Metal-ceramic Specimens Research Articles

Validation of two clinical color measuring instruments for use in dental research

ObjectiveThere are several shade matching instruments developed for clinical use, but the validity of their use in dental research has not been thoroughly investigated. The objective of this study is to evaluate the accuracy of using two clinical color measuring instruments, VitaEasyshade and Spectroshade, against a referent laboratory color measuring instrument (Spectroradiometer PR670). Methods and materialsThe validity and repeatability of the referent laboratory color measuring instrument was assessed using standard color patches with certified CIE L*a*b* values. 10% of the 240 color patches were randomly selected and measured ten times in a random order to test for repeatability. 16 metal ceramic specimens, fabricated from base metal alloy veneered with porcelain of different Vita Classic shades, were measured for L*a*b* values using the PR670, Vita EasyShade and the Spectroshade. The CIE L*a*b* values obtained from the three color measuring instruments were compared using repeated measures ANOVA and post hoc using the Bonferroni test. The color difference, CIEDE2000 (∆E00), between the gold standard (PR670) and the two color measuring instruments were also determined and compared against the known perceptible color difference. ResultsL*a*b* values varied significantly between the three instruments. When comparing the mean ΔE00, the differences in values between PR670 and Spectroshade were not clinically significantly. However, the mean ΔE00 values between PR670 and Vita Easyshade were both clinically and statistically significant. ConclusionThe lack of clinical significance in values obtained from the SpectroShade when compared to those obtained by the PR670 suggests that the SpectroShade may be recommended for use in dental color research. Clinical significanceThe SpectroShade instrument and PR670 spectroradiometer provided values that lacked clinical significance, suggesting that its use may be highly beneficial for clinical shade matching as well as color research.

Effect of Bonding Agent on Metal-Ceramic Bond Strength between Co-Cr Fabricated with Selective Laser Melting and Dental Feldspathic Porcelain.

To investigate the effect of bonding agent on the bonding strength between Co-Cr dental alloy, prepared by selective laser melting (SLM), and feldspathic porcelain. The experiments were conducted according to ISO 9693 and the conventional protocols for the production of metal-ceramic dental restorations. After Al2 O3 air-particle abrasion, metal substrates of Co-Cr dental alloy specimens were bonded, using bonding agent (25 specimens), with dental porcelain positioned in layers (opaque, dentin, enamel). Control specimens (25) were also produced without bonding agent. Bonding strength was measured using 3-point bending tests, and the results were statistically analyzed using the t-test and Weibull statistics. Elemental (by SEM/EDS) and crystallographic analyses (by XRD) were conducted on the bonding agent, along cross sections of alloy-porcelain interfaces, and on fracture surfaces. Cohesive fracture occurred (on the porcelain side). The application of the bonding agent decreased the average bonding strength (from 42.27 ± 5.85 to 36.25± 3.26 MPa, P = 0.00006), attributed to the nonexisting reaction between the TiO2 -rich bonding agent and the Co-Cr alloy, but it increased the Weibull modulus (from 7.84 to 12.16), which reflects the reliability of the bond in the tested metal-ceramic specimens. Although the application of bonding agent slightly decreased the bonding strength, all the measured values of the metal-ceramic specimens produced by the SLM technique, with or without the bonding agent, are markedly higher than the minimum value required by ISO 9693 (25 MPa). Moreover, the use of bonding agent favors the increase of the Weibull modulus.

The effect of food medium on the wear behaviour of veneering porcelain: An in vitro study using the three-body abrasion mode

ObjectivesThe present study examined the effect of food medium on the three-body wear behaviour of veneering porcelain derived from porcelain-fused-to-metal crowns. MethodsSeventy-four rectangular metal–ceramic specimens were prepared using Ceramco III as the veneering porcelain. After storage in distilled water at 37 °C for 2 days, the specimens were tested with a custom-designed chewing machine with a stainless steel ball as antagonist (350 N loads, 2.4 × 106 cycles). Testing was performed using water, silica beads, poly(methyl) methacrylate beads, millet seed slurry, chicken slurry or celery slurry as abrasive medium. Wear analysis of the veneering porcelain was performed using a 3D profilometer after every 300,000 wear cycles and analysed with one-way analysis of variance and post-hoc pairwise comparison procedures. Worn surfaces were examined with scanning electron microscopy. ResultsThe wear curves of all experimental groups demonstrated three wear stages (running-in, steady wear and severe wear) with characteristic microstructure of worn surfaces. All the three food items selected in the present study (celery, chicken and millet seeds) had lower hardness compared with the veneering porcelain and produced less abrasion of the porcelain than a two-body wear system (water only). Abrasive wear produced with silica particles was the highest for the veneering porcelain. ConclusionThe wear process of veneering porcelain in porcelain-fused-to-metal restorations is affected by the type of food consumed during mastication. Clinical significanceExcessive abrasion may lead to premature failure of porcelain-fused-to-metal restorations. The importance of the wear behaviour of dental ceramic materials cannot be overstated. Three-body wear is an unavoidable consequence of oral function and occurs daily during eating. Understanding the effect of food particles on the wear behaviour of dental porcelain provides insight into the clinical performance and durability of these restorations.

