Zirconia in fixed prosthesis. A literature review

Vertical Marginal Discrepancy of a Monolithic Zirconia Crown with Different Cement Spaces

The long-term clinical success of indirect restorations highly depends on their marginal integrity. The cement space is an element that might affect the marginal integrity, but it can be altered during the configuring of the computer-assisted designing/computer-aided manufacturing (CAD-CAM) restoration. However, there is controversy in the literature regarding the effect of the cement space on the precision of zirconia crown marginal adaptation. The aim of this study was to measure the vertical marginal discrepancies between different cement thickness settings for CAD-CAM monolithic zirconia restorations. Material and Methods. An artificial mandibular right molar tooth mounted on a typodont was prepared for a zirconia crown using the standard method. The study sample consisted of 30 zirconia crowns (Zenostar Zr Translucent Zirconia, Weiland Dental, Germany) milled using an (iMes-iCore) milling machine. Each group of 10 crowns was designed with 30-50 and 70 μm spacer thicknesses. The vertical marginal adaptation at the center of the four different planes (mesial, distal, buccal, and palatal) was measured under a microscope at 40x magnification. A one-way analysis of variance test was used for statistical analysis. Results. The mean of Group 30 was 27.45; of Group 50 was 22.22; and of Group 70 was 22.90. There was no statistically significant difference between the groups (p ≥ 0.5). Conclusions. The increase in the cement space up to 70 μm did not influence the vertical marginal adaptation of the monolithic zirconia crowns.

Effect of coping materials zirconia or polyetheretherketone with different techniques of fabrication on vertical marginal gap and fracture resistance of posterior crowns with composite veneering

BACKGROUND

Insufficient research has been conducted in the literature assessing the performance of zirconia and polyetheretherketone (PEEK) crowns in relation to the essential requirements of successful restorations, such as fracture resistance or margin adaptation. The purpose of this study was to evaluate the effect of the coping materials zirconia or PEEK with different fabrication techniques on the vertical marginal gap and fracture resistance of posterior crowns with composite veneering.

METHODS

Ceramic copings (n = 18) restoring mandibular first molar were fabricated from zirconia (Zircon.x, Presidentdental, Germany), milled PEEK (PEEK CAD) (breCAM.BioHPP, Bredent, Germany) and pressed PEEK (PEEK Press) (BioHPP Granules, Bredent, Germany) six specimens each (n = 6). The copings were veneered with high impact polymer composite (HIPC) material (breCAM.HIPC, Bredent, Germany). The vertical marginal gap was captured under a magnification of 40X. Five equidistant marks on each surface of the die distinguished the points of measurement for a total of 20 readings per sample. The analysis was completed using an image analysis system (ImageJ 1.53t, National Institute of Health, USA). The specimens were loaded to failure at a crosshead speed of 1 mm/min and the load at failure was recorded to measure the fracture resistance.

RESULTS

The marginal gap was analyzed using one-way ANOVA followed by Tukey's post hoc test. Fracture resistance was analyzed using Welch one-way ANOVA followed by the Games-Howell post hoc test. Marginal gap values showed a significant difference between the tested groups, with zirconia having significantly lower gap values (48.67 ± 11.98 µm) than both the PEEK CAD (108.00 ± 20.08 µm) and Press groups (108.00 ± 25.10 µm) (p < 0.001). However, the results of fracture resistance showed no significant difference (p = 0.06) with 1687.47 ± 253.29 N, 2156.82 ± 407.64 N, 2436.72 ± 725.93 N for zirconia, PEEK CAD, and Press, respectively. The significance level was p < 0.05.

CONCLUSIONS

Zirconia framework crowns have a smaller vertical marginal gap than milled and pressed PEEK crowns. Crowns fabricated from zirconia, PEEK CAD, or PEEK Press frameworks and veneered with composite resin have comparable fracture resistance lower than the maximum biting force in the posterior region.

CLINICAL RELEVANCE

Posterior crowns with zirconia frameworks are preferred over milled and pressed PEEK frameworks regarding margin adaptation, although all can safely survive the maximum occlusal forces without fracture.

Ultra-Translucent Zirconia Laminate Veneers: The Influence of Restoration Thickness and Stump Tooth-Shade

This in vitro study aimed to evaluate the final shade of translucent zirconia laminate veneers with varying thicknesses over teeth with different shades. Seventy-five chairside computer-aided design/computer-aided manufacturing (CAD/CAM) shade A1 third-generation zirconia dental veneers, with thicknesses of 0.50 mm, 0.75 mm, and 1.00 mm, were placed on resin composite teeth with shades ranging from A1 to A4. The laminate veneers were divided into groups based on thickness and background shade. All restorations were evaluated with a color imaging spectrophotometer, to map the veneer surface from A1 to D4. Regardless of the thickness or background shade, all dental veneers showed color alteration from the original shade. Veneers with 0.5 mm thickness tended to display the B1 shade, while veneers with 0.75 mm and 1.0 mm thickness primarily exhibited the B2 shade. The thickness of the laminate veneer and background shade significantly modified the original shade of the zirconia veneer. One-way analysis of variance was performed and a Kruskal-Wallis test was used to determine the significance between the three veneer thicknesses groups. The results indicated that the thinner restorations showed higher values with the color imaging spectrophotometer, suggesting that thinner veneers may result in more consistent color matching. This study underscores the importance of carefully considering thickness and background shade when selecting zirconia laminate veneers, to ensure optimal color matching and overall aesthetic outcomes.

