Insertion and removal torques according to orthodontic mini-screw design

Jung-Yul Cha; Tae-Min Yoon; Chung-Ju Hwang

doi:10.4041/kjod.2008.38.1.5

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Cha, Yoon, and Hwang: Insertion and removal torques according to orthodontic mini-screw design

Original Article

Korean Journal of Orthodontics

Korean Journal of Orthodontics 2008; 38(1): 5-12.

Published online: 29 February 2008

DOI: https://doi.org/10.4041/kjod.2008.38.1.5

Insertion and removal torques according to orthodontic mini-screw design

Jung-Yul Cha, DDS, MSD, PhD^a, Tae-Min Yoon, DDS, MSD^b, Chung-Ju Hwang, DDS, MSD, PhD^c

^aFull-time lecturer, Department of Orthodontics, College of Dentistry, Yonsei University, Seoul, Korea.

^bGraduate student, Department of Orthodontics, College of Dentistry, Yonsei University, Seoul, Korea.

^cProfessor, Department of Orthodontics, College of Dentistry, Dental Science Research Institute, Yonsei University, Seoul, Korea.

Corresponding author: Chung-Ju Hwang. Department of Orthodontics, College of Dentistry, Yonsei University, Shinchon-Dong 134, Seodaemun-Gu, Seoul 120-752, Korea. +82 2 2228 3106; hwang@yuhs.ac.

Received 22 June 2007 Revised 11 October 2007 Accepted 13 October 2007

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.

Keywords: Orthodontic mini-screw, Insertion torque, Removal torque

Figures and Tables

Fig 1

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

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.

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.

Fig 4

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

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.

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.

Table 1

Insertion and removal torque for loading periods by mini-screw type.

SD, Standard deviation; Sig, significance; NS, not significant.

Table 2

Mobility change for loading periods

PT, Periotest value; SD, standard deviation; Sig, significance; NS, not significant; Statistically significant difference between cylinder and taper mini-screw by independent t-test, ^*p < 0.05. PT with -8 to +9 indicates clinically firm teeth or implant is well osseointegrated, PT over +10 indicates implant is not or not sufficiently osseointegrated (Shulte and Lukas24, 1992).

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