Dental Zirconia Adhesion with Silicon Compounds Using Some Experimental and Conventional Surface Conditioning Methods

Background  

Clinically, in dental practice the durability of zirconia adhesion is the key to successful long-term all-ceramic structures, e.g. fixed partial dentures (FPDs).     

Zirconia ceramics in metal-free implant dentistry

Because of their outstanding mechanical properties, chemical stability, and biocompatibility, 3-mol % yttria-stabilised tetragonal zirconia polycrystals (3Y-TZP), known as zirconia ceramics in dentistry, are an important choice for various types of prosthesis. In addition to extensive use for crown and bridge construction, considerable interest has been generated for applications in implant dentistry, including full-contour zirconia crowns as supra-constructions, zirconia abutments, and novel zirconia implants. However, their use among dentist and researchers is controversial, especially compared with the well-established implants made of titanium alloys. As a latecomer, the merits and limitations of 3Y-TZP are awaiting careful investigation. Design, manufacturing, and clinical operation guidelines are urgently needed. The aim of this review was to address the present status of the application of zirconia ceramics related to implant dentistry by analysing the published data from both in vitro and in vivo studies. Suggestions are provided for potential improvements and suitable applications of zirconia ceramics in metal-free implant dentistry.     

Grinding and polishing efficiency of a novel self-glazed zirconia versus the conventional dry-pressed and sintered zirconia ceramics

ABSTRACT

The grinding and polishing efficiency of self-glazed zirconia and Zenostar zirconia, prepared by wet and dry approaches, respectively, were evaluated. Each sample was divided into two subgroups (n?=?5). One was ground, and the other was polished by following the clinical adjustment protocol. Statistics were analysed by independent t-test to a significance level of p?<?.05. More material was ground off in self-glazed zirconia than in Zenostar zirconia (p?<?.05) during the same period, especially during the coarse grinding procedure (p?<?.05), whereas the grinding efficiency in fine grinding stage was not significantly different (p?>?.05). The polishing efficiency of the whole and of the fine polishing procedure of the two kinds of zirconia was significantly different (p?<?.05). It thus can be concluded that grinding and polishing efficiency of a novel self-glazed zirconia is significantly higher than that of the conventional Zenostar zirconia.     

Analysis of nonisothermal sintering of nanocrystalline and microscaled ceramic materials

Abstract

Abstract

Sintering involves consolidation of powders under the application of heat to form solids of higher density and is often the final step in the processing of ceramic materials. The time–temperature cycles used in sintering affect the kinetics and, in turn, influence the quality of the sintered product. Considering the densification mechanisms controlled by grain boundary diffusion along with interface reaction and the grain growth mechanism, this paper presents a systematic numerical study on the sintering of nanocrystalline yttria tetragonal stabilised zirconia and microscaled α-alumina, to bring out the effects of the time–temperature cycles on their sintering behaviour. Effects of initial grain size are also examined. Based on the studies, empirical correlations are developed that relate the final grain size and the sintering time to the temperature cycle. The results serve as guidelines in the design of time–temperature cycles for the sintering of the two material systems considered.     

The colour of monolithic zirconia restorations determined by spectrophotometric examination

ABSTRACT

Objective: The aim of this in vitro study is to examine the optical effects of monolithic zirconia of different translucency and thickness, combined with substrates of different colours. Materials and methods: Zirconia specimens of two colours (A2P1, WHITE) were used for the study, three try-in pastes (Variolink Esthetic); substrates were prepared from nine types of materials (six VITA SIMULATE, three metals). Measurements were carried out at the Faculty of Atomic Physics of the Technical University of Budapest with the state-of-the-art PerkinElmer® Lambda 1050 spectrophotometer. Results: The colouring of zirconia has a major effect on dE values resulting in different colour perceptibility and acceptability. Try-in pastes, however, have no significant effects overall. Conclusion: Applying coloured zirconia is highly eligible for preparing aesthetic crowns as their substrate-covering effect makes it possible to reproduce the desired colour. Uncoloured zirconia nonetheless is unaffected by the substrate material, especially above a certain layer thickness.     

Shear bond strength of PEEK and PEEK-30GF cemented to zirconia or titanium substrates

Objectives: The aim of this study was to evaluate the use of dual-cure resin cement to promote the bonding between a veneering PEEK and zirconia or titanium surfaces.

Materials and methods: The surface of titanium and sintered zirconia disks were gritblasted, ultra-sonically cleaned in distilled water, and dryed by oil-free air. Then, a adhesive system was applied on the clean and dry surfaces. Disks of PEEK or 30% glass-reinforced PEEK were cut from a rod and their surface were acid etched and therefore the PEEK roughness was analysed using a contact profilometer. A resin cement was then applied between the substrates and the veneering PEEK and light cured for 4 Shear bond strength tests were performed on PEEK-cement to zirconia or titanium interfaces. Scanning electron microscopy (SEM) analyses were performed to evaluate the samples surface, interface and failure mode.