The effect of layer thickness on the porcelain bond strength of laser-sintered metal frameworks

Statement of problemLaser sintering has become a common manufacturing technique in the fabrication of metal-ceramic restorations. The layer thickness of the sintering process may affect the surface morphology and hence the porcelain bond strength. However, limited information is available on the effect of layer thickness on porcelain bond strength. PurposeThe purpose of this in vitro study was to evaluate the porcelain bond strength of direct metal laser-melted (DMLM) cobalt-chromium (Co-Cr) metal frameworks sintered with 25-μm and 50-μm layer thicknesses. Material and methodsThirty metal frameworks (n=10) were fabricated by using the lost-wax technique (group C [control]), DMLM with a 25-μm layer thickness (group L25), and DMLM with a 50-μm layer thickness (group L50) according to the International Organization for Standardization (ISO) 9693-1. The surface roughness of 1 metal specimen from each group was analyzed by atomic force microscopy. After porcelain firing, a 3-point bend test was applied to each metal-ceramic specimen as in ISO 9693-1. In addition, 1 metal framework from each group was prepared and examined by scanning electron microscopy to evaluate surface morphology. Data were analyzed statistically by using 1-way analysis of variance and the Tukey honestly significant difference tests (α=.05). ResultsGroup C and group L25 showed significantly higher (P<.001) mean porcelain bond strength values than group L50, and no significant bond strength difference was found between groups C and L25. All groups generally exhibited an adhesive type of failure. ConclusionsThe results indicate that layer thickness may affect the porcelain bond strength of DMLM metal frameworks.

Evaluation of a Novel Computer Color Matching System Based on the Improved Back-Propagation Neural Network Model.

To explore the feasibility of a novel computer color-matching (CCM) system based on the improved back-propagation neural network (BPNN) model by comparing it with the traditional visual method. Forty-three metal-ceramic specimens were fabricated by proportionally mixing porcelain powders. Thirty-nine specimens were randomly selected to train the BPNN model, while the remaining four specimens were used to test and calibrate the model. A CCM system based on the improved BPNN model was constructed using MATLAB software. A comparison of the novel CCM system and the traditional visual method was conducted by evaluating the color reproduction results of 10 maxillary central incisors. Metal-ceramic specimens were fabricated using two color reproduction approaches. Color distributions (L*, a*, and b*) of the target teeth and of the corresponding metal-ceramic specimens were measured using a spectroradiometer. Color differences (ΔE) and color distributions (ΔL*, Δa*, and Δb*) between the teeth and their corresponding specimens were calculated. The average ΔE value of the CCM system was 1.89 ± 0.75, which was lower than that of the visual approach (3.54 ± 1.11, p < 0.01). With respect to color distributions, substantial differences were found between the two color-matching systems, except for ΔL* (p > 0.05). The novel CCM system produced greater accuracy in color reproduction within the given color space than the traditional visual approach.

Effect of Jig Design and Assessment of Stress Distribution in Testing Metal-Ceramic Adhesion.

