Porcelain Layer Research Articles

SEM observation and wettability of variously processed and fractured surface of dental zirconia

Current dental zirconia has several problems in clinical application such as chipping, fracture and detachment. To reduce these problems the surface after various treatments was analyzed by SEM observation, contact angle measurement and surface roughness measurement, and compared. The surface after mirror polishing was smooth. Porcelain layering was smooth except large formed grooves by bubbles. After sandblast and tribochemical treatments, the surfaces showed several micron-sized caving with micron to submicron-level irregularities. Sandblast and tribochemical treatments with the lager roughness had the smaller water contact angle than silicone wheel polishing. Clinically fractured surface of zirconia showed a more complex structure than manually fractured surface, which may be due to the various mode of stress to be imposed repetitively to various direction.

Influence of Glazed Zirconia on Dual-Cure Luting Agent Bond Strength

The current study evaluated the influence of a novel surface treatment that uses a low-fusing porcelain glaze for promoting a bond between zirconia-based ceramic and a dual-cure resin luting agent. Bond strengths were compared with those from airborne particle abrasion, hydrofluoric acid etching, and silanization-treated surfaces. Twenty-four yttrium-stabilized tetragonal zirconia (Cercon Smart Ceramics, Degudent, Hanau, Germany) discs were fabricated and received eight surface treatments: group 1: 110 μm aluminum oxide air-borne particle abrasion; group 2: 110 μm aluminum oxide airborne particle abrasion and silane; group 3: 50 μm aluminum oxide airborne particle abrasion; group 4: 50 pm aluminum oxide airborne particle abrasion and silane; group 5: glaze and hydrofluoric acid;group 6: glaze, hydrofluoric acid, and silane;group 7: glaze and 50 pm aluminum oxide airborne particle abrasion; and group 8: glaze,50 pm aluminum oxide airborne particle abrasion and silane. After treatment, Enforce resin cement (Dentsply, Caulk, Milford, DE, USA) was used to fill an iris cut from microbore Tygontubing that was put on the ceramic surface to create 30 cylinders of resin cement in each treatment group (n=30). Micro shear bond test-ing was performed at a cross head speed of 0.5mm/min. One-way analysis of variance, and multiple comparisons were made using Tukey's test (p<0.5). The bond strength was affected only by surface treatments other than silanization. The groups that utilized the low-fusing porcelain glaze with airborne particle abrasion or hydrofluoric acid showed bond strength values statistically superior to groups that utilized conventional airborne particle abrasion treatments with 50 or 110 pm aluminum oxide (p<0.001). The treatment that utilized low-fusing porcelain glaze and hydrofluoric acid showed bond strength values statistically superior to remaining groups (p<0.001). Treatment of zirconia ceramic surfaces with a glaze of low-fusing porcelain significantly increased the bond strength of a dual-cure resin luting agent to the ceramic surface.

Thermal gradients and residual stresses in veneered Y-TZP frameworks

Objectives The occurrence of “chipping” of all-ceramic restorations with Y-TZP frameworks has resulted in various designs and cooling procedures recommended for reducing such behavior. In this paper the temperature gradients during fast and slow cooling for conventional and anatomical designs are compared as well as an optical procedure to directly compare the influence of cooling rate on residual stress. Methods This investigation quantifies the temperature gradients between the inner and outer surfaces of crowns measured with thermocouples during two different cooling methods with uniform and anatomical frameworks. In the first method the crown was removed from the furnace after commencement of cooling whereas for the second method the crown was cooled to the glass transition temperature (600 °C) before removal. Direct observation of the residual stresses was made with an optical polarimeter and thin slices of veneered copings. Results This study observed that slow cooling decreases the temperature differences but still differences of up to 88 °C were observed. For the fast cooled crown, temperature differences of more than 100 °C for the uniform and 140 °C for the anatomical framework at temperatures above the glass transition temperature were recorded. Optical polarimeter observations indicated much lower stresses within the porcelain layer upon cooling by removing the crown below the glass transition temperature. Conclusion Slow cooling during the final veneering of dental restorations with zirconia frameworks reduces the temperature gradients and residual stresses within the porcelain layer, which represent one possible cause for chipping. An anatomical designed framework did not show the same reduction extent.

