Dental Ceramic Materials Research Articles

Application of Tetragonal Nano-Zirconia in Ceramic Teeth

Nano-zirconia (Nano-ZrO2) has good natural color, high strength, high toughness, high chemical stability, excellent corrosion resistance and resistant to chemical attack and microbial erosion particularly, which is one of the biocompatible inert materials and is widely used in biology, medicine and other fields. There are cubic (c-ZrO2), tetragonal (t-ZrO2) and monoclinic (m-ZrO2) phase three different crystal structures of zirconia (ZrO2) in normal atmosphere and different temperatures. In the three different crystal structures, t-ZrO2 has the best performance for ceramic dental materials. However, ZrO2 is usually in the form of m-ZrO2 at room temperature. So to study the synthesis and stabilization methods at room temperature of nano-t-ZrO2 is very important in scientific significance and application prospects.

Comparative radiopacity of ceramics and metals with human and bovine dental tissues

Ceramics should be radiopaque enough to be seen on radiographs and to be distinguishable from tooth structures. Information on the radiopacity of different ceramics used in restorative dentistry is limited. The purpose of this study was to investigate the radiopacity of ceramics in comparison with human and bovine dental hard tissues and metals. A total of 128 disk-shaped specimens, 6 × 1 mm (n=8), were prepared from dental ceramic materials and metals. The optical densities of each material, along with 2 tooth sections (canine and molar teeth), bovine dentin and enamel specimens, and 2 different aluminum step wedges, were measured from radiographic images using a transmission densitometer. The optical densities of the specimens were used to determine the equivalent aluminum thicknesses. The data were analyzed by nonparametric 1-way ANOVA (Kruskal-Wallis) and Student-Newman-Keuls multiple range tests for post hoc comparison (α=.05). Among ceramic materials, Cercon Zirconia had the highest and the Cergo Pressable Ceramic had the lowest radiopacity values. Cergo Pressable Ceramic, Noritake Super Porcelain EX3 dentin, IPS Empress e.max Press, Cercon Kiss dentin, IPS Empress 2, Cercon Ceram dentin, bovine dentin, human canine, and molar tooth dentin radiopacity measurements were not significantly different. The radiopacity measurements of In-Ceram Alumina, In-Ceram Spinell, Celay Alumina, Titanium alloy (Ti-6Al-4V), Celay Zirconia, In-Ceram Zirconia, NiCr alloy, Wieland Zirconia, Cercon Zirconia, and 22-carat gold were significantly higher than that of bovine enamel (P<.05). Significant differences in radiopacity were found among ceramic materials, when compared to metals, bovine enamel and human and bovine dentin. Cercon and Wieland Zirconia had high radiopacity values, which were similar to metals.

A clinical consideration of current dental zirconia CAD/CAM restorations

Currently there is no dental ceramic material can be used in all dental situations need to be restored. However, in view of recent clinical reports, the most viable alternative is zirconia ceramic. Clinical success of dental zirconia restorations strongly depends on proper selection of materials, accurate laboratory procedure and final cementation, which can be achievable with the correct understanding of zirconia. As dental materials, zirconia ceramics have a very bright future, because they are being used increasingly in the anterior region as implant fixtures, as well as crown and bridge restorations and implant abutments. Many dental ceramics showing poor clinical performance have been gone from the dental market. However, in terms of outstanding mechanical properties and esthetic nature, new dental materials can replace zirconia ceramics will not be available in the foreseeable future.

