Background: The color stability of dental restorative materials is important for long-term clinical success. Objectives: The objective of this study was to examine the effect of thermocycling on the color and translucency stability of monolithic zirconia. Materials and methods: A total of 80 disc-shaped spe- cimens (1 cm diameter) were produced from monolithic zirconia material, Katana High Translucent (Kuraray Noritake Dental, Kurashiki, Japan). The specimens were prepared in four different thicknesses: 0.5 mm, 1 mm, 1.5 mm and 2 mm. Before thermocycling, color measurements of the specimens were made by a spectrophotometer (Spectro Shade TM MICRO; MHT Optic Research AG, Milan, Italy). After the thermal aging procedure, the color measurement was repeated. Data obtained from the study were analyzed with descriptive statistics, correlation analysis, one-way ANOVA and Tukey’s tests. Results: After thermocycling, the L *, a *, b * values decreased at all thicknesses. The maximum change in the L *, a * and b * values was observed in 0.5-mm-thick specimens, while the least change was observed in 2-mm-thick specimens. The amount of color change in the specimens after thermocycling was found to be the highest in 0.5-mm-thick specimens (Δ E = 0.91 ± 0.02), and the lowest in 2-mm-thick specimens (Δ E = 0.85 ± 0.01). While a statistically significant color change (Δ E ) was observed in 0.5-mm-thick specimens (p < 0.05), a sta- tistically insignificant color change (Δ E ) was observed (p > 0.05) in 1-mm, 1.5-mm, and 2-mm-thick specimens. After thermocycling, the translucency parameter (TP) values decreased at all thicknesses. The highest change in the TP values was observed in 0.5-mm-thickspecimens (1.09 ± 0.03), while the lowest change was observed in 2-mm-thickspecimens (0.40 ± 0.04). While a statistically significant change in the TP values was observed in 0.5-mm-thick specimens (p < 0.05), there was a statistically insignificant change in the TP How to cite this paper: Koseoglu, M.,
11 Read more
changes in L* parameter of monolithic zirconia were different from those in metal-ceramic or all-ceramic restorations. They reported a significant decrease in L* value at the initial 0.1-mm thickness reduction; but, no further significant changes were observed in this param- eter with more thickness reductions. This was suggested to be related to the polycrystalline monolayer structure of monolithic zirconia, which does not have any veneer- ing porcelain. The first 0.1-mm thickness reduction might have reduced the scattering, which caused lower L* value. However, as the thickness reduction proceed- ed, monolithic zirconia could act as an opaque core and induced internal reflection. Hence, they concluded that the reduced reflection could compensate for the increas- ed internal reflection and kept the L* value stable. 
of crystalline phase transformation (I.e. transformation toughening) (Hannink, 2000; Giordano et al., 2008). Ceramic crowns made of zirconia can be constructed with an inner core of zirconia and an outer layer with sintered porcelain as for ordinary metal-ceramic (MC) crowns. This will give the crown a good aesthetic appearance together with an assumed high mechanical strength (Long, 2012). The problem, however, has been fractures in the veneering porcelain due to adhesion difficulties between zirconia and the veneering material (Kim, 2013; Zahran et al., 2008). During the past few years manufacturers have developed a monolithic zirconia for fixed dental prosthesis (FDP) system utilizing a tooth-colored zirconia. In this system, full ceramic restorations of zirconia without the veneering porcelain are fabricated using a dental CAD/CAM system for the process in total without the adhesion difficulties between the zirconia and the veneering porcelain. The aesthetic properties of monolithic zirconia are however poorer as compared to zirconia cores with veneering porcelain. This may be due to the fact that monolithic zirconia crowns are fabricated as one homogenous color (Long, 2012). Even though zirconia has a high fracture toughness on its own, the preparation of the tooth is still of importance for the stress state within the crown-tooth complex (Sharhbaf, 2013). An adequate preparation will give higher mechanical retention to the zirconia crown & bridge and decrease the risk of breakage, especially in the posterior part where the bite forces are higher. Recommendations are therefore given by the manufacturers concerning preparation and minimal requirements concerning removal of tooth substance. The following are the Tooth Preparation Guidelines for a zirconia crown and bridge by the dental advisor (John).