Hot Isostatically Pressed Nano 3 mol% Yttria Partially Stabilised Zirconia: Effect on Mechanical Properties

Objective: To investigate the flexural strength of hot isostatically pressed nano 3 mol% yttria partially stabilised zirconia and conventionally sintered micro 3 mole% yttria partially stabilised zirconia. Methods: A total of 40 bar-shaped (2 mm × 4 mm × 16 mm) specimens were prepared from hot isostatically pressed nano 3 mol% yttria partially stabilised zirconia (CeramaZirc Nano HIP, Precision Ceramics) and conventionally sintered micro 3 mole% yttria partially stabilised zirconia (CeramaZirc, Precision Ceramics). Two groups were prepared for each material (n = 10), with one serving as ‘control’ and the other being cyclically loaded using a chewing simulator (7 kg; 250 k cycles): SEM imaging was also undertaken on selected specimens. Flexural strength until fracture was recorded (ISO 6872). Paired and unpaired t-tests were chosen to compare mean outcomes between the four groups (p < 0.05). Results: Significant statistical difference was only found between the means of control specimens. CeramaZirc Nano HIP had the highest mean value (1048.9 MPa), whilst the lowest was seen for CeramaZirc after loading (770 MPa). Values for both materials were higher without loading than after loading. Values after cyclical loading showed large SD values (276.2−331.8) in comparison to ‘control’ (66.5−100.3). SEM imaging after cyclical loading revealed a smoother and less destructed surface of CeramaZirc Nano HIP compared to CeramaZirc. Significance: HIP nano zirconia exhibited inferior strength, surface polishability and behaviour to loading. Therefore, further investigation on the behaviour of such materials should be conducted before recommending for clinical use.

Fatigue strength of 5Y-FSZ: glazing and polishing effects

OBJECTIVE

The aim of this study was to evaluate the effect of four different finishing procedures on the fatigue strength of a fully stabilized zirconia (5Y-FSZ) material.

MATERIALS AND METHODS

Disc-shaped specimens of a 5Y-FSZ (Katana UTML, Kuraray Noritake) were made (ISO 6872-2015), grinded with 600- and 1200-grit silicon carbide paper, sintered as recommended, and randomly assigned into four groups according to the finishing technique: C (control, as-sintered), P (polished with polishing rubbers), G (glaze application - powder/liquid technique), and PG (polished with polishing rubbers + glaze application - powder/liquid). Then fatigue strength (staircase method), X-ray diffraction (XRD), and scanning electron microscopy (SEM) analyses were performed.

RESULTS

The C group presented the lowest fatigue strength, while the PG group presented the highest. The P and G groups presented intermediate behavior, presenting similar statistical results. XRD showed similar crystalline phase patterns for all groups. SEM images revealed some changes in the zirconia surface, with the P group presenting some scratches on the surface, while the scratches in the PG group were filled with the glaze material.

CONCLUSION

None of the techniques analyzed in this study impaired the fatigue strength of fully stabilized zirconia. Importantly, the polishing rubbers combined with glaze application (PG group) improved its fatigue strength.

CLINICAL RELEVANCE

The polishing rubbers followed by glaze application improve the fatigue strength in ultra-translucent zirconia.

Novel translucent monolithic zirconia fixed restorations in the esthetic zone

Novel translucent monolithic zirconia has improved optical properties, and it may fulfill patient's esthetic demands and overcome the chipping risk of bilayer metal-ceramic restorations. New zirconia's microstructures allow us to mimic natural teeth.

Evidence-based prosthodontics

The practice of evidence-based dentistry has assumed an integral part in today's world. It allows us to achieve self-motivated, problem-based learning, which eventually leads to acquiring clinically sound and relevant information that has a strong backing of evidence on a scientific basis. This would enhance the diagnosis but also the prognoses and treatment that are administered with the highest of ethical standards. Due to the advancement in material studies, dentistry, especially prosthodontics, is getting more intricate and complex due to the dynamic state in the development of new dental materials and equipment. The best evidence is sought through vast empirical literature consisting of controlled trials and reviews. Modern clinical practice should be concurrent with the latest scientific evidence that brings high standards to the treatment options and patient's values. This review highlights the evidence based dentistry on prosthodontics while also addressing the issues it poses in modern day dental practice.

Annealing-Induced Off-Stoichiometric and Structural Alterations in Ca2+- and Y3+-Stabilized Zirconia Ceramics

In the current study, high-temperature stability was investigated in two types of zirconia ceramics stabilized with two different additives, namely, calcia and yttria. The evolutions of structure and oxygen-vacancy-related defects upon annealing in air were investigated as a function of temperature by combining X-ray diffractometry with Raman, X-ray photoelectron and cathodoluminescence spectroscopies. We systematically characterized variations in the concentration of oxygen vacancies and hydroxyl groups during thermal treatments and linked them to structural alterations and polymorphic transformation. With this approach, we clarified how the combined effects of different dopants and temperature impacted on structural development and on the thermal stability of the oxygen-vacancy-related defect complex.

Fracture resistance and failure mode of layered translucent zirconia with different crown designs

This study investigated the impact of different veneering design on the fracture resistance and failure mode of layered translucent zirconia crowns, compared to the full monolithic zirconia crowns. Ninety crowns with different designs were divided into six groups (n=15); one fully contoured monolithic crown (FMC), one fully veneered with porcelain (FVC), or four partially veneered designs. All crowns were thermo-cycled, and then loaded to failure in a universal testing machine. The fracture resistance (N) and fracture modes were assessed. One-way ANOVA was performed followed by Tukey's multiple comparison (α<0.05). Results demonstrated that all the tested partially veneered designs exhibited enhanced fracture resistances and were comparable to that of the full-contour monolithic translucent zirconia crowns.

