Effect of interfacial variables on metal-porcelain bonding

Technical assessment of shear bond strength at ceramo-alloy interface after various surface treatment combinations and application of metal bonding agent

BACKGROUND

Bonding between metal and ceramic is one of the most important aspects of a successful prosthesis. Various methods have been recommended for preparing the metal surface to enhance the bond between metal and ceramic including the use of a metal bonding agent.

OBJECTIVE

This study aims to evaluate and compare the shear bond strength of the metal-ceramic (M-C) interface after combinations of various surface treatments including the application of a metal bonding agent.

METHOD

40 Ni-Cr alloy specimens were made and divided into 4 groups of 10 each based on the combination of surface treatments. Sandblasting, surface grinding, and Oxidation heat treatment (OHT) were performed on specimens from Group 1 (Control). In addition, Group 2 specimens received ultrasonic cleaning, Group 3 steam cleaning, and Group 4 metal bonding agent application. Following surface treatments on all specimens, porcelain build-up was performed, and shear bond strength was tested in a Digital Universal testing machine. The statistical tests used were independent t-test and ANOVA.

RESULTS

Results revealed that Group 4 specimens had the highest mean value of shear bond strength of 39.087 MPa while Group 3 specimens showed the least mean shear bond strength of 18.154 MPa with highly statistically significant results (p< 0.001).

CONCLUSION

The surface treatments and application of bonding agent to metal prior to porcelain application resulted in increased shear bond strength of the metal-ceramic interface.

Effect of oxidation heat treatment with airborne-particle abrasion on the shear bond strength of ceramic to base metal alloys

STATEMENT OF PROBLEM

Oxidation heat treatment has been studied to increase the metal-ceramic bond strength. However, information about its use with cobalt-chromium (Co-Cr) alloys is lacking.

PURPOSE

The purpose of this study was to evaluate the effect of oxidation heat treatment and oxidation heat treatment with alumina airborne-particle abrasion on the metal-ceramic bond strength of Co-Cr alloys compared with that of nickel-chromium (Ni-Cr) alloys.

MATERIAL AND METHODS

In total, 165 metal cylinders (∅5×8 mm) made of 5 base metal alloys were obtained by casting: 2 Ni-Cr (Fit Cast-SB and Fit Cast-V) and 3 Co-Cr alloys (Keragen, StarLoy C, and Remanium 2001). The specimens were divided into groups (n=11): no treatment, oxidation heat treatment, and oxidation heat treatment with airborne-particle abrasion. Oxidation heat treatment was performed starting at 650 °C and rising to 980 °C. The airborne-particle abrasion was performed with 100-μm alumina (0.2-MPa pressure, 5 seconds). One specimen had the surface topography and composition evaluated by scanning electron microscopy and energy dispersive X-ray spectrometry. The feldspathic ceramic was applied to the base metal alloy specimens (n=10). Shear tests were performed to obtain the metal-ceramic bond strength (MPa). The failure modes were evaluated. Data were evaluated by 2-way ANOVA and the Tukey post hoc test, Pearson correlation, and Fisher exact tests (α=.05).

RESULTS

The group without treatment showed the highest roughness. The treatments increased oxygen and chromium levels and decreased nickel, molybdenum, and tungsten levels. Oxidation heat treatment provided an increase in metal-ceramic bond strength (P<.05) for base metal alloys with over 7% molybdenum (Fit Cast-SB, Fit Cast-V, and Remanium 2001). With oxidation heat treatment with airborne-particle abrasion, there was improvement only in Fit Cast-SB. No treatment was better for StarLoy C. A weak correlation was found between metal-ceramic bond strength and failure mode (ρ=.166; P=.043). The mixed failures were prevalent in Co-Cr alloys (P<.001) and oxidation heat treatment with airborne-particle abrasion (P=.008).

CONCLUSIONS

The oxidation heat treatment was only beneficial for base metal alloy with a molybdenum content of over 7%. Although the oxidation heat treatment with alumina airborne-particle abrasion was a better treatment for Fit Cast-SB, its use is not justified because it showed no difference for oxidation heat treatment and requires another step in the surface treatment.

