Color- and strength-graded zirconia: Strength, light transmission, and composition.

STATEMENT OF PROBLEM: Natural teeth are graded in terms of translucency and strength. Graded zirconia materials are now available with a higher yttria content on the top or in the enamel zone to increase surface translucency and a lower yttria content on the bottom or in the dentin zone to increase strength. Such materials could provide multiple advantages over uniform materials and reduce the need for porcelain veneering in anterior artificial crowns; however, studies on the properties of these materials are lacking. PURPOSE: The purpose of this in vitro study was to measure and compare the biaxial flexural strength, percentage light transmission, elemental content, and phase content of zones within and among color graded zirconia blocks and color- and strength-graded zirconia blocks. MATERIAL AND METHODS: Disks of a color graded material (Katana STML) and a strength- and color-graded material (IPS e.max ZirCAD Prime) were fabricated (Zircom Furnace). Biaxial flexural strength was measured using a piston-on-3-ball test in a universal testing machine (n=10). Absolute light transmission was measured with a spectrophotometer. Elemental compositions were quantified for 3 zones in each of the 2 zirconia materials using X-ray fluorescence analysis. Zirconia phase fractions were quantified for 3 zones using X-ray diffraction analysis (XRD). Where appropriate, 2-way ANOVA, 1-way ANOVA, and Tukey multiple pairwise comparison testing were used to determine which of the 6 zones differed from one another (α=.05). RESULTS: The color-graded zirconia exhibited gradients in light transmission and differences in phase content in the 3 zones measured. The color- and strength-graded zirconia exhibited gradients in light transmission, biaxial flexural strength, elemental composition, and phase content in the 3 zones measured. The bottom, dentin, or intaglio layer of a strength graded zirconia material was substantially stronger than all other zones of either material (P<.05). The top, enamel, zones of both materials possessed high light transmissibility (P<.05). The 2 materials differed with respect to biaxial strength (P<.001), light transmission (P<.02), elemental composition, and phase composition overall, as well as in most zone-by zone comparisons (P<.05). The performance and composition of the color graded material was consistent with it being a 5Y material throughout. The performance and composition of the color and strength graded material was consistent with it having a 3Y bottom zone and a 5Y top zone. CONCLUSIONS: A strength-graded and color-graded zirconia material offers potential advantages in both strength and translucency.

A step-by-step technique to create an ideal color match, form, and surface texture to all-ceramic restorations.

OBJECTIVES: Although the presence of a chairside CAD/CAM system in the dental office saves time and cost, it deprives the dentist from the dental technologist' skills and experience. The dentist now has to gain and acquire knowledge and skills about how to finish, characterize, stain, and glaze ceramic restorations. The main objectives of this article is to teach novel and reproducible techniques for surface color, texture, glaze and polish for either the chairside or laboratory fabricated indirect ceramic restoration. CLINICAL CONSIDERATIONS: A protocol for intraoral characterization of monolithic ceramics; the "Triple R" protocol for tooth color mimicking was followed. It consist of three steps: (1) "Recognize" tooth color shapes, (2) "Record" the present color shapes in the patient dentition by drawing a color map for the color shapes extension and determine which luster paste stain to be used for replicating them, and (3) "Replicate" intraorally the recorded color shapes guided by the adjacent natural teeth using low fusing ceramic pastes (shades and stains) for color shape replication. Also, the final touch technique was followed to shape, texture and final surface finish of dental restorations. It is composed of 5 basic levels which we call dental "micro-esthetics that define shape, texture, and surface luster. CONCLUSIONS: Following the steps of both; the "Triple R" protocol and the "FINAL TOUCH" technique will help to reproduce the final shade of the restoration to create the illusion of a natural tooth to the observer. CLINICAL SIGNIFICANCE: This article shows how combining two practical methodologies to record and replicate both color shapes and surface texture of natural teeth may extend mimicking, that is, step by step natural tooth shade beyond the limitations of the available commercial shade guides.

Influence of yttria content and surface treatment on the strength of translucent zirconia materials.