Results: Surface treatment with acid etching decreased the average roughness of PEEK-based surfaces. oMicroscopic analyses by SEM revealed morphological aspects of a poor bonding between the resin-based cement and PEEK. Those aspects could be confirmed by the low mean values in shear bond strength. The fracture analysis showed that the main failure mode was adhesive, which explain the low values of shear bond strength.

Conclusion: PEEK is a promising material for dental applications. However, significant improvements on surface modifications and in chemical composition of the cement are still required for dental applications involving cementation of PEEK or PEEK-30GF to zirconia or titanium concerning a desirable long-term clinical performance of prosthetic structures.     

Quantitative Separations of La(III) from Alkaline Earth Metal Ions Using a New,Poorly Crystalline Inorganic Ion Exchanger: Niobium Molybdate

Abstract

During our systematic studies of niobium compounds (1–4) as ion-exchange materials, it was found that niobium molybdate has a high thermal stability and can be more easily converted into a poorly crystalline form than the tin (5), thorium (6), titanium (7), and chromium (8) molybdates studied in our laboratories. We therefore decided to investigate the ion-exchange behavior of this material. The results are given below.     

Enhanced hydrophilicity and tribological behavior of dental zirconia ceramics based on picosecond laser surface texturing

Zirconia ceramics are promising restorative materials that are being extensively used in clinical dental prosthodontics such as inlays, implant crowns and fixed bridges due to their high strength, high toughness, high corrosion resistance and excellent esthetical effects. However, in addition to the superior mechanical and physical properties, the biocompatibility is a more important index to evaluate the performance of the ceramic implant dentures. The aim of the current work is to improve the biocompatibility of zirconia ceramic implants by surface modification. To achieve this goal, a bionic design method was used to imitate the natural human perikymata structure and a series of microtextures were fabricated on the zirconia surfaces by the picosecond laser processing. The effectiveness of the microtextures on the biocompatibility of zirconia ceramics was quantified in terms of the contact angle, the friction coefficient and the surface wear signatures. The results indicate that the laser texturing has a significant effect on the wettability and the tribological behavior of zirconia ceramic dental implants. To improve the biocompatibility of the zirconia ceramic implants, a smaller groove width with an appropriate groove depth is favorable.     

Clinical Satisfaction and Quality of Ceramic Fixed Dentures

It is known that several factors can affect the clinical success and durability of fixed partial dentures. Therefore, the aim of the present study was to present a literature review about the longevity, clinical success, and quality, as well as, patients' and dental surgeons' satisfaction of ceramic fixed dentures. High rate of patients' satisfaction has been observed in relation to the esthetic of ceramic crowns. In addition, the literature has shown that dental ceramics can be used in several clinical situations with high success rate and longevity. Despite of failures and complications of ceramic restorations, nowadays, with the improvement of mechanical properties of such materials, ceramic crowns present a favorable prognosis and can be used in several clinical situations with high success rate, clinical quality, and great patients' satisfaction.     

Bond strength of veneering porcelain to zirconia after different surface treatments

Aim: The aim of this study was to evaluate the effect of various surface treatments on the bond strength of veneering feldspathic porcelain to zirconia. Methods: Fifty yttria-stabilized tetragonal zirconia polycrystalline specimens were divided into five groups (n = 10) according to various surface treatments. The groups were as follows: Group 1: control group with liner application and no further surface treatment; Group 2: air-particle abrasion with 110 μm of alumina (Al₂O₃) particles; Group 3: grinding with a diamond disk; Group 4: Nd:YAG laser irradiation (the laser and the energy parameters were 10 Hz, and 2 W and 200 mJ, and the pulse duration (short pulse) range was up to 180 μs); Group 5: selective infiltration etching (SIE). After surface treatments, a liner application was performed for all surfaces according to the manufacturer’s instructions. Veneering porcelain was applied on zirconia surfaces using a Teflon mold. Shear bond strength was tested using a universal testing machine. The fractured surface morphologies were examined with scanning electron microscopy. The data were statistically analyzed using Mann–Whitney U and Kruskal–Wallis tests (α = .05). Results: The Megapascal values of the bonding groups were as follows: G1 = 8.62 ± 1.12, G2 = 13.87 ± 5.08, G3 = 12.31 ± 3.35, G4 = 17.32 ± 6.16, and G5 = 16.17 ± 4.55. Statistically significant differences were observed between the control group and the other groups (p < 0.05). Group 4 had the highest bond strength while G1 showed the lowest bond strength. No significant differences were found between the Nd:YAG, grinding, sandblasting, and SIE groups. Conclusion: Surface treatments had different effects on the shear bond strength of feldspathic porcelain to zirconia. Surface treatment techniques used in this study can be used on zirconia specimens prior to liner application to obtain an acceptable bond strength of veneering porcelain to zirconia. The effect of Nd:YAG laser irradiation and SIE techniques on bond strength of veneering ceramic to zirconia should be evaluated with further studies.     