Design of a new, multi-purpose, light-curing adhesive comprising a silane coupling agent, acidic adhesive monomers and dithiooctanoate monomers for bonding to varied metal and dental ceramic materials

A newly designed, light-curing adhesive was investigated for its bonding effectiveness to porcelain, alumina, zirconia, Au, Au alloy, Ag alloy, Au-Ag-Pd alloy, and Ni-Cr alloy. Four experimental adhesives were prepared using varying contents of the following: a silane coupling agent [3-methacryloyloxypropyltriethoxysilane (3-MPTES)], acidic adhesive monomers [6-methacryloyloxyhexyl phosphonoacetate(6-MHPA),6-methacryloyloxyhexyl3-phosphonopropionate(6-MHPP)and 4-methacryloyloxyethoxycarbonylphthalic acid (4-MET)], and dithiooctanoate monomers [6-methacryloyloxyhexyl 6,8-dithiooctanoate (6-MHDT) and 10-methacryloyloxydecyl 6,8-dithiooctanoate (10-MDDT)]. After all adherend surfaces were sandblasted and applied with an experimental adhesive, shear bond strengths (SBSs) of a light-curing resin composite (Beautifil II, Shofu Inc., Kyoto, Japan) to the adherend materials after 2,000 times of thermal cycling were measured. For the experimental adhesive which contained 3-MPTES (30.0 wt%), 6-MHPA (1.0 wt%), 6-MHPP (1.0 wt%), 4-MET (1.0 wt%), 6-MHDT (0.5 wt%) and 10-MDDT (0.5 wt%), it consistently yielded the highest SBS for all adherend surfaces in the range of 20.8 (4.8)-30.3 (7.9) MPa, with no significant differences among all the adherend materials (p>0.05). Therefore, the newly designed, multi-purpose, light-curing adhesive was able to deliver high SBS to all the adherend materials tested.

치과용 세라믹 재료의 전β 방사능 준위

In all of dental ceramics, these materials contained the radio-isotopes with natural abundance ratio. After dental treatment, remained dental ceramics in the oral cavity is caused for human internal dose. In this study, the gross beta activity levels were measured in dental materials including 22 dental ceramics, 1 resin, and 2 cements for estimation of human internal dose. In dental ceramic samples, the obtained results showed that the gross beta activity level varied between 1.317 ~ 2.935 Bq/g and the gross beta activity level was 2.379 Bq/g. And the same level for dentine, opacious dentine, translucent and enamel were 2.479 Bq/g, 2.491 Bq/g, 2.470 Bq/g and 2.069 Bq/g, respectively. The gross beta activity level of temporary resin and cements were negligible, compare to the same level of dental ceramics. The high gross beta activity level observed in opacious dentine code OD-A4 is 2.935 Bq/g thus mainly ascribable to 40K. The reduction of the radiation level of natural radio-isotopes and the improvement of the dental ceramic materials should be required for internal dose reduction.

Effects of stress rate and calculation method on subcritical crack growth parameters deduced from constant stress-rate flexural testing

Objectives To more efficiently determine the subcritical crack growth (SCG) parameters of dental ceramics, the effects of stressing rate and choice of statistical regression model on estimates of SCG parameters were assessed. Methods Two dental ceramic materials, a veneering material having a single critical flaw population (S) and a framework material having partially concurrent flaw populations (PC), were analyzed using constant stress-rate testing, or “dynamic fatigue”, with a variety of testing protocols. For each material, 150 rectangular beam specimens were prepared and tested in four-point flexure according to ISO6872 and ASTM1368. A full-factorial study was conducted on the following factors: material, stress rate assumed vs. calculated, number of stress rates, and statistical regression method. Results The proportion of specimens for which the statistical models over-estimated reliability was not significantly different based on regression method for Material S ( P = 0.96, power = 94%) and was significantly different based on regression method for Material PC ( P < 0.001). The standard method resulted in SCG parameters, n and ln B, of 35.9 and −11.1 MPa 2 s for Material S and 12.4 and 9.61 MPa 2 s for Material PC, respectively. Significance The method of calculation that uses only the median strength value at each stress rate provided the most robust SCG parameter estimates. Using only two stress rates resulted in fatigue parameters comparable to those estimated using four stress rates having the same range. The stress rate of each specimen can be assumed to be the target stress rate with negligible difference in SCG parameter estimates.

