Effects of zirconia additives on β-tricalcium-phosphate cement for high strength and high injectability

Injectable calcium phosphate cements (CPCs) exhibit many advantages as bone substitution materials. However, the strength of injectable CPCs after setting are often insufficient. In our previous studies, mechano-chemically modification of β-tricalcium phosphate cement powder through a planetary ball-milling process exhibited simultaneous improvement in the strength and injectability of CPC. Two plausible effects of this process are: changes in the CPC powder properties and zirconia abrasion powder contamination from the milling pot and balls. The objective of the present study is to separately evaluate these two effects on the strength and injectability of CPCs.The calculated injectability of the cement paste with and without the addition of zirconia powder were higher than 65% at 6 h after mixing. These values were much higher than that of the CPC paste without mechano-chemically modification, and similar to that of CPC with zirconia abrasion powder contamination. By contrast, the compression strength of the set CPC with zirconia powder additives were higher than that without the addition, and similar to that of CPC with zirconia abrasion powder contamination. These results suggest that the changes in the CPC powder properties due to mechano-chemically modification mainly affected the injectability of the CPC paste, and the zirconia abrasion powder contamination of the CPC powder affected the strength of the set CPC.     

Effects of surface treatments on the shear bond strength of luting cements to zirconia

Objective: The aim of this in vitro study was to evaluate the effect of surface treatments on the shear bond strength of resin cements to zirconia. Material and methods: Sintered zirconia specimens (n = 192) were divided into four different surface treatment groups: control (no treatment); airborne-particle abrasion; glaze layer and hydrofluoric acid (HF) application, and hot etching solution application. Then, each group was divided into four subgroups (n = 12), and three different resin cements were applied to the zirconia surfaces. The shear bond strength value of each specimen was measured after 5000 thermo cycles. The failure types were examined with a stereomicroscope and the effects of the surface treatments were evaluated with a scanning electron microscope. Results were analyzed using analysis of variance and Tukey’s post hoc tests (α = 0.05). Results: The surface treatment and resin cement type significantly affected the bond strength results (p < 0.05). For all resin cements, the airborne-particle abrasion treatment increased the shear bond strength values (p < 0.05). The glaze layer & HF application increased shear bond strength values for all groups, except the Single Bond Universal-RelyX Unicem Aplicap group (p < 0.05). The surface roughness values of airborne-particle abraded specimens were similar to comparable values for specimens from the control group and the hot etching solution group (p > 0.05). The glaze layer & HF application group produced the highest surface roughness values (p < 0.05). Conclusion: The results of this study recommend using the appropriate combination of surface treatment and adhesive/silane coupling agent to achieve durable zirconia-resin bonding.     

Effects of twin boundaries and pre-existing defects on mechanical properties and deformation mechanisms of yttria-stabilized tetragonal zirconia

In annealing of yttria-stabilized tetragonal zirconia (YSTZ), {011}-specific twins and sub-surface defects are often observed, however their effects on the martensitic phase transformation and deformation behavior of YSTZ have never been investigated. In this work, the roles of twin boundaries (TBs) and pre-existing defects in determining the mechanical properties and subsequent deformation mechanisms of YSTZ nanopillars are studied. Using large-scale molecular dynamics simulations, we show that Young’s modulus and strength of YSTZ decrease with the increase of TB density, but the ductility of YSTZ pillars increases. Phase transformation behavior is found to be correlated to TB density. The sensitivity of mechanical responses of twinned structures to pre-existing defects is also studied. A competitive mechanism between TB-induced phase transformation and void-induced phase transformation is observed. When the diameter of a pre-existing void is smaller than a critical value, only TB-induced phase transformation occurs, which leads to void-insensitive mechanical properties.     

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.     

Effects of different surface treatments of zirconia on the bond strength of self-adhesive resinous cement

Purpose: The aim of this study was to evaluate the effects of different zirconia surface treatments on the bond strength of two self-adhesive resinous cements (SARC).

