牙本质层对人牙力学性能的影响研究

牙釉质位于牙冠的外层,是人体内的最硬组织,具有优异的力学性能和耐磨性;相比牙釉质,内层的牙本质含有较多的有机物,具有较高的韧性。采用显微硬度仪和激光共聚焦扫描显微镜,研究牙本质层去除前后牙釉质的表面硬度和断裂韧性,分析牙本质层对人牙力学性能和耐磨性的影响。结果表明,牙本质层的存在对外层牙釉质的维氏硬度值无显著影响,但一旦去除牙本质层,牙釉质表面断裂韧性降低,载荷越大,断裂韧性降低越明显。可见,牙齿的力学性能与其独特的微观结构密切相关,牙冠内层硬度较低的牙本质的存在能提高牙齿抵抗脆性破坏的能力。     

牙本质层对人牙力学性能的影响

牙釉质位于牙冠的外层,是人体内的最硬组织,具有优异的力学性能和耐磨性;相比牙釉质,内层的牙本质含有较多的有机物,具有较高的韧性。采用显微硬度仪和激光共聚焦扫描显微镜,研究牙本质层去除前后牙釉质的表面硬度和断裂韧性,分析牙本质层对人牙力学性能和耐磨性的影响。结果表明,牙本质层的存在对外层牙釉质的维氏硬度值无显著影响,但一旦去除牙本质层,牙釉质表面断裂韧性降低,载荷越大,断裂韧性降低越明显。可见,牙齿的力学性能与其独特的微观结构密切相关,牙冠内层硬度较低的牙本质的存在能提高牙齿抵抗脆性破坏的能力。     

非晶Ni－W镀层结构及性能研究

本文采用硫酸镍、柠檬酸盐和钨酸钠为基本组分的镀液，获取了非晶Ｎｉ－Ｗ镀层。利用扫描电镜、Ｘ射线衍射仪、磨损实验机等对镀层形貌、结构、硬度、耐磨和耐蚀性进行了分析探讨。结果表明：在本实验条件下，Ｎｉ－Ｗ非晶镀层的耐磨性优于硬铬，耐酸性优于不锈钢。热处理能够提高镀层的硬度和耐磨性。     

非晶Ni—W镀层结构及性能研究

本文采用硫酸镍、柠檬酸盐和钨酸钠为基本组分的镀液，获取了非晶Ｎｉ－Ｗ镀层，利用扫描电镜、Ｘ射线衍射仪、磨损实验机等对镀层形貌、结构、硬度、耐磨和耐蚀性进行了分析探讨。结果表明：在本实验条件下，Ｎｉ－Ｗ非晶镀层的耐磨性优于硬铬。耐酸性优于不锈钢。热处理能够提高镀层的硬度和耐磨性。     

H13热作模具钢稀土硼碳氮多元共渗

对H13热作模具钢稀土硼碳氮共渗工艺进行了研究，并对其共渗层的组织、硬度及耐磨性和抗氧化性进行了测试与分析，结果表明与碳氮硼共渗工艺相比，稀土硼碳氮共渗层的硬度、耐磨性和抗氧化性明显提高。稀土元素的渗入不仅提高了渗层的硬度、耐磨性和抗氧化性，并且使过渡层的硬度变化减缓，增强了基体与共渗层的结合，为共渗层提供强有力的支撑作用。     

天然牙釉质/纯钛摩擦磨损行为的研究

对天然牙釉质与TA2纯钛球组成的摩擦副进行了实验研究，结合显微分析，研究了牙釉质的摩擦磨损行为。结果表明牙冠外层釉质的摩擦学特性与釉质的基本结构釉柱的排列方向密切相关，釉质在He面上的耐磨性明显优于垂直方向。     

激光处理对人牙釉质酸蚀和耐磨性能的影响

以人牙釉质为研究对象,对牙釉质表面进行激光处理,对激光处理前后牙釉质的表面形貌、力学性能和耐磨性能进行分析,旨在探索激光处理对牙齿酸蚀的抑制和修复作用,为激光在牙齿酸蚀抑制方面的临床应用提供理论指导。结果表明,原始牙釉质表面和酸蚀牙釉质表面经激光处理后,其表面硬度均显著提高、抗酸蚀能力增强;但是,激光处理会导致牙釉质表面变得粗糙,出现大量裂纹和孔洞,牙齿表面的弹性模量降低,表面脆性增大,从而使得牙齿耐磨性显著降低,造成的损伤重于酸蚀。     

碳纳米管镍基复合刷镀层的组织和性能

研究了碳纳米管镍基复合刷镀层的组织、显微硬度和耐磨性等。结果表明：与常规镀层相比，含有碳纳米管的复合镀层组织明显细化，显微硬度有较大的提高，硬度热稳定性和耐磨性得到了明显的提高。     