Effects of thickness of different types of high-translucency monolithic multilayer precolored zirconia on color accuracy: An in vitro study

STATEMENT OF PROBLEM

High-translucency monolithic multilayer precolored zirconia provides acceptable esthetics and eliminates chipping of the veneering porcelain. However, the color is not always consistent with the standard Vita shade guide, and the color saturation may vary with the thickness of the zirconia.

PURPOSE

The purpose of this in vitro study was to characterize the effect of thickness on the color accuracy of high-translucency monolithic multilayer precolored zirconia.

MATERIAL AND METHODS

Plate-shaped (20×20 mm) Vita A2 shade high-translucency monolithic multilayer precolored zirconia specimens of 3 types (SHT Multilayer, AT Multilayer, and 3D Multilayer) in 4 thicknesses (0.5, 1.0, 1.5, and 2.0 mm) were fabricated (N=120, n=10). A spectrophotometer was used to measure the color attributes (CIELab) against gray or A2 substrates to evaluate the color accuracy based on differences in color (ΔE) (versus the Vita shade guide) and chroma. Statistical analysis was performed by using the Pearson correlation, 2-way ANOVA, and post hoc Scheffé test (α=.05).

RESULTS

Against gray substrates, thickness was significantly positively correlated with all color attributes. Against A2 substrates, L∗ values increased with an increase in thickness; however, a∗, b∗, and chroma values remained stable. Zirconia with a thickness of 1.0 mm exhibited the lowest ΔE, regardless of the type, except for AT Multilayer against A2 substrates, where the lowest ΔE was achieved at 0.5 mm. At thicknesses ≥1.0 mm, the ΔE between the 2 substrates was imperceivable.

CONCLUSIONS

Thickness affected the color accuracy of different high-translucency monolithic multilayer precolored zirconia types. It appears that the optimal thickness in terms of color accuracy is 1.0 mm. These results could be used as a reference for the selection and preparation of abutments in clinical applications.

Influence of the chemical composition of monolithic zirconia on its optical and mechanical properties. Systematic review and meta-regression

PURPOSE

This systematic review set out to investigate the influence of chemical composition and specimen thickness of monolithic zirconia on its optical and mechanical properties. Meta-analysis and meta-regression analyzed the effects of variations in percentages of yttrium, aluminum, and specimen thickness of monolithic zirconia.

STUDY SELECTION

The review followed recommendations put forward in the PRISMA checklist. An electronic search for relevant articles published up to October 2019 was conducted in the Pubmed, Cochrane, Scopus, Scielo, and Web of Science databases, with no language limits and articles published in the last 10 years. From 167 relevant articles; applying inclusion criteria based on the review's PICO question, 26 articles were selected for qualitative synthesis (systematic review) and 24 for quantitative synthesis (meta-analysis). Experimental in vitro studies published were selected and their quality was assessed using the modified Consort scale for in vitro studies of dental materials.

RESULTS

The variables yttrium, aluminum and thickness were analyzed in random effects models, observing high heterogeneity ( > 75%), and finding statistically significant influences on the properties of monolithic zirconia (p<0.05).

CONCLUSIONS

Within the review's limitations, it may be concluded that variations in the percentage of yttrium and aluminum influence the optical and mechanical properties of monolithic zirconia, making it more or less esthetic and resistant in relation to each variable. The clinical implications of these findings can help select the most appropriate type of zirconia to meet the different clinical needs when restoring different regions (posterior or anterior).

Fracture Load of CAD/CAM Fabricated Cantilever Implant-Supported Zirconia Framework: An In Vitro Study

The fracture resistance of computer-aided designing and computer-aided manufacturing CAD/CAM fabricated implant-supported cantilever zirconia frameworks (ISCZFs) is affected by the size/dimension and the micro cracks produced from diamond burs during the milling process. The present in vitro study investigated the fracture load for different cross-sectional dimensions of connector sites of implant-supported cantilever zirconia frameworks (ISCZFs) with different cantilever lengths (load point). A total of 48 ISCZFs (Cercon, Degudent; Dentsply, Deutschland, Germany) were fabricated by CAD/CAM and divided into four groups based on cantilever length and reinforcement of distal-abutment: Group A: 9 mm cantilever; Group B: 9 mm cantilever with reinforced distal-abutment; Group C: 12 mm cantilever; Group D: 12 mm cantilever with reinforced distal-abutment (n = 12). The ISCZFs were loaded using a universal testing machine for recording the fracture load. Descriptive statistics, ANOVA, and Tukey's test were used for the statistical analysis (p < 0.05). Significant variations were found between the fracture loads of the four ISCZFs (p = 0.000); Group-C and B were found with the weakest and the strongest distal cantilever frameworks with fracture load of 670.39 ± 130.96 N and 1137.86 ± 127.85 N, respectively. The mean difference of the fracture load between groups A (810.49 + 137.579 N) and B (1137.86 ± 127.85 N) and between C (670.39 ± 130.96 N) and D (914.58 + 149.635 N) was statistically significant (p = 0.000). Significant variations in the fracture load between the ISCZFs with different cantilever lengths and thicknesses of the distal abutments were found. Increasing the thickness of the distal abutment only by 0.5 mm reinforces the distal abutments by significantly increasing the fracture load of the ISCZFs. Therefore, an increase in the thickness of the distal abutments is recommended in patients seeking implant-supported distal cantilever fixed prostheses.

