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Objective: To quantify the biomechanical properties of the bovine periodontal ligament (PDL) in postmortem sections and to apply these properties to study orthodontic tooth intrusion using finite element analysis (FEA). We hypothesized that PDL's property inherited heterogeneous (anatomical dependency) and nonlinear stress-strain behavior that could aid FEA to delineate force vectors with various rectangular archwires. Materials and Methods: A dynamic mechanical analyzer was used to quantify the stress-strain behavior of bovine PDL. Uniaxial tension tests using three force levels (0.5, 1, and 3 N) and samples from two anatomical locations (circumferential and longitudinal) were performed to calculate modulus. The Mooney-Rivlin hyperelastic (MRH) model was applied to the experimental data and used in an FEA of orthodontic intrusion rebounded via a 0.45-mm step bend with three archwire configurations of two materials (stainless steel and TMA). Results: Force levels and anatomical location were statistically significant in their effects on modulus ( P < .05). The apical part had a greater stiffness than did the middle part. The MRH model was found to approximate the experimental data well ( r = 0.99), and it demonstrated a reasonable stress-strain outcome within the PDL and bone for FEA intrusion simulation. The force acting on the tooth increased five times from the 0.016 × 0.022-inch TMA to the 0.019 × 0.025-inch stainless steel. Conclusions: The PDL is a nonhomogeneous tissue in which the modulus changed in relation to location. PDL nonlinear constitutive model estimated quantitative force vectors for the first time to compare intrusive tooth movement in 3-D space in response to various rectangular archwires. [ABSTRACT FROM AUTHOR]

Objective: To determine the histological reaction of the root and bone as a mini–implant approaches the root. Materials and Methods: Two kinds of mini–implants were inserted into the buccal alveolar bone of 4 beagles (2 males and 2 females). The specimens were classified as the near–root group, the PDL contact group, the root contact group, and the root perforation group. Cementum resorption, dentin resorption, cementum repair, cementum growth, ankylosis, root cracking, and root fracture were assessed as the implant neared the root. Results: The incidence of root resorption increased when the mini–implant was less than 0.6 mm from the root in the near–root group and PDL contact group. Root cracking and root fracture occurred in the root contact group and root perforation group. Bone resorption and ankylosis were observed in some specimens. However, some specimens of the PDL contact group and root contact group had cementum growth or little root resorption despite proximity to the root. In the root perforation group, root resorption and ankylosis occurred on the side opposite the insertion. Conclusions: There is a risk of root contact and severe tissue damage from a thick mini–implant and the drilling procedure, either of which can induce root resorption or ankylosis. Use of smaller mini–implants may reduce root contact and tissue damage. However, the small mini–implant may need enhancement of its stability. [ABSTRACT FROM AUTHOR]