Femtosecond laser microstructuring of monolithic zirconia: Effects of laser parameters on resin bond strength

This study aimed to investigate the effects of different femtosecond (fs) laser treatment protocols on the surface roughness (Ra) and shear bond strength (SBS) of resin cement to zirconia. A total of 110 zirconia specimens were divided into 11 subgroups according to the surface treatment: Control (C), airborne-particle abrasion (APA), laser irradiation applying 400 mW, 600 mW, and 800 mW of 90 fs laser pulses with 1, 5, and 10 repetitions (Fs_(400/1), Fs_(400/5), Fs_(400/10), Fs_(600/1), Fs_(600/5), Fs_(600/10), Fs_(800/1), Fs_(800/5), and Fs_{(800/10) )}, respectively). Ra values were measured using a profilometer, and topographical changes were evaluated under a scanning electron microscope. X-ray diffraction analyses were performed to determine the crystallographic changes. Self-adhesive resin cement was bonded to zirconia specimens, and SBS tests were conducted. C and Fs_(800/10) groups exhibited the lowest and the highest Ra and SBS values, respectively. Regardless of the fs laser power, application of five and 10 repetitions resulted in higher Ra values than air-abrasion. Fs_(400/10), Fs_(600/5), Fs_(600/10), Fs_(800/5), and Fs_(800/10) groups showed higher SBS values than the APA group (p < .05), while SBS of other laser groups did not differ from the APA group (p > .05). Fs laser treatment protocols used in this study may be promising for zirconia-resin bonding. However, the effects of these treatments on the mechanical properties of zirconia need evaluation.     

Effect of monolithic zirconia on the degree of conversion of two resin cements analyzed by FT-IR/ATR spectroscopy

Objective: This study aimed to evaluate the degree of conversion (DC) of two different resin cements polymerized under the monolithic zirconia specimens in different thicknesses and colors.

Material and methods: Partially stabilized monolithic zirconia blocks (inCoris TZI) were cut into three different thicknesses (0.5, 1.0, and 2.0 mm) and the specimens were divided into four color groups (A1, A2, A3, and A4). The light transmittance of each specimen was measured. Panavia F 2.0 or Variolink N resin cement was applied into teflon mold and irradiated using the light emitting diode curing unit for 20 s under monolithic zirconia specimen (n = 10). The resin cement specimens were stored at room temperature under dry conditions. The DC of each specimen was measured by Fourier transform infrared-attenuated total reflection (FT-IR/ATR) spectroscopy after the 1st and 10th day. Data were analyzed with two-way analysis of variance (ANOVA), two-way repeated measures ANOVA, three-way repeated measures ANOVA, and the Tukey least significant difference (LSD) tests (α = 0.05).

Results: The light-cure resin cement groups showed higher DC than the dual-cure resin cement groups (p < 0.05). The DC of both resin cements reduced with an increase in the thickness and darkening of the color of monolithic zirconia specimens. There was a statistically meaningful increase in the 10th-day values for dual-cure resin cement (p < 0.05), whereas there were no significant differences between the 1st- and 10th-day values for light-cure resin cement (p > 0.05).

Conclusion: The use of light-cure resin cement can be suggested for the luting of monolithic zirconia restorations.     

Bond strength of fiber posts and short fiber-reinforced composite to root canal dentin following cyclic loading*

The aim of this study was to evaluate the effect of cyclic loading on the bond strength of fiber posts and short fiber-reinforced composite (FRC) to root canal. One hundred single-rooted teeth were divided into two groups according to the material used for luting fiber posts: (1) Resin-core material (Gradia Core, GC Corp.) and (2) Short FRC (EverX Posterior, GC Corp.). Then the specimens were randomly assigned into three sub-groups according to the post material and the groups are indicated as follows: (1) Short FRC (EverX Posterior) used instead of post and core, (2) Fiber post (GC post, GC Corp.) cemented with resin-core (Gradia Core), (3) Fiber post (GC post, GC Corp.) cemented with short FRC (EverX Posterior), (4) Experimental fiber post cemented with resin-core (Gradia Core, GC Corp), (5) Experimental fiber post cemented with short FRC (EverX Posterior). Then the specimens were subdivided into a further two groups in accordance with the storage condition (cyclic loading and 24 h water storage-control group) (n = 10/per group). The micropush-out bond strength between root dentin and posts was measured. Data were analyzed using three-way ANOVA and Tukey HSD tests (α = 0.05). Micropush-out bond strength of the posts to dentin was significantly affected by the type of post material (p < 0.05). However, the load cycling and the resin-based luting agent used had no effect on bond strength values (p = 0.706 and p = 0.346, respectively).     