Porcelain monolayers and porcelain/alumina bilayers reinforced by Al2O3/GdAlO3 fibers

Aim. This work tested the effect of the addition of Al 2O 3/GdAlO 3 longitudinal fibers in different contents to veneering porcelain of two dental all ceramic systems. Methods: Fibers (0.5 mm diameter) obtained by the Laser Heated Pedestal Growth (LHPG) method were added to bar-shaped specimens made by veneer porcelain (monolayers) or both the veneer and the core ceramic (bilayers) of two all-ceramic systems: In-Ceram Alumina–glass infiltrated alumina composite (GIA) and In-Ceram 2000 AL Cubes–alumina polycrystal (AP) (VITA Zahnfabrik). The longitudinal fibers were added to veneering porcelain (VM7) in two different proportions: 10 or 17 vol%. The bars were divided into nine experimental conditions ( n = 10 ) according to material used: VM7 porcelain monolayers, VM7/GIA, VM7/AP; and according to the amount of fibers within the porcelain layer: no fibers, 10 vol% or 17 vol%. After grinding and polishing the specimens were submitted to a three point bending test (crosshead speed = 0.5 mm/min) with porcelain positioned at tensile side. Data were analyzed by means of one-way ANOVA and a Tukey‘s test ( α = 5 % ). Scanning electronic microscopy (SEM) was conducted for fractographic analysis. Results. Regarding the groups without fiber addition, VM7/AP showed the highest flexural strength (MPa), followed by VM7/GIA and VM7 monolayers. The addition of fibers led to a numerical increase in flexural strength for all groups. For VM7/GIA bilayers the addition of 17 vol% of fibers resulted in a significant 48% increase in the flexural strength compared to the control group. Fractographic analysis revealed that the crack initiation site was in porcelain at the tensile surface. Cracks also propagated between fibers before heading for the alumina core. Conclusions. The addition of 17 vol% of Al 2O 3/GdAlO 3 longitudinal fibers to porcelain/glass infiltrated alumina bilayers significantly improved its flexural strength. 10 vol% or 17 vol% of fibers inclusion increased the flexural strength for all groups.

The effect of porcelain thickness and surface liner application on the fracture behavior of a ceramic system

Objectives To determine the effect of porcelain thickness and the application of a surface liner (SL) on the flexural strength ( σ) of a ceramic system. Methods One hundred twenty bar-shaped specimens of yttria-stabilized zirconia-based ceramic were fabricated and randomly divided into two groups according to the application of SL: A – applied; B – not applied. The specimens were further divided according to the porcelain veneer thickness ( n = 20): 0–0.5 mm; 1–1.0 mm; 2–2.0 mm. All specimens were tested in 3-point bending with the porcelain under tension. The maximum load was recorded at first sign of fracture, the σ was calculated and the mode of failure was determined. Data was statistically analyzed using one-way ANOVA, Tukey ( α = 0.05) and Weibull distribution. Results The SL application had no effect ( p = 0.723) while the porcelain thickness had a significant effect ( p = 0.000) on the mean σ values. No significant differences in mean σ values were found with same porcelain thickness. A 0.5-mm thick porcelain layer (groups A0 and B0) showed greater mean σ values than other groups. The Weibull modulus ( m) ranged from 6 (groups A1 and B2) to 9 (groups A0, A2 and B0). The predominant mode of failure for all groups was fracture initiation at the porcelain surface propagating to the ceramic interface. Significance The porcelain thickness influenced the mean σ values, but the SL had no significant effect on the flexural strength and the mode of failure of the ceramic system examined.

Evaluation of Interfacial Bonding Strength between Laser Textured Metal Coping and Porcelain

