Effects of Aging Torque Controllers on Screw Tightening Force and Bacterial Micro-Leakage on the Implant-Abutment Complex

Aim: We assess the accuracy of torque controllers after several aging processes and the bacterial leakage on Implant-Abutment complexes (IAC).Methods: A total of 12 spring-type and 12 friction-type torque controllers and 48 IAC (24 conical and 24 hexagonal connections) were evaluated. Chemical, mechanical, temperature, and pressure-aging methods were applied individually to replicate clinical use. Torque controller accuracy was analyzed before and after aging using a calibrated gauge. To assess bacterial leakage, the IAC were suspended in a bacterial medium for 24 h. Direct Contact Test (DCT) and Polymerase Chain Reaction Test (RT-PCR) analyzed the infiltration of F. nucleatum and P. gingivalis into the IAC micro-gap. Results: A significant decrease in torque after 10 days of aging was found. The spring-type torque controller was affected the most, regardless of the aging method (P < 0.05). PCR results indicated that all groups exhibited significantly more bacterial leakage, regardless of the method used (P < 0.05). The conical IAC demonstrated more bacterial leakage of P. gingivalis compared with the hexagonal IAC (P = 0.07). DCT found bacterial growth in the IAC only before aging and was not identified after aging. Conclusion: Aging affects torque accuracy. A reduction in force was noticed after 10 days. The conical IAC exhibits more bacterial leakage, although this was not statistically significant.

Loss of α-actinin-3 confers protection from eccentric contraction damage in fast-twitch EDL muscles from aged mdx dystrophic mice by reducing pathological fibre branching

ABSTRACTThe common null polymorphism (R577X) in the ACTN3 gene is present in over 1.5 billion people worldwide and results in the absence of the protein α-actinin-3 from the Z-discs of fast-twitch skeletal muscle fibres. We have previously reported that this polymorphism is a modifier of dystrophin deficient Duchenne Muscular Dystrophy. To investigate the mechanism underlying this we use a double knockout (dk)Actn3KO/mdx (dKO) mouse model which lacks both dystrophin and sarcomere α-actinin-3. We used dKO mice and mdx dystrophic mice at 12 months (aged) to investigate the correlation between morphological changes to the fast-twitch dKO EDL and the reduction in force deficit produced by an in vitro eccentric contraction protocol. In the aged dKO mouse we found a marked reduction in fibre branching complexity that correlated with protection from eccentric contraction induced force deficit. Complex branches in the aged dKO EDL fibres (28%) were substantially reduced compared to aged mdx EDL fibres (68%) and this correlates with a graded force loss over three eccentric contractions for dKO muscles (∼35% after first contraction, ∼66% overall) compared to an abrupt drop in mdx upon the first eccentric contraction (∼73% after first contraction, ∼89% after three contractions). In dKO protection from eccentric contraction damage was linked with a doubling of SERCA1 pump density the EDL. We propose that the increased oxidative metabolism of fast-twitch glycolytic fibres characteristic of the null polymorphism (R577X) and increase in SR Ca2+ pump proteins reduces muscle fibre branching and decreases susceptibility to eccentric injury in the dystrophinopathies.

Interconnected Fluid-Filled Cells Design for Reduction of Linear Acceleration and Force Transfer to Prevent Concussion

Regardless of efforts in improving helmet technologies, sport related concussions continue to be a problem. In an effort for advancing helmet liners, this research investigated a design comprised of interconnected fluid-filled cell structures that consist of a primary cell connecting to one or more secondary cells through a channel. When the primary cell undergoes impact, it deforms and pushes the fluid from the primary to secondary cells, which expand accordingly. This fluid motion absorbs the impact and dissipates energy, thereby reducing the force and acceleration transfer to a contacting body. Structures made with two hyper elastic polymers, silicone and polyurethane, were investigated in simulation and experimentation. For both materials, increasing the number of secondary cells in the structure will decrease the amount of force transfer and resulting acceleration. The optimized design, with one primary and two secondary cells, showed reduction of force by 25.2% and resulting acceleration of 80.7 m/s2 when using silicone, while cells made of polyurethane showed a 33.5% reduction of force and resulting acceleration of 72.5 m/s2. In comparison, a commercial liner (Vengeance DCT TPU Lateral Helmet Liner by Schutt® tested using the same test procedures, showed reduction in force by 24.3% and resulting acceleration of 87.0 m/s2.

