K2O-Al2O3-SiO2系统牙科玻璃陶瓷与牙本质粘结强度的实验研究

目的：研究K2O-Al2O3-SiO2系统牙科陶瓷材料在使用Variolink Ⅱ树脂粘结剂时与牙本质的粘结强度。方法：依据”白榴石微晶化”热处理温度制备K2O-Al2O3-SiO2系统牙科玻璃陶瓷瓷锭;在已拔除的前磨牙中选择24个无龋坏、无裂纹者即刻完成根管充填;在每个离体牙的近中邻殆面制备Ⅱ类洞型,洞型的颊舌径3mrn、近远中径4mm、洞型顶部到洞底的轴壁长2mm、近中邻轴壁宽1mm;随机将离体牙分成两组制作嵌体蜡型,第1组离体牙使用K2O-Al2O3-SiO2系统牙科玻璃陶瓷材料制作嵌体,第2组离体牙使用IPS—Empress牙科陶瓷材料制作嵌体,两组嵌体均使用Variolink Ⅱ树脂粘结材料进行粘结,粘结后的所有样本均承受300次5℃～55℃的热循环;将样品修整成1．5mm×1．5min×3．0mm的立方体,其中陶瓷与牙体各占1／2,用微拉伸方法进行粘结强度测试。结果：K2O-Al2O3-SiO2系统牙科玻璃陶瓷和IPS—Empress牙科陶瓷与牙本质的粘结强度分别为（11．28±5．36）MPa和（12．61±1．74）MPa。结论：在使用Variolink Ⅱ粘结材料的情况下,K2O-Al2O3-SiO2系统牙科玻璃陶瓷和IPS—Empress牙科陶瓷与牙本质的粘结强度没有显著性差别。     

两种树脂粘接剂粘接K2O-Al2O3-SiO2系统牙科玻璃陶瓷Ⅴ类洞嵌体的效果比较

目的评价2种树脂粘接剂与K2O-Al2O3-SiO2系统牙科玻璃陶瓷嵌体的粘接效果。方法24颗离体牙随机分为自固化组和双固化组,每组12颗,均预备Ⅴ类洞,分别使用自固化型树脂粘接剂和双重固化型树脂粘接剂粘接K2O-Al2O3-SiO2系统牙科玻璃陶瓷嵌体,热循环300次后浸入林格溶液待用。每组随机抽取6个样本,浸入品红溶液24 h后测量洞壁的染色渗透度。3个月后扫描电镜下观察余下6个样本粘接剂的丧失情况。结果自固化组粘接剂-牙体界面的染色渗透度小于双固化组（χ2=5.383,P=0.02）,粘接剂裂隙量小于双固化组（t=4.24,P〈0.001）。双固化组个别样本在陶瓷-粘接剂界面和粘接剂-牙体界面均出现粘接剂裂隙量较大的区域。结论自固化型树脂粘接剂粘接K2O-Al2O3-SiO2系统牙科玻璃陶瓷Ⅴ类洞嵌体的效果优于双重固化型树脂粘接剂。     

白榴石微晶化增强牙科玻璃陶瓷机制的实验研究

目的 探讨K2O(氧化钾）在白榴石微晶化增强牙科玻璃陶瓷的原材料组分与比例方面的规律以及白榴石微晶含量对该玻璃陶瓷抗压强度的影响。方法 利用特定的热处理温度程序对不同K2O含量的玻璃陶瓷原材料进行热处理，比较热处理后样品的显微结构及其中白榴石微晶的含量，测试各组玻璃陶瓷的抗压强度。结果 高钾配比组原材料热处理后的样品中白榴石微晶化情况良好，分布均匀，晶粒约0.8μm，其玻璃陶瓷的抗压强度可达206.6MPa。白榴石微晶化增强的牙科玻璃陶瓷的抗压强度与白榴石微晶含量之间呈相关关系。结论 K2O在原材料中的配比对白榴石微晶化及其增强的牙科玻璃陶瓷的显微结构和相关性能有较大影响。白榴石微晶含量对该玻璃陶瓷的抗压强度有明显影响。     

