[Stress distribution in press-fit orthodontic microimplant bone interface].
OBJECTIVE
The goal of this study is to analyse the stress distribution in the press-fit microimplant-bone interface and its indications for immediate loading of orthodontic microimplant.


METHODS
Three-dimensional finite element models were created of a 20 mm section of posterior mandible simplified in isosceles trapezoid shape, 30 mm in height, 10mm in upper side width, 14 mm in lower side width,with a single microimplant, 1.2 mm in diameter, 6 mm in length embedded in the bone. The cortical bone thickness was assumed as 1.6 mm. Cortical and cancellous bone were modeled as transversely isotropic and linearly elastic materials. Titanium was modeled as isotropic and linearly elastic material. Perfect bonding was assumed at microimplant- bone interfaces. ANSYS 9.0 finite element analysis software was used to generate the simplified finite element models of the local mandible-implant complex. 0 mm, 0.05 mm and 0.1 mm press-fit were arbitrarily set to the implant-bone interface to mimic the situation of immediate placement of microimplant. Stresses in the microimplant-bone interface were calculated under these "press-fit".


RESULTS
Stresses distributed mainly in the cortical bone interface. At Omm press-fit, the stress was 0 MPa. For 0.05mm press-fit, the stress was 1648 MPa in mesio-distal direction, 1782MPa in occluso-gingival direction;and for 0.1 mm, it reached 2012MPa in mesio-distal direction, 2110MPa in occluso-gingival direction. As the "press-fit" increased, the stresses increased accordingly.


CONCLUSIONS
Values of initial stress in the microimplant-bone interface due to press-fit generated by immediately placed microimplant were very high in these limited and simplified three dimensional finite element models. It reminded us that the initial stress be taken into consideration when immediate loading of the microimplant is planned. Supported by Research Fund of Health Bureau of Zhejiang Province (2005B104).
Wu
Jian-chao
JC
Department of Orthodontics,School of Dentistry, Zhejiang University, Hangzhou 310006, Zhejiang Province, China. wujianchao555@163.com
Huang
Ji-na
JN
Zhao
Shi-fang
SF
Xu
Xue-jun
XJ
D001842:Bone and Bones; D015921:Dental Implants; D003799:Dental Stress Analysis; D020342:Finite Element Analysis; D006801:Humans; D021621:Imaging, Three-Dimensional; D057893:Immediate Dental Implant Loading; D008334:Mandible; D008954:Models, Biological; D052280:Orthodontic Anchorage Procedures; D016382:Orthodontic Appliance Design; D009971:Orthodontics, Corrective; D013314:Stress, Mechanical; D014025:Titanium
D015921:Dental Implants; D014025:Titanium