Evaluation of Alveolar Bone Thickness Around the Incisors in Various Skeletal Patterns: A Cephalometric Study

HIGHLIGHTS

The study provides insight into the amount of alveolar bone covering the roots of incisors to allow the orthodontist to plan the treatment accordingly and avoid any ill effects of contacting the roots with the cortical bone of the alveolar housing.

INTRODUCTION

Anterior teeth are the key consideration in the line of diagnosis and treatment planning for the orthodontist. Even for patients the prime focus is the front teeth in the chief complaints regardless of any other malocclusion and deformities.¹

Teeth are surrounded by the alveolar bone, the severity of which, predicts the amount of tooth movement that can be brought about orthodontically.² Movement of the tooth outward will lead to bone loss, and traumatized placement; optimized positioning of the teeth is of paramount importance for functional stability and esthetics.^3–6

Class II malocclusion is the most prevalent malocclusion in the northern part of India with proclination of maxillary incisors being the major concern.⁷ During retraction, it is imperative that the position and inclination of incisor roots be well within the cancellous bone and never in proximity to the cortical bone.^8,9

Although few studies have been carried out to determine the position of incisors within the alveolus, the effect of malocclusion and ethnicity factors is yet to be investigated. This can be done using lateral cephalograms which are a convenient and cost-effective technique to study skeletal and dentoalveolar patterns.^4,10,11

Hence, our study aims to determine the thickness of alveolar bone around maxillary and mandibular incisors in various skeletal patterns in the North Indian population.

MATERIALS AND METHODOLOGY

RESULTS

• U1 at apex: U1 lab apex was significantly increased in group I as compared to group III (0.002) and group IV (0.008), and group II was significantly increased than group III (0.020). While the opposite was true for values of U1 pal apex (Tables 1 and 2).

• U1 at middle: While no significant intergroup difference was observed for U1 lab middle, the alveolar width was significantly increased in group IV (0.020) than in group I (Tables 1 and 2).

• L1 at apex: The value for L1 lab apex was significantly increased in group III as compared to group II (0.011) and group IV (0.000). Also, group I showed a significant difference (0.035) in L1 lab apex than group IV whereas the intergroup difference between the values of L1 pal apex was not significant (Tables 1 and 2).

• L1 at middle: No significant difference was found in intergroup comparison for L1 Lab middle and L1 Pal middle values (Tables 1 and 2).

• Incisal inclination: The upper central incisor showed highly significant (0.000) proclination in groups I, II, and IV as compared to group III. The inclination of the lower central incisor was significantly increased in group I (0.000) and group II as compared to group III (0.004) and group IV (0.003) (Tables 1 and 3).

DISCUSSION

Skeletal discrepancies in adult patients can be managed through two main treatment options usually by orthodontic camouflage or in combination with orthognathic surgery. Patients who are reluctant to surgery have to be treated by orthodontic camouflage where compensation of maxillary and mandibular teeth is done to overcome skeletal disharmony. However, the position of the root apex housed in the alveolar bone needs to be thoroughly studied to explain its proximity to the cortical bone. Quite a few studies use lateral cephalogram for evaluating the alveolar bone since it is economical, effortless, and easily available.^4,5,11–15

Furthermore, Nayak et al. found similar results of reduced lingual bone of all incisors.¹⁴ Rojo–Sanchis J et al. conducted a systematic review and meta-analysis on the effect of modifying factors on facial alveolar bone thickness and reported that the bone overlying the anterior teeth is generally very thin typically in females and those over 50 years of age.¹⁶ Hence, any contact with the cortical bone during treatment may bring about iatrogenic damage. These may include root resorption, bone loss, and periodontal problems such as dehiscence and fenestrations. Additionally, tooth movement may also be hampered. Therefore, it becomes imperative to determine the position of incisors in the alveolus to diagnose and plan treatment for various skeletal malocclusions. The current study was undertaken to establish and evaluate the incisor position while taking into consideration the skeletal malocclusion.

• Class I: The maxillary and mandibular central incisors were found to be proclined as compared to class II division 2 malocclusion (Tables 1 and 3). In cases of Angle’s class I malocclusion with the orthognathic maxilla and mandible, the bimaxillary protrusion is a relatively common finding in the Indian population.¹⁷ In such instance, the alveolar bone width labial to the root apex of U1 was increased and the palatal bone was decreased in comparison to class II division 2 and class III malocclusion owing to proclined maxillary central incisors (Tables 1 and 2) This was also noted by Chu et al. in the Asian population where the palatal bone plate was thin in severely proclined maxillary incisors in class I malocclusion.¹⁸ Similar observations were found by Gracco et al. in maxillary incisors with severe proclination.¹⁹ Moreover, in this study, the palatal bone at the middle of the root of the maxillary central incisor was also found to be reduced. Proclination of mandibular central incisors also led to a wide labial bone at its root apex (Tables 1 and 2). Do TA et al. found similar results in their study stating that the palatal bone thickness had a negative correlation with the buccolingual angulation of lateral incisors.²⁰

• Therefore, the bimaxillary protrusion may be well treated by retraction of interiors since the apex is nearer to the palatal bone, and tipping the teeth lingually will place the roots in the center of the alveolus.

