Enhanced bioactivity and low temperature degradation resistance of yttria stabilized zirconia/clay composites for dental applications

Yttria stabilized zirconia (YSZ)/clay composites were produced to improve osseointegration and undesired tetragonal-to-monoclinic phase transformation (low temperature degradation, LTD) of YSZ ceramics so that long-term clinical success of YSZ implants is achieved. Various amounts (0.5,1,2, and 4 wt%) of clay was incorporated to YSZ. Predetermined amounts of clay and YSZ were mixed and pressed uniaxially at 15 MPa into compacts that were subsequently pressureless sintered at 1450 °C. Density, compressive strength, hardness and indentation crack resistance of 4 wt% clay incorporated YSZ/clay composite were 5.77 ± 0.01 g/cm³, 1188 ± 121 MPa, 1223 ± 9 HV, and 4.4 ± 0.1 MPa√m, respectively. Additionally, biological properties of YSZ/clay composites were assessed in vitro using bone cells. Incorporation of 4 wt% clay significantly enhanced bone cell proliferation, spreading, and functions. Moreover, a significant increase in the LTD resistance of YSZ was achieved upon 4 wt% clay incorporation. The findings collectively suggest that YSZ/clay composites have a potential to be used as an alternative material for dental applications.     

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.     

Influence of surface treatments on topography and bond strength of densely-sintered zirconium-oxide ceramic

The aim of this study was to evaluate the effect of surface treatments on the roughness and bond strength of dental materials containing MDP to zirconium oxide ceramic. Forty square-shaped zirconium-oxide ceramic blocks (Lava Zirconia, 3M-ESPE) were treated as follows: (CT) polished only; (SB) sandblasting (110 µm aluminum oxide particles) or (SC) silica coating (110 µm particles). Roughness of treated surface was measured using a profilometer (Ra) and by atomic force microscope (AFM). Two resin luting agents were used after silane application: self-adhesive (Rely X U200, 3M-ESPE) and dual cure (Rely X Ultimate, 3M-ESPE). The samples were submitted to microshear bond strength test. The failure analysis was performed. Data were submitted to ANOVA and Tukey test (α=0.05). Bond strength results ranged from 20.44 (CT+Ultimate) to 34.37 MPa (SC+U200) after 24 h and from 12.03 (CT+Ultimate) to 27.44 MPa (SC+U200) after 12 months of storage with SC statistically superior to the other treatments. Mean values of roughness varied from 0.07 (CT) to 0.85 µm (SC). The both resin luting agents showed similar results to all surface treatment groups. Silica coating provided the best treatment of the ceramic surface.     

Effect of cigarette smoking on the bond strength between resin cement and dental CAD/CAM ceramics

Although the effects of cigarette smoking on several dental problems have been widely studied, the association between tobacco exposure and resin-ceramic bonding is rarely reported. This study investigated the resin-ceramic adhesion (shear bond strength, SBS) and associated risk factors on three selected dental CAD/CAM ceramics using a novel model to simulate the exposure to cigarette smoking. Specimens from IPS e.max® CAD, Vitabloc® Mark II for Cerec and Zirconia Cercon were prepared and treated using silicacoating and silane. A layer of resin cement was applied on the treated ceramic surfaces and light activated. Specimens were placed in a chamber and challenged with various numbers of cigarettes (0, 1, 5, 10, and 15). Then, the specimens were subjected to SBS test and fractured surfaces were examined using scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometry (EDX) to determine the failure mode and surface composition. Overall, the mean SBS of IPS e.max^® CAD (9.6 ± 3.4 MPa), Vitabloc^® Mark II for Cerec (9.3 ± 2.5 MPa) and Zirconia Cercon (8.7 ± 3.0 MPa) did not show any statistical significant difference (p = 0.192 > 0.05), such that the adhesion of resin bonded to glass-based ceramics (IPS e.max® CAD and Vitabloc® Mark II for Cerec) decreased with cigarette smoke exposure, but increased for the resin bonded to zirconia ceramic (Zirconia Cercon). Furthermore, the number of cigarettes has a statistically significant effect on the SBS (p = 0.001), such that in general 5 cigarettes yielded the lowest mean SBS (7.6 ± 2.1 MPa). SEM-EDX analyses showed mostly adhesive failures in all experimental groups with changes in surface morphology and chemical composition after smoking challenge. Cigarette smoking produces a different effect on resin-ceramic bonding depending on ceramic type that may be due to chemical reactions in the bonding interface and changes in temperature and moisture. Further work should explore the mechanism to which cigarette smoke affects the resin-ceramic bonding and its clinical relevance.     

