Impaction-modified densely sintered yttria-stabilized tetragonal zirconium dioxide: methodology, surface structure, and bond strength

The objectives of the study were to describe a novel method for producing zirconium dioxide specimens with a cementation surface that allows adhesive cementation techniques, to describe the surface structure and to evaluate the bond strength. Forty-eight pairs of specimens were fabricated and adhesively luted together. Three different surfaces were tested: impaction-modified surfaces created by using glass granules (G), impaction-modified surfaces created by using polymer granules (P) and a nonmodified control surface (C). Two bonding systems were used, Variolink(?)II (VA) or Panavia?F 2.0 (PA). During the different fabrication steps, the surfaces were examined under light microscope and analyzed with an optical interferometer. All groups were thermocycled and subjected to shear bond strength test. The groups with modified cementation surfaces showed significantly higher shear bond strength: 34.9 MPa (VA-G), 30.9 MPa (VA-P), 29.6 MPa (PA-P), and 26.1 MPa (PA-G) compared with the relevant control group: 20.5 MPa (VA-C) and 17.8 MPa (PA-C). The groups with surface modification showed a rougher surface structure and significantly fewer fractures between the cement and the zirconium dioxide surfaces compared to the control groups where all failures were adhesive. Impaction modification with an impaction medium pressed into the cementation surface of zirconium dioxide-based reconstructions can be used in combination with an additive production technique to increase bond strength. Both modification techniques described in the study result in a rougher surface structure and higher shear bond strength compared to the control groups.     

上釉技术对氧化钇稳定四方相氧化锆多晶陶瓷粘接及力学性能的影响

文题释义：氧化钇稳定四方相氧化锆多晶陶瓷：是以氧化钇为稳定剂、四方相为主要物相的氧化锆陶瓷，其具有较高的抗弯强度(900-1 200 MPa)和断裂韧性(9-10 MPa·m^1/2)。由于这些优异的机械性能，氧化钇稳定四方相氧化锆多晶陶瓷成为口腔冠桥修复中应用最广泛的陶瓷之一。 相变增韧机制：为氧化锆增韧的一种方法。稳定剂使四方相氧化锆在室温下可以处于亚稳态，但是在应力作用下亚稳态的四方相氧化锆易转化为单斜相氧化锆，同时伴有3%-5%的体积膨胀，这个过程能弥合微裂纹且消耗断裂能，提高氧化锆陶瓷的韧性。 背景：任何表面处理都应在不损害原有氧化钇稳定四方相氧化锆多晶陶瓷强度的前提下提高其粘接强度。目前缺乏上釉技术对氧化钇稳定四方相氧化锆多晶陶瓷粘接强度影响的资料，并且其对氧化钇稳定四方相氧化锆多晶陶瓷力学性能的影响尚不明确。 目的：评估上釉技术对氧化钇稳定四方相氧化锆多晶陶瓷力学行为及其与树脂水门汀粘接强度的影响。 方法：制作氧化钇稳定四方相氧化锆多晶陶瓷试件并随机分为4组：A组，表面不做任何处理；B组，110 μm氧化铝颗粒喷砂；C组，上釉+氢氟酸酸蚀；D组，上釉+氢氟酸酸蚀+硅烷化。检测每组试件的表面显微形貌、粗糙度、晶相结构、元素组成、剪切粘接强度和弯曲强度，并观察剪切粘接强度测试后所有断面的断裂模式。 结果与结论：①经表面处理后的试件粗糙度明显增大，降序排列依次为C组(0.62±0.01) μm、D组(0.55±0.02) μm、B组(0.11±0.02) μm、A组(0.05±0.01) μm，5组间粗糙度比较差异有显著性意义(P < 0.05)；②B组试件表面含有2.2%单斜相氧化锆，而其他组含量均为零；③除锆和氧2种元素外，B组还含有铝元素6.49%，C和D组分别含有硅元素18.67%和25.78%；④A、B、C、D组的剪切粘接强度分别为(3.11±0.40)，(4.23±0.45)，(6.62±0.60)，(10.46±0.83) MPa，组间两两比较差异均有显著性意义(P < 0.05)；⑤A、B、C和D组的三点弯曲强度分别为(961.07±75.53)，(1 234.73±114.09)，(1 024.28±120.51)，(1 036.09±80.10) MPa，其中A、C和D组两两比较差异无显著性意义(P > 0.05)，B组与A、C、D组比较差异有显著性意义(P < 0.05)；⑥结果表明，上釉技术未明显提升氧化钇稳定四方相氧化锆多晶陶瓷的弯曲强度，但上釉后经氢氟酸蚀刻并硅烷化处理可显著增强氧化钇稳定四方相氧化锆多晶陶瓷与树脂水门汀之间的粘接强度。 ORCID: 0000-0002-8066-2498(徐小敏) 中国组织工程研究杂志出版内容重点：生物材料；骨生物材料; 口腔生物材料; 纳米材料; 缓释材料; 材料相容性；组织工程     