• Class II division 1: The central incisors in maxillary and mandibular arches were proclined in comparison to class II division 2 as in line with the classical feature of class II division I malocclusion (Tables 1 and 3). Andrews et al. examined the position of maxillary and mandibular central incisors in alveolar bone and also concluded that mandibular central incisors in class II exhibited signs of positional compensation for the anteroposterior skeletal discrepancy.¹² Our results are in accordance with those by Baysal et al. who observed a positive correlation between lingual bone and lower incisors with protrusive mandibular incisors in the class II group.²¹ The width of the alveolar bone labial and palatal to the root apex of the maxillary central incisor was similar to that seen in class I malocclusion (Tables 1 and 2). Tian et al. in their study, assessed the alveolar bone thickness in different inclinations of maxillary incisors and found similar results of increased labial alveolar bone at the apex of flared maxillary incisors.²² On the contrary, the labial alveolar bone at the apex of L1 was thinner (Tables 1 and 2) probably due to the forwardly positioned mandibular central incisors to compensate for large overjet and anteroposterior skeletal disharmony. These results are in accordance with those by Baysal et al. who observed a positive correlation between lingual bone and lower incisors with protrusive mandibular incisors in the class II group.²¹

• Hence, the proclined maxillary anterior may be retracted safely for correction of a skeletal discrepancy, whereas due to thin labial bone at the apex of mandibular incisors, the tipping of the lower anterior should be avoided. Furthermore, over-retraction of the upper anterior can also cause increased nasolabial angle and compromise the profile of the patient.

• Class II division 2: As commonly observed as a distinguishing feature, the maxillary and mandibular central incisors were found to be retroclined in the samples of this study (Tables 1 and 3). Due to the retroclined maxillary central incisors, the labial alveolar bone at the root apex was thinner, and the palatal alveolar bone was thicker as opposed to class I and class II division I (Tables 1 and 2). This was in agreement with that by Tian et al. where the root of the maxillary incisor was closer to the labial cortical plate implying a thin alveolar bone in cases of negatively inclined upper incisors and thicker palatal bone over its roots.²² While, for the mandibular central incisors, the labial bone at the apex showed increased width than in class III patterns (Table 3). This may be due to the retroclination of mandibular anterior to a larger extent in class III (Tables 1 and 3).

• Thus, compensation for skeletal discrepancy seems impossible by tipping the anterior teeth lingually without associated sequelae.

• Class III: The maxillary central incisors in class III malocclusion were proclined in comparison to class II division 2, while the mandibular central incisors showed retroclination in relation to class I and class II division 1 malocclusion (Tables 1 and 3). This result strongly agrees with previous studies which depicted compensation of maxillary and mandibular central incisors to skeletal class III pattern.^23–25 The labial alveolar bone width at the apex of U1 was reduced and palatal bone at the apex and middle was increased in comparison to the class I pattern (Tables 1 and 2). This may be attributed to the slightly upright position of U1 in class III than in class I cases. Ma J et al. analyzed the morphology of alveolar bone around anterior teeth in skeletal classes II and III cases with a severe vertical pattern. They inferred that the maxillary incisor roots were placed more lingually and had a thinner alveolar bone in skeletal class III cases.²⁶

• On the contrary, the alveolar bone present labially to the apex of L1 showed marked thinness as compared to class I and class II division 2 malocclusion (Tables 1 and 2). Yamada et al. showed similar results wherein they studied the alveolar bone around mandibular incisors in cases with mandibular prognathism.²⁷ Also, they concluded that the incisor root was closer to the labial cortical plate than the lingual with a maximum value for the lingual to be 4.7 mm and for the labial to be 1.9 mm.^5,27

In conclusion, mandibular prognathism cases cannot be solely treated by overcompensation as the root of lower incisors is close to the labial cortical plate and we must abstain from tipping it lingually.

Through the current study, we aim to evaluate the position of the root in the alveolar housing by determining the width of bone present labially and lingually to the maxillary and mandibular incisors in various patients with skeletal disharmony. This knowledge is necessary to plan and carry out orthodontic tooth movement without encountering any side effects for efficient orthodontic treatment. Ghassemian M et al. assessed the facial bone at points 1–5 mm from the alveolar crest.¹⁷ Their study concluded there is a high chance of fenestration in the anterior maxillary arch.

Lastly, the goal is to place the teeth upright in the alveolar bone as only then can we achieve a stable occlusion with good periodontal health and favorable esthetics.²⁸

CONCLUSION

• It was verified through our study that maxillary and mandibular incisors show dental compensations for skeletal deviations.

• The alveolar bone covering the maxillary incisors showed a similar pattern of thinner palatal bone in class I with bimaxillary protrusion and class II division 1. While the same was true for mandibular incisors in class I, labial bone in the case of class II division 1 was found to be thinner.

• The alveolar bone covering the root apices labially in cases of maxillary and mandibular incisors in class II division 2 and mandibular incisors in class III was significantly thin.

• The above findings should be kept in mind by the orthodontist during treatment planning and before proceeding with the intended mechanics for treating skeletal malocclusion through correction of incisal inclination.

ORCID

Deepankar Bhatnagar https://orcid.org/0000-0002-7260-6461

Harjoy Khatria https://orcid.org/0000-0003-0535-2980

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