钾铝硅系统牙科玻璃陶瓷嵌体边缘适合性的实验研究

目的：研究双固化粘结剂粘结钾铝硅（K2O-Al2O3-SiO2）系统牙科玻璃陶瓷的微渗漏情况。方法：制备钾铝硅系统牙科玻璃陶瓷瓷锭;选择清理24颗离体牙,即刻完成根管充填;在每颗离体牙的颊舌面颈部各预备一个V类洞型;将离体牙随机分成两组,第1组离体牙不预备粘结间隙、第2组离体牙预备约100μm的粘结间隙;用＂热压铸入＂法制作牙科陶瓷嵌体,用VariolinkⅡ双固化粘结剂粘结;从每组样本中随机抽取6颗离体牙,浸入25℃的品红溶液中24h,测量染色剂在洞壁的染色深度;另外12颗离体牙浸入25℃的复方生理盐水中2个月,在SEM下观察样本粘结剂的丧失情况。结果：染色渗透实验和SEM分析显示,两组样本均在陶瓷/粘结剂界面产生较高的边缘封闭质量（组1样本中陶瓷/粘结剂界面裂隙量的平均值为（12.4±4.5）%,明显低于组1样本中粘结剂/牙体界面裂隙量的平均值（38.9±8.8）%;组2样本中陶瓷/粘结剂界面裂隙量的平均值为（32.6±15.8）%,明显低于组2样本中粘结剂/牙体界面裂隙量平均值（67.9±23.1）%;没有粘结间隙的样本比有粘结间隙的样本具有更好的边缘适合性能（组1样本粘结剂裂隙量的平均值（15.7±7.3）%,明显低于组2样本中者（57.4±19.5）%。结论：较大的粘结间隙不能完全补偿双固化粘结系统树脂的聚合收缩,在使用双固化粘结系统粘结K2O-Al2O3-SiO2系统牙科玻璃陶瓷嵌体时应该避免制备较大的粘结间隙。     

白榴石微晶化增强牙科玻璃陶瓷的热处理温度制度的研究

目的 探索白榴石微晶化的热处理温度制度。方法 根据白榴石的化学式和K20-Na2O-Al2O3-SiO2系统相图制定原材料配比，在预设的熔融、成核、析晶温度中选择最佳温度；利用偏振光显微镜和x射线衍射分析仪观察样品的形态及显微结构特性。结果 玻璃融熔温度为1600℃，成核温度为1200℃，晶化温度为1500℃；微晶化后的自榴石晶粒约0．8μm，在玻璃基质中分布均匀。结论 按照一定的热处理温度制度。白榴石可以在玻璃中微晶化。     

氧化磷含量对新型牙科玻璃陶瓷微观结构和强度的影响

目的：分析不同氧化磷含量对新型牙科二硅酸锂玻璃陶瓷微观结构和强度的影响。方法：通过调控Li2O、SiO2、K2O、Al2O3、ZrO2-P2O5玻璃系统中氧化磷（P2O5）的含量（0.5%,1.0%,1.5%和2.0%）,并进行相应的热处理,应用X射线衍射技术（XRD）,电子扫描显微术（SEM）分析制备的各组玻璃陶瓷的微观形貌,根据ISO6872标准测试玻璃陶瓷的弯曲强度,进行统计学分析。结果：各组玻璃陶瓷样本的主晶相均为二硅酸锂（Li2Si2O5）,随着P2O5含量的改变,析出晶体的形貌和分布有显著不同。1.0%组玻璃陶瓷具有最高的弯曲强度值。结论：通过调控P2O5含量,可制备具有高强度和适宜微观形貌的二硅酸锂玻璃陶瓷。     

K2O-Na2O-Al2O3-SiO2系统牙科微晶玻璃匹配氧化铝陶瓷的初步研究

目的:研究 K₂O-Na₂O-Al₂O₃-SiO₂系统牙科微晶玻璃匹配氧化铝陶瓷的热处理温度制度。方法:根据氧化铝陶瓷的热膨胀系数调整K₂O-Na₂O-Al₂O₃-SiO₂系统牙科微晶玻璃的原材料配比,利用K₂O-Na₂O-Al₂O₃-SiO₂系统牙科微晶玻璃的热处理温度制度形成微晶玻璃-氧化铝陶瓷复合材料;利用偏振光显微镜和X射线衍射分析仪观察样品的形态及显微结构特性,利用材料试验机测试材料的抗压强度。结果:经过原材料组份的调整,白榴石晶粒约1.0 μm、在玻璃基质中分布均匀;微晶玻璃-氧化铝陶瓷复合材料的抗压强度为500 MPa。结论:K₂O-Na₂O-Al₂O₃-SiO₂系统牙科微晶玻璃的热处理温度制度适合匹配氧化铝陶瓷。     

