Effect of Ligament Properties on Nonlinear Dynamics and Wear Prediction of Knee Prostheses.

Although wear is known as the primary cause of long-time failure of total knee arthroplasty (TKA), it can be vital in short- and midterm TKA failure due to laxity. One of the reasons leading to joint laxity and instability is ligamentous insufficiency. This study, therefore, aims to investigate the effects of insufficient ligaments-related knee laxity on both nonlinear dynamics and wear of TKA. The study hypothesizes (a) ligamentous insufficiency can increase TKA damage; (b) stiffness reduction of each of the posterior cruciate ligament (PCL) and medial-lateral collateral ligaments (MCL-LCL) can differently contribute to TKA damage. A forward dynamics methodology is developed and the ligament behavior is simulated employing an asymmetric nonlinear elastic model. External loads and moment, due to the presence of all soft tissues, e.g., muscles and hip joint reaction forces, applied to the femoral bone are determined using a musculoskeletal approach linked to the developed model. A mesh density analysis is performed and comparing outcomes with that available in the literature allows for the assessment of our approach. From the results acquired, reduced PCL stiffness leads to an increase in linear wear rates and results in the maximum damage in TKAs. However, the maximum linear wear rates on both condyles occur once the stiffness of all ligaments is reduced. Moreover, the worn area of the tibia surface increases with the reduction in MCL-LCL stiffness on the medial condyle. The joint with insufficient PCL also shows a considerable increase in ligament forces right after toe-off.

Effect of oral vitamin D supplementation on dry eye disease patients with vitamin D deficiency.

CLINICAL RELEVANCE: Dry eye disease (DED) and vitamin D deficiency are both common clinical entities. Vitamin D has been reported to play a significant role in ocular surface homeostasis. BACKGROUND: This study aimed to determine the therapeutic effect of oral vitamin D supplementation in dry eye disease patients with vitamin D deficiency. METHODS: A randomized, controlled study was completed in 100 patients with dry eye disease and concurrent vitamin D deficiency (< 20 ng/ml). Participants were randomly allocated to 8 weeks of oral vitamin D supplementation with both groups receiving conventional dry eye treatment with artificial tears. Schirmer's, tear break-up time (TBUT) and osmolarity tests were measured before and after eight weeks of treatment. RESULTS: The mean age of participants was 36.8 ± 8.56 years in the treatment group (n: 50) and 34.8 ± 10.13 year in the control group (n: 50). After eight weeks of treatment the mean differences in Schirmer's, TBUT and tear osmolarity were 2.38 ± 1.55 mm, 3.95 ± 1.48 s and -16.9 ± 6.28 mOsm/L, respectively in the treatment group, and 0.7 ± 0.86 mm, 0.92 ± 1.57s and -3.34 ± 2.0 mOsm/L respectively in the control group (p < 0.001 for all parameters). The treatment group demonstrated a more significant improvement than the control group in Schirmer's, TBUT and osmolarity values (p < 0.001). CONCLUSION: Vitamin D supplementation as an adjuvant to routine dry eye treatment improves ocular surface hemostasis parameters, results in better tear stability and a more improved tear osmolarity in patients with vitamin D deficiency.

A particle swarm-based algorithm for optimization of multi-layered and graded dental ceramics.

The thermal residual stresses (TRSs) generated owing to the cooling down from the processing temperature in layered ceramic systems can lead to crack formation as well as influence the bending stress distribution and the strength of the structure. The purpose of this study is to minimize the thermal residual and bending stresses in dental ceramics to enhance their strength as well as to prevent the structure failure. Analytical parametric models are developed to evaluate thermal residual stresses in zirconia-porcelain multi-layered and graded discs and to simulate the piston-on-ring test. To identify optimal designs of zirconia-based dental restorations, a particle swarm optimizer is also developed. The thickness of each interlayer and compositional distribution are referred to as design variables. The effect of layers number constituting the interlayer between two based materials on the performance of graded prosthetic systems is also investigated. The developed methodology is validated against results available in literature and a finite element model constructed in the present study. Three different cases are considered to determine the optimal design of graded prosthesis based on minimizing (a) TRSs; (b) bending stresses; and (c) both TRS and bending stresses. It is demonstrated that each layer thickness and composition profile have important contributions into the resulting stress field and magnitude.