Evaluation of the effect of different surface treatments on the bond strength of non-precious alloy‒ceramic interface: An SEM study

Background. Dental porcelain has excellent esthetics in combination with biocompatibility and is one of the most commonly used restorative materials. Its low tensile strength remains a major drawback. The porcelain-fused-to-metal restorations have been introduced to increase the fracture resistance of dental porcelain. The aim of this study was to evaluate the effect of different surface treatments on the bond strength of a non-precious alloy to ceramic. Methods. The present cross-sectional observational study was conducted with forty samples of cobalt‒chromium that were fabricated with porcelain interposed between the two metal test pieces. The metal was subjected to combinations of different surface treatments. The samples group A (n=10) were not subjected to any surface treatments. Group B samples underwent sandblasting and surface grinding. Group C samples were subjected to sandblasting, surface grinding and degassing; and group D samples underwent sandblasting, surface grinding, ultrasonic cleaning and degassing. The tensile bond strength was measured in a universal testing machine, and a scanning electron microscope (SEM) was used to obtain images of the samples after surface treatment to determine the surface irregularities and after the debonding of the samples for the type of the bond failure. ANOVA was used for the statistical analysis. Results. The results showed significant variations in the tensile bond strength between the four groups (F=251.05, P=0.000). The SEM images of group A showed no surface irregularities; group C samples exhibited surface irregularities more than those in group B. Group D had the highest surface irregularities. SEM evaluations showed a statistically significant difference in the type of bond failure (P<0.001). Conclusion. Based on the results of this study, it can be concluded that the surface treatments on the metal increased the bond strength of the metal‒ceramic interface significantly. A combination of sandblasting, surface grinding and ultrasonic cleaning, followed by degassing, resulted in the highest tensile bond strength.

Calcium silicate layer on titanium fabricated by electrospray deposition

Titanium and its alloys have been used as implant materials. Non-ideal osseointegration of the implant materials has facilitated the development of the bioactive coatings on the implant surfaces. In this work, the bioactive calcium silicate (CaSi) powder prepared in a green synthesis route was used to cover the surface of Ti implants by a facile electrospray deposition method. Post annealing in air was also applied to form the oxidation layer on the Ti surface with the aim of increasing the bond strength between the CaSi coating layer and Ti substrate. For the characterization of the coatings several analytical methods such as X-ray diffraction, scanning electron microscopy, secondary neutral mass spectrometry, and Raman-spectroscopy were used, in addition to the measurement of bond strength and corrosion resistance. The results indicated a uniform CaSi layer with a thickness of about 1 μm deposited on the Ti substrate. Annealing in the range of 700-900 °C in air resulted in the formation of rutile phase of TiO₂; more importantly, annealing at 800 °C did not significantly affect the composition of the CaSi layer consisting of β-Ca₂SiO₄. The bond strength between the coating layer and Ti substrate can be remarkably enhanced at an annealing temperature of 700 or 800 °C compared with the as-prepared coating without annealing. The annealed coatings had a better corrosion resistance than the as-prepared coating. It is concluded that the electrospray method associated with the post-annealing can be successfully used for the deposition of a CaSi layer with a defined structure and composition on titanium implants.

Oxide layer characteristics and interfacial analysis of porcelain fused to high-gold alloy using multitechnique analysis methods

BACKGROUND/PURPOSE

In a previous fractural study, high-gold crowns possessed the second highest fracture force. The objective of this study is to analyze the interface of porcelain fused to high-gold alloy using different observation devices.

MATERIALS AND METHODS

High-gold crowns specimens with the morphology of a maxillary second premolar were compressed vertically in the center of the occlusal surface until fracture using a universal testing machine. The fractured surfaces were examined using scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (SEM/EDX) to determine the failure mode. The ceramic-metal interface of the crown was examined with electron probe microanalysis (EPMA). In addition, sheet specimens with dimensions of 10 × 9 × 4 mm3 were prepared to examine the surface morphology and composition of high-gold alloy after oxidation using X-ray photoelectron spectrometer (XPS).

RESULTS

The average fracture force was 1368 ± 312 N. Photograph of fractured crown and SEM/EDX analyses reveal that the crown initially suffered from cohesive failure in the upper and middle regions, with the fracture occurring mostly within the ceramic. XPS results and both EPMA color photomicrographs of crown and sheet specimens show that indium was observed along the porcelain-metal interface with a 1- to 2-μm disrupted zone of oxide layer.