STATEMENT OF PROBLEM: Newly developed translucent zirconia materials have been used for anterior monolithic complete coverage restorations. Surface treatments can improve adhesion, as well as decrease or increase the strength of ceramics. However, information on the influence of surface treatments on the strength of translucent zirconias is sparse. PURPOSE: The purpose of this in vitro study was to measure and characterize the effects of different surface treatments, including airborne-particle abrasion, on the strength of different translucent 4 mol% and 5 mol% yttria-stabilized zirconia materials. MATERIALS AND METHODS: Disks (N=160) made from 4 types of translucent yttria-stabilized zirconia materials were surface-treated in 4 ways: Control groups were hand-polished with 2000-grit silicon carbide abrasive paper; as-machined; glass bead airborne-particle abraded; and alumina airborne-particle abraded. The biaxial flexural strength was measured by using a piston-on-3-ball test in a universal testing machine. The simple main effects of material type and surface treatment and their interaction on biaxial flexural strength were evaluated with 2-way ANOVA (α=.05). A priori, 1-way ANOVA and the Tukey multiple comparisons tests were used within material and treatment types (α=.05). Surface morphology was assessed by using scanning electron microscopy. Translucency, absolute transmittance, was measured by using a spectrophotometer. RESULTS: Two-way ANOVA revealed that the effects of zirconia type, surface treatment, and their interaction all significantly affected biaxial flexural strength (P<.001). One-way ANOVA revealed that the 4Y material was stronger than all 5Y materials, regardless of surface treatment; all 5Y materials were ranked from strongest to weakest as polished; as-machined, or glass bead abraded; and alumina abraded. The 4Y material was stronger when alumina abraded than when glass bead abraded. Scanning electron microscopy showed that as-polished surfaces were smoother than all others; as-machined and glass bead abraded surfaces displayed little difference; alumina abraded was the roughest; and differences among materials were not discerned. The 1-way ANOVA and multiple comparisons testing showed that the 4Y material had less absolute transmittance, approximately 5% less, than all the 5Y materials. CONCLUSIONS: Zirconia material type and surface treatment influenced the strength of translucent zirconia materials; a 4 mol% zirconia material was stronger than 5 mol% zirconia materials for all surface treatments tested; airborne-particle abrasion using alumina had a slight strengthening effect on a 4 mol% zirconia but had a weakening effect on 5 mol% materials; airborne-particle abrasion by using alumina produced the roughest surfaces on all materials; and the 4 mol% material was slightly less translucent than the 5 mol% materials.

Analysis of color and fluorescence of different dentin ceramics and natural human dentin's to enhance shade matching.

OBJECTIVES: This study aimed to compare the color and fluorescence of five dentin ceramic systems with human dentin to enhance shade matching. MATERIALS AND METHODS: Five dentin ceramic systems, including Vita, GC, Creation, Noritake, and Ivoclar in 16 shades, and 12 human dentins, were prepared. The fluorescence and color coordinates were measured at 380-780 nm. A light source including a visible and a ultraviolet (UV) complemented with a geometry 45° illumination and 0° observer was used. The mean minimum difference in color coordinates and fluorescence efficiency was statistically analyzed before and after UV excitation by one-way ANOVA (p < 0.05). Post-hoc multiple comparisons were performed using the LSD test (p < 0.05). RESULTS: While the fluorescence efficiency of Noritake and Ivoclar ceramics displayed no significant difference with natural dentin, Vita, GC, and Creation ceramics presented a lower fluorescence compared to the natural dentin (p < 0.05). Noritake and Ivoclar had a better color match with human dentin than the other ceramics. Studying the color differences under UV showed that just Creation offers statistically worse performance than the other ceramic. CONCLUSIONS: The color and fluorescence of the used different brands of dentin ceramic are not the same as the human dentin. However, Noritake and Ivoclar presented the most similarity. CLINICAL SIGNIFICANCE: Knowledge of ceramic and natural teeth fluorescence is essential for acceptable reproduction of optical properties in esthetic restorations.

The Photoshop Smile Design Technique.