Academy of Operative Dentistry Hollenback Memorial Prize

Dr Mackert is professor in the Department of Oral Rehabilitation, School of Dentistry, Medical College of Georgia (MCG), Augusta, Georgia. He holds joint appointments in the Department of Oral Biology and the School of Graduate Studies. He has conducted research on dental amalgam and ceramic materials and has received $2.8 million in NIH funding as a principal investigator and more than $1 million as co-investigator. He has published 45 papers in refereed journals, 11 chapters and monographs in books and symposium proceedings and 66 abstracts. In addition, he has testified twice before Congressional committees and before legislative and policymaking bodies in multiple states on the safety of dental amalgam. He is first author of a monograph on mercury exposure from dental amalgam fillings that was published by the World Health Organization. Dr Mackert has been interviewed on the amalgam controversy by Time magazine, U.S. News &amp; World Report, The Washington Post, the Wall Street Journal, National Public Radio, Consumer Reports, The Boston Globe, USA Today, Harper's Bazaar, Redbook, Men's Health magazine, Fitness magazine, McCall's magazine and other media outlets.He received his DMD degree in 1976 from the MCG School of Dentistry and his PhD in materials science in 1979 from the School of Engineering and Applied Science of the University of Virginia. After a one-year visiting lectureship at the Gifu College of Dentistry (now Asahi University School of Dentistry) in Japan, Dr Mackert joined the faculty of the MCG School of Dentistry in 1980. In 1992, Dr Mackert was a visiting scientist in the Ceramics Processing Research Laboratory at the Massachusetts Institute of Technology.Dr Mackert is a member of Omicron Kappa Upsilon, the American Dental Association and the International Association for Dental Research. He is a fellow in the Academy of Dental Materials and the International College of Dentists. He is a Distinguished Alumnus of the MCG School of Dentistry and recipient of a Presidential Citation from the American Dental Association. He has served on the Oral Biology and Medicine Study Section and the Special Grants Review Committee of the National Institute of Dental and Craniofacial Research, the Council on Scientific Affairs of the American Dental Association, the Scientific and TechnicalAdvisory Board of Quackwatch, Inc and other advisory panels. He has presented 51 invited lectures at local, national and international venues, including the 1990 NortonMRossMemorial Lecture at theAmerican Dental Association.The Academy of Operative Dentistry is pleased to present the 2010 Hollenback Prize to Dr J Rodway Mackert, Jr.

Ceramic Inlays: A Case Presentation and Lessons Learned from the Literature

Ceramic dental restorative materials offer an esthetic alternative to dental amalgam or gold. There is uncertainty relative to the longevity of ceramic inlay restorations. Recently published long-term research studies reveal general clinical performance trends. These trends are discussed while presenting a ceramic inlay case. Successful clinical use of ceramic inlay materials is absolutely dependent on the creation of an uncompromised adhesive tooth/ceramic interface. Ceramic inlay restorations perform well in terms of long-term retention, color match, and anatomic contour stability. These restorations all experience limited margin deterioration that does not predispose to marginal discoloration or secondary caries. Patients rarely suffer from postoperative sensitivity secondary to ceramic inlay placement. Ceramic inlays fail predominantly as a result of crack propagation from material flaws leading to bulk fracture. Some superficial ceramic defects may be repaired with composite resin. Internal material flaws are minimized by industrial production of indirect pressable glass-ceramic materials or ceramic blocks designed for computer-aided design/computer-assisted manufacturing (CAD/CAM). External surface flaws are limited by careful polishing techniques. Strategic placement of ceramic inlays in teeth that are not subject to heavy occlusal loading will result in more predictable long-term performance. Preparation design to prevent flexure of ceramic inlay materials is essential. Use of ceramic inlays to restore defects in posterior teeth requires careful attention to detail. Placement of ceramic inlay materials in high-stress areas may result in less predictable long-term performance. Ceramic inlays are advantageous for restoring moderately sized defects when optimal control of restoration contours and esthetics is desired.

