sortase A与变异链球菌致龋性关系的代谢组学研究

目的 探索srtA基因编码的转肽酶sortase A（SrtA）影响变异链球菌致龋性的机制。方法 采用基于¹H核磁共振波谱（NMR）的代谢组学方法,比较野生型变异链球菌UA159与srtA基因缺陷型变异链球菌UA159的胞外代谢产物;联合使用主成分分析和正交偏最小二乘法—判别分析鉴定不同菌株之间代谢产物的差异。结果 大多数有差异性的代谢产物是未知的,可识别的差异性代谢产物有亮氨酸和缬氨酸（δ 0.92×10^-6~1.20×10^-6）、乳酸（δ 1.28×10^-6）、酮戊二酸（δ 3.00×10^-6）、甘氨酸（δ 3.60×10^-6）。结论 在进一步完善微生物代谢产物数据库的基础上,¹H NMR代谢组学可用于龋病病因的研究。     

不同表面处理方法对氧化锆基底材料与饰面瓷结合强度的影响

目的 比较不同表面处理方法对氧化锆基底与饰面瓷之间的结合强度及结合界面微观结构的影响。方法 将WIELAND氧化锆瓷块胚体烧结制成10 mm×5 mm×5 mm大小试件33个。将试件随机分为3组,每组11个。喷砂组在烧结前进行喷砂处理;处理剂组先喷砂处理,再烧结结合衬底瓷;对照组不做处理。3组基底瓷材料采用粉浆涂塑法烧结5 mm×5 mm×5 mm大小的饰面瓷。每组随机抽取1个基底瓷及双层瓷试件,采用扫描电镜、能谱分析方法,研究氧化锆底瓷与饰面瓷之间的结合情况。其余试件则通过电子拉伸机测试结合界面的剪切强度,并用SPSS 17.0软件对实验数据进行统计学分析。结果 喷砂组、处理剂组、对照组试件的剪切强度分别为（18.06±0.59）、（21.04±1.23）、（13.80±1.54） MPa,各组间差异均有统计学意义（P<0.01）。结论 氧化锆胚体烧结前喷砂处理能提高氧化锆基底冠与饰面瓷的结合强度,结合衬底瓷的应用能提高氧化锆基底冠与饰面瓷的结合强度。     

磷酸酯类单体与氧化锆间化学反应模型的建立及作用机制

目的 对磷酸酯单体10-甲基丙烯酰氧癸二氢磷酸酯（MDP）提高四方相氧化锆与树脂间化学粘接的作用机制进行解释。方法 分别构建MDP、四方相氧化锆陶瓷晶体以及两者反应的数字模型,采用热力学方法对MDP分子与四方相氧化锆晶体簇相互作用的吉布斯自由能和平衡常数进行计算。结果MDP与四方相氧化锆晶体簇可能发生单配位形式和双配位形式的结合,其吉布斯自由能分别为-147.761和-158.073 kJ·mol^-1,说明MDP能够与四方相氧化锆晶体发生化学结合,平衡常数较高（4.95×10²⁷）的双配位结合形式较平衡常数较低（7.72×10²⁵）的单配位结合形式更为稳定。结论 MDP能够通过与四方相氧化锆陶瓷以双配位形式发生化学结合来提高其与树脂的粘接强度。     

