Computed tomographic characterization of mini-implant placement pattern and maximum anchorage force in human cadavers

Am J Orthod Dentofacial Orthop. 2011 Sep;140(3):356-65. doi: 10.1016/j.ajodo.2010.05.024.

Abstract

Introduction: The purpose of this investigation was to characterize the placement pattern and factors influencing the primary stability of mini-implants in human cadavers. The factors studied were mini-implant length, placement depth, bone density, and bone type.

Methods: Sixty standard mini-implants (6, 8, and 10 mm; 20 of each size) were placed into the maxillas and mandibles of 5 fresh human cadavers. Computed tomography imaging was used to measure the placement pattern, bone density, and thickness surrounding each device. The mini-implants were subsequently subjected to increasing tensile forces (pull-out force) until failure, and the maximum mechanical anchorage force of each was recorded with a dynamometer. A statistical model was realized by using MATLAB version 7.5.0 with Statistics Toolbox 7 (MathWorks, Natick, Mass) including the maximum anchorage force, mini-implant length, bone type, placement depth, and density surrounding each section of the mini-implant.

Results: Placement depth was strongly dependent on mini-implant length: 15% of the 6-mm implants failed to anchor their parallel sections into cortical bone, but 95% of the 10-mm mini-implant parallel sections penetrated beyond the buccal cortical bone; all 20 tips of the 6-mm mini-implants (100%) reached cancellous bone, whereas 75% of the 10-mm implants penetrated both cortical plates, reaching the lingual cortical bone. Longer mini-implants were associated with greater incidences of sinus and bicortical perforations. The correlation coefficients between the initial maximum mechanical anchorage force and the studied factors were as follows: bone density and placement depth combined (r = 0.65, P <0.001), mini-implant length (r = 0.45, P = 0.004), bone density (r = 0.42, P = 0.007), and placement depth (r = 0.29, P = 0.06).

Conclusions: During mini-implant length selection, the clinician should consider the important trade-off between anchorage and risk of placement complications or damage to the tissues. Longer mini-implants enable more anchorage; however, they are associated with a higher risk of damage to neighboring structures. Placement depth and bone density at the site of mini-implant placement are the best predictors of primary stability.

MeSH terms

  • Aged, 80 and over
  • Alveolar Process / diagnostic imaging*
  • Alveolar Process / surgery
  • Bone Density
  • Cadaver
  • Dental Implantation, Endosseous / methods
  • Dental Implants*
  • Dental Stress Analysis*
  • Female
  • Humans
  • Male
  • Miniaturization
  • Orthodontic Anchorage Procedures / instrumentation*
  • Orthodontic Anchorage Procedures / methods
  • Orthodontic Appliance Design*
  • Statistics, Nonparametric
  • Stress, Mechanical
  • Tensile Strength
  • Tomography, X-Ray Computed

Substances

  • Dental Implants