Different in vivo impact of Dynamin 2 mutations implicated in Charcot-Marie-Tooth neuropathy or Centronuclear Myopathy

Dynamin 2 (DNM2) is a ubiquitously expressed GTPase implicated in many cellular functions such as membrane trafficking and cytoskeleton regulation. Dominant mutations in DNM2 result in tissue specific diseases affecting peripheral nerves (Charcot-Marie-Tooth neuropathy, CMT) or skeletal muscles (Centronuclear myopathy, CNM). However, the reason for this tissue specificity is unknown, and it remains unclear if these diseases share a common pathomechanism. To compare the disease pathophysiological mechanisms in skeletal muscle, we exogenously expressed wild-type DNM2 (WT-DNM2), the DNM2-CMT mutation K562E, or DNM2-CNM mutations R465W and S619L causing adult and neonatal forms respectively, by intramuscular adeno-associated virus (AAV) injections. All muscles expressing exogenous WT-DNM2 and CNM or CMT mutations exhibited reduced muscle force. However, only expression of CNM mutations and WT-DNM2 correlated with CNM-like histopathological hallmarks of nuclei centralization and reduced fiber size. The extent of alterations correlated with clinical severity in patients. Ultrastructural and immunofluorescence analyses highlighted defects of the triads, mitochondria and costameres as major causes of the CNM phenotype. Despite the reduction in force upon expression of the DNM2-CMT mutation, muscle histology and ultrastructure were almost normal. However, the neuromuscular junction was affected in all DNM2 injected muscles, with the DNM2-CMT mutation inducing the most severe alterations, potentially explaining the reduction in force observed with this mutant. In conclusion, expression of WT and CNM mutants recreate a CNM-like phenotype, suggesting CNM mutations are gain-of-function. Histological, ultrastructural and molecular analyses pointed to key pathways uncovering the different pathomechanisms involved in centronuclear myopathy or Charcot-Marie-Tooth neuropathy linked to DNM2 mutations.

Evaluation of the Asymmetry of Leg Muscles Forces in the Subjects with Anterior Cruciate Ligament Reconstruction

Running asymmetry has not been assessed among patients with anterior cruciate ligament (ACL) deficiency. The aim of this study was to evaluate the spatiotemporal and muscle force asymmetry indexes in the subjects with ACL reconstruction (ACLR) compared with normal subjects. Eight individuals with a reconstructed ACL and eight individuals with intact ACLs were participated in this study. A Vicon motion analysis system and two Kistler force plates were used to record data. Muscle forces analysis was done by the use of OpenSim software. The results of this study showed that ACLR group had a significant weakness in hip abductor, extensor, and adductor muscles of the affected limb compared with healthy subjects (p < 0.05). In ACLR group, asymmetry of gluteus minimus muscle force was significantly greater than that of healthy group (p = 0.04). After the reconstruction of the ACL, there is still a significant asymmetry in muscle force as well as a reduction in force production of ACLR group especially in reconstructed side which put a person at high risk of reinjuries. Thus, strengthening of these muscles on the affected side to increase running performance of ACLR group is recommended.

Leadership in a Fiscally Distressed School District: The Case of Daly City Schools

This case positions the reader as the superintendent of Daly City Community Schools (DCCS), a mid-sized public school district located in the Midwestern United States facing a fiscal crisis. The case requires the reader to propose fiscal alternatives to a school board. For example, the case might invite the reader to consider the appointment of an emergency financial manager, implement a “reduction in force” strategy, or declare Chapter 9 bankruptcy as part of an overarching plan to achieve fiscal stability. Through the case experience, students will become familiar with the actions available to educational leaders working within a fiscally distressed school district, as well as the political consequences that these actions have for a variety of stakeholders.