Surface characterization of dental ceramics and initial streptococcal adhesion in vitro

Objectives The aim of this in vitro study was to investigate the surface properties of dental ceramic materials belonging to different ceramic classes, and to correlate the findings to the initial adherence of three oral streptococcal strains. Methods Rectangular specimens were prepared from different ceramic materials (glass/lithium disilicate glass/glass-infiltrated zirconia/partially sintered zirconia/hipped zirconia ceramic) and polished; surface roughness (Ra) was determined. Glass plates were used as a control. Specimens were incubated with phosphate-buffered saline or an artificial saliva (protein mixture; 2 h, 37 °C). Surface free energy ( γ t) and its polar ( γ p) and disperse ( γ d) contribution were determined prior to and after artificial saliva exposure. Uncoated and protein-coated specimens were incubated with Streptococcus gordonii DSMZ 6777, Streptococcus oralis DSMZ 20068 or Streptococcus sanguinis DSMZ 20068 suspension for 2.5 h at 37 °C ( n = 15 for each treatment and strain). Adherent streptococci were quantified fluorometrically. Results The lithium disilicate glass ceramic showed the highest values for Ra; the lowest values were found for the glass ceramic, the partially sintered zirconia and the hipped zirconia ceramic. Protein coating caused a significant increase in γ t and γ p, but not in the control material. The control material showed higher values for streptococcal adhesion than all ceramic materials. After protein coating, only slight and random differences in streptococcal adhesion were found between the various ceramic materials. Significance Dental ceramic materials show differences in terms of Ra, γ t and initial streptococcal adhesion; however, correlations between surface properties and streptococcal adhesion were poor.

The Fabrication and Properties of Biscuit-Sintered Y-TZP Ceramics for Dental Applications

Moderately porous Y-TZP dental ceramics were designed to combine the high strength and fracture toughness of densely sintered Y-TZP and the relatively low elastic modulus of porous Y-TZP ceramics. The materials were produced by biscuit-sintering dry-pressed pellets at different temperatures in an ambient air atmosphere. The flexural strength progressively increased with the fractional density, starting from 150–200 MPa at 55–60 % of theoretical density (TD), and exceeding 500 MPa at &gt;80 % TD. The elastic modulus of the early-stage sintered material was matched with that of dentine, but the flexural strength was too low for a practical application. Strength values equal to or higher than those of the existing dental glass-ceramics and glass-infiltrated ceramic materials were achieved with specimens sintered to 8085 % TD, but the elastic modulus of these ceramics (100130 GPa) was about two times higher than that of dentine. Soft grinding of the biscuit-sintered samples resulted in a noticeable increase in the surface roughness, also leading to a significant strength reduction.

Translucency and biaxial flexural strength of four ceramic core materials

Objectives To assess the relative translucencies and flexural strengths of four dental restorative ceramic core materials. Methods Eight disk specimens (14 mm in diameter × 0.5 ± 0.05 mm in thickness) were prepared for each group of four ceramic core materials (IPS Empress 2 dentin, VITA In-Ceram Alumina, VITA In-Ceram Zirconia, Cercon Base Zirconia), according to the manufacturers’ instructions. A color meter was used to measure the relative translucencies of the specimens. The biaxial flexure test (ISO 6872) was then used to measure their flexural strengths. Data for relative translucency (0.0–1.0), fracture load (N) and biaxial flexural strength (MPa) were analyzed by one-way ANOVA, followed by Tukey's multiple comparison test for significant findings ( α = 0.05). Results For relative translucency: IPS Empress 2 (0.78 ± 0.03), VITA In-Ceram Alumina (0.94 ± 0.01), VITA In-Ceram Zirconia (1.00 ± 0.01), Cercon Base Zirconia (1.00 ± 0.01), P < 0.0001. For biaxial flexural strength: IPS Empress 2 (355.1 ± 25.7), VITA In-Ceram Alumina (514.0 ± 49.5), VITA In-Ceram Zirconia (592.4 ± 84.7), Cercon Base Zirconia (910.5 ± 95.3), P < 0.0001. Significance IPS Empress 2 and VITA In-Ceram Alumina were significantly more translucent than the two opaque zirconia-containing core materials. IPS Empress 2 was significantly weaker, and Cercon Base Zirconia was significantly stronger, than the other two ceramic core materials.

