Indirect miniscrew anchorage: biomechanical loading of the dental anchorage during mandibular molar protraction-an FEM analysis.
OBJECTIVE
While there are many studies in the literature addressing direct miniscrew anchorage, the biomechanical effects of indirect miniscrew anchorage remain unknown. The aim of the present study was to biomechanically analyze the load on the anchor teeth during mandibular molar protraction using different types of anchorage.


METHODS
Four finite element method (FEM) models of the right mandible were created using the morphological CT data of a 21-year-old male. All models were morphologically identical, but they differed in anchorage type (dental anchorage, direct miniscrew anchorage, indirect miniscrew anchorage with one anchor tooth, indirect miniscrew anchorage with two anchor teeth). To analyze the load on the dental anchorage during mandibular molar protraction, we measured the induced effective strain (µstrain) at specific control points on the alveolar bone.


RESULTS
With indirect miniscrew anchorage, we observed that the effective strain at an average of 7.21 μstrain (one anchor tooth) or 6.57 μstrain (two anchor teeth) was almost as high as in pure dental anchorage where no miniscrew was used (mean 8.38 µstrain). In contrast, we noted significantly lower strain values in conjunction with direct miniscrew anchorage. We observed highly significant differences between direct and indirect simulated miniscrew anchorage (p=0.008).


CONCLUSIONS
Our FEM results reveal relatively high loads on the dental anchorage when using indirect miniscrew anchorage. This may carry an increased risk of anchorage loss during mandibular molar protraction; however, further studies are necessary to confirm this.
Department of Orthodontics, University of Munich, Goethestr. 70, 80336, Munich, Germany, cholberg@med.lmu.de.
Christof
C
Holberg
Philipp
P
Winterhalder
Nikola
N
Holberg
Andrea
A
Wichelhaus
Ingrid
I
Rudzki-Janson
D000328:Adult; D001732:Bite Force; D001863:Bone Screws; D019245:Compressive Strength / Q000502:physiology; D003198:Computer Simulation; D017076:Computer-Aided Design; D003799:Dental Stress Analysis / Q000379:methods*; D020342:Finite Element Analysis; D017276:Friction; D006801:Humans; D008297:Male; D008334:Mandible / Q000000981:diagnostic imaging / Q000502:physiology*; D008904:Miniaturization; D008954:Models, Biological; D008963:Molar / Q000000981:diagnostic imaging / Q000502:physiology*; D052280:Orthodontic Anchorage Procedures / Q000295:instrumentation* / Q000379:methods; D016382:Orthodontic Appliance Design / Q000379:methods; D011859:Radiography; D013314:Stress, Mechanical; D013718:Tensile Strength / Q000502:physiology; D014087:Tooth Movement Techniques / Q000295:instrumentation*; D020390:Tooth Socket / Q000000981:diagnostic imaging / Q000502:physiology