食物粒度和硬度对人牙釉质三体磨粒磨损特性的影响

在往复滑动摩擦磨损试验台上对比考察了三体磨粒磨损过程中,食物颗粒的粒度和硬度对人牙釉质摩擦学特性的影响。结果表明:当食物颗粒硬度较高时,随着粒度减小,稳态摩擦因数略有降低,牙釉质磨损表面形貌逐渐由剥落为主转变为犁削效应;对于低硬度食物颗粒,随着粒度增加,稳态摩擦因数显著降低,牙釉质磨损表面形貌则由犁削效应转变为轻微擦伤。当食物颗粒粒度相同时,食物硬度对牙釉质的摩擦与磨损行为均有明显影响,食物颗粒硬度越高,稳态摩擦因数越高,磨损越严重。     

金刚石涂层的合理利用

刀具的金刚石涂层具有非常高的硬度和耐磨性，但仅仅具有有限的耐粘和耐高温性能。这样就导致了它们应用在非常专业钻削主要由(具备强烈磨蚀作用的)塑料加工组成的领域，其中，这主要包括在航空工业中用得越来越多的纤维加强塑料。     

Erosion behaviors of human tooth enamel at different depth

In vitro erosion behaviors of human tooth enamel at different depth have been investigated in citric acid solution with pH 3.20. Erosion time of 3 min was used. The microtribological behaviors of eroded surfaces were also examined using nanoscratch technique. Results showed that erosion properties of enamel were closely associated with its location. Erosive substance loss increased from the outer to the interior enamel. Additionally, compared with the outer enamel, the influence of erosion on subsequent friction and wear behaviors appeared more significant in the interior enamel. Understanding of dental erosion would be useful for improving clinical management of toothwear.     

Microtribological behaviour of human tooth enamel and artificial hydroxyapatite

The microtribological behaviour of human tooth enamel and artificial hydroxyapatite has been studied and compared in this paper using a nano-scratch tester, aiming to extend the understanding of the wear mechanism of enamel. Results showed that the microtribological behaviour of enamel differed obviously from that of artificial hydroxyapatite. Compared with the artificial hydroxyapatite, more significant plastic deformation happened to the enamel under low loads, but no brittle delamination mechanism occurred even under high loads. Enamel microstructure plays an extremely significant role in its microtribological behaviour. The results would be helpful for the development of new dental restorative materials.     

人牙釉质的磨损机制研究

以钛合金为对摩材料,考察了人牙釉质在人工唾液介质中的滑动磨损进程,结合微观分析,研究了牙釉质的磨损机制。结果表明:在摩擦过程中,随着釉质表面发生脆性剥落,磨损从两体接触磨损转变为三体磨粒磨损,磨损加剧;随着接触时间增长,硬质磨屑尺寸变小,磨损率降低,进入稳定磨损阶段。牙釉质磨损为机械磨损过程,釉质表面基本无摩擦化学作用。     

人牙釉质和合成羟基磷灰石力学性能的对比研究

鉴于人牙釉质由96%～97%质量比的羟基磷灰石构成,选用合成羟基磷灰石作为空白对照样,通过纳米压痕仪、SEM、EDX等考察和分析不同载荷下人牙釉质和合成羟基磷灰石的力学性能,初步分析人牙釉质内部微观结构对其力学性能的贡献。结果表明:在相同载荷作用下,人牙釉质的硬度和弹性模量低于合成羟基磷灰石,且压痕较深。牙釉质和合成羟基磷灰石的硬度和弹性模量均随载荷增大而降低,压痕深度随载荷增大而增大,其中,合成羟基磷灰石的硬度和弹性模量随载荷增大而降低的幅度略大于人牙釉质。可见,人牙釉质的力学性能与其内部微观结构密切相关。     

Effects of cutting conditions on microhardness and microstructure in high-speed milling of H13 tool steel

In the present study, high-speed side milling experiments of H13 tool steel with coated carbide inserts were conducted under different cutting parameters. The microhardness and microstructure changes of the machined surface and subsurface were investigated. A finite element model, taking into account the actual milling process, was established based on the commercial FE package ABAQUS/Explicit. Instantaneous temperature distributions beneath the machined surface were analyzed under different cutting speeds and feed per tooth based on the model. It was found that the microhardness on the machined surface is much higher than that in the subsurface, which indicates that the surface materials experienced severe strain hardening induced by plastic deformation during the milling process. Furthermore, the hardness of machined surface decreases with the increase of cutting speed and feed per tooth due to thermal softening effects. In addition, optical and scanning electron microscope (SEM) was used to characterize the microstructures of cross sections. Elongated grains due to material plastic deformation can be observed in the subsurface, and white and dark layers are not obvious under present milling conditions. The thickness of plastic deformation layer beneath the machined surface increases from 3 to 10 μm with the increase of cutting speed and feed per tooth. The corresponding results were found to be consistent and in good agreement with the depth of heat-affected zone in finite element analysis (FEA).     

