Korean J Orthod.  2018 Sep;48(5):283-291. 10.4041/kjod.2018.48.5.283.

Histomorphometric evaluation of the bone surrounding orthodontic miniscrews according to their adjacent root proximity

• Oh HJ
• Cha JY
• Yu HS
• Hwang CJ

• KMID: 2421313
• DOI: http://doi.org/10.4041/kjod.2018.48.5.283

Abstract

OBJECTIVE
This study was conducted to perform histomorphometric evaluations of the bone surrounding orthodontic miniscrews according to their proximity to the adjacent tooth roots in the posterior mandible of beagle dogs.
METHODS
Four male beagle dogs were used for this study. Six orthodontic miniscrews were placed in the interradicular spaces in the posterior mandible of each dog (n = 24). The implanted miniscrews were classified into no loading, immediate loading, and delayed loading groups according to the loading time. At 6 weeks after screw placement, the animals were sacrificed, and tissue blocks including the miniscrews were harvested for histological examinations. After analysis of the histological sections, the miniscrews were categorized into three additional groups according to the root proximity: high root proximity, low root proximity, and safe distance groups. Differences in the bone-implant contact (BIC, %) among the root proximity groups and loading time groups were determined using statistical analyses.
RESULTS
No BIC was observed within the bundle bone invaded by the miniscrew threads. Narrowing of the periodontal ligament space was observed in cases where the miniscrew threads touched the bundle bone. BIC (%) was significantly lower in the high root proximity group than in the low root proximity and safe distance groups. However, BIC (%) showed no significant differences among the loading time groups.
CONCLUSIONS
Regardless of the loading time, the stability of an orthodontic miniscrew is decreased if it is in contact with the bundle bone as well as the adjacent tooth root.

Keyword

Miniscrew; Root proximity; Bone–implant contact; Bundle bone

MeSH Terms

Animals
Dogs
Humans
Male
Mandible
Periodontal Ligament
Tooth Root

Figure

• 

  Figure 1 Experimental protocol used in the present study. Immediately after implantation, the miniscrews on the left side were loaded. At 3 weeks after implantation, the miniscrews on the right side were loaded and the force on the left side was reactivated. At 4 weeks after implantation, the animals received intravenous tetracycline for fluorescence microscopy. At 6 weeks, the animals were sacrificed. TC, Tetracycline; IV, intravenous.

• 

  Figure 2 Miniscrews placed in interradicular spaces in the posterior mandible of beagle dogs. An orthodontic force is applied using an elastomeric chain. U, No loading group (screw placed between the second and third premolars); L, loading groups (one screw is placed between the third and fourth premolars, while another is placed between the fourth premolar and first molar).

• 

  Figure 3 Classification of orthodontic miniscrews according to the proximity to the adjacent tooth roots using hematoxylin and eosin-stained sections (12.5×). A, High root proximity group. The miniscrew is in contact with the adjacent tooth root. B, Low root proximity group. The miniscrew is touching the bundle bone or the periodontal ligament but not contacting the adjacent root. C, Safe distance group. The miniscrew is placed in the interradicular septum, without any contact with the bundle bone.

• 

  Figure 4 Root proximity of an orthodontic miniscrew without orthodontic loading and low root proximity, with atrophic changes in the adjacent periodontal ligament. A, A hematoxylin and eosin-stained section (50×). The arrow indicates a miniscrew thread touching the bundle bone. The distance from the miniscrew to the root surface is 0.494 mm. Narrowing of the periodontal ligament space can be observed (area in the box, shown in B). B, A fluorescence microscopy image with high magnification (100×). Active bone deposition can be observed as a bright green line (arrow) at the alveolar bone surface facing the periodontal ligament space.

• 

  Figure 5 Effects of the proximity of an orthodontic miniscrew body to the bundle bone on the surrounding bone. The images show hematoxylin and eosin-stained sections. A and C, These are miniscrews with low root proximity. The miniscrew threads are invading the bundle bone (boxes, 12.5×). The miniscrew in A was loaded immediately after insertion, whereas the miniscrew in C was loaded at 3 weeks after insertion. The area in the box in A is shown in B, while the area in the box in C is shown in D. B and D, There is no direct bone–implant contact around the threads within the bundle bone (yellow arrows, 100×). Resorption of the adjacent tooth root can be observed (blue arrows).

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