In testing adhesion using shear bond test, a combination of shear and tensile forces occur at the interface, resulting in complex stresses. The jig designs used for this kind of test show variations in published studies, complicating direct comparison between studies. This study evaluated the effect of different jig designs on metal-ceramic bond strength and assessed the stress distribution at the interface using finite element analysis (FEA). Metal-ceramic (Metal: Ni-Cr, Wiron 99, Bego; Ceramic: Vita Omega 900, Vita) specimens (N = 36) (diameter: 4 mm, veneer thickness: 4 mm; base diameter: 5 mm, thickness: 1 mm) were fabricated and randomly divided into three groups (n = 12 per group) to be tested using one of the following jig designs: (a) chisel (CH) (ISO 11405), (b) steel strip (SS), (c) piston (PI). Metal-ceramic interfaces were loaded under shear until debonding in a universal testing machine (0.5 mm/min). Failure types were evaluated using scanning electron microscopy (SEM). FEA was used to study the stress distribution using different jigs. Metal-ceramic bond strength data (MPa) were analyzed using ANOVA and Tukey's tests (α = 0.05). The jig type significantly affected the bond results (p = 0.0001). PI type of jig presented the highest results (MPa) (p < 0.05) (58.2 ± 14.8), followed by CH (38.7 ± 7.6) and SS jig type (23.3 ± 4.2) (p < 0.05). Failure types were exclusively a combination of cohesive failure in the opaque ceramic and adhesive interface failure. FEA analysis indicated that the SS jig presented slightly more stress formation than with the CH jig. The PI jig presented small stress concentration with more homogeneous force distribution compared to the CH jig where the stress concentrated in the area where the force was applied. Metal-ceramic bond strength was affected by the jig design. Accordingly, the results of in vitro studies on metal-ceramic adhesion should be evaluated with caution. When adhesion of ceramic materials to metals is evaluated in in vitro studies, it should be noted that the loading jig type affects the results. Clinical observations should report on the location and type of ceramic fractures in metal-ceramic reconstructions so that the most relevant test method can be identified.

Surface Roughness of Dental Porcelain Fused-To-Nickel Chromium Using Different Polishing Materials and Glazing Techniques

Background: Rough dental porcelain surface due to incorrect glazing technique or occlusal adjustment can cause wear of opposing teeth and tissue irritation. The aim of this study was to measure the surface roughness of low-fusing dental porcelain after treatment with different polishing materials and glazing techniques. Materials and Methods: Seventy metal-ceramic specimens were fabricated and divided into seven groups according to type of surface treatment. Group I: Unglazed porcelain (control group). Group II: Porcelain polished with sandblast powder and then autoglazed, Group III: Porcelain polished with sandblast powder and then applied glaze. Group IV: Porcelain polished with sandblast powder and then porcelain rubber wheels. Group V: Porcelain polished with sandblast powder, porcelain rubber wheel and then polishing paste. Group VI: Porcelain polished with sandblast powder, porcelain rubber wheels, polishing paste and then autoglazed Group VII: Porcelain polished with sandblast powder, porcelain rubber wheels, polishing paste and then applied glazed. The surface roughness averages “Ra” of the specimens have been determined using the profilometer. Results: One way – ANOVA showed highly significant differences among tested groups. Group I showed roughest group with highly significant differences among all tested groups. Followed by group II with highly significant differences, then group III which showed no significant differences with group VII, which is the smoothest group scored. Also group IV showed “Ra” values compared with group VI. While group V showed slightly significant differences with group VII (LSD test). Conclusion: Polished porcelain with (rubber wheel and polishing paste) can be considered a good alternative to applied glazed of porcelain restoration which is characterized by time consuming and sensitive technique. Moreover, autoglazing porcelain followed by polishing or without polishing , proved to be disadvantageous since it increases surface roughness

Comparison of the metal-ceramic bond after recasting and after laser sintering

Statement of problemFailure of the bond between metal and ceramic is common with metal ceramic prostheses. PurposeThe purpose of this in vitro study was to investigate how recasting affects the metal-ceramic bond strength for 1 base metal and 1 noble alloy compared with laser-sintered Co-Cr alloy by using a procedure based on ANSI/ADA Specification No. 38. Material and methodsOne laser-sintered (Co-Cr) and 2 metal (Co-Cr, Pd-Ag) alloys were used. Metal strips (25×3×0.5 mm) were obtained with 2 different methods: torch melting and laser sintering. Twelve alloy specimens were processed for each group. Vita VM13 porcelain layers (8×3×1.1 mm) were fabricated at the centers of the metal frameworks. Specimens containing 100% fresh alloy were used in the first casting group (control). Metal ceramic specimens were prepared for each alloy, and no new metal was added to the second and third castings. The findings were statistically analyzed and compared with a 2-way analysis of variance (ANOVA). ResultsThe second casting of the noble alloy-ceramic specimen had the highest mean metal-ceramic bond strength in flexure. No significant differences were found between the laser-sintered Co-Cr and the Pd-Ag metal ceramic specimens after the first and third castings. ConclusionAll groups had adequate porcelain bond strength, except C2 (second casting of Co-Cr alloy) and C3 (third casting of Co-Cr alloy). Co-Cr alloy fabricated with new laser-sintering techniques is a promising alternative for metal ceramic restorations. Further research is needed before its use can be advocated in the dental laboratory.

