2种方法制作金属基底冠边缘适合性和金瓷结合力比较

目的 比较激光打印金属基底冠与铸造钴铬合金基底冠边缘适合性及金瓷结合力的差异。方法 分别采用激光打印制作钴铬合金基底冠（A组）和传统铸造法制作钴铬合金基底冠（B组）各10个,均以下颌第一磨牙全冠牙体为金属代型,将制作好的基底冠放置于标准代型。体式显微镜下观察基底冠边缘与代型肩台间间隙,以评估边缘适合性;利用万能测试机对基底冠进行加载实验,以评估金瓷结合力。比较2种方法制作的基底冠边缘适合性和金瓷结合力的差异,采用SPSS 25.0软件包对数据进行统计学分析。结果 A组金属基底冠与代型肩台间隙为（48.52±5.26）μm,显著小于B组的（76.25±8.37）μm（P<0.05）;A组金属基底冠金瓷结合强度为（11.35±3.29）N,显著高于B组的（7.24±2.07）N（P<0.05）。电镜下观察,A组金属层与瓷层结合更为紧密。结论 激光打印和传统铸造法制作的金属基底冠边缘适合性和金瓷结合力均在可接受范围,而激光打印的金属基底冠边缘适合性更好、金瓷结合力更强,是理想的金属基底冠制作技术。     

Effect of finish line design on stress distribution in bilayer and monolithic zirconia crowns: a three‐dimensional finite element analysis study

This study evaluated the influence of different finish line designs and abutment materials on the stress distribution of bilayer and monolithic zirconia crowns using three‐dimensional finite element analysis (FEA). Three‐dimensional models of two types of zirconia premolars – a yttria‐stabilized zirconia framework with veneering ceramic and a monolithic zirconia ceramic – were used in the analysis. Cylindrical models with the finish line design of the crown abutments were prepared with three types of margin curvature radius (CR): CR = 0 (CR0; shoulder margin), CR = 0.5 (CR0.5; rounded shoulder margin), and CR = 1.0 (CR1.0; deep chamfer margin). Two abutment materials (dentin and brass) were analyzed. In the FEA model, 1 N was loaded perpendicular to the occlusal surface at the center of the crown, and linear static analysis was performed. For all crowns, stress was localized to the occlusal loading area as well as to the axial walls of the proximal region. The lowest maximum principal stress values were observed when the dentin abutment with CR0.5 was used under a monolithic zirconia crown. These results suggest that the rounded shoulder margin and deep chamfer margin, in combination with a monolithic zirconia crown, potentially have optimal geometry to minimize occlusal stress.     

Functional,compositional, and regulatory analyses of imported and non-imported single dental crowns

The aims of the study were to investigate functional and esthetic properties, the composition of the alloy, and the content of hazardous elements of single dental crowns with metal skeleton and fired porcelain. Epoxy models made from full mouth impressions taken of a patient with a crown preparation of the right maxillary first permanent molar were used for production of identical polyether impressions, which were distributed to dentists in Norway. The dentists sent the impressions to their regular dental laboratories. All 55 crowns collected were anonymized and examined. Of the crowns received, 35 were made in Norway, 12 were imported, and 8 were of unknown origin. The evaluation of functional properties revealed that 50% of the Norwegian, 42% of the imported, and 25% of the unknown-origin crowns were considered unacceptable. The composition of the alloy was not in accordance with that stated by the manufacturer for 17%, 13% and 20% of the crowns, where this information was provided. The lead content of the alloy exceeded the limit set by the ISO 22674: 2016 for 18% of the crowns in total. The statement that shall follow the work according to EU-regulations was not complete for approximately 75% of the works received.     

Investigation of Failure Mechanisms in Ceramic Composites as Potential Railway Brake Disc Materials

Ceramic composite materials have been efficiently used for high-temperature structural applications with improved toughness by complementing the shortcomings of monolithic ceramics. In this study, the fracture characteristics and fracture mechanisms of ceramic composite materials were studied. The ceramic composite material used in this study is Nicalon ceramic fiber reinforced ceramic matrix composites. The tensile failure behavior of two types of ceramic composites with different microstructures, namely, plain-weave and cross-ply composites, was studied. Tensile tests were performed on two types of ceramic composite material specimens. Microstructure analysis using SEM was performed to find out the relationship between tensile fracture characteristics and microstructure. It was found that there was a difference in the fracture mechanism according to the characteristics of each microstructure. In this study, the results of tensile tests, failure modes, failure characteristics, and failure mechanisms were analyzed in detail for two fabric structures, namely, plain-weave and cross-ply structures, which are representative of ceramic matrix composites. In order to help understanding of the fracture process and mechanism, the fracture initiation, crack propagation, and fracture mechanism of each composite material are schematically expressed in a two-dimensional figure. Through these results, it is intended to provide useful information for the design of ceramic composite materials based on the mechanistic understanding of the fracture process of ceramic composite materials.     