Esthetic or cosmetic dentistry has become one of the main areas of dental practice emphasis and growth for the past several decades. Many articles have been written and courses taught over the years on concepts of smile design to develop a treatment plan for an esthetic outcome for the patient. The beauty of digital smile design is that patients can see the potential esthetic outcomes of treatment options in minutes. While other dental processes would still need to be completed (ie, generating casts, testing vertical changes and esthetics with a mock-up, etc), using smile design software to visualize the end result is a way to get acceptance by the patient prior to starting the physical processes. This article will show how the authors use Adobe® Photoshop® to edit pre-treatment images of a patient to create digitally enhanced or altered smiles, which could help the dental professional with analysis and treatment planning. It will also help them articulate and present the smile analysis options to the patient.

Effect of tooth substrate and porcelain thickness on porcelain veneer failure loads in vitro.

STATEMENT OF PROBLEM: Bonded porcelain veneers are widely used esthetic restorations. High success and survival rates have been reported, but failures do occur. Fractures are the commonest failure mode. Minimally invasive or thin veneers have gained popularity. Increased enamel and porcelain thickness improve the strength of veneers bonded to enamel, but less is known about dentin or mixed substrates. PURPOSE: The purpose of this in vitro study was to measure the influences of tooth substrate type (all-enamel, all-dentin, or half-dentin-half-enamel) and veneer thickness on the loads needed to cause initial and catastrophic porcelain veneer failure. MATERIAL AND METHODS: Model discoid porcelain veneer specimens of varying thicknesses were bonded to the flattened facial surfaces of incisors with different enamel and dentin tooth substrates, artificially aged, and loaded to failure with a small sphere. Initial and catastrophic fracture events were identified and analyzed statistically and fractographically. RESULTS: Fracture events included initial Hertzian cracks, intermediate radial cracks, and catastrophic gross failure. All specimens retained some porcelain after catastrophic failure. Cement failure occurred at the cement-porcelain interface not at the cement-tooth interface. Porcelain veneers bonded to enamel were substantially stronger and more damage-tolerant than those bonded to dentin or mixed substrates. Increased porcelain thickness substantially raised the loads to catastrophic failure on enamel substrates but only moderately raised the loads to catastrophic failure on dentin or mixed substrates. The veneers bonded to half-dentin-half-enamel behaved remarkably like those bonded wholly to dentin. CONCLUSIONS: Porcelain veneers bonded to enamel were substantially stronger and more damage-tolerant than those bonded to dentin or half-enamel-half dentin.

New High-Translucent Cubic-Phase-Containing Zirconia: Clinical and Laboratory Considerations and the Effect of Air Abrasion on Strength.

Fabricating all-ceramic restorations with minimal or no application of a secondary phase while maintaining esthetics has been a sought-after goal of the dental profession. The objective has been development of a monolithic material with optical properties similar to the natural tooth without the need for layering porcelain. This article examines some of the newer cubic zirconia materials used in a monolithic form. The authors discuss laboratory-processing issues that affect esthetics, including evaluation of colorizing, sintering, finishing, and polishing, and assess initial translucency testing of several materials while evaluating the effect of air abrasion on flexural strength of these cubic zirconias. Lastly, the article demonstrates an anterior single-unit monolithic case with several of the newer materials.

A Technique Using Calibrated Photography and Photoshop for Accurate Shade Analysis and Communication.

This article reviews the critical aspects of controlling the shade-taking environment and discusses various modalities introduced throughout the years to acquire and communicate shade information. Demonstrating a highly calibrated digital photographic technique for capturing shade information, this article shows how to use Photoshop® to standardize images and extract color information from the tooth and shade tab for use by a ceramist for an accurate shade-matching restoration.

Updating Classifications of Ceramic Dental Materials: A Guide to Material Selection.

The indications for and composition of today's dental ceramic materials serve as the basis for determining the appropriate class of ceramics to use for a given case. By understanding the classifications, composition, and characteristics of the latest all-ceramic materials, which are presented in this article in order of most to least conservative, dentists and laboratory technicians can best determine the ideal material for a particular treatment.