Effect of ceramic surface treatments on the bond strength of different composite resins

This study was aimed to observe the relationship between the different surface treatments and the bond strength of both composite based adhesive cement and zirconia ceramic. Thirty-two zirconia ceramic discs were fabricated by following the instructions of manufacturer (5 × 5 × 1.5 mm). Four subgroups were obtained from the specimens according to the specified surface treatments respectively: (a) C: control groups: no treatment; (b) SB: sandblasting with 125 μm aluminum oxide particles for 10 s; (c) SC: silica coating for 10 s; (d) Nd :YAG laser . The composite resin specimens Panavia F and Clearfil SA were introduced and polymerized to the treated bonding areas. Afterwards the specimens were stored in distilled water at 37 °C during 24 h, and the shear test was applied. The data were statistically analyzed by ANOVA and Duncan tests. The bond strength was stated significantly higher in silica coating/Panavia F group (23.35 MPa). The lowest bond strength was stated in control groups cemented with Clearfil SA (12.25 MPa). As a result it was determined that the bond strength has affected the both surface treatments and cement types (p < 0.001). The silica coating –treated zirconia ceramic recorded a significant increase in mean bond strength values.     

Effect of femtosecond laser beam angle and formed shape on surface roughness and shear bond strength between zirconia and resin cement

Achieving adhesion between resin cement and zirconia requires pretreatment of the surface. This in vitro study aimed to evaluate the effect of femtosecond laser beam angle and the shape of the formed surfaces, on the roughness and shear bond strength (SBS) of resin cement to zirconia ceramic. Seventy Y-TZP ceramic specimens were divided into seven groups (n = 10). A femtosecond laser irradiation was performed on the ceramic surface of three shapes (spiral (SP), square (SQ) and circular (CI) and at two angles (30 and 90°) to give SP-30, SQ-30 and CI-30 and SP-90, SQ-90 and CI-90, respectively. After treatment, the surface roughness of all specimens was evaluated using a profilometer. One specimen from each group was analysed using a scanning electron microscope. The bonded specimens were thermocycled 5000 times and then an SBS test was performed. Kruskal-Wallis and Mann-Whitney U tests were used to analyse surface roughness and SBS values. The control group had statistically lower surface roughness (R_a) values than the treated groups (p < 0.05). SP-30 and SQ-30 laser treated specimens showed higher R_a values than the other specimens. Statistically significant SBS values (p = 0.000) were observed between the groups. All laser treated samples showed greater SBS compared to the control group. SP-30, SQ-30 and SQ-90 groups showed the highest SBS values. Within the limitations of this experimental study, the highest mean values for R_a and SBS were achieved with SP and SQ surfaces using a 30° angle laser beam.     

The influence of zirconia fibre on ablative composite materials

ABSTRACT

Zirconia fibres have excellent high temperature ablation resistance and have been widely used in ablative materials. In this paper, zirconia fibre was used for reinforcing the ablative composite materials to study the influence of zirconia fibre had upon the mechanical properties and the high temperature ablation properties of such composites. The results showed that the bending strength of the material was also good and reached a maximum of 13.05?MPa. After sintering at 1400°C, the bending strength was also great which could reach 13.05?MPa. In addition, the corrosion resistance of the composites was excellent and the oxygen-acetylene line ablation rate was 0.03?mm?s^?1 when the fibre content was 30?wt-%.     