Comparison of the metal-to-ceramic bond strengths of four noble alloys with press-on-metal and conventional porcelain layering techniques

New noble alloys for metal ceramic restorations introduced by manufacturers are generally lower-cost alternatives to traditional higher-gold alloys. Information about the metal-to-ceramic bond strength for these alloys, which is needed for rational clinical selection, is often lacking. The purpose of this study was to evaluate the bond strength of 4 recently introduced noble alloys by using 2 techniques for porcelain application. Aquarius Hard (high-gold: 86.1 gold, 8.5 platinum, 2.6 palladium, 1.4 indium; values in wt. %), Evolution Lite (reduced-gold: 40.3 gold, 39.3 palladium, 9.3 indium, 9.2 silver, 1.8 gallium), Callisto 75 Pd (palladium-silver containing gold: 75.2 palladium, 7.1 silver, 2.5 gold, 9.3 tin, 1.0 indium), and Aries, (conventional palladium-silver: 63.7palladium, 26.0 silver, 7.0 tin, 1.8 gallium, 1.5 indium) were selected for bonding to leucite-containing veneering porcelains. Ten metal ceramic specimens that met dimensional requirements for International Organization for Standardization (ISO) Standard 9693 were prepared for each alloy by using conventional porcelain layering and press-on-metal methods. The 3-point bending test in ISO Standard 9693 was used to determine bond strength. Values were compared with 2-way ANOVA (maximum likelihood analysis, SAS Mixed Procedure) and the Tukey test(α=.05). Means (standard deviations) for bond strength with conventional porcelain layering were as follows: Aquarius Hard(50.7 ±5.5 MPa), Evolution Lite (40.2 ±3.3 MPa), Callisto 75 Pd (37.2 ±3.9 MPa), and Aries (34.0 ±4.9 MPa). Forthe press-on-metal technique, bond strength results were as follows: Aquarius Hard (33.7 ±11.5 MPa), Evolution Lite(34.9±4.5 MPa), Callisto 75 Pd (37.2 ±11.9 MPa), and Aries (30.7 ±10.8 MPa). From statistical analyses, the following 3 significant differences were found for metal-to-ceramic bond strength: the bond strength for Aquarius Hard was significantly higher for conventional porcelain layers compared with the press-on-metal technique; the bond strength for Aquarius Hard with conventional porcelain layers was significantly higher than the bond strengths for the other 3 alloys withconventional porcelain layers; and the bond strength for Aquarius Hard with conventional porcelain layers was significantly higher than the bond strength for Callisto 75 Pd with conventional porcelain layers and the other 3 alloys with the press-on-metal technique. For both conventional layering and press-on-metal techniques, all 4 noble alloys had a mean metal-to-ceramic bond strength that substantially exceeded the 25 MPa minimum in the ISO Standard 9693. The results for Aries support themanufacturer's recommendation not to use the press-on-metal technique for alloys that contain more than 10% silver.

Effect of pretreatments on the metal–ceramic bonding strength of a Pd–Ag alloy

ObjectivesThe purpose of this study was to evaluate the efficacy of surface treatments on the bonding properties between a metal and ceramic. MethodsSixty metal specimens were divided equally into four groups of 15 samples each. These groups received different treatments (Gr1: 250μm Al2O3+preoxidation; Gr2: 250μm Al2O3+degassing; Gr3: 120μm Al2O3+preoxidation; Gr4: 120μm Al2O3+degassing). Bond strengths were evaluated using a three-point bending test. The results were analyzed using 2-way ANOVA and Tukey's test. Scanning electron microscopy and energy dispersive spectroscopy were used to observe the microscopic features, elemental compositions and distributions, and diffusion in the specimens. Mechanical profiler was used to measure the roughness of metal surface. ResultsThe bond strengths of the four groups ranged from 45.00±3.63MPa to 51.61±5.91MPa, with significant differences (P<.05). The specimen that received the pretreatment of 250μm Al2O3 air-particle abrasion+degassing had the highest bond strength. Heating under different oxygen partial pressures caused the final Pd–Ag alloys to have varying degrees of internal oxidation and different quantities of metallic nodules. None of the elements in either the ceramic or the Pd–Ag alloy layer diffused into the other layer. ConclusionsThe metal–ceramic specimen subjected to air-particle abrasion with 250μm Al2O3 and degassed before porcelain firing had significantly higher bond strength than specimens treated differently.