表面处理技术提高修复体金瓷结合强度的研究进展

背景：金瓷修复体具有效果美观及组织相容性好、强度高等优点。 目的：综述近几年来不同表面处理技术提高金瓷结合强度的成果。 方法：应用计算机检索CNKI数据库、OVID数据库有关提高修复体金瓷结合强度的相关文章,英文关键词为“bond strength of porcelain,PFM,surface treatment technology,preoxidation,sol-gel,plasma-spray”;中文关键词为“金瓷结合,金属烤瓷全冠,表面处理,预氧化,溶胶凝胶,等离子”。 结果与结论：金瓷结合强度是修复体成功应用的主要方面。利用适当的金属表面处理技术改善瓷与合金的结合强度,可以达到更完美的修复效果。预氧化工艺、深冷处理、溅射喷金技术、等离子喷涂技术、溶胶凝胶技术、纳米过渡性介质技术、真空镀膜技术等几种表面处理技术都不同程度的地提高了金瓷结合强度,但有些技术尚在不断完善中,等待广大学者进一步继续研究。     

饰瓷温度烧结对氧化锆陶瓷与树脂黏结剂剪切强度的影响

背景：研究已证实硅烷偶联剂和喷砂等表面处理方式,以及增加氧化锆陶瓷表面的微裂纹可提高氧化锆陶瓷与树脂黏结剂间的黏结强度,但有关多次反复烧结是否会对氧化锆陶瓷黏结剪切强度产生影响尚缺少相关研究。 目的：测试饰瓷温度烧结对牙科氧化锆陶瓷与树脂黏结剂黏结剪切强度的影响。 方法：从40片氧化锆瓷片随机选择20片,分成 5组,按照常规烧结程序分别烧结0(对照组),2,4,6,8次,热处理起始温度为500 ℃,最终温度1 000 ℃,升温速率55 ℃/min,抽真空时间7 min。每次烧结最终温度恒定不变。将各组分别用树脂黏结剂与剩余未烧结的陶瓷片对位黏结,用万能材料试验机测黏结界面的剪切强度;使用扫描电镜观察剪切后的试件断面形貌。 结果与结论：烧结4,6,8次组试件剪切强度高于对照组(P < 0.05);烧结2次组试件剪切强度稍高于对照组,但差异无显著性意义(P > 0.05);烧结8次组试件剪切强度高于烧结4,6次组(P < 0.05)。未烧结氧化锆陶瓷表面未见裂纹;经过2次烧结后表面可见细微裂纹;经过4次烧结后表面可见裂纹增多;经过6次烧结后表面已经开始有明显变化,裂纹增多并伴有细微空隙产生,少量黏结剂残留;经过8次烧结后表面可见裂纹与空隙明显增多并有黏结剂残留。表明经过4,6,8次烧结后的氧化锆陶瓷对树脂黏结剂有较好的黏结剪切强度,烧结8次后的黏结剪切强度最强。中国组织工程研究杂志出版内容重点：生物材料;骨生物材料; 口腔生物材料; 纳米材料; 缓释材料; 材料相容性;组织工程全文链接：     