Dynamic wear characteristics and fracture strength of high-translucent monolithic zirconia crowns

The dental ceramic restorations inevitably undergo a wear damage. The dynamic wear behavior and fracture strength after wear fatigue of the high-translucent zirconia crowns have rarely been studied. In the present study, the zirconia crowns were fabricated using a high-translucent zirconia material and subsequently cemented to the PMMA abutments with a resin cement. The specimens were fixed in a chewing simulator and dynamically loaded for 3.6 million fatigue cycles (a maximal load of 350 N, 1.7 Hz). The wear volume and wear rate at the designated checkpoints between 0–36 × 10⁵ cycles with an interval of 3 × 10⁵ cycles were measured. The fracture strength of the zirconia specimens before wear fatigue as well as after 9, 24 and 36 × 10⁵ cycles was analyzed. The morphology of the wear surface was observed by SEM. The results showed that the wear volume increased with the wear cycles. In the initial stage (0–9 × 10⁵ cycles), the wear rate remained at a significantly high level (about 0.289–0.349 mm³/10⁵ cycles). Subsequently, it decreased rapidly and stabilized at a relatively low level (about 0.052–0.081 mm³/10⁵ cycles). As the number of fatigue cycles was increased, the fractured strength decreased significantly, except after 9 × 10⁵cycles. The worn surface after wear were flattened, and only a small number of scattered cracks and small punctate defects were observed. The high-translucent zirconia crowns exhibited dynamic wear characteristics, and the fracture strength decreased significantly.     

Effect of different surface treatments on the shear bond strength of resin cement to zirconia ceramic and metal alloy*

The bonding of resin cement to ceramic materials plays an important role in dentistry. The purpose of this study is to evaluate the effects of various surface treatments on the shear bond strength (SBS) of zirconia ceramic and metal alloy. A total of 60 specimens were prepared from Y-TZP ceramic and metal alloy. The specimens were divided into three subgroups (n = 10) that received different surface treatments for each material. An Er:YAG laser (ER), a femtosecond laser (FS), and air-borne particle abrasion (A) were employed as surface treatments. One specimen from each group was analyzed using a scanning electron microscope (SEM) at 500 x magnification after surface treatments. The self-adhesive resin cement was then bonded to the treated surfaces using a Teflon mold. The specimens were thermocycled for 5,000 cycles at 5–55 °C, and then the SBS test was performed. Kruskal–Wallis and Mann–Whitney U tests were used to determine the differences between the groups (p = 0.05), and failure modes were evaluated for each specimen. Statistical analyses revealed significant differences between the surface treatment methods. The mean SBS values of the air-borne particle-abraded groups were higher than those of the other groups. The femtosecond-irradiated groups of each material showed significantly higher SBS values than the Er:YAG-irradiated groups (p < 0.05). Within the limitations of this study, air-borne particle abrasion and the femtosecond laser were more effective than Er:YAG laser treatment.     

Effect of Er,Cr:YSGG laser surface conditioning on the adhesion of fiber- reinforced composite and zirconia intraradicular posts to the root dentin

This study evaluated the influence of Er,Cr:YSGG laser surface conditioning on push-out bond strength of different root posts to the root dentin. Extracted (N = 27, n = 9 per group) and endodontically treated human mandibular premolars were prepared to receive the posts. Three types of posts, namely quartz fiber (D), glass fiber (S), and zirconium dioxide post (C) were luted with resin cement. The posts were randomly assigned to one of the surface conditioning method: (a) No conditioning, control (L0), (b) Er,Cr:YSGG laser at 175 mJ, 3.5 W for 60 s (L1), and (c) at 225 mJ, 4.5 W for 60 s, with 60 μs pulse duration and repetition rate was 20 Hz (L2) irradiation. Six sections (two coronal, two middle, and two apical) were made in each tooth yielding to 1 mm thick specimens. The specimens were stored in distilled water at 37?°C for 24 h and push-out bond strength (MPa) was tested in a Universal Testing Machine (1 mm/min). Data were analyzed using Kruskall–Wallis and Dunns`s post hoc tests (α = 0.05). In group D, both laser treated groups (L1:16.16 ± 19.89; L2:8.24 ± 9.26) presented significantly less bond strength compared to control group (L0:28.3 ± 16.8) (p < 0.001). Mean push-out bond strength values did not significantly differ according to the root segments (coronal, middle, and apical) (p = 0.106). Application of Er,Cr:YSGG laser, with the parameters tested, did not increase the bond strength of zirconium glass fiber and zirconium oxide posts. Laser surface conditioning decreased the bond strength of quartz fiber posts in the root canal.     

