61), 80.3% (n = 49) had a size reduction of the contralateral tooth.
| Dental anomaly | Prevalence rate in study sample | Reference values | Difference chi-square |
OR | 95% CI OR |
|
|---|---|---|---|---|---|---|
| Small maxillary lateral incisor | 38.8% 49/126 |
4.7% 47/1000 |
Baccetti, 1998 | 167.71 P <0.001 |
12.90 | (8.12-20.49) |
| PDC | 5.2% 6/115 |
1.7% 25/1450 |
Dachi and Howell, 1961 | 6.7 P <0.010 |
3.14 | (1.26-7.81) |
| Mandibular second premolar distoangulation | 3.9% 5/126 |
0.20% 52/26264 |
Matteson et al, 1982 | 82.71 P <0.001 |
20.83 | (8.18-53.05) |
| Mandibular second molar mesioangulation | 0.0% 0/126 |
0.06% 3/5000 |
Grover and Lorton, 1985 | 0.08 P = 0.783 (NS) |
0.00 | (—-) |
The prevalences of PDC and distal angulation of mandibular second premolars were significantly increased in the sample compared with the general population: 5.2% (OR, 3.1) and 3.9% (OR, 20.8), respectively ( Table II ). In contrast, no difference was observed for the frequency of mesial angulation of mandibular second molars in the sample compared with the reference values ( Table II ).
Results
In the sample of 126 patients with agenesis of maxillary lateral incisors, 51.6% (n = 65) had bilateral expression, and 27.7% (n = 35) had right unilateral and 20.7% (n = 26) had left unilateral expression.
The prevalence of other permanent tooth agenesis in the sample, excluding third molars, was 18.2%, a 3-fold increased prevalence (OR, 3.5) compared with reference values in the general population ( Table I ). The frequencies of maxillary second premolar (OR, 7.5), mandibular second premolar (OR, 2.7), and mandibular third molar (OR, 2.0) agenesis were significantly higher in the sample compared with the general population ( Table I ). No differences between the sample and the reference values were observed for the prevalence of supernumerary teeth ( Table I ).