The effect of surface coating on the bond strength of machinable ceramics

This study examined the nature of the surface presented by a machinable feldspathic porcelain and by a machinable glass-ceramic for bonding to conventional composite luting agents and measured the bond strengths which may be achieved with various surface treatments. There was no significant difference between the bond strengths achieved to etched porcelain, Silicoated porcelain or etched glass-ceramic. Silicoated glass-ceramic specimens showed a significantly higher adhesive assembly strength (p = 0.02). Examination of the fractured specimens showed that in all cases the failure involved part cohesive failure of the ceramic surface and part failure at the cement-ceramic interface.     

The bond strength of light-curing composite resin to finally polymerized and aged glass fiber-reinforced composite substrate

OBJECTIVE: This study examines the shear bond strength of visible light-curing composite resin (VCR) to aged glass fiber-reinforced composite (FRC) substrate with multi-phase polymer matrix. METHODS: Linear polymethyl methacrylate and dimethacrylate monomer preimpregnated unidirectional glass fiber reinforcement was used as an adhesion substrate for low-viscosity diacrylate veneering composite resin and restorative composite resin. A total of 60 test specimens were divided into three groups according to the brand and the use of an intermediate monomer resin (IMR). The used IMRs were either BisGMA-HEMA-resin, BisGMA-TEGDMA resin or the controls were left without the IMR treatment. Dry- and water-stored FRC-substrates were used for adhering the VCR with or without the IMR. The shear bond strength of the VCR to the substrate was measured for dry and thermocycled specimens and the results were analyzed with multi-variate ANOVA. RESULTS: The highest mean shear bond strength (23.9 +/- 4.8 MPa) was achieved with FRC/BisGMA-HEMA/VCR combination when the FRC substrate was water stored and the test specimen was thermocycled. FRC/BisGMA-TEGDMA/VCR combination resulted in 15.7 +/- 6.0 MPa with the water-stored FRC substrate and after thermocycling of the test specimens. The lowest shear bond strength (1.0 +/- 0.5 MPa) was obtained with FRC/VCR combination with water-stored substrate and after thermocycling of the test specimens. Significant differences were found between the mean values of three groups according to the use of IMR (p<0.001). The storage conditions of the FRC substrate were related to brand of the IMR or the composite (p<0.001). High mean values of the shear bond strength after thermocycling fatigue were related to the type of IMR (p<0.001). SIGNIFICANCE: The results suggest that the IMRs used in this study greatly influence the mean shear bond strength values when the test specimens are thermocycled.     

Initial adhesion of glass-fiber-reinforced composite to the surface of porcine calvarial bone

The aim of this preliminary study was to compare the initial bond strength of the glass-fiber-reinforced composite veil to the surface of the porcine calvarial compact bone using different adhesives. Fiber-reinforced composite (FRC) made of E-glass fiber veil with the BisGMA-PMMA resin system was used in the study. For the shear bond strength test, porcine calvarial bone cubes were mounted into resin matrix. FRC-veil discs were bonded to compact bone with different types of adhesives: (A) BisGMA-HEMA based (3M-ESPE Scotchbond Multi-Purpose Adhesive), (B) 4-META/UDMA/BisGMA based (Unifil Bond Bonding Agent) and MDP based (Clearfil Se Bond adhesive), (C) UDMA/BisGMA/PMMA-based experimental adhesive, and (D) silane-based (APS, ICS, MPS) experimental adhesives. The surface of the bone was mechanically roughened and was either used as such, treated with dental primers (Unifil Bond Self-etching Primer, Clearfil Se Bond Primer), or treated with an experimental silane mixture (APS, ICS, MPS), or with a mixture of the experimental silane liquid and Clearfil Se Bond Primer. The 3M-ESPE Scotchbond Multi-Purpose Adhesive and UDMA/BisGMA/PMMA experimental adhesive gave poor results in the shear bond test (0.58 and 0.40 MPa, respectively). Unifil Bond Bonding Agent and Clearfil Se Bond adhesive with respective primers markedly improved the shear bond strength; with Unifil the result was 3.40 MPa, and with Clearfil it was 6.19 MPa. When the bone surface was primed with a mixture of Clearfil Se Bond Primer and Clearfil Porcelain Bond Activator, the Clearfil Se Bond adhesive-impregnated FRC veil gave the best adhesion to the bone surface in this test: 9.50 MPa. The addition of bioactive glass granules between the veil and the bone lowered the shear bond strength in the test system described above to 6.72 MPa. The test systems with the silane mixture were also promising. In the SEM study, it was found that the mechanical treatment reveals the pores of the bone surface. Chemical treatments of the bone surface improved the adhesion of the FRC veil to the bone. The results showed that the adhesion of the FRC to the surface of the bone can be significantly improved with mechanical roughening and with special chemical treatments of the bone surface.     

