Cortical bone thickness and root proximity at mandibular interradicular sites: implications for orthodontic mini-implant placement

Ju-Eun Lim; Won-Hee Lim; Youn-Sic Chun

doi:10.4041/kjod.2008.38.6.397

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Lim, Lim, and Chun: Cortical bone thickness and root proximity at mandibular interradicular sites: implications for orthodontic mini-implant placement

Original Article

Korean Journal of Orthodontics

Korean Journal of Orthodontics 2008; 38(6): 397-406.

Published online: 31 December 2008

DOI: https://doi.org/10.4041/kjod.2008.38.6.397

Cortical bone thickness and root proximity at mandibular interradicular sites: implications for orthodontic mini-implant placement

Ju-Eun Lim, DDS, MSD^a, Won-Hee Lim, DDS, MS, PhD^b, Youn-Sic Chun, DDS, MSD, PhD^c

^aPostgraduate student, Department of Orthodontics, Graduate School of Clinical Dentistry, Ewha Womans University, Korea.

^bAssistant Professor, Department of Orthodontics, School of Dentistry, Seoul National University, Korea.

^cProfessor, Department of Orthodontics, Graduate School of Clinical Dentistry, Ewha Womans University, Korea.

Corresponding author: Won-Hee Lim. Department of Orthodontics, School of Dentistry, Seoul National University, 275-1, Yeongeon-dong, Jongno-gu, Seoul 110-749, Korea. +82 2 2072 0272; whlim@snu.ac.kr

Received 20 May 2008 Revised 2 October 2008 Accepted 6 October 2008

Abstract

Objective

The purpose of this study was to provide clinical guidelines to indicate the best location for mini-implants as it relates to the cortical bone thickness and root proximity.

Methods

CT images from 14 men and 14 women were used to evaluate the buccal interradicular cortical bone thickness and root proximity from mesial to the central incisor to the 2nd molar. Cortical bone thickness was measured at 4 different angles including 0°, 15°, 30°, and 45°.

Results

There was a statistically significant difference in cortical bone thickness between the second premolar/ first permanent molar site, central incisor/central incisor site, between the first/second permanent molar site and in the anterior region. A statistically significant difference in cortical bone thickness was also found when the angulation of placement was increased except for the 2 mm level from the alveolar crest. Interradicular spaces at the 1st/2nd premolar, 2nd premolar/1st permanent molar and 1st/2nd permanent molar sites are considered to be wide enough for mini-implant placement without root damage.

Conclusions

Given the limits of this study, mini-implants for orthodontic anchorage may be well placed at the 4 and 6 mm level from the alveolar crest in the posterior region with a 30° and 45° angulation upon placement.

Keywords: Mini-implant, Cortical bone thickness, Root proximity

Figures and Tables

Fig 1

A, 3D reconstructed CT image using V-works 4.0™; B, bisect the image along a line that passes the contact point and perpendicular to the occlusal plane; C, bisected and 90° right-rotated sagittal image between Lt. and Rt. mandibular central incisors.

Fig 2

Measurement of cortical bone thickness. Cortical bone thickness was measured in 4 different angles (0°, 15°, 30°, 45°) at 2, 4, 6 mm height from the alveolar crest.

Fig 3

Measurement of root proximity. 'Central' means the closest distance between the tangent lines, each one tangent to the proximal root surface. 'Buccal' means the distance between the intersecting points which are made by two tangent lines, one is tangent to proximal root surface and the other is tangent to buccal root surface. 'Horizontal' means the closest distance from 'buccal' to 'central'.

Fig 4

Mean value of cortical bone thickness in the mandible. Inter-bar connecting lines mean significant differences between one and the other (p < 0.05). 1, Central incisor; 2, lateral incisor; 3, canine; 4, first premolar; 5, second premolar; 6, first molar; 7, second molar.

Fig 5

Cortical bone thickness with different angulations at the 2 mm level. Inter-bar connecting lines mean significant differences between one and the other (p < 0.05). 1, Central incisor; 2, lateral incisor; 3, canine; 4, first premolar; 5, second premolar; 6, first molar; 7, second molar.

Fig 6

Cortical bone thickness with different angulations at the 4 mm level. Inter-bar connecting lines mean significant differences between one and the other (p < 0.05). 1, Central incisor; 2, lateral incisor; 3, canine; 4, first premolar; 5, second premolar; 6, first molar; 7, second molar.

Fig 7

Cortical bone thickness with different angulations at the 6 mm level. Inter-bar connecting lines mean significant differences between one and the other (p < 0.05). 1, Central incisor; 2, lateral incisor; 3, canine; 4, first premolar; 5, second premolar; 6, first molar; 7, second molar.

Fig 8

Mean value of root proximity in the mandible. 1, Central incisor; 2, lateral incisor; 3, canine; 4, first premolar; 5, second premolar; 6, first molar; 7, second molar.

Table 1

Cortical bone thickness (Mean ± SD) with different angulations at 2, 4, 6 mm levels (unit; mm)

^aSignificant difference between 0° and 15° (p < 0.05); ^bsignificant difference between 0° and 30° (p < 0.05); ^csignificant difference between 0° and 45° (p < 0.05); ^dsignificant difference between 15° and 30° (p < 0.05); ^esignificant difference between 15° and 45° (p < 0.05); ^fsignificant difference between 30° and 45° (p < 0.05); 1, central incisor; 2, lateral incisor; 3, canine; 4, first premolar; 5, second premolar; 6, first molar; 7, second molar.

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