CONCLUSION

In2O3 and Au were found along the interface from the multitechnique analysis methods; the presence of this oxide at the boundary promotes ceramic-metal adhesion. In2O3 is suggested to be beneficial for the second highest fracture resistance in a previous fractural study of implant-supported crowns.

Interfacial analysis of porcelain fused to high-palladium alloy with different observation methods

Background/purpose

In a previous fractural study of implant-supported crowns, it was found that the palladium−silver crowns possessed the highest fracture force. The ceramic–metal interface was examined to explain its high resistance to fracture.

Materials and methods

Palladium−silver crowns with the morphology of a maxillary second premolar were prepared following standard dental laboratory procedures. Crown specimens were compressed vertically in the center of the occlusal surface until fracture, using a universal testing machine. The fractured surfaces were examined using scanning electron microscopy combined with energy dispersive X-ray spectroscopy to determine the failure mode. The ceramic–metal interface of the crown was examined with electron probe microanalysis. Additionally, sheet specimens with a dimension of 10 × 9 × 4 mm³ were prepared to examine the surface morphology and composition of palladium−silver alloy after oxidation and porcelain-fused-to-metal firing cycles.

Results

The average fracture force was 1425 ± 392N. Analyses with scanning electron microscopy combined with energy dispersive X-ray spectroscopy revealed that the failure mode was cohesive within the ceramic layer. Electron probe microanalysis micrographs indicated that Sn and In were found to distribute only on the alloy side of the ceramometal crown. Energy dispersive X-ray spectroscopy analysis and electron probe microanalysis micrographs confirmed that ZnO had diffused into the ceramic phase.

Conclusion

In₂O₃, SnO₂, and ZnO were found along the interface; the presence of these oxides at the boundary promotes ceramic–metal adhesion, and this resulted in cohesive failure of the ceramic layer. ZnO was found to diffuse into the ceramic phase, and it is suggested to be beneficial for high fracture resistance in the present study.

Influence of a bonding agent on the bond strength between a dental Co-Cr alloy and nine different veneering porcelains

Adequate bonding between dental veneering porcelains and non-precious metal alloys is a main factor for the long-term functionality of porcelain fused to metal restorations. Although a huge number of veneering porcelains are on the market, only few studies have reported about the role of bonding agents for the bond strength at their respective interface to cobalt-chromium (Co-Cr). The aim of this study was to compare the influence of a metal-ceramic bonding agent for Co-Cr alloys on the bond strength of metal-ceramic systems. The bond strength test was done according to ISO 9693 with additional detection of the first acoustic crack initiated signal while testing. The bonding agent had only minor effects on the bond strength of the different Co-Cr/ceramic systems. Only three of the nine studied systems showed statistically significant differences (p<0.05) upon applying the bonding agent. Scanning electron microscopy (SEM) showed cracks predominantly caused by adhesive failure. Based on this study, Co-Cr alloys veneered with porcelains with and without a bonding agent exceeded the minimum bond strength of 25 MPa required according to ISO 9693. However, if bond strength values based on acoustic signals were calculated, values below the threshold of 25 MPa could be observed. Such findings are important for failures caused by the occurrence of early cracks.

Preventing high-temperature oxidation of Co–Cr-based dental alloys by boron doping

We demonstrate that the high-temperature oxidation of biomedical Co–Cr-based alloys during manufacturing can be retarded by boron doping.

Comparison of the microstructure and phase stability of as-cast, CAD/CAM and powder metallurgy manufactured Co-Cr dental alloys

OBJECTIVE

The objective of this study was to identify the different microstructures produced by CC, PM and as-cast techniques for Co-Cr alloys and their phase stability following porcelain firings.

METHODS

Three bi-layer porcelain veneered Co-Cr specimens and one monolithic Co-Cr specimen of each alloy group [cast, powder metallurgy (PM), CAD/CAM (CC)] were manufactured and analyzed using electron backscatter diffraction (EBSD), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD). Specimens were treated to incremental numbers of porcelain firings (control 0, 5, 15) with crystallographic data, grain size and chemical composition subsequently obtained and analyzed.

