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.

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.

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.

Rely X^(TM) Veneer试色糊剂遮色性的临床评价

目的:观察Rely XTM Veneer试色糊剂的遮色性。方法:100颗变色的上前牙,其中50颗全瓷冠修复、50颗全瓷贴面修复(均为Ips-empressⅡ系统制作)。粘接前用试色糊剂[A1、A3、Transluent(Trt)、White opaque(WOT)和B0.5 opaque(B0.5)]代替粘接剂对基牙进行遮色,遮色后用ShadeEye-NCC电脑比色仪测定修复体的L*、a*、b*值,并记录测点的瓷层厚度。数据采用SAS6.12软件处理,根据公式色ΔE=[(ΔL*)2+(Δa*)2+(Δb*)2]1/2、L=L*、C=[(a*)2+(b*)2]1/2、H=arctan(b*/a*)计算并分析每种糊剂试色后的ΔE、L、C和H。,单因素方差分析全冠和贴面组的ΔE、L、C和H。结果:全瓷冠采用5种试色糊剂遮色后,WOT组的色差最大,与A1、A3、Trt、B0.5组之间有统计学差异(P<0.05);全瓷贴面采用5种试色糊剂遮色后,WOT组的色差最大,B0.5组次之,WOT组和与A1、A3、Trt组之间有统计学差异(P<0.05);贴面组与全冠组的色差间有统计学差异(P<0.05)。结论:WOT糊剂的遮色性最强,B0.5糊剂次之,其余3种糊剂的遮色性较为接近;瓷层厚度影响粘接剂的遮色效果。

阻燃联合染色改性杨木单板工艺

以酸性大红3R为染料、磷酸二氢铵为阻燃剂对杨木单板进行联合处理,探究阻燃染色同步处理单板的可行性,选择阻燃剂质量分数、染料质量分数、温度和时间为考察因素,以上染率、色差和氧指数为性能评价指标,通过直观和方差分析得出了影响单板上染率、色差及氧指数的显著因素及最佳工艺方案。此外,利用扫描电镜⁃能谱仪(SEM⁃EDS)对阻燃剂及染料分子在单板内部的分布状态进行了观察,并对它们的特征元素质量分数进行测定。在此基础上,采用模糊数学综合评判法对这3个评价指标进行了综合评判。结果表明:单板进行阻燃染色同步处理具有一定的可行性,提升了木材的染色效果,单板表面颜色偏暗偏黄,在实际生产过程中可以对染色配方进行调整以达到目标染色效果。上染率最佳工艺方案为:阻燃剂质量分数15%,染料质量分数1.5%,温度80℃,时间3 h。色差最佳工艺方案为:阻燃剂质量分数20%,染料质量分数2.0%,温度80℃,时间3 h。氧指数最佳工艺方案为:阻燃剂质量分数30%,染料质量分数0.5%,温度80℃,时间4 h。SEM⁃EDS分析表明,阻燃剂质量分数太高(30%)容易使分子间发生团聚,导致导管孔隙发生堵塞,P、S特征元素的增加表明阻燃剂与染料分子成功进入单板内部。通过模糊数学综合评判法得出阻燃染色单板综合性能的最佳工艺参数为:阻燃剂质量分数30%,染料质量分数0.5%,温度80℃,时间3 h。

Er:YAG激光对瓷贴面粘接性能影响的研究进展

瓷贴面因其美观微创等优点成为近年来牙齿美容修复的首要选择,深受广大医患的青睐。瓷贴面突出的美学性能与良好的粘接界面密不可分,粘接前贴面的表面处理成为影响粘接的重要因素。瓷贴面的常规处理方法包括氢氟酸酸蚀、喷砂、硅烷化及硅涂层处理等。然而随着以上常规处理方法的缺陷逐渐显现,激光逐渐走入国内外诸多学者的研究视线,其在瓷贴面粘接方面的有效作用已得到充分的研究与肯定。适宜能量参数的Er:YAG激光可在不破坏贴面表面微观结构的同时有效粗化瓷贴面粘接表面,更有利于与树脂水门汀之间形成良好的粘接界面。本文就瓷贴面的分类、常规处理方法、Er:YAG激光对瓷贴面粘接界面的影响及Er:YAG激光在粘接应用中的能量参数设置作一综述,并展望今后的发展前景。

