The Effect of Alumina Content on Fracture Property of All-ceramics Zirconia

The purpose of the present study was to evaluate the effect ofA1203 content on the fracture property of all-ceramics ZrO2. To improve the all-ceramics ZrO2 restoration mechanics properity ,96 samples containing 0,5,10 and 15 wt% of A1203 particles were prepared by cold isostatic pressing （200 MPa） and 1 550 ℃ sintered .The phase was analyzed by X-ray diffraction analysis and the bulk densities of the samples were made using Archimedes principle. Samples were randomly divided into four groups. In each group, 24 specimens were prepared so that the angle between notch and specimen＇s long axis is 90° and 60°. Notch depths were 1 mm for all samples. Samples were loaded with three-point bending method. 90° cut samples were used to measure fracture toughness while 60°cut samples were used to observe fracture curve by taking points on the fracture extension path under microscope, plotting points on coordinates, generating fitting curve by software ＂Origin＂, and analyzing the microstructure of the specimen fracture surfaces by scanning electron microscopy （SEM）.The results show that the increment ofA1203 has insignificant effect on the densification of all-ceramic ZrO2.XRD analysis shows that the specimen is comprised of t-ZrO2 and a- A1203 before fracture while fracture surface is m-ZrO2, t-ZrO2 and a-A1203. ZrO2 containing 10% A1203 has the optimum mechanical properties and unconspicuous crack propagation and distribution. The observations may provide a reference for the materials selection, shaoe design, and production orocess of all-ceramic crown and bridge.

Mechanical Properties of a new Dental all-ceramic Material-zirconia Toughened Nanometer-ceramic Composite

目的 :口腔全瓷修复体以其独特优越性受到医患青睐 ,但脆性问题一直限制其应用范围及使用可靠性。本研究旨在研制用于玻璃渗透全瓷修复的纳米氧化锆增韧陶瓷并全面检测评价其力学性能。方法 :采用化学共沉淀与球磨相结合的方法合成纳米氧化锆增韧陶瓷 (α -Al2 O3 /nZrO2 ceramicspowder ,W) ,扫描电镜评价陶瓷材料的粉体形态特征及粒度分布。预制氧化锆含量不同的陶瓷粉体 (5wt% ,10wt% ,15wt%and 2 0wt% ) ,采用粉浆涂塑技术将材料制成标准试件 ,并在不同温度下 (12 0 0～ 16 0 0℃ )烧结成型 ,用三点弯曲法及单边刀口梁法检测材料试件的抗弯强度和断裂韧性。结果 :1)α -Al2 O3 /nZrO2 材料粉体粒度分布范围大致为 0 .0 2～ 3.0 μm ,其中超细粉体 (低于 0 .1μm)占 2 0 % ;2 )不同烧结温度组试件的力学强度有显著差异 (P <0 .0 5 ) ,14 5 0℃和 16 0 0℃组高于12 0 0℃组 ;3)相同烧结温度下不同氧化锆含量组材料强度有显著差异 ,一定范围内氧化锆含量增高有助于材料的增韧增强。结论 :本研究所研制的纳米氧化锆增韧陶瓷材料组分配比及微观特征能增韧增强材料 。

Study on Acoustic Emission Characteristics of Deformation Damage Process of Zirconia Ceramics

Zirconia ceramics have become increasingly widely used in recent years and are favored by relevant enterprises. From the traditional dental field to aerospace, parts manufacturing has been used, but there is limited research on the deformation and damage process of zirconia ceramics. This article analyzes the acoustic emission characteristics of each stage of ceramic damage from the perspective of acoustic emission, and explores its deformation process characteristics from multiple perspectives such as time domain, frequency, and EWT modal analysis. It is concluded that zirconia ceramics exhibit higher brittleness and acoustic emission strength than alumina ceramics, and when approaching the fracture, it tends to generate lower frequency acoustic emission signals.

Influence of Abutment Material on the Stress of Implant-supported All-ceramic Single Crown

In order to investigate the influence of abutment material on the stress of implant-supported all-ceramic single crown, a 3D finite element model of implant-supported mandibular first premolar was computed by COSMOS/M 2.85 software. Alumina, zirconia, and titanium were used as abutment materials respectively. Vertical 600 N and horizontal 225 N load was applied on the occlusal surface. The results show that the stress distribution of implant-supported single crown was similar for different abutment materials. Maximum stresses within the crown were higher when titanium abutment was used. Maximum stress of titanium abutment was lower than that of ceramic abutment. Within the screw and fixture, maximum stresses had no difference under vertical loading but higher as titanium abutment was used under horizontal loading. There was no difference of maximum stress within the bone when different abutment materials were used. The present findings indicate that the abutment material had no influence on the stress distribution of implant-supported all- ceramic single crown but maximum stress when the titanium abutment was lower than that of ceramic abutment.