Heat treatment of silanized feldspathic ceramic: Effect on the bond strength to resin after thermocycling

PurposeThis study aimed to evaluate the effect of heat treatment (at 77 °C) of a silanized feldspathic ceramic on microtensile bond strength (μTBS) with a resin cement before and after being aged by thermocycling.Material and methodsTwenty-four blocks (12×10×4 mm³) of a CAD/CAM feldspathic ceramic (Vitablocks Mark II, Vita) were obtained and randomly divided into three groups, according to the surface treatment prior to the cementation: Group AS – hydrofluoric acid 10%+silane; Group S77 – silane+heating at 77 °C for 60 s; and Group AS77 – hydrofluoric acid 10%+silane+heating at 77 °C for 60 s. Ceramic blocks were cemented to composite resin blocks with a resin cement. The sets were subsequently cross-sectioned into 1 mm² beams for μTBS testing. The beams of each group were randomly divided into two subgroups: aging (thermocycling, 12,000 cycles between 5 °C and 55 °C) and non-aging (tested immediately). One-way ANOVA and Tukey's test (α=0.05) and Weibull analysis (95% CI) were used to analyze the data.ResultsGroup AS77 had the lowest pre-test failure number during the cutting among the groups. There was no significant difference (p=0.255) between the μTBS mean values of the non-aged groups. After aging, the mean value of S77 was significantly lower than those of AS77 and AS (p=0.005). There was no difference in the Weibull modulus (m) and characteristic strength (σ₀) of the aged and non-aged groups for all comparisons. Before aging, heat treatment of silanized feldspathic ceramic (non acid-etched surface) demonstrated bond strength similar to that achieved with hydrofluoric-acid-etching treatment however, it had lower bond strength after aging.ConclusionThe combination of hydrofluoric-acid-etching treatment with heat treatment silanized feldspathic ceramic did not improve the bond strength of the interface.     

Comparison of methanol/hydrochloric,ferric chloride acid versus tribochemical silica coating for adhesion of resin cement to zirconium dioxide

This study compared air-abrasion and etching regimens on adhesion of resin luting agent to zirconium dioxide. Ceramic specimens (LAVA, 3 M ESPE) (N = 16) were embedded in acrylic resin and exposed surfaces were polished. The specimens were randomly assigned into four groups (n = 12, 3 specimens for each disc): SC: Air-borne particle abrasion (30 μm aluminum oxide particles coated with silica, CoJet, 3 M ESPE); MH: Heated chemical solution (Methanol-800 mL; 37% Hydrochloric Acid-200 mL; Ferric Chloride-2 g) at 100 °C for 30 min, MHP: Primer (Metal/Zirconia Primer, Ivoclar Vivadent) + MH, P: Primer only (Metal/Zirconia Primer). Cylindrical molds (internal diameter: 0.7 mm; height: 1.5 mm) were placed on each conditioned specimen, filled with resin cement (Multilink Automix) and photo-polymerized for 60 s. After 24 h, the molds were removed and the specimens were stored in distilled water at 37 °C for six months). Microshear test was performed in a Universal Testing Machine (1 mm/min). Failures types were classified as adhesive, mixed, or cohesive. In another set of specimens (n = 2 per group) contact angle measurements were recorded. Data were analyzed statistically using Kruskal–Wallis and Dunn’s tests (α = 0.05). The surface conditioning method significantly affected the mean bond strength (MPa) (p < 0.0001): SC(18.3 ± 0.3)^a < P(5.00 ± 0.07)^b < MHP(4.7 ± 0.08)^c < MH(0.84 ± 0.01)^c. While Group SC showed mainly adhesive (58%) and mixed (41.7%) failure types, groups MH, MHP, and P presented exclusively adhesive failures. SC, MHP, and P (29–32°) showed lower contact angle than MH (78.9°). Volume loss was the highest with MHP (9.92 μl) followed by SC (9.67 μl).     

