Chairside CAD/CAM materials. Part 1: Measurement of elastic constants and microstructural characterization

Objective

A deeper understanding of the mechanical behavior of dental restorative materials requires an insight into the materials elastic constants and microstructure. Here we aim to use complementary methodologies to thoroughly characterize chairside CAD/CAM materials and discuss the benefits and limitations of different analytical strategies.

Intracellular calcium dynamics dependent on defined microtopographical features of titanium

Detailed insights into the complex cellular behavior at the biomaterial interface are crucial for the improvement of implant surfaces with respect to their acceptance and integration. The cells perceive microtopographical features and, in consequence, rearrange their adhesion structures like the actin cytoskeleton and adaptor proteins. But little is known about whether these altered cellular phenotypes have consequences for intracellular calcium signaling and its dynamics. To elucidate if an artificial, geometrical microtopography influences calcium ion (Ca²⁺) mobilization in osteoblasts, human MG-63 cells were stained with the calcium dye Fluo 3-acetoxymethyl ester and set on defined silicon–titanium (Ti) arrays with regular pillar structures (P5, 5 × 5 × 5 μm) and compared with planar Ti. To induce an immediate calcium signal, cells were stimulated with adenosine 5′-triphosphate (ATP). Interestingly, osteoblasts on micropillars expressing a shortened actin cytoskeleton were hampered in their calcium mobilization potential in signal height as well duration. Even the basal level of the intracellular Ca²⁺ concentration was reduced, which was accompanied by a disturbed fibronectin synthesis. The expression of the voltage-sensitive calcium channels Ca_v1.2, Ca_v1.3 (L-type) and Ca_v3.1, Ca_v3.2, Ca_v3.3 (T-type) as well as the signaling proteins phospho-AKT and phospho-GSK3α/β remained unaffected on pillars. The topography-dependent calcium dynamics observed here provide new insights into how topographical cues alter cell functions – via the intracellular Ca²⁺ signaling.     

Multi-level characterization of human femoral cortices and their underlying osteocyte network reveal trends in quality of young,aged, osteoporotic and antiresorptive-treated bone

Characterization of bone's hierarchical structure in aging, disease and treatment conditions is imperative to understand the architectural and compositional modifications to the material and its mechanical integrity. Here, cortical bone sections from 30 female proximal femurs – a frequent fracture site – were rigorously assessed to characterize the osteocyte lacunar network, osteon density and patterns of bone matrix mineralization by backscatter-electron imaging and Fourier-transform infrared spectroscopy in relation to mechanical properties obtained by reference-point indentation. We show that young, healthy bone revealed the highest resistance to mechanical loading (indentation) along with higher mineralization and preserved osteocyte-lacunar characteristics. In contrast, aging and osteoporosis significantly alter bone material properties, where impairment of the osteocyte-lacunar network was evident through accumulation of hypermineralized osteocyte lacunae with aging and even more in osteoporosis, highlighting increased osteocyte apoptosis and reduced mechanical competence. But antiresorptive treatment led to fewer mineralized lacunae and fewer but larger osteons signifying rejuvenated bone. In summary, multiple structural and compositional changes to the bone material were identified leading to decay or maintenance of bone quality in disease, health and treatment conditions. Clearly, antiresorptive treatment reflected favorable effects on the multifunctional osteocytic cells that are a prerequisite for bone's structural, metabolic and mechanosensory integrity.     

Towards long lasting zirconia-based composites for dental implants. Part I: Innovative synthesis,microstructural characterization and in vitro stability