Porcelain fracture at the interface between metal and porcelain is one of the most common clinical failures. For the clinical longevity, metal-ceramic prostheses must have satisfactory bond strength of the metal structure to porcelain. In this in-vitro study, to evaluate the effect of mechanical texturing of cast metal alloy for the interfacial bonding strength, sandblasting with Al2O3 and laser surface texturing in two different metal alloys were compared. To fabricate cast specimens, Ni-Cr and Ni-Cr-Ti alloy were casted with 25 x 0.5 x 3mm bar. Before porcelain application, 5 specimens of cast Ni-Cr alloy and 5 specimens of cast Ni-Cr-Ti alloy were abraded at 3-4bar air pressure, using 50μm aluminium oxide particles for 10s at 10cm distance. Other each 5 specimens of cast Ni-Cr alloy and Ni-Cr-Ti alloy were treated with laser surface texturing. The laser work was done with femtosecond laser. After surface treatment, surface morphology was observed under optical photographs and FE-SEM. Surface roughness and wettability were examined. All specimens were followed by application of opaque and body porcelain layers by recommendation of manufacturer. For the three point bending test, porcelain was added to the metal specimens to the dimension of 8 x 3 x 1mm in the central portion of each metal specimen. The device, containing the metal-ceramic specimen, was placed on a universal testing machine and loaded at cross head speed of 1.50mm/min until fracture of the specimen occurred. The failure load was recorded in a computer using software provided by the manufacturer of the testing machine. After the bonding test, FE-SEM was used to examine the fracture site and interface between textured metal alloys and porcelain.

The effect of surface treatment on bond strength of layering porcelain and hybrid composite bonded to zirconium dioxide ceramics

The purpose of this study was to investigate the differences between Rocatec (as surface treatment) and #600 polishing (as control) on shear bond strength of layering porcelain and hybrid composite to zirconium dioxide ceramics. Manufactured zirconia blocks used in this study were yttrium partially stabilized zirconia (YTZ(®)), and veneering materials were NobelRondo Zirconia Dentin A2 High Value (NZR) and Estenia C&B (ES). Total 48 zirconia blocks were fabricated (10 mm × 10 mm × 20 mm). The blocks of 24 each were treated by Rocatec and #600 paper, respectively. Surface treated zirconia blocks were divided into two groups, according to veneering materials of NZR and ES. NZR was fired and ES was polymerized to zirconia. The fabricated specimen was fixed to mounting jig and applied shear force using the universal testing machine at a crosshead speed of 0.5 mm/min. All results were statistically analyzed by two-way ANOVA and Tukey's test. EPMA analysis and SPM analysis of specimen interface were carried out. Mean shear bond strength of each condition was: NZR/#600; 23.3 (S.D. ±7.0) MPa, NZR/Rocatec; 26.9 (S.D. ±7.0) MPa, ES/#600; 10.7 (S.D.±2.4) MPa, ES/Rocatec; 12.5 (S.D.±0.8) MPa. From the results of this study, shear bond strength of layering porcelain to zirconia was higher than that of restorative hybrid resin. However the more study will be needed, the appropriate choice of materials became the gides to the expansion of the applied cases of metal-free prothesis.

Mechanical testing of indirect composite materials directly applied on implant abutments.

To test the strength to failure and fracture mode of three indirect composite materials directly applied onto Ti-6Al-4V implant abutments vs cemented standard porcelain-fused-to-metal (PFM) crowns. Sixty-four locking taper abutments were randomly allocated to four groups and were cleaned in ethanol in an ultrasonic bath for 5 min. After drying under ambient conditions, the abutments were grit blasted and a custom 4-cusp molar crown mold was utilized to produce identical crowns (n = 16 per group) of Tescera (Bisco), Ceramage (Shofu), and Diamond Crown (DRM) according to the manufacturer's instructions. The porcelain-fused-to-metal crowns were fabricated by conventional means involving the construction and a wax pattern and casting of a metallic coping followed by sintering of increasing layers of porcelain. All crowns were loaded to failure by an indenter placed at one of the cusp tips at a 1 mm/min rate. Subsequently, fracture analysis was performed by means of stereomicroscopy and scanning electron microscopy. One-way ANOVA at 95% level of significance was utilized for statistical analysis. The single load to failure (± SD) results were: Tescera (1130 ± 239 N), Ceramage (1099 ± 257 N), Diamond Crown (1155 ± 284 N), and PFM (1081 ± 243 N). Stereomicroscopy analysis showed two distinct failure modes, where the loaded cusp failed either with or without abutment/metallic coping exposure. SEM analysis of the fractures showed multiple crack propagation towards the cervical region of the crown below a region of plastic deformation at the indenter contact region. The three indirect composites and PFM systems fractured at loads higher than those typically associated with normal occlusal function. Although each material had a different composition and handling technique, no significant differences were found concerning their single load to fracture resistance among composite systems and PFM.