Effect of laser etching on the fracture strength of the monolithic zirconia and fiber-reinforced composite inlay-retained fixed partial dentures

Aim: The aim of this study was to evaluate the fracture strength of monolithic zirconia and fiber-reinforced composite (FRC) inlay-retained FPDs, both of which are cemented to the laser-etched cavity surfaces.

Materials and Methods: Eighty freshly extracted sound human teeth were used. A premolar and a molar tooth were embedded in an autopolymerizing acrylic resin. Forty acrylic resin models were randomly divided into two groups including monolithic zirconia and FRC inlay-retained FPDs (n = 20). Then, these groups were divided into two subgroups according to conditioning of the cavity surfaces with or without Er:YAG laser etching. Monolithic zirconia inlay-retained FPDs were produced by an inLab MC XL milling device using monolithic zirconia blocks. Tescera? Fiber Reinforcement Materials were used for the FRC inlay-retained FPDs. After 10.000 thermal cycles, fracture strength test was applied to the specimens.

Results: The monolithic zirconia inlay-retained FPDs exhibited the highest fracture strength than the FRC inlay-retained FPDs. Fracture strength was increased with laser etching for both restorative materials (p < 0.05).

Conclusion: Laser etching had positively effect on the fracture strength of the inlay-retained FDPs.     

Bonding of novel self-glazed zirconia dental ceramics

ABSTRACT

Bonding behaviours of a novel self-glazed zirconia dental material were investigated. The effect of a preformed porous nanoceramic bonding surface and the different cleansing methods on saliva-contaminated bonding surfaces was assessed in this in vitro study. Cleaning procedures commonly used in dental offices were tested. All specimens demonstrated adhesive fracture patterns except for airborne particle abrasion group, which resulted in mixed-type fracture pattern and the highest bonding force values. No statistically significant differences in bonding force values were found between self-glazed zirconia with and without a preformed porous nanoceramic bonding surface when bonded with the self-adhesive resin cement (RelyX? Unicem 2). Scanning electron micrographs revealed no interaction between the bonding surface and the resin cement after priming. Mechanical retention is the predominant bonding mechanism between the bonding surface and the luting resin cement.     

Fatigue behaviours of the zirconia dental restorations prepared by two manufacturing methods

The fatigue behaviours were evaluated on a novel zirconia dental restoration known as self-glazed zirconia (SG), prepared by a precision additive 3D gel deposition approach, compared with a conventional zirconia (CZ) restoration, shaped by CNC milling of zirconia blanks made by cold isostatic pressing. Eight fixed partial dentures made by each method were subjected to fracture test, without or with the application of 5-million fatigue cycles, respectively. The processing defects, grain size, and t–m phase transformation were examined by SEM and XRD. The results revealed that the fracture force of the SG restorations was higher than that of the CZ restorations in both cases, which ascribed to the fact that more voids and larger grains in the conventional versus in the SG restorations. The t–m phase transformation was observed only on the fracture surfaces of both materials subjected to fatigue test. Both zirconia restorations meet the clinical requirement.     

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.     

The Effect of Heat Treatment and Feldspathic Glazing on Some Mechanical Properties of Zirconia

Purpose

In dental practice, zirconia substructures for crowns and fixed partial dentures are veneered with feldspathic porcelain for better aesthetical properties. The purpose of this study was to evaluate the effect of heat treatment during the veneering process on the mechanical properties of zirconia.

Methods

105 zirconia (ICE Zirkon, Zirkonzahn, Italy) disc shaped specimens were divided into seven groups (n?=?15/group) and sintered at 1500 °C. Control specimens (group 1) were left as such. Specimens in the study groups were: 2) one heat treatment in a porcelain firing furnace; 3) a heat treatment with two firing cycles; 4) one heat treatment with a thin coating of feldspathic glazing on the tension side; 5) two heat treatments with a thin coating of feldspathic wash and glazing on the tension side; 6) one heat treatment with a thin coating of feldspathic glazing on the compression side; 7) two heat treatments with a thin coating of feldspathic wash and glazing on the compression side. Biaxial flexural strength and surface microhardness of the specimens (diameter 19 mm, thickness 1.2 mm) were measured. The effect of heat treatment and feldspathic glazing on the phase transformations of zirconia was determined by XRD-analysis. The data were calculated using ANOVA-analysis.