In order to fulfill the clinical requirements for strong, tough and stable ceramics used in dental applications, we designed and developed innovative zirconia-based composites, in which equiaxial α-Al₂O₃ and elongated SrAl₁₂O₁₉ phases are dispersed in a ceria-stabilized zirconia matrix. The composite powders were prepared by an innovative surface coating route, in which commercial zirconia powders were coated by inorganic precursors of the second phases, which crystallize on the zirconia particles surface under proper thermal treatment. Samples containing four different ceria contents (in the range 10.0–11.5 mol%) were prepared by carefully tailoring the amount of the cerium precursor during the elaboration process. Slip cast green bodies were sintered at 1450 °C for 1 h, leading to fully dense materials. Characterization of composites by SEM and TEM analyses showed highly homogeneous microstructures with an even distribution of both equiaxial and elongated-shape grains inside a very fine zirconia matrix.Ce content plays a major role on aging kinetics, and should be carefully controlled: sample with 10 mol% of ceria were transformable, whereas above 10.5 mol% there is negligible or no transformation during autoclave treatment.Thus, in this paper we show the potential of the innovative surface coating route, which allows a perfect tailoring of the microstructural, morphological and compositional features of the composites; moreover, its processing costs and environmental impacts are limited, which is beneficial for further scale-up and real use in the biomedical field.     

反复熔铸对牙科烤瓷合金显微结构的影响

目的: 探讨反复熔铸对钴铬、纯钛、钯铜镓、金铂烤瓷合金显微结构的影响。方法: 在真空加氩气保护环境下,将4种烤瓷合金单纯反复熔铸1~3次。每次再熔铸前,烤瓷合金均经过课题组前期研究所得“烤瓷合金再熔铸前最佳处理方法”处理,根据金属显微组织检验方法（GB/T13298-2015）,分别对熔铸前、熔铸1~3次后的烤瓷合金进行研磨、抛光、浸蚀,采用金相显微镜或扫描电镜检测金相显微结构。结果: 随着熔铸次数增加,钴铬烤瓷合金晶粒粗化、晶粒间基质和晶界间化合物增多。纯钛烤瓷合金随熔铸次数增加,晶粒粗化明显。2次熔铸后,晶粒有等轴化倾向,3次熔铸则出现针刺状β相。钯铜镓烤瓷合金在2、3次熔铸后,晶粒结构略有长大。金铂烤瓷合金晶粒结构未随熔铸次数发生明显改变。结论: 反复熔铸显著改变钴铬、纯钛、钯铜镓烤瓷合金的显微结构,建议由厂家回收再利用烤瓷合金废旧料。     

心房颤动患者心房肌细胞超微结构及凋亡水平的改变

探讨心房颤动(简称房颤)与心房肌组织细胞学重构的关系。38例风湿性心脏病二尖瓣狭窄换瓣术者,其中窦性心律者13例(A组)、阵发性及房颤持续时间小于6个月者8例(B组)、房颤持续时间大于6个月者17例(C组)。外科手术时取三组患者右心耳少许,利用透射电镜观察心房肌细胞超微结构改变,以及利用TUNEL法标记心房肌细胞凋亡并计算凋亡指数。结果:B、C组心房肌细胞超微结构有明显变化,如心肌纤维稀疏、排列紊乱,细胞收缩成分减少、线粒体肿胀、肌浆网扩张,纤维组织增生、细胞水肿、坏死表现;C组变化更明显。B、C组细胞凋亡指数与A组比较,显著增高(分别为44.53%±11.08%,67.96%±16.09%vs19.68%±15.36%,P均<0.05);房颤持续时间越长其凋亡指数越高。结论:心房肌的组织细胞学重构可能在房颤的发生或维持中起重要作用。     

Impact of oral ibandronate 150 mg once monthly on bone structure and density in post-menopausal osteoporosis or osteopenia derived from in vivo μCT

