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The aim of this study was to investigate the stress components (S1 and S3) that appear in the periodontal membrane (PDM), when subjected to transverse and vertical loads equal to 1 N. A further aim was to quantify the alteration in stress that occurs as alveolar bone is reduced in height by 1, 2.5, 5, 6.5, and 8 mm, respectively. Six three-dimensional (3D) finite element models (FEM) of a human maxillary central incisor were designed. The models were of the same configuration except for the alveolar bone height. Special attention was paid to changes of the stress components produced at the cervical, apical, and sub-apical levels. In the absence of alveolar bone loss, a tipping force of 1 N produced stresses, which reached 0.072 N/mm2 at the cervical margin, up to 0.0395 N/mm2 at the apex and up to 0.026 N/mm2 sub-apically. In the presence of 8 mm of alveolar bone loss, the findings were -0.288, 0.472, and 0.722 N/mm2, respectively. Without bone loss, an intruding force of the same magnitude produced stresses of -0.0043, -0.0263, and 0.115 N/mm2, respectively, for the same areas and sampling points. In the presence of 8 mm of alveolar bone loss the findings were -0.019, -0.043, and 0.185 N/mm2 for intrusive movement. The results showed that alveolar bone loss caused increased stress production under the same load compared with healthy bone support (without alveolar bone resorption). Tipping movements resulted in an increased level of stress at the cervical margin of the PDM in all sampling points and at all stages of alveolar bone loss. These increased stress components were found to be at the sub-apical and apical levels for intrusive movement.

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Purpose: To compare short implants (SH; 4-8 mm) to standard implants (ST; longer than 8 mm) in edentulous jaws, evaluating pri-implant marginal bone levels (MBLs) changes, implant failures (IFs), complications, and prosthesis failures (PFs). Materials and Methods: Electronic searches were conducted through the PubMed, Web of Science, EMBASE, Scopus, the Cochrane Central Register of Controlled Trials, and ClinicalTrials.gov to locate all randomized controlled trials (RCTs) comparing SH to ST. Meta-analysis procedures were performed on the weighted mean difference (WMD) and standardized mean difference (SMD) of MBLs using Stata. Results: Twenty-three articles were included in this review. The WMD of MBLs when comparing SH to ST in both jaws up to 1-year follow-up was statistically significant preferring SH (WMD: −0.09 [CI: −0.12, −0.06], I 2 : 67.0%). The efficacy of SH vs ST on SMD of MBLs was moderate (SMD: −0.43 [CI: −0.57, −0.28], I 2 : 55.7%). There were no significant differences in IF (RR: 0.75 [0.44,1.27]) and PF (RR: 0.58 (0.22,1.581), and significantly higher biological complications (RR: 0.25 [0.15, 0.40]) for SH was observed compared to the ST in both jaws up to 1-year follow-up.Conclusions: SH and ST implants showed the comparable outcomes except biological complication preferring SH. Future systematic review and meta-analysis with longer and larger RCTs are required to confirm the present outcomes.

The purpose of this study was to evaluate the influence of the stress/strain distribution in buccal bone of an anterior maxillary implant using 3 bone thicknesses under 5 different loading angles. Different testing conditions incorporating 3 buccal bone thicknesses, 3 bone compositions, and 5 loading angles of an anterior maxillary implant were applied in order to investigate the resultant stress/strain distribution with finite element analysis. The maximum equivalent stress/strain increased with the decreasing of loading angle relative to the long axis. In addition to loading angle, bone quality and quantity also influenced resultant stress distribution. Dental practitioners should consider combinations of bone composition, diameter, and load angulations to predict success or failure for a given implant length and diameter.

BackgroundThe ideal built-in tip and torque values of the straight wire appliance reduce the need for wire bending and hence reduce chair time. The vertical position of the bracket on the tooth surface can alter the torque exerted on the tooth. This is a result of the altered surface curvature observed at each vertical position. To further clarify the role of vertical bracket positioning on the applied torque and the resultant stresses in the periodontal ligament (PDL), we designed a mandibular first premolar using finite element modeling.MethodsCone beam computed tomography of 52 patients (83 lower first premolars) was selected to be included in the study. Curvature was measured for points along the labial surface with increasing distances (0.5 mm increments) from the cusp tip by calculating the angle between tangents drawn from these points and the axis joining the cusp tip and the root apex. The mean values for each distance were calculated, and a finite element model was designed incorporating these mean values. The resultant stress and hydrostatic pressure in the PDL were calculated using finite element analysis.ResultsThe labial surface of the mandibular first premolar demonstrated a 26.39° change from 2.5 to 6 mm from the cusp tip. The maximum Von-Mises stress and hydrostatic pressure in the PDL were observed at the root apex for all of the bracket positions, and these values demonstrated, respectively, a change of up to 0.059 and 0.186 MPa between two successive points.ConclusionsIt can be concluded that the variation in the vertical position of the bracket can have an important effect on the torque and subsequently on the stresses and pressures in the PDL.

According to our optimized system, the TPA design with the highest energy and moment, but the lowest mesializing force associated with derotating a maxillary molar tooth was a parallel wire II design (i.e. adding a straight wire).