The better performances of the experimental microimplant, under both laboratory and clinical conditions (although statistically insignificant in the latter), demonstrate the superiority of the new asymmetric thread.
Aim. To find thresholds at which laypersons and dental professionals from Jordanian population perceive abnormalities in sagittal positioning of upper and lower jaws as a major determinant to facial profile esthetics. Materials and Methods. Using photo editing software, a baseline profile image of a young male was manipulated on a 2 mm incremental basis to move each of the upper and lower jaws backward and forward relative to true vertical line (TVL) at which four variables of maxillary and mandibular retrusion and protrusion were researched. A total of 120 participants divided equally into four groups of laypersons, general dental practitioners (GDPs), orthodontists, and oral and maxillofacial surgeons (OMFSs) rated the images using an analog scale of 100 mm long. The image that showed the first statistical difference compared to the baseline was considered as a threshold of abnormality. Results. Laypersons, GDPs, and OMFSs perceived the abnormality in the maxillary retrusion at −5 mm to TVL, while orthodontists defined that at −3 mm. All dental professionals perceived the abnormality in the maxillary protrusion at +1 mm to TVL while the layperson group at +3 mm. A threshold of −7 mm mandibular retrusion to TVL was abnormally perceived by all groups. All dental professionals realized the abnormality in the mandibular protrusion at 0 mm to TVL while the laypersons at +2 mm. Conclusion. These thresholds regarding profile esthetics may contribute to the process of establishing proper orthodontic treatment planning that suits the highest facial esthetic standards.
Objective: To find an optimal force that can be loaded onto an orthodontic microimplant to fulfill the biomechanical demands of orthodontic treatment without diminishing the stability of the microimplant. Materials and Methods: Using the finite element analysis method, 3-D computer-aided design models of a microimplant and four cylindrical bone pieces (incorporating cortical bone thicknesses of 0.5, 1.2, 2.0, and 3.0 mm) into which the microimplant was inserted were used. Various force magnitudes of 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, and 4.0 N were then horizontally and separately applied to the microimplant head as inserted into the different bone assemblies. For each bone/ force assembly tested, peak stresses developed at areas of intimate contact with the microimplant along the force direction were then calculated using regression analysis and compared with a threshold value at which pathologic bone resorption might develop. Results: The resulting peak stresses showed that bone pieces with thicker cortical bone tolerated higher force magnitudes better than did thinner ones. For cortical bone thicknesses of 0.5, 1.2, 2.0, and 3.0 mm, the maximum force magnitudes that could be applied safely were 3.75, 4.1, 4.3, and 4.45 N, respectively. Conclusions: For the purpose of diminishing orthodontic microimplant failure, an optimal force that can be safely loaded onto a microimplant should not exceed a value of around 3. 75-4.5 N. (Angle Orthod. 2016;86:221-226.)
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