Wettability modification of zirconia by laser surface texturing and silanization

This paper presents the modification of wettability by nanosecond laser surface textured followed by silanization to fabricate the superhydrophobic zirconia surface. Surface modification by varying the pitch between channels leads to micro-channel and micro-grid pattern with different surface roughness. The generated morphological and metallurgical modifications of the surface are measured by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Numerous micro-pits and cracks in the laser-treated areas can be observed from SEM, which indicates crack propagation dominating the process of laser ablation of zirconia. The surface is superhydrophilic with laser-texturing instantly, whose wettability is modified over time. By analyzing the XPS, carbon content, especially C-C (H) groups, is important for the time-dependent wettability. The hydrophobicity of all laser-textured surfaces is improved after silanization. Laser texturing with smaller pitch (50 μm and 70 μm) leads to superhydrophobic surfaces after silanization, which may be due to the modification of physicochemical properties of substrate by very rapid local heating and cooling on the thick surface layer. Overall, the investigations indicate that wettability modifications can be attributed to the surface's microstructure, which depend on laser processing parameters, and chemical composition, especially in terms of −CF₃, −CF₂, and C-C (H).     

Adhesive bond strength and compressive strength of a novel bulk fill composite with zirconia nano-hybrid filler

The aim of the study was to investigate the adhesive bond and compressive strength of novel bulk fill resin composite with zirconia (Zr) nano-hybrid filler. Sixty molars were mounted in acrylic resin with flat occlusal surface. Half of the specimen (n = 30) were bonded using total etch (TE) and the other half with self-etch (SE) technique. Specimens treated with SE (n = 30) and TE (n = 30) bonding protocol were divided into three groups, based on the type of bulk fill build-up materials (ZC–ZirconCore, MC–MulticCore Flow and LC–Luxacore Dual), resulting in six study groups [MC-TE, MC-SE, LC-TE, LC-SE, ZC-TE, ZC-SE]. Cylindrical (3 × 3 mm) build-ups were performed followed by shear bond strength testing (crosshead speed-1 mm/min). Ten specimens for each bulk fill build-up material (MC, LC and ZC) were prepared for compressive strength testing. All specimens were tested for maximum failure loads (crosshead speed?0.5 cm/min). Analysis of variance and paired t-test were performed to statistically analyze the data. TE technique showed significantly higher bond strength values as compared to SE technique (p < 0.001) for all three materials (MC, LC and ZC). Shear bond strength for MC [TE,17.88(2.00)-SE,9.43(0.98)] and LC [TE,18.91(2.57)-SE,6.35(1.12)] groups were significantly higher than ZC group [TE,13.99(1.09)-SE,4.61(0.84)]. Specimens in ZC group (266.73 ± 9.76) showed significantly higher compressive strength in comparison to MC (247.66 ± 9.72) (p = 0.004) and LC (249.87 ± 13.17) (p < 0.001) groups. Zirconia nano-hybrid filler resin bulk fill material has comparatively high compressive strength and low bond strength making them suitable for clinical applications in the posterior region with favorable conditions for adhesive bonding.     

Effect of hot-etching treatment on shear bond strength of zirconia to resin cement

ABSTRACT

The purpose of this study was to evaluate the effect of hot-etching surface treatment on the shear bond strength between zirconia ceramics and resin cement. Ceramic cylinders were divided randomly into 10 groups (n?=?10) according to different surface treatments (blank control; airborne particle abrasion; hot-etching for 10?min; hot-etching for 30?min; hot-etching for 60?min) and whether or not performed thermal cycling fatigue test. Flat enamel surfaces, were prepared from human permanent incisors and were bonded to the zirconia discs. All specimens were subjected to shear bond strength test by a universal testing machine. All data were statistically analysed using one-way analysis of variance and multiple comparison least significant difference tests (α?=?0.05). Hot-etching for 60?min treatment produced higher bond strengths than the other treatment. Surface treatment of zirconia with a hot-etching solution might enhance surface roughness and bond strength between zirconia and resin cement.     

