Journal List > Korean J Orthod > v.38(1) > 1043574

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

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.

Figures and Tables

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.
kjod-38-5-g002
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.
kjod-38-5-g003
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.
kjod-38-5-g005
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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Table 1
Insertion and removal torque for loading periods by mini-screw type.
kjod-38-5-i001

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

Table 2
Mobility change for loading periods
kjod-38-5-i002

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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