RESULTS

EBSD datasets of the cast alloy indicated large grains >200 μm whereas PM and CC alloy consisted of mean arithmetic grain sizes of 29.6 μm and 19.2 μm respectively. XRD and EBSD results both indicated the highest increase in hcp content (>13vol%) for cast Co-Cr alloy after treatment with porcelain firing while PM and CC indicated <2vol% hcp content. A fine grain interfacial layer developed on all surfaces of the alloy after porcelain firing. The depth of this layer increased with porcelain firings for as-cast and PM but no significant increase (p>.05) was observed in CC. EDS line scans indicated an increase in Cr content at the alloy surface after porcelain firing treatment for all three alloys.

SIGNIFICANCE

PM and CC produced alloy had superior fcc phase stability after porcelain firings compared to a traditional cast alloy. It is recommended that PM and CC alloys be used for porcelain-fused-to-metal restorations.

Fracture strength of porcelain fused to metal crowns made of cast, milled or laser-sintered cobalt-chromium

AIMS

The aim was to compare the fracture strength of porcelain fused to metal crowns with copings fabricated in Co-Cr using different manufacturing techniques (casting, milling and laser-sintering) with crowns manufactured in a high-gold alloy.

METHODS

A total of 50 identical crowns were fabricated and sub-divided into five groups; cast Co-Cr, milled Co-Cr, two groups of laser-sintered Co-Cr and a control group cast in a high-gold alloy. After thermocycling (5000 cycles, 5-55°C) and pre-load (30-300 N, 10,000 cycles) the crowns were loaded until fracture. Load (N) and fracture mode were recorded.

RESULTS

There was a significant difference (p < 0.05) in fracture strength between the control group and one of the laser-sintered groups. The mean values (N) for the groups were as follows: cast Co-Cr, 1560 ± 274; milled Co-Cr, 1643 ± 153; laser-sintered Co-Cr 1, 1448 ± 168; laser-sintered Co-Cr 2, 1562 ± 72; control group, 1725 ± 220.

CONCLUSION

There is no difference in strength between Co-Cr crowns produced using the different production technologies: casting, milling or laser-sintering. Metal ceramic crowns made with copings fabricated in a high-gold alloy present numerically higher fracture strength than crowns made with copings fabricated in Co-Cr alloys. The difference is confirmed when analyzing the fracture surfaces, but the difference in fracture strength value is limited and is only significant with regard to one of the two laser-sintered groups.

Effect of a magnetron-sputtered ZrSiN/ZrO2 film on the bond strength of commercially pure titanium to porcelain

STATEMENT OF PROBLEM

The excessively thick and nonadherent titanium oxide layer formed during the porcelain sintering process can cause bonding problems between titanium and porcelain.

PURPOSE

The purpose of this study was to evaluate the effect of a magnetron-sputtered ZrSiN/ZrO2 composite film on the bond strength of commercially pure titanium (CP Ti) to porcelain.

MATERIAL AND METHODS

Sixty-eight cast titanium specimens were prepared according to the ISO 9693 standard and then divided into 2 coated and 2 noncoated groups (n=17). The ZrSiN/ZrO2 composite film was deposited on specimens of the 2 coated groups by magnetron sputtering. A low-fusing porcelain was applied on 1 coated group and 1 noncoated group. A surface profilometer, surface roughness tester, energy-dispersive X-ray analysis (EDS), scanning electron microscopy (SEM), and x-ray diffraction (XRD) were used to examine the characteristics of the film and the interfacial properties, while the bond strength of titanium-porcelain specimens was analyzed with the 3-point bend test. The results were analyzed with an independent samples t test (α=.05).

RESULTS

The mean bond strength of ZrSiN/ZrO2-coated CP Ti to porcelain (43.67 ±2.08 MPa) was significantly higher than that of the noncoated group (35.44 ±3.56 MPa). A generally cohesive failure mode was observed in the coated group, but the failure mode in the noncoated group was adhesive. EDS data showed that the ZrSiN/ZrO2 film effectively prevented the intrusion of oxygen into the Ti substrate.

CONCLUSIONS

The data suggested that the magnetron-sputtered ZrSiN/ZrO2 film could significantly improve the bond strength of CP Ti to porcelain and this may have clinical significance.

