STATEMENT OF PROBLEMS: Conventional feldspathic porcelain is used extensively as a restorative material and it is subjected to grinding and polishing during fabrication and delivery procedures. There is still considerable controversy concerning the best methods to achieve the strongest porcelain restorations after such adjustments. PURPOSE: The objective of this study was to investigate the effects of (1) overglazing, (2) selfglazing, and (3) fine polishing on the flexural strength and fracture toughness of feldspathic dental porcelain. MATERIAL AND METHOD: Ninety porcelain disks were prepared for flexural strength test and sixty porcelain disks were fabricated for fracture toughness test. Specimens were divided into three groups for each test as follows: 1) overglazed 2) self-glazed 3) polished. The flexural strength of feldspathic porcelains was determined by ring-on-ring biaxial flexural strength test. The fracture toughness values of three experimental groups were obtained by indentation fracture toughness test. RESULTS: The flexural strength of overglazed group was significantly higher than that of selfglazed and polished group (P<0.05), while the difference between self-glazed and polished group was not significant (P>0.05). The fracture toughness values of overglazed and polished group were significantly higher than that of self-glazed group (P<0.05), while the difference between overglazed and polished group was not significant (P>0.05). CONCLUSIONS: This results supported the use of polishing as an alternative to glazing metal ceramic restorations, as it was not detrimental in flexural strength and fracture toughness. But, under the conditions of this study, overglazing was the ideal surface finishing method of feldspathic dental porcelain.
Dental Porcelain* ; Metal Ceramic Alloys

PURPOSE: The porcelain fused to gold has been widely used as a restoration both with the natural esthetics of the porcelain and durability and marginal fit of metal casting. However, recently, due to the continuous rise in the price of gold, an interest towards materials to replace gold alloy is getting higher. This study compared the bond strength of porcelain to millingable palladium-silver (Pd-Ag) alloy, with that of 3 conventionally used metal-ceramic alloys. MATERIALS AND METHODS: Four types of metal-ceramic alloys, castable nonprecious nickel-chrome alloy, castable precious metal alloys containing 83% and 32% of gold, and millingable Pd-Ag alloy were used to make metal specimens (n=40). And porcelain was applied on the center area of metal specimen. Three-point bending test was performed with universal testing machine. The bond strength data were analyzed with a one-way ANOVA and post hoc Scheffe's tests (alpha=.05). RESULTS: The 3-point bending test showed the strongest (40.42 +/- 5.72 MPa) metal-ceramic bond in the nonprecious Ni-Cr alloy, followed by millingable Pd-Ag alloy (37.71 +/- 2.46 MPa), precious metal alloy containing 83% of gold (35.89 +/- 1.93 MPa), and precious metal alloy containing 32% of gold (34.59 +/- 2.63 MPa). Nonprecious Ni-Cr alloy and precious metal alloy containing 32% of gold showed significant difference (P<.05). CONCLUSION: The type of metal-ceramic alloys affects the bond strength of porcelain. Every metal-ceramic alloy used in this study showed clinically applicable bond strength with porcelain (25 MPa).
Alloys* ; Dental Porcelain* ; Esthetics ; Metal Ceramic Alloys

PURPOSE: The purpose of this study was to evaluate the level of electro-chemical corrosion and surface roughness change for the cases of Ti abutment connected to restoration made of base metal alloys. MATERIALS AND METHODS: It was hypothesized that Ni-Cr alloys in different compositions possess different corrosion resistances, and thus the specimens (13x13x1.5 mm) in this study were fabricated with 3 different types of metal alloys, commonly used for metal ceramic restorations. The electrochemical characteristics were evaluated with potentiostat (Parstat 2273A) and the level of surface roughness change was observed with surface roughness tester. Paired t-test was used to compare mean average surface roughness (Ra) changes of each specimen group. RESULTS: All specimens made of nickel-chromium based alloys, average surface roughness was increased significantly (P < .05). Among them, the Ni-Cr-Be alloy (0.016 +/- 0.007 microm) had the largest change of roughness followed by Ni-Cr (0.012 +/- 0.003 microm) and Ni-Cr-Ti (0.012 +/- 0.002 microm) alloy. There was no significant changes in surface roughness between each metal alloys after corrosion. CONCLUSION: In the case of galvanic couples of Ti in contact with all specimens made of nickel-chromium based alloys, average surface roughness was increased.
Alloys ; Chromium Alloys ; Corrosion ; Family Characteristics ; Metal Ceramic Alloys ; Titanium

OBJECTIVETo compare the color differences of different metal bases and different opaque thickness, and evaluate the best thickness of opaque on different metal bases.