降钙素基因相关肽对血清饥饿作用下MC3T3-E1成骨细胞凋亡和自噬的影响

目的 研究血清饥饿条件下降钙素基因相关肽（CGRP）对小鼠MC3T3-E1成骨细胞凋亡、自噬的影响以及二者之间的关系,以进一步明确CGRP对成骨细胞的保护机制。方法 体外培养小鼠MC3T3-E1成骨细胞。采用流式细胞术和蛋白质印迹检测正常血清、无血清（血清饥饿）、3-MA预处理+血清饥饿培养的成骨细胞的凋亡和微管相关蛋白1轻链3（LC3）蛋白的表达。采用蛋白质印迹检测正常血清、血清饥饿、血清饥饿+不同浓度（10^-10、10^-9、10^-8、10^-7 mol·L^-1）CGRP培养的成骨细胞的LC3和P62蛋白表达;采用蛋白质印迹检测正常血清、血清饥饿、血清饥饿+10^-8 mol·L^-1 CGRP培养不同时间（2、6、12、24、48、72 h）的成骨细胞的LC3蛋白表达,流式细胞数检测细胞凋亡,MDC染色检测细胞自噬泡。采用流式细胞术检测正常血清、血清饥饿、血清饥饿+10^-8 mol·L^-1 CGRP、3-MA预处理+血清饥饿、3-MA预处理+血清饥饿+10^-8 mol·L^-1 CGRP培养24 h的成骨细胞的凋亡。结果 血清饥饿培养时成骨细胞的LC3Ⅱ蛋白表达及细胞凋亡较正常血清时增加,3-MA预处理+血清饥饿培养时成骨细胞的凋亡较血清饥饿时增加（P<0.01）。与正常血清相比,血清饥饿、血清饥饿+CGRP培养时LC3Ⅱ蛋白表达增加,P62蛋白表达降低,以血清饥饿+10^-8 mol·L^-1 CGRP培养24 h时LC3Ⅱ/Ⅰ比值最高;血清饥饿+10^-8 mol·L^-1 CGRP培养能抑制成骨细胞的凋亡,促进自噬泡的合成。3-MA预处理后MC3T3-E1成骨细胞凋亡增加,CGRP部分逆转3-MA预处理所增加的成骨细胞凋亡。结论 CGRP能够增强血清饥饿下MC3T3-E1成骨细胞的自噬活性,并可能通过促进自噬抑制成骨细胞的凋亡。     

神经肽P物质及骨形态发生蛋白信号通路在ST2细胞成骨分化过程中的作用

目的 探讨神经肽P物质（SP）在ST2细胞（小鼠骨髓间充质干细胞）成骨分化过程中的作用及机制,以期为颞下颌关节骨关节炎的治疗提供依据。方法 对第3代ST2细胞分别用0、10^-10、10^-8 、10^-6、10^-5 mol·L^-1 SP培养,24、48、72 h后采用CCK-8实验检测细胞增殖情况。以10^-6 mol·L^-1 SP培养第3代ST2细胞1、3、5、7 d后,采用酶联免疫吸附试验（ELISA）检测上清液中碱性磷酸酶（ALP）、Ⅰ型胶原蛋白（CollaⅠ）和骨钙素（OCN）的表达,免疫荧光染色检测细胞ALP活性。分别用SP、Noggin（骨形态发生蛋白信号通路抑制剂）、SP+Noggin和2%胎牛血清培养ST2细胞,采用ELISA法检测上清液中ALP、CollaⅠ和OCN的表达。结果 CCK-8结果显示,24、48、72 h时均以10^-6 mol·L^-1 SP促进ST2细胞增殖活性最为明显（P<0.01）。ELISA结果显示,ALP表达在5 d时较对照组差异最为明显（P<0.01）,CollaⅠ和OCN的表达在7 d时较对照组差异最为明显（P<0.05）;免疫荧光结果显示,ALP活性在5 d时最强;加入抑制剂Noggin后,ALP、CollaⅠ和OCN表达量均降低。结论 SP可促进ST2细胞增殖和成骨分化,骨形态发生蛋白信号通路可能参与了此过程。     

抑菌浓度米诺环素对成骨细胞增殖、分化和矿化的影响

目的 研究抑菌浓度的米诺环素对成骨细胞增殖、分化和矿化及Runt相关转录因子2（Runx2）、碱性磷酸酶（ALP）、骨桥蛋白（OPN）mRNA表达的影响。方法 将米诺环素溶液（0、0.1、0.5、1、10 μg·mL^-1）与原代成骨细胞共培养,CCK-8检测增殖活性,通过ALP活性检测、茜素红染色、荧光定量聚合酶链反应检测探讨米诺环素对成骨细胞分化、矿化的影响。结果 0.1、0.5、1 μg·mL^-1的米诺环素可以促进细胞的增殖,上调ALP、Runx2 mRNA的表达水平,增加钙含量及钙化结节的形成,其中1 μg·mL^-1具有最大促进作用（P<0.05）;当浓度为10 μg·mL^-1时这种促进作用开始下降,并对ALP活性和OPN表达有显著抑制作用（P<0.01）。结论 适宜抑菌浓度的米诺环素能促进成骨细胞增殖,上调Runx2、ALP、OPN的表达水平,促进成骨细胞分化和矿化。     

