Maxillary incisor root morphology in patients with nonsyndromic tooth agenesis: A controlled cross-sectional pilot study


This study aimed to investigate the association between root morphology of maxillary incisors and nonsyndromic tooth agenesis in patients compared with a control group without agenesis.


This controlled cross-sectional pilot study (1:4) was performed with a random sample of 335 records from Brazilian applicants for orthodontic treatment, paired by sex and age. Panoramic and periapical radiographs were analyzed to diagnose tooth agenesis and to assess root morphology. The agenesis group (n = 67) included patients with nonsyndromic tooth agenesis, and the control group (n = 268) included patients without tooth agenesis. The statistical analysis included the Student t test and z test, conditional logistic regression, and odds ratio estimates.


Occurrence of root morphological changes was significantly higher among patients with agenesis ( P <0.05). Significant morphological changes (short, blunt, apically bent, and pipette-shaped roots) were found in the roots of remaining teeth when comparing agenesis and control groups ( P <0.05). Patients with agenesis were more likely to show root morphological changes (odds ratio, 74.23; 95% confidence interval, 16.93-325.46; P <0.001).


Patients with agenesis are more likely to present root morphological changes, which should be considered to minimize problems during orthodontic treatments.


  • This article is the first to assess root morphology in patients with agenesis.

  • Patients with agenesis were more likely to show root morphological changes.

  • The most observed root morphological changes were pipette shaped and apically bent.

  • Only patients with agenesis presented apically bent and blunt root morphology.

Nonsyndromic tooth agenesis is one of the most prevalent congenital anomalies occurring in the permanent dentition. Genetic, epigenetic, and environmental factors contribute to the congenital absence of teeth, and recent studies have demonstrated the predominant role of genetics in the etiology of this condition. The various clinical phenotypic expression of this genetic defect reflects its heterogeneity, as it is frequently associated with the presence of other skeletal and dental abnormalities. Previous studies reported changes in facial morphology such as bimaxillary retrusion, reduced maxillary jaw size, and decreased vertical facial dimension. The association with other dental anomalies such as palatally displaced canines, distoangulation of mandibular second premolars, , tooth transposition, delayed tooth formation, maxillary lateral incisor microdontia, , , and reduced mesiodistal crown size of all remaining teeth, has also been demonstrated, frequently requiring an interdisciplinary approach to achieve an esthetic dentition.

The treatment of patients affected with hypodontia is challenging in most cases, and orthodontic and restorative interventions are generally necessary for proper management. The literature has stated for quite some time that a relatively frequent consequence of orthodontic treatment is root resorption. In most patients, this resorption is minor and of no clinical significance. However, a few teeth exhibit severe resorption, and there is no single explanation for the cause. Some risk factors are mentioned, especially for maxillary incisors, and great emphasis has been given to the potential relationship between the occurrence of root resorption and abnormal root morphology, such as pipette-shaped, blunt, pointed, short, long, dilacerated, and narrow roots.

As previously stated, the association between agenesis and reduction of the crown size of maxillary lateral incisors and several other teeth has been extensively cited. , In addition, it is reasonable to assume that if changes in the crown size of the remaining teeth may be present, then changes may also occur in the root portion, which would require more care if orthodontic treatment was necessary. After performing a comprehensive literature review, no articles were found that showed a potential association between the occurrence of tooth agenesis and root morphological changes of maxillary incisors. This research could provide valuable information for clinical practice, helping to estimate the risk of severe root resorption at an early stage in orthodontic treatment. If planning is performed considering all predictive factors, different protocols can be established, attempting to promote the lowest impact on affected teeth.

Therefore, this study aimed to investigate the association between root morphology of maxillary incisors and nonsyndromic tooth agenesis in patients. We hypothesized that patients with tooth agenesis have a significantly higher prevalence of morphological changes in roots of the remaining maxillary incisors.

Material and methods

This controlled cross-sectional pilot study was performed in accordance with the Code of Ethics of the World Medical Association (Declaration of Helsinki) and the Ethics Board of the Brazilian Ministry of Health (Resolution CNS/MS 466/2012) for research involving humans. This project was approved by the independent Ethics Committee of the School of Dentistry of the Federal University of Sergipe (Protocol #152). The privacy rights of all subjects were observed, and no identifying information was used.

The STROBE (STrengthening the Reporting of OBservational studies in Epidemiology) tool was used to aid the research performance and the reporting of results. This study was nested in a retrospective design that included preorthodontic exams of 3400 subjects randomly selected from February 2014 to February 2016 from a single radiographic center located in the Northeast region of Brazil. Similar to previous studies, , patients ranging in age from 8 to 30 years, of either sex and with good quality radiographs were included. The exclusion criteria were incomplete records (x-rays, intraoral photographs, clinical notes), craniofacial malformations and syndromes, and history of previous orthodontic treatment or permanent tooth extraction. The diagnosis of previous extractions was assumed to be based on the available anamnesis’ data, enclosed to the patients’ exams (panoramic, periapical and cephalometric radiographs, and photographs) performed at the radiographic center. All exams of each patient were obtained on the same day.