Influence of the processing route of porcelain/Ti-6Al-4V interfaces on shear bond strength

This study aims at evaluating the two-fold effect of initial surface conditions and dental porcelain-to-Ti-6Al-4V alloy joining processing route on the shear bond strength. Porcelain-to-Ti-6Al-4V samples were processed by conventional furnace firing (porcelain-fused-to-metal) and hot pressing. Prior to the processing, Ti-6Al-4V cylinders were prepared by three different surface treatments: polishing, alumina or silica blasting. Within the firing process, polished and alumina blasted samples were subjected to two different cooling rates: air cooling and a slower cooling rate (65°C/min). Metal/porcelain bond strength was evaluated by shear bond test. The data were analyzed using one-way ANOVA followed by Tuckey's test (p<0.05). Before and after shear bond tests, metallic surfaces and metal/ceramic interfaces were examined by Field Emission Gun Scanning Electron Microscope (FEG-SEM) equipped with Energy Dispersive X-Ray Spectroscopy (EDS). Shear bond strength values of the porcelain-to-Ti-6Al-4V alloy interfaces ranged from 27.1±8.9MPa for porcelain fused to polished samples up to 134.0±43.4MPa for porcelain fused to alumina blasted samples. According to the statistical analysis, no significant difference were found on the shear bond strength values for different cooling rates. Processing method was statistically significant only for the polished samples, and airborne particle abrasion was statistically significant only for the fired samples. The type of the blasting material did not cause a statistically significant difference on the shear bond strength values. Shear bond strength of dental porcelain to Ti-6Al-4V alloys can be significantly improved from controlled conditions of surface treatments and processing methods.

Effect of surface treatments on adhesion of low-fusing porcelain to titanium as determined by strain energy release rate

OBJECTIVE

This study evaluated the effect of different chemical surface treatments on the surface characteristics of commercially pure titanium (cp Ti) and the adhesion of the porcelain-titanium system by means of strain energy release rate (G-value, J/m(2)). Surface roughness and morphology of treated cp Ti were additionally evaluated.

METHODS

Two hundred and thirty specimens of machined cp Ti plates grade II were prepared. The specimens were divided into ten groups in each test according to the surface treatment used; Gr 1 (control; machined), Gr 2 (sandblasted), Gr 3 (CH(2)Cl(2) for 5 min), Gr 4 (CH(2)Cl(2) for 10 min), Gr 5 (10% H(2)O(2) for 5 min), Gr 6 (10% H(2)O(2) for 10 min), Gr 7 (30% H(2)O(2) for 5 min), Gr 8 (30% H(2)O(2) for 10 min), Gr 9 (9% HF for 5 min) and Gr 10 (9% HF for 10 min). Titanium-porcelain (Vita Titankeramik) was applied to each group for testing the adhesion. The G-value (J/m(2)) was measured with a four-point bending configuration. Following fracture testing specimens were examined with a scanning electron microscope (SEM). Surface roughness and SEM analysis were carried out. Data were analyzed using ANOVA and Tukey's test.

RESULTS

Groups treated with 9% HF or CH(2)Cl(2) baths for 10 or 5 min showed the highest adhesion values (J/m(2)) (34.23±4.31, 30.75±4.91, 28.92±4.33 and 22.54±3.58) respectively among the groups. The machined groups demonstrated the lowest value (8.18±1.95) (J/m(2)). SEM analysis indicated a combination of cohesive and adhesive fractures for 9% HF, CH(2)Cl(2), sandblasted and 30% H(2)O(2) (10 min) groups, while mainly adhesive fractures were found with the other groups. There was no direct correlation between surface roughness and adhesion.

SIGNIFICANCE

Adhesion between porcelain and cp Ti can be improved by the use of certain chemical surface treatments prior to porcelain firing as alternative techniques to sandblasting treatment.

Color change during the surface preparation stages of metal ceramic alloys

STATEMENT OF PROBLEM

Even though metal ceramic restorations (MCRs) are widely used by clinicians, the influence of the metal on the color of overlaying porcelain is unknown.

PURPOSE

The purpose of this study was to analyze the color alterations of different types of metal ceramic alloys during several stages of metal surface preparation and to determine the effect of those changes on the resulting color of opaque porcelain (OP).

MATERIAL AND METHODS

Seven different types of alloys (3 base metal, 3 noble, and 1 high noble) were used to prepare disk-shaped specimens (1 mm × 10 mm, n=3), followed by OP application (0.1 mm). L*a*b* values of specimens were recorded after different stages of metal surface preparation (ingot, after casting, after oxidation, and after the OP application) in addition to the shade tab of OP B1 (target shade). L*a*b* values of alloys were measured from the ingot structure to the OP application stage and statistically analyzed (Repeated measures ANOVA, and Bonferroni corrected paired t test, α=.05). L*a*b* values of OP applied groups and the OP shade tab (target shade) were analyzed (1-way ANOVA with Dunnett's multiple comparison test, α=.05). The color differences of the target shade both before and after OP application were calculated and statistically analyzed (1-way ANOVA, Ryan-Einot-Gabriel-Welsch Multiple Range Test, α=.05).