Spectrophotometric Analysis of Tooth Color Reproduction on Anterior All‐Ceramic Crowns: Part 1: Analysis and Interpretation of Tooth Color

Color matching of a natural maxillary central incisor is one of the most difficult challenges in clinical dentistry. Accurate color determination and interpretation of tooth color information in ceramic work is an important step in achieving success in ideal color reproduction. In this case study, factors that influence tooth color determination were analyzed, and the process of interpretation of tooth color information was assessed based on scientific color data using a novel dental spectrophotometer system. An all-ceramic crown for a maxillary right central incisor was the subject of this color assessment. The contralateral incisor was an intact natural tooth that was bleached and then used as the target shade for an all-ceramic crown. The dental spectrophotometer (Crystaleye, Olympus, Tokyo, Japan) was used for tooth color measurement and analysis. The target tooth, prepared tooth, maxillary arch, and face images were captured for color information. Tooth color stabilization related to tooth bleaching and tooth dehydration was assessed. Based on tooth color data obtained by the dental spectrophotometer, color was analyzed in several different areas of a tooth using CIELAB (Commission Internationale de l'Eclarirage) color coordinates L*, a*, b*, and color difference Delta E. Interpretation of the tooth color information was made in each of porcelain layers on a blue map, and its intensions for color reproduction were described. Throughout this spectrophotometric assessment, the process of stabilized tooth color determination, tooth color analysis, interpretations, and fabrication of a blue map for porcelain work was clarified with color data as scientific evidence. The use of a dedicated dental spectrophotometer allows the evaluation and measurement of the color of a bleached tooth. This allows the laboratory technician to more precisely understand the bleached tooth shade as well as when the bleached tooth color has become stable enough to match to a contralateral all-ceramic crown restoration.

Effect of repeated firings on the color of opaque porcelain applied on different dental alloys

Although metal ceramic fixed restorations are commonly preferred by clinicians, there remain a limited number of studies on how opaque porcelain color is affected by fabrication procedures, such as the number of firings and types of metal alloys. The purpose of this study was to determine the effects of various types of metal alloys on the color of opaque porcelain after repeated firings. Seven different types of metal ceramic alloys (3 base metals: Metalloy CC, chromium cobalt (B-MCC); Heraenium NA, nickel chromium (B-HNA); Argeloy NP, nickel chromium beryllium (B-ANP); 3 noble metals: Ceradelta, palladium silver (N-CD); Cerapall 2, palladium (N-CP2); V-Delta SF, gold palladium (N-VDSF); and 1 high noble metal: V-Gnathos Plus, gold platinum (HN-GP)) were used to support a 0.1-mm-thick layer of opaque porcelain (IPS d.SIGN Opaquer, shade B1) to determine the metal alloys' effect on the opaque porcelain color after repeated porcelain firings. Opaque porcelain was applied on specimens (16 mm x 1 mm) prepared from each type of alloy. The specimens (n=21) were subjected to 1 opaque firing, 4 consecutive dentin firing cycles, and 1 glaze firing cycle. Delta E values were calculated for all metal alloy groups from opaque firing (control group) to each subsequent firing stage within each tested alloy group. One-way ANOVA and Fisher's least significant difference tests were performed to determine the differences between alloys. In addition, DeltaE values calculated after repeated firings were analyzed by 1-way ANOVA and paired t test, to determine whether repeated dentin firing stages affected the color of opaque porcelain (alpha=.05). After the first and second dentin firings, the color shift in opaque porcelain was significant for all tested alloy groups (P<.001). The color of opaque porcelain changed significantly after the third dentin firing for all groups except for B-HNA and N-VDSF (P<.001). After the fourth dentin firing, the color of opaque porcelain changed significantly for all tested alloy groups (P=.022 for B-ANP, P=.042 for N-VDSF, and P<.001 for remaining alloys). After glaze firing, the color change in opaque porcelain was significant in all but the N-CP2 group (P=.002 for N-VDSF, P=.014 for HN-GP, and P<.001 for remaining alloys). Delta E values showed that B-MCC after the first dentin firing, N-CD after the second dentin firing and glaze firing, and B-ANP after the third and fourth dentin firings showed significantly different DeltaE values than all remaining test alloys (P<.001). Subsequent porcelain firings significantly affected the color of a 0.1-mm-thick layer of opaque porcelain for all alloys tested. After the third and fourth firings, 1 base metal alloy (B-ANP) showed significantly greater color change than the remaining dental alloys when the color difference was compared to baseline. In addition, the color change in a noble alloy (N-CD) was significantly less than that of the other alloys after glaze firing. However, color shifts after repeated dentin firings were imperceptible (DeltaE<2.6) and clinically acceptable (DeltaE<5.5) for each type of alloy.