Evaluation of the mechanical properties and porcelain bond strength of cobalt-chromium dental alloy fabricated by selective laser melting

Limited information is available regarding the microstructure and mechanical properties of dental alloy fabricated by selective laser melting (SLM). The purpose of this study was to evaluate the mechanical properties of a cobalt-chromium (Co-Cr) dental alloy fabricated by SLM and to determine the correlation between its microstructure and mechanical properties and its porcelain bond strength. Five metal specimens and 10 metal ceramic specimens were fabricated to evaluate the mechanical properties of SLM Co-Cr dental alloy (SLM alloy) with a tensile test and its porcelain bond strength with a 3-point bending test. The relevant properties of the SLM alloy were compared with those of the currently used Co-Cr dental alloy fabricated with conventional cast technology (cast alloy). The Student t test was used to compare the results of the SLM alloy and the cast alloy (α=.05). The microstructure of the SLM alloy was analyzed with a metallographic microscope; the metal ceramic interface of the SLM porcelain bonded alloy was studied with scanning electron microscopy, energy dispersive x-ray spectroscopy, and an electron probe microanalyzer. Both the mean (standard deviation) yield strength (884.37 ± 8.96 MPa) and tensile strength (1307.50 ±10.65 MPa) of the SLM alloy were notably higher than yield strength (568.10 ± 30.94 MPa) and tensile strength (758.73 ± 25.85 MPa) of the currently used cast alloy, and the differences were significant (P<.05). The porcelain bond strength of the SLM alloy was 55.78 ± 3.02 MPa, which was similar to that of the cast alloy, 54.17 ± 4.96 MPa (P>.05). Microstructure analysis suggested that the SLM alloy had a dense and obviously orientated microstructure, which led to excellent mechanical properties. Analysis from scanning electron microscopy, energy dispersive x-ray spectroscopy, and the electron probe microanalyzer indicated that the SLM alloy had an intermediate layer with elemental interpenetration between the alloy and the porcelain, which resulted in an improved bonding interface. Compared with the currently used cast alloy, SLM alloy possessed improved mechanical properties and similar porcelain bond strength.

Wettability and bond strength between leucite-reinforced dental porcelains and Co-Cr alloy

A series of methods has been used to evaluate metal ceramic bond strength. However, little attention has been paid to the wettability and interfacial reactions of dental porcelain/alloy systems, which may affect the bond strength of metal ceramic restorations. The purpose of this study was to understand the wetting and spreading behaviors, the interfacial reactions, and the bonding mechanism of ceramic to metal with TiO2 and MoO3 added to the dental porcelain. Two leucite-reinforced dental porcelains were used in the study. Twelve Co-Cr alloy sheets (15× 10× 2 mm) divided into 2 groups were used to evaluate the wetting process, and 12 Co-Cr alloy sheets (25× 3× 0.5 mm) (Bego) divided into 2 groups were used for the 3-point bond strength test. The wetting process of the porcelain/alloy systems was observed in situ with a Tommi optical dimension measurement system using a modified sessile drop method. The reaction products of the interfacial region were determined by Raman spectra analyses. Metal ceramic specimens were tested in 3-point bending at a crosshead speed of 1.5 mm/min according to ISO 9693 requirements, and the results were statistically analyzed with 1-way ANOVA (α=.05). The addition of TiO2 and MoO3 in the dental porcelain improved the wettability of the dental porcelain/Co-Cr alloy system. The bond strength of the porcelain modified with TiO2 and MoO3 was 43 ±2 MPa and that of the unmodified porcelain was 38 ±3 MPa. The fracture of the 2 metal ceramic systems occurred near the porcelain layer. The application of TiO2 and MoO3 to the leucite-reinforced porcelain can improve the wettability of porcelain on alloy. Porcelain/alloy wettability can be used as a guide to improve the bonding property between dental porcelain and alloys.

