A Cone-beam Computed Tomography Evaluation of Mandibular Anterior Alveolar Bone Dimensions in Class I and Class II Skeletal Patterns

INTRODUCTION

A healthy periodontium, alveolar bone, and gingiva determine the life span of a tooth in the oral cavity. A basic criterion for efficient tooth movement during orthodontic treatment and stable tooth position after orthodontic treatment is the viable bone width around the tooth. Applying unplanned orthodontic forces can result in unhealthy bone remodeling around the alveolus, thus leading to gingival recession, external root resorption, fenestration, and dehiscence.¹

Current literature proves the correlation exists between vertical growth patterns and the thickness of the surrounding bone.^2,3 In a study by Handelman, patients with low mandibular plane angles possess wider lingual bone widths in the maxillary and mandibular incisor region and high mandibular angle cases have a thinner labial bone in the region of the mandibular incisor.⁴ Patients with the increased vertical dimension of the face have a reduced amount of supporting bone compared with short face or horizontal growth pattern patients and so it restricts the range of movements available for teeth. To maintain an ideal overbite in long face patients, there is a continuous eruption of incisors and thus the alveolus undergoes thinning and weakening of the buccolingual walls.⁴

During orthodontic treatment, the position and movement of the mandibular incisors play a crucial role in the diagnosis and treatment planning of skeletal class II and class III malocclusions. In a recent study by Coşkun and Kaya,⁵ no significant difference was found between skeletal class I, class II, and class III groups when the buccal and lingual cortical bone thickness was concerned, but a significant difference was noticed between the three groups for the thickness of cancellous bone (Figs 1 to 4).

Therefore, the maximum anterior limit of the mandibular incisors should be set before the treatment, especially in patients with severe skeletal discrepancies where incisor movement is limited by the health of the periodontal tissues, condition of the surrounding bone, and the anatomy of the symphysis.^6,7

MATERIALS AND METHODS

The cone-beam computed tomography (CBCT) scans of 30 patients [class I-10 patients, class II-20 (10-high angle, 10-low angle)], collected from the Department of Oral Medicine and Radiology, Kalinga Institute of Dental Sciences, Bhubaneswar, Odisha were evaluated. To standardize the parameters, the patient selection was done under the following criteria:

• Orthodontically untreated, nongrowing adults with class I and II malocclusion in the age group of 20 to 40 years.
• Patients with healthy periodontium and without any radiographic bone pathology.
• Patients without any craniofacial anomalies or systemic diseases.
• Patients without any missing or unerupted mandibular permanent incisors.
• Patients without any history of trauma to the lower anterior teeth.
• Patients without any crowding or spacing in the mandibular anterior alveolar segment.
• Patients without any prosthetic crowns on the mandibular incisors.

The CBCT apparatus used in the study was HYPERION X9 (QR SRL Co, Verona, Italy) at 90 kV, 10 mA, and voxel size 0.3 × 0.3 × 0.3 with a field of view (FOV) 11 × 8 cm. The images obtained were analyzed with NNT software (version 4.6, Italy). A multiplanar reconstruction (MPR) was taken and the facial height index (FHI) was used to find out the facial growth pattern.⁸ Facial height index is the ratio of the posterior facial height (PFH) to the anterior facial height (AFH).⁹ Based on FHI, facial growth pattern was classified as hyperdivergent (FHI values %3C;0.649), normal (FHI values between 0.65 and 0.75), and hypodivergent (FHI values %3E;0.751). Wit’s analysis was used to find out the skeletal anteroposterior relationship.¹⁰

The CBCT images of the mandible were not distorted or magnified and were displayed simultaneously with their coronal, axial, and sagittal slices so that the mandibular anterior tooth regions could be accurately measured in three dimensions. The axial plane was selected to derive the cross-section of the mandibular central incisors. The sagittal and coronal planes were adjusted so that they would pass through the center of the long axis of the root of the central incisor with the sagittal plane perpendicular to the patient’s arch in the axial view. In the sagittal section, buccal and lingual alveolar crestal thickness was measured. Along the long axis of the root, from the most coronal level of the alveolar bone crest, alveolar bone width measurements were made along the sagittal reference planes at the alveolar crest level and 3, 6, and 9 mm apical to the CEJ. Buccal and lingual bone thickness was measured from the most buccal and lingual aspects of the root outline to the most buccal and lingual aspects of the alveolar bone outline in the sagittal plane.