Influence of Different Luting Agents on the Stress Distributions of Implant-supported All-ceramic Single Crown

The purpose of this study was to investigate the influence of different luting agents on the stress distribution within the crown, abutment and peri-implant bone of implant-supported all-ceramic single crown. A three-dimensional finite element model of an implant-supported single crown for the first premolar of mandible was created by COSMOS 2.85. Resin-modified glass ionomer and two different resin adhesives were used to cement the crown and abutment. Vertical 600 N and horizontal 225 N loads were applied to stimulate the condition of chewing. The stress distributions within the all-ceramic crown, abutment and peri-implant bone were analyzed. The experimental results show that the stress distributions of all-ceramic crown, abutment, implant and peri-implant bone were similar when different luting agents were used. The result of present study indicated that luting agents had no influence on the stress distributions of implant-supported all-ceramic single crown.

Insightful Understanding of the Role of the Mechanical Properties in Defining the Reliability of All-Ceramic Dental Restorations: A Review

Since the last two decades, restorative dentistry has been witnessing an increased acceptance of the use of the well-known all-ceramic materials for the fabrication of single dental restorations, such as inlays, onlays, crowns, anterior and posterior fixed partial dentures (PFPDs). These restorations certainly offer the potential for better biocompatibility coupled with superior aesthetic qualities, especially when compared with the conventional prostheses made from porcelain that is fused with metal ceramic restorations. However, brittleness and extreme sensitivity of all-ceramic materials to micro-like defects or cracks that are inherently present, or may grow, in their microstructure during different laboratory fabrication steps, during necessary clinical adjustments, or from post-placement chewing activity, remain major shortcomings of these dental restorations. In fact, many researchers are of the opinion that the improved mechanical properties can significantly improve the lifetime of all-ceramic restorations and result in enhanced reliability. Therefore, efforts of researchers, as well as manufacturers, have been directed towards the improvement of the mechanical properties in order to overcome such limitations. This article reviews the characterization of the most important mechanical properties that can delineate the behavior of all-ceramic dental materials upon loading. These include fracture mechanics, the brittle nature of ceramics, the relationship between microstructural features and fracture behavior, sources of cracks and flaws that may initiate a fracture and the effect of different fabrication procedures and/or clinical adjustments on the mechanical behavior of dental ceramics are also reviewed and discussed.

Nacre-inspired Zirconia/Carbon Nanocomposites with High Strength and Toughness

Inspired by structures of natural shells,zirconia-carbon nanocomposites were obtained by using natural chitin from shrimp shells as templates via the sol-gel route in this study.Chitin was dispersed in the water and chelated with the zirconia precursors by amidogen.After a heat treatment for carbonization,nacre-like structures of carbon-zirconia nanocomposites were successfully synthesized.Due to the toughening mechanism of tetragonal zirconia,the mechanical properties of carbon-zirconia composites are further improved.The as-received zirconia/carbon nanocomposite with best mechanical property has a hardness of 5.88GPa and an elastic modulus of 80.6 GPa,which is even stronger than natural shells.This work might facilitate a versatile platform for developing green nanocomposites with reasonably good mechanical properties.

Replacement of Unesthetic Posterior Metal Crowns with Monolithic Zirconia Crowns: A Case Report

Advances in metal-free materials and the popularization of Computer-Aided Design and Manufacturing (CAD/CAM) have led to the wide clinical use of all-ceramic crowns for esthetic restorations. A 72-year-old woman presented to our hospital with unesthetic restorations on the right upper and lower posterior teeth. Intraoral examination revealed poorly fitting metal crown margins. Defective prostheses were removed, and provisional restorations were provided to stabilize the mandibular position. Optical impressions and the maxillomandibular relationship were recorded using an intraoral scanner, and monolithic zirconia crowns were fabricated using CAD/CAM technology for complete veneer crown restorative treatment. Occlusal examination revealed an improvement in occlusal force distribution at initial examination (right side: 33.5%, left side: 66.5%) after placement of the zirconia crowns (right side: 54.9%, left side: 45.1%). Occlusal force and occlusal force distribution area also showed an increasing trend. The Oral Health Impact Profile short form (OHIP-14) score decreased from 7 points at initial examination to 0 points after prosthodontic treatment. Appropriate diagnosis and treatment planning contributed to the increased occlusal force and balanced occlusal force distribution. Therefore, the present case indicates the potential of monolithic zirconia crowns to achieve both esthetic and stable functional outcomes.