Methods: Two hundred and eight cylindrical specimens were obtained from Y-TZP zirconia (half with diameter 3.2 mm and half with 4.8 mm). After sintering and polishing, specimens were divided into four groups (n = 26), according to surface treatment: Control (no treatment); Sandblasting (Al₂O₃ particles); Rocatec (Al₂O₃ particles, tribochemical silica coating and silane application); Laser (Nd: YAG laser: 20 Hz, 100 mJ, 0.2 J/cm²). The surface roughness (Ra) was evaluated after the surface treatments, and the groups were divided into two subgroups (n = 13), according to the SARC tested: RelyX U200 and Bifix SE. The 2.2-mm cylinders were bonded to 4.8-mm cylinders and stressed until failure under shear using a universal testing machine. Bond strength and Ra were analyzed using ANOVA, and Tukey’s test (α = 0.05).

Results: Surface treatment was significant (p < 0.0001), but cement type (p = 0.73) was not. Related to roughness, significant differences were found for the treatment type (p < 0.0001), with laser being the treatment with higher Ra values.

Conclusions: Nd:YAG laser produced a rougher surface and a higher bond strength compared with sandblasting, silicatization, and control groups.     

Effect of tetragonal zirconia nanoparticle content on enamel strength

The fracture failure of enamel is caused by hole-type flaws and cracks generally present in enamel. In this study, the effect of tetragonal zirconia nanoparticles (nano-t-ZrO₂) on enamel strength was investigated. The addition of nano-t-ZrO₂ improved the surface morphology and reduced the porosity of the enamel as determined by morphological and porosity distribution analyses. The strain on the enamel surface was recorded using a strain gauge attached to the enamel surface. The crack initiation force and strain were measured using the strain gauge, and the crack propagation diagrams at various stages of the tensile process were recorded. The relationship between the crack initiation energy and nano-t-ZrO₂ content was found to be non-linear. Nano-t-ZrO₂ affected the strength of the enamel. Moreover, the tensile force required for the appearance of cracks first increased and then decreased with an increase in the nano-t-ZrO₂ content. The addition of nano-t-ZrO₂ to the enamel matrix suppressed the formation of stress concentration regions and decreased the brittleness of the enamel. At a nano-t-ZrO₂ content of more than 5 wt%, the ZrO₂ particles agglomerated.     

Effects of granule compaction procedures on defect structure, fracture strength and thermal conductivity of AlN ceramics

The effect of granule compaction procedures on defect structure, fracture strength and thermal conductivity was examined for AlN ceramics using the same starting granules. For this study, changing the order of the cold isostatic pressing (CIP) and dewaxing procedure was performed, which changed the compaction behavior of the granule bed. The structural examination of green and sintered bodies showed that the change of granule strength strongly influenced the size and concentration of the granule related defects in sintered bodies. A large difference of the fracture strength associated with the change of granule strength was noted, and it was ascribed to the difference between the defect structures in the sintered bodies. On the other hand, the thermal conductivity was kept almost constant (> 150 W/m K) against the process alteration.     

Microscopic interpretation of granule strength in liquid media

This paper reports experimental studies illustrating the effects of partially wetting liquids on the mechanical strength of model granules composed of autoadhesive polystyrene particles. The liquids were prepared by mixing different amounts of isopropanol with pure water and their wetting behaviour was characterised by contact angle measurements on polystyrene surfaces and also by their surface tensions. The strength of the granules was measured by diametric compression while being immersed in the liquid media. The Young's modulus and yield stress were inferred from the compression data using elasto-plastic contact mechanics theory. A reduction in the granule strength was observed at a ‘critical’ isopropanol concentration, which was interpreted in terms of solvation forces. Existing micromechanical models of particle assemblies were examined in order to interpret the dependence of the mechanical properties on the wetting behaviour of the liquid environment. The work provides a basis for understanding some of the factors that are important in the dispersion and dissolution of granules in liquid media.     