Studies on mechanical strength, thermal expansion of layering porcelains to alumina and zirconia ceramic core materials

The aim of this study was to evaluate and clarify the various mechanical properties and behavior of layering porcelains (Tokuyama Dental Ceramic, IPS Empress 2, Cerabien, Vitadura, Creation) used for veneering high-strength ceramic core materials. The layering porcelains studied exhibited the following range of mechanical properties: compressive strength at 586-1091 MPa, bending strength at 30-97 MPa, diametral tensile strength at 16-28 MPa, Vickers hardness at 481-647 Hv, and fracture toughness at 1.36-2.05 MPa x m1/2. Results of this study indicated that the mechanical shortcomings of conventional porcelain, such as brittleness and hardness, have been overcome by the enhanced mechanical properties of layering porcelain, resulting in improved fracture toughness.

Effect of Ferrule and Bonding on the Compressive Fracture Resistance of Post and Core Restorations

The purpose of this study was to compare the fracture resistance of endodontically treated teeth restored with different post and core systems in combination with complete metal crowns in teeth with no coronal structure. Fifty extracted mandibular premolars were divided into five groups. The coronal portion of each tooth was removed at the cementoenamel junction (CEJ) in all groups except Group 1. In this group the teeth were sectioned 1 mm above the CEJ to create a ferrule. After root canal preparations, cast posts were placed in the first four groups. Prefabricated glass fiber posts and composite cores were placed in the fifth group. An opaque porcelain layer was applied to the metal post surfaces in the third group and an alloy primer was applied to the posts in the fourth group before using Panavia F2 resin cement. No bonding agent or surface treatments were used for the first and second groups. A Ni-Cr full cast crown for each sample was prepared and cemented. A compressive load was applied at an angle of 45 degrees to the crown with a universal testing machine. After 500,000 mechanical cycles at 1.5Hz, the maximum load at fracture (N) was recorded. Significantly higher fracture resistance values (216.87 N) and survival rates (75%) were demonstrated for non-ferrule teeth restored with opaque layered posts than for other non-ferrule groups. The prefabricated post group showed the most favorable fracture pattern in all test groups (P=0.04). Either a ferrule preparation or bonding with the use of an opaque porcelain layer can increase the fracture resistance of teeth with little remaining tooth structure that are restored with cast crowns following endodontic therapy. Bonding cast posts to the tooth structure has a significant effect on compensating for the lack of a ferrule on endodontically treated teeth.

Analysis of elemental maps from glaze to body of ancient Chinese Jun and Ru porcelain by micro-X-ray fluorescence

The reasons how the middle layer of Ru and Jun porcelain between the glaze and body came into being are still not completely understood. Here, elemental maps from the glaze to the body of pieces of ancient Chinese Ru and Jun porcelain were analyzed by micro-X-ray fluorescence. The results show the middle layer was probably formed by the chemical composition of the glaze turning into glassy states and undergoing complex physical–chemical reactions with the body. However, the middle layer of Jun porcelain was formed by the chemical composition of the glaze turning into glassy states and then infiltrating the body at high temperatures during the firing process.

Colorimetric analysis of opaque porcelain fired to different base metal alloys used in metal ceramic restorations