RESULTS

As noted in Table 1, in class I average growing patients, the minimum and maximum mean buccal alveolar bone thickness was recorded at the alveolar crest (0.52 ± 0.05 mm) and 9 mm from the alveolar crest (3.61 ± 0.20 mm), respectively. A similar trend was noted with the lingual alveolar bone thickness too. But in the class II patients, the high-angle patients showed minimum buccal and lingual alveolar thickness at 3 mm (0.49 ± 0.03 mm) and the alveolar crest level (0.69 ± 0.09 mm), respectively, whereas both maximum buccal (1.85 ± 0.18 mm) and lingual (2.52 ± 0.07 mm) bone thickness was seen at 9 mm from the alveolar crest. In class II low-angle cases, both the minimum buccal (0.64 ± 0.11 mm) and minimum lingual (0.61 ± 0.12 mm) alveolar bone thickness was noted at the alveolar crest level. At a level 9 mm from the alveolar crest, a maximum buccolingual thickness of 3.08 ± 0.11 and 2.46 ± 0.14 mm, respectively, was observed in class II low-angle patients.

DISCUSSION

This study was conducted on CBCT scans of 30 nonorthodontically treated patients. The sample was divided into three groups class I average, class II cases based on Wit’s appraisal. The class II group was further divided into low- and high-angle cases basing on the FHI. The study was done to compare mandibular anterior alveolar bone morphology among these groups.

The amount of bone present in the mandibular incisor region is important when sagittal movements are considered in orthodontics like cases of premolar extractions,¹¹ distalization using temporary anchorage devices, and cases requiring large compensations.² The structure of the mandibular symphysis plays a pivotal role in restricting the movement of the incisors as the buccolingual alveolar bone thickness of the lower anterior teeth is thinner than other areas intraorally and definitely more susceptible to periodontal disease.¹² It has been reported in the literature that any kind of tooth movement on average causes 10% shortening of roots.^13–15

Cone-beam computed tomography used in the study has emerged as an efficient diagnostic imaging tool for studying the anatomical and pathological aspects of the oral and maxillofacial region. Technical efficacy in CBCT imaging is related to the quality of the image. The dimensional accuracy of CBCT images with a typical voxel size of 0.3 to 0.4 mm has been already well established.¹⁶ Tomographic imaging is still considered as the gold standard method for the evaluation of the bone anatomy, but according to the current recommendation of the American Academy of Oral and Maxillofacial Radiology (AAOMR) CBCT can be advised for cases where its use will be essential for the establishment of diagnosis or treatment planning but only after analyzing the radiation burden and stochastic effects.¹⁷

In this study, class I average growing patients have thicker buccal and lingual alveolar thickness at all levels except at the alveolar crest where the class II patients exhibit greater marginal bone thickness. When we further compare among the high and low growth patterns in skeletal class II patients, at the alveolar crest level, the lingual alveolar thickness is more in high-angle cases and less in low-angle cases. At a level 3 mm from the alveolar crest, the low-angle cases exhibit thicker buccal and thinner lingual bone width. A similar trend was noted at 9 mm from the alveolar bone crest, where buccal bone thickness in low-angle cases and lingual bone thickness is more in high-angle cases. At 6 mm from the alveolar crest, low-angle cases show greater buccal and lingual alveolar bone thickness.

If we compare within the groups, in class I average growing patients the lingual alveolar bone is thicker in all sites except at 9 mm from the alveolar crest level. But a study by Baysal et al.¹⁸ concluded that labial alveolar bone thickness of lower incisors was significantly higher in the class I group compared with that of the class II group.