磁共振弥散加权成像在甲状腺结节性病变诊断中的价值

目的 探讨磁共振弥散加权成像（diffusion weighted imaging, DWI）在甲状腺结节性病变诊断中的价值。方法：按照前瞻性设计,对临床拟诊为甲状腺结节性病变的100例患者,采用自旋平面回波弥散加权成像（spin-echo echo-planar imaging,SE EPI）序列扫描,b值取800 s/mm²,测量病变区的ADC值,应用SPSS17.0软件包中的t检验比较良、恶性病变ADC值的差异,并采用接收者工作特征曲线（receiver operating characteristic curve,ROC）确定良、恶性病变的ADC界值。结果：100例患者中,共检出结节155个,位于左叶67个,右叶80个,峡部8个;其中良性结节91个（结节性甲状腺肿87例,占56.13%;腺瘤4例,占2.58%）,恶性结节64个（乳头状癌55例,占35.48%;滤泡癌3例,占1.94%;不典型增生6例,占3.87%）;恶性结节的ADC值[（1.295±0.281）×10^-3 mm²/s明显低于良性结节[(2.033±0.387)×10^-3 mm²/s,差异有显著性（P=0.000）;根据ROC曲线确定良恶性界值为1.550×10^-3mm²/s,诊断敏感度和特异度分别为93.4%和82.8%,曲线下面积值为0.945。结论：甲状腺恶性结节性病变的平均ADC值低于良性,DWI序列在甲状腺结节性病变的鉴别诊断中具有重要价值。     

尼古丁调控人牙周膜细胞自噬水平的实验研究

目的 探讨尼古丁对人牙周膜细胞（hPDLCs）自噬水平的影响。方法 选取因正畸治疗而拔除的前磨牙,采用组织块法分离培养hPDLCs。通过Western blot法筛选尼古丁影响hPDLCs自噬的最佳作用时间及浓度,使用透射电子显微镜（TEM）和免疫荧光染色法检测该作用时间及浓度下hPDLCs自噬体形成情况和自噬标志蛋白LC3的表达情况。结果 LC3Ⅱ蛋白表达在尼古丁作用的12 h内持续升高,从而确定12 h为最佳作用时间;LC3Ⅱ蛋白表达上调具有尼古丁浓度依赖性,1×10^-5 mol·L^-1为尼古丁最佳作用浓度。TEM和免疫荧光染色证实尼古丁在此浓度及作用时间下hPDLCs细胞质内自噬体的数量增加,自噬标志蛋白LC3表达升高。结论 在一定条件下,尼古丁能够上调hPDLCs自噬水平,为进一步研究细胞自噬与吸烟相关牙周炎的关系奠定了基础。     

微波烧结和常规烧结对牙科用氧化锆半透性影响的对比研究

目的 研究微波烧结对氧化锆半透性的影响并与常规烧结对比,分析半透性与显微结构的相关性。方法 选取Lava和Zenostar两种品牌氧化锆试件各10个,每组5个试件,常规烧结组温度分别为1 500 ℃和1 490 ℃,保温2 h;微波烧结组均以15 ℃·min^-1升温至1 420 ℃,保温30 min。用ShadeEye NCC电脑比色仪测量各试件在白背景下和黑背景下的明度的分级（L*）、红到绿两色相极的变化（a*）、黄到蓝两色相极的变化（b*）值,并计算半透性参数（TP）,阿基米德排水法测量各试件的密度,扫描电镜（SEM）观察各试件的显微结构。结果 与常规烧结相比,微波烧结Lava和Zenostar氧化锆晶粒尺寸小且均匀一致,密度和TP值虽较高,但差异并无统计学意义（P>0.05）。Lava氧化锆的TP值大于Zenostar氧化锆（P<0.001）。结论 微波烧结氧化锆瓷的半透性能与常规烧结相当。     

