Magnetic resonance imaging of rodent teeth

In this paper, the anatomical structures of rat jaws are studied using magnetic resonance imaging (MRI) with high spatial resolution. In vivo microimages of teeth from 3- and 12-week-old (young and adult) rats have been performed. A 2 T nuclear magnetic resonance microscope was used to collect, with multiple orientations, non-invasive 2D data images using the spin-echo technique. MRI appears well suited to give images of the oral area and may represent a useful tool for diagnosis of dental diseases and more particularly of pulp pathologies. This work was presented at the ESMRMB meeting in Brussels, September 1997.     

FEA evaluation of material stiffness changes for a polymer assisted 3D polycaprolactone/β-tricalcium phosphate scaffold in a mandibular defect reconstruction model

In bone regenerative engineering, the biomechanical performance of the scaffold at the bone-tissue interface is a key consideration. The evaluation of this parameter is a crucial step in designing, optimizing and manufacturing of bone substitute materials for clinical application, but is as yet comparatively unexplored. To this end, we utilized a novel polymer-assisted method to fabricate a three-dimensional (3D) Polycaprolactone/β-Tricalcium phosphate scaffold. The compressive modulus was measured and the data used to inform finite element analysis. The scaffolds achieved a maximum compressive moduli of 151 MPa, close to that of cortical bone. Further computational simulations were performed to determine the stresses and local scaffold adaptation profile, using data from computer tomography scans of the mandible. Local stresses were simulated based on the density changes in new bone forming in the scaffold at different stages of healing. The stress distribution in the mandible, scaffold center and scaffold interface were explored for a static load of 200 N, which corresponds to the load of adult mastication near the incisors. The analysis revealed that the maximum cross-sectional stress at the scaffold center and at the scaffold interface was 2.7 and 4.12 MPa respectively. The majority of the stress was localized in the bone of the mandible, with the scaffold bearing minimal loading at the start, but more over time as infiltration of more new bone progressed.     

Metals in mandibles of stored product insects: do zinc and manganese enhance the ability of larvae to infest seeds?

Although high concentrations of zinc and manganese were found in mandibles of insect larvae that bore into seeds, these metals were not detected in mandibles of insect larvae that attack previously damaged seeds. Metals were present in the larval mandibles of a lepidopteran, the Angoumois grain moth (Sitotroga cerealella), and eight coleopterans, the lesser grain borer (Rhyzopertha dominica), cigarette beetle (Lasioderma serricorne), drugstore beetle (Stegobium paniceum), spider beetle (Gibbium aequinoctiale), warehouse beetle (Trogoderma variabile), cadelle (Tenebroides mauritanicus), larger black flour beetle (Cynaeus angustus), and cowpea weevil (Callosobruchus maculatus). Larvae of these species can chew into seeds. Larvae of six other coleopterans, the varied carpet beetle (Anthrenus verbasci), sawtoothed grain beetle (Oryzaephilus surinamensis), rusty grain beetle (Cryptolestes ferrugineus), red flour beetle (Tribolium castaneum), longheaded flour beetle (Latheticus oryzae), and granary weevil (Sitophilus granarius) have little if any ability to chew into seeds, and did not have metal in their mandibles. Larvae of the granary weevil hatch and feed within seeds that were penetrated previously during egg deposition by adults. However, newly hatched larvae of the cowpea weevil and the Angoumois grain moth have to bore through the seed coat before they begin feeding, and they have mandibles with high concentrations of zinc. These data support the hypothesis that deposition of zinc and/or manganese in larval mandibles enhances the larva's ability to penetrate seeds.     

Dual-motion fretting behavior of mandibular cortical bone against pure titanium

Dual-motion fretting tests of flat cortical bone specimens from fresh human mandible against pure titanium (TA2) ball were carried out on a modified test rig with tilt angle of 45°. The imposed maximal loads varied from 100 to 200 N. Dynamic characteristics of dual-motion fretting tests were analyzed in combination with micro-examinations via optical microscopy (OM), laser confocal scanning microscopy (LCSM) and scanning electron microscopy (SEM) together with energy dispersive X-ray spectrum (EDX). Two types of F-D curves (the trapezoid and elliptic mode) were recorded during the tests. The examination showed that the wear scars of the dual-motion fretting were asymmetric, and the tangential component of dual-motion fretting was in the mixed fretting regime. Under the lower imposed load, only some detachment of particles and scratches without cracking were observed even after 5×10⁴ cycles. The main wear mechanisms of the dual-motion fretting damage were the abrasive and adhesive wear. Under higher imposed loads, the cracks initiated and propagated mainly at the high stress side of contact edges. The wear mechanisms of the dual-motion fretting of cortical bone under higher imposed loads were the combination of the adhesive wear, abrasive wear, cracking and lubrication of the human bone tissue debris. And the lubrication of the debris played an important role during the dual-motion fretting processes.     

