Angled-predrilling depth and mini-implant shape effects on the mechanical properties of self-drilling orthodontic mini-implants during the angled insertion procedure

Abstract

Objective: To investigate the effects of orthodontic mini-implant (OMI) shape and angledpredrilling depth on the mechanical properties of OMIs during the angled insertion procedure. Materials and Methods: A total of 30 OMIs (self-drilling type, 7 mm in length) were allocated into six groups according to the OMI shape (cylindrical or tapered) and angled-predrilling depth (control, 1.5-mm and 4.0-mm angled-predrilling; predrilled with 1-mm-diameter drill-bit), as follows: C-con, C-1.5, C-4.0, T-con, T-1.5, and T-4.0 groups (N 5 5 per group). The OMIs were installed at an angle of 60u in double-layer artificial bone blocks that simulated the cortical and cancellous bone (SawboneH). Total insertion time (TIT), maximum insertion torque (MIT), total insertion energy (TIE), and inclination of the time-torque graph (INC) were measured. Results: Within the same shape group, angled-predrilling had a shorter TIT than did the control (control vs 1.5; control vs 4.0; all P , .05). MIT and TIE decreased in the order of control, 1.5-mm, and 4.0-mm angled-predrilling (control vs 1.5; 1.5 vs 4.0; all P , .05), but INC increased from control to 1.5-mm angled-predrilling and decreased from 1.5-mm to 4.0-mm angled-predrilling within the same shape group (control vs 1.5, 1.5 vs 4.0; all P , .05). The MIT of the tapered group was greater than that of the cylindrical group (C-con vs T-con, C-1.5 vs T-1.5; all P , .05, C-4.0 vs T-4.0; P , .01). In the same angled-predrilling depth, no differences were observed in TIE between the cylindrical and tapered groups (C-1.5 vs T-1.5, C-4.0 vs T-4.0; all P . .05). Conclusions: In angled-predrilling insertion of OMIs into thick cortical bone, tapered OMIs might be a better choice than cylindrical OMIs for increasing primary stability because of higher MIT and similar TIE values. (Angle Orthod. 2012;82:881-888.)

Effects of repeated sterilization cycles on primary stability of orthodontic mini-screws

“…It has been suggested [16][17][18][19] that maximum insertion torque can be used as a reliable parameter to determine whether primary mini-screw stability can be achieved. In 2006 Motoyoshi et al 20 tried to determine an ideal range for placement torque that would yield improved mini-screw success rates.…”

Microdamage generation by tapered and cylindrical mini-screw implants after pilot drilling

“…18 To avoid excessive insertion torque, one approach is to change the shape of the MSI. For example, some studies demonstrate that tapered MSIs generate higher insertion torque with higher primary stability than cylindrical MSIs, 3,7,[19][20][21] but they can produce excessive insertion torques, potentially damaging the bone. 13,17,[22][23][24] The latter findings correspond to finite element analyses, which suggest that tapered MSIs induce high stresses in the cortical bone 25 around the implant neck.…”

Insertion Torque and Pull-Out Strength of Orthodontic Mini-implants Comparing Manual and Motor Insertion Methods

“…Thus, retention results are a function of mini-implant design and insertion method only. Synthetic bone has been widely used in in vitro studies, 6,7,[13][14][15][16] and although these studies do not precisely reproduce clinical settings, they can provide standardized information on the receptor bone. It should be noted that because this is an in vitro study, it only addresses mechanical questions regarding mini-implant/bone imbrication, which closely approximates the primary stability achieved in vivo soon after mini-implant insertion.…”