Selective Laser Melting of Al-Based Matrix Composites with Al2O3 Reinforcement: Features and Advantages

Aluminum matrix composites (AMC) are of great interest and importance as high-performance materials with enhanced mechanical properties. Al₂O₃ is a commonly used reinforcement in AMCs fabricated by means of various technological methods, including casting and sintering. Selective laser melting (SLM) is a suitable modern method of the fabrication of net-shape fully dense parts from AMC with alumina. The main results, achievements, and difficulties of SLM applied to AMCs with alumina are discussed in this review and compared with conventional methods. It was shown that the initial powder preparation, namely the particle size distribution, sphericity, and thorough mixing, affected the final microstructure and properties of SLMed materials drastically. The distribution of reinforcing particles tends to consolidate the near-melting pool-edges process because of pushing by the liquid–solid interface during the solidification process that is a common problem of various fabrication methods. The achievement of an homogeneous distribution was shown to be possible through both the thorough mixing of the initial powders and the precise optimization of SLM parameters. The strength of the AMCs fabricated by the SLM method was relatively low compared with materials produced by conventional methods, while for superior relative densities of more than 99%, hardness and tribological properties were obtained, making SLM a promising method for the Al-based matrix composites with Al₂O₃.     

糖尿病前期中医证型及证素特点分析＊

目的 探讨糖尿病前期的中医证型及证素分布特点。方法 检索中国知网、万方及维普三大数据库中收录的自建库以来有关糖尿病前期证型的临床研究文献，对中医证型进行规范整理，建立数据库，提取证素，运用数据挖掘技术中的关联分析、聚类分析探究证素分布规律。结果 共纳入10篇文献，总有效病例1620例，证型经规范处理后整理为18个，主要证型为脾虚痰湿证。共提取证素13个，主要病位证素为脾，主要病性证素为气虚、湿和痰，关联分析显示脾—湿支持度和置信度最高，聚类分析结果可得到3个聚类组。结论 糖尿病前期病位在脾，气虚、脾、痰、湿是常见证素，临床诊治糖尿病前期应注重从脾论治，需辨证施治。     

Objective evaluation of abutment tooth preparation for preformed metal crowns for primary molars in Japanese preclinical training

Evaluation of abutment tooth shape for preformed metal crowns for primary teeth in preclinical training depends on the subjective opinion of the instructor providing the training. Thus, the student's grade will likely vary according to teacher grading. In this study, we explored the potential for objective evaluation by comparing evaluations performed by teaching personnel (teacher grading) of abutment teeth for preformed metal crowns for primary teeth prepared by students at a dental school with evaluation by a three-dimensional (3D) laser morphometric system (system grading). The subjects of the evaluations were 139 abutment teeth for preformed metal crowns for primary teeth that had been prepared by fourth-year students at Asahi University School of Dentistry during preclinical pediatric dentistry training. A tooth prepared by a teacher following instruction criteria was used as the reference tooth, and system grade points were calculated from deductions made for insufficient and excessive cutting. Teacher grade points varied among teachers. We found that teachers prioritized contours of the margin, buccal and lingual sides, and adjacent surfaces in their evaluations. System grading showed that most students carried out insufficient cutting. The mean (SD) teacher and system grade points were 57.7 (9.7) and 75.7 (4.7), respectively, and these grade points were positively correlated (r = 0.500). System grading provides a simple 3D visual assessment of insufficient and excessive cutting that can be used for instructing students.     