结内液化区域对口腔鳞状细胞癌转移淋巴结表观弥散系数测量的影响

目的研究结内液化部分对口腔鳞状细胞癌（oral squamous cell carcinoma, OSCC）转移淋巴结在DW-MRI影像中表观弥散系数（ADC值）测量的影响。方法结合术后病理检查结果,分析25例OSCC患者的DW-MRI影像资料,分别选取和测量转移淋巴结实质部分和包括液化部分在内的整个转移淋巴结的ADC值,采用SPSS 17.0软件包中的两独立样本t检验比较2组ADC值间的差异。结果所有病例中存在颈淋巴结转移者11例,共检出15个转移淋巴结,其中8个转移淋巴结内发生明显局部液化,测量转移淋巴结实质部分（SMLN组）和包括液化部分在内的整个淋巴结（LMLN组）的平均ADC值分别为（872.1±22.65）×10^-6 mm²/s（n=15）、（1073±16.99）×10^-6mm²/s（n=8）。两独立样本t检验显示,SMLN组与LMLN组ADC值间具有显著差异 (P<0.05)。结论OSCC转移淋巴结内的液化区域可以造成选区内平均ADC值升高,如果在测量ADC值时选区内包含明显液化区域,则可能降低DW-MRI对OSCC颈部转移淋巴结诊断的准确性。     

微波二次烧结牙科纳米氧化锆全瓷材料的实验研究

目的：研究微波二次烧结工艺对牙科纳米氧化锆陶瓷材料的烧结密度,维氏硬度以及显微结构的影响,探索微波二次烧结牙科纳米氧化锆的烧结工艺。方法：将制作的30片氧化锆圆片试件随机分为实验组和对照组,每组15片。对照组按厂家推荐烧结程序进行常规二次烧结,实验组采用微波二次烧结。烧结后每组试件内6片用于测量氧化锆的烧结密度,6片用于测量氧化锆的维氏硬度,3片用于氧化锆的电镜扫描,实验组和对照组测试结果分别进行对比。结果：微波二次烧结的牙科纳米氧化锆材料的密度,维氏硬度均高于常规二次烧结的氧化锆,结果具有统计学意义（P〈0．05）,扫描电镜（SEM）下观察到微波二次烧结的牙科纳米氧化锆材料晶粒排列更紧密,晶体颗粒更小。结论：微波二次烧结工艺能够应用于牙科氧化锆陶瓷的二次烧结,缩短了牙科氧化锆陶瓷烧结时间,优化了牙科纳米氧化锆陶瓷材料的部分机械性能。     

Two-body wear of dental porcelain and substructure oxide ceramics

The aim of this in vitro study was to investigate the two-body wear of different ceramics. Two-body wear tests were performed in a chewing simulator with steatite and enamel antagonists, respectively. Specimens were loaded in a pin-on-block design with a vertical load of 50 N for 1.2 × 10(5) cycles; (f = 1.6 Hz; lateral movement, 1 mm; mouth opening: 2 mm). Human enamel was used as a reference. Three zirconia ceramics, three veneering porcelains, two glass-infiltrated and one lithium disilicate ceramic were investigated. Veneering and lithium disilicate ceramics were glazed before testing. Surface roughness Ra (SP6, Perthen-Feinprüf, G) and wear depth were determined using a 3D scanner (Laserscan 3D, Willytec, G). SEM (Quanta FEG 400, FEI, USA) pictures of the worn specimens and antagonists were made for evaluating wear performance. Veneering porcelain provided wear traces between 71.2 and 124.1 μm (enamel antagonist) and 117.4 and 274.1 μm (steatite). Wear of the steatite antagonists varied between 0.618 and 2.85 mm2. No wear was found for zirconia and glass-infiltrated substructure ceramics. Also, no wear was found for the corresponding antagonists. Wear of specimens and antagonists was strongly material dependent. No visible wear was found on zirconia and glass-infiltrated ceramics. Porcelain and lithium disilicate ceramic showed a comparable or lower wear than the enamel reference. Antagonist wear was found to be lower when specimens were made of substructure oxide ceramics instead of veneering porcelain. From the point of wear testing, zirconia may be used for the fabrication of fixed dental prosthesis without veneering.     

