Journal of Dr. NTR University of Health Sciences

: 2022  |  Volume : 11  |  Issue : 1  |  Page : 6--10

Appraisal of root-crown ratio of maxillary incisors in various skeletal and dental malocclusions

G V D Harsha1, CV Padma Priya1, Siva Kumar Arunachalam2, D P K Varma1, V Goutham Chakravarthy1, Anoosha Manda1,  
1 Department of Orthodontics, Vishnu Dental College, Bhimavaram, Andhra Pradesh, India
2 Department of Community and Children's Oral Health Care, The International Medical University, Kuala Lumpur, Malaysia

Correspondence Address:
Dr. G V D Harsha
Department of Orthodontics, Vishnu Dental College, Bhimavaram - 534 202, Andhra Pradesh


Background: Shortening of the dental roots denoted by a decrease in root-crown ratio is a common manifestation of root resorption. Several natural conditions place roots at risk of resorption without any pathology. To date, information regarding root resorption in sagittal malocclusions is deplete in the literature. Aims: To measure and associate the root-crown ratio of maxillary incisors in different malocclusions. Methods: About 85 patients were allocated to three groups, Skeletal and Angle's Class I, Class II and Class III. Panoramic radiographs and periapical radiographs for maxillary incisors (340 teeth) using paralleling technique were taken and traced. Length of the root and crown were assessed and root-crown ratios were calculated. Results: The root-crown ratio was significantly lower in Skeletal and Angle's Class III group (P < 0.05) compared to Classes I and II groups. Gender predilection was found to be absent. Conclusion: Root resorption of maxillary incisors was observed in Skeletal and Angle's Class III patients. Maxillary central incisors were observed to have decreased root-crown ratios compared to maxillary lateral incisors irrespective of malocclusion.

How to cite this article:
Harsha G V, Padma Priya C V, Arunachalam SK, Varma D P, Chakravarthy V G, Manda A. Appraisal of root-crown ratio of maxillary incisors in various skeletal and dental malocclusions.J NTR Univ Health Sci 2022;11:6-10

How to cite this URL:
Harsha G V, Padma Priya C V, Arunachalam SK, Varma D P, Chakravarthy V G, Manda A. Appraisal of root-crown ratio of maxillary incisors in various skeletal and dental malocclusions. J NTR Univ Health Sci [serial online] 2022 [cited 2022 Jul 4 ];11:6-10
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External apical root resorption is defined as the loss of apical root tissue. It causes the shortening of the dental roots which is implicated by a decrease in the root-crown ratio. Uslu et al.[1] found that there was an association between short roots and malocclusion. A study by Uehara et al.[2] dictated that malocclusion itself was a risk factor for shortening of roots. Literature on root resorption dictated that treated Class II malocclusions exhibited root resorption.[3]

Anatomic details like root form and size, heavy masticatory forces, occlusal trauma due to premature contacts and gender have been reported to influence the root resorption.[4] Moreover, among all teeth, maxillary incisors were reported with greater incidence of root resorption among all teeth.[5]

So, knowing the etiology and assessing root resorption is important prior to the start of orthodontic treatment. This article aimed to assess the root-crown ratio of maxillary incisors in sagittal skeletal and dental malocclusions with no history of orthodontic treatment to assess root resorption.

 Materials and Methods

The subjects comprised of healthy patients of age range between 12 and 35 years, with Skeletal and Angle's Classes I, II and III malocclusions with full complement of dentition. Patients who enrolled for the treatment at Orthodontics and Dentofacial Orthopaedics department were included. Ethical clearance with the Institutional Review Board (IRB) no. VDC/IEC/2014-08 was granted by the Ethical committee was obtained dated- 21/01/2014.


Before commencing the actual study, a pilot study was carried out to check feasibility and to estimate the sample size. Based on the findings of the pilot study, the actual sample size was found to be 85 patients. Patients who had a previous history of orthodontic treatment, history of trauma and patients with dental anomalies like impaction, agenesis, dilaceration, fusion, gemination and craniofacial syndromes, cleft lip and palate patients were excluded from the study. Patients with periodontitis, attrition, bruxism and systemic disorders like diabetes, bronchial asthma, allergy, thyroid and parathyroid disorders were eliminated from the study. The study was well explained to the subjects.


After the initial examination, lateral cephalographs were obtained and traced to assess the skeletal morphology [Table 1]. Based on the inclusion criteria and sample size estimation, 45, 25 and 15 patients for Skeletal and Angle's Classes I, II and III groups, respectively, were included. Panoramic radiographs and periapical radiographs for maxillary incisors using paralleling technique were obtained for all the patients before initiation of the orthodontic treatment. All the radiographs were obtained from the same radiographic machine with a magnification of 10% to rule out the magnification error.{Table 1}

