Microhardness of Ni-Cr alloys under different casting conditions.

Braz Oral Res. 2006 Jan-Mar;20(1):40-6

Authors: Bauer JR, Loguercio AD, Reis A, Rodrigues Filho LE

This study evaluated the microhardness of Ni-Cr alloys used in fixed prosthodontics after casting under different conditions. The casting conditions were: (1-flame/air torch) flame made of a gas/oxygen mixture and centrifugal casting machine in a non-controlled casting environment; (2-induction/argon) electromagnetic induction in an environment controlled with argon; (3-induction/vacuum) electromagnetic induction in a vacuum environment; (4-induction/air) electromagnetic induction in a non-controlled casting environment. The 3 alloys used were Ni-Cr-Mo-Ti, Ni-Cr-Mo-Be, and Ni-Cr-Mo-Nb. Four castings with 5 cylindrical, 15 mm-long specimens (diameter: 1.6 mm) in each casting ring were prepared. After casting, the specimens were embedded in resin and polished for Vickers microhardness (VH) measurements in a Shimadzu HMV-2 (1,000 g for 10 s). A total of 5 indentations were done for each ring, one in each specimen. The data was subjected to two-way ANOVA and Tukey's multiple comparison tests (alpha = 0.05). The VH values of Ni-Cr-Mo-Ti (422 +/- 7.8) were statistically higher (p < 0.05) than those of Ni-Cr-Mo-Nb (415 +/- 7.6). The lowest VH values were found for Ni-Cr-Mo-Be (359 +/- 10.7). The VH values obtained in the conditions induction/argon and induction/vacuum were similar (p > 0.05) and lower than the values obtained in the conditions induction/air and flame/air torch (p < 0.05). The VH values in the conditions induction/air and flame/air were similar (p > 0.05). The microhardness of the alloys is influenced by their composition and casting method. The hardness of the Ni-Cr alloys was higher when they were cast with the induction/air and flame/air torch methods.

PMID: 16729173 [PubMed - indexed for MEDLINE]

Efficacy of ultrasound in removal of intraradicular posts using different techniques.

J Oral Sci. 2005 Sep;47(3):117-21

Authors: Braga NM, Alfredo E, Vansan LP, Fonseca TS, Ferraz JA, Sousa-Neto MD

The efficacy of ultrasound in removing cast metal posts was evaluated in this in vitro study using one or two ultrasound units and ultrasonic vibration for various lengths of time. The crowns of 30 healthy maxillary canines were removed, the roots were embedded in acrylic resin blocks, and the root canals were treated endodontically. The canals were prepared and their impressions were taken with self-curing acrylic resin. After casting with copper-aluminum alloy, the posts were blasted with aluminum oxide and cemented with Panavia F resin cement. The specimens were divided into five groups. In groups I and II, only one ultrasound unit was used for 30 and 60 s, respectively; in groups III and IV, two ultrasound units were used simultaneously for 30 and 60 s, respectively; in group V, ultrasound was not used (control). Ultrasonic vibrations were applied with an Enac OE-5 ultrasound unit and an ST-09 tip. All samples were subjected to traction on an Instron machine (model 4444) at a cross-head speed of 1 mm/min. Analysis of the results revealed a statistically significant difference between the groups (ANOVA, P < 0.01); however the difference between groups II and IV was not statistically significant. The efficacy of ultrasound in removing intraradicular posts was confirmed, and the most effective technique was the use of two ultrasound units, independent of the length of time ultrasound was applied.

PMID: 16313088 [PubMed - indexed for MEDLINE]

The influence of mold temperature on the fit of cast crowns with commercially pure titanium.

