Jennifer R. Melander

Gender-Dependence of Bone Structure and Properties in Adult Osteogenesis Imperfecta Murine Model

Osteogenesis imperfecta (OI) is a dominant skeletal disorder characterized by bone fragility and deformities. Though the oim mouse model has been the most widely studied of the OI models, it has only recently been suggested to exhibit gender-dependent differences in bone mineralization. To characterize the impact of gender on the morphometry/ultra-structure, mechanical properties, and biochemical composition of oim bone on the congenic C57BL/J6 background, 4-month-old oim/oim, +/oim, and wild-type (wt) female and male tibiae were evaluated using micro-computed tomography, three-point bending, and Raman spectroscopy. Dramatic gender differences were evident in both cortical and trabecular bone morphological and geometric parameters. Male mice had inherently more bone and increased moment of inertia than genotype-matched female counterparts with corresponding increases in bone biomechanical strength. The primary influence of gender was structure/geometry in bone growth and mechanical properties, whereas the mineral/matrix composition and hydroxyproline content of bone were influenced primarily by the oim collagen mutation. This study provides evidence of the importance of gender in the evaluation and interpretation of potential therapeutic strategies when using mouse models of OI.

ERGONOMIC LAPAROSCOPIC TOOL HANDLE DESIGN

Twenty-two subjects were tested and categorized according to hand size (small, medium, or large). Each subject selected the best location for a trackball and a trigger on a handle. Each subject specified the optimum diameter/size of the handle that he or she preferred. Additionally, subjects selected their preferred pivot range for opening and closing the handle. Finally, each subject exerted his or her preferred force for the trackball and trigger controls in the selected positions. Based on the data collected in this experiment, the recommended handle diameter is in the range of 4.3 to 5.7 cm. The recommended handle pivot is the range of 8.1 to 17.3 degrees for the open and closed positions. The recommended trackball actuation force is 3.0 lbs and the recommended ratchet actuation force is 0.6 lbs, on average.

Correlation of Impression Removal Force with Elastomeric Impression Material Rigidity and Hardness

PURPOSE Difficult impression removal has been linked to high rigidity and hardness of elastomeric impression materials. In response to this concern, manufacturers have reformulated their materials to reduce rigidity and hardness to decrease removal difficulty; however, the relationship between impression removal and rigidity or hardness has not been evaluated. The purpose of this study was to determine if there is a positive correlation between impression removal difficulty and rigidity or hardness of current elastomeric impression materials. MATERIALS AND METHODS Light- and medium-body polyether (PE), vinylpolysiloxane (VPS), and hybrid vinyl polyether siloxane (VPES) impression materials were tested (n = 5 for each material/consistency/test method). Rigidity (elastic modulus) was measured via tensile testing of dumbbell-shaped specimens (Die C, ASTM D412). Shore A hardness was measured using disc specimens according to ASTM D2240-05 test specifications. Impressions were also made of a custom stainless steel model using a custom metal tray that could be attached to a universal tester to measure associated removal force. Within each impression material consistency, one-factor ANOVA and Tukeys post hoc analyses (α = 0.05) were used to compare rigidity, hardness, and removal force of the three types of impression materials. A Pearsons correlation (α = 0.05) was used to evaluate the association between impression removal force and rigidity or hardness. RESULTS With medium-body materials, VPS exhibited significantly higher (p ≤ 0.05) rigidity and hardness than VPES or PE, while PE impressions required significantly higher (p ≤ 0.05) removal force than VPS or VPES impressions. With light-body materials, VPS again demonstrated significantly higher (p ≤ 0.05) hardness than VPES or PE, while the rigidity of the light-body materials did not significantly differ between materials (p > 0.05); however, just as with the medium-body materials, light-body PE impressions required significantly higher (p ≤ 0.05) removal force than VPS or VPES. Moreover, there was no positive correlation (p > 0.05) between impression removal force and rigidity or hardness with either medium- or light-body materials. CONCLUSIONS The evidence suggests that high impression material rigidity and hardness are not predictors of impression removal difficulty.