The popularity of base metal alloys has considerably increased in recent years because of their superior mechanical properties as well as the high cost of noble alloys. However, there is disagreement about their effect on the opaque porcelain color and the color differences among base metal alloys. The purpose of this in vitro study was to determine and compare the influence of various commercially available base metal alloys (excluding titanium-based systems) on the resulting color of opaque porcelain with the use of a colorimetric device. Fourteen different types of Ni-Cr and 3 different types of Co-Cr porcelain bonding alloys were selected with a Au-Pd alloy (V-Delta SF) as the control group for colorimetric measurements and determination of color shift after opaque application. Shade B1 of an opaque porcelain (IPS d.SIGN Opaquer) was applied (0.1 mm) to all specimens (16 mm x 1 mm). The color coordinates of each specimen were measured with a chromameter. The data were displayed in L*, a*, and b* values according to the CIELAB system, and the color differences (DeltaE) between base metal alloys and the control group were calculated. Data were statistically analyzed with 1-way ANOVA (alpha=.05). The ANOVA was followed by Dunnett's multiple comparison test for comparisons with the control group to determine specifically which groups were significantly different from the control group. The L* value of only 1 base metal alloy was significantly different from the control group (P<.001). All base metal alloy groups except 3 had a* values which were significantly different from the control group a* value (P=.001 for Rexillium III, P=.008 for Heracles N, and P<.001 for the remaining 12 alloys), whereas only 3 base metal alloys were not statistically significantly different from the control group in the means of b* values (P<.001). All base metal alloys to which opaque porcelain was applied had significantly different DeltaE values in comparison with the control group (P<.001). The data of the study indicated that a 0.1-mm-thick layer of opaque porcelain applied on the Ni-Cr and Co-Cr alloys did not reliably reproduce the color of opaque porcelain. However, within the limitations of this study, the color differences of base metal alloys measured according to the control group are within clinically acceptable limits (DeltaE<3.5).

Effect of Framework Shape on the Fracture Strength of Implant‐Supported All‐Ceramic Fixed Partial Dentures in the Molar Region

The aim of the present study was to clarify the effects of the shape of the zirconium framework of implant-supported, all-ceramic fixed partial dentures (FPDs) on the fracture strength and fracture mode. This study consisted of mechanical strength testing and 3D finite element analysis (FEA). The three framework shapes used in this study were: (1) conventional shape (control); (2) convex shape: 1.0-mm curve in the direction of the occlusal surface; and (3) concave shape: 1.0-mm curve in the direction of the gingival surface. Five frameworks were made for each condition (total: 15). A load (N) was applied until the FPD fractured. For FEA, a 3D model consisting of cortical bone, cancellous bone, implant bodies, and superstructure was constructed. The results of the mechanical strength test showed that fracture load was 916.0 +/- 150.1 N for the conventional shape, 1690.5 +/- 205.3 N for the convex shape, and 1515.5 +/- 137.0 N for the concave shape. The mean final fracture load for the FPDs with frameworks was the highest for the convex shape; however, a critical crack in the veneer porcelain (736.5 +/- 145.2 N) was confirmed during loading for the convex shape. Stress distribution maps for all conditions showed that tensile stress was generated at the veneer porcelain on the gingival side of the mesial and distal connectors of the pontic; however, there were differences in the maximum value and stress distribution within the framework. The shape of the framework, particularly the shape of the pontic-connector interface, affects the stress distribution, fracture strength, and fracture mode of all-ceramic FPDs, and stress concentration inside a framework may induce cracking of layering porcelain.

Analyses of layer-thickness effects in bilayered dental ceramics subjected to thermal stresses and ring-on-ring tests

Objectives The purpose of this study was to analyze the stress distribution through the thickness of bilayered dental ceramics subjected to both thermal stresses and ring-on-ring tests and to systematically examine how the individual layer thickness influences this stress distribution and the failure origin. Methods Ring-on-ring tests were performed on In-Ceram Alumina/Vitadur Alpha porcelain bilayered disks with porcelain in the tensile side, and In-Ceram Alumina to porcelain layer thickness ratios of 1:2, 1:1, and 2:1 were used to characterize whether failure originated at the surface or the interface. Based on (1) the thermomechanical properties and thickness of each layer, (2) the difference between the test temperature and the glass transition temperature, and (3) the ring-on-ring loading configuration, the stress distribution through the thickness of the bilayer was calculated using closed-form solutions. Finite element analyses were also performed to verify the analytical results. Results The calculated stress distributions showed that the location of maximum tension during testing shifted from the porcelain surface to the In-Ceram Alumina/porcelain interface when the relative layer thickness ratio changed from 1:2 to 1:1 and to 2:1. This trend is in agreement with the experimental observations of the failure origins. Significance For bilayered dental ceramics subjected to ring-on-ring tests, the location of maximum tension can shift from the surface to the interface depending upon the layer thickness ratio. The closed-form solutions for bilayers subjected to both thermal stresses and ring-on-ring tests allow the biaxial strength of the bilayer to be evaluated.