METHODSPrecious metal, gold sediment and Ni-Cr plates were prepared as bases, then opaque samples of 0.05, 0.1, 0.2, 0.3, 0.4 and 0.5 mm thickness were fabricated on such plates. Minolta chromatics meter CR-321 was used to examine the color properties of these samples, and deltaE was calculated to evaluate the color difference of the specimens.

RESULTSFor the restoration based on Ni-Cr and precious alloys, the color of restorations was not affected by the color of metal bases as the thickness of opaque reached 0.3 mm, and the chromatic value deltaE < 1.5 NBS. For the restoration based on gold sediment, the color of restoration was not affected by the color of metal as the thickness of opaque reached 0.1 mm, and the chromatic value deltaE < 1.5 NBS.

CONCLUSIONDifferent opaque thickness was necessary to obtain ideal color appearance in clinic. As the opaque thickness increased, the color of restoration based on Ni-Cr and noble metal increased but the color of restoration based on gold sediment decreased.

OBJECTIVETo study the effect of solid phase transformation on the metal-ceramic compatibility of Co-Cr alloy during firing programs.

METHODS9 foils of Co-Cr and Ni-Cr alloy with the dimension of 25 mmx3 mmx0.5 mm were casted using lost wax technology respectively. Among them, 6 specimens were subjected to metal-ceramic bonding strength test (three point bending method), the ceramic layer of 3 specimens were removed for X-ray diffraction (XRD) analysis. One cylindrical specimen of each alloy was casted for the test of coefficient of thermal expansion, cooling curves were recorded.

RESULTSThe metal-ceramic bonding strength of Ni-Cr, Co-Cr alloy was (49.1 +/- 3.40), (40.9 +/- 2.02) MPa respectively. There was significant difference between the two groups' bonding strength (P = 0.00). The coefficient of thermal expansion in the 20-500 degrees C interval of Ni-Cr and Co-Cr alloy was 13.9 x 10(-6), 13.8 x 10(-6) x K(-1) respectively. XRD analysis indicated that the microstructure of Ni-Cr alloy was austenite. While Co-Cr alloy was constituted by fcc phase, hcp phase and sigma phase.

CONCLUSIONDuring the cooling procedure, the transformation of fcc phase to hcp phase and segregation of needle-like sigma phase intensify the linear contraction speed of Co-Cr alloy, which decreases the metal-ceramic adaptability.

OBJECTIVETo investigate the influences of recasting on the mechanical properties of Au-Pt ceramic alloy.

METHODSAu-Pt ceramic alloy samples were prepared and recast for 3 times without adding any new Au-Pt ceramic alloy. The tensile strength, 0.2% yield strength, percentage of elongation, flexural strength, flexural modulus and Vickers hardness of each specimen were measured.

RESULTSBeing cast for different times, the Au-Pt ceramic alloy showed no significant differences on their tensile strength, 0.2% yield strength, percentage of elongation, flexural strength or Vickers hardness. The flexural modulus of the Au-Pt alloys being cast for 2 or 3 times was significantly higher than that of the alloys being cast for 1 time (P < 0.05). CONCLUSION Au-Pt ceramic alloy can be recast for 3 times at least, without any decrease in the mechanical properties.

OBJECTIVETo compare the shear bond strength(SBS) of cast Co-Cr alloys and selective laser melting(SLM) Co-Cr alloys with those of dental porcelain.