Comparison of the Effect of Different Ceramic Alloys and Porcelain Systems upon the Color of Metal–Ceramic Restorations: An In Vitro Study

The exact replication of natural tooth color in a metal ceramic restoration is a challenging fact as its affected by enumerable factors. Research revealing the influence of base metal alloys with different porcelain systems on the color of the restorations have shown minimal interest. The aim of the study was to evaluate the optical influence of different alloys (mainly base metal) and ceramic systems affecting the final color of metal-ceramic restorations. Four commercial ceramic alloys, two Ni-Cr, one Co-Cr and a high-noble alloy were combined with two porcelains in metal-ceramic specimens with a standardized thickness of layers. Ten disc-shaped specimens were prepared for each alloy/porcelain combination. High-noble was used as control group. Only opaque and dentin layers were applied. The specimens were analysed with Spectrophotometer, and data were obtained in the CIELAB color system. The recorded data were analysed with a one-way ANOVA and multiple range test by tukey-HSD procedure to identify the significant groups at 5% level. The final color of the metal-ceramic specimens were significantly affected by both type of the alloy and the porcelain systems used (P<0.0001). The Co-Cr alloy-porcelain combination produced least color difference when compared with the high-noble control group. There was significant difference (P<0.0001) between both the brands of Ni-Cr alloy-porcelain systems. For all the alloy-porcelain combinations VMK 95 porcelain showed minimum color difference compared to the d-SIGN porcelain group. The final color of metal ceramic specimens was influenced both from the type of base metal alloy substructure and from the type of overlying porcelain.

Improvement in Ti-porcelain bonding by SiO2 modification of titanium surface through cast method

This study aimed to improve Ti-porcelain bonding strength through SiO2 modifications. Wax patterns were coated with SiO2 mixed with tetraethoxy silane (group C), patterns without coating were used as controls and subdivided into sandblasting group (group S) and polishing group (group P). Castingsurfaces were analyzed with XRD, while Ti-ceramic interfaces were characterized using SEM/EDS. Metal-ceramic specimens were tested in three point bending, and characterizations were also analyzed with SEM/EDS of porcelain debonding surfaces. In group C, SiO2 and Ti5Si3 phases were observed; SEM micrograph showed that Ti-porcelain had a compacted interface, and EDS maps of the interface illustrated the diffusion of Si, Al, and Sn to Ti, and cohesive fracture within the bonding agent. The bond strength of group C was 39.04±5.0 MPa, which was 15% higher than that of group S and 32% higher than that of group P. SiO2 coating could improve Ti-porcelain bond strength.

Effect of four different surface treatments on shear bond strength of three porcelain repair systems: An in vitro study

Background:Ceramic fracture in metal ceramic restorations are serious and pose an aesthetic and functional dilemma both for the patients and the dentist. This has created a demand for the development of practical repair options which do not necessitate the removal and remake of entire restorations.Aim:To evaluate and compare the effect of four different surface treatments on shear bond strength of metal ceramic specimens with three commercially available porcelain repair systems.Materials and Methods:Specimens were fabricated with a base-metal ceramic alloy and divided into three groups, to evaluate three porcelain repair systems. Each group was divided into four subgroups based on surface treatment (A) sandblasting, (B) sandblasting followed by etching with 9% HF (Hydrofluoric acid) on surrounding ceramic, (C) Use of a diamond bur on exposed metal followed by etching with 37% H3PO4 and (D) Control groups (D1, D2, D3 for three groups of porcelain repair system which was not subjected to further treatment after finishing with 240 grit silicon carbide paper grinding. Shear bond strength of each group of specimens based on surface treatment were evaluated with a universal testing machine after storing in distilled water for 7 days. One way ANOVA and Tukey-HSD procedure were used to compare the mean values between and among the groups.Results:The mean shear bond strength of group III (10.402 ± 1.055) were significantly higher than group I (8.647 ± 0.990) and group II (8.099 ± 0.600) for all surface treatments. However the mean values of shear bond strength of sub-group A were significantly higher than sub-group C and D but were not significantly higher than sub-group B.Conclusion:The results of this study suggest that in fractured metal ceramic restorations the exposed metal surface treated with sandblasting or sandblasting and etching the surrounding ceramic surface with HF can increase the shear bond strength of the repaired metal ceramic area. Porcelain repair systems which contain hybrid composites and 4-META as primer had increased bond strength.