二次熔融烧结法制备牙科用可切削云母基玻璃陶瓷

目的:通过二次熔融烧结法制备以云母为主晶相的牙科用可切削玻璃陶瓷。方法:在1500℃下熔融K2O-MgO-Al2O3-SiO2-F系统基础玻璃,其玻璃粉经过冷等静压成型后无压烧结获得牙科用可切削玻璃陶瓷。采用DTA-TGA确定基础玻璃的核化和晶化温度,采用XRD和SEM分析烧结体的物相组成和微观形貌,以及采用三点弯曲法和压痕法测定烧结体的力学性能。结果:K2O-MgO-Al2O3-SiO2-F系统的核化温度和晶化温度分别选择680℃和1020℃。烧结体的整体析晶比较缓慢,结晶度约为35.48%,主晶相为氟硅云母,晶体呈立方或扁平状,交错排列。烧结体的弯曲强度和断裂韧性分别为(144.50±9.75)MPa和(1.25±0.26)MPa.m1/2。结论:二次熔融烧结法制备的云母基玻璃陶瓷能够满足临床牙体缺损修复的要求。     

氧化钾的含量对牙科微晶玻璃析晶性能的影响

目的 研究氧化钾（K2O）的含量对牙科微晶玻璃析晶性能的影响。方法 在Li2O-SiO2-Al2O3-P2O5-ZnO体系的基质玻璃中添加不同含量的K2O,根据差热分析（DTA）曲线确定微晶玻璃的热处理制度,采用X射线衍射分析和扫描电子显微镜（SEM）观测来比较不同的K2O含量对牙科Li2O-SiO2-Al2O3-P2O5-ZnO体系微晶玻璃析晶成分和显微结构的影响。结果 K2O的引入有助于降低玻璃基体的粘度,促进基质玻璃的析晶。在基质玻璃中添加5.3 wt%的K2O可以使玻璃在热处理后析出较多的二硅酸锂晶体,晶体呈板条状,长度约为4 μm,在玻璃基质中分布均匀。 结论 添加一定量的K2O有助于提高牙科Li2O-SiO2-Al2O3-P2O5-ZnO体系微晶玻璃的析晶性能。     

氧化锆/磷酸镧可切削复相陶瓷的制备及机械性能研究

目的 利用氧化锆粉体和磷酸镧粉体复合,制备可用于制作牙科修复体并适合牙科加工的氧化锆陶瓷。通过调整原料的成分、配比、添加稳定剂并对材料进行机械性能研究,以期获得一种满足牙科修复体要求的可切削氧化锆/磷酸镧复相陶瓷。方法 通过对氧化锆/磷酸镧复相陶瓷抗弯强度、断裂韧性、维氏硬度、X线衍射显微结构分析等方面的检测分析,来确定氧化锆/磷酸镧复相陶瓷的成分配比以及工艺参数。结果 10%磷酸镧含量组1%稳定剂(Y2O3)加入量时机械性能最佳,抗弯强度(590.36±45.67)MPa,断裂韧性(6.62±0.51)MPa.m1/2;20%磷酸镧含量组3%Y2O3加入量时机械性能最佳,抗弯强度(568.91±28.72)MPa,断裂韧性(3.79±0.13)MPa.m1/2;30%磷酸镧含量组5%Y2O3加入量时机械性能最佳,抗弯强度(405.90±18.06)MPa,断裂韧性(2.46±0.08)MPa.m1/2;40%磷酸镧含量组7%Y2O3加入量时机械性能最佳,抗弯强度(200.90±14.46)MPa,断裂韧性(2.1±0.12)MPa.m1/2。结论 新型牙科氧化锆/磷酸镧复相可切削陶瓷材料烧结制备性能良好,机械性能优良。     