METHODSA dental porcelain (Vita) was applied on cast and SLM Co-Cr alloy specimens (n = 10). SBS test was conducted, and fracture mode analysis was determined. Student's t-test by SPSS 13.0 software was employed to analyze the data.

RESULTSThe SLM Co-Cr alloy specimens had lower SBS values than the cast Co-Cr alloy specimens (P > 0.05). The metal-porcelain bond strength value of the cast group was (33.11 +/- 4.98) MPa, and that of the SLM group was (30.94 +/- 5.98) MPa. The specimens in both test groups exhibited mixed failure.

CONCLUSIONThe metal-porcelain system processed by SLM exhibit a bond strength that is similar to that of the cast group. This system also display a high precision.

OBJECTIVETo investigate the influence of repeated sintering on the color of two porcelain-fused-to-titanium, and the differences between the two porcelains.

METHODSThirty samples were prepared and sintered for 9 times. The color of samples were measured following sintering 1, 3, 5, 7, 9 times by ShadeEye NCC colorimeter according to two brands of porcelains with CIE1976L*a*b* color system, and calculated relevant chrome, chromatism and hue, and statistical analysis.

RESULTSWhen two brands of porcelains were sintered 5 times, the color parameters had no significant change and sintered continuely, the color parameters of L* and a* had obvious changes, but can't be observed by eyes.

CONCLUSIONThe color parameters of titanium-porcelains have no significant change after repeated sintering.

OBJECTIVETo study the bonding characteristic of Titanium and RG experiment porcelain.

METHODS5 specimens with a size of 10 mm x 5 mm x 1.4 mm were cast from pure titanium. Then 1 mm of RG experiment opaque and body porcelain were fused on the surface of the titanium specimens. The interface of titanium and porcelain was analyzed with a scanning electron microscope with energy-despersive spectrometry; 6 metal specimens with the size of 25 mm x 3 mm x 0.5 mm were cast from Ni-Cr alloy and a uniform thickness of 1 mm of VMK 99 porcelain was veneered on the central area of 8 mm x 3 mm 18 metal specimens as the same size were cast from pure titanium. The uniform thickness of 1 mm of VITA TITANKERAMIK porcelain, of Noritake super porcelain Ti-22 and of RG experiment porcelain were veneered on every 6 specimens respectively in the central area of 8 mm x 3 mm. The specimens were subjected to a three-point bending test on a load-test machine with a span of 20 mm, then the failure loads were recorded and statistically analysised. The RG porcelain/titanium crown was fabricated by fusing RG opaque porcelain and body porcelain to cast titanium substrate crown.

RESULTSThe SEM results show no porosity and crackle were found in the interface. The energy-dispersive spectrometry show that there are Si, Ti and O in the 1 micro m layer between porcelain and titanium, which suggesting titanium and experiment porcelain bonding well. The three point test showed the fracture force for the combinations of titanium/VITA TITANKERAMIK porcelain, titanium/Noritake super porcelain Ti-22 and titanium/RG experiment porcelain were (7.233 +/- 2.539) N, (5.533 +/- 1.199) N and (6.316 +/- 1.433) N respectively. There were not statistically significant differences among them (t test, P < 0.01). The fracture force for the Ni-Cr alloy/VMK99 porcelain combination (12.733 +/- 3.297) N was significantly greater than those of the cast titanium/porcelain (t test, P > 0.05). The crown was translucent with no crack.

CONCLUSIONRG porcelain is well compatible with titanium.

OBJECTIVETo evaluate the usage of moiré interferometre in porcelain-fused-metal interfacial fracture mechanics.

METHODSRaster was produced on the surface of samples with different thickness of porcelain and metal in 5 groups. The stripes of u field and v field under different load were collected. Then the rupture tenacity Jc was calculated and the extensions of flaws were observed.

RESULTSStress concentration appeared around the flaws under load conditions. The stripe became denser under more load. The rupture tenacity Jc and the direction of flaw extension of each group were different.

CONCLUSIONMoiré interferometre can be used in the study of porcelain-fused-metal interfacial fracture mechanics and to prognosticate the direction of flaw extension.