Fit of zirconia all-ceramic crowns with different cervical margin designs, before and after porcelain firing and glazing.

The purpose of this study is to investigate the fit of zirconia cores and all-ceramic crowns prepared with different cervical margin designs. The radius of curvature between the axial wall and the occlusal surface was set to 1 mm in an abutment using the cervical shoulder marginal design (S) and to 0.2 and 0.5 mm in abutments with round shoulders (0.2RS and 0.5RS, respectively). The internal gaps of the cores were 45-138 µm (S), 41-141 µm (0.2RS), and 43-133 µm (0.5RS). The internal gaps of the all-ceramic crowns were 40-115 µm (S), 45-113 µm (0.2RS), and 42-126 µm (0.5RS). There were no significant differences in one-way ANOVA for any region in any marginal design before and after firing the porcelain. The marginal gaps between the all-ceramic crowns and dies were 27 ± 25 (S), 30 ± 29 (0.2RS), and 24 ± 27 µm (0.5RS), again with no significant differences in one-way ANOVA.

Mechanical properties of hard resins for crowns and bridges.

PURPOSE: Hard resins for crowns and bridges are widely used for esthetic restorations. The objective of this study was to evaluate the mechanical properties of new commercial hard resins and to compare the results with those of the other hard resins previously investigated. METHODS: Dentin and enamel made with two new hard resins (Epricord: EP, Kuraray, Co., Ltd., Osaka, Japan and Prossimo: PR, GC, Co., Ltd., Tokyo, Japan) were used in this study. Regarding the fundamental characteristics, the thermal expansion/shrinkage coefficient, the filler content, the polymerization shrinkage, and the wear were examined. Regarding the strength of resin, the bending strength, hardness, compression strength, elastic modulus, and fracture strength of a jacket crown were measured. RESULTS: These resins showed comparatively lower levels than the other hard resins regarding the bending strength, hardness, compression strength, and fracture strength of the jacket crown. The total filler content rate and wear amount of these resins exhibited similar values to those of the other resins. The thermal expansion/ shrinkage coefficients of these resins exhibited higher values than those of the other resins. EP showed a different tendency from PR about the compression strength, elastic modulus, and polymerization shrinkage. CONCLUSIONS: PR and EP did not show dramatically better physical properties. However, the results of each examination in this study may be acceptable clinically. The results of each investigation changed according to the products used, and proper use for each case and application was suggested.

Galvanic corrosion of ferritic stainless steels used for dental magnetic attachments in contact with an iron-platinum magnet.

This study was an examination of the galvanic corrosion of ferritic stainless steels, namely SUS 444, SUS XM27, and SUS 447J1, in contact with a Fe-Pt magnet. The surface area ratio of each stainless steel to the Fe-Pt magnet was set at 1/1 or 1/10. Galvanic corrosion between the stainless steels and the magnet was evaluated by the amount of released ions and the electrochemical properties in 0.9% NaCl solution. Although each stainless steel showed sufficient corrosion resistance for clinical use, the amount of ions released from each tended to increase when the stainless steel was in contact with the magnet. When the surface area ratio was reduced to 1/10, the amount of Fe ions released from the stainless steels increased significantly more than when there was no contact. Since contact with the magnet which possessed an extremely noble potential created a very corrosive environment for the stainless steels, 447J1 was thus the recommended choice against a corrosion exposure as such.

[Thermal expansion of layering porcelains for the tetragonal stabilized zirconia].

PURPOSE: 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. METHODS: 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. RESULTS: 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. CONCLUSION: The core material and layering porcelains have a suitable relationship.

Fit of metal ceramic crowns cast in Au-1.6 wt% Ti alloy for different abutment finish line curvature.