Bond strength of binary titanium alloys to porcelain

The purpose of this study was to investigate the bond strength between porcelain and experimental cast titanium alloys. Eleven binary titanium alloys were examined: Ti-Cr (15, 20, 25 wt%), Ti-Pd (15, 20, 25 wt%), Ti-Ag (10, 15, 20 wt%), and Ti-Cu (5, 10 wt%). As controls, the bond strengths for commercially pure titanium (KS-50, Kobelco, Japan) and a high noble gold alloy (KIK, Ishifuku, Japan) were also examined. Castings were made using a centrifugal casting unit (Ticast Super R, Selec Co., Japan). Commercial porcelain for titanium (TITAN, Noritake, Japan) was applied to cast specimens. The bond strengths were evaluated using a three-point bend test according to ISO 9693. Since the elastic modulus value is needed to evaluate the bond strength, the modulus was measured for each alloy using a three-point bend test. Results were analyzed using one-way ANOVA/S-N-K test (alpha = 0.05). Although the elastic moduli of the Ti-Pd alloys were significantly lower than those of other alloys (p = 0.0001), there was a significant difference in bond strength only between the Ti-25Pd and Ti-15Ag alloys (p = 0.009). The strengths determined for all the experimental alloys ranged from 29.4 to 37.2MPa, which are above the minimum value required by the ISO specification (25 MPa).     

应用烤瓷套冠修补崩瓷冠桥的可行性研究

背景：有临床科室采用瓷套冠方法对烤瓷冠桥崩瓷患者进行崩瓷修补,取得了不错效果。 目的：检测烤瓷套冠单冠黏结强度的大小,判断烤瓷套冠在修补崩瓷临床应用中的可行性,同时观察烤瓷套冠修复崩瓷过程中喷砂处理和硅烷偶联剂处理金属黏结表面对其黏结强度的影响。 方法：用失蜡法铸造相同规格钴铬合金套冠,选择表面无气孔、无铸造缺陷的试件20件,常规打磨,超声清洗后随机分为4组,分别进行喷砂处理、硅烷偶联剂处理及喷砂+硅烷偶联剂处理,以未作任何处理的为对照组。将处理后的试件用聚羧酸锌水门汀进行黏结,采用万能力学测试仪测试拉伸强度。 结果与结论：对照组、喷砂组、硅烷偶联剂组、喷砂+硅烷偶联剂组的拉伸强度分别为(0.68±0.04),(1.00±0.02),(1.31±0.08),(1.09±0.04) kN,各组间比较差异有显著性意义(P均< 0.01)。对照组金属表面光滑,可见一些不规则的表浅细小纹络;喷砂组金属表面呈现出不规则的鳞状突起,有利于黏结剂的渗入;硅烷偶联剂组金属表面表现为规则的蜂窝状结构,有利于黏结剂的嵌合;喷砂+硅烷偶联剂组金属表面表现为大小不等的金属突起,金属表面粗糙,利于黏结。说明喷砂和硅烷偶联剂均能显著提高金属套冠间的黏结强度,并且硅烷偶联剂处理效果最好,其次为喷砂联合硅烷偶联剂处理。中国组织工程研究杂志出版内容重点：生物材料;骨生物材料; 口腔生物材料; 纳米材料; 缓释材料; 材料相容性;组织工程全文链接：     