Vonlays: a conservative esthetic alternative to full-coverage crowns.

Porcelain veneers have long been a popular restorative option that have evolved into a well-accepted treatment that can be fabricated in various ways. Onlays are another common treatment modality used in contemporary dentistry to restore large areas of decay and to replace old restorations. With the availability of newer high-strength materials such as lithium disilicate and processing technologies like CAD/CAM and heat pressing, dental professionals are now able to produce highly esthetic, high-strength restorations that blend seamlessly with the natural dentition while also withstanding posterior occlusal forces. This has resulted in innovative methods of providing minimally invasive dentistry. One such approach is a combination restoration the authors call a "vonlay," which, as demonstrated in this case report, can be used as an alternative to coverage crowns to restore damaged posterior teeth.

Clinical effectiveness of flash teeth whitening, a novel method for teeth bleaching.

Flash teeth whitening is a two-step, once-daily method for whitening teeth that combines the use of a fine aerosol mist of a stabilized, concentrated hydrogen-peroxide solution and a saliva-activated, effervescent oral powder that is poured directly onto the tongue. An in-vivo study was conducted to evaluate the efficacy and safety of the flash teeth whitening method at three timed intervals in a 3-week period. Objective and subjective tooth-shade rating methods were used at baseline, after initial treatment, and after 1 and 3 weeks of once-daily use. A significant whitening effect was observed. Data also indicated a progressively improved whitening effect, suggesting that sequential use may optimize the whitening results, with maximum whitening occurring between 1 and 3 weeks of once-daily use. The study demonstrated that flash teeth whitening effectively whitens teeth. This novel method is suitable for safe use as an out-of-office treatment as a primary whitener, or as a maintenance method for keeping whitened teeth white, offering dentists a potential alternative tooth whitening recommendation that is easy to use, safe, and effective and improves the condition of soft tissue when used as directed.

Wear of enamel opposing zirconia and lithium disilicate after adjustment, polishing and glazing.

OBJECTIVES: To compare the wear and opposing enamel wear of adjusted (A); adjusted and polished (AP); and adjusted and glazed (AG) zirconia and lithium disilicate. METHODS: Specimens (n=8) were prepared of lithium disilicate (A, AP, and AG), zirconia (A, AP, and AG), veneering porcelain, and enamel (control). Surface roughness was measured for each ceramic. In vitro wear was conducted in the UAB-chewing simulator (10 N vertical load/2mm slide/20 cycles/min) with lubricant (33% glycerin) for 400,000 cycles. Isolated cusps of extracted molars were used as antagonists. Scans of the cusps and ceramics were taken at baseline and 400,000 cycles with a non-contact profilometer and super-imposed to determine wear. Data were analyzed with ANOVA and Tukey-Kramer post hoc tests (alpha=0.05). RESULTS: A and AP zirconia showed no detectable signs of wear, and the veneering porcelain demonstrated the most wear. All other ceramics showed significantly less volumetric loss than the veneering porcelain, comparable to enamel-enamel wear. Veneering porcelain produced the most opposing enamel wear (2.15 ± 0.58 mm(3)). AP lithium disilicate and zirconia showed the least amount of enamel wear (0.36 ± 0.09 mm(3) and 0.33 ± 0.11 mm(3) respectively). AG lithium disilicate had statistically similar enamel wear as AP lithium disilicate, but A lithium disilicate had more enamel wear. A and AG zirconia had more enamel wear than AP zirconia. No statistically significant difference was seen between the enamel-enamel group and any other group except the veneering porcelain. CONCLUSIONS: Zirconia has less wear than lithium disilicate. Wear of enamel opposing adjusted lithium disilicate and zirconia decreased following polishing. CLINICAL SIGNIFICANCE: Zirconia experiences less and lithium disilicate experiences equivalent occlusal wear as natural enamel. It is preferable to polish zirconia and lithium disilicate after adjustment to make them wear compatible with enamel. Veneering of zirconia and lithium disilicate should be avoided in areas of occlusal contact to prevent enamel wear.