On the brittleness of enamel and selected dental materials

Although brittle material behavior is often considered undesirable, a quantitative measure of “brittleness” is currently not used in assessing the clinical merits of dental materials. Objective To quantify and compare the brittleness of human enamel and common dental restorative materials used for crown replacement. Methods Specimens of human enamel were prepared from the third molars of “young” (18 ≤ age ≤ 25) and “old” (50 ≤ age) patients. The hardness, elastic modulus and apparent fracture toughness were characterized as a function of distance from the DEJ using indentation approaches. These properties were then used in estimating the brittleness according to a model that accounts for the competing dissipative processes of deformation and fracture. The brittleness of selected porcelain, ceramic and micaceous glass ceramic (MGC) dental materials was estimated and compared with that of the enamel. Results The average brittleness of the young and old enamel increased with distance from the DEJ. For the old enamel the average brittleness increased from approximately 300 μm −1 at the DEJ to nearly 900 μm −1 at the occlusal surface. While there was no significant difference between the two age groups at the DEJ, the brittleness of the old enamel was significantly greater (and up to four times higher) than that of the young enamel near the occlusal surface. The brittleness numbers for the restorative materials were up to 90% lower than that of young occlusal enamel. Significance The brittleness index could serve as a useful scale in the design of materials used for crown replacement, as well as a quantitative tool for characterizing degradation in the mechanical behavior of enamel.

Investigations of subcritical crack propagation of the Empress 2 all-ceramic system

Introduction The mechanical properties and slow crack propapagation of the all-porcelain system Empress ® 2 (Ivoclar Vivadent, Schaan, Liechtenstein) with its framework compound Empress ® 2 and the veneering compounds “Empress ® 2 and Eris ® were examined. Methods For all materials, the fracture strength, Weibull parameter and elastic moduli were experimentally determined in a four-point-bending test. For the components of the Empress ® 2 system, the fracture toughness K IC was determined, and the crack propagation parameters n and A were determined in a dynamic fatigue method. Using these data, life data analysis was performed and lifetime diagrams were produced. The development of strength under static fatigue conditions was calculated for a period of 5 years. Results The newly developed veneering ceramic Eris ® showed a higher fracture strength ( σ 0 = 66.1 MPa) at a failure probability of P F = 63.2%, and crack growth parameters ( n = 12.9) compared to the veneering ceramic Empress ® 2 ( σ 0 = 60.3 MPa). For Empress ® 2 veneer the crack propagation parameter n could only be estimated ( n = 9.5). This is reflected in the prognosis of long-term resistance presented in the SPT diagrams. For all materials investigated, the Weibull parameter m values (Empress ® 2 framework m = 4.6; Empress ® 2 veneer m = 7.9; Eris ® m = 6.9) were much lower than the minimum demanded by the literature ( m = 15). Significance The initial fracture strength value alone is not sufficient to characterize the mechanical resistance of ceramic materials, since their stressability is time-dependent. Knowledge about the crack propagation parameters n and A are of great importance when preclinically predicting the clinical suitability of dental ceramic materials. The use of SPT diagrams for lifetime calculation of ceramic materials is a valuable method for comparing different ceramics.

A New Method for Evaluating Thermal Compatibility of Multi-Layer Dental Ceramic Composites

Dental ceramic materials do not always show linear expansion behavior. In general, thermal contraction behavior of dental porcelain can be described with the polynomial function: L/L= C+α1 T+α2 T2. In addition, a new method for taking into consideration of nonlinear contraction behavior of dental ceramics is proposed for calculating thermal mismatch value (α) between substrate and veneering materials. Discs of eight substrate/veneer combinations (n=10) were fabricated for thermal shock testing. In this study, a stepwise multiple regression analysis was performed to determine the relationship between thermal shock test results and thermal mismatch value (α) on these combinations. A high degree of correlation was found between αs-b and T. The new method proves to be a reliable one to predict thermal compatibility of multi-layer dental ceramic composites.

