Effects of different mandibular fracture patterns on the stability of miniplate screw fixation in angle mandibular fractures.

The aim of the present study was to evaluate the effects of horizontally favourable and unfavourable mandibular fracture patterns on the fixation stability of titanium plates and screws by simulating chewing forces. Favourable and unfavourable mandibular fractures on 22 sheep hemimandibles were fixed with 4-hole straight titanium plates and 2.0mm×7mm titanium screws according to the Champy technique. Hemimandibles were mounted with a fixation device in a servohydraulic testing unit for compressive testing. Displacement values under 20, 60, 100, 120, 150, 200N, maximum displacements, and maximum forces the model could resist before breakage were recorded and compared. The authors found no statistically significant differences between the groups for the displacement values in the force range 60-200N (60, 100, 120, 150 and 200N). Statistically significant differences for maximum displacement values (displacement values at the breaking forces) between the groups were found (P<0.05). There was no evidence for the need to apply different treatment modalities to mandibular fractures regardless of whether the factures are favourable or not.

A biomechanical and spectroscopic study of bone from rats with selenium deficiency and toxicity.

Selenium, being an essential mineral in the mammalian diet, is important in providing protection against oxidative damage. Numerous in vitro studies of selenium compounds reveal a very high correlation between catalytic activity of selenium compounds and toxicity. The present study was designed to investigate the effects of dietary selenium on the biomechanical properties of bone. New born rats of both sexes were fed with either a control, or a selenium- and vitamin E-deficient, or a selenium-excess and vitamin E-adequate diet. We obtained the stiffness (modulus of elasticity) of bones (femur and tibia) by tensile test for all groups considered. Both the deficient and the excess groups have decreased biomechanical strength with respect to the control group. To support our biomechanical results for both experimental groups, X-ray diffraction analysis and FTIR spectroscopic study were performed on the femurs and tibiae. The X-ray diffraction analysis showed that the intensities of the peak observed at around 2theta degrees = 31.820, in the control femur and tibia are stronger than the intensities of the corresponding peak of two experimental groups. In FTIR spectroscopy, the disappearance and/or reduction of the intensities of some carbonate bands in the two experimental groups indicate that there is a decrease in crystallinity and mineral contents which, together with X-ray diffraction analysis, correlate very well with the biomechanical data.

Synthesis and mechanical properties of interpenetrating networks of polyhydroxybutyrate-co-hydroxyvalerate and polyhydroxyethyl methacrylate.

Naturally occurring, biocompatible, and biodegradable polyhydroxybutyrate-co-hydroxyvalerate (PHBV), and synthetic, non-degrading polyhydroxyethylmethacrylate (PHEMA) membranes were prepared and their mechanical properties were studied. Their performances were compared with the interpenetrating networks (IPN) prepared by photopolymerization of HEMA in the presence of PHBV. The modulus of elasticity, failure stress and failure strain indicated that the IPNs are viscoelastic with properties closer to PHEMA but much stronger than PHEMA homopolymers. Incorporation of PHBV (7, 14 and 22% HV) affected the mechanical properties positively. Increasing the PHBV content increased the modulus of elasticity and failure stress nearly in all samples tested. PHBV (7, 14, and 22% HV, 300 mg) samples showed an approximately 17-30 fold increase in terms of modulus of elasticity and 7-10 fold increase in terms of failure stress. The scanning electron micrographs of the membranes showed that the PHEMA membranes are more porous than the PHBV membranes but the IPN structure displayed channels on the membrane surface indicating that HEMA polymerization was achieved by using the PHBV as a scaffold. With the use of the present technique, it is possible to synthesize supramolecular structures from molecules that are not compatible and miscible with each other.

The shape of the lumbar vertebral canal in newborns.

STUDY DESIGN: This study used geometric measurement criteria to assess the incidence of a trefoil spinal canal configuration in neonates. OBJECTIVES: To examine the shape of the neonatal lumbar vertebral canal with regard to its shape and the incidence of trefoilness. SUMMARY OF BACKGROUND DATA: Many studies consider the trefoil canal to be a developmental feature. Because of a lack of neonatal samples it is still unknown whether some individuals are prone to develop a trefoil spinal canal because of genetically determined factors. METHODS: The last two lumbar vertebrae of 31 term neonatal cadavers from the collection of the Anatomy Department of Ondokuz Mayis University were examined. After removal, the vertebrae were processed and embedded in paraffin blocks to enable accurate sectioning at the pedicle level. Subsequently, unmagnified images were obtained through a color photocopy machine. These two-dimensional images were digitalized, and accurate measurements were made to determine the circularity and the trefoilness. RESULTS: Trefoilness assessment indicated that the trefoil-shaped spinal canal does not exist in newborns. The spinal canal at this age is mostly dome-shaped. CONCLUSIONS: In accordance with the previous hypotheses made by other authors, the authors of this study found that the trefoil shape of the lumbar vertebra does not occur at the end of the intrauterine period.

Effect of dietary selenium and vitamin E on the biomechanical properties of rabbit bones.

It is generally agreed that combined deficiency of selenium and vitamin E leads to several abnormalities including Kashin-Beck disease which is an endemic and chronic degenerative osteoarthrosis. The abnormalities can be reversed by the administration of various forms of selenium and vitamin E. The present study was designed to investigate the effects of dietary selenium and vitamin E on bone tissue and on the biomechanical properties of bone. Young rabbits of both sexes were fed with either a selenium- and vitamin E-adequate diet (control group), or a selenium- and vitamin E-deficient diet or a selenium-excess diet. The selenium-deficient diet resulted in a significant decrease in plasma selenium level and the selenium-excess diet resulted in a significant increase in the plasma selenium level with respect to the corresponding control values (p < 0.05). The diets did not affect the blood cell counts considerably but erythrocyte glutathione peroxidase activity increased (decreased) relatively when the plasma selenium level increased (decreased) (p < 0.05). The light microscopic investigations of the bone tissues of the two experimental groups indicate that the findings of the present work are compatible with osteomalacia. The biomechanical properties of the bones from the three groups were determined experimentally with bending tests. Both the Se- and vitamin E-deficient diet and the Se-excess diet decreased the biomechanical strength of the bones significantly while the bones belonging to the control group always had the largest modulus of elasticity (p < 0.05).