Influence of surface treatment on the wear of solid zirconia

Abstract

Objective. Recently there has been talk of the use of full-contour solid zirconia crowns or bridge restorations with no porcelain overlay. This could be a useful solution for patients with bruxism or limited interocclusal space. However, the hardness of zirconia could affect the opposite natural dentition. The aim of this in-vitro study was to investigate the role of surface treatments on the wear of a zirconia material and its antagonist. Materials and methods. Fifty plates (10 × 10 × 1 mm) made of zirconia (LavaMulti^? ZrO₂, 3M ESPE), divided into five equal groups, were sandblasted and ground under standardized conditions with a fine-grit diamond bur (Komet Brasseler, Germany) to simulate clinical conditions. Group (a) was only fired, (b) was fired and sandblasted, (c) only ground, (d) was ground and additionally polished (EVE Ceramic Polishing-Set, Pforzheim) and (e) was ground and glazed. Wear behavior was measured with a pin-on-disk apparatus ABREX against 6 mm steatite balls as antagonists (45°, 5 N load, 5000 cycles, water). The amount of wear was determined topographically using a 3-D profilometer (Concept 3D, Mahr, Germany) by measuring the height loss of the antagonist and the depth of wear Pt of the zirconia. Results. In groups (a), (b), (c) and (d) the wear value Pt could not be determined (<1 μm). Wear values of the antagonists (steatite balls) revealed a similar outcome in contact with (b), (c) and (e) in the range of 81–85 μm, whereas (e) was more abrasive but not significantly. A noticeable difference in the wear of the antagonist showed group (d) to have the smallest value. Conclusion. Polished zirconia seems to have the lowest wear on the antagonists, in contrast with the other kinds of surface treatment.     

Novel speed sintered zirconia by microwave technology

ObjectiveContinuous efforts have been made to hasten the zirconia densification process without compromising properties. This study evaluated the long-term structural durability of microwave speed-sintered zirconia (MWZ) relative to a conventionally sintered zirconia (CZ).MethodsAs-machined dental 3Y-TZP discs (Ø12 × 1.2 mm) were speed sintered at 1450 °C for 15 min using an industrial microwave oven, while conventional sintering was conducted in a standard dental furnace at 1530 °C for 2 h. Both were followed by natural cooling. The total sintering time was 105 min for MWZ and 600 min for CZ. Groups were compared regarding density, grain size, phase composition, and fracture resistance. Structural durability was investigated employing two fatigue protocols, step-stress and dynamic fatigue.ResultsCompared to CZ, MWZ exhibited a slightly lower density (MWZ = 5.98 g/cm³, CZ = 6.03 g/cm³), but significantly smaller grain sizes (MWZ = 0.53 ± 0.09 μm, CZ = 0.89 ± 0.10 μm), lower cubic-zirconia contents (MWZ = 15.3%, CZ = 22.7%), and poorer translucency properties (TP) (MWZ = 13 ± 1, CZ = 29 ± 0.8). However, the two materials showed similar flexural strength (MWZ = 978 ± 112 MPa, CZ = 1044 ± 161 MPa). Additionally, step-stress testing failed to capture the fatigue effect in 3Y-TZP, whereas dynamic fatigue revealed structural degradation due to moisture-assisted slow-crack-growth (SCG). Finally, MWZ possessed a slightly higher Weibull modulus (MWZ = 7.9, CZ = 6.7) but similar resistance to SCG (MWZ = 27.5, CZ = 24.1) relative to CZ.SignificanceDental 3Y-TZP with similar structural durability can be fabricated six-times faster by microwave than conventional sintering.     