Influence of different etching protocols on the reliability of resin bonding to CAD/CAM feldspathic porcelain

ObjectivesTo evaluate the effects of different acid etching times on the mechanical strength of dental porcelain as well as the influence on the reliability of resin bonded CAD/CAM porcelain veneer.Material and MethodsRectangular CAM/CAM feldspathic porcelain (Mark II, Vita Zahnfabrik) specimens (12 mm×10 mm×4 mm) were prepared and polished with silicon carbide abrasive paper under running water. All the samples were randomly divided into four groups according to the corresponding etching protocols: control group (without any treatment), group A (etched with a gel etchant containing 5% hydrofluoric acid for 30 s and rinsed with de-ionized water), group B (etched for 1 min and rinsed), group C (etched for 2 min and rinsed). After silanization, resin stubs were adhered on porcelain surface. There are 25 resin–porcelain samples prepared in each group and subjected to the shear bond strength testing. Weibull analysis was conducted to evaluate of the reliability of resin–porcelain bonding. For each of the etching method, eight additional porcelain samples (3 mm×2 mm×10 mm) were prepared and etched. Then, surface roughness (R_a), microhardness (Vickers Hardness) and biaxial flexural strengths were measured on these porcelain specimens. Energy dispersive X-ray spectrometry technique was used to assess the changes in surface chemical composition after etching and the surface topography was recorded under atomic force microscope (AFM) and scanning electron microscopy (SEM).ResultsThe reliability of resin to CAD/CAM porcelain bonding was decreased with the increase in HF etching time. The application of HF etching for 30 s decreased the Vickers hardness number (HV) significantly from 651.6 (control group) to 488.7 (group A). With the extension of etching time, the Vickers hardness number was further reduced to 430.1 (group B) and 305.7 (group C). However, the biaxial flexural strengths of these four groups were not statistically significant different (p>0.05). AFM revealed the porous structures on the porcelain surface at microscopic level.ConclusionsThe application of HF to etch the CAD/CAM feldspathic porcelain surface reduced the microhardness number. Etching with 5% hydrofluoric acid on dental porcelain for more than 1 min might impair the reliability of resin bonded porcelain veneer.     

Anti-CMAS corrosion mechanism of Al2O3 pore sealing and laser remelting on thermal barrier coatings

The sol-dip-coating method and surface laser remelting technology are applied to form an Al₂O₃ layer on a YSZ coating surface to effectively block the environmental sediment CMAS. The behaviour and mechanism for CMAS corrosion of the coating are investigated, and the interfacial reliability of the coating and matrix is calculated by using the Monte Carlo method. The bonding force between the Al₂O₃ sol and YSZ coating can be effectively improved by laser surface treatment. Samples subjected to a laser pretreatment and posttreatment (YL-AL) of the YSZ coating are found to show the best interfacial bonding strength between Al₂O₃ and YSZ. Furthermore, the YL-AL sample shows a higher CMAS resistance than the laser posttreatment (Y-AL) samples, which effectively combines the chemical resistance of Al₂O₃ to CMAS and the physical resistance of the laser re-melted densification layer against CMAS penetration.     

Effect of thermal cycling and low pressure sandblasting on the bond strength of a self-adhesive cement to Y-TZP zirconia