Effect of connector size and design on the fracture resistance of monolithic zirconia fixed dental prosthesis

Background. Designing a high strength all-ceramic fixed partial denture with favorable esthetics can be challenging for clinicians; this study aimed to evaluate the effect of connector size and design on the fracture resistance of monolithic zirconia fixed dental prostheses.

Methods. Two groups of twenty 3-unit monolithic zirconia (Sirona inCoris TZI, Sirona Dental Systems GmbH) bridges, extending from the mandibular first premolar to the first molar with different connector sizes (9 mm² and 12 mm²), were divided into two subgroups with different connector designs (round and sharp). The specimens were subjected to the three-point bending test to obtain the fracture-bearing load. The results were reported using descriptive statistics (mean ± standard deviation). Mann-Whitney U test was used to compare the fracture load in two types of designs for each connector size and two connector size types for each connector design. The significance level was considered at P<0.05.

Results. The minimum failure load was related to the group with a 9-mm² connector size and a sharp embrasure design (1054.4±133.89 N), and the highest mean value belonged to the group with 12-mm² connector size and rounded embrasure design (1599.8±167.09 N). Mann-Whitney U test indicated a significant difference between the mean failure load of the rounded and sharp embrasure designs in the 9-mm² connector size (P =0.007). However, the difference was insignificant in the 12-mm² connector size (P =0.075).

Conclusion. Sharp embrasure design is not recommended for high-stress areas with restricted occlusogingival height. A 9-mm2 connector size for 3-unit monolithic zirconia fixed dental prosthesis (FDP), which is recommended by the manufacturer, should be used more cautiously

Prospective study of monolithic zirconia crowns: clinical behavior and survival rate at a 5-year follow-up

Purpose To evaluate the clinical behavior and survival of full coverage monolithic zirconia crowns on posterior teeth over a 5-year follow-up.Methods Fifty patients were recruited and underwent restoration with a Lava Plus monolithic zirconia crown (Lava™ Frame Zirconia, 3M Espe, Germany) on premolars or molars. Patients were monitored over a 5-year follow-up (2014-19), recording any biological and/or mechanical complications; these data were used to estimate the crowns' success rate. Periodontal clinical parameters were recorded (pocket probing depth (PPD), plaque index (PLI), bleeding on probing (BOP), and gingival recession (GR)). Wear to the zirconia crowns and antagonist teeth were also evaluated with Geomagic software (3D Systems, U.S.A.). Patients' satisfaction with treatment was evaluated in a questionnaire.Results For the 50 monolithic zirconia crowns analyzed, the survival rate was 98% after 5 years. Only 6% of the crowns presented some type of complication (two debonding and one root fracture). No fracture or fissures were detected. GR and BOP were the only clinical parameters found to be significantly greater around teeth restored with crowns. The monolithic zirconia crowns suffered less wear than the enamel of antagonist teeth. Patient's general satisfaction with treatment was high.Conclusions Monolithic zirconia crowns on posterior teeth are a highly predictable treatment option, with a high survival rate. The single treatment failure was due to a biological complication arising from root fracture. This treatment may be recommended as a treatment that conserves dental structure, and requires minimal dental preparation.

Publication trends in journal of clinical and experimental dentistry

Background

Journal of Clinical and Experimental Dentistry (J Clin Exp Dent; JCED) is an English language journal published by the Spanish Society of Oral Surgery, and has been online since 2009. It is indexed in PubMed Central and Scopus since 2012, with monthly publications since 2016. The purpose of this article was to review and analyse the publications in this journal since its inception, over a period of 11 years (2009-2019).

Material and Methods

This paper assessed the number, type and subjects of the articles published in the journal over 11 years. The institutions of the first authors, number of PubMed citations and the Hirsch (h5) index was assessed and analysed.

Results

The manuscripts published in JCED have gradually increased over the years, with Original research articles accounting for the bulk of contributions. The journal publishes articles mainly from the subjects of Oral Pathology and Operative Dentistry and Endodontics. Articles published in JCED are indexed in PubMed Central (since 2012), Scopus, DOI system, and Google Scholar. A country-wise mapping of the (first) author’s institutions revealed significant contributions from researchers from all over the world. With an h5 index of 26, the journal was ranked among the top six multispeciality journals. The most cited articles were the literature reviews on common oral lesions (recurrent apthous stomatitis and candidiasis).

Conclusions

The journal has contributed to the growth of scientific literature pertaining to subjects from all the fields of dentistry. Over the past 11 years, JCED has served as a platform for large number of manuscripts in all the disciples of dentistry, from researches all over the world.

Key words:Publication trends, Journal of Clinical and Experimental Dentistry, Bibliometrics.

Color accuracy of different types of monolithic multilayer precolored zirconia ceramics

STATEMENT OF PROBLEM

The use of monolithic multilayer precolored zirconia facilitates the production of esthetic restorations in a convenient and straightforward manner. However, the accuracy of the final color is not clear.

PURPOSE

The purpose of this in vitro study was to determine the color accuracy of different types of monolithic multilayer precolored zirconia ceramics of varying thicknesses.