Effect of porcelain and enamel thickness on porcelain veneer failure loads in vitro.

STATEMENT OF PROBLEM: Bonded porcelain veneers are widely used esthetic restorations. Although high success and survival rates have been reported, failures occur. Fracture is the most common failure mode. Fractures range from incomplete cracks to the catastrophic. Minimally invasive or thin partial veneers have gained popularity. PURPOSE: The aim of this study was to measure the influences of porcelain veneer thickness and enamel substrate thickness on the loads needed to cause the initial fracture and catastrophic failure of porcelain veneers. MATERIAL AND METHODS: Model discoid porcelain veneer specimens of varying thickness were bonded to the flattened facial surfaces of incisors, artificially aged, and loaded to failure with a small sphere. Individual fracture events were identified and analyzed statistically and fractographically. RESULTS: Fracture events included initial Hertzian cracks, intermediate radial cracks, and catastrophic gross failure. Increased porcelain, enamel, and their combined thickness had like effects in substantially raising resistance to catastrophic failure but also slightly decreased resistance to initial Hertzian cracking. Fractographic and numerical data demonstrated that porcelain and tooth enamel behaved in a remarkably similar manner. As porcelain thickness, enamel thickness, and their combined thickness increased, the loads needed to produce initial fracture and catastrophic failure rose substantially. Porcelain veneers withstood considerable damage before catastrophic failure. CONCLUSIONS: Increased enamel thickness, increased porcelain thickness, and increased combined enamel and porcelain thickness all profoundly raised the failure loads necessary to cause catastrophic failure. Enamel and feldspathic porcelain behaved in a like manner. Surface contact damage occurred initially. Final catastrophic failure followed flexural radial cracking. Bonded porcelain veneers were highly damage tolerant.

Prosthetic soft tissue management following two periimplant graft failures: a clinical report.

A 53-year-old man experienced 2 soft tissue graft failures resulting in sizable hard and soft tissue defects in the esthetic zone following implant placement. A third connective tissue graft surgery was successful in repairing the defect and significantly improving soft tissue quality. A screw-retained, interim implant prosthesis was instrumental in gradually shaping the soft tissue over the course of the 3 surgeries. The interim prosthesis was modified numerous times to achieve a balance of esthetics, surgical protection, and gingival contours. The initial form of the prosthesis was designed to protect the surgical site and allow space for postsurgical edema. In its final form, the tissue side of the interim prosthesis pontic was designed to mimic the cross-sectional profile of a natural central incisor root but modified to deliver gentle pressure until maximum papilla height was achieved. The definitive restoration was fabricated to mimic the final design of the interim restoration and gingival architecture.

Fatigue behavior of the resinous cement to zirconia bond.

PURPOSE: Resinous cements are widely used for luting zirconia restorations. Adhesive failures have occurred at the cement/zirconia interface, rather than at the cement/dentin interface, suggesting that the cement/zirconia bond may lack durability; however, few comprehensive, comparative evaluations of fatigue effects have been reported. The rate of fatigue-induced loss of bond strength may be a more important predictor of long-term success than a single snapshot of bond strength after an arbitrary number of thermocycles. Previous studies have failed to identify trends by investigating bond strengths at several different numbers of cycles. This may result in invalid conclusions about which cements have superior bond strengths. The purpose of this study was to investigate the effects of artificial aging by thermocycling and resinous cement type on bond strengths to zirconia. MATERIALS AND METHODS: The effect of the number of thermocycles (0, 1, 10, 100, 1000, and 10,000) on the bond strengths of five resinous cements, two of which were used with and without a primer, and an oxygen-inhibiting gel, was studied. Specimens were randomly assigned to thermocycle number/cement-type test groups. Because zirconia has a very low thermal diffusivity, exceptionally long thermocycle dwell times were used. Cylinders of zirconia were bonded end-to-end. One end of each bonded specimen was insulated, specimens were thermocycled and tested in shear, and bond strengths were calculated and analyzed. RESULTS: Two-way ANOVA revealed that the effects of cement type, the number of thermocycles, and their interaction all significantly affected bond strength (p < 0.0001). By 10,000 cycles, most cements had lost at least half of their initial bond strengths, and two cements effectively recorded zero bond strengths. Failure modes were cement specific, but adhesive modes predominated. Fatigue resistance of two cements was greatly improved by use of a primer and an oxygen-inhibiting gel, as recommended by their respective manufacturers. CONCLUSIONS: Both the type of resin cement and the number of thermocycles influenced bond strength. Fatigue through thermocycling affected different cement types in different ways. Some materials displayed more rapid loss of bond strength than others. Cements differed in their failure modes.