Silica infiltration on translucent zirconia restorations: Effects on the antagonist wear and survivability

ObjectiveTo assess potential antagonist wear and survival probability of silica-infiltrated zirconia compared to glass-graded, glazed, and polished zirconia.MethodsTable top restorations made of 3Y-TZP (3Y), 5Y-PSZ (5Y), and lithium disilicate (LD) were bonded onto epoxy resin preparations. Each zirconia was divided into five groups according to the surface treatment: polishing; glaze; polishing-glaze; glass infiltration; and silica infiltration. The LD restorations received a glaze layer. Specimens were subjected to sliding fatigue wear using a steatite antagonist (1.25 ×10⁶ cycles, 200 N). The presence of cracks, fractures, and/or debonding was checked every one/third of the total number of cycles was completed. Roughness, microstructural, Scanning electron microscopy, wear and residual stress analyses were conducted. Kaplan–Meier, Mantel–Cox (log-rank) and ANOVA tests were performed for statistical analyses.ResultsThe survival probability was different among the groups. Silica infiltration and polishing-glaze led to lower volume loss than glaze and glass-infiltration. Difference was observed for roughness among the zirconia and surface treatment, while lithium disilicate presented similar roughness compared to both glazed zirconia. Scanning electron microscopy revealed the removal of the surface treatment after sliding fatigue wear in all groups. Compressive stress was detected on 3Y surfaces, while tensile stress was observed on 5Y.Significance3Y and 5Y zirconia behaved similarly regarding antagonist wear, presenting higher antagonist wear than the glass ceramic. Silica-infiltrated and polished-glazed zirconia produced lower antagonist volume loss than glazed and glass-infiltrated zirconia. Silica-infiltrated 3Y and lithium disilicate restorations were the only groups to show survival probabilities lower than 85%.     

The Correlation of Surface Roughness Parameters of Zirconia and Lithium Disilicate with Steatite Wear

Purpose

Various surface roughness parameters are utilized to describe the surface in the tooth to ceramics abrasion and to assess the resulting wear. The use of three-dimensional parameters may offer a better estimation for wear and an improved deduced clinical surface treatment. The aim of this study was to determine the influence of various surface roughness parameters of zirconia and lithium disilicate ceramics on the wear of steatite antagonists.

Material and methods

Forty zirconia specimens with a diameter of 7 mm and a thickness of 3 mm and 40 lithium disilicate specimens with the dimensions 10×10×4 mm were each divided into five subgroups. Two subgroups were treated with different clinically established diamond burs; a third subgroup was treated with a silicone polishing set. Two additional subgroups were produced by glazing the surfaces after treatment. Surface roughness parameters were determined by laser scanning microscopy. All specimens underwent 1.2 million loading cycles using steatite antagonists. After regular intervals of cycles, precision impressions were made to assess the wear. The correlation between wear and different roughness parameters was evaluated using the Spearman correlation test.

Results

For the glazed zirconia, unglazed zirconia, and glazed lithium disilicate specimens no significant correlations (p > 0.05) between the investigated roughness parameters and antagonist wear could be found. In the unglazed lithium disilicate groups, significant (p ≤ 0.05) correlations with steatite substance loss could be found for several roughness parameters after 1.2 million cycles.

Conclusions

For lithium disilicate, it seems not sufficient to use only one roughness parameter to indicate the wear behavior of the surface. There was no correlation between wear and the tested roughness parameters of zirconia surfaces.     

牙科氧化锆瓷摩擦磨损性能的研究

目的研究牙科氧化锆瓷的摩擦磨损性能以及与天然牙釉质摩擦磨损性能匹配情况。方法微摩擦磨损试验机上,以滑石瓷为对磨物,人工唾液润滑下对Upcera ST和Zenostar Zr Translucent氧化锆瓷、牙釉质和饰面瓷进行摩擦磨损实验。实验前,用激光共聚焦显微镜测试件表面粗糙度Ra;实验结束后,光学显微镜下观察滑石瓷磨斑形貌、测量滑石瓷磨斑面积;激光共聚焦显微镜测量试件磨斑宽度;扫描电镜下观察试件磨斑的微观形貌。采用单因素方差分析进行统计学分析。结果饰面瓷的磨斑宽度大于其它3种材料（P〈0.01）,饰面瓷对磨物滑石瓷磨斑面积大于氧化锆瓷和牙釉质（P〈0.05）。结论与饰面瓷对比,氧化锆瓷具有更佳耐磨性及较低对磨物磨损,并且与天然牙釉质的磨擦学性能相似。     