MATERIAL AND METHODS

Eighty cubical A2-shade monolithic multilayer precolored zirconia ceramic specimens (15×15 mm) of 2 different thicknesses (1.0 mm and 1.5 mm) and 4 zirconia brands (UPCERA EXPLORE [UPEX], KATANA Zirconia STML [STML], Enamel ZR Multi-5 [EZM5], and Aidite 3D Pro Zir [A3DM]) were fabricated and divided into 8 groups (n=10). The Commission Internationale de l'Eclairage (CIELab) values were measured against 3 different backing substrates (gray, transparent, and A2) by using a spectrophotometer. The color difference (ΔE) between the backing substrates of each group and the Vita A2 Shade Guide, translucency parameter (TP), and chroma (C) values were calculated to evaluate the accuracy of the final color. Statistical analysis was performed by using ANOVA and the post hoc Tukey HSD tests (α=.05).

RESULTS

The ΔE values for UPEX and STML exceeded the clinically acceptable thresholds for gray and transparent backing substrates (ΔE>3.7) and were higher than those for the A2 backing substrate. A3DM showed less ΔE from the shade guide for all the backing substrates (P<.05), and the corresponding ΔE values were within the clinically acceptable threshold (ΔE<3.7). The TP value was inversely proportional, and the C value was proportional to thickness. For the zirconia ceramics with identical thicknesses, UPEX and STML exhibited the highest TP values, and A3DM showed the lowest C value (P<.05).

CONCLUSIONS

At a specific thickness, color accuracy was mainly affected by the type of monolithic multilayer precolored zirconia ceramic, and the high transparency of ceramics will cause color differences.

Comparative evaluation of natural enamel wear against polished yitrium tetragonal zirconia and polished lithium disilicate - An in vivo study

Aim:

The aim of this study is to compare wear of the natural teeth against polished yttrium tetragonal zirconia and polished lithium disilicate crowns.

Study Setting and Design:

Experimental type of study.

Materials and Methods:

Polished yttrium tetragonal zirconia and polished lithium disilicate crowns were fabricated and given to 15 patients each (n=15). Crowns were fabricated opposing natural tooth. Patients were recalled after 1year and impression were recorded with opposing arch and baseline and final cast were scanned and superimposed using 3 D scanner.

Statistical Analysis Used:

Data collected by experiments were computerized and analyzed using the Statistical Package for Social Sciences (SPSS) version 16.0. The normality of the data was checked using the Kolmogorov-Smirnov test and Shapiro-Wilk tests. The data were normally distributed. Statistical analysis was done by using tools of descriptive statistics such as Mean, and Standard Deviation for representing quantitative data (enamel wear measured in μm) Parametric tests: Student t-test for intergroup comparison was done.

Results:

No statistical difference were found between wear of opposing enamel for polished yttrium tetragonal and polished lithium disiliacte crowns [p=0.446].

Conclusion:

Within the limitations of the study, it can be concluded that polished lithium disilicate showed better clinical outcome than polished yttrium tetragonal zirconia, though the evaluated data was statistically non significant.

"CAD-on" Interfaces - Fracture Mechanics Characterization

PURPOSE

To apply fracture mechanics methodology to determine the interfacial fracture toughness of the interfaces present in "CAD-on" crowns consisting of CAD/CAM milled lithium disilicate veneers glass-fused to CAD/CAM milled yttrium oxide stabilized tetragonal zirconia polycrystal framework.

MATERIALS AND METHODS

The notchless triangular prism specimen fracture toughness test was used to determine interfacial fracture toughness. Four groups, each consisting of (6 × 6 × 6 × 12) mm prisms (n = 22), were produced. Half-size [(6 × 6 × 6 × 6) mm] specimens of IPS e.max CAD and IPS e.max ZirCAD were approximated under vibration with Crystal Connect fusing glass and sintered according to manufacturer's guidelines to obtain the following three interfaces: (1) e.max CAD/Crystal Connect/e.max CAD (Group I); (2) Zir CAD/Crystal Connect/Zir CAD (Group II); and (3) Zir CAD/Crystal Connect/e.max CAD (Group III). For Group IV (control, based on the "press-on" veneering technique), half-size [(6 × 6 × 6 × 6) mm] IPS e.max ZirCAD prisms were coated with ZirLiner and pressed with IPS e.max ZirPress ingots to obtain (6 × 6 × 6 × 12) mm prisms. All specimens were tested using a computer controlled material testing machine. Results were analyzed with one-way ANOVA, Scheffé multiple means comparisons (α = 0.05) and Weibull statistics. All fractured surfaces were characterized with a light microscope. Selected fractured surfaces were characterized under a scanning electron microscope.

RESULTS

All experimental groups demonstrated a cohesive mode of failure in the fusing glass layer. The number and size of defects appeared to correlate with the variability of fracture toughness values. There were no significant differences between the fracture toughness of the "CAD-on" interfaces (p = 0.052). The results suggested that the fracture toughness of Crystal Connect limited the interfacial fracture toughness values. The "CAD-on" fracture toughness value (Group III) was significantly greater than that of the ZirPress "press-on" control (Group IV) (p < 0.001).

CONCLUSION

The "CAD-on" process results in stronger bonding between veneer and framework, compared to conventional veneering. The clinical use of "CAD-on" crowns could therefore be advocated. The selection of any restorative material requires a thorough analysis of advantages, limitations and results from clinical studies to inform the clinical decision in a case-by-case approach.

Effects of different surface treatments on the shear bond strength of veneering ceramic materials to zirconia

PURPOSE

To evaluate and compare the effect of different materials and techniques on the shear bond strength of veneering ceramic materials to zirconia.