Machine learning potential for Ab Initio phase transitions of zirconia

Zirconia has been extensively used in aerospace,military,biomedical and industrial fields due to its unusual combination of high mechanical,electrical and thermal properties.However,the fundamental and critical phase transition process of zirconia has not been well studied because of its difficult first-order phase transition with formidable energy barrier.Here,we generated a machine learning interatomic potential with ab initio accuracy to discover the mechanism behind all kinds of phase transition of zirconia at ambient pressure.The machine learning potential precisely characterized atomic interactions among all zirconia allotropes and liquid zirconia in a wide temperature range.We realized the challenging reversible first-order monoclinic-tetragonal and cubicliquid phase transition processes with enhanced sampling techniques.From the thermodynamic information,we gave a better understanding of the thermal hysteresis phenomenon in martensitic monoclinic-tetragonal transition.The phase diagram of zirconia from our machine learning potential based molecular dynamics simulations corresponded well with experimental results.

Effect of Zirconia Corundum Addition on Properties of Chrome Corundum Castables

In order to investigate the effect of zirconia corundum on the preparation of chrome corundum castables,samples were prepared using tabular corundum,white fused corundum,active alumina micropowder,chromium oxide micropowder and fused ziconia corundum particles as the main raw materials,and pure calcium aluminate cement as the binder.The effects of the fused zirconia corundum particles addition(1-0.5 mm,0,4.5%,9%,and 18%,by mass)on the linear change rate,the apparent porosity,the cold modulus of rupture,and the thermal shock resistance of chrome corundum castables were studied,and the microstructure of the samples was analyzed.The results show that:(1)with the zirconia corundum addition increasing,the permanent linear change on heating of the samples gradually increases,the apparent porosity gradually increases,the cold modulus of rupture gradually decreases,and the thermal shock resistance gradually increases;(2)according to SEM,it can be found that the phase transformation of ZrO2 after heat treatment leads to a large number of microcracks in the material.On one hand,the cold modulus of rupture of the material is reduced;on the other hand,the thermal shock resistance of the material is improved.

Preparation and Mechanical Properties of Zirconia Ceramics Doped with Different Y_(2)O_(3)Contents

The sintering behavior and mechanical properties of zirconia doped with 2.0mol%-3.0mol%Y_(2)O_(3)were studied by pressure-less sintering.The experimental results show that the densification temperature of zirconia ceramics increases gradually with the decrease of Y_(2)O_(3)doping content by which decreases the sintering driving force due to the lower oxygen vacancy concentration of the systems.Furthermore,the bending strength and fracture toughness of the prepared zirconia ceramics increase with the decrease of Y_(2)O_(3)doping content.It can be attributed to the fact that the phase stability of tetragonal zirconia decreases with the decrease of Y_(2)O_(3)doping content,which is easier to induce"phase transformation toughening"and dissipate impact energy.The relative density,bending strength and fracture toughness of 2.0 mol%Y_(2)O_(3)doped zirconia ceramics(2.0Y-ZrO_(2))sintered at 1525℃are 99.00%,1256.65±20.82 MPa and 9.85±0.13 MPa·m^(1/2),respectively.

极薄氧化锆贴面的研究进展

全瓷贴面修复是改善牙齿形态、色泽和排列的常用方法。随着口腔陶瓷材料和修复体加工方式的不断发展,微创/无创贴面修复是医生和患者对牙齿修复提出的共同要求。本文回顾了全瓷贴面的发展历程和应用现状,对极薄氧化锆贴面相关的新材料、新工艺做一介绍,并对其技术前景和临床效果进行展望。