The aim of this investigation was to assess the influence of several surface treatments on the shear bond strength (SBS) of a self-adhesive resin cement containing 10-methacryloxydecyl-dihydrogenphosphate monomer to densely sintered zirconia ceramic, before and after thermal cycles. Hundred densely sintered zirconia cylinders were divided into five groups (n = 20). Each of them received a different surface treatment: (1) control [No_T], with the zirconia surface unconditioned, (2) low pressure air abrasion [Sand_S], (50 μm, 1 bar), (3) standardized air abrasion [Sand_H], (50 μm, 2.8 bar), (4) standardized Rocatec? Plus (silica-coated alumina oxide) air abrasion (2.8 bar) and silanization [Roc_H], (5) low pressure Rocatec? Plus (silica-coated alumina oxide) air abrasion (1 bar) and silanization [Roc_S]. Five more surface-treated specimens were addressed to scanning electron microscope for qualitative observations. After specimen fabrication, subgroups of 10 bonded samples were stored in water either for 24 h (T1) or subjected to 5000 thermal cycles (T2); SBSs were determined with a universal testing machine at a crosshead speed of 1 mm/min. At T1, mean SBSs (MPa) obtained for the examined groups were: [Sand_H] 16.24 ± 2.95; [Sand_S] 16.01 ± 2.68; [Roc_H] 17.17 ± 1.64; [Roc_S] 15.92 ± 1.99. All surface treatments positively affected (p < 0.05) the initial self-adhesive cement adhesion to zirconia with respect to No_T (13.29 MPa). Artificial aging decreased the bond strength in all test groups significantly, but no spontaneous debonding was observed in [No_T]: at T2, SBS values ranged from 7.76 ± 2.37 (No_T) to 8.89 ± 1.74 (Sand_S), with no statistically significant difference between groups (p = 0.5293). Both air abrasion with alumina oxide and Rocatec? universal bonding system, used with hard or low air pressure, produced comparable effects on cement–zirconia interface before and after thermal cycles. After artificial aging, minimal differences in bond strength values between sandblasted and control groups were not of statistical significance.     

The effect of mechanical roughening and chemical treatment on shear bond strength of urethane dimethacrylate denture base resin

Relining of ill-fitting denture is often required to establish the fit of denture base, hence better retention and stability of the prostheses. However clinical success depends on the ability of reline resin to bond with denture base. The effect of surface preparations of urethane dimethacrylate (UDMA) denture base resin (Eclipse) on the shear bond strength (SBS) to auto-polymerizing polyethyl methacrylate reline material was evaluated. Eclipse specimens were mechanically prepared using two different tungsten carbide burs and submitted to chemical treatments either with dichloromethane (Secure adhesive) or methyl acetate (Eclipse Bonding Agent). Reline resin was then applied to the prepared surface and shear bond strength was tested after 24 h. Data was analyzed using two-way ANOVA and post-hoc Tukey HSD test at p=0.05. The morphological changes of Eclipse surfaces after preparations were also observed under SEM. The results showed that SBS was significantly affected by mechanical roughening, chemical treatment and their interactions. Higher reline SBS values were observed for Eclipse specimens without mechanical roughening compared to those with roughening. Both chemical agents improved reline SBS with the highest bond strength shown when chemically treated using Secure adhesive. For mechanically roughened specimens, Eclipse Bonding Agent (BA) resulted in significantly higher reline bond strength than Secure adhesive. SEM showed different surface appearance of Eclipse resin with various mechanical and chemical preparations.     

Experimental and computational study on sintering of ceramic coating layers with complex porous structures

This study investigated the sintering behavior of an yttria-stabilized zirconia coating for thermal barrier coatings (TBCs) with a complicated porous structure via both experiment and simulation using the finite element method for samples with only a coating (free coating) and samples with coating on a substrate (constrained coating). Sintering and grain growth proceeded from the bottom of the coating, and the coating bent convex upward in the free coating. In the constrained coating, sintering and grain growth proceeded in a manner similar to the free coating; however, the degrees of sintering and grain growth were small. Furthermore, sintering and grain growth were delayed because of substrate constraints. As a simulation result, the free coating was bent in a manner similar to the experiment. The experimental results could be reproduced in terms of time dependency and temperature dependency. The decrease in the porosity of the constrained coating was delayed compared with that in the free coating because of substrate constraints. This simulation result was able to reproduce the experimental results. Thus, the sintering behavior for the complex porous structures of TBCs can be predicted by experimental research and simulation, which could aid in the development of a prediction technology for the delamination of coatings (TBC lifetime).     