The effect of ibandronate 150 mg/once monthly in the treatment of post-menopausal osteopenia and osteoporosis on bone micro-structure at the distal tibia and radius has not been considered to date. Seventy post-menopausal women with osteoporosis or osteopenia were recruited. All subjects received calcium and vitamin D supplementation and were randomized to either a group which took 150 mg ibandronate oral monthly or a placebo group over a 12-month period. μCT measures of the distal tibia and radius were conducted every three months, with DXA lumbar spine and hip measurements conducted only pre and post and serum markers of bone formation and resorption measured every 6 months. After 12-months no significant impact of ibandronate on the primary outcome measures bone-volume to tissue-volume and trabecular separation at the distal tibia (p ≥ 0.15) was found. Further multiple regression analyses of the primary end-points indicated a significant effect favoring the ibandronate intervention (p = 0.045). Analysis of secondary end-points showed greater increases in distal tibia cortical thickness, cortical density and total density (p ≤ 0.043) with ibandronate and no significant effects at the distal radius, but greater increases of hip DXA-BMD and lumbar spine DXA-BMD (p ≤ 0.017). Ibandronate use resulted in a marked reduction in bone turnover (p < 0.001). While ibandronate resulted in greater mineralization of bone, this effect differed from one body region to another. There was some impact of ibandronate on bone structure (cortical thickness) at the distal tibia, but not on bone-volume to tissue-volume or trabecular separation.     

Relations between tensile impact properties and microstructure of compact bone

Summary Standardized human and beef femoral compact bone specimens were tested in tensile impact and the dynamic mechanical properties were determined. The microstructure of 45 beef and 47 human bone specimens were examined histologically to determine if there is a structural basis to account for strength differences in the bone samples. Strong negative correlations were obtained between the maximum stress and the percentage area of secondary osteons in each specimen. For human bone samples, the energy absorption capacity and the modulus of elasticity were also found to have strong negative correlations with the percentage area of secondary osteons present in each specimen. Linear regression equations were obtained describing the impact strength properties in terms of the percentage areas of secondary osteons and cavities in the samples.Fracture surfaces of the tested bone specimens were examined in a scanning electron microscope. Most surfaces exhibited a fairly rough texture indicating a quasi-cleavage type of failure. Fractographic analysis of bone fracture surface was helpful in understanding the micromechanics of bone fracture.Presented in part at the 21st Annual Meeting of Orthopaedic Research Society     

Constraint stress, microstructural characteristics, and enhanced mechanical properties of a special fibroblast-embedded collagen construct

Cell-contracted collagen gels could provide rejection-free biomaterials for tissue engineering, but their application is limited by relatively low mechanical strength. We developed a special type I collagen construct (based on embedded fibroblasts) that was formed into a gel thread by using two anchors to constrain gel contraction in one direction. Each gel thread contained 2 mg of type I collagen and 1.0 x 10(6) fibroblasts, and had an initial volume of 3 mL. After 9 days in culture, this preparation was transformed into a thread-like construct measuring 26 x 2.3 x 0.21 mm. Investigation of the microstructure showed that the collagen fibrils longitudinally between two cells had most aligned with the direction of the constraint stress and had assumed higher density than those in the freely contracted controls. During culturing, the constraint stress first increased then decreased, with implications for the nature of the interaction between the embedded cells and collagen matrix. Under uniaxial tensile testing, the ultimate stress and material modulus increased by factors of 6 and 16, respectively, compared with controls, while the maximal strain decreased by 590%. Compared with the similar constructs in the literature, the thread gel was fabricated by means of a novel mold configuration so that it contracted to thread shape much faster, and more importantly, the constraint force was firstly reported in this article. The improved mechanical properties show that the gel thread could be an effective biomaterial for such tissue engineering applications as the fabrication of blood vessels, ligaments, and tendon grafts.     

急性心房颤动模型心房肌超微结构改变及替米沙坦对其影响

目的观察急性心房颤动(简称房颤)模型心房肌细胞超微结构的改变及替米沙坦对其干预作用。方法30只新西兰纯种大白兔随机分为:假手术对照组、非给药模型组和给药模型组。用快速心房起搏法建立兔房颤模型,利用透射电镜观察房颤形成8 h后心房肌细胞超微结构改变。结果与假手术对照组比较,非给药模型组心房肌细胞超微结构有明显变化,如心肌细胞肌原纤维排列紊乱、线粒体肿胀、细胞器明显减少、细胞染色质凝集类似凋亡改变等,而给药模型组变化较轻。结论房颤时心房肌的组织细胞学会发生重构,血管紧张素受体阻滞剂类药物可拮抗房颤时的组织细胞重构。