Braz Oral Res. 2005 Apr-Jun;19(2):139-43

Authors: Fragoso WS, Henriques GE, Contreras EF, Mesquita MF

Commercially pure titanium (CP Ti) has been widely applied to fabricate cast devices because of its favorable properties. However, the mold temperature recommended for the manufacture of casts has been considered relatively low, causing inadequate castability and poor marginal fit of cast crowns. This study evaluated and compared the influence of mold temperature (430 degrees C--as control, 550 degrees C, 670 degrees C) on the marginal discrepancies of cast CP Ti crowns. Eight bovine teeth were prepared on a mechanical grinding device and impressions were used to duplicate each tooth and produce eight master dies. Twenty-four crowns were fabricated using CP Ti in three different groups of mold temperature (n = 8): 430 degrees C (as control), 550 degrees C and 670 degrees C. The gap between the crown and the bovine tooth was measured at 50 X magnification with a traveling microscope. The marginal fit values of the cast CP Ti crowns were submitted to the Kruskal-Wallis test (p = 0.03). The 550 degrees C group (95.0 microm) showed significantly better marginal fit than the crowns of the 430 degrees C group (203.4 microm) and 670 degrees C group (213.8 microm). Better marginal fit for cast CP Ti crowns was observed with the mold temperature of 550 degrees C, differing from the 430 degrees C recommended by the manufacturer.

PMID: 16292448 [PubMed - indexed for MEDLINE]

Evaluation of the castability of a Co-Cr-Mo-W alloy varying the investing technique.

Braz Dent J. 2005;16(1):50-5

Authors: Carreiro Ada F, Ribeiro RF, Mattos Mda G, Rodrigues RC

The purpose of this study was to compare the castability of Co-Cr-Mo-W (Remanium 2000), Ni-Cr (Durabond) and Co-Cr-Mo (Vera PDI) alloys invested with either conventional (phosphate- and silica-based) or mixed investing techniques. A 10 X 10 mm square-shaped nylon net containing 100 open squares served as a template for construction of wax patterns, which were invested with phosphate-based investment (Termocast), silica-based investment (Refrafil) and mixed investing technique (2-mm layer phosphate investment plus filling with silica investment). Forty-five cast specimens (5 per experimental condition) were obtained and sandblasted with aluminum oxide. The number of completely reproduced cast segments was counted to obtain a percentage designated "castability value", which indicated the accuracy of the alloy to reproduce mold details. Statistical analysis using two-way ANOVA and Tukey's test showed that, comparing the alloys, Remanium 2000 had statistically similar castability (p>0.05) to Vera PDI and lower than Durabond (p<0.05). Considering the mixed technique results, Remanium 2000 yielded lower castability value (p<0.05) than Durabond and Vera PDI alloys, which showed similar results to each other (p>0.05). In conclusion, the castability of the Co-Cr-Mo-W alloy (Remanium 2000) was comparable to that of the Co-Cr alloy (Vera PDI) and worse than that of the Ni-Cr alloy (Durabond). Except for Remanium 2000, the mixed investing technique considerably improved the accuracy of the alloys to reproduce cast details, compared to the phosphate-based investment. The mixed investing technique appears as a viable alternative to improve castability of base metal alloys without decreasing the surface quality of the metallic pieces.

PMID: 16113934 [PubMed - indexed for MEDLINE]

[The effect of mold temperature on the accuracy of titanium castings]

Shanghai Kou Qiang Yi Xue. 2004 Aug;13(4):305-7

Authors: Zhong LF, Li HY, Yang XD

PURPOSE: To study the effect of mold temperature on the accuracy of titanium castings invested in the ZrP99 investment. METHODS: 30 artificial stone dies simulated the post-tooth and their corresponding complete crown wax patterns were made with a truncated cone-shape standard brass model with round sleeves. They were divided randomly into five groups and each group had six samples. Four group wax patterns were invested in ZrP99 investment as test groups and one group was invested in Titavest-CB investment as control. The test group moulds were cast at the mould temperature 600 degrees centigrade, 450 degrees centigrade, 300 degrees centigrade, 150 degrees centigrade, respectively. Measure the distance separating the gingival margin of the crown and the shoulder of the die in the same way as for the wax pattern. The casting accuracy was represented by the discrepancies derived from the space distance measurements made with wax patterns and cast crowns. t test and one-way ANOVA were used for statistical analysis. RESULTS: Measurement of the casting accuracy indicated that the casting accuracy of the control group was higher than all the test groups. When the mold temperature was lower than 450 degrees centigrade, the accuracy of the castings invested in ZrP99 investment was improved significantly with the mold temperature raised. CONCLUSION: To satisfy the requirement of the clinical practice in the point of the casting accuracy, the mold temperature of ZrP99 investment must be chosen higher than 300 degrees centigrade.