Background: Patients susceptible to periodontal disease and dental caries, including those who undergo fixed prosthodontic treatments use chemical plaque control agents. However, these mouthrinses may result in adverse effects such as discoloration of the restorative materials. The aim of this study was to compare the color stability of monolithic zirconia and feldspathic porcelain after immersion in two different mouthrinses: 0.2% Chlorhexidine digluconate (CHX), or Listerine®. Color change was evaluated by color spectrophotometer and according to the Commission Internationale de l ’ Eclairage (CIELab) system.
On the basis of the obtained findings, almost all the tested monolithic zirconia materials exhibited high load strengths. In a previous study, the fracture strength of YSZ was reported to be in the range of 900–1200 N . In another study, the fracture strength of YSZ- FDPs was reported to be over 2000 N under static load- ing . Eroğlu et al.  studied the fatigue behavior of zirconia-ceramic and reported a fracture strength of 2333 N for three-unit FPDs. Each specimen was sub- jected to 100,000 chewing cycles at a 50 N load and a 0.5 Hz frequency on the pontic with a 16 mm 2 con- nector size. No specimen fractured during dynamic load- ing, similar to the present study. The dimensions of the connector area are crucial for determining the strength of FDPs. In the current study, a connector size of 9 mm 2 was selected according to the manufacturer’s suggestion. Table 4 Mean values and standard deviations (SD) for fracture load (N) of the monolithic zirconias
Partially veneered monolithic (semimonolithic) crown design with porcelain coverage on the buccal area only might be a feasible method to overcome both the issues with chip-off fractures and the poor esthetics of full monolithic zirconia crowns. In this way, it might be possible to exclude the por- celain on surfaces subjected to wear and high loads such as the occlusal tables and the marginal ridges. Such a design has become common today but is not always sanctioned in the manufacturers’ recommendations for the materials and is consequently used without the support from manufacturers’ instructions. 15,16 Scientific studies on this subject are lacking.
10 Read more
Based on the results of the present study; the first null hypothesis were different veneer ceramic techniques would not effected the fracture strength of zirconia crowns was rejected. Also the collected data support to rejected the second null hypothesis which was resin cement type would noteffected on the fracture strength of both bilayered zirconia and monolithic zirconia single crowns. In combination with CAD/CAM fabrication, monolithic/full-anatomic crown restorations seemed to be reliable and robust. Previous studies evaluating the fracture strength of all-ceramic monolithic crowns indicate a superior performance for the monolithic design. According to the authors, the reason of enhanced performance of monolithic crowns is the elimination of the interface between core and veneer, which is believed to be the weak link in bilayer systems with no doubt (Guess et al., 2010; Silva et al., 2011). Another in vitro study evaluated the load-bearing capacity of four different zirconia based crowns, including zirconia core with veneer layer produced either by powder build-up or CAD/CAM technique, glazed monolithic zirconia, and polished monolithic zirconia.