In the current study, all sites in class II high-angle patients exhibit thicker lingual bone thickness than the buccal counterpart. Whereas in class II low-angle cases, all sites have a greater buccal bone thickness except at 6 mm from the alveolar crest level. As concluded by Veli et al.,¹⁹ the buccal cortical bone thickness varies depending on the sites between and within the jaws and according to the growth pattern. The thickness of mandibular and maxillary buccal cortical bone increased toward the apical area in all regions which were studied regardless of the growth pattern. As the buccal cortical bone is thinner in high-angle patients, difficulties may be encountered in achieving primary stability during miniscrew treatment.²⁰

Yet another study by Baysal and Uysal²¹ in the year 2014 concluded that myofunctional appliances used for sagittal correction in class II division 1 patients resulted in proclined lower anteriors as an adverse effect along with an increase in the mandibular length as the desired effect. So, while treating such patients we should keep the mandibular anterior bone dimensions in mind to manage iatrogenic effects if any.

Pandis et al.,²² Pandis et al.,²³ and Fleming et al.²⁴ reported that the self-ligating bracket system produced greater expansion in the intercanine, interpremolar, and intermolar regions when compared with the conventional system. The conventional extraction series bracket system also results in root prominences due to inadvertent expression of tip and torque values. Therefore, during treatment planning with a self-ligating or conventional bracket system, the buccal and lingual alveolar bone dimensions in the maxilla and mandible should be examined preferably through 3D radiography to offer the patients with favorable outcomes.

CONCLUSION

This study was conducted with CBCT images obtained from 30 nonorthodontically treated patients. The sample was further divided into two groups class I average growing patients and class II patients based on the value from Wit’s appraisal. The class II group was further divided into low- and high-angle cases based on the FHI value. The study was done to compare mandibular anterior alveolar bone thickness among these groups. The following conclusions were derived from the study:

• In class I average growing patients, the lingual alveolar bone is thicker than the buccal alveolar bone.
• Class II high-angle patients exhibit thicker lingual bone thickness and class II low-angle cases have a greater buccal bone thickness in the mandibular anterior region.

REFERENCES

1. Reitan K. Clinical and histologic observations on tooth movement during and after orthodontic treatment. Am J Orthod 1967;53(10):721–745. DOI: 10.1016/0002-9416(67)90118-2.

2. Tsunori M, Mashita M, Kasay K. Relationship between facial types and tooth and bone characteristics of the mandible obtained by CT scanning. Angle Orthod 1998;68:557–562.

3. Gracco A, Luca L, Bongiorno MC, et al. Computed tomography evaluation of mandibular incisor bony support in untreated patients. Am J Orthod Dentofacial Orthop 2010;138(2):179–187. DOI: 10.1016/j.ajodo.2008.09.030.

4. Handelman CS. The anterior alveolus: its importance in limiting orthodontic treatment and its influence on the occurrence of iatrogenic sequelae. Angle Orthod 1996;66(2):95–109.

5. Coşkun İ, Kaya B. Relationship between alveolar bone thickness, tooth root morphology, and sagittal skeletal pattern: A cone beam computed tomography study. J Orofac Orthop 2019;80(3):144–158. DOI: 10.1007/s00056-019-00175-9.

6. Yared KF, Zenobio EG, Pacheco W. Periodontal status of mandibular central incisors after orthodontic proclination in adults. Am J Orthod Dentofacial Orthop 2006;130(1):6.e1–6.e8. DOI: 10.1016/j.ajodo.2006.01.015.

7. Ten Hoeve A, Mulie RM. The effect of anteropostero incisor repositioning on the palatal cortex as studied with laminagraphy. J Clin Orthod 1976;10:804–882.

8. Horn AJ. Facial height index. Am J Orthod Dentofacial Orthop 1992;102(2):180–186. DOI: 10.1016/0889-5406(92)70031-5.

9. Gebeck TR, Merrifield LL. Orthodontic diagnosis and treatment analysis—concepts and values. Part I. Am J of Orthod Dentofacial Orthop 1995;107(4):434–443. DOI: 10.1016/S0889-5406(95)70097-8.