Considering that there are no previous studies on this subject, the sample size calculation was performed by setting hypothetical statistical parameters based on the clinical and epidemiological relevance of the expected findings. The minimum sample size desired for this study was calculated using an expected odds ratio (OR) of 2.5, which is equivalent to a medium effect size, a probability of exposure among controls of 50%, as the prevalence of root morphological changes was unknown at the beginning of the study, a statistical power of 90.0% (β = 0.10), and a standard error of 5% (α = 0.05). The Power and Sample Size Calculation software (Vanderbilt University, Nashville, Tenn) was used, indicating a minimum sample size of 67 cases and 268 controls to meet the requirements. The outcome variable was tooth agenesis, and the investigated exposure variables were root morphological changes. The case group included patients with tooth agenesis, and the control group included patients without tooth agenesis. Four controls were paired individually with each agenesis case according to sex and age.

Cases of tooth agenesis were evident from the radiographs alone. One single operator, previously trained and calibrated, using the same protocol and the visual method, performed evaluation. Consistent with previous studies, , panoramic and periapical radiographs were analyzed using a negatoscope in subdued ambient lighting. In case of periapical radiographs, only those of the anterior region were used. In order to avoid visual fatigue, 20 radiographs were evaluated per day. For patients under 10 years of age, a subsequent panoramic radiograph was evaluated in order to confirm agenesis of the second premolar. If this subsequent exam was not available, the patient was excluded. For patients under 11 years of age, periapical radiographs were carefully evaluated in order to observe if roots of maxillary central and lateral incisors were completely formed. If apex formation was not observed in any tooth, the patient was excluded.

Besides tooth agenesis, the presence of root morphological changes at maxillary incisors was investigated at periapical radiographs. Roots were morphologically classified as normal, short, blunt, apically bent, and pipette shaped, following the similarity to the drawing of Levander and Malmgren ( Fig 1 ). In order to calculate the intraobserver error, 30% of patient radiographs were randomly selected by using an online randomization program ( ) and were re-examined after 1 month. The new data were compared with those of the original collection, and agreement between them was substantial (kappa, >0.90), confirming the reproducibility and reliability of the evaluations.

Root morphology classification, adapted from Levander and Malmgren. A, normal root; B, short root; C, blunt root; D, apically bent root; and E, pipette-shaped root.

Statistical analysis

SPSS software (version 20.0; IBM, Chicago, Ill) was used for data analysis. Descriptive and comparative statistical analysis was performed on patients with agenesis and controls regarding the occurrence of root morphological changes. The 2 groups were compared for age using the Student t test, while the z test was applied for comparison of proportions, both with level of significance set at 5% ( P <0.05). In addition, conditional logistic regression was applied to determine the association between tooth agenesis and root morphological changes, allowing to estimate OR and their respective 95% confidence intervals. The omnibus test and the residue analysis were performed to verify the validity of the statistical model.


Table I shows the variables used for group pairing and the assessment of root morphology. There were no statistically significant differences between case and control groups regarding age and sex, which indicates a successful pairing. The occurrence of root morphological changes was significantly higher among patients with agenesis (n = 24; 92.3%) than for control subjects (n = 2; 7.7%). Significant morphological changes in roots of remaining teeth were found between agenesis and control groups ( P <0.05). Among patients with agenesis, the following morphological changes were observed: short (n = 5), blunt (n = 3), apically bent (n = 8), and pipette shaped (n = 8). Interestingly, from the 268 control subjects, only 2 showed root morphological changes (1 short and 1 pipette-shaped root).

Table I
Descriptive and comparative statistics between agenesis and control groups regarding age, sex, and root morphology
Variables Agenesis (n = 67) Control (n = 268) Total (n = 335)
Mean (SD) 18.1 (5.1) 18.1 (5.2) 18.1 (5.2)
Median (IQR) 16.9 (14.8-20.1) 17.7 (13.6-21.9) 17.7 (13.9-21.8)
Female 53 (20.0) 212 (80.0) 265 (100.0)
Male 14 (20.0) 56 (80.0) 70 (100.0)
Root morphological changes
Present 24 (92.3) 2 (7.7) 26 (100.0)
Absent 43 (13.9) 266 (86.1) 309 (100.0)
Root morphology
Normal 43 (13.9) 266 (86.1) 309 (100.0)
Short 5 (83.3) 1 (16.7) 6 (100.0)
Blunt 3 (100.0) 0 (0.0) 3 (100.0)
Apically bent 8 (100.0) 0 (0.0) 8 (100.0)
Pipette shaped 8 (88.9) 1 (11.1) 9 (100.0)
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Mar 9, 2020 | Posted by in Orthodontics | Comments Off on Maxillary incisor root morphology in patients with nonsyndromic tooth agenesis: A controlled cross-sectional pilot study
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