Considering the effect of aging on roughness (Ra) values, BL specimens pre- sented higher values after chewing simulation. Unlike, GM and PM specimens were rougher before than after chewing simulation. This result may be explained by the SEM of the glazed specimen (Figure 3(b)), which reveals that the glaze material was removed by the abrasion against the antagonist surface during chewing simulation, exposing zirconia and making the occlusal surface smooth- er after aging. For PM specimens, even though control samples (unaged) already presented the lowest roughness values among the groups, it seems that the chewing simulation promoted a surface smoothening effect, slightly decreasing the surface roughness even further. In accordance with this study, Janyavula et al  evidenced that polished monolithic zirconia specimens had lower roughness (Ra) values than bi-layer zirconia crowns. The low roughness of PM zirconia specimens after chewing simulation needs to be evaluated with caution. Humid- ity, loading and grain size are all contributing factors to phase transformation on zirconia surface. The PM group was the only one abrading zirconia directly against the antagonist, which means that the material was unprotected in the oral-like environment. Even though the high number of cycles was designed to simulate 5 years of aging, the frequency of the cyclic loading (approximately 2.5 Hz) was much higher than the average human mastication frequency, so that the study could be accomplished within a reasonable period of time. It appears that time would also play a role in the infiltration of water through the microcracked layer of the transformed Y-TZP surface, causing further transformation and subsequent damage. More studies are needed to clarify the role of those factors on roughness and phase transformation of zirconia specimens.
12 Read more
Objective: the purpose of this multicenter retrospective study was to report on survival, success, and complication rates in monolithic zirconia restorations on teeth and implants. Materials and Methods: data on 671 monolithic zirconia restorations was collected by five prosthodontists from three different specialty practice centers, including a dental school and two private practice centers. Restorations included single crowns and multiple-unit fixed dental prostheses on teeth and implants in the posterior area (premolar and molars). Follow-up time was up to 62 months. Results: mean follow-up time was 28.1±12.9 months. A total of 671 units, 534 single crowns, and 137 multi- unit restorations. Cumulative survival and success rates at 5 years were 97.4%, and 93.8% respectively. Complications presented in 11 restorations out of 671 and included: decementation, abutment screw loosening, restoration crack, restoration fracture, and tooth fracture. No significant differences were observed between tooth-supported and implant-supported restoration (p=0.42), single crowns and multiple-unit restorations (p=0.07), bruxers and non-bruxers (p=0.57). Patients with group function occlusal scheme had significantly less survival rates (p=0.001). Conclusion: the use of monolithic zirconia for restorations on the posterior teeth and implants seems to be promising as it provides a durable solution with a low rate of complications.
The accuracy of fit is considered as one of the main factors in establishing the long-term functional success of the restoration, which is influenced by several factors, one of them is the impression technique. The objective of this in vitro study was to evaluate and compare the marginal and internal fitness of monolithic CAD/CAM zirconia crowns fabricated from four different conventional impression techniques and intra-oral digital impression using silicone replica technique. Two metal dies for a dentoform maxillary right first molar tooth were fabricated using lost wax technique: one for the dentoform before its preparation and the other one after preparation of the dentoform tooth to receive a monolithic zirconia crown. Impressions were then taken using vinyl polysiloxane impression material with four different conventional impression techniques (two-step putty/wash with and without spacer, one-step single and dual viscosity) and digital impression. All conventional impressions were poured with type IV gypsum product to produce thirty-two die stones, which were then scanned extra-orally using in Eos X5 extra-oral scanner. Forty crowns were then designed and fabricated (eight crowns for each technique). Marginal and internal gaps were measured using silicone replica technique. The measurements were done using a digital microscope at twenty-one different measuring points for each specimen, which represented four different areas of measurement (margin, chamfer, axial and occlusal). The data were then analyzed using One-way ANOVA test and LSD test. The digital impression yielded the least mean marginal and internal gaps as compared with all conventional impression groups with statistically significant and highly significant differences. Among the four conventional impression groups, the results showed that the two-step putty/wash impression technique without spacer yielded the least mean marginal and internal gaps followed by the two-step putty/wash impression technique with spacer with statistically significant difference between them, while the one-step dual viscosity impression technique yielded the greatest mean marginal and internal gaps, but with statistically non-significant difference with the one-step single viscosity impression technique. As a conclusion, it is recommended to use intra-oral scanner, when available, to take a digital impression for the tooth preparation as it produced crowns with better marginal and internal fitness than conventional impression. Otherwise, the two-step putty/wash impression technique could be the next choice, which is preferred over both one-step impression techniques.