Fine structure of tooth enamel in the yellowing human teeth: SEM and HRTEM studies

Objective : The aim of this study was to clarify an influence of the fine structure of human tooth enamel to the yellowing teeth. Materials and methods : Sound maxillary first premolars of 15–50‐year‐old females that were extracted for the orthodontic treatment were used as the test samples. The tooth enamel sections of these teeth that prepared by ion polishing were observed by scanning electron microscopy (SEM). Furthermore, the fine structure of substance filling the inter‐rod spaces was analyzed by high resolution transmission electron microscopy (HRTEM). Results : In white tooth, the inter‐rod spaces were observed at the width of about 0.1 μm, while in yellow tooth, the inter‐rod spaces were not clearly observed by SEM. HRTEM observations revealed for the first time that the inter‐rod spaces were filled with fine particles of poorly crystallized hydroxyapatite in the yellow tooth. In yellow tooth, it was considered that the color of the inner dentin was recognized due to the decrease of light scattering by filling the tooth enamel inter‐rod spaces. The generation of particles in the tooth enamel inter‐rod spaces was considered to be caused by the long‐time progression of calcification. Conclusions : These results suggested that the change in fine structure, filling in inter‐rod spaces of tooth enamel, was related to progression of calcification in the inter‐rod spaces with advancing age and one of the factors of yellowness of human tooth. Microsc. Res. Tech. 79:14–22, 2016. © 2015 Wiley Periodicals, Inc.     

Study of <Emphasis Type="Italic">in vitro</Emphasis> wear of human tooth enamel

Wear behavior of human tooth enamel against titanium alloy has been investigated under the lubrication of artificial saliva, using a reciprocating sliding wear test machine with a normal load of 20 N, a reciprocating amplitude of 500 μm, and a frequency of 2 Hz. Tests lasting up to 10, 100, 1000, 2000, and 5000 cycles were conducted, respectively. The worn surface of enamel after different cycles was analyzed by means of various microscopic examinations. The results showed that, a delamination mechanism occurred on the surface of enamel at the early stage of wear. The wear rapidly increased in depth with the number of cycles. As the wear proceeded, the surface of enamel was gradually covered with a wear particle layer, and the wear rate decreased. Finally the wear of enamel stayed stable. Microscopic examinations indicated that the wear of enamel was controlled by the mechanical removal of materials without obvious changes in the compositions and crystal structures of the enamel. The enamel rods were worn away after the inter-rod enamel.     

稀土对激光熔覆金属陶瓷复合层的影响

采用CO2横流激光器在45#钢基体表面熔覆添加不同含量的稀土氧化物CeO2的镍基TiC金属陶瓷复合层;对熔覆层进行了显微组织观察、显微硬度测量、耐磨性能和耐腐蚀性能测试。结果表明,加入适量的稀土氧化物CeO2,可促进晶粒细化,有效地减少复合层中的裂纹、孔洞和夹杂,提高熔覆层的组织均匀性及表面硬度,明显改善熔覆复合层的耐磨及耐蚀性能。     

Antibacterial efficacy and remineralization capacity of glycyrrhizic acid added casein phosphopeptide‐amorphous calcium phosphate

The aim was to evaluate remineralization capacity and antibacterial efficiency of Tooth Mousse and various amounts of glycyrrhizic acid added Tooth Mousse on primary tooth enamel. Three groups were formed; Group 1 (CPP‐ACP), Group 2 (CPP‐ACP + 5% glycyrrhizic acid), and Group 3 (CPP‐ACP + 10% glycyrrhizic acid) in order to evaluate remineralization capacity. Enamel samples were immersed in demineralization solution and then remineralization agents were applied. Surface microhardness and SEM analyses were performed at the beginning, after demineralization and remineralization. For antibacterial tests, four groups were formed; Group 1, Group 2 and Group 3 and Group 4 (control). Biofilms were then exposed to 10% sucrose eight times per day for 7 days. After biofilm growth period, samples were treated with materials to evaluate antibacterial efficiency except control group. After application of materials, samples were incubated 2 more days at 37°C and at the end of this period, absorbance values of biofilms were determined and data were analyzed. An increase in microhardness values was Group 2 > Group 3 > Group 1, respectively, but there were no significant differences. After remineralization, microhardness values showed significant increases when compared to demineralized groups, but there was no significant difference. All groups showed decreased absorbance value of biofilm when compared with control group but they were insignificant. It was observed that both in Group 2 and Group 3, glycyrrhizic acid did not have a negative effect on remineralization and although they have an increase, it was insignificant. Although glycyrrhizic acid added CPP‐ACP groups showed increased antibacterial activity, they were not statistically significant.