Permanent maxillary incisors were traced with a tip measuring 0.5 mm on acetate sheets using 10× magnification lens from periapical radiographs and panoramic radiographs and points like root apex point (a), cemento-enamel junction (b) and incisal edge point (c) were marked [Figure 1]. The length of the root and crown of maxillary incisors were assessed from panoramic and periapical radiographs by using 'Method of Lind'.[6] For measuring the root-crown ratio, three parallel reference lines were drawn on the basis of the points traced. Crown height (C) was measured along the perpendicular lines, from line 'b' to line 'c' and root length (RL) was measured along the perpendicular lines, from line 'a' to line 'b' using digital Vernier caliper (Mitutoyo, Japan). The root-crown ratio of an individual tooth was calculated by dividing the root length by the crown length (RL/C).{Figure 1}

Statistical analysis

Statistical tests were performed using conventional SPSS 21 statistical analysis software (IBM SPSS statistics for Windows, Version 21.0 Armonk, NY, IBM Corp). Analysis of variance (ANOVA) and post hoc Tukey tests were used for measuring the mean variation of the root-crown ratio between Classes I, II and III groups. The differences in the mean root-crown ratio among variables like gender and between Class II div 1 and 2 were assessed by unpaired t-test.

Method error

To assess intra-examiner reproducibility and reliability of the measurements, all radiographs were retraced at an interval of 2 months.[7] To assess the inter-examiner reliability 10% of the total patient radiographs were retraced. Kappa statistics was applied to determine any differences.


Among all malocclusions, the root-crown ratios of the maxillary incisors in Skeletal and Angle's Class III (mean = 1.25) were significantly (P < 0.05) lesser than Class I and Class II groups (mean of Class I = 1.45, mean of Class II = 1.58) [Table 2]. However, there was no statistically significant difference in the root-crown ratio between Division 1 and Division 2 of Class II malocclusion [Table 3]. The males and females exhibited similar root resorption and there was no gender predilection [Table 4].{Table 2}{Table 3}{Table 4}

Inter-examiner reliability and intra-examiner reliability showed agreement with values of 0.80 and 0.86, respectively.


Root resorption is directly proportional to the root-crown ratio which implicates that a decrease in the root-crown ratio represents the presence of root resorption. The root-crown ratios were chosen instead of linear measurements like root and crown lengths because ratios were unaffected by radiographic proportional changes.[8] The present study demonstrated that Skeletal and Angle's Class III malocclusion group exhibited the least root-crown ratios compared to the other groups which implies that root resorption was found in Skeletal and Angle's Class III malocclusion. Also, Class I group exhibited lower root-crown ratios than Class II group, but were not statistically significant. Within Class II malocclusion group, no significant differences of root-crown ratio between Division 1 and Division 2 were observed. On observation, maxillary central incisors had decreased root-crown ratios compared to maxillary lateral incisors irrespective of malocclusion.

The present study revealed decreased root-crown ratio in Skeletal and Angle's Class III malocclusions. A possible explanation could be owed to skeletal malformation. Fernandez et al.[9] elucidated that certain dental anomalies could be specific for some skeletal malocclusion patterns and they share similar genetic contributions. Also, one more reason could be a possible disturbance during odontogenesis.

Arntsen et al.[10] noted that the lengths of maxillary incisors were affected in Class III malocclusion prior to the orthodontic treatment. They studied root resorption in various skeletal malocclusions and assessed in profile radiographs. There could be possible overlapping of all incisors in the profile radiographs. So, panoramic radiographs and periapical radiographs with paralleling technique were opted for the assessment in this study.

Literature on root resorption dictated that patients with open-bite malocclusion were at risk for root resorption.[11] Tongue thrusting may be a possible etiological factor of root resorption in the open-bite patients where detrimental forces were applied by the tongue. The presence of more number of open bites in the Class III sample compared to the other groups may also be responsible for the decrease in the root-crown ratios in Class III group.

Association between root resorption and gender was also assessed. A negative correlation of gender and root resorption was found in the present study. Various studies found a positive correlation for gender predilection where females were reported to have more root resorption compared to males (Massler and Perreault, 1954; Newman, 1975).[12],[13]

Root resorption is directly correlated to the age of the individual and increases with an increase in age.[13] The present study included patients with the age of 12-35 years because complete root formation of maxillary lateral incisors takes place by 12 years.

The present study suggests that shorter dental roots were found in Skeletal and Angle's Class III than other patients with various malocclusions. The findings of this study are considered to be important for orthodontic diagnosis and treatment. As various studies dictate that root resorption depends on the type, technique and force levels of orthodontic treatment;[14],[15] so, Class III malocclusion can be considered as a risk factor for root resorption and should be assessed thoroughly prior to orthodontic treatment. Diagnostic aids, such as 3D imaging techniques like computed tomography and cone beam computed tomography, are more likely to help for detecting the resorption lacunae.


Patients with Skeletal and Angle's Class III had an unfavorable root-crown ratio for maxillary incisors compared to Skeletal and Angle's Class I and Class II groups.Root resorption did not show any gender predilection.Maxillary central incisors were observed to have decreased root-crown ratios compared to maxillary lateral incisors irrespective of malocclusion.

So, these factors should be kept in mind before starting the orthodontic treatment in various malocclusions, which exhibited resorption even before the start of the orthodontic treatment.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


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