14 Read more
ranged from 379 to 501 MPa . Fractures that had origins on the glass veneer surface had failure stresses between 31 MPa and 38 MPa. In the present study, the maximum tensile stresses which were produced in zirconia layer when various loads were applied [Table/Fig-12], are substantially less than the failure stresses for zirconia reported in the above literature (379-501 MPa). Also, zirconia has high tensile and flexural strength which ranges from 900-1200 MPa and high modulus of elasticity of upto 200 GPa with unique property of transformation toughening. Thus, zirconia cores are able to withstand the high occlusal stresses occurring during function. But, the strength of a non-homogenous (layered) all ceramic structure is determined by its weakest component which is usually the core-veneer bond strength or the veneering material itself, which has to be strong enough to withstand the stresses of mastication to prevent delamination and fracture of the veneering material. However, according to Aboushelib, zirconia core-ceramic veneer bond strength is lower than for other all-ceramic systems. He evaluated the microtensile strength and bond strength of a variety of widely used core and veneering ceramics and found that despite the high microtensile strength (340 MPa) of zirconia, its bond strength with veneering ceramic was 29 MPa. The MTBS test has proven to be a reliable test for evaluating the bond strength of composite materials to a variety of substrates .
As mentioned previously, according to the applied OEM specification, the minimum requested number of thermal cycle to pass the thermal cycling fatigue test is 250 cycle. The cracking mode is different when YPSZ top coat is produced by either APS or EB-PVD techniques  and it may be influenced also by coating thickness. Normally the thicker TBCs provide a greater temperature drop across the coatings. In addition, the increased thickness of the coating will increase the stored elastic strain energy and hence the energy release rate for a crack . Thus, the failure mechanisms that cause spallation of thick TBCs are expected to be different in some degree from those of the traditional thin TBCs. Failure of thin plasma sprayed TBCs occurs in most cases by interface delamination due to different thermomechanical properties of the coating and substrate and oxidation of the bond coat [14– 17]. In particular, thick TBCs have a worse thermal shock resistance than thin TBCs.In the Thermal shock test the type of damage is only by peel off. The peel off shows the starting of damage. The coated specimen was planned to keep for 250 cyles. After coating, the specimens were examined visually for appearance and tested in Thermal shock equipment for thermal resistance.The table 4 determines the weight loss of the specimen coated by yitria stabilized zirconia (8% Y 2 O 3 +
2.5. Slip Preparation and Characterization For studying suspension rheological flow characteristics of oxide powders, several suspensions were prepared at conditions where they could be cast. Rheological tests permit to identify the conditions where the suspensions are better dispersed. For these tests, zirconia and ceria- stabilized zirconia suspensions were prepared in water and ethanol with different solid loading, by using two different deflocculants such as Darvan (i.e. polymeth- crylic acid) and M2OC (i.e. ammonium polyacrylate), by varying their concentrations and by varying the pH of the suspension.
13 Read more
generated in monolithic diamond Raman lasers. However, if only yellow output (573nm) is desired, the use of coatings with greater transmission for the higher Stokes orders is likely to improve the conversion efficiency to the yellow by eliminating cascaded Raman conversion. This may also improve the output beam quality at the 1 st
was stabled at the higher temperature. However, all of the SZ synthesis process depend on the ZrO 2 precusor to obtain the stable and active catalyst. The crystal sizes of SZ catalysts were calculated Table 1: Acidity value of sulfated zirconia (SZ) Sample Acidity value (mmol/g)
zirconia compared to its control and other conditioned zirconia material groups (Figure 2C and Figure 3C) may be due to two reasons: Firstly the BN zirconia fine practicle size make the anti-agglomerated chelating action of CA more prominent with the formation of a ligand exchange reaction complex. Secondly, ZrO 2 chelation was more evident due to a low presence of the coloring agent within its content.