酸化ジルコニウムセラミックス用レヤリング陶材の熱膨張に関する研究

The purpose of this study was to investigate the coefficients of thermal expansion and shrinkage of an all-ceramic system (cercon) smart ceramics, DeguDent) utilizing tetragonal stabilized zirconia. The coefficients of thermal expansion and shrinkage of the core material and the layering porcelains (dentin and enamel) used in this study were measured according to the ISO 9693 standard. Five specimens for the core material and ten specimens for each layering porcelain were tested. The core specimens were milled, sintered, ground and polished. Five of the specimens for each layering porcelain were fired two times, and the remaining five specimens were fired four times. The fired layering porcelain specimens were ground and polished. The coefficients of thermal expansion and shrinkage were evaluated using a push-rod dilatometer at a heating rate of 5 degrees C /min over temperature ranges of 25-700 degrees C for the core, and 25-550 degrees C for the layering porcelain. For each specimen, the coefficients of thermal expansion was determined to be between 25 and 500 degrees C from the plotted curve of expansion versus temperature. For the core material, the coefficients of thermal expansion and shrinkage showed almost the same value (10.8 x 10(-6)/ degrees C). For the layering porcelains, the coefficients of thermal expansion and shrinkage ranged from 9.3-11.1 x 10(-6)/ degrees C. The difference of the coefficients of thermal expansion and shrinkage between the core materials and the layering porcelains was -0.3-1.5 x 10(-6)/ degrees C. The specimens fired two times and the specimens fired four times exhibited almost the same value for each layering porcelain. The core material and layering porcelains have a suitable relationship.

Comparative study of ceramic-to-metal bonding

Dentists and technicians have used dental ceramics associated with different types of alloys without taking into account the characteristics of compatibility of these materials. Knowing the properties of the alloy and ceramic used in metal/ceramic restorations is a key factor for treatment success. The purpose of this study was to evaluate the bond strength of a palladium-silver alloy (Pors-on 4) to 3 ceramics (Ceramco, Noritake and Vita VMK-68) using shear forces at the metal-ceramic interface. A stainless steel cylindrical matrix was used for preparation of the metal dies, application of ceramic and shear strength testing. Thirty palladium-silver alloy cylinders received two layers of opaque and two layers of body porcelain, and shear tests were performed in a universal testing machine at a cross-head speed of 0.5 mm/min. Shear bond strength means (in MPa) were: 28.21(Ceramco), 28.96 (Noritake) and 24.11 (Vita VMK-68). One-way ANOVA did not show statistically significant differences (p>0.05) among the materials. The results of this study indicate that the three evaluated ceramic systems are suitable to be used in combination with the tested palladium-silver alloy.

A Study of the Aging of α-Al2O3 Dielectric Material in DBD Plasma

The performance of dielectric material is a key factor against a long time action in dielectric barrier discharge (DBD) plasma. In this study, the aging of the Al2O3 dielectric material was studied by the Atomic Force Microscope (AFM), X-ray Photoelectron spectrum (XPS) and Auger electron spectrum (AES) methods. The results showerd that the performance of the dielectric does not descend after an 1000 h aging experiment. Therefore the thin dielectric layers of α-AL2O3 porcelain with a purity above 99% can sustain a long time action of DBD plasma and form gas ionization discharges steadily.

Laser densification of extruded dental porcelain bodies in multi‐material laser densification process

PurposeCommercial dental porcelain powder was deposited via slurry extrusion and laser densified to fabricate dental restorations in a multi‐material laser densification (MMLD) process.Design/methodology/approachA dental porcelain slurry was made from ball milled dental porcelain powders and extruded using the MMLD system. Extruded lines and rings were laser densified under different conditions in order to study how to build fully dense porcelain layers without warping and cracking during the MMLD process.FindingsThe geometric cross section of laser densified porcelain lines were dependent on laser processing parameters. Laser densified single ring showed no warping, and multiple layer body after laser densification showed cracks in the rings. The interface microstructure suggested good bonding between multiple layers. The mechanism to achieve single porcelain ring without warping and cracking is discussed. Alternate ways to build physical tooth layer by layer are proposed.Originality/valueIn the MMLD process, dental porcelain slurry was extruded from a human tooth computer file and laser densified to manufacture dental restorations based on solid freeform fabrication (SFF) principles. The understanding developed will pave the way for fabricating a physical dental restoration unit in the near future.