Progress in carbon nanotube based dental ceramic material

Carbon nantubes composites draws more and more attention these days. Its application provides new potential for the reinforcement and toughness of dental ceramic. In this paper, the properties of carbon nanotube, carbon nanotube based ceramic composites and its mechanics of toughness, and the future trend of carbon nanotube in dental ceramic material, have been reviewed.

Characterization of novel dental obturation materials

Abrasion behavior of new nanohybrid polymer + ceramic dental materials designed for filling dental cavities is reported. The polymer matrix is a polyurethane while the dispersed phases include particles of silica and alumina with the diameters below 100 nm. Several commercial obturation materials are investigated by the same technique. The authors' new nanohybrids show clearly superior resistance to abrasion wear – in one case some 20 times better than a commercial sample. Moreover, the new materials exhibit low toxicity, short curing times (<10 min), good dimensional stability (low contraction), high chemical resistance and good pigmentation capacity and they are easy to prepare and show good adhesion to the substrate (dentine or enamel).

Contact-Driven Crack Formation in Dental Ceramic Materials

Natural human tooth consists of multiple layered quasi-brittle biomaterials, which make dental restorations experience a complex stress state under masticatory contact loading. As such, many restorations are prone to failure and a constant effort is made to improve the mechanical characteristics of the restorative materials. Clinical observations have shown that improved strengths and fracture toughness in ceramic materials do not necessarily lead to an anticipated higher functional longevity of the restoration. While substantial experimental investigations have been carried out to identify the contact induced fracture in such multi-layer material systems, numerical modelling of this event was largely unexplored. This paper presents a new numerical method to account for micro-damage driven fracture in various multi-layered biomaterial structures. In this study, a Rankine constitutive model is adopted and the crack initiation and propagation are automatically implemented in an explicit finite element (FE) framework. The effects of indenter radius, surface curvature and thickness of layered biomaterials on the cracking patterns are investigated. The results show good agreement with the experimental studies in literature.

Effect of various treatment and glazing (coating) techniques on the roughness and wettability of ceramic dental restorative surfaces

Surface treatment procedures such as grinding and polishing are needed to provide the ceramic dental restorative materials with proper fitting and occlusion. The treated surfaces are customarily glazed to improve the strength and smoothness. Though smoothness and wetting of the dental surfaces are important to minimize bacterial plaque retention, influence of the surface treatment and glazing procedures on the final surface roughness and its correlation to wettability are overlooked. In this work, effect of various treatment (diamond fraising, stoning, sanding and aluminum oxide and rubber polishing) and glazing (auto and overglazing) techniques on the final roughness and the resulting wettability of dental ceramic surfaces were investigated using scanning electron microscopy (SEM) observations and atomic force microscopy (AFM) scans, 75 scans per sample. The surfaces were characterized and assigned an average roughness measure, R a. The wettability of the same surfaces was evaluated using micro-contact angle measurements (25 micro-bubbles placed on a grid on each surface) to correlate the final surface roughness and wettability. The results show that overglazing prevails over surface irregularities from different treatment procedures and provides homegeneously smooth surfaces with mean R a < 10 nm. It also produces uniformly wetted surfaces with low contact angles around 20°. The autoglazed surfaces are less smooth (mean R a around 50 nm) and displays sporadic topographic irregularities. They display larger and less uniform contact angles ranging between 35° and 50°. The results suggest that overglazing should be preferred after surface treatment to obtain a smooth and well-wetted dental ceramic surface.