An investigation of the shear bond strength of compomer restorative material to enamel and dentine

The aim of this study was to investigate the effect of one step adhesives on the shear bond strength of a compomer restorative material to both enamel and dentine. Human extracted teeth were used for the study. Ten samples were prepared for both enamel and dentine specimens for each of the five groups: Tooth, no etch, Prime and Bond NT (P+B NT); tooth, Non-Rinse Conditioner (NRC), P+B NT; tooth, NRC, Prime and Bond 2.1 (P+B 2.1); tooth, etch, P+B NT; tooth, etch, P+B 2.1. The specimens were subjected to bond testing. The shear bond strength was measured using an Inston 1193 testing machine using a cross head speed of 1 mm/minute. The specimens were tested to destruction. The results show that for the enamel specimens the highest bond strength was recorded for those specimens subjected to Etch, P+B 2.1 (22.1 MPa) and Etch P+B NT (20.0 MPa). The groups of specimens which did not undergo etching had very low bond strengths ranging from 11.4 MPa for NRC, P+B 2.1, 8.5 MPa for NRC P+B NT to 6.9 MPa for P+B NT. For the dentine specimens, for all of the groups, the shear bond strengths were low. Those groups subjected to etching produced the highest values of 7.9 MPa for NRC P+B 2.1 with the lowest value of 6.1 MPa for NRC P+B NT. These bond strengths were significantly lower than those achieved for bonding to enamel. Prime and Bond NT and Prime and Bond 2.1, used in conjunction with acid etching, produce satisfactory bond strengths of compomer restorative material to enamel. Bond strengths to dentine were low.     

不同表面处理对Ceramage聚合瓷黏结强度的影响

背景：长期以来修复材料与基牙的黏接技术一直是口腔修复学的研究热点,其中尤为引人关注的是黏结工件的表面处理工艺。 目的：对比观察8种表面处理方法对Ceramage聚合瓷黏结强度的影响,筛选适合Ceramage聚合瓷的表面处理方法。 方法：将Ceramage聚合瓷制成试件80个,随机分成8组,分别采用喷砂,酸蚀,偶联剂,喷砂+酸蚀,喷砂+偶联剂,酸蚀+偶联剂,喷砂+酸蚀+偶联剂处理聚合瓷表面并与树脂黏结剂黏结,对照组不进行任何处理。在37 ℃水浴24 h后测试样本剪切强度,并用扫描电镜观察处理后的聚合瓷表面形貌。 结果与结论：各组的剪切强度值由高到低分别为：喷砂+酸蚀+偶联剂处理组(31.12±2.81) MPa,喷砂+酸蚀组(27.62±1.70) MPa,酸蚀+偶联剂组(27.31±2.18) MPa,喷砂+偶联剂组(26.91±1.97) MPa,喷砂组(24.23±2.03) MPa,偶联剂组(23.50± 2.19) MPa,酸蚀组(17.61±2.14) MPa,对照组(8.13±0.63) MPa,除喷砂组、偶联剂组之间,喷砂+酸蚀组、喷砂+偶联剂组、酸蚀+偶联剂组之间比较差异无显著性意义外(P > 0.05),其余组间比较差异均有显著性意义(P  < 0.05)。结果显示7种表面处理方法都提高了黏结强度,喷砂、酸蚀联合硅烷偶联剂处理的聚合瓷黏结强度最高,是适合Ceramage聚合瓷黏结的表面处理方法。     

Effects of airborne-particle abrasion, sodium hydroxide anodization, and electrical discharge machining on porcelain adherence to cast commercially pure titanium