10. Jacobson A. The “Wits” appraisal of jaw disharmony. Am J Orthod and Dentofacial Orthop 1975;67(2):125–138. DOI: 10.1016/0002-9416(75)90065-2.

11. Fuhrmann RA. Three-dimensional evaluation of periodontal remodeling during orthodontic treatment. Semin Orthod 2002;8(1):23–28. DOI: 10.1053/sodo.2002.28168.

12. Holmes PB, Wolf BJ, Zhou JA. CBCT atlas of buccal cortical bone thickness in interradicular spaces. Angle Orthod 2015;85(6):911–919. DOI: 10.2319/082214-593.1.

13. Sameshima GT, Sinclair PM. Predicting and preventing root resorption: part II. Treatment factors. Am J Orthod Dentofacial Orthop 2001;119(5):511–515. DOI: 10.1067/mod.2001.113410.

14. Sameshima GT, Sinclair PM. Characteristics of patients with severe root resorption. Orthod Craniofac Res 2004;7(2):108–114. DOI: 10.1111/j.1601-6343.2004.00284.x.

15. Segal GR, Schiffman PH, Tuncay OC. Meta analysis of the treatment-related factors of external apical root resorption. Orthod Craniofac Res 2004;7(2):71–78. DOI: 10.1111/j.1601-6343.2004.00286.x.

16. Ballrick JW, Palomo JM, Ruch E, et al. Image distortion and spatial resolution of a commercially available cone-beam computed tomography machine. Am J Orthod DentofacialOrthop 2008;134(4):573–582. DOI: 10.1016/j.ajodo.2007.11.025.

17. American Academy of Oral and Maxillofacial Radiology AAOMR. Clinical recommendations regarding use of cone beam computed tomography in orthodontics. Position statement by the American Academy of Oral and Maxillofacial Radiology. OralSurg Oral Med Oral Pathol Oral Radiol 2013;116(2):238–257. DOI: 10.1016/j.oooo.2013.06.002.

18. Baysal A, Ucar FI, Buyuk SK, et al. Alveolar bone thickness and lower incisor position in skeletal class I and class II malocclusions assessed with cone-beam computed tomography. Korean J Orthod 2013;43(3):134–140.

19. Veli I, Uysal T, Baysal A, et al. Buccal cortical bone thickness at miniscrew placement sites in patients with different vertical skeletal patterns. J Orofac Orthop 2014;75(6):417–429. DOI: 10.1007/s00056-014-0235-7.

20. Ozdemir F, Tozlu M, Germec-cakan D. Cortical bone thickness of the alveolar process measured with cone-beam computed tomography in patients with different facial types. Am J Orthod Dentofac Orthop 2013;143(2):190–196. DOI: 10.1016/j.ajodo.2012.09.013.

21. Baysal A, Uysal T. Dentoskeletal effects of Twin Block and Herbst appliances in patients with class II division 1 mandibular retrognathyEur. J Orthod 2014;36:164–172.

22. Pandis N, Polychronopoulou A, Eliades T. Self-ligating vs conventional brackets in the treatment of mandibular crowding: a prospective clinical trial of treatment duration and dental effects. Am J Orthod Dentofacial Orthop 2007;132(2):208–215. DOI: 10.1016/j.ajodo.2006.01.030.

23. Pandis N, Polychronopoulou A, Makou M, et al. Mandibular dental arch changes associated with treatment of crowding using self-ligating and conventional brackets. Eur J Orthod 2010(3):1–6. DOI: 10.1093/ejo/cjp123.

24. Fleming PS, DiBiase A, Sarri G, et al. Comparison of mandibular arch changes during alignment and leveling with 2 preadjusted edgewise appliances. Am J Orthod Dentofacial Orthop 2009;136(3):340–347. DOI: 10.1016/j.ajodo.2007.08.030.