Results

Repeated heat treatment did not influence the mechanical properties of zirconia (p?>?0.05). No difference (p?>?0.05) was found in terms of the surface microhardness between the groups. Some transformation from the tetragonal to the monoclinic phase was seen on the surface of the specimens after heat treatment and feldspathic glazing coating.

Conclusions

Repeated heat treatment does not affect the strength of zirconia milled in the green-stage form.     

Fracture resistance of endodontically treated maxillary incisors restored with zirconia posts: effect of the internal plateau preparation

ABSTRACT

We report on a new approach to increase the fracture resistance of endodontically treated teeth. We propose a preparation of horizontal internal plateau (IP) in dentine and the use of retentive zirconia posts to achieve a more favourable load transmission. The aim of our work was to investigate the effect of the IP depth and the post diameter on the fracture resistance and the failure mode of maxillary central incisors. Seventy-two teeth were, divided into six groups of 12. IP 4?mm in diameter and 0, 1 or 2?mm in depth was prepared and zirconia posts of two diameters luted. Specimens were loaded until failure and fractures were classified as reparable or not. Two-way ANOVA, Tukey’s HSD test and Poisson regression were used for statistical analysis (α?=?0.05). Significantly improved fracture resistance and predominantly favourable failure modes were found when 2-mm deep IP is prepared.     

Wear performance of self-glazed zirconia crowns with different amount of occlusal adjustment after 6 months of clinical use

ABSTRACT

The amount of enamel wear on the antagonist occlusal surfaces caused by self-glazed zirconia crowns was compared with that caused by contralateral natural teeth. Thirteen self-glazed zirconia crowns were placed in situ. The impressions of self-glazed zirconia crowns, their antagonists and the control teeth were taken and scanned at baseline and 6-month follow-up. The patients were divided into two groups, the self-glazed crowns in one group were subjected to a large amount of grinding with well polishing (LaP group, n?=?7), while the other group required a little amount of grinding with well polishing (LiP group, n?=?6). Statistics were analysed by two-sided paired Student’s t-tests to a significance level of p?<?.05. The results revealed that the maximum and mean enamel wear significantly different between the antagonists of self-glazed crowns and the control teeth (p?<?.05). Increased amount of enamel wear was found in LaP group (p?<?.05). The self-glazed zirconia crowns caused more enamel wear of antagonists than natural teeth after 6 months. Occlusal adjustment and polishing were considered as possible confounders which affected wear behaviour.     

Low temperature degradation resistant nanostructured yttria-stabilized zirconia for dental applications

When used in prosthetic dentistry, zirconia encounters severe durability issues due to low temperature degradation: exposure to humidity results in a transition from tetragonal to monoclinic phase, associated to disruptive integrity loss. Recently it has been shown that size-induced stabilization helps maintaining zirconia in tetragonal form, when the grain size is reduced to the nano-range. Objective of this work is to demonstrate the applicability of High Pressure Field Assisted Sintering (HP-FAST) to the preparation of dense, nanostructured samples of tetragonal yttria stabilized zirconia, with yttria content between 0.5 and 3 mol% and showing resistance to low temperature degradation. The yttria stabilized zirconia nanopowders were prepared by a hydrothermal method. Sintering by HP-FAST was performed at 900 °C in 5 min, under a pressure of 620 MPa. Resistance to low temperature degradation was tested at 134 °C, under vapor pressure, for up to 40 h. Both pristine and aged samples were characterized by X-ray diffraction, high-resolution scanning electron microscopy and nanoindentation tests in continuous stiffness measurement mode. The sintered samples presented a grain size between 20 and 30 nm and low or null monoclinic content. Both parameters resulted unaffected by ageing. The best results in terms of phase composition and mechanical properties have been obtained with the material containing 1.5 mol% of yttria. These results induce to reconsider the use of yttria stabilized zirconia as material for dental prosthetic systems requiring long-term durability.     

Influence of the crystalline structure of ZrO2 on the metallic properties of Pt in Pt/WO3–ZrO2 catalysts

The influence of the crystalline structure of ZrO₂ on the metallic properties of Pt, when supported on WO₃–ZrO₂, was studied. Pt supported on tetragonal zirconia loses its metallic properties while when supported on monoclinic zirconia it presents good metallic activities. WO₂,^2- deposited on amorphous Zr(OH)₄ before calcination generates an active material for n‐butane isomerization. The larger the fraction of the tetragonal phase of zirconia in this material, the higher the isomerization activity and the lower the metallic activity of Pt. This revised version was published online in July 2006 with corrections to the Cover Date.