Effect of different surface shapes formed by femtosecond laser on zirconia-resin cement shear bond strength

Objective: The purpose of this study was to evaluate the effect of different surface shapes formed by femtosecond (FS) laser on zirconia (Y-TZP)-resin cement shear bond strength (SBS). Background data: All ceramic restoration is used as an alternative to metal-ceramic restorations, due to its better aesthetics, strength, and toughness properties. However, bond strength of restoration to tooth and other materials is effective to long term success of the restoration, and to achieve it surface treatment is required on ceramic surface. Materials and methods: Forty square-shaped zirconia samples were prepared and assigned to four groups of 10. The details of the groups are as follows: Group A, square-shaped recessed surface; Group B, square-shaped projection surface; Group C, circular-shaped recessed surface; Group D, circular-shaped projection surface. The SBSs values were performed with a universal testing machine at a crosshead speed of 1 mm/min. The data were analyzed statistically using analysis of variance (ANOVA) and Tukey HSD multiple comparisons tests. Results: The one-way ANOVA results on SBSs of the zirconia material bonded with resin cement revealed significant differences among the groups (p < 0.05). The Tukey HSD test results revealed that Group B and D had significantly higher SBS values than other groups (p < 0.05), but there were no significant differences between each other (p > 0.05). Additionally, Group A and C had significantly lower values than other groups (p < 0.05). Conclusions: Different surface shapes formed by FS laser provided a significant increase in SBSs. The SBS values of projection surfaces of circular and square-shapes are greater than that of recessed surfaces of circular and square-shapes.     

Effect of aging process on some properties of conventional and multilayered translucent zirconia for monolithic restorations

The purpose of this study was to evaluate the surface characteristics and optical and mechanical properties of materials through hydrothermal aging using different types of translucent monolithic zirconia.Three conventional materials (LT, KT, and ET) and three multilayered materials (LM, KM, and EM) of translucent monolithic zirconia were investigated. 45 bar-shaped specimens in each group were fabricated for the measurement of surface characteristics and mechanical properties and were randomly divided into 3 subgroups. 10 plate-shaped specimens in each group were fabricated for the measurement of optical properties. All specimens were autoclaved for 0, 5, and 10 h, respectively. The various properties of translucent monolithic zirconia, such as phase distribution, surface roughness, surface texture, elemental analysis, total transmittance (Tt), contrast ratio (CR), three point flexural strength (TFS), nanoindentation hardness (NH), and Young's modulus (YM), were measured through different tests. Statistical analyses were performed with one-way ANOVA, Tukey HSD post hoc test, independent sample t-test, paired sample t-test, and two-way ANOVA (α = 0.05).After aging, the monoclinic phase of all groups increased relative to the tetragonal phase. All groups exhibited an increase in the surface roughness and oxygen levels, but exhibited a decrease in the zirconium and yttrium levels (P < .05). All groups had increased microcracks and grain push-out. Tt increased and CR decreased in the LT, KT, and ET groups. However, Tt decreased and CR increased in the LM, KM, and EM groups (P < .05). The TFS, NH, and YM showed a decreasing tendency, but there were no significant difference in several materials (P > .05).Alterations in the surface characteristics were found on the surfaces of translucent monolithic zirconia after aging. The aging process caused conventional materials to become more translucent, but multilayered materials were more opaque. The various properties of translucent monolithic zirconia were affected by the materials fabricated with different types after aging.     