High-translucent yttria-stabilized zirconia ceramics are wear-resistant and antagonist-friendly

ObjectivesTo evaluate two-body wear of three zirconia ceramics stabilized with 3, 4 and 5 mol% yttria and to compare their wear behavior with that of a lithium-disilicate glass-ceramic.MethodsSixteen rectangular-shaped specimens made from three grades of zirconia ceramics and a lithium-disilicate glass-ceramic were polished and dynamically loaded in a chewing simulator (2 kg vertical load, 2.1 Hz) under water at 90 °C for 1.2 × 10⁶ cycles (about 7 days) in the ball-on-plate mode against steatite antagonists. Surface roughness was measured before and after wear testing. Wear tracks were scanned with a non-contact 3D profilometer and super-impositions were used to determine wear loss of the antagonists. Wear surfaces were imaged by SEM. XRD and micro-Raman spectroscopy were used to characterize phase transformation and stress status in the worn and unworn areas of the zirconia ceramics.ResultsIndependent of fracture toughness, strength and aging-susceptibility, the three zirconia ceramics showed a similar and limited amount of wear (∼10 μm in depth) and were more wear-resistant than the lithium-disilicate glass-ceramic (∼880 μm in depth). Abrasive wear without obvious cracks was observed for all investigated zirconias, whereas the glass-ceramic with a lower fatigue threshold and high susceptibility to surface dissolution exhibited significant abrasion, fatigue and corrosion wear. All three zirconia ceramics yielded a lower antagonist wear than the glass-ceramic and no significant differences were found between the zirconia ceramics.SignificanceIn the context of this study, high-translucent zirconia ceramics stabilized with a higher yttria content, recently introduced in the dental field, were as wear-resistant and antagonist-friendly as conventional high-strength zirconia and suitable for monolithic restorations.     

Wear performance of substructure ceramics and veneering porcelains

Aim

The aim of this in vitro study was to compare the two-body wear resistance of substructure zirconia and veneering porcelain versus steatite and human enamel antagonists, respectively.

Materials and methods

Two-body wear tests were performed in a chewing simulator with steatite and enamel antagonists (enamel cusps). A pin-on-block design with a vertical load of 50 N for 1.2 × 10⁵ cycles; (f = 1.6 Hz; lateral movement: 1 mm, mouth opening: 2 mm) was used for the wear test. For quantification of the wear resistance, wear tests were performed with standardized steatite spheres. Human enamel was used as a reference. Five zirconia ceramics and four veneering porcelains were investigated. One zirconia ceramic was tested with superficial glaze, which was applied after polishing or sandblasting, respectively. Surface roughness R_a (SP6, Perthen-Feinprüf, G) and wear depth were determined using a 3D-Profilometer (Laserscan 3D, Willytec, G). SEM (Quanta FEG 400, FEI, USA) pictures were used for evaluating wear performance of both, ceramics and antagonists.

Results

No wear was found for zirconia substructures. Veneering porcelain provided wear traces between 186.1 ± 33.2 μm and 232.9 ± 66.9 μm (steatite antagonist) and 90.6 ± 3.5 μm and 123.9 ± 50.7 μm (enamel). Wear of the steatite antagonists varied between 0.812 ± 0.256 mm² and 1.360 ± 0.321 mm² for zirconia and 1.708 ± 0.275 mm² and 2.568 ± 0.827 mm² for porcelain. Enamel generally showed wear, cracks or even fractures at the ridge, regardless whether opposed by zirconia or porcelain/glaze. Enamel was polished, when opposed to zirconia, or plowed, provoked and grinded, when opposed to porcelain/glaze.

Conclusion

The results of the wear test with steatite or enamel antagonists indicated no measurable wear on zirconia surfaces. Porcelain showed higher wear than zirconia, but comparable or lower wear than an enamel reference. Antagonistic wear against zirconia was found to be lower than wear against porcelain.