Korean J Orthod.  2011 Aug;41(4):280-287. 10.4041/kjod.2011.41.4.280.

The comparison of torque values in two types of miniscrews placed in rabbits: tapered and cylindrical shapes: Preliminary study

• Kim KH
• Chung C
• Yoo HM
• Park DS
• Jang IS
• Kyung SH

• KMID: 2274262
• DOI: http://doi.org/10.4041/kjod.2011.41.4.280

Abstract

OBJECTIVE
This study compared the stability of cylindrical miniscrews (Cy, 7 mm in length) with that of tapered miniscrews (Ta, 5 mm in length), using torque values to determine if the healing time before loading affects the stability of the miniscrew and if the insertion torque is associated with the removal torque measured after a few weeks of healing.
METHODS
Ta and Cy with different thread lengths were placed in the tibias of 12 female New Zealand white rabbits (body weight: 3.0 - 3.5 kg), and the maximum insertion torque values (ITV) were measured. No orthodontic forces were applied so as to allow us to determine the pure effects of the different shapes. After 3 different healing periods (2, 4, and 6 weeks), maximum removal torque values (RTV) were measured immediately before the rabbits were sacrificed.
RESULTS
No miniscrews were loosened. There were no significant differences in ITV or RTV between the Ta and Cy nor were there any significant differences in the ITV and RTV between the 3 groups, which had different healing periods. There was a correlation between the ITV and RTV.
CONCLUSIONS
Shorter Ta showed similar stability as Cy, as determined by torque values. This result strongly suggests that the tapered shape is more advantageous than the cylindrical shape. The RTV did not increase significantly over time. It is recommended that a miniscrew be loaded immediately; waiting a few weeks before loading should be avoided. The correlation between the ITV and RTV suggests that the ITV can be used to estimate a screw's future stability.

Keyword

Tapered shape; Torque; Miniscrew; Stability

MeSH Terms

Female
Humans
Rabbits
Tibia
Torque

Figure

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  Fig. 1 Diameters and thread lengths of 2 types of miniscrews.

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  Fig. 2 Two miniscrews were placed into each tibia after making 1 mm (diameter) pilot holes with a distance of 15 mm between them.

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  Fig. 3 The digital torque gauge used in this study.

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  Fig. 4 Scatter plot of the RTV and ITV of 48 miniscrews. Ta, Tapered miniscrew; Cy, cylindrical miniscrew; RTV, removal torque value; ITV, insertion torque value.

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