In vitro and in vivo mechanical stability of orthodontic mini-implants

Abstract

Objective: To compare in vivo and in vitro mechanical stability of orthodontic mini-implants (OMIs) treated with a sandblasted, large-grit, and anodic-oxidation (SLAO) method vs those treated with a sandblasted, large-grit, and acid-etching (SLA) method.

Materials and methods: Fifty-four titanium OMIs (cylindrical shape, drill-free type; diameter = 1.45 mm, length = 8 mm, Biomaterials Korea Inc, Seoul, Korea) were allocated into control, SLA, and SLAO groups (N = 12 for in vivo and N = 6 for in vitro studies per group). In vitro study was carried out on a polyurethane foam bone block (Sawbones, Pacific Research Laboratories Inc, Vashon, Wash). In vivo study was performed in the tibias of Beagles (6 males, age = 1 year, weight = 10 to 13 kg; OMIs were removed at 8 weeks after installation). For insertion and removal of OMIs, the speed and maximum torque of the surgical engine were set to 30 rpm and 40 Ncm, respectively. Maximum torque (MT), total energy (TE), and near peak energy (NPE) during the insertion and removal procedures were statistically analyzed.

Results: In the in vitro study, although the control group had a higher insertion MT value than the SLA and SLAO groups (P < .01), no differences in insertion TE and NPE or in any of the removal variables were noted among the three groups. In the in vivo study, the control group exhibited higher values for all insertion variables compared with the SLA and SLAO groups (MT, P < .001; TE, P < .01; NPE, P < .001). Although no difference in removal TE and removal NPE was noted among the three groups, the SLAO group presented with a higher removal MT than the SLA and control groups (P < .001).

Conclusions: SLAO treatment may be an effective tool in reducing insertion damage to surrounding tissue and improving the mechanical stability of OMIs.

Figure 1

(a) The orthodontic mini-implant (OMI) used in the present study (cylindrical shape, drill-free type, outer diameter  =  1.45 mm, inner diameter  =  1.0 mm, length  =  8 mm, OAS-T1508, Biomaterials Korea Inc, Seoul, Korea). (b) Surface topography (scanning electron microscope, 1500×); from the left, control group, SLA (sandblasted, large-grit, and acid-etching) group, and SLAO (sandblasted, large-grit, and anodic-oxidation) group.

Figure 2

(a) In vitro insertion of OMIs into the artificial bone block of polyurethane foam (Sawbones, Pacific Research Laboratories Inc, Vashon, Wash). (b) In vivo insertion of OMIs into the tibia of a Beagle.

Figure 3

(a) Definition of insertion variables. Insertion maximum torque (MT, Ncm) is the maximum torque recorded during the insertion procedure. Insertion total energy (TE, J) is the total energy recorded from the beginning of insertion to the point at which the insertion MT is reached. Insertion near peak energy (NPE, J) is the energy measured from the point of insertion MT to 8 seconds before that point (four rotations). (b) Definition of removal variables. Removal MT (Ncm) is the maximum torque recorded during the removal procedure. Removal TE (J) is the total energy recorded from the point at which the removal MT is reached to the end of the removal procedure. Removal NPE (J) is the energy measured from the point of the removal MT to 4 seconds after that point (two rotations).

Figure 4

Ground section of samples (20×; staining with Multiple Stain Solution, Polyscience Inc, Warrington, Fla). From the left, control group, SLA group, and SLAO group.