Effect of multi-walled carbon nanotubes on microstructure and fracture properties of carbon fiber-reinforced ZrB2-based ceramic composite

Multi-walled carbon nanotubes (MWCNTs) were used to optimize the microstructure and improve the fracture properties of hot-pressed carbon fiber-reinforced ZrB₂-based ultra-high temperature ceramic composites. Microstructure analysis indicated that the introduction of MWCNTs effectively reduced the carbon fiber degradation and prevented fiber-matrix interfacial reaction during processing. Due to the presence of MWCNTs, the matrix contained fine ZrB₂ grains and in-situ formed nano-sized SiC/ZrC grains. The fracture properties were evaluated using the single edge-notched beam (SENB) test. The fracture toughness and work of fracture of the C_f/ZrB₂-based composite with MWCNTs were 7.0±0.4 MPa m^1/2 and 379±34 J/m², respectively, representing increases of 59% and 87% compared to those without MWCNTs. The excellent fracture properties are attributed to the moderate interfacial bonding between the fibers and matrix, which favour the toughening mechanisms, such as fiber bridging, fiber pull-out and crack deflection at interfaces.     

Effect of surface conditioning methods on the microtensile bond strength of repair composite to indirect restorative materials

This study evaluated the effect of surface conditioning methods on the microtensile bond strength (µTBS) of a restorative composite to indirect restorative materials. Blocks (5?×?5 × 4?mm³) (N?=?72) of (a) Zirconia (In-Ceram Zirconia, Vita) (ZR), (b) lithium disilicate glass ceramic (IPS Empress II, Ivoclar Vivadent) (LD), (c) Indirect resin composite (Gradia, GC) (GR) were fabricated (n?=?24 per group) and divided randomly into three groups: 1-Control: no conditioning, 2-Silane coupling agent, 3-Hydrofluoric acid (9.5%) (HF)+silane. Each block was duplicated in resin composite. The adhesion surfaces were conditioned with airborne-particle abrasion (110?µm Al₂O₃ particles). Half of the conditioned blocks received no bonding and the other half one coat of bonding (ED Primer II, Kuraray). Each conditioned block was bonded to a composite block with a resin luting agent (Panavia F2.0, Kuraray). The blocks were sectioned into 1?mm² microsticks and tested for microtensile bond strength (µTBS) (0.5?mm/min) in a μTBS testing machine. Failure types were evaluated under stereomicroscope and Scanning Electron Microscope (SEM). Data were analyzed using three-way ANOVA, Bonferroni corrected and independent sample t-tests (p?<?0.05). Significant effect of the bonding (p?<?0.001) and surface conditioning (p?<?0.001) were observed in all groups. The highest mean bond strength values were obtained in the bonded, HF etched and silanized groups of ZR, LD and GR (12.4?±?2.9, 28.1?±?1.5 and 27.2?±?2?MPa, respectively). HF acid?+?silane increased the repair bond values in all materials. Majority of the failure types were adhesive for ZR group, whereas HF?+?silane conditioned LD and GR groups presented predominantly cohesive failures in the cement.     

The effect of different in-office bleaching techniques and etching procedures on bond strength of orthodontic brackets

The aim of this study was to compare the effects of different in-office bleaching techniques and acid/laser etching on bond strength of orthodontic brackets. Ninety-six extracted human premolar teeth were used in the study. The teeth were randomly divided into four groups according to different in-office bleaching techniques (n = 24); Group I: Diode laser-assisted bleaching, Group II: Er:YAG laser-assisted bleaching, Group III: In-office bleaching with LED, Group IV: Unbleached (control). After the samples were kept in artificial saliva for 2 weeks, each group were randomly divided into 2 subgroups according to etching methods; a–acid etching; b–laser etching. For laser etching Er,Cr:YSGG laser was used at 1.5 W, 15 Hz with 140 μs pulse duration for 20 s. For acid etching, 37% phosphoric acid was used for 30 s. The shear bond strength testing was performed using Instron Testing Machine with a crosshead speed of 1mm/min. Adhesive Remnant Index (ARI) scores were also measured. Data was analyzed using two-way ANOVA, Bonferroni, Kruskal Wallis and Mann Whitney U tests (p < 0.05). No statistically significant differences were found between bleaching groups and control (p > 0.05). There were statistically significant differences between acid and laser etching within each group (p < 0.05). Acid etching caused significantly higher bond strength values (p < 0.05). While no statistically significant differences were observed between the ARI scores of bleaching and control groups (p > 0.05), acid etching caused statistically higher ARI scores than laser etching groups (p < 0.05). In conclusion in-office bleaching either with LED or laser before bracket bonding did not affect bond strength. Prior to bracket bonding, acid etching of enamel caused higher shear bond strength values than laser etching.     