PMID: 15349673 [PubMed - indexed for MEDLINE]

Artifacts from dental casting alloys in magnetic resonance imaging.

J Dent Res. 2003 Aug;82(8):602-6

Authors: Shafiei F, Honda E, Takahashi H, Sasaki T

The potential advantage of magnetic resonance imaging (MRI) has been limited by artifacts due to the presence of metallic materials. For quantitative evaluation of the magnitude of artifacts from dental casting alloys and implant materials in MR imaging, 11 dental casting or implant materials were imaged by means of 1.5 T MRI apparatus with three different sequences. Mean and standard deviation of water signal intensity (SI) around the sample in the region of interest (1200 mm(2)) were determined, and the coefficient of variation was compared for evaluation of the homogeneity of the SI. A variety of artifacts with different magnitudes was observed. Only one of the samples, composed mainly of Pd, In, and Sb, showed no artifacts in all imaging sequences. We concluded that selection of specific dental casting alloys according to their elemental compositions could minimize the metal artifacts in MRI; however, titanium alloys currently pose a problem with respect to causing MRI artifacts.

PMID: 12885843 [PubMed - indexed for MEDLINE]

Effect of zirconia-modified magnesia investment on the casting of pure titanium.

Kaohsiung J Med Sci. 2003 Mar;19(3):121-6

Authors: Hung CC, Hou GL, Tsai CC, Huang CC

Several investigations have examined magnesia-based investments for pure titanium casting. However, the thermal expansion value was insufficient at low casting temperatures and high interfacial reactivity occurred at high casting temperatures. The purpose of this investigation was to modify a magnesia-based investment by adding a heat-resistant mold material, zirconia, in different ratios to produce a more accurate titanium casting. The thermal expansion value was measured using a new precise automatic laser recording machine and pure titanium was cast using an argon casting machine. The marginal accuracy was measured using a stereomicroscope and the interfacial reactivity of the titanium was evaluated using X-ray diffraction analysis. The results indicate that adding different amounts of zirconia to a magnesia-based investment can increase its thermal expansion value and decrease the interfacial reactivity of the titanium. Maximal thermal expansion in the zirconia-modified investments significantly increased by 5-6 weight % (wt%) and peaked at 1.62% expansion. Selevest with 5 wt% zirconia had the smallest mean marginal discrepancy, 21.70 microm at 750 degrees C. Analysis of variance indicates significant differences in marginal discrepancy between zirconia-modified investments (p < 0.001). Adding zirconia can also decrease the interfacial reactivity of the titanium. The data indicated that proper amounts of zirconia (5-6 wt%) added to a magnesia-based investment can produce a more accurate and less interfacial reactive pure titanium casting.

PMID: 12751872 [PubMed - indexed for MEDLINE]

Evaluation of a reproduction technique for the study of the enamel composite/bracket base area.

J Orthod. 2000 Sep;27(3):261-6

Authors: Wilner FJ, Oliver RG

The objective of the study was to evaluate a reproduction method that would enable the study of the enamel/ bracket/composite interface in vivo, and consisted of in vitro assessment of two different impression materials to compare reproduction of brackets bonded to extracted teeth followed by in vivo assessment of the superior material. In vitro standard edgewise brackets were bonded to two extracted teeth and impressions were taken using two different types of low viscosity silicone-based impression materials. A medium viscosity silicone impression material was used to support the original impression. Three impressions of both the gingival and occlusal aspect of the bracket base region were obtained using each of the impression materials. Replicas were then prepared for SEM viewing and these compared to SEMs of the real teeth for reproduction of detail. A 3-point Reproducibility Index was used to compare the SEM photographs of the comparable replicas. One impression material was clearly superior to the other and produced an acceptably accurate representation of the true clinical situation in three out of four samples. This material also performed well in the in vivo situation. The technique described is satisfactory for the production and analysis of SEM pictures of the enamel/composite/ bracket base interface in vivo.