Anisotropic Wear Resistance of Human Mandible Cortical Bone

In order to evaluate the wear resistance, nanoscratch tests were conducted along different directions in the axial and the cross sections of mandible cortical bone, with the progressive loads from 0.1 to 80 mN. The morphology of scratch scars was showed via a field emission scanning electron microscope and an AMBIOS XP-2 stylus profilometer. The results indicated that the wear resistance of axial section was better than that of cross section. Furthermore, the wear resistance of axial section was affected by the different arrangement of lamellae. The wear degree was slighter when the scratches were conducted along the direction paralleling the osteon. The wear mechanism of cortical bone became more complicated with the increasing loads. It changed from the simple elastic–plastic deformation to the combination of deformation, delamination, and microcrack’s propagation.     

Historical biomonitoring of fluoride pollution by determining fluoride contents in roe deer (Capreolus capreolus L.) antlers and mandibles in the vicinity of the largest Slovene thermal power plant

Roe deer antlers/mandibles are a useful tool for determination of ambient fluoride pollution. Antlers have a well-defined annual cycle of growth, therefore they represent a natural standardisation of samples during winter months. On the contrary, mandibles accumulate fluorides during the whole life of an organism, thus they reflect aggregated effect of fluoride pollution trough the life-span of an organism. Both tissues are easily available; mandibles are often systematically collected with the purpose of cognitive management and control, and antlers could be gathered from private well-dated hunters' collections.Considering these benefits, fluoride contents were measured in 141 antlers (period 1960-2007) and 220 mandibles (period 1997-2009) of roe deer, shot in the vicinity of the largest Slovene Thermal Power Plant of Šoštanj (ŠTPP) as one of the major sources of fluorides in Slovenia. Fluoride contents in antlers significantly differed among age categories, and ranged from 110 to 1210 mg/kg in yearlings, 130 to 2340 mg/kg in young adults, and 250 to 2590 mg/kg in older adults, respectively. Fluoride levels in mandibles were also significantly different among age categories, and ranged from 30.0 to 227 mg/kg in fawns, 33.8 to 383 mg/kg in yearlings, and 61.5 to 1020 mg/kg in adults, respectively.Comparison of these results with previously reported fluoride contents in antlers and mandibles of roe deer from different areas of Europe revealed that the study area has never been extensively contaminated with fluorides. Moreover, trends of fluoride contents in both tissues confirmed a significant decrease of fluoride pollution in the area after the years 1995 and 2000, when flue-gas cleaning devices were constructed on the ŠTPP. Indeed, highly positive correlations between annual emissions from the ŠTPP and mean annual fluoride contents in antlers/mandibles confirmed that both tissues may be a useful tool for assessing temporal trends in ambient fluoride pollution.     

双期矫治儿童安氏Ⅱ1下颌后缩错畸形的临床应用

目的应用双期矫治的方法,对下颌后缩引起的安氏Ⅱ1分类患者进行矫治。方法1期矫正采用activator,Ⅱ期矫正采用直丝弓。结果双期矫治中1期治疗能纠正骨骼矢状关系不调,改善了侧面外形,同时降低了Ⅱ期矫治的难度。结论双期矫治儿童安氏Ⅱ1下颌后缩错畸形有明显疗效。     

基于实体模型的牙颌组织三维有限元建模问题探讨

通过常用牙颌组织三维有限元建模方法的简述与比较 ,提出了自己的基于DICOM数据的高精度建模方法 ,该方法保留了实体模型的几何信息 ,可保证良好的几何相似性 ;建模速度快 ;不损坏实物模型。适用于临床医疗的实际需要 ,为有限元方法在口腔医学的应用提供了一条颇具成效的思路。并给出了相应的应用实例