Bonded functional esthetic prototype: an alternative pre-treatment mock-up technique and cost-effective medium-term esthetic solution.

As the economy has receded in recent years, many patients have been inclined to reject dental treatment beyond what they feel is the minimal amount necessary. Increasingly, there has been reluctance to take on the expense of full-mouth restorations and time-consuming procedures. Consequently, clinicians can benefit from innovative, conservative, interim solutions that enable them to provide segment treatment with long-term stability and esthetics, with lower initial cost. The bonded functional esthetic prototype (BFEP) allows fabrication of up to 14 teeth from composite in 1 hour, providing either a pre-treatment restoration or a long-term provisional solution until further treatment can be completed. As demonstrated herein, the BFEP enables superb function, stability, and esthetics in the interim while dispersing the cost of definitive treatment over time.

Retrieval of a defective cement-retained implant prosthesis.

As the popularity of cement-retained implant prosthetics grows, so, too, does the need for retreatment. The predictable removal of cement-retained implant crowns has often proven difficult due to a multitude of variables, including locating the access and stripped screws. The techniques discussed in this article address these issues, thus simplifying the retreatment process.

The Photoshop Smile Design technique (part 1): digital dental photography.

The proliferation of digital photography and imaging devices is enhancing clinicians' ability to visually document patients' intraoral conditions. By understanding the elements of esthetics and learning how to incorporate technology applications into clinical dentistry, clinicians can predictably plan smile design and communicate anticipated results to patients and ceramists alike. This article discusses camera, lens, and flash selection and setup, and how to execute specific types of images using the Adobe Photoshop Smile Design (PSD) technique.

The use of slow heating and slow cooling regimens to strengthen porcelain fused to zirconia.

STATEMENT OF PROBLEM: Porcelain fused to zirconia prostheses are widely used. However, porcelain chipping, spalling, fracture, and delamination are common clinical problems. Residual stresses of thermal origin have received attention, but clear data and firing guidelines remain absent. PURPOSE: The purpose of this study was to measure the influence of heating and cooling protocols on the strength of porcelain fused to zirconia. MATERIAL AND METHODS: A modified 4-point flexural testing technique was used to measure strength, and porcelain buttons were bonded to the beam between the 2 central loading points. Beams (n=54) were made of a tetragonal polycrystalline zirconium dioxide that was partially stabilized with an yttria core and a feldspathic dental porcelain. Three different heating rates and 3 different cooling regimens were used during firing. Two-way analysis of variance (ANOVA) was used to evaluate the 2 main effects of the heating and cooling regimens and their interaction with the delamination force (α=.05). The Tukey multiple comparisons test was used to identify differences among heating or cooling regimens. RESULTS: During loading, the porcelain buttons separated from the zirconia beams because of delamination within the porcelain, which was close to the porcelain to zirconia interface. ANOVA revealed that the effects of the cooling regimen and heating rate had statistically significant effects on failure load (P<.05). The effect of the cooling regimen was greater than that of the heating regimen. CONCLUSIONS: Slow cooling and slow heating regimens should be used when firing porcelain to zirconia. Cooling regimens were found to be more influential than heating rates. Failure was localized to the porcelain adjacent to the porcelain-zirconia interface, not to the interface itself, indicating that the residual stresses of thermal origin within the porcelain dominated. The preparation of zirconia with 50 µm aluminum oxide at a pressure of 0.34 MPa was sufficient to prevent interfacial failure.