循环温度与咬合力作用下下颌中切牙瓷贴面三维有限元应力分析

目的:旨在采用三维有限元法研究下颌中切牙瓷贴面在循环温度与咬合力作用下应力分布的规律。方法:采用CBCT扫描下颌中切牙,建立下颌中切牙瓷贴面三维有限元模型,分别在循环温度、循环咬合力及循环温度叠加循环咬合力作用下,应用有限元分析软件分析下颌中切牙瓷贴面Von Mises应力、最大主应力(正值为拉应力,负值为压应力)的分布情况。结果:瓷贴面在低温循环作用下Von Mises应力值均大于高温循环作用下。在低温循环下,瓷贴面抛光面中央为拉应力集中区,最大主应力峰值为29.33 MPa。在高温循环下,瓷贴面组织面中央大部分区域为拉应力集中区,最大主应力峰值为9.25 MPa。在循环咬合力作用下,斜向循环加载时Von Mises应力峰值为40.22 MPa,正向循环加载Von Mises应力峰值为27.29 MPa。斜向循环加载时,瓷贴面的颈缘为拉应力集中区,最大主应力峰值为28.70 MPa。正向循环加载时,瓷贴面的切端加载区周围为拉应力集中区,最大主应力较小。在循环温度叠加循环咬合力作用下,瓷贴面在两种载荷叠加作用下的应力值大于单独循环温度与单独咬合力作用下的应力值。结论:单独循环温度、循环咬合力对瓷贴面的安全性影响较小,循环温度与循环咬合力有一定的协同作用。

正畸直丝弓矫治技术联合烤瓷贴面治疗在前牙美学修复中的应用

目的:探讨正畸直丝弓矫治技术和烤瓷贴面两种方式联合治疗在前牙修复中的美学效果。方法:回顾性分析2019年1月-2022年1月笔者医院收治的76例前牙美学修复患者的临床资料,采用常规烤瓷冠修复的患者纳入对照组(n=36),正畸直丝弓矫治联合烤瓷贴面修复治疗的患者纳入联合组(n=40)。比较两组治疗后的临床疗效(整体牙齿功能、颜色满意度、边缘合适性、牙周健康状况、术后敏感),美学效果[红色美学指数(Pink esthetic score,PES)和白色美学指数(White esthetic score,WES)评分],以及治疗完成6个月内两组的并发症发生情况和满意度。结果:治疗后,联合组在整体牙齿功能、边缘合适性、牙周健康状况和术后敏感的临床表现上明显优于对照组(P<0.05),两组患者在颜色满意度上差异无统计学意义(P>0.05),联合组患者的PES评分、WES评分明显高于对照组(P<0.05);治疗完成6个月内,联合组患者并发症发生率明显低于对照组,其满意度评分明显高于对照组(均P<0.05)。结论:正畸直丝弓矫治技术和烤瓷贴面两种方式联合治疗应用于前牙修复中可取得良好临床疗效和美学效果,安全性较高且患者满意,值得临床推广应用。

Surface characteristics of electroless nickel plated electromagnetic shielding wood veneer

Wood is a kind of porous natural material with very poor electro-conductivity, and it has almost no function of electromagnetic shielding. The method of electroless nickel plating was used to produce wooden material with electrical and effective electromagnetic shielding properties. Ni-P alloy layer was obtained on wood surface. The surface feature of plated wood veneer was observed by SEM and the surface composition and microstructure of the layer under different conditions were investigated by EDS and XRD respectively. Meanwhile, the relevant surface resistivity and electromagnetic shielding effectiveness were measured. Correlations of the phosphorous content in the layer to the structure of Ni-P alloy, electro-conductivity and electromagnetic shielding of plated veneers were discussed. SEM photos showed that the surface of electroless nickel plated veneers were covered with Ni-P alloy layer entirely, which made wood veneers more like metal. At the same time, the results showed that with the decreasing of the phosphorous content in the layer, the microstructure of Ni-P alloy layer transformed to be microcrystalline and electro-conductivity and electromagnetic shielding effectiveness were improved. When the phosphorous content was less than 2.37wt pct in the layer, the microstructure of Ni-P alloy layer was microcrystalline structure and its sur- face resistivity and electromagnetic shielding effectiveness were nearly 0.5Ω/□ and 55-60dB respectively.

