Effects of Mechanics for Uprighting Partially Impacted Mandibular Second Molar with Miniscrew Anchorage Using CBCT Imaging: A Finite Element Method

Abstract

The purposes of this study were: (1) to evaluate the optimal force magnitude that can be applied to the initial uprighting of partially-impacted mandibular second molars without exceeding the hydrostatic pressure of the periodontal ligament (PDL) capillary vessels’ blood pressure, which is 0.0047 megapascal (MPa); and (2) to describe the von Mises stress distribution patterns in each tooth and initial tooth indisplacement, using the finite element method. A three-dimensional finite element model was developed from CBCT images. Various pushing forces, 35-150 grams, from an interradicular miniscrew head, which was placed in the cortical bone between the second premolar (#35) and first molar (#36) roots, to a buccal mini-tube on the impacted second molar tooth (#37), were applied to evaluate the optimal force magnitude. Moreover, the result of the first research purpose (the optimal force magnitude) was used to simulate the von Mises stress distribution in each tooth and the initial tooth displacement. The greatest force magnitude that was equivalent to the hydrostatic pressure of the PDL, when a single pushing uprighting force was applied, was 80 grams. The maximum von Mises stress distributions in teeth #37, #36, and #35 were 4.805 MPa, 2.242 MPa, and 0.623 MPa, respectively. Additionally, the region of maximum von Mises stress was on the contact area of each tooth. The displacement pattern of the target tooth was distal crown tipping, slightly distal root movement, lingual crown tipping, buccal root tipping and disto-lingual rotation of the crown. Besides, this study found that teeth #36 and #35 were displaced, though force was not directly applied to it. Teeth #36 and #35 had slight distal crown tipping, lingual crown tipping, and extrusion.