氧化锆和氧化镧共掺杂对堇青石多孔陶瓷性能的影响

为实现堇青石相的低温合成,采用粒度为≤0.044 mm的煅烧高岭土、粒度为≤0.074 mm的烧结镁砂和d_(50)=2.6μm的二氧化硅微粉为主要原料,以分析纯的氧化锆和氧化镧为烧结助剂,以聚乙烯醇PVA溶液为结合剂,按照堇青石理论配比,在60 MPa压力下成型为φ30 mm×30 mm的试样,干燥、煅烧后制备了堇青石多孔陶瓷。研究了烧结助剂氧化锆添加量(外加质量分数为0、8%)、氧化镧添加量(外加质量分数分别为0、0.2%、0.4%、0.6%、0.8%)和煅烧温度(分别为1200、1250及1300℃)对堇青石多孔陶瓷常温物理性能、物相组成和显微结构的影响。结果表明:1)在1300℃下,当试样中引入8%(w)氧化锆和0.6%(w)氧化镧时,试样的物理性能较优;2)氧化锆和氧化镧共掺杂可在显气孔率变化较小的情况下,提高试样的力学性能,且促进堇青石相的生成;3)氧化锆和氧化镧共掺杂可一定程度上降低堇青石相的合成温度,提高试样的综合性能。

皮秒激光不同图案化处理氧化锆陶瓷对其粘接性能的影响

目的:研究皮秒激光在牙科氧化锆表面不同图案化扫描处理的结果,以及对氧化锆表面粘接性能的影响。方法:选取160例烧结氧化锆陶瓷试件,随机分为8个研究组,分别为空白对照组(A组)、喷砂对照组(B组)、皮秒激光处理组(C-H组,分别为:皮秒激光蜂窝状扫描、喷砂后皮秒激光蜂窝状扫描、皮秒激光横线状扫描、喷砂后皮秒激光横线状扫描、皮秒激光井字格状扫描、喷砂后皮秒激光井字格状扫描)。扫描电镜观察表面微观组织形貌;激光共聚焦显微镜观察3D形貌,原子力显微镜测量表面粗糙度Ra;X射线衍射仪观测表面晶相组成的转变;电子万能试验机测量抗弯强度,测定氧化锆陶瓷与自粘型树脂水门汀的剪切强度;光学体式显微镜下观察断裂模式;采用SPSS26.0对所得结果进行单因素方差分析及多重检验。结果:皮秒激光在氧化锆表面扫描后,可分别得到蜂窝状、平行的等间距横线状及等间距井字格状图案;不同图案化处理后氧化锆表面粗糙度不同,横线状B组最大,为14.92μm;激光表面处理不会导致表面晶相转变;经过皮秒激光处理后,剪切粘接强度明显增加(P<0.05),C组的粘接强度最大,为(26.86±1.53)MPa,约为A组的7.4倍;断裂模式由A组与B组的完全粘结破坏转变为内聚破坏和混合破坏;激光处理后的氧化锆陶瓷抗弯强度满足临床应用要求。结论:皮秒激光对氧化锆表面进行图案化处理能够提高氧化锆与树脂水门汀的粘接强度,是一种有前景的氧化锆表面改性方法。

不同清洁方法对高透氧化锆粘接强度和表面润湿性的影响

目的:研究不同清洁方法对唾液污染的高透氧化锆与自粘接树脂水门汀间剪切粘接强度和表面润湿性的影响。方法:制备80个高透氧化锆试件,随机分为5组(n=16),即对照组(无污染处理)、75%乙醇组、喷砂组、清洁剂组和大气压冷等离子体处理组等。测量表面接触角,测试剪切粘接强度,观察断裂模式。采用SPSS 26.0软件包对数据进行统计学分析。结果:大气压冷等离子体组的接触角最小(P<0.05);喷砂组、清洁剂组及大气压冷等离子体组的剪切粘接强度与对照组相比,无统计学差异(P>0.05),但均显著大于75%乙醇组(P<0.05);大气压冷等离子体组混合断裂模式增多。结论:喷砂、清洁剂及大气压冷等离子体清洁唾液污染的高透氧化锆,可获得与未被唾液污染前相当的粘接强度;大气压冷等离子体可显著提高高透氧化锆的表面润湿性。

