Korean J Orthod.  2008 Feb;38(1):5-12. 10.4041/kjod.2008.38.1.5.

Insertion and removal torques according to orthodontic mini-screw design

• Cha JY
• Yoon TM
• Hwang CJ

• KMID: 1481501
• DOI: http://doi.org/10.4041/kjod.2008.38.1.5

Abstract

OBJECTIVE
This study was designed to analyze the primary and secondary stability characteristics of orthodontic mini-screws of tapered design when compared with the cylinder mini-screw.
METHODS
A total of 48 mini-screws were placed into the buccal alveolar bone of the mandible in 6 male beagle dogs. Comparison was made between tapered and cylinder type mini-screws (Biomaterials Korea, Seoul, Korea). Maximum insertion torque (MIT) was measured using a torque sensor (Mark-10, MGT 50, USA) during installation, and maximum removal torque (MRT) was recorded after 3 and 12 weeks of loading.
RESULTS
Taper mini-screws showed a higher MIT value of 22.3 Ncm compared with cylinder mini-screw showing 13.6 Ncm (p < 0.001). The MRT of the taper mini-screw showed a significantly higher value of 9.1 Ncm than those of cylinder mini-screw of 5.7 Ncm at 3-weeks after installation (p < 0.05). However, there was no difference in the MRT value between the taper and cylinder mini-screws at 12 weeks of loading.
CONCLUSIONS
These results showed that the high insertion torque of the taper mini-screw design increases initial stability until 3 weeks of loading, but does not have any effect on the secondary stability at 12 weeks of loading.

Keyword

Orthodontic mini-screw; Insertion torque; Removal torque

MeSH Terms

Animals
Dogs
Humans
Korea
Male
Mandible
Torque

Figure

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  Fig 1 Drawing of cylindrical type (1507C) & taper type (1507T) mini-screws (unit: mm).

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  Fig 2 Schematic image for mini-screw insertion. a and b, Axial and sagittal images for the localization of mini-screws; c, force applied groups were reciprocally loaded by elastic-chain. FCS, force applied cylinder mini-screw; FTS, force applied taper mini-screw; CCS, control group of cylinder mini-screw; CTS, control group of taper mini-screw.

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  Fig 3 Timetable for placing mini-screw. w, weeks; FCS, force applied cylindrical mini-screw; FTS, force applied taper mini-screw; CCS, control group of cylindrical mini-screw; CTS, control group of taper mini-screw.

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  Fig 4 Insertion and removal torque (Ncm) for screw types. Statistically significant difference between periods by independent t-test; *p < 0.001.

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  Fig 5 Graphs of insertion and removal torque for loading periods. Statistically significant difference between periods by independent t-test and Scheffe test, *p < 0.05; †p < 0.01; ‡p < 0.001.

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  Fig 6 Graph of mobility change for loading periods. Cylinder-E, Cylinder type of experimental group; Cylinder-C, cylinder type of control group; Taper-E, taper type of experimental group; Taper-C, taper type of control group, *p < 0.05.

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