Yield and mechanical properties of veneer from Brachystegia nigerica

In an effort to find suitable wood from natural forest to meet the demand for veneer products, the yield and tensile strength of veneers produced from Brachystegia nigerica were investigated. Two trees of B. nigerica were separately selected from 10 different natural forest zones while two logs were obtained from each tree. The logs were debarked and steamed in a vat prior to rotary peeling and slicing for veneer production. The optimum steam temperature was determined by considering different temperatures： 50℃, 60℃, 70℃, 80℃ and 90℃ for 24 h. Thereafter, optimum steam time was determined at the optimum temperature by considering durations of 24, 48, 72 and 96 h. The average taper of 0.75 mm per 1.0 m length was recorded for B. nigerica, indicating that the logs were reasonably cylindrical; thereby its logs are good for the production of veneer. The yield ranged from 44% to 61% with an average of 52% of the log input. The tensile strength of the veneer was tested perpendicular to grain and both peeled and sliced veneers had the highest tensile strength between 70℃ and 90℃, suggesting that softening of wood polymers, especially lignin, is between 70℃ and 90℃. The optimum temperature and time for veneer production are 70℃ and 48 h, respectively. Commercial production of veneer from B. nigerica is feasible based on the yield and mechanical properties of the obtained veneer, thereby encouraging the expansion of the scope of its utilization.

Productive test of a newly drying technology of veneer： intermittent-contact drying of veneer with flexible screen belt

A newly drying technology, intermittent-contact drying of veneer with flexible screen belt (ICD-fbs), was invented and used in poplar veneer drying. Productive test was carried out for validating the practical use of this drying method. The test result shows that to dispose flexible screen belts on the two sides of hot board could help steam discharge remarkably. The veneer dried using ICD-fsb method had smooth and level surface, less deformation and warping, even moisture content, and high utilization rate. The time for opening hot board to discharge steam,which, early or late, is a key to obtain good drying result, was determined at the time when the core's temperature of veneer reaches 100℃ (vaporization). Using ICD-fsb method, the shrinking rates in tangent of veneer were from 1.90% to 2.26% for veneer of 0.4 mm in thickness,2.49% to 4.50% for veneer of 1 mm in thickness and 1.34% to 3.30% for veneer of 1.7 mm in thickness, which are much lower than the results obtained by other drying methods. The method of ICD-fsb offers a reliable technological guarantee for solving the deformation problem of veneer drying, especially the deformation of wood from quick-growing plantation.

Equilibrium thallium isotope fractionation and its constraint on Earth’s late veneer

Equilibrium isotope fractionation of thallium(Tl) includes the traditional mass-dependent isotope fractionation effect and the nuclear volume effect(NVE). The NVE dominates the overall isotope fractionation, especially at high temperatures. Heavy Tl isotopes tend to be enriched in oxidized Tl^3+-bearing species. Our NVE fractionation results of oxidizing Tl^+ to Tl^3+ can explain the positive enrichments observed in ferromanganese sediments. Experimental results indicate that there could be0.2–0.3 e-unit fractionation between sulfides and silicates at 1650 ℃. It is consistent with our calculation results,which are in the range of 0.17–0.38 e-unit. Importantly,Tl’s concentration in the bulk silicate Earth(BSE) can be used to constrain the amount of materials delivered to Earth during the late veneer accretion stage. Because the Tl concentration in BSE is very low and its Tl isotope composition is similar with that of chondrites, suggesting either no Tl isotope fractionation occurred during numerous evaporation events, or the Tl in current BSE was totally delivered by late veneer. If it is the latter, the Tl-contentbased estimation could challenge the magnitude of late veneer which had been constrained by the amount of highly siderophile elements in BSE. Our results show that the lateaccreted mass is at least five-times larger than the previously suggested magnitude, i.e., 0.5 wt% of current Earth’s mass. The slightly lighter 205 Tl composition of BSE relative to chondrites is probable a sign of occurrence of Tlbearing sulfides, which probably were removed from the mantle in the last accretion stage of the Earth.

Ceramic Laminate Veneers: Materials Advances and Selection

Porcelain laminate veneers have been a common treatment strategy in dental clinics. It is a conservative method for treatment of esthetic and functional problems in anterior region of oral cavity. Wide range of dental ceramics is now available on market for fabrication of laminate veneers. Clinician should have enough knowledge regarding the composition and properties of these materials in order to be able to choose the appropriate one according to clinical situations.