MATERIALS AND METHODS

136 sintered zirconia cubes were prepared and randomly divided into four study groups according to corresponding methods of surface treatment and materials: GLN (grinding followed by laser scanning using Noritake Cerabien ZR), SLN (sandblasting followed by laser scanning using Noritake Cerabien ZR), GLV (grinding followed by laser scanning using VITA VM 9), and SLV (sandblasting followed by laser scanning using VITA VM 9). Spraying technique was performed to coat the core. Profilometer, SEM, XRD, EDS, universal testing machine, and stereomicroscope were used to record surface roughness Ra, surface morphology, phase transformation, elemental compositions, shear bond strength SBS values, and failure types, respectively. Specimens were investigated in unaged (not immersed in artificial saliva) and aged (stored in artificial saliva for a month) conditions to evaluate SBS values.

RESULTS

Grinding and GLN as first and second surface treatments provided satisfactory Ra values in both conditions (1.05 ± 0.24 µm, 1.30 ± 0.21 µm) compared to sandblasting and other groups (P<.05). The group GLN showed the highest SBS values in both conditions (30.97 ± 3.12 MPa, 29.09 ± 4.17 MPa), while group SLV recorded the lowest (23.96 ± 3.60 MPa, 22.95 ± 3.68 Mpa) (P<.05). Sandblasting showed phase transformation from t-m. Mixed failure type was the commonest among all groups.

CONCLUSION

GLN showed to be a reliable method which provided satisfactory bond strength between the veneer ceramic and zirconia. This method might preserve the integrity of fixed dental crowns.

Fracture load of metal-ceramic, monolithic, and bi-layered zirconia-based posterior fixed dental prostheses after thermo-mechanical cycling

OBJECTIVES

This study aims to evaluate the fracture load of differently fabricated 3-unit posterior fixed dental prostheses (FDPs) with an intermediate pontic.

METHODS

Fifty sets of two stainless-steel abutments were randomly assigned to five groups (n = 10 each) depending on the material and technique used for manufacturing the FDPs: (1) Metal-ceramic (MC, control); (2) Lava Zirconia (LZ, bi-layered); (3) Lava Plus (LM, monolithic); (4) VITA In-Ceram YZ (YZ, bi-layered); and (5) IPS e-max ZirCAD (ZZ, bi-layered). After being luted to the dies, all FDPs were submitted to thermo-mechanical cycling (120,000 masticatory cycles, 50 N; plus 774 thermal cycles of 5 °C/55 °C, dwell time: 30 s). Samples were then subjected to a three-point bending test until fracture in a universal testing machine (cross-head speed: 1 mm/min). Fracture load of the veneering ceramic (VF) and total fracture load (TF) were recorded. Microstructure and failure patterns were assessed. Data was analysed using one-way ANOVA and Tukey HSD post-hoc tests (α = 0.05).

RESULTS

MC restorations recorded higher VF and TF values than did zirconia FDPs (p = 0.0001), which showed no between-group differences. Within the bi-layered groups, TF was significantly higher than VF. LM pieces registered lower average grain size than did LZ specimens (p = 0.001). Overall, the connector was the weakest part.

CONCLUSIONS

All of the groups tested could withstand clinical chewing forces in terms of average fracture load. Zirconia-based samples performed similarly to each other, but showed lower mean fracture load values than did metal-ceramic ones.

CLINICAL SIGNIFICANCE

Monolithic zirconia may be recommendable for solving the chipping problem.

Thermal cracks of implant-based zirconia four-unit restorations: A fractographic analysis of two restorations fractured during production

Two zirconia-based 4-unit restorations intended for the same patient fractured during the veneering process even though the prolonged cooling protocol recommended by the manufacturers was used. Fractographic analyses revealed that both restorations fractured as a result of thermal shock, but at different times during production. Further investigation is necessary to optimize the firing protocols for large zirconia-based restorations and avoid fracture due to thermal shock.

Load-bearing capacity of various CAD/CAM monolithic molar crowns under recommended occlusal thickness and reduced occlusal thickness conditions

PURPOSE

The goal of this study was to evaluate the fracture resistances of various monolithic crowns fabricated by computer-aided design and computer-aided manufacturing (CAD/CAM) with different thickness.

MATERIALS AND METHODS

Test dies were fabricated as mandibular molar forms with occlusal reductions using CAD/CAM. With different occlusal thickness (1.0 or 1.5 mm), a polymer-infiltrated ceramic network (Enamic, EN), and zirconia-reinforced lithium silicate (Suprinity, SU and Celtra-Duo, CD) were used to fabricate molar crowns. Lithium disilicate (e.max CAD, EM) crowns (occlusal: 1.5 mm) were fabricated as control. Seventy crowns (n=10 per group) were bonded to abutments and stored in water for 24 hours. A universal testing machine was used to apply load to crown until fracture. The fractured specimens were examined with a scanning electron microscopy.

RESULTS

The type of ceramics and the occlusal thickness showed a significant interaction. With a recommended thickness (1.5 mm), the SU revealed the mean load similar to the EM, higher compared with those of the EN and CD. The fracture loads in a reduced thickness (1.0 mm) were similar among the SU, CD, and EN. The mean fracture load of the SU and CD enhanced significantly when the occlusal thickness increased, whereas that of the EN did not.

CONCLUSION

The fracture loads of monolithic crowns were differently influenced by the changes in occlusal thickness, depending on the type of ceramics. Within the limitations of this study, all the tested crowns withstood the physiological masticatory loads both at the recommended and reduced occlusal thickness.

