Finite element modeling of the free boundary effect on gyroid additively manufactured samples.

There is a significant need for models that can capture the mechanical behavior of complex porous lattice architectures produced by 3D printing. The free boundary effect is an experimentally observed behavior of lattice architectures including the gyroid triply periodic minimal surface where the number of unit cell repeats has been shown to influence the mechanical performance of the lattice. The purpose of this study is to use finite element modeling to investigate how architecture porosity, unit cell size, and sample size dictate mechanical behavior. Samples with varying porosity and increasing number of unit cells (relative to sample size) were modeled under an axial compressive load to determine the effective modulus. The finite element model captured the free boundary effect and captured experimental trends in the structure's modulus. The findings of this study show that samples with higher porosity are more susceptible to the impact of the free boundary effect and in some samples, the modulus can be 20% smaller in samples with smaller numbers of unit cell repeats within a given sample boundary. The outcomes from this study provide a deeper understanding of the gyroid structure and the implications of design choices including porosity, unit cell size, and overall sample size.

Novel anthropomorphic hip phantom corrects systemic interscanner differences in proximal femoral vBMD.

Quantitative computed tomography (QCT) is increasingly used in osteoporosis studies to assess volumetric bone mineral density (vBMD), bone quality and strength. However, QCT is confronted by technical issues in the clinical research setting, such as potentially confounding effects of body size on vBMD measurements and lack of standard approaches to scanner cross-calibration, which affects measurements of vBMD in multicenter settings. In this study, we addressed systematic inter-scanner differences and subject-dependent body size errors using a novel anthropomorphic hip phantom, containing a calibration hip to estimate correction equations, and a contralateral test hip to assess the quality of the correction. We scanned this phantom on four different scanners and we applied phantom-derived corrections to in vivo images of 16 postmenopausal women scanned on two scanners. From the phantom study, we found that vBMD decreased with increasing phantom size in three of four scanners and that inter-scanner variations increased with increasing phantom size. In the in vivo study, we observed that inter-scanner corrections reduced systematic inter-scanner mean vBMD differences but that the inter-scanner precision error was still larger than expected from known intra-scanner precision measurements. In conclusion, inter-scanner corrections and body size influence should be considered when measuring vBMD from QCT images.

Effects of age and sex on the strength and cortical thickness of the femoral neck.

A group of 48 men (22 aged 65-75 years, 26 aged 80-90 years) and 59 women (32 aged 65-75 years, 27 aged 80-90 years) were enrolled in the Age, Gene/Environment Susceptibility-Reykjavik study and imaged with in vivo volumetric Quantitative Computed Tomography (QCT) to investigate the effects of age and sex on femoral neck structure and strength. Femoral neck cross-sectional moment of inertia for bending directions near those of standing and walking (I(AP)), bending strength (M(y)), and axial compressive strength (F(y)) were computed at the location of minimum cross-sectional area (minCSA). Local cortical thickness was computed in the inferior femoral neck based on density profiles extending through the cortex of the minCSA femoral neck section. Multivariate models accounting for height, weight, and age group (younger or older) showed that men had a 46% higher M(y) and a 23% higher F(y) than women, while women had a 13% thicker inferior cortex than men. Cortical thickness in the inferoposterior region of the femoral neck was significantly related to bending and axial strength after adjusting for overall volumetric bone mineral density. Both minCSA and I(AP) were higher in the older, gender-pooled age group, but F(y) and M(y) did not differ between the two age groups. The results suggest that age-related expansion of the femoral neck primarily occurs in the superior and inferior directions and helps maintain homeostasis of femoral neck stiffness and strength. The higher bending strength of the male femoral neck may partly explain why elderly men have a lower risk of hip fracture than elderly women.

Anaesthesia for insertion of ear tubes in children: comparison of propofol, thiopentone and halothane.

To determine the quality of anaesthesia and speed of recovery after propofol anaesthesia for myringotomy in children, 100 children 2-12 years were randomized to one of four anaesthetic regimens for induction/maintenance: thiopentone (STP) (5 mg.kg-1)/halothane, propofol (3 mg.kg-1)/halothane, halothane/halothane or propofol (3 mg.kg-1)/propofol bolus (0.5 mg.kg-1 every 3 min (10 mg.kg-1.h-1)). Nitrous oxide (70%) in oxygen (30%) was used to facilitate insertion of an intravenous catheter and was continued throughout the anaesthetic. We found that the incidence of intraoperative movement in response to surgical stimulation was significantly greater in the prop/prop group 32%, compared with the three other groups (P < 0.02). Although some recovery variables (time to response to questions, sit unaided, tolerate oral fluids, and discharge with fluids) were achieved more rapidly by the prop/ prop group than the other three groups, the times to open eyes, obey commands and, most importantly, discharge from recovery without fluids did not differ between the prop/prop and the hal/ hal groups. We conclude that there is little benefit in using propofol as an induction agent alone or in combination with a propofol maintenance anaesthetic for paediatric myringotomy and tube surgery.

Sterilization of dental instruments and devices: an update.

Dental sterilization techniques have become a focus of attention as a result of disclosure of occupational HIV transmission from an infected dentist to a cluster of patients. Although there has never been a confirmed report of a patient acquiring an infectious blood-borne disease from a dental instrument or device, recommendations for universal sterilization of dental handpieces and other devices have recently been implemented. Because of the higher rate of hepatitis B virus transmissability in the dental health care environment, an upgrade in sterilization protocols may be warranted. Stringent sterilization standards are especially necessary in higher-risk institutional dental care settings. However, a high rate of dental sterilization errors has been reported and traced to operator error. Recent institutional dental sterilization policy changes have been developed to reduce the chance of sterilization error, further diminishing the risk of cross contamination.

Oral cancer mortality in Maryland.

Oral cancer mortality is one of the most preventable types of cancer deaths when the lesion is detected early. The survival rate is quite low, however, when oral cancer is diagnosed at an advanced stage. While the Maryland oral cancer incidence rate is lower than the US average, the state ranks fourth in the country for overall age-adjusted oral cancer mortality; Maryland's African-American population has the highest oral cavity and pharyngeal mortality rate. Delayed diagnosis may explain this occurrence since groups at high risk for developing oral cancer, such as the elderly and minority groups, do not have ready access to the Maryland oral health care system. As the elderly annually use physicians' services almost twice as much as they use dentists' services, physicians are encouraged to routinely complete an oral cavity and pharyngeal examination. Inclusion of oral health services into a Maryland health system reform benefits package would also improve routine screening frequency for oral cancer.