Experimental evaluation of the bond strength between a CoCrMo dental alloy and porcelain through a composite metal–ceramic graded transition interlayer

ObjectivesThe purpose of this study was to evaluate the shear bond strength between CoCrMo dental alloy and porcelain restorations by application of different metal–ceramic transitional interfaces aiming at improvement of the bond strength and fracture tolerances. MethodsSeveral metal–ceramic specimens with different composite interlayers were produced. The interlayers consisted of metal/ceramic composites with different metal volume fractions (20M; 40M; 60M; 80M). The metal–ceramic bond strength as well as the fracture strength of the composites and monolithic base materials were assessed by the means of a shear test performed in a universal test machine. The interfaces of fractured and untested specimens were examined by the means of optical microscopy. The microstructures of monolithic base materials were analyzed using SEM/EDS. The elastic and inelastic properties of the homogeneous compositions were additionally evaluated using dynamic mechanical analysis. ResultsThe bond strength results obtained for metal–ceramic gradated specimens were the highest (261±38MPa) for 40vol% metal in the interlayer [40M] vs. 109±27MPa for a direct metal–ceramic joint. The Young's moduli and the fracture resistance of the composites revealed an increasing trend for increasing metal contents. SignificanceThis study shows that a graded transition between metal and ceramic, provided by a metal/ceramic composite interlayer, is regarded for an increase by 2.5 times in the bond strength between the two materials relative to conventional sharp transitions. The elastic modulus of the composites used as interlayers might be very reasonably approximated by a micromechanical model.

Applicability of CIELAB/CIEDE2000 formula in visual color assessments of metal ceramic restorations

ObjectivesTo investigate the applicability of color-difference formula (CIELAB or CIEDE2000) in visual color assessments of metal-ceramic specimens in small color-difference ranges. MethodsMetal-ceramic specimens using mixture of gradient ratio porcelain powders were fabricated to create a color pool. Color differences of specimen pairs were calculated using the CIELAB (ΔEab∗) and CIEDE2000 (ΔE00). A questionnaire, composed of 1 target and 3 enactment specimens, was designed. For formula-determination, the enactment specimen with the minimum ΔE to the target specimen was registered as FS. For visual-assessment, twenty participants were asked to finish the questionnaire by choosing the most color-matched enactment specimen to the target. The percentage of the FS been selected (PFS) was calculated, which was used to represent the consistence of formula-determination and visual-assessment. Binomial Tests were used to compare the differences between PFS values and 33% (the randomized probability of the FS been selected was one out of three, approximate 33%). Regression analysis was used to determine the correlation between ΔEab∗ and ΔE00 values. ResultsA linear regression equation was drawn as ΔE00=−0.049+0.619×ΔEab∗. There were no significant differences between PFS values and 33% within the range of ΔEab∗<2.0, whereas PFS values were significantly higher than 33% when ΔEab∗>2.0 (P<0.001). There was a tendency of selecting the enactment specimens with lower L* values and higher b* or C′ values, within the range of 1.0<ΔEab∗<2.0. ConclusionsCIE color-difference formulas were not applicable for visual color assessments of metal-ceramic specimens within the color-difference range of ΔEab∗<2.0.

The effect of thermal and mechanical cycling on bond strength of a ceramic to nickel-chromium (Ni-Cr) and cobalt-chromium (Co-Cr) alloys

This study evaluates the effect of thermo-mechanical cycling (TMC) on the bond strength of a ceramic to three cobalt-chromium (Co-Cr) and two nickel-chromium (Ni-Cr) alloys. One hundred metal-ceramic specimens were prepared. While half of the specimens from each metal-ceramic combination (n = 10) were tested after storage in water at 37°C for 24 hours, the other half were subjected to TMC before testing. The bond strength was evaluated by the flexural strength test according to ISO 9693:1999 (E) recommendations. TMC decreased the bond strength of the tested metal-ceramic systems as compared to the water storage (control groups) (P=0.04). Although metal alloys were significantly different from each other in their bond strength with porcelain (P<0.001), the effect of TMC on the various metal-ceramic systems was not significantly different (P=0.99). It may be concluded that base metal-ceramic bond strength is affected by aging and the effect is relatively the same for all the tested porcelain-metal systems.