Correlation between fracture toughness and leucite content in dental porcelains

OBJECTIVES: To determine the correlation between fracture toughness and leucite content in dental porcelains. The mechanisms by which leucite influences the fracture toughness of dental porcelains were also investigated. METHODS: Six porcelains were tested: A (Ceramco I/Dentsply), B (Ceramco II/Dentsitply), C (Finesse/Dentsply), D (d.Sign/Ivoclar), Cb (Cerabien/Noritake) and V (Vitadur Alpha/Vita). Bar-shaped specimens were produced, and their fracture toughness was determined by means of the single-edge precracked beam (SEPB) method. The test consisted of fracturing the specimen after a precrack was generated by a bridge-anvil device. KIc was calculated based on fracture force and size of the precrack. Microstructural analysis and determination of the leucite volume fraction were performed on polished specimens etched with 2% HF for 15s by means of scanning electron microscopy. Fractographic analysis was performed on fracture surfaces. RESULTS: Porcelains A and B presented the highest leucite contents (22%) and similar KIc values (1.23 and 1.22 MPa m1/2, respectively), significantly higher than the other materials. Porcelains C and D presented similar K(Ic) values (0.81 and 0.93 MPa m1/2, respectively), but different leucite contents (6 and 15%, respectively). Porcelain D presented higher KIc compared to porcelains Cb and V (0.71 and 0.75 MPa m1/2, respectively), which presented similar values and the lowest leucite contents (0%). Fractographic analysis showed that porcelains with higher leucite content presented higher incidence of crack deflection. CONCLUSIONS: For the materials evaluated in this study, the leucite content was directly related to KIc. The main toughening mechanism observed was crack deflection around leucite particles and clusters.     

The crystallization of an aluminosilicate glass in the K2O-Al2O3-SiO2 system.

OBJECTIVES: The aims of the study were to explore the nucleation and crystallization kinetics of an aluminosilicate glass in K2O-Al2O3-SiO2 system and to characterize it. OBJECTIVES: A starting glass composition of wt%; 64.2% SiO2, 16.1% Al2O3, 10.9% K2O, 4.3% Na2O, 1.7% CaO, 0.5% LiO and 0.4% TiO2 was heated in an electric furnace and later quenched to produce glasses. The glass powders were heat treated using differing heat treatment schedules and quenched. Dta, Xrd, Eds and Sem analyses were used to characterize and explore the crystallization kinetics of the glasses. RESULTS: Phase separation of the glasses was identified and characterized in the glasses. Tetragonal leucite, cubic leucite and sanadine glass-ceramics were produced. Fine leucite crystals (1 microm2) were crystallized with minimal matrix microcracking. SIGNIFICANCE: Amorphous phase separation appeared to be an important precursor to nucleation and crystal growth in the alkali aluminosilicate glasses explored. It was possible to control the crystallization of tetragonal leucite and sanidine phases by selected heat treatment of glass powders and monoliths, resulting in the production of fine grained tetragonal leucite glass-ceramics.     

Phase identification in dental porcelains for ceramo-metallic restorations

Most commercial dental porcelains designed for ceramo-metallic restorations are partially crystallized feldspathic glasses (glass-ceramics) that consist of low (tetragonal) leucite (K2O.Al2O3.4SiO2) crystals embedded in a glassy matrix. In this work, we have identified the crystalline phases in eight commercial dental porcelains (four enamels and four dentin bodies) in both powder (unfired) and sintered forms, by x-ray diffraction, emission spectroscopy analysis, reflection optical microscopy, and scanning electron microscopy. Besides low leucite and glass, we have found a second crystalline phase in the sintered and slow-cooled porcelains that we propose to be potash feldspar (K2O.Al2O3.6SiO2). It was impossible to ascertain whether these synthetic crystals may be sanidine, orthoclase, or microcline. The precipitation of feldspar during cooling is explained in terms of the crystallization behavior of typical body compositions in the ternary-phase diagram K2O-Al2O3-SiO2. Ceramography confirms the martensitic (displacive) nature of the transformation from high (cubic) to low (tetragonal) leucite upon cooling.     

Fracture toughness (KIc) of a dental porcelain determined by fractographic analysis.