RESULTS

The L* values of all alloys changed significantly after each stage except for 2 alloys (V-Deltaloy SF (N-VDSF)) and (Gnathos Plus (HN-GP)) after casting and airborne-particle abrasion (P<.05). The a* value of all alloys increased after casting. Changes in the a* coordinate were significant except for one of the base metal alloys (P<.05). The a* coordinate changes of alloys showed variation in direction after oxidation and OP application (P<.05). The b* coordinate changes of alloys showed variation in direction after each stage (P<.05). The L*a*b* values of some OP applied alloys were significantly different from that of the OP shade tab (P<.05). Color difference values (ΔE (OP applied alloy-target shade)) of 2 OP-applied alloys (Cerapall 2 (N-CP2) and Ceradelta (N-CD)) were significantly different (P<.05) and higher than the other OP-applied alloys.

CONCLUSIONS

The achromatic color behavior of different alloys was all in the same direction at all metal surface preparation stages. The chromatic behavior of the different alloys was primarily towards the same direction after casting and airborne-particle abrasion, whereas it varied after oxidation and OP application. The color difference of OP for all alloys, regardless of their type, was not visually perceivable when compared to the target shade (ΔE<2.6).

X-Ray diffraction and scanning electron microscopy-energy dispersive spectroscopic analysis of ceramõmetal interface at different firing temperatures

Objective:

Porcelain chipping from porcelain fused to metal restoration has been Achilles heel till date. There has been advent of newer ceramics in past but but none of them has been a panacea for Porcelain fracture. An optimal firing is thus essential for the clinical success of the porcelain-fused to metal restoration. The aim of the present study was to evaluate ceramo-metal interface at different firing temperature using XRD and SEM-EDS analysis. Clinical implication of the study was to predict the optimal firing temperature at which porcelain should be fused with metal in order to possibly prevent the occasional failure of the porcelain fused to metal restorations.

Materials and Methods:

To meet the above-mentioned goal, porcelain was fused to metal at different firing temperatures (930–990°C) in vacuum. The microstructural observations of interface between porcelain and metal were evaluated using X-ray diffraction and scanning electron microscopy with energy dispersive spectroscopy.

Results:

Based on the experimental investigation of the interaction zone of porcelain fused to metal samples, it was observed that as the firing temperature was increased, the pores became less in number as well as the size of the pores decreased at the porcelain/metal interface upto 975°C but increased in size at 990°C. The least number of pores with least diameter were found in samples fired at 975°C. Several oxides like Cr₂O₃, NiO, and Al₂O₃ and intermetallic compounds (CrSi₂, AlNi₃) were also formed in the interaction zone.

Conclusions

It is suggested that the presence of pores may trigger the crack propagation along the interface, causing the failure of the porcelain fused to metal restoration during masticatory action.

Surface analysis of porcelain fused to metal systems

OBJECTIVE

The effect of four different, commonly performed, metal-ceramic alloy, surface preparation stages, were investigated to observe surface compositional changes.

METHODS

Two metal-ceramic alloys were examined (Pd/Ag alloy and a Ni/Cr alloy). Discs 12 mm diameter and 2mm thick were produced using the lost wax casting process. Prior to casting alloy ingots were examined using X-ray fluorescence spectrometry (XRF) to determine bulk composition. The four preparation stages were (1) devesting and Al2O3 blasted; (2) ground smooth and Al2O3 blasted; (3) oxidation firing; (4) firing cycle for opaque porcelain application. X-ray photoelectron spectroscopy (XPS) surface analysis was performed after each surface preparation stage to determine changes in surface composition. SEM with EDS was also used to identify surface composition.

RESULTS

XRF and manufacturers compositional analysis of the alloys showed similar findings for the major elements. XPS analysis showed that at preparation stages 3 and 4 evidence of elemental migration to the surface (In with Pd/Ag alloy and Cr and Mn with Ni/Cr alloy). Alumina was also seen on the alloy surfaces, with SEM/EDS confirming Al2O3 particles embedded in the surface of the alloys.