Asymmetry in kinematic generalization between visual and passive lead-in movements are consistent with a forward model in the sensorimotor system

In our daily life we often make complex actions comprised of linked movements, such as reaching for a cup of coffee and bringing it to our mouth to drink. Recent work has highlighted the role of such linked movements in the formation of independent motor memories, affecting the learning rate and ability to learn opposing force fields. In these studies, distinct prior movements (lead-in movements) allow adaptation of opposing dynamics on the following movement. Purely visual or purely passive lead-in movements exhibit different angular generalization functions of this motor memory as the lead-in movements are modified, suggesting different neural representations. However, we currently have no understanding of how different movement kinematics (distance, speed or duration) affect this recall process and the formation of independent motor memories. Here we investigate such kinematic generalization for both passive and visual lead-in movements to probe their individual characteristics. After participants adapted to opposing force fields using training lead-in movements, the lead-in kinematics were modified on random trials to test generalization. For both visual and passive modalities, recalled compensation was sensitive to lead-in duration and peak speed, falling off away from the training condition. However, little reduction in force was found with increasing lead-in distance. Interestingly, asymmetric transfer between lead-in movement modalities was also observed, with partial transfer from passive to visual, but very little vice versa. Overall these tuning effects were stronger for passive compared to visual lead-ins demonstrating the difference in these sensory inputs in regulating motor memories. Our results suggest these effects are a consequence of state estimation, with differences across modalities reflecting their different levels of sensory uncertainty arising as a consequence of dissimilar feedback delays.

Release of fascial compartment boundaries reduces muscle force output

Most limb muscles operate within a compartment defined by fascial layers that enclose a muscle or groups of muscles within a defined space. These compartments are important clinically, because fluid accumulation can cause ischemia and tissue necrosis if untreated. Little is known, however, about how fascial enclosures influence healthy muscle function. One previous study showed that removing a fascial covering reduced the force output of a muscle under maximal stimulation. We hypothesized that such reduction in force output was due to a change in the muscle length following fasciotomy and that a reduced force output could be explained by the length-tension relationship of muscle. Thus we predicted that the maximum force across a range of lengths would be unchanged following fasciotomy. We measured maximal tetanic force output in a wing muscle in wild turkeys both before and after removal of fascia that enclosed the muscle in a compartment. Our hypothesis was not supported. The length-tension curve of this muscle showed that removal of fascia reduced maximum force output to 72 ± 10% of the prefascial release condition. Thus a reduction in muscle force following fasciotomy was not explained by a change in muscle length. The mechanism underlying reduction in force is unclear, but it suggests that the assumption underlying most isolated muscle experiments, i.e., removal of a muscle from its situation in vivo does not influence its maximal mechanical output, may need reexamining. NEW & NOTEWORTHY Most limb muscles are enclosed within compartments bound by robust fascial sheets. The mechanical significance of the close packing of muscle and fascia is largely unexplored. We used an animal model to show that removal of a fascial covering reduces the maximal force developed during contraction. These results raise questions about the use of isolated muscles to estimate muscle performance and suggest that a muscle's mechanical surrounding influences performance by mechanisms that are not understood.

Evaluation of degradation of force of esthetic elastomeric chains

Introduction Elastomers are considered important allies to orthodontic treatment and due to the aesthetic demand, aesthetic elastomers are increasingly used in adult patients. Objective The aim of this experimental in vitro study was to evaluate the degradation of force of esthetic elastomeric chains, of three different sizes: short, medium and long. Material and method For evaluating the degradation of force, 90 elastomeric chain segments were used, divided into 9 Groups (n=10), as follows: Morelli short elastomer, Morelli medium, Morelli long, Orthometric short, Orthometric medium, Orthometric long, American Orthodontic short, American Orthodontic medium and American Orthodontic long. Acrylic plates with pins were used to provide stretching of the elastomeric chains. The initial stretching force of the elastomeric chain was 150 grams, measured by a tensiometer. After this, they were prestretched to 50% of their original length, measured in an Instron 4411 Universal test machine, and placed on the seating pin on the plate. The plate was immersed in artificial saliva at 37 °C in a plastic receptacle, and removed for measurement after a time interval of 21 days. For statistical analysis, the methodology of mixed models for repeated measures in time and Tukey-Kramer test were used. Degradation of the forces was analyzed by 2-way analysis of variance (ANOVA) and the Tukey test. Result All the elastomeric chains showed statistically significant reduction in force (p<0.05). The American Orthodontic elastomeric chains showed higher reduction in force values, irrespective of the elastic size (p<0.05). Conclusion The three commercial brands studied underwent significant reduction in the quantity of force released; the American Orthodontic brand of elastomer showed the highest value of degradation in force.