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 effects of dry and wet grinding on the strength of dental zirconia

The purpose of this study was to evaluate the effect of different dry and wet surface finishing on the mechanical strength and surface characters of a dental yttria-stablized zirconia ceramic (Y-TZP). Surface grinding treatments with a dental air turbine handpiece were performed with: coarse diamond (DC) and fine diamond (DF), tungsten carbide (Tc) and fine tungsten carbide (TcF) burs with or without water coolant. Air particle abrasion with 50?µm alumina (APA), combination of burs treatments or burs-abrasion, i.e. DC-TcF and DC-APA, were also performed with non-treatment group as control (C). Statistical analyses (α?=?0.05) on results revealed that all surface treatments significantly increased the surface roughness (Ra) than control (p?<?0.05), whilst decreased breaking force (BFN) and biaxial flexural strength (BFS). Tungsten carbide surface treatment could significantly lower (p?<?0.05) BFS and BFN, but DC only significantly lowered BFN. DC and tungsten carbide treatments exhibited significantly lower BFS values in wet than dry. A positive correlation was found between the BFS and BFN with the number of fragments. Only tetragonal phase of ZrO2 was presented by XRD. Synchrotron XRD revealed the (101) peak exhibits a broadening effect in the tungsten carbide treated specimens (38?nm for Tc and 30?nm for TcF), i.e. grain sizes in these specimens were smaller than the control (60?nm for C). This study outcome suggested that tungsten carbide burs should be avoided for grinding Y-TZP because of significant reduction in the BFS. Water cooling during grinding did not consistently reduce the potential heat damaging effects expected with dry grinding.     

Biaxial flexural strength and Weilbull characteristics of adhesively luted hybrid and reinforced CAD/CAM materials to dentin: effect of self-etching ceramic primer versus hydrofluoric acid etching

Abstract

This study evaluated the influence of the surface treatment and aging on the biaxial flexural strength of ceramic materials cemented to a dentin analogue. One hundred twenty disc-shaped specimens were allocated into 12 groups considering three study factors: ceramic material (lithium disilicate, leucite-based ceramic and hybrid ceramic), surface treatment (10% hydrofluoric acid etching?+?silane or self-etching glass-ceramic primer) and Aging (with 10,000 thermocycles of 5–37–55?°C or without). A tri-layer assembly was designed to mimic a cemented restoration (Variolink N) into a dentin analogue. All samples were submitted to the biaxial flexural strength assay. The flexural strength in MPa was calculated using the finite element method for each sample considering thickness, material properties, and the load to fracture during the in vitro test. Fractographic analysis was also performed. The data was evaluated using three-way ANOVA and Tukey test (α?=?5%). ANOVA showed influence for the Material*Treatment*Aging interaction on the flexural strength (p?=?0.011). The highest strength was calculated for lithium disilicate ceramic?+?self-etching ceramic primer without aging (499?±?17?MPa)^A and the lowest value for hybrid ceramic material?+?acid etching with aging (424?±?48?MPa)^E. According to the Weibull modulus, the most predictable strength was calculated for lithium disilicate?+?acid etching after aging. Acid etching or self-etching ceramic primer promotes similar immediate biaxial flexural strength for each evaluated ceramic. In the long-term, superior strength was observed using acid etching for lithium disilicate and the self-etching ceramic primer for the hybrid ceramic while no difference was observed for leucite-based ceramic.

Clinical implications: Some protocols combining the CAD/CAM ceramic material and the surface treatment could present suitable and stable flexural strength.     

表面处理对可生物降解黄麻/PLA复合材料结构和性能的影响

采用注塑成型法制备了生物降解黄麻短纤维增强PLA复合材料,通过力学性能测试及SEM,探讨了碱处理、碱和硅烷偶联剂KH550同时处理对复合材料结构和性能的影响。结果表明:两种处理方法均能够增加黄麻纤维的表面粗糙度,但碱和偶联剂KH550同时处理的效果要优于碱处理,且KH550改善了黄麻短纤维与PLA树脂之间的界面黏结性能提,高了黄麻/PLA复合材料的拉伸强度和弯曲强度。     

The effects of water flow rate on shear bond strength of self etch resin cement to dentin surface after Er,Cr:YSGG laser etching