The aim of this study was to determine the effect of airborne-particle abrasion (APA), sodium hydroxide anodization (SHA), and electrical discharge machining (EDM) on cast titanium surfaces and titanium-porcelain adhesion. Ninety titanium specimens were cast with pure titanium and the alpha-case layer was removed. Specimens were randomly divided into three groups. Ten specimens from each group were subjected to APA. SHA was applied to the second subgroups, and the remaining specimens were subjected to the EDM. For the control group, 10 specimens were cast using NiCr alloy and subjected to only APA. Surfaces were examined by using scanning electron microscope and a surface profilometer. Three titanium porcelains were fused on the titanium surfaces, whereas NiCr specimens were covered with conventional porcelain. Titanium-porcelain adhesion was characterized by a 3-point bending test. Statistical analysis showed that the porcelain-metal bond strength of the control group was higher than that of the titanium-porcelain system (p < 0.05). There were no significant differences between the bond strengths of titanium groups (p 0.05), except the bond strengths of Noritake Super Porcelain TI-22 groups on which APA and SHA were applied (p < 0.05). SHA and EDM as surface treatment did not improve titanium-porcelain adhesion when compared to APA.     

Evaluation of an experimental dental porcelain

The aim of this study was to evaluate fracture toughness, hardness, ceramic/metal bond strength and microstructure of experimental dental porcelain and compare it with commercial type. Specimens of specific dimensions were prepared. Fracture toughness was assessed by a three-point bending test. The Vickers hardness was measured using a microhardness tester. The ceramometal bond strength was measured using a universal testing machine. The load was applied at the porcelain/metal interface via a chisel edged blade with a crosshead speed of 2.0 mm/min until fracture. The polished specimens of dental porcelain were chemically etched and the microstructure was analyzed with a scanning electron microscope. The results showed comparable fracture toughness and bond strength for both materials, while the experimental porcelain exhibited higher hardness. The experimental porcelain showed uniform cohesive failure while the commercial type showed mixed mode of failure. The microstructure of the experimental porcelain was tetragonal leucite crystals dispersed randomly in a glass matrix. The leucite crystals exist in two forms, acicular and rod like structures. It was concluded that the experimental porcelain has adequate fracture toughness and ceramic/metal bond strength that can resist the rapid crack propagation and its consequent catastrophic failure, which indicates a material serviceability in the oral cavity.     

氮化钛涂层和黏结瓷对钛瓷结合强度的影响

背景：氮化钛涂层与黏结瓷均可改善钛瓷结合强度。 目的：观察氮化钛涂层和Noritake Ti-22黏结瓷对钛瓷结合强度的影响。 方法：将32个纯钛铸件表面喷砂后分为4组：纯钛组、氮化钛涂层组、黏结瓷涂布组、氮化钛涂层联合黏结瓷涂布组。将处理后各组试件中间部分烤瓷,运用三点弯曲方法测试各组金瓷结合强度。 结果与结论：纯钛组钛瓷结合力低于氮化钛涂层组、黏结瓷涂布组、氮化钛涂层联合黏结瓷涂布组(P < 0.05),后3组组间结合强度差异无显著性意义(P > 0.05)。氮化钛涂层组、黏结瓷涂布组、氮化钛涂层联合黏结瓷涂布组钛瓷界面结合紧密,无明显孔隙和气泡;纯钛组钛瓷结合界面有明显孔隙。说明氮化钛涂层和黏结瓷的应用有利于提高钛瓷结合强度,单两种处理方法同时作用并不能更好地提高钛瓷结合强度。     

Wear of conventional and cross-linked ultra-high-molecular-weight polyethylene acetabular cups against polished and roughened CoCr femoral heads in a biaxial hip simulator