homogeneous copper catalyst . Atwater et al. have shown that several classes of aqueous organic contami- nants, can be deeply oxidized, using dissolved oxygen over supported noble metal catalysts (5% Ru-20% Pt/C), at a temperature 393 - 433 K and pressure between 2.3 and 6 atmospheres . Carlo et al.  have reported that lanthanum strontium manganites are very active catalysts for the catalytic wet oxidation of phenol. Castro et al.  have reported that polymer-supported metal complexes have been used as catalysts for the catalytic wet hydro- gen peroxide oxidation of Phenol with high yield; how- ever the unacceptable point was leaching of the metal. In the present work, we explored the effectiveness of zirco- nia-supported noble metals (Pt and Pd) and bismuth promoted zirconia supported noble metals for the oxida- tion of phenol in aqueous solution.
restoration. Beside the mechanical properties and esthetics, the long-term clinical success of zirconium restorations can be influenced by marginal adaptation, which is a very important factor for the longevity of the restored teeth.  Zirconia ceramics have no glassy matrix that is why it appears relatively opaque, thus; required the application of porcelain veneering on their surfaces to achieve acceptable shading and characterization. Undergoes heat treatment cycles in process of the veneering porcelain firing and effect of the fitness of restoration. 
12 Read more
To circumvent these problems, columns consisting of a block of a porous solid, called monolith or rod, prepared on a silica base either by a sol-gel process using polycondensation of alkoxysilanes or by polymerization of organic monomers, is developed. The essential advantages of monolithic columns come from the possibility to optimize proportions of monomers and cross-linkers so as to control the average size of the throughput channels and the porons. More and more analysts have sensed these advantages, and have achieved a lot of groundbreaking findings in this area, especially the monolithic applications in separation science . Therefore, there is no wonder that reviews on the preparation of monoliths with chiral surface flourish in recent years-. However, as far as we know, not any review is exclusively focused on the monoliths with protein as chiral selectors. In this section, the preparation of monoliths with protein as chiral selectors would be introduced in detail, and we hope this article can illuminate those who are interested in preparing “protein” monoliths.
Abstract: The purpose of this study was to evaluate the biomechanical and histological behavior of a ceria-stabilized zirconia–alumina nanocomposite (NanoZr) in comparison with that of 3 mol% yttria-stabilized tetragonal zirconia polycrystalline (3Y-TZP) in Sprague Dawley rats. Cylindrical NanoZr and 3Y-TZP implants (diameter 1 mm, length 2 mm) were used. Implant- surface morphology and surface roughness were determined by scanning white-light interfer- ometry and scanning electron microscopy, respectively. The cylindrical zirconia implants were placed at the distal edge of the femur of Sprague Dawley rats. At weeks 2, 4, and 8, the interfacial shear strength between implant and bone was measured by push-in test. Histological analysis was performed using hard-tissue sections. Bone–implant contact (BIC), the thickness of new bone around the implant within the bone marrow area, and osteoclast numbers were evaluated. The average surface roughness of 3Y-TZP (Sa 0.788 µm) was significantly higher than that of NanoZr (Sa 0.559 µm). The shear strengths of 3Y-TZP and NanoZr were similar at 2 weeks, but at 4 and 8 weeks the shear strength of NanoZr was higher than that of 3Y-TZP. The average BIC values within the bone marrow area for 3Y-TZP and NanoZr were 25.26% and 31.51% at 2 weeks, 46.78% and 38% at 4 weeks, and 47.88% and 56.81% at 8 weeks, respectively. The average BIC values within the cortical area were 38.86% and 58.42% at 2 weeks, 66.82% and 57.74% at 4 weeks, and 79.91% and 78.97% at 8 weeks, respectively. The mean BIC value did not differ significantly between the two zirconia materials at any time point. The NanoZr implants were biocompatible, capable of establishing close BIC, and may be preferred for metal-free dental implants.
10 Read more