Effect of hydrothermal aging on dental multilayered zirconia for monolithic restorations: An in vitro study

The aim of this in vitro study was to investigate the changes in mechanical, optical, and surface properties of multilayered zirconia during hydrothermal aging.One conventional block (Katana Zirconia HT) and three multilayered blocks (Katana Zirconia ML, STML, and UTML) of monolithic zirconia were examined. Bar-shaped specimens were autoclaved at 134°C and 0.2MPa for 0, 5, and 10 h. The Young's modulus, three-point flexural strength, and nanoindentation hardness were measured to evaluate the mechanical properties. The surface roughness, phase distribution, surface microstructure, and elemental composition were measured to analyze the surface properties. The contrast ratio and total transmittance were measured via spectrophotometry to evaluate the optical properties. Statistical differences were analyzed using appropriate ANOVA, Tukey HSD post hoc tests, and independent and paired sample t-tests (α = .05).The monoclinic phase increased gradually after hydrothermal aging. The yttrium and zirconium concentrations decreased, and the oxygen concentration and the surface roughness increased in all specimens (P<.05) after the aging process. All specimens showed significant grain push-out and microcracks. The total transmittance increased, and the contrast ratio and Young's modulus decreased in all specimens (P<.05) after the aging process. The nanoindentation hardness and three-point flexural strength exhibited a decreasing tendency after the aging process. However, there were no statistical differences (P>.05) between the materials. Significant interactions between material grades and hydrothermal aging were found for all the properties studied (P<.001).Microstructural alterations and significant phase transformations were detected on the surface of the multilayered zirconia after hydrothermal aging. The hydrothermal aging led to increased surface roughness, opaqueness, and elasticity of multilayered zirconia. The optical, mechanical, and surface properties of multilayered zirconia were influenced by the grade of the material after hydrothermal aging. Careful consideration of the grade of materials is necessary for the appropriate selection of multilayered zirconia ceramics for monolithic restorations.     

氢气刻蚀法制备Pt/CNTs复合材料及其热稳定性

采用碳化硅高温热分解法制备整齐排列的直立碳纳米管阵列,并对其进行Pt金属粒子修饰,通过氢气刻蚀法可以将闭口碳纳米管阵列开口,并将Pt纳米粒子嵌入到碳纳米管中。这种新型Pt/CNTs复合材料具有独特的电子限域效应,有助于抑制金属催化剂的烧结,对提高其后续催化活性和应用性能有着重要意义。     

Effect of HF and NaOH etching on the composition and structure of SiOC ceramics

Porous SiOC ceramics were prepared with tetraethoxysilane (TEOS) and vinyltriethoxysilane (VTES) as sol?gel precursors, and followed by etching with HF and NaOH solution. The microstructure evolution and chemical etching as a function of pyrolysis temperature were investigated. The amorphous carbon increases as rising the temperature from 800 ^oC to 1200 ^oC, and the graphitic carbon increases with further etching by HF and NaOH. However, the effect of pyrolysis temperature on the structure of C is more significant. The hydroxylation reaction and phase separation of SiOC ceramics results in the increase of SiO₄ unit, which reacts with HF and NaOH to form micro- and mesopores. The existence of mesopore after HF etching provides more specific surface area and pore volume. However, NaOH etching produces more micropores, and the contribution of micropores to specific surface area and pore volume is higher than that of mesopores. Although HF and NaOH etching increase the specific surface area of SiOC ceramics, the etching effect of NaOH is superior to that of HF etching, and the carbon-enriched SiOC ceramics are obtained after NaOH etching.