The wear of acetabular cups made from conventional gamma-sterilized, and electron-beam cross-linked ultra-high-molecular-weight polyethylene was studied with a biaxial hip wear simulator. The femoral heads were either polished or roughened so that they represented the type of roughening and the value of surface roughness (R(a) = 0.14-0.18 micro m) observed in the roughest explanted femoral heads. The lubricant was diluted calf serum, and the test length 3 million cycles. The mean wear rate and standard deviation of conventional polyethylene cups against polished and against roughened heads was 11.6 +/- 0.07 and 64.4 +/- 10.1 mg per 1 million cycles, respectively. The latter value closely corresponds to that measured from explanted Charnley prostheses. Against polished heads, cross-linked polyethylene cups showed net weight gain, whereas against roughened heads, their mean wear rate was 2.4 +/- 0.3 mg per 1 million cycles. The mean equivalent circle diameters of polyethylene wear particles produced in the above four categories were: conventional/roughened 0.32 micro m, cross-linked/roughened 0.29 micro m, conventional/polished 0.28 micro m, cross-linked/polished 0.23 micro m. The size ranges and shapes were close to those seen in particles isolated from tissue samples. In conclusion, the tests indicated that electron-beam irradiation effectively reduces the harmful polyethylene wear particle production in total hip arthroplasty.     

Fibre reinforced bioresorbable composites for spinal surgery

Composites containing different amounts of beta-tricalcium phosphate (beta-TCP) embedded in a poly-lactide (PLA70) matrix with and without poly-lactide (PLA96) fibre reinforcement were studied and the feasibility of using these composites in spinal fusion implants was examined. Compressive yield strength was measured in two directions: parallel to (83-97 MPa) and perpendicular to (108-123 MPa) the laminated structure of the composites. In the parallel direction, the addition of beta-TCP decreased compressive yield strength while in the perpendicular direction this was increased when compared to plain specimens (p<0.05). Fibre reinforcement had no significant effect on compressive yield strength (p<0.05), but did increase impact strength by 127-216% for notched specimens (parallel direction) and by about 65% for un-notched specimens (perpendicular direction) (p<0.05). A 24 week in vitro analysis of implant prototypes in simulated body fluid revealed a decrease in compressive yield strength, which was greater for the samples containing 50 wt.% beta-TCP than for those containing 25 wt.% beta-TCP. After 12 weeks incubation the composites retained 66-99% of their initial compressive strength, depending on composition. After 24 weeks incubation the lowest compressive strength was 51% (56 MPa: 50/50) and the highest was 94% (90 MPa: 75/25) of the initial value. Calcium phosphate precipitation on the surfaces of the materials in vitro was also observed. The initial compressive strengths of the studied composites were comparable to materials used in spinal fusion applications, but adequate strength retention behaviour needs to be confirmed before undertaking clinical experiments.     

Textural characterization of finished and polished composites over time of intraoral exposure

This in situ study sought to evaluate the surface roughness evolution of resin composites finished and polished by different methods. A total of 108 rectangular-shaped specimens of a microfilled and a hybrid composite were cured against a Mylar matrix strip and left unpolished or instrumented with diamond burs, Al2O3-coated disks, Al2O3-impregnated UDMA disk, or with diamond burs followed by either one of the disks. After specimens had been profiled for the average surface roughness (Ra, microm), 18 volunteers wore a removable palatal appliance, which accommodated one specimen of each one of the 12 groups investigated. Surface roughness for up to 28 days of intraoral exposure was then measured at 1- or 7-day intervals. A split-plot ANOVA (alpha = 0.05) revealed a significant interaction between group and time. Tukey's test and regression analyses ascertained that initially finishing with burs only provided the roughest surface to both composites. Unpolished surfaces and those specimens polished with Al2O3-coated disks, regardless of previous use of diamond burs, attained smoother surface. The Al2O3-impregnated UDMA disk was capable of smoothening the surface of the hybrid material previously finished with diamond burs. The roughness achieved after finishing and polishing composites may be either smoothened or roughened after intraoral exposure. On the basis of the roughness range, it is advisable to use Al2O3-coated disks, regardless of whether diamond burs were previously used. Al2O3-impregnated UDMA disks (with or without previous application of diamond burs) may be also suitable for instrumenting hybrid restoratives.     