Comparative fracture behavior of monolithic and veneered zirconia posterior fixed dental prostheses

The purpose of this study was to evaluate and to compare the fracture load and the fracture pattern of monolithic and veneered zirconia posterior fixed dental prostheses (FDPs). Twenty standardized steel dies were prepared to receive posterior 3-unit FDPs. Specimens were randomly divided into 2 groups (n=10): (1) Lava Zirconia, and (2) Lava Plus. All FDPs were cemented using glass ionomer cement and subjected to thermal and mechanical cycling at 5-55ºC with a 30-s dwell time for 120,000 masticatory cycles. All specimens were subjected to a three-point bending test until fracture. Data were statistically analyzed using Student's t test, paired t-test and Weibull statistics (α=0.05). No differences were observed in fracture load between the groups. Veneering ceramic fractured before than framework in veneered zirconia group. The fracture pattern was different. The tested groups demonstrated clinically acceptable fracture load values. Monolithic zirconia solves the chipping problem.

Influence of the Conditioning Method for Pre-Sintered Zirconia on the Shear Bond Strength of Bilayered Porcelain/Zirconia

This study evaluated the bond strength of veneering porcelain with an experimental conditioner-coated zirconia. Pre-sintered Y-TZP specimens (n = 44) were divided in two groups based on conditioning type. After sintering, all sample surfaces were sandblasted and layered with veneering porcelain. Additionally, half of the specimens in each group underwent thermal cycling (10,000 cycles, 5–55 °C), and all shear bond strengths were measured. After testing, the failure mode of each fractured specimen was determined. Differences were tested by parametric and Fisher’s exact tests (α = 0.05). The differences in bond strength were not statistically significant. Adhesive fractures were dominantly observed for the non-thermal cycled specimens. After thermal cycling, the conditioner-coated group showed cohesive and mixed fractures (p = 0.0021), whereas the uncoated group showed more adhesive fractures (p = 0.0021). Conditioning of the pre-sintered Y-TZP did not change the shear bond strength of the veneering porcelain, but did improve the failure mode after thermal cycling.

Veneered Zirconia-Based Restorations Fracture Resistance Analysis

PURPOSE

To examine the effects of the veneering technique on the fracture resistance of zirconia-based crowns.

MATERIALS AND METHODS

An artificial tooth was prepared with a 1.2 mm heavy chamfer finish line and 8° taper. The prepared tooth was scanned using CAD/CAM technology to fabricate 45 cobalt chromium (CoCr) testing dies. One CoCr die was scanned, and 45 zirconia copings were milled and divided according to the veneering technique into three groups of 15 specimens each: layering veneering (LV) using Vita Vm9, overpressing veneering (OV) using Vita Pm9, and digital veneering (DV) using Vita Triluxe forte. The crowns were cemented onto the testing dies using glass ionomer cement. The specimens were thermocycled (3000 cycles, 5° to 55°) then statically loaded (3.7 mm ball, 0.5 mm/min crosshead speed) until failure. Failed crowns were inspected using a magnifier, and failure patterns were identified. One-way ANOVA and multiple comparison Bonferroni tests were applied for statistical analysis of the results.

RESULTS

Means and standard deviations of failure loads were 1200 ± 306 N for the LV group, 857 ± 188 N for the OV group, and 638 ± 194 N for the DV group. The differences in failure loads were statistically significant between all groups (p < 0.05). Failure mode was predominantly cohesive for LV and OV groups, whereas it was predominantly adhesive for the DV group.

CONCLUSIONS

The LV group was superior to other groups in terms of fracture resistance, while the DV group was inferior to the other groups in the same aspect.

Influence of Different Framework Designs on the Fracture Properties of Ceria-Stabilized Tetragonal Zirconia/Alumina-Based All-Ceramic Crowns

The aim of this study was to evaluate the fracture load and failure mode of all-ceramic crowns with different ceria-stabilized tetragonal zirconia/alumina nanocomposite (Ce-TZP/A) framework designs. Four frameworks (anatomical shape: AS, with a buccal or lingual supporting structure: BS and LS, or buccal and lingual supporting structures: BLS) were fabricated. All frameworks were veneered with porcelain to fabricate all-ceramic crowns followed by cementation to tooth analogs. The fracture load of each crown either without or with pre-loading (1.2 million cycles, 49 N) was measured. The failure mode was classified into partial or complete fracture. Differences were tested for significance (p < 0.05) by a two-way Analysis of Variance (ANOVA), followed by Tukey’s test and by Fisher’s exact test, respectively. Without pre-loading, supporting structures did not influence the fracture load or failure mode. Partial fractures were the most common failure mode. Pre-loading promoted the severity of the failure mode, although the fracture load among the framework designs was not influenced. In the AS group, prefailures were observed during pre-loading, and complete fractures were significantly increased after pre-loading. In contrast, the failure mode of the BLS group remained unchanged, showing only partial fracture even after pre-loading. This Ce-TZP/A framework design, comprised of an anatomical shape with additional buccal and lingual structures, has the potential to reduce the chipping of the veneering porcelain.

Fixed dental prostheses with vertical tooth preparations without finish lines: A report of two patients

Tooth abutments can be prepared to receive fixed dental prostheses with different types of finish lines. The literature reports different complications arising from tooth preparation techniques, including gingival recession. Vertical preparation without a finish line is a technique whereby the abutments are prepared by introducing a diamond rotary instrument into the sulcus to eliminate the cementoenamel junction and to create a new prosthetic cementoenamel junction determined by the prosthetic margin. This article describes 2 patients whose dental abutments were prepared to receive ceramic restorations using vertical preparation without a finish line.