OBJECTIVES: The purpose of this study was to evaluate the fit of metal ceramic crowns cast in Au-1.6 wt% Ti alloy and investigate the effect of abutment finish line curvature on the fit of crowns. METHODS: Three types of finish line curvature abutments were prepared (1, 3 and 5mm-curvature). For each type of abutment, five metal ceramic crowns of the facial veneered type were fabricated, which were cast in Au-1.6 wt% Ti alloy. Used as controls, another fifteen specimens were made from a commercially available gold alloy. The fit was measured in the as-cast and after porcelain application. RESULTS: In the as-cast specimens, the greater the finish line curvature was, the larger the gaps exhibited at the mesial and distal margins of copings, compared with labial and lingual margins. The distal margin of copings for 5mm-curvature abutments showed the largest gap (35 (7) microm). After porcelain application, the greater was the finish line curvature, the larger the labial marginal gap became (mean 44, 34, 25 microm, respectively, for 5, 3, 1mm-curvature). However, there was no significant difference on marginal gaps between specimens of Au-1.6 wt% Ti alloy and control gold alloy. SIGNIFICANCE: This study indicated that the metal ceramic crowns cast in Au-1.6 wt% Ti alloy had equivalent accuracy to those that cast in control gold alloy, and the abutment finish line curvature had a significant effect on the marginal fit of metal ceramic crowns.

Grindability of cast Ti-Cu alloys.

OBJECTIVE: The purpose of the present study was to evaluate the grindability of a series of cast Ti-Cu alloys in order to develop a titanium alloy with better grindability than commercially pure titanium (CP Ti), which is considered to be one of the most difficult metals to machine. METHODS: Experimental Ti-Cu alloys (0.5, 1.0, 2.0, 5.0, and 10.0 mass% Cu) were made in an argon-arc melting furnace. Each alloy was cast into a magnesia mold using a centrifugal casting machine. Cast alloy slabs (3.5 mm x 8.5 mm x 30.5 mm), from which the hardened surface layer (250 microm) was removed, were ground using a SiC abrasive wheel on an electric handpiece at four circumferential speeds (500, 750, 1000, or 1250 m/min) at 0.98 N (100 gf). Grindability was evaluated by measuring the amount of metal volume removed after grinding for 1min. Data were compared to those for CP Ti and Ti-6Al-4V. RESULTS: For all speeds, Ti-10% Cu alloy exhibited the highest grindability. For the Ti-Cu alloys with a Cu content of 2% or less, the highest grindability corresponded to an intermediate speed. It was observed that the grindability increased with an increase in the Cu concentration compared to CP Ti, particularly for the 5 or 10% Cu alloys at a circumferential speed of 1000 m/min or above. SIGNIFICANCE: By alloying with copper, the cast titanium exhibited better grindability at high speed. The continuous precipitation of Ti(2)Cu among the alpha-matrix grains made this material less ductile and facilitated more effective grinding because small broken segments more readily formed.

Mechanical properties and microstructures of cast Ti-Cu alloys.

OBJECTIVES: This study evaluated the mechanical properties of cast Ti-Cu alloys with the hope of developing an alloy for dental casting with better mechanical properties than unalloyed titanium. METHODS: Ti-Cu alloys with five concentrations of copper (0.5, 1.0, 2.0, 5.0 and 10.0 mass%) were made in an argon-arc melting furnace. The alloys were cast into magnesia-based molds using a centrifugal casting machine. The microstructure, microhardness profile of the specimen cross section, tensile strength, yield strength, and elongation were determined for the castings. Scanning electron microscope fractography was undertaken for the fractured surfaces after tensile testing. XRD was performed on the polished specimens. Results were analyzed using one-way ANOVA and the Student-Newman-Keuls tests. RESULTS: The mean tensile strengths of all the cast Ti-Cu alloys were significantly (p<0.05) higher than for cast commercially pure titanium (CP Ti). Of the Ti-Cu alloys tested, the 5 and 10% Cu alloys had significantly higher strength than the rest. The 10% Cu alloy exhibited the lowest mean elongation. CP Ti and the 0.5 and 1% Cu alloys showed higher ductility. The bulk hardness of all the cast Ti-Cu alloys, except for the 10% Cu alloy, and CP Ti was approximately the same. SIGNIFICANCE: By alloying with copper, the cast titanium became stronger. Increases in the tensile strength (30%) and yield strength (40%) over CP Ti were obtained for the 5% Cu alloy. Elongation was approximately 3%, which was similar to cast Ti-6Al-4V. Ti-Cu alloys, such as the 5% Cu alloy, could be used for prosthetic dental applications if other properties necessary for dental castings are obtained.