二氧化锆全瓷冠修复前牙的效果及对局部炎症状态的影响

目的:探究及观察二氧化锆全瓷冠修复前牙的效果及对局部炎症状态的影响。方法:选取2019年1月—2021年1月深圳市龙岗区妇幼保健院口腔科的100例需进行前牙冠修复的患者为研究对象,根据随机数字表法分为对照组(镍铬合金烤瓷冠组)和观察组(二氧化锆全瓷冠组),每组50例。比较两组的修复效果(颜色匹配度、完整度及边缘密合度)、不良情况发生率、局部炎症状态指标[龈沟液炎症因子白介素-1β(IL-1β)及白介素-6(IL-6)、炎症介质前列腺素E2(PGE2)]、炎症趋化因子[调节活化正常T细胞表达和分泌因子(RANTES)]、患者满意度。结果:观察组的颜色匹配度、完整度及边缘密合度均显著优于对照组,不良情况发生率显著低于对照组,差异均有统计学意义(P<0.05)。治疗前,两组的局部炎症状态指标比较,差异均无统计学意义(P>0.05);治疗后3、6个月,观察组的局部炎症状态指标均显著优于对照组,患者满意度显著高于对照组,差异均有统计学意义(P<0.05)。结论:二氧化锆全瓷冠修复前牙的效果较好,且可有效控制患者的局部炎症状态,更受患者认可。

钨钼烧结炉用氧化锆质顶盖结构的优化研究

结合当前钨钼烧结炉用氧化锆顶盖砖的使用情况,利用ANSYS软件,模拟分析了氧化锆顶盖砖异常损坏的原因,并通过对不同厚度、不同体积密度顶盖砖使用过程中应力场的模拟研究,对顶盖砖结构优化进行了探索。结果表明:顶盖砖在使用过程中的最大拉应力为27MPa,远远超过了材料的结合强度,从而造成“断裂”和“龟裂”,导致寿命降低;顶盖砖的体积密度和厚度对其使用过程中的热应力有着显著的影响,当氧化锆顶盖砖的体积密度在3.0~4.6g/cm^(3)时,降低体积密度可以减小顶盖砖使用过程中的热应力,综合体积密度对氧化锆空心球砖其他性能的影响,将当前用顶盖砖的体积密度提高至3.3g/cm^(3),厚度减薄至50mm时,顶盖砖使用过程中的最大热应力只有10.27MPa,而顶盖砖的抗折强度达到13.6MPa,从而有效改善其使用寿命。

氧化锆增强铝基复合材料的制备及性能研究

铝合金由于其强度高、质量轻、价格低等多重优势,在汽车制造、航空航天、水下装备等各个领域都极具应用前景。利用机械搅拌铸造方法制备了不同质量分数纳米氧化钇稳定氧化锆(yttrium oxide stabilized zirconia,YSZ)的Al-YSZ复合材料,研究纳米YSZ质量分数对铝基复合材料组织和性能的影响。研究结果表明,添加的纳米YSZ均匀分布在Al基体中,不与Al基体发生反应。同时能够作为异质形核剂细化晶粒,并通过Orowan强化机制提升复合材料的力学性能。添加质量分数为8%的纳米YSZ的复合材料具有较好的强度和塑性。同时,在受到外力作用时,纳米YSZ会发生从四方到单斜的相变,并产生一定的体积膨胀,在吸收能量的同时改善了复合材料内部的晶格畸变,从而提高了铸态复合材料的塑性。

氧化锆全冠的临床应用原则及新进展

氧化锆全冠在口腔修复领域得到了广泛的应用。传统氧化锆机械性能佳,但半透性较差,透明氧化锆的出现大大提高了氧化锆的美学性能。但在临床中,应对影响全锆冠美学修复效果的因素进行综合考量,选择最合适的全锆冠修复体,同时临床医师需要根据患者实际情况合理设计牙体预备量以及预备方式。在氧化锆的临床粘接过程中,要对基牙和修复体做好表面处理,选择合适的粘接剂以获得良好的粘接强度和美观性。

医用氧化锆陶瓷磨削表面粗糙度的声发射智能预测

医用氧化锆陶瓷(Y-TZP)是较好的齿科修复体材料,为了得到较好的齿科修复体性能对于其制造精度特别是表面粗糙度的要求比较高,但其是硬脆难加工材料,为了提高医用氧化锆陶瓷磨削加工表面质量和加工效率,在对医用氧化锆陶瓷磨削过程中的声发射信号分频段进行相关性分析的基础上,提取磨削声发射840~850kHz敏感频段信号中与磨削表面粗糙度强相关的12组特征值,构建了具有较高预测精度的随机森林神经网络,最终医用氧化锆陶瓷磨削表面粗糙度声发射预测最大相对误差低于8.37%,研究结果对医用氧化锆陶瓷磨削表面粗糙度在线智能监测有较大的参考价值。