The aim of the present study was to evaluate the effect of water flow rate on the morphological features of dentin and shear bond strength (SBS) of self-etching resin cement after Er,Cr:YSGG laser etching. Dentin specimens obtained from extracted human third molars were randomly assigned to four groups (n = 23), including one that received no laser irradiation (control-group D) and three others with different laser parameters: 2.25 W, 50 Hz, 60% air with water flow rates of 19 mL/min-100% water (group A), 2.25 W, 50 Hz, 6.75 mL/min-50% water (group B), and 2.25 W, and 50 Hz, 2.75 mL/min-25% water (group C). The morphological features of each group were examined with scanning electron microscopy and atomic force microscopy. The SBS of resin cement disks (Panavia F2.0, Kuraray; Tokyo, Japan) (3 mm in diameter and 2 mm in height) to the dentin specimens was measured using a universal testing machine at a cross head speed of 0.5 mm/min. Bond strength values were analyzed with one-way ANOVA/Tukey tests. There were no significant differences between the SBS values of groups A and B (p > 0.05). However, the SBS values of these groups were significantly higher when compared to groups C and D (p < 0.001). Er,Cr:YSGG laser application with water flow rates of 6.75 or 19 mL/min resulted in better dentin surface alterations and increased the SBS of self-etching resin cement to dentin.     

On the effect of pulsed laser ablation on shear strength and mode I fracture toughness of Al/epoxy adhesive joints

The present work describes an experimental study about the shear strength and the mode I fracture toughness of adhesive joints with substrates pre-treated by pulsed laser ablation. An ytterbium-doped pulsed fiber laser was employed to perform laser irradiation on AA6082-T4 alloy. Morphological and chemical modifications were evaluated by means of surface profilometry, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Thick adherend shear tests were carried out in order to assess the shear strength while the mode I fracture toughness was determined using the double cantilever beam. For comparison, control samples were prepared using classical surface degreasing. The results indicated that laser ablation has a favorable effect on the mechanical behavior of epoxy bonded joints; however, while a + 20% increase was recorded for shear strength, a remarkable threefold enhancement of fracture toughness was observed with respect to control samples. XPS analyses of treated substrates and SEM observations of the fracture surfaces indicated that laser pre-treatment promoted chemical and morphological modifications able to sustain energy dissipation through mechanical interlocking. As a result cohesive failure within the adhesive bond-line was enabled under predominant peel loading.     

Effects of Y-TZP blank manufacturing control and addition of TiO2 nanotubes on structural reliability of dental materials

Titanium dioxide (TiO₂) nanotubes have been applied to enhance the mechanical and biological properties of dental materials. Yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) have been increasingly used in dentistry as a substructure for crowns and fixed partial prostheses. Aside from its optimal clinical results, Y-TZP is prone to failures due to microstructure-related defects introduced in the manufacturing process that may lower its structural and clinical reliability. The purpose of this study was to evaluate the role of the manufacturing process of blanks as well as their original composition modification by addition of TiO₂ nanotubes (0%, 1%, 2% and 5% in volume) while controlling all manufacturing steps. Materials were subjected to a biaxial flexural strength test, a fractographic qualitative analysis by scanning electron microscopy (SEM), a microstructure evaluation in field emission-SEM and X-ray diffraction. Values of flexural strength were subjected to ANOVA, Tukey (α = 0.05) and Weibull statistics. Grain size values were subjected to Kruskal-Wallis and Dunn tests (α = 0.05). Highlights of the results include that for experimental Y-TZP added 2% vol TiO₂ nanotube ceramics presented flexural strength values at 577 MPa and Weibull modulus (m) at 8.1. The addition of TiO₂ nanotubes in different blends influenced experimental Y-TZP properties, leading to lower flexural strength, although they presented higher m than the commercial Y-TZP. Nanotubes also led to bigger grain sizes, more pores and a slight increase in the monoclinic phase, influencing the microstructure of Y-TZP. Y-TZP blank manufacturing control as well as addition of TiO₂ nanotubes led to higher m values and, hence, greater structural reliability.