A closed-form formulation for the conformal articulation of metal-on-polyethylene hip prostheses: Contact mechanics and sliding distance.

Using Hertz contact law results in inaccurate outcomes when applied to the soft conformal hip implants. The finite element method also involves huge computational time and power. In addition, the sliding distance computed using the Euler rotation method does not incorporate tribology of bearing surfaces, contact mechanics and inertia forces. This study, therefore, aimed to develop a nonlinear dynamic model based on the multibody dynamic methodology to predict contact pressure and sliding distance of metal-on-polyethylene hip prosthesis, simultaneously, under normal walking condition. A closed-form formulation of the contact stresses distributed over the articulating surfaces was derived based upon the elastic foundation model, which reduced computational time and cost significantly. Three-dimensional physiological loading and motions, inertia forces due to hip motion and energy loss during contact were incorporated to obtain contact properties and sliding distance. Comparing the outcomes with that available in the literature and a finite element analysis allowed for the validation of our approach. Contours of contact stresses and accumulated sliding distances at different instants of the walking gait cycle were investigated and discussed. It was shown that the contact point at each instant was located within the zone with the corresponding highest accumulated sliding distance. In addition, the maximum contact pressure and area took place at the stance phase with a single support. The stress distribution onto the cup surface also conformed to the contact point trajectory and the physiological loading.

The Effect of Maxillary First Molar Root Length on the Success Rate of Buccal Infiltration Anesthesia.

INTRODUCTION: Several variables may influence anesthesia success in maxillary molars. This investigation was conducted to evaluate the effect of root length on the success rate of infiltration injections of 2% lidocaine with 1:80,000 epinephrine. METHODS: One hundred maxillary first molars with irreversible pulpitis were treated. After the administration of a buccal infiltration injection of 2% lidocaine with 1:80,000 epinephrine, the patients' pain during dentin cutting, pulp exposure, and root canal instrumentation were evaluated using the Heft-Parker visual analog scale. No or mild pain was considered as success. Data were analyzed by the point-biserial correlation test and receiver operating characteristic curve analysis. RESULTS: Overall, 61% of the teeth had successful anesthesia after the administration of a single buccal infiltration injection of anesthetic solution. The point-biserial correlation test showed that the teeth that had palatal and distobuccal roots with longer root lengths showed significantly higher anesthesia failure (P < .05). However, receiver operating characteristic curve analysis did not show a clinically useful cutoff point of root length corresponding with anesthesia failure. CONCLUSIONS: Maxillary first molars having irreversible pulpitis with longer roots may have more anesthesia failures after a single buccal infiltration injection with 2% lidocaine and 1:80000 epinephrine.

Caspase-3 is a component of Fas death-inducing signaling complex in lipid rafts and its activity is required for complete caspase-8 activation during Fas-mediated cell death.

Since its discovery, caspase-8 has been placed at the apex of the proteolytic cascade triggered by death receptor (DR) cross-linking. Because of its capacity to interact with the cytoplasmic portion of DR, it has been suggested that caspase-8 acts independently of other caspases in the initiation of Fas and other DR signaling. In this study, we demonstrate that in Jurkat cells, caspase-3 cleavage is an early step during Fas-induced apoptosis. We show that caspase-3 processing into its p20 occurs rapidly after Fas cross-linking, in the absence of mitochondrial depolarization and caspase-9 activation. Moreover, caspase-3 is present in lipid rafts of untreated Jurkat cells and peripheral T lymphocytes. Caspase-3, caspase-8, and Fas-associated death domain are further recruited to lipid rafts of Jurkat cells following anti-Fas treatment. Fas immunoprecipitation reveals that caspase-3 is a component of the death-inducing signaling complex, suggesting that this cysteine protease is in close proximity to caspase-8. Furthermore, transduction of Jurkat cells with a caspase-3 dominant-negative form inhibits caspase-8 processing and results in inhibition of apoptosis, suggesting that caspase-3 activity is required for caspase-8 activation. Overall, these findings support a model whereby caspase-3 is a component of the death-inducing signaling complex located in lipid rafts, and as such, is involved in the amplification of caspase-8 activity by the mitochondrion.