In vitro evaluation of low-temperature aging effects and finishing procedures on the flexural strength and structural stability of Y-TZP dental ceramics

Yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) ceramic material has been reported to possess exceptionally high flexural strength; however, the strength of Y-TZP ceramics can be affected by surface treatments performed by dental laboratory technicians and by intraoral conditions. This study investigated the influence of low-temperature-degradation (LTD) treatment, airborne-particle abrasion, and polishing on the flexural strength and structural stability of a Y-TZP ceramic material. By sectioning zirconia ceramic blocks (Vita In-Ceram YZ blocks) into 25 x 4 x 2-mm bars, 310 specimens were fabricated and divided into 9 groups: Group C, as-sintered (control); group B24h, boiled in water for 24 hours; group B7d, boiled in water for 7 days; group H6h, stored in humidified air at 250 degrees C for 6 hours; group H24h, stored in humidified air at 250 degrees C for 24 hours; group H7d, stored in humidified air at 250 degrees C for 7 days; group P, polished; group A, airborne-particle abraded; and group AB, airborne-particle abraded and boiled for 7 days. The flexural strengths (MPa) of all specimens were determined by using a 3-point bending test. The variability was analyzed by using Weibull statistics. Pairwise differences among the 9 groups were evaluated by using confidence intervals (95%) for scale and shape parameters. From every block used, 8 specimens were obtained and every specimen was marked according to the location of its origin from the original block. Surfaces of the specimens were evaluated by using scanning electron microscopy (SEM) at various magnifications. X-ray diffraction analysis was performed to identify possible tetragonal-to-monoclinic phase transformations. Energy dispersive spectroscopy (EDS) was used to obtain information on the chemical composition. Aging or "finishing" treatments had no significant negative effects on flexural strengths. Mean flexural strengths ranged from 796.7 to 950.2 MPa. Group A exhibited the highest mean flexural strength (950.2 MPa). Weibull modulus values ranged between 5.6 and 9.3. Tetragonal-to-monoclinic phase transformation was detected for a specimen boiled for 24 hours. More tetragonal-to-monoclinic phase transformation was detected for specimens boiled for 7 days and stored in humidified air at 250 degrees C for 7 days. The SEM examination of fractured surfaces revealed sintering defects, and EDS analysis showed less yttria concentration on Y-TZP specimens that were boiled for 7 days. Within the limitations of this study, the results suggested that the LTD procedures and the polishing treatment used did not reduce the flexural strengths of zirconia bars. Airborne-particle abrasion increased the flexural strength of specimens. Although polishing, airborne-particle abrasion, and various low-temperature degradation (LTD) treatments did not significantly degrade the strength of the Y-TZP ceramic material, LTD resulted in loss of yttria. Over time, gradual dissolution of yttria could decrease the tetragonal-phase stability and long-term clinical serviceability of this dental ceramic material.

Surface roughness of five different dental ceramic core materials after grinding and polishing

In clinical practice, core materials can be exposed after adjustments are made to previously-luted all-ceramic restorations. The purpose of this study was to evaluate the surface roughness of five different dental ceramic core materials after grinding and polishing. Five different ceramic core materials, Vita In-Ceram Alumina, Vita In-Ceram Zirconia, IPS Empress 2, Procera AllCeram, and Denzir were evaluated. Vita Mark II was used as a reference material. The surface roughness, Ra value (mum), was registered using a profilometer. The measurements were made before and after grinding with diamond rotary cutting instruments and after polishing with the Sof-Lex system. The surface of representative specimens was evaluated qualitatively using scanning electron microscopy (SEM). Results were statistically analysed using analysis of variance (anova) supplemented with Scheffè's and Bonferroni multiple-comparison tests. Before grinding, Procera AllCeram and Denzir had the smoothest surfaces, while IPS Empress 2 had the coarsest. After grinding, all materials except IPS Empress 2 became coarser. Polishing with Sof-Lex provided no significant (P > 0.05) differences between Denzir, Vita Mark II and IPS Empress 2 or between Procera AllCeram and In-Ceram Zirconia. There were no significant differences (P > 0.05) either between the ground and the polished Procera AllCeram or In-Ceram Alumina specimens. Polishing of Denzir, IPS Empress 2 and In-Ceram Zirconia made the surfaces smoother compared with the state after grinding, whereas the polishing effect on Procera AllCeram and In-Ceram Alumina was ineffective. The findings of the SEM evaluation were consistent with the profilometer readings.