Screw removal torque evaluation in implants with cone morse and external hexagon platforms in anterior cantilever

This study aims to evaluate the screw removal torque on prosthetic platforms of Cone Morse (CM) and External Hexagon (EH) implants in crowns with anterior cantilever. Materials and Methods: in vitro study with a sample consisting of 20 test specimens of 2 elements (21 and 22), with n = 40; load is simulated on element 21 or on cantilever of 22. Samples were divided into 4 groups consisting of 10 test specimens on CM implants (groups 1 and 2), and 10 test specimens on EH implants (groups 3 and 4). The test specimens were manufactured using cylindrical PVC pipes measuring 22 x 19.05 mm filled with acrylic resin. The implants were fixed with a centralization device. Components used were EUCLAs and UCLAs with a chrome-cobalt alloy molten base. The metal bases were scanned, the crowns were digitally waxed, made on CAD/CAM system, and cemented on the metal bases with Panavia cement. Torque was applied using 20N for CM and 32N for EH, according to the manufacturers’ instructions. The test specimens were then subjected to a cycling process consisting of 1,000,000 cycles at a frequency of 2 Hz. The cyclic process applied axial forces to the surface (palate face of 21 and 22). Two cycling processes were carried on, the first on the palate face of 21 and the second on the palate face of 22. Between the two, screws were removed and replaced by new ones. The screw removal torque was measured using a digital torque meter. Results were analyzed with Student’s t test and variance analysis. Statistical calculations were conducted in SPSS 23 using 5% of significance. Results: Student’s t test showed significantly lower removal torque values in comparison with initial torque for both CM and EH connection implants and force applied to elements 21 and 22 (p < 0.001) or 22 (p < 0.001). Considering torque loss, there was no significant effect of the interaction between type of implant connection and site of force application (p = 0.094). Removal torque was significantly lower than initial torque for both implants (CM and EH). Conclusion: Torque loss occurred both in CM and EH. There was no significant effect of the interaction between connections and site of force application.

The effect of 12 weeks of mechanical vibration on root resorption: a micro-CT study

Objective The aim was to investigate the effect of mechanical vibration on root resorption with or without orthodontic force application. Material and methods Twenty patients who required maxillary premolar extractions as part of orthodontic treatment were randomly divided into two groups of 10: no-force group and force group. Using a split-mouth procedure, each patient’s maxillary first premolar teeth were randomly assigned as either vibration or control side for both groups. A buccally directed vibration of 50 Hz, with an Oral-B HummingBird device, was applied to the maxillary first premolar for 10 min/day for 12 weeks. After the force application period, the maxillary first premolars were extracted and scanned with micro-computed tomography. Fiji (ImageJ), performing slice-by-slice quantitative volumetric measurements, was used for resorption crater calculation. Total crater volumes were compared with the Wilcoxon and Mann–Whitney U tests. Results The total crater volumes in the force and no-force groups were 0.476 mm3 and 0.017 mm3 on the vibration side and 0.462 mm3 and 0.031 mm3 on the control side, respectively. There was no statistical difference between the vibration and control sides (P > 0.05). There was more resorption by volume in the force group when compared to the no-force group (P < 0.05). Conclusion Mechanical vibration did not have a beneficial effect on reducing root resorption; however, force application caused significant root resorption.

Optoregulated force application to cellular receptors using molecular motors

Progress in our understanding of mechanotransduction events requires noninvasive methods for the manipulation of forces at molecular scale in physiological environments. Inspired by cellular mechanisms for force application (i.e. motor proteins pulling on cytoskeletal fibers), we present a unique molecular machine that can apply forces at cell-matrix and cell-cell junctions using light as an energy source. The key actuator is a light-driven rotatory molecular motor linked to polymer chains, which is intercalated between a membrane receptor and an engineered biointerface. The light-driven actuation of the molecular motor is converted in mechanical twisting of the entangled polymer chains, which will in turn effectively “pull” on engaged cell membrane receptors (e.g., integrins, T cell receptors) within the illuminated area. Applied forces have physiologically-relevant magnitude and occur at time scales within the relevant ranges for mechanotransduction at cell-friendly exposure conditions, as demonstrated in force-dependent focal adhesion maturation and T cell activation experiments. Our results reveal the potential of nanomotors for the manipulation of living cells at the molecular scale and demonstrate a functionality which at the moment cannot be achieved by other technologies for force application.

Impact of Orthodontic Forces on Plasma Levels of Markers of Bone Turnover and Inflammation in a Rat Model of Buccal Expansion

Plasma levels of protein analytes might be markers to predict and monitor the kinetics of bone and tissue remodeling, including maximization of orthodontic treatment stability. They could help predict/prevent and/or diagnose possible adverse effects such as bone dehiscences, gingival recession, or root resorption. The objective of this study was to measure plasma levels of markers of bone turnover and inflammation during orthodontic force application in a rat model of orthodontic expansion. Two different orthodontic forces for bilateral buccal expansion of the maxillary arches around second and third molars were applied in 10 rats equally distributed in low-force (LF) or conventional force (CF) groups. Four rats served as the control group. Blood samples were collected at days 0, 1, 2, 3, 6, 13, 21, and 58. Longitudinal concentrations of osteoprotegerin (OPG), soluble receptor activator of nuclear factor kappaB ligand (sRANKL), interleukin-4 (IL-4), interleukin-6 (IL-6), interleukin-10 (IL-10), tumor necrosis factor α (TNF), and parathyroid hormone (PTH) were determined in blood samples by a multiplex immunoassay. CF and LF resulted in a significantly maxillary skeletal expansion while the CF group demonstrated significantly higher expansion than the LF group in the long term. Bone turnover demonstrated a two-phase response. During the “early phase” (up to 6 days of force application), LF resulted in more sRANKL expression and increased sRANKL/OPG ratio than the CF and control animals. There was a parallel increase in PTH levels in the early phase in response to LF. During the “late phase” (6–58 days), the markers of bone turnover were stable in both groups. IL-4, IL-6, and IL-10 levels did not significantly change the test groups throughout the study. These results suggest that maxillary expansion in response to different orthodontic forces follows different phases of bone turnover that may be force specific.

Effects of Skeletally Supported Anterior en Masse Retraction with Varied Lever Arm Lengths and Locations in Lingual Orthodontic Treatment: A 3D Finite Element Study

Objective. This study is aimed at analyzing different points of force application during miniscrew supported en masse retraction of the anterior maxillary teeth to identify the best line of action of force in lingual orthodontic treatment. Materials and Methods. Three-dimensional (3D) finite element models were created to stimulate en masse retraction with different heights and positions of the miniscrew and lever arm to change the force application points; a 150 g retraction force was applied from the miniscrew to the lever arms, and the initial tooth displacements were analyzed. Results. Lingual crown tipping and occlusal crown extrusion were seen at all heights and positions of the miniscrew and lever arm, but when the miniscrew height was at 8 mm and the power arm was located between the lateral incisors and canines, these tipping patterns were less than those obtained with a 4.5 mm high miniscrew and a lever arm located distal to the canines. Conclusion. All miniscrew heights and lever arm positions showed initial lingual crown tipping and labial root tipping with occlusal crown extrusion. However, the 8 mm miniscrew height and the lever arm located between the lateral incisor and canine showed fewer amounts of these tipping patterns than a 4.5 mm miniscrew height and lever arm located distal to the canines. Therefore, this could be the preferred point of force application during en masse retraction in lingual treatment with additional torque control methods.