All-ceramic restorations: A review of the literature

ObjectivesCeramics can simulate the visual character of the tooth substance successfully and are biocompatible materials. However, a wide range of ceramic materials and systems on the market are available for use in dentistry. Therefore, it is the aim of this article to provide an overview of dental ceramics, their classifications, methods of construction, and clinically relevant aspects that enable the reader to select the most appropriate ceramic for a particular clinical situation.Material and methodsThe PubMed (MEDLINE) search engine was used to gather the most recent information on dental ceramics. The search was restricted to a ten-year period (January 1, 2010–December 31, 2019) and only English-language studies. A Boolean search of the PubMed data set was implemented to combine a range of keywords: (ceramics OR all-ceramics OR dental porcelain OR polycrystalline OR porcelain fused to metal OR ceramometal OR procera OR e max OR zirconia OR In-ceram OR Inlays OR Onlays OR Overlays OR Endocrown) AND (survival rate OR success rate OR clinical outcomes OR classification) AND (humans). Studies were also obtained by manual searches and from Google Scholar.ResultsBy using this process, 2173 articles and studies were obtained. More studies were also obtained by manual searches and from Google Scholar. The most relevant published studies were chosen and used in the current review.ConclusionAll-ceramic restoration use has increased in recent years. This increase has been attributed to patients’ demand for good aesthetics and an improvement in the materials’ mechanical and aesthetic properties as well as to required minimally invasive tooth preparation and the methods of fabrication. The success of ceramic restorations depends on several factors, such as selection of material, restoration design, occlusion, and cementation media.     

女童特发性中枢性性早熟中医证素特点研究

目的探讨女童特发性中枢性性早熟(ICPP)的中医证素特征。方法对确诊的61例女童特发性中枢性性早熟患儿,采用证素辨证和积分方法,提取病位、病性证素,对其进行统计分析。结果ICPP的病位证素为肾、肝,与脾、心、肺的差异有统计学意义(P<0.05)。病性证素为阴虚、热、湿、痰,阴虚、热积分高于湿、痰(P<0.05)。促性腺激素释放激素(GnRH)激发试验后LH峰值/FSH峰值与肾证素积分呈正相关(OR=7.922,P<0.05)。结论女童ICPP阴虚火旺最多见,可兼夹痰湿,病位主要在肝肾。     

金属螺钉与聚氨酯橡胶慢性脊髓损伤大鼠模型的分析比较

目的:比较金属螺钉与聚氨酯橡胶压迫的慢性脊髓损伤（CSCI）大鼠模型的优劣，探索适合CSCI研究的大鼠模型。方法: 108只雄性Sprague-Dawley大鼠完全随机分组为假手术组（n=36）、金 属螺钉组（n=36）和聚氨酯橡胶组（n=36），记录造模术前及术后2.5 h、7 d、14 d、21 d、28 d各组下肢行为学运动功能评分（BBB评分）和体感诱发电位（SEP），取C5段脊髓组织行苏木精-伊红染色 法（HE）和原位末端标记法（TUNEL）染色。结果:BBB评分:金属螺钉组与聚氨酯橡胶组较假手术组均明显降低（金属螺钉组比假手术组，t=9.671，P<0.000 1；聚氨酯橡胶组比假手术组，t=4.997， P=0.002 5），且金属螺钉组评分低于聚氨酯橡胶组（t=2.705，P=0.035 3），金属螺钉组持续下降，聚氨酯橡胶组则于术后21 d降至最低后开始上升。SEP:金属螺钉组与聚氨酯橡胶组较假手术组均出 现潜伏期延长（金属螺钉组比假手术组，t=18.02，P<0.000 1；聚氨酯橡胶组比假手术组，t=10.82，P<0.000 1）和波幅下降（金属螺钉组比假手术组，t=145.5，P<0.0001；聚氨酯橡胶组比假手术组， t=3.97，P= 0.007 4），且金属螺钉组潜伏期延长时间长于聚氨酯橡胶组，金属螺钉组波幅降低幅度先大于聚氨酯橡胶组，后较之略低。HE染色:金属螺钉组与聚氨酯橡胶组均出现脊髓损伤的病理表现 ，且金属螺钉组从腹侧到背侧渐进性加重，聚氨酯橡胶组则表现为一致性。TUNEL染色:金属螺钉组与聚氨酯橡胶组较假手术组TUNEL阳性细胞数明显增多（金属螺钉组比假手术组，t=4.722，P=0.003 2 ；聚氨酯橡胶组比假手术组，t=8.263，P=0.000 2），且主要集中于脊髓灰质前角。金属螺钉组在术后第7天阳性细胞数达到最高，之后明显减少，聚氨酯橡胶组在术后逐渐增加至术后21 d达到最高。结 论:两种模型均有效地模拟了CSCI，金属螺钉CSCI模型适合损伤程度逐渐加重的CSCI研究，聚氨酯橡胶CSCI模型则适合压迫程度稳定的CSCI研究。