Effect of Airborne-Particle Abrasion and Mechanico-Thermal Cycling on the Flexural Strength of Glass Ceramic Fused to Gold or Cobalt-Chromium Alloy

To evaluate the effect of airborne-particle abrasion and mechanico-thermal cycling on the flexural strength of a ceramic fused to cobalt-chromium alloy or gold alloy. Metallic bars (n = 120) were made (25 mm × 3 mm × 0.5 mm): 60 with gold alloy and 60 with Co-Cr. At the central area of the bars (8 mm × 3 mm), a layer of opaque ceramic and then two layers of glass ceramic (Vita VM13, Vita Zahnfabrick) were fired onto it (thickness: 1 mm). Ten specimens from each alloy group were randomly allocated to a surface treatment [(tungsten bur or air-particle abrasion (APA) with Al(2) O(3) at 10 mm or 20 mm away)] and mechanico-thermal cycling (no cycling or mechanically loaded 20,000 cycles; 10 N distilled water at 37°C and then thermocycled 3000 cycles; 5°C to 55°C, dwell time 30 seconds) combination. Those specimens that did not undergo mechanico-thermal cycling were stored in water (37°C) for 24 hours. Bond strength was measured using a three-point bend test, according to ISO 9693. After the flexural strength test, failure types were noted. The data were analyzed using three factor-ANOVA and Tukey's test (α= 0.05). There were no significant differences between the flexural bond strength of gold and Co-Cr groups (42.64 ± 8.25 and 43.39 ± 10.89 MPa, respectively). APA 10 and 20 mm away surface treatment (45.86 ± 9.31 and 46.38 ± 8.89 MPa, respectively) had similar mean flexural strength values, and both had significantly higher bond strength than tungsten bur treatment (36.81 ± 7.60 MPa). Mechanico-thermal cycling decreased the mean flexural strength values significantly for all six alloy-surface treatment combinations tested when compared to the control groups. The failure type was adhesive in the metal/ceramic interface for specimens surface treated only with the tungsten bur, and mixed for specimens surface treated with APA 10 and 20 mm. Considering the levels adopted in this study, the alloy did not affect the bond strength; APA with Al(2) O(3) at 10 and 20 mm improved the flexural bond strength between ceramics and alloys used, and the mechanico-thermal cycling of metal-ceramic specimens resulted in a decrease of bond strength.

Shear bond strengths of pressed and layered veneering ceramics to high-noble alloy and zirconia cores

Heat-pressed ceramics to metal alloys and zirconia have been available for some time. However, information regarding their shear bond strengths is limited. The purpose of this study was to evaluate the shear bond strengths of heat-pressed and layered ceramics with regard to their corresponding high-noble alloy and zirconia cores. Forty cylinders (approx. 5 mm in diameter) of high-noble alloy (Olympia) were cast and divided into 4 groups (n=10). Metal cylinders were veneered with ceramics to produce shear test specimens: Group PMI with IPS InLine POM; Group LMI with IPS InLine; Group PMC with Pulse press-to-metal; and Group LMC with Authentic Pulse Metal ceramic. Forty cylinders (approx. 5 mm in diameter) of zirconia (Lava) were obtained and divided into 4 groups (n=10). These cylinders were veneered with ceramics to produce shear test specimens: Group PZI with IPS e.max ZirPress; Group LZI with IPS e.max. Ceram; Group PZV with VITA PM9; and Group LZV with VITA VM9. The veneering ceramics, 3 mm in thickness, were either pressed or layered to their corresponding cylinders. Thermal cycling was performed at 5°C and 55°C for 20,000 cycles with a 20 second dwell time. Shear bond strength testing was conducted in a universal testing machine, and the failure strengths were recorded. Fracture surfaces were characterized visually, under a stereomicroscope, and with a scanning electron microscope (SEM). Data were analyzed using rank-based Kruskal-Wallis and Mann-Whitney tests with Bonferroni correction to adjust for multiple comparisons (α=.05). For metal ceramic specimens, the mean (SD) shear bond strengths ranged from 37.8 (20.6) MPa to 66.4 (22.1) MPa. There were significant differences between Groups PMI and PMC and between Groups LMI and PMC, in which Groups PMI and LMI had significantly higher strength values than Group PMC (P=.041). For zirconia ceramic specimens, the mean (SD) shear bond strengths ranged from 30.03 (9.49) MPa to 47.2 (13.0) MPa, with Group LZV having a significantly higher shear bond strength value than Group LZI (P=.012). Half of the Group PZV specimens failed during thermal cycling, and Group PZV was, therefore, excluded from statistical analysis. For all shear bond strength testing specimens, cohesive failures in the veneering ceramics were observed. For shear bond strength of veneering ceramics to high-noble alloy, there was no significant difference between pressing and layering with the same manufacturer. For shear bond strength of veneering ceramics to zirconia, there was no significant difference between the pressed and layered groups.