Effects of ceramic shade and thickness on the micro-mechanical properties of a light-cured resin cement in different shades

Abstract

Objective. The aim of this study was to evaluate the micro-mechanical properties of a light-cured resin cement in four different shades when polymerized through a leucite-reinforced glass-ceramic in different shades and thicknesses. Materials and methods. A light-cured resin cement in four different shades (HV+1, HV+3, LV-1 and LV-3) was selected for this study. The specimens were cured by using a LED-unit (Bluephase®, IvoclarVivadent) for 20 s under a leucite-reinforced glass-ceramic (IPS Empress® CAD, IvoclarVivadent) in two different shades (A1 and A3) of different thicknesses (1 and 2 mm). Specimens cured directly, without an intermediate ceramic, served as control. The specimens were stored after curing for 24 h at 37°C by maintaining moisture conditions with distilled water. Micro-mechanical properties (indentation modulus, E; Hardness, HV; creep, Cr) of the resin cements were measured with an automatic microhardness indenter (Fisherscope H100C, Germany). Twenty groups were included (n = 3), while 10 measurements were performed on each specimen. Data were statistically analyzed by using one-way ANOVA and Tukey’s post-hoc test, as well as a multivariate analysis to test the influence of the study parameters. Results. Significant differences were observed between the micromechanical properties of the tested resin cements (p < 0.05). The resin cement shade showed the highest effect on the micromechanical properties (Partial-eta squared (η_P²)-E = 0.45, η_P²-HV = 0.59, η_P²-Cr = 0.29) of the resin cement, followed by ceramic thickness (η_P²-E = 0.38, η_P²-HV = 0.3, η_P²-Cr = 0.04) and ceramic shade (η_P²-E = 0.2, η_P²-HV = 0.26). Conclusions. Resin cement shade is an important factor influencing the mechanical properties of the material. Light shades of a resin cement express higher E and HV as well as lower Cr values compared with the darker ones.     

(iii) Bearing surfaces

Alternative bearings surfaces to polyethylene have reduced wear and have led to improved patient outcomes, allowing younger and more active patients to be considered for joint replacements. These bearing surfaces have been developed largely as a response to osteolysis and loosening associated with polyethylene particulate debris. This has led to the evolution of various forms of cross-linked polyethylene and to the greater use of hard-on-hard bearings. The use of metal-on-metal led to resurfacing hip replacements and to the use of large head metal-on-metal hip replacements. Although metal-on-metal bearings have a number of theoretical advantages, the release of metal debris and ions from some designs has been catastrophic. In the future new bearing surfaces must be more thoroughly tested pre-clinically and in well-designed clinical series.     

Forty years of ceramic-on-ceramic THR bearings

The evolution of ceramic bearings for Total Hip Joint Replacement (THR), which have now been in clinical use for over 40 years, is reviewed from a historical perspective with emphasis on the characteristics of the composite materials in clinical use today, their mechanical properties, and wear behavior. Evidence is provided about the advantage of today’s composite ceramics over those of previous generations in terms of increased reliability and minimum wear, especially in the case of bearings operating under abnormal conditions (edge loading and microseparation).     

Preclinical evaluation of injectable bone substitute materials

Injectable bone substitutes (IBSs) represent an attractive class of ready‐to‐use biomaterials, both ceramic‐ and polymer‐based, as they offer the potential benefit of minimally invasive surgery and optimal defect filling. Although in vitro assessments are the first step in the process of development, the safety and efficacy of an IBS strongly depend on validated preclinical research prior to clinical trials. However, the selection of a suitable preclinical model for performance evaluation of an IBS remains a challenge, as no gold standard exists to define the best animal model. In order to succeed in this attempt, we identified three stages of development, including (a) proof‐of‐principle, (b) predictive validity and (c) general scientific legitimacy, and the respective criteria that should be applied for such selection. The second part of this review provides an overview of commonly used animals for IBSs. Specifically, scientific papers published between January 1996 and March 2012 were retrieved that report the use of preclinical models for the evaluation of IBSs in situations requiring bone healing and bone augmentation. This review is meant not only to describe the currently available preclinical models for IBS application, but also to address critical considerations of such multi‐factorial evaluation models (including animal species, strain, age, anatomical site, defect size and type of bone), which can be indicative but in most cases edge away from the human reality. Consequently, the ultimate goal is to guide researchers toward a more careful and meaningful interpretation of the results of experiments using animal models and their clinical applications. Copyright © 2012 John Wiley & Sons, Ltd.     

Development of Scheelite Tailings-Based Ceramic Formulations with the Potential to Manufacture Porcelain Tiles,Semi-Stoneware and Stoneware

New ceramic formulations based on scheelite tailing were developed, and their potential in the ceramic industry was evaluated. Green bodies with different contents of scheelite tailing (0–8 wt%) were sintered (1150 °C, 1200 °C, and 1250 °C) and characterized in terms of the main mineralogical phases, microstructure, and physico-mechanical properties. The mullite was the main phase identified in all sintered temperatures. This result was also ratified with the aid of scanning electron microscope (SEM) images, in which small needles of the mullite were detected. The presence of mullite is required because it contributes to increasing the mechanical resistance of the material. The physico-mechanical properties measured (water absorption, linear shrinkage, apparent porosity, and flexural strength) were compared to the ISO 13006, and the samples sintered at 1150 °C presented potential to be used as semi-stoneware, while those sintered at 1200 °C and 1250 °C can be employed stoneware and porcelain tiles, respectively.     

Structural Ceramics Modified by Water Treatment Plant Sludge

Water treatment plant (WTP) sludge is actively used in building materials production. The object of this research was modifying additives for ceramic bricks from WTP aluminium-containing sludge. The research aim of this study was to determine the suitability of a million-plus population city’s WTP sludge as a burning-out additive in the production of structural ceramics and to establish the optimal conditions for obtaining products with the best characteristics. The raw water belongs to water belongs to the hydrocarbonate class, the calcium group, and it is of low turbidity (1.5–40 mg/L kaolin). Sludge, sourced from WTP sedimentation tanks, was dewatered by adding lime or by using the freezing-thawing method. The spray-dried WTP sludge is introduced into the clay in amounts of 5% to 20% by weight. The addition of 20% reduces the sensitivity of the clay to drying, reduces the density of ceramic by 20% and simultaneously increases its compressive strength from 7.0 to 10.2 MPa. The use of WTP sludge as a modifying additive, pretreated by the freezing-thawing method, makes it possible to obtain ceramic bricks with improved properties. The results can be used for WTP sludge containing aluminium obtained by treating water of medium turbidity and medium colour.