Late veneer and the origins of volatiles of Earth

Late veneer is an important paradigm in early Earth and planetary studies.It refers to the late addition of extraterrestrial materials to the Earth’s mantle after the core formation,which leads to the overabundances of highly siderophile elements in the primitive upper mantle.In this review,the origin,evolution,and expansion of the late veneer hypothesis are summarized,including some unresolved problems.I hope this review would be helpful for the new entrants to this field.

Effects of Hydrothermal Environment on the Deformation of the Thin Bamboo Bundle Veneer Laminated Composites

To overcome warping in thin bamboo bundle veneer laminated composites(TBLC),their hydrothermal deformation characteristics were systematically investigated in this study.It was found that TBLCs accelerated the release of internal stress in the thickness direction in a hydrothermal environment,which increased their warpage.TBLCs showed increased warpage in the width and diagonal directions upon increasing the temperature.The warpage of Type E increased by 155.88%and 66.67%in the width and diagonal directions,respectively,when the temperature increased from 25
C to 100
C.The symmetrical TBLC with cross-lay-up and odd layers displayed better hydrothermal stability.We revealed that the deformation of the TBLCs could be regulated under the synergistic effect of water and temperature.These results provide a scientific basis for improving the uniformity of bamboo bundle composite materials and for developing thin bamboo bundle fiber composite materials with designable structures and controllable performance.

Effect of the Thickess on Color of Porcelain Laminate Veneer

Objective : To evaluate the color change of the two-layer porcelain laminate veneer after adding veneering porcelain of different thickness to the 0. 2 mm thick aluminum oxide. Methods : Ten aluminum oxide disks were randomized into 2 groups. Each of five disks was veneered with Vita Lumin Shade 54 porcelain of thickness 0/0.4 mm and 0. 6 mm respectively. The L'a'b* color notations of the substrate covered with nan-veneered disks and 2 thickness porcelain veneered disks were measured separately and the color differences (AE) were calculated. Results ?Statistically significant differences in color coordinates of dark substrates were recorded after the substrate was covered by an aluminum oxide disk and also after the addition of veneering porcelain to the aluminum oxide disks in group 1 (P=0. 000 2) and group 2(P=0. 007 5) and between 2 groups (P=0. 000 1). Conclusion -The ability of masking underlying discoloration was increased and shifted to gray when the thickness of veneering porcelain increased.

Shear bond strengths between alumina-toughened zirconia cores and veneering ceramics and their susceptibility to aging

Objective:To evaluate the shear bond strength(SBS) between alumina-toughened zirconia (ATZ) cores and veneering ceramics,investigate the effect of aging in artificial saliva on SBS and compare it with that of yttria-stabilized tetragonal zirconia polycrystals(Y-TZP).Methods:Bars of ATZ and Y-TZP were layered with veneering ceramics in accordance to the recommendation of the manufacturer.Half of each group(n = 10) was aged at 134℃.(under 2 bar pressure) in an autoclave for 48 h.Subsequently,all specimens were subjected to shear force in a universal testing machine.The interface and fractured surface of the specimens were evaluated using scanning electron microscopy and X-ray energy dispersive spectroscopy.Results:The initial mean SBS values in MPa±SD were 28.9±8.0 for ATZ and 26.2±7.6 for Y-TZP.After aging,the mean SBS values for ATZ and Y-TZP were 22.9±4.9 MPa and 22.8±6.9 MPa,respectively.Neither the differences between the SBS values of the ATZ and Y-TZP groups nor the influence of aging on all groups were statistically significant.Conclusions:The SBS between the ATZ core and the veneering ceramics was not affected by aging.The SBS of ATZ to veneering ceramics was not significantly different compared with that of Y-TZP.

Detection of Veneer Moisture Content by Surface-circle-shaped Resistance

This paper, with veneer as a particularly detected target, deals with a new method for detecting veneer moisture content. Surface resistance is measured by the fixed pressure, circle-shaped point and surface-touched detector. With the help of the computer, the veneer moisture and its distribution will be detected in a faster way with no harm to the veneer surface.

Constitutive Equation of Laminated Veneer Lumber (LVL) at Large Deformation Condition

The stress-strain relation of laminated veneer lumber (LVL) was established by the method of regression, and its constitutive equation at large deformation and constant loading conditions was given to predict the static mechanical behaviors of LVL.