PMID: 11099559 [PubMed - indexed for MEDLINE]

The effects of different storage conditions on polyether and polyvinylsiloxane impressions.

J Am Dent Assoc. 1998 Jul;129(7):1014-21

Authors: Purk JH, Willes MG, Tira DE, Eick JD, Hung SH

While being shipped to a laboratory, impressions can be exposed to excessive temperatures. This study compared the effects of different time and temperature storage conditions, including temperature extremes of 66 C and -10 C, on the accuracy of addition silicone and polyether impressions. The greatest distortion generally occurred as a result of the 66 C temperature extreme. The authors recommend that impressions be poured in stone according to manufacturers' specifications before being shipped to a dental laboratory.

PMID: 9685767 [PubMed - indexed for MEDLINE]

A simplified pattern for a cast metal post.

J Am Dent Assoc. 1998 Feb;129(2):223

Authors: Heilman ME

PMID: 9495056 [PubMed - indexed for MEDLINE]

Segregation in precious-metal dental-casting alloys.

J Dent Res. 1993 Mar;72(3):587-91

Authors: Dr&#xE1;pal S, Pomajbík J

The aim of this study was to conduct a theoretical analysis of segregation in Au-Ag-Cu and Ag-Pd-Au-Cu dental-casting alloys, and to confirm and extend the results experimentally. Both theoretical and experimental data showed greater segregation in the Ag-Pd-Au-Cu alloy than in the Au-Ag-Cu alloy. There was very little segregation of gold, zinc, and platinum, while between the dendrites copper increased and silver and palladium decreased.

PMID: 8450118 [PubMed - indexed for MEDLINE]

The fit of gold-alloy full-crown castings made with ceramic casting ring liners.

J Dent Res. 1992 Dec;71(12):1865-70

Authors: Earnshaw R, Morey EF

Measurements were made of the fit of gold-alloy full-crown castings produced with dry ceramic ring liners. When used with vacuum investing, these liners absorb relatively large amounts of water from the investment mix (thereby reducing its original W/P ratio) and then function as wet liners, thus increasing the investment's potential expansion and giving castings which are consistently larger than when air investing is used. With four of the five liners tested, investing in air produced many castings which were unacceptably undersized (inaccuracy worse than -0.2%). The fifth liner, an industrial material 2 mm thick, gave only one casting out of 12 which was outside this limit, although all castings were undersized to a lesser extent. Vacuum investing gave improved casting accuracy; with four of the five liners, the improvement was highly significant (p < 0.001), and with the fifth, probably significant (p < 0.05). Even with vacuum investing, however, with only two of the liners did all castings show inaccuracies within +/- 0.2%. With the other three liners, some castings (ranging from 2/10 to 7/9) had inaccuracies worse than -0.2%. With both air and vacuum investing, changing from one liner to another caused changes in relative casting accuracy which were often significant (p < 0.01) or highly significant (p < 0.001). In casting techniques where a ceramic ring liner is used, the choice of specific lining material and the choice between investing in air or under vacuum are important factors which can have a major effect on the fit of castings.

PMID: 1452884 [PubMed - indexed for MEDLINE]

The fit of gold-alloy full-crown castings made with pre-wetted casting ring liners.