Zirconia based dental ceramics: structure, mechanical properties, biocompatibility and applications

Zirconia (ZrO₂) based dental ceramics have been considered to be advantageous materials with adequate mechanical properties for the manufacturing of medical devices.

Resin bonding of metal brackets to glazed zirconia with a porcelain primer

Objective

The aims of this study were to compare the shear bond strength between orthodontic metal brackets and glazed zirconia using different types of primer before applying resin cement and to determine which primer was more effective.

Methods

Zirconia blocks were milled and embedded in acrylic resin and randomly assigned to one of four groups: nonglazed zirconia with sandblasting and zirconia primer (NZ); glazed zirconia with sandblasting, etching, and zirconia primer (GZ); glazed zirconia with sandblasting, etching, and porcelain primer (GP); and glazed zirconia with sandblasting, etching, zirconia primer, and porcelain primer (GZP). A stainless steel metal bracket was bonded to each target surface with resin cement, and all specimens underwent thermal cycling. The shear bond strength of the specimens was measured by a universal testing machine. A scanning electron microscope, three-dimensional optical surface-profiler, and stereoscopic microscope were used to image the zirconia surfaces. The data were analyzed with one-way analyses of variance and the Fisher exact test.

Results

Group GZ showed significantly lower shear bond strength than did the other groups. No statistically significant differences were found among groups NZ, GP, and GZP. All specimens in group GZ showed adhesive failure between the zirconia and resin cement. In groups NZ and GP, bonding failed at the interface between the resin cement and bracket base or showed complex adhesive and cohesive failure.

Conclusions

Porcelain primer is the more appropriate choice for bonding a metal bracket to the surface of a full-contour glazed zirconia crown with resin cement.

Effects of core characters and veneering technique on biaxial flexural strength in porcelain fused to metal and porcelain veneered zirconia

PURPOSE

The purpose of this study was to assess the impact of the core materials, thickness and fabrication methods of veneering porcelain on prosthesis fracture in the porcelain fused to metal and the porcelain veneered zirconia.

MATERIALS AND METHODS

Forty nickel-chrome alloy cores and 40 zirconia cores were made. Half of each core group was 0.5 mm-in thickness and the other half was 1.0 mm-in thickness. Thus, there were four groups with 20 cores/group. Each group was divided into two subgroups with two different veneering methods (conventional powder/liquid layering technique and the heat-pressing technique). Tensile strength was measured using the biaxial flexural strength test based on the ISO standard 6872:2008 and Weibull analysis was conducted. Factors influencing fracture strength were analyzed through three-way ANOVA (α≤.05) and the influence of core thickness and veneering method in each core materials was assessed using two-way ANOVA (α≤.05).

RESULTS

The biaxial flexural strength test showed that the fabrication method of veneering porcelain has the largest impact on the fracture strength followed by the core thickness and the core material. In the metal groups, both the core thickness and the fabrication method of the veneering porcelain significantly influenced on the fracture strength, while only the fabrication method affected the fracture strength in the zirconia groups.

CONCLUSION

The fabrication method is more influential to the strength of a prosthesis compared to the core character determined by material and thickness of the core.

Fracture resistance and failure mode of posterior fixed dental prostheses fabricated with two zirconia CAD/CAM systems

Background

In recent years there has been an improvement of zirconia ceramic materials to replace posterior missing teeth. To date little in vitro studies has been carried out on the fracture resistance of zirconia veneered posterior fixed dental prostheses. This study investigated the fracture resistance and the failure mode of 3-unit zirconia-based posterior fixed dental prostheses fabricated with two CAD/CAM systems.

Material and Methods

Twenty posterior fixed dental prostheses were studied. Samples were randomly divided into two groups (n=10 each) according to the zirconia ceramic analyzed: Lava and Procera. Specimens were loaded until fracture under static load. Data were analyzed using Wilcoxon´s rank sum test and Wilcoxon´s signed-rank test (P<0.05).

Results

Partial fracture of the veneering porcelain occurred in 100% of the samples. Within each group, significant differences were shown between the veneering and the framework fracture resistance (P=0.002). The failure occurred in the connector cervical area in 80% of the cases.

Conclusions

All fracture load values of the zirconia frameworks could be considered clinically acceptable. The connector area is the weak point of the restorations.

Key words:Fixed dental prostheses, zirconium-dioxide, zirconia, fracture resistance, failure mode.

Influence of surface preparation on fracture load of resin composite-based repairs

The purpose of the present study is to evaluate the fracture load of composite-based repairs to fractured zirconium oxide (Z) crowns and to ceramic-fused-to-metal (CM) crowns, comparing different mechanical surface preparation methods. A total of 75 crowns were repaired; samples then underwent dynamic loading and thermocycling. Final fracture load values for failure of the repaired crowns were measured and the type of fracture registered. Group I: CM: Surface preparation with a diamond bur + 9.5% Hydrofluoric Acid (HF) etching; Group II): CM: air-particle (Al2O3) + 9.5% HF; Group III: CM: Silica coating (SiO2); Group IV): Z: air-particle (Al2O3) + HF 9.5%; Group V) Z: Silica coating (SiO2). Of the three CM groups, Group I (CM-diamond bur) showed the highest mean failure value, with significant difference in comparison with Group III (CM-silica coating). For the zirconia groups, the highest value was obtained by Group V (silica coating).

Key words:Crown, ceramic-fused-to-metal, zirconia, resin-composite, ceramic covering.