SIGNIFICANCE

Surface composition is very different from the batch composition. Surface preparation stage 3 is essential in bringing to the alloy surface elements which could be directly involved in the metal-ceramic bond. Elements and their oxides, in various forms, cover the surface of the alloys. Al2O3 particles can remain embedded in the alloy surface during porcelain application.

SEM/EDS evaluation of porcelain adherence to gold-coated cast titanium

The adhesion between titanium and dental porcelain is related to the diffusion of oxygen to the reaction layer formed on cast-titanium surfaces during porcelain firing. The diffusion of oxygen could be suppressed by coating the titanium surface with a thin gold layer. This study characterized the effects of gold coating on titanium-ceramic adhesion. ASTM grade II CP titanium was cast into a MgO-based investment (Selevest CB, Selec). The specimen surfaces were air abraded with 110-microm Al(2)O(3) particles. Gold coating was applied on titanium surfaces by three methods: gold-paste (Deck Gold NF, Degussa-Ney) coating and firing at 800 degrees C for three times, single gold-paste coating and firing followed by sputter coating (40 mA, 500 s), and sputter coating (40 mA, 1000 s). Surfaces only air abraded with Al(2)O(3) particles were used as controls. An ultra-low-fusing dental porcelain (Vita Titankeramik, Vident) was fused on titanium surfaces. Specimen surfaces were characterized by SEM/EDS and XRD. The titanium-ceramic adhesion was evaluated by a biaxial flexure test (N = 8), and area fraction of adherent porcelain (AFAP) was determined by EDS. Numerical results were statistically analyzed by one-way ANOVA and the Student-Newman-Keuls test at alpha = 0.05. SEM fractography showed a substantial amount of porcelains remaining on the gold-sputter-coated titanium surfaces. A new Au(2)Ti phase was found on gold-coated titanium surface after the firing. Significantly higher (p <.05) AFAP values were determined for the gold-sputter-coated specimens compared to the others. No significant differences were found among the other groups and the control. Results suggested that gold coatings used in this study are not effective barriers to completely protect titanium from oxidation during the porcelain firing, and porcelain adherence to cast titanium can be improved by gold-sputter coating used in the present study.

Ceramic bonding to a dental gold-titanium alloy

Investigations of the metal-ceramic bonding of the alloy Au98.2Ti1.7Ir0.1 (wt) in comparison with a well-approved traditional Au-Pt-Pd-based alloy were performed. Bond strength of both alloys, measured with a three-point flexure bond test, was in the same order of magnitude. Failure mode was different for both alloys. Failure of the bonding of the Au-Ti-Ir alloy predominantly occurred at the alloy-oxide interface. On the Au-Pt-Pd alloy more ceramic residues were observed. Sandblasting the metal surface with alumina increases the roughness of the surface, but only slightly increases the bond strength, independent of the grain size of the alumina. Immersion in a corrosive solution of sodium chloride and lactic acid reduced the bond strength of both alloys by about 35%. While this decrease for the Au-Pt-Pd alloy occurred after an immersion time of only two days, it took about 35 days for the Au-Ti alloy. The results indicate that the alloy Au98.2Ti1.7Ir0.1 (wt) provides sufficient ceramic adherence. The results also proved that the three-point flexure bond test used is a sensitive method for measuring metal-ceramic bond strength, thus supporting the decision to integrate this test within the international standard ISO 9693.

Fusing of dental ceramics to titanium

Titanium is known as a useful biometal because of its good biocompatibility and mechanical performance. However, titanium is chemically an exceptional metal, reacting strongly with gaseous elements like oxygen, hydrogen, and nitrogen and also dissolving them extensively. This high reactivity causes problems, for example, when dental ceramics are fused to titanium. Commercial ceramic-titanium systems are increasingly used in prosthetic dentistry, but little is known about the microstructure and composition of the system. Better understanding of chemical reactions between ceramics and titanium is necessary if mechanically more compatible ceramic-titanium bonds are to be developed. This review deals with titanium as a metal, titanium's affinity for nonmetallic elements (especially oxygen), and reactions with other elements. Different aspects are discussed relative to the fusing of dental ceramics to titanium.