Thermal and related studies of some zirconia gels

The thermal properties of a number of zirconia gels, prepared with various precipitants, have been studied by thermogravimetry, differential thermal analysis and evolved gas analysis. The results obtained show that ligands derived from the various precipitants are incorporated in these gels and strongly influence their high temperature behaviour. The observed properties are interpreted on the basis of a defect structure involving O^2- vacancies generated through the removal of these ligands at higher temperatures.     

Effects of polymer structure on the onset of processing defects in linear low density polyethylenes

Linear low density polyethylenes are manufactured by copolymerizing ethylene with 1-alkenes, yielding a linear polyethylene backbone with short side chains. Due to the nature of the catalyst used in the polymerizaton, multimodal branching distributions are typically obtained. In this report, we have investigated the processability of four 1-octene linear low density polyethylenes as a function of the short chain branching distribution. Analytical techniques such as ¹³C nuclear resonance spectroscopy, size exclusion chromatography, differential scanning calorimetry, and temperature rising elution fractionation, in particular were used to elucidate the molecular structure. Processability measurements were made using various extrusion techniques and dynamic mechanical analyses.It was determined that in the absence of any variations in molecular weight, the polymers with the higher proportions of linear polyethylene showed inferior processability In terms of onset of surface imperfections at lower extrusion rates. Polymers with worse processability characteristics also exhibited higher zero shear viscosities.     

Effect of scale of operation on granule strength in high shear granulators

Results of a study on the influence of operation scale and impeller speed of high shear mixer granulators on the strength of granlues are reported in this paper. Calcium carbonate particles have been granulated in four scales of a geometrically similar high shear granulator (Cyclomix) with 1, 5, 50 and 250 L capacities. For the smallest scale, the effect of a small deviation from geometric similarity was also investigated. An aqueous solution of polyethylene glycol was used as the binder. Three scaling rules of constant tip speed, constant shear stress and constant Froude number have been used to determine the impeller speed for the different scales of the granulators. The granules produced in these experiments have been dried and tested for strength using side crushing test method. The data have then been analysed and compared. Operation of granulators according to the constant tip speed rule produces granules with a similar strength for all four scales, followed by a similar trend for the constant shear stress rule, albeit to the less extent. The constant Froude number rule produces a heterogeneous strength distribution and is not a suitable criterion for scaling-up of high shear granulators. The distribution of granule strength has been fitted to the normal, log-normal and Weibull distributions. Weibull distribution fits the data well for the constant tip speed operations.     

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.     

Effects of symmetrical bonding defects on tensile shear strength of lap joints having ductile adhesives

In this paper we examine the effect on joint strength of depleting the bond line of a relatively flexible adhesive (polyethylene) while maintaining a constant adhesive film thickness. It is shown that the tensile shear strength of a lap specimen is not governed by edge effects but rather by the bonded area. By using limit analysis of the plasticity theory, we demonstrate why the tensile shear strength of the joint is insensitive to stress concentrations at the bonding defects.     

Effects of chitosan and zirconia on setting time,mechanical strength,and bioactivity of calcium silicate‐based cement

In this research, we aimed at improving the setting properties and biocompatibility of the mineral trioxide aggregate‐like cements while maintaining the main chemical formula. Consequently, chitosan and zirconium oxide were added to the cement instead of bismuth oxide to improve the mechanical behavior, limit the possible toxicity, and enhance the bioactivity of the cements. Adding zirconia resulted in a shorter setting time and adding chitosan contributed to the setting time, mechanical strength, and biocompatibility at the same time. Thus, cements containing both chitosan and zirconia had the shortest setting time, highest compressive strength, and apatite‐forming ability.     

Effect of density on change in strength of refractories

Conclusions It was experimentally established that the spread in strength values of oxide refractories is mainly due to the spread in apparent density (bulk density). This phenomenon cannot be considered in isolation from density characteristics. There exists a direct relationship between the individual values of apparent density and maximum compressive and tensile strength for individual series of specimens. The contingency factor has no decisive value in explaining the various strength factors of refractory materials.To improve the production technology of refractory products it is necessary to take into account those factors which affect the changes in the density of individual specimens and throughout the volume of each specimen.Translated from Ogneupory, No. 5, pp. 45–49, May, 1968.