Bond strength of adhesively luted ceramic discs to different core materials

The purpose of this in vitro study was to compare the shear bond strengths of resin, glass-ionomer, and ceramic-based core materials to all ceramic discs. Five core materials (Core max, Sankin; Clearfil AP-X, Kuraray; Empress Cosmo, Ivoclar-Vivadent; Photocore, Kuraray; Dyract Extra, Dentsply) were prepared as discs 10 mm in diameter and 2 mm in height according to the manufacturer's instructions. Ten disc specimens per group were prepared, and dentin served as the control. All resin specimens were embedded in autopolymerizing acrylic resin, with one surface facing up. All ceramic discs (IPS Empress I, Ivoclar-Vivadent) 3 mm in diameter and 2 mm in height were prepared and bonded to core specimens with a dual-curing luting resin cement (Variolink II, Vivadent). Specimens were stored in distilled water at 37 degrees C. Shear bond strength of each sample was measured after 24 h using a universal testing machine at a crosshead speed of 0.5 mm/min. The data were analyzed with one-way analysis of variance and Tukey HSD tests (alpha = 0.05). Shear bond strength varied significantly depending on the core material used (p < 0.05). Clearfil AP-X and Photocore showed the highest shear bond strength value while Empress Cosmo provided the lowest (p < 0.05). There were no statistically significant differences among Clearfil AP-X, Photocore, and Core-Max (p > 0.05). And also there were no statistically significant differences between Dyract Extra and the control group (p > 0.05). In vitro shear bond strengths of ceramic discs bonded to resin-based core materials showed higher bond strength values than ceramic-based core material.     

Effect of surface treatment on the shear bond strength of three resin cements to a machinable feldspatic ceramic

The aim of this study was to evaluate the shear bond strength of three resin cements to Vita Mark II ceramics under different pretreatments of the ceramic surface and to examine whether simplified pretreatment procedures would result in satisfying results compared to the state of the art. RelyX Unicem (RXU), Calibra (CAL), and Variolink II (VAR) were used as resin cements and bonded to machine milled feldspatic disks, pretreated in five different ways. (1) no pretreatment of the ceramic surface; (2) surface etched with hydrofluoric acid (HF); (3) ceramic surface silanized; (4) ceramic surface etched (HF) and silanized, (5) ceramic surface etched (HF), silanized, and covered with Heliobond. The shear bond strengths were measured initially, after 5000 and 10,000 thermocycles (TC). After 10,000 TC for CAL only procedure 5 resulted in a reliable adhesion median value of 10.7 MPa. VAR showed median values of 24.6, 17.2, and 18.1 MPa for pretreatments 5, 3, and 4, respectively. RXU performed 25.9, 22.0, and 11.0 MPa for procedures 5, 4, and 3, respectively. For procedure 2, RXU revealed the significantly highest value with 15.4 MPa (U-test, p = 0.05). Only RXU-luted specimens of procedure 1 survived the 10,000 thermocycles. The results revealed that a simplification of the ceramic pretreatment for VAR and RXU might be possible.     

Calcium phosphate apatites with variable Ca/P atomic ratio III. Mechanical properties and degradation in solution of hot pressed ceramics.

Calcium deficient hydroxyapatite powders Ca(10-x)(PO4)(6-x)(HPO4)x(OH)(2-x) (0 < or = x < or = 1) were hot pressed to produce dense hydroxyapatite-tricalcium phosphate (HAP/TCP) biphasic materials. Ceramics hot pressed at 1000 degrees C were composed of an homogeneous distribution of the HAP and beta-TCP grains with an average size of 0.2 microm. Grain growth was observed for TCP loading > 70 wt%. The strength exhibited a maximum of sigma(f) = 150 MPa for 90/10 (w/w) HAP/TCP and it dropped for smaller and greater amounts of TCP. This value was twice that of pure HAP. When placed in Ringer's solution, only the surface of biphasic compounds was degraded after 60 days of immersion with a preferential etching of the TCP phase. After hot pressing at 1200 degrees C, grain growth was observed and the mechanical properties were decreased. This was explained by the allotropic transformation alpha/beta of TCP.