OBJECTIVES: Fractographic analysis of indentation cracks is performed following flexure testing as part of the ASTM (1999) standard for fracture toughness, KIc, determination in advanced ceramics. This method depends on the conduciveness of the material towards fractographic interpretation. The purpose of this study was to evaluate the use of fractography in fracture toughness methods with a feldspathic dental porcelain, in which KIc was measured fractographically as well as numerically using two controlled-flaw beam bending techniques. METHODS: The following methods for KIc determination were applied to a dental porcelain containing a leucite volume fraction of 15-20%: (1) surface crack in flexure (SCF) (dependent upon fractographic analysis); and (2) indentation strength (IS) at indentation loads of 9.8 and 19.6 N (applying both standard numeric calculations and fractographic analysis). The testing environments were (1) ambient air (IS and SCF) and (2) flowing dry nitrogen (SCF). RESULTS: No significant differences were found between numeric and fractographic KIc values for the IS technique at both indentation loads (9.8 and 19.6 N) in ambient air, although KIc values were sensitive to indentation load. Due to the presence of residual stresses, stable crack extension was observed fractographically in all IS specimens, as evidenced by differences between initial (ainitial) and critical (acritical) crack dimensions. For the SCF method, there was a significant difference in toughness between specimens tested in air versus dry nitrogen, however no fractographic evidence for chemically assisted slow crack growth (SCG) was observed. SIGNIFICANCE: The SCF method as described by the ASTM standard was applicable to the feldspathic porcelain and produced very comparable results with the numeric toughness calculations of the IS procedure. However, fractographic analysis of the surface crack was somewhat difficult for this glassy ceramic compared with polycrystalline ceramics. Knowledge about stable crack extension or slow crack growth and its fractographic appearance is essential when estimating the toughness from examination of flaw dimensions on fractured surfaces since large calculation errors may occur if these effects are not taken into account.     

Stress induced phase transformation of a cesium stabilized leucite porcelain and associated properties.

OBJECTIVES: The addition of CS2O to dental porcelains might provide a means for controlling the thermal expansion and toughness of feldspathic porcelains. The purpose of this investigation was to determine for a leucite porcelain the effect of CS2O content upon its coefficient of thermal expansion (alpha), toughness, hardness, and content of low (tetragonal) leucite and high (cubic) leucite. METHODS: In order to determine the amount of low leucite in the specimens, an x-ray calibration curve for low leucite and an internal standard of copper was obtained using quantitative x-ray diffraction techniques. Utilizing a stress induced phase transformation between low and high leucite, an x-ray intensity conversion ratio (r) was determined for high leucite so that the calibration curve for low leucite could be used to determine the amount of high leucite present in the experimental porcelains. Specimens were prepared with various amounts of CS2O (0.0, 0.5, 1.0, 1.5, 2.0 mol%) so that, except for the as-received porcelain (A), all had the same thermal history. Specimens were tested for content of low and high leucite, hardness (Vickers), toughness (indentation-strength method), and coefficient of thermal expansion (alpha) over two temperature ranges (30-500 degrees C and 30-640 degrees C). Fractured surfaces were examined with a scanning electron microscope (SEM). For each property, specimen groups were compared for statistical differences. These comparisons were statistically analyzed using analysis of variance (ANOVA) and Fisher's protected least significant differences (PLSD). RESULTS: Quantitative x-ray examination of abraded and heat-treated specimens demonstrated that a stress induced phase transformation occurred which could be reversed by heat treatment. The conversion ratio was determined as r = 1.93 +/- 0.29. The addition of CS2O lowered the wt% of low leucite from 63 +/- 6% to 0% and increased the amount of high leucite from 0% to 62 +/- 5%. ANOVA showed that the addition of CS2O had a significant effect on alpha (p < 0.0001), hardness (p < 0.005), and toughness (p < 0.0001). CS2O significantly (PLSD) lowered the alpha (p < 0.0001), hardness (p < 0.01), and toughness (p < 0.0001) of a high-content leucite porcelain. SIGNIFICANCE: A stress induced phase transformation of high leucite to low leucite was demonstrated and, as a consequence, suggested the potential for phase transformation toughening. The alpha of a leucite porcelain could be controlled by stabilizing high (cubic) leucite to room temperature with the fraction of high leucite dependent upon the amount of CS2O added. A method was developed to determine the amount of high leucite present in a porcelain.