Bond strength of three porcelains to two forms of titanium using two firing atmospheres

STATEMENT OF PROBLEM

Problems with casting and porcelain bonding are encountered when titanium is used in metal-porcelain restorations. The oxidation characteristics of titanium are the main problem. The bonding mechanisms in titanium-porcelain systems are complex and poorly understood.

PURPOSE

An in vitro investigation was performed to evaluate the bonding characteristics of 3 titanium-porcelain systems in various firing conditions.

MATERIAL AND METHODS

This study evaluated the bonding strength of 3 commercial titanium porcelains fired in a vacuum and in an argon atmosphere to cast and noncast commercially pure titanium, using a 3-point bending test according to DIN 13927 and SEM with energy-dispersive spectrometry analysis. The results were compared with an Ni-Cr alloy and a conventional porcelain that was chosen as a control.

RESULTS

The Ni-Cr-conventional porcelain system fired in an argon atmosphere had significantly higher bond strength than the other systems (P<.001). In addition, the bond strength of the titanium-spark erosion-Noritake Ti22 combination, fired in an argon atmosphere, was significantly higher than the other titanium-porcelain groups, which had results similar to those obtained with the vacuum-fired, Ni-Cr-conventional porcelain and argon-fired titanium-cast-Noritake Ti22 groups. On the other hand, the bond strength of the titanium-TiBond and titanium-Vita Titankeramik groups was below the lower limit value in the DIN 13927 standard for the 3-point bending test (25 MPa). Although the results of the Duncan multiple range test showed that firing in an argon atmosphere did not affect the bond strength of the titanium-Vita Titankeramik groups, the titanium-spark erosion-TiBond group, or the titanium-cast-Noritake Ti22 group, argon firing improved the bond strengths of the Ni-Cr-conventional porcelain group, the titanium-cast-TiBond group, and the titanium-spark erosion-Noritake Ti22 porcelain group. It was also found that there were no significant differences between the bond strengths of cast and non-cast titanium groups; an exception was the titanium TiBond groups in which the porcelain was fired in a vacuum.

CONCLUSION

The oxide layer produced on titanium was considered to have a potentially adverse effect on titanium-porcelain bonding. It was also concluded that matching the titanium-porcelain combination is the main determinant for optimal bonding. Firing in an argon atmosphere that limited the oxidation of titanium improved the titanium-porcelain bond in some of the groups.

Influence of metal surface finishing on porcelain porosity and beam failure loads at the metal-ceramic interface

STATEMENT OF THE PROBLEM

Investigators suggest that metals should be finished in 1 direction before porcelain application to minimize metal irregularities and trapped contaminants. These irregularities are thought to be focal points for porosity and crack propagation.

PURPOSE

This study investigated the influence of metal finishing and sandblasting on (1) porosity production at the porcelain-metal interface, and (2) porcelain-metal beam failure load.

MATERIAL AND METHODS

Eighty cast metal samples were divided into 4 test groups: (A) bidirectional finish/sandblasting; (B) unidirectional finish/sandblasting (C) bidirectional finish only; and (D) unidirectional finish only. The porcelain applied was 1.5 mm thick. Samples were sectioned longitudinally. Half of the samples were subjected to a 3-point flexural test. The remaining samples were sectioned into 4 slices and were examined with a light microscope (x500). Number and diameter of porosities at the metal-porcelain interface were recorded.

RESULTS

Mean loads at failure (lbs) were as follows: A, 11.1 +/- 1.3 (5.03 +/- 0.58 Kg); B, 11.2 +/- 1.7 (5. 08 +/- 0.77 Kg); C, 4.0 +/- 1.8 (1.81 +/- 0.81 Kg); and D, 5.0 +/- 2. 1 (2.26 +/- 0.95 Kg). Groups A and B were significantly different from groups C and D (P<.0001). Nonsandblasted samples (C and D) exhibited a separation at the ceramometal interface, which prevented quantification of porosity size and number. Average interface porosity sizes (microm) (A, 8.99 +/- 1.92; B, 10.03 +/- 1.86) showed no significant difference. The mean interface porosity number (A, 62. 3 +/- 16.02; B, 67.4 +/- 10.01) showed no significant difference.

CONCLUSION

Direction of metal finishing did not affect the porosity number and size at the ceramometal interface or the beam failure loads. Sandblasting increased the beam failure loads. Nonsandblasted samples showed detachment of the porcelain from the metal.