Silorane resin supports proliferation, differentiation, and mineralization of MLO-A5 bone cells in vitro and bone formation in vivo†

Methyl methacrylate used in bone cements has drawbacks of toxicity, high exotherm, and considerable shrinkage. A new resin, based on silorane/oxirane chemistry, has been shown to have little toxicity, low exotherm, and low shrinkage. We hypothesized that silorane-based resins may also be useful as components of bone cements as well as other bone applications and began testing on bone cell function in vitro and in vivo. MLO-A5, late osteoblast cells, were exposed to polymerized silorane (SilMix) resin (and a standard polymerized bisGMA/TEGDMA methacrylate (BT) resin and compared to culture wells without resins as control. A significant cytotoxic effect was observed with the BT resin resulting in no cell growth, whereas in contrast, SilMix resin had no toxic effects on MLO-A5 cell proliferation, differentiation, nor mineralization. The cells cultured with SilMix produced increasing amounts of alkaline phosphatase (1.8-fold) compared to control cultures. Compared to control cultures, an actual enhancement of mineralization was observed in the silorane resin-containing cultures at days 10 and 11 as determined by von Kossa (1.8-2.0 fold increase) and Alizarin red staining (1.8-fold increase). A normal bone calcium/phosphate atomic ratio was observed by elemental analysis along with normal collagen formation. When used in vivo to stabilize osteotomies, no inflammatory response was observed, and the bone continued to heal. In conclusion, the silorane resin, SilMix, was shown to not only be non cytototoxic, but actually supported bone cell function. Therefore, this resin has significant potential for the development of a nontoxic bone cement or bone stabilizer.

Processing of yttrium aluminosilicate (YAS) glasses for dental composites

Two series of silicate glasses were processed to micron-size, sub-micron size, and nanoparticles using three different milling systems: ball milling, attrition, and high-energy milling. The effect of milling time and media size on particle size and contamination were investigated in aqueous and isopropanol suspensions. The particle size was determined using a laser-diffraction particle size analyzer and scanning electron microscopy. The smallest glass particles with a median particle size of 0.3 µm were achieved by a two-step comminution process in a high energy mill.

Estimation of Properties of a Photoinitiated Silorane-based Composite with Potential for Orthopaedic Applications

We have synthesized a filler-reinforced silorane composite that has potential applications in orthopaedic surgery, such as for a bone stabilizer. The purpose of the present work was to develop a method for estimating four properties of this material; namely, maximum exotherm temperature, flexural strength, flexural modulus, and fracture toughness. The method involved the use of mixture design-of-experiments and regression analysis of results obtained using 23 formulations of the composite. We validated the estimation method by showing that, for each of four composite formulations that were not included in the method development, the value of each of the aforementioned properties was not significantly different from that obtained experimentally. Our estimation method has the potential for use in the development of a wide range of orthopaedic materials.

Measuring Strain in Bone Cement With Carbon Nanotubes

While great strides have been made in the design of dental composites and orthopaedic implants, improvements are still needed. For instance the life span of dental polymer composites is known to be significantly shorter than traditional amalgam restorations [1]. Similarly, the early failure rate of orthopaedic implants often leads to an intentional delay in the treatment of painful, debilitating joints to ensure patients don’t outlive the functional life of their prosthetics [2]. Stress concentrations within biomaterials may be partially to blame for these premature failures.Copyright

Polymerization Stress and the Influence of TOSU Addends on Methacrylate Composites

The aesthetic appeal of composite-resin restoratives promotes their use, however their functional life is significantly shorter when compared to their metal counterparts.1 One possible reason is the effect of polymerization stress on marginal integrity. Shrinkage of the composite, and its associated stress, has been found to cause gap formation and stress interactions between the restorative and the adhesive. These gaps offer an ideal niche for bacteria, and, when compounded by the mechanical strain of chewing, can lead to premature failure of the restorative.2,3 Additionally, it is well known that incomplete conversion of the double bonds occurs during methacrylate polymerizations.4–7 A high degree of conversion is needed to prevent the presence of potentially hazardous monomers.8Copyright

Model of Silorane Composite for Bone Stabilization Application

Improvements in body armor and battlefield medical care have resulted in an increase in survival rates but also an increase in survivable battlefield extremity injuries (Covey 2002; Covey 2006; Owens, Kragh et al. 2007). It is well known that these traumatic extremity injuries require adequate stabilization to achieve an optimal healing outcome. Extremity fractures also affect a large proportion of the civilian population. In 2005, 5.7 million Americans suffered an injury resulting in bone fracture (CDC/NCHS). Transport of these domestically injured individuals to medical facilities also requires stabilization to avoid further injury.Copyright