J Dent Res. 1992 Dec;71(12):1858-64

Authors: Morey EF, Earnshaw R

Measurements were made of the fit of full-crown gold-alloy castings produced with two types of pre-wetted ring liner (asbestos and cellulose) and a typical gypsum-bonded investment (Cristobalite Inlay, Sybron/Kerr Products, Romulus, MI; W/P = 0.40). Laboratory measurements were made of the effects of the liners on potential investment expansion, and properties of the lining materials considered relevant to casting accuracy were also measured. There was a wide variation in values for mean dimensional inaccuracy. One liner produced a series of castings all of whose inaccuracies lay within the range +/- 0.1%, with a mean value of + 0.01%. With the other five liners, all or most castings were undersize. With three, all or most castings showed inaccuracies worse than -0.2%. The values for casting inaccuracy with the various liners showed a probable correlation with potential investment expansion (p < 0.05); however, no correlation was found between casting inaccuracy and any apparently relevant liner properties, alone or in combination. In casting techniques which use a pre-wetted ring liner, the choice of a specific lining material is an important factor which has a significant effect on casting inaccuracy. With at least three of the six liners tested, a higher investment expansion was needed for accurate full-crown castings to be ensured.

PMID: 1452883 [PubMed - indexed for MEDLINE]

The effects of cleaning on the kinetics of in vitro metal release from dental casting alloys.

J Dent Res. 1992 Jul;71(7):1417-22

Authors: Wataha JC, Craig RG, Hanks CT

The kinetics of the release of elements from six dental casting alloys into cell-culture medium was assessed by means of atomic absorption spectroscopy. Alloys were evaluated in the polished and polished-cleaned conditions so that the effects of cleaning could be determined. Auger scanning microscopy was used for analysis of the surfaces of selected alloys before and after exposure to the cell-culture medium. Release patterns for each element were characterized by the shape of the dissolution vs. time curve, concentration of the element at 12 h as a percentage of the 72-hour concentration, and the relative slope of the curve from 48 to 72 h. Three patterns of release were observed for elements in these alloys. Type I patterns had logarithmic shapes with relatively large 12-hour concentrations and low 48-72-hour slopes. Type II patterns had logarithmic shapes but with moderate 12-hour concentrations and 48-72-hour slopes. Type III patterns were polynomial in shape, had relatively low 12-hour concentrations, and had large 48-72-hour slopes. Cleaning did not change the pattern of release but did generally significantly decrease the quantities of elements released (p = 0.05). The type of dissolution vs. time curve appeared to be dependent upon the element and the composition of the alloy. When cleaning reduced dissolution, surface analyses showed that the cleaning process increased the abundance of elements such as Au and Pd and reduced the abundance of Ag and Cu. Elements which were released from the alloys were more abundant on the surface than in the bulk in both polished and polished-cleaned conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

PMID: 1629458 [PubMed - indexed for MEDLINE]

The release of elements of dental casting alloys into cell-culture medium.

J Dent Res. 1991 Jun;70(6):1014-8

Authors: Wataha JC, Craig RG, Hanks CT

Ten dental casting alloys were tested for alloy-element release into cell-culture medium, and this release was related to alloy composition, alloy microstructure, and alloy cytotoxicity (previously determined). Cell-culture medium was analyzed for alloy elements by flame atomic absorption. Concentrations of elements in the medium were normalized by dividing them by their atomic abundance in the alloy, giving element medium-alloy ratios (EMA ratios). Results showed that Au, In, and Pd generally did not dissolve into the medium, but that Ag, Cd, Cu, Ga, Ni, and Zn frequently dissolved. Comparison of EMA ratios for Ag, Cu, and Zn showed that each element retained a behavioral identity in diverse metallurgical environments, but that these environments influenced the release behavior to some degree. Some EMA ratios in multiphase alloys were greater than those in solid solutions, and EMA ratios showed great diversity within all the alloys. Nominal composition seemed to be of little value in the prediction of metal release unless the composition supported multiple-phase formation. In addition, release of alloy elements did not, in itself, completely predict alloy cytotoxicity measured previously. However, cytotoxicity was associated with metal release in each case. The commercial alloys used in this study exhibited more complex and less predictable release behavior than did the simpler ternary alloy systems used by previous investigators. It is believed that the use of commercial preparations is necessary for their in vivo behavior to be modeled.

PMID: 2045570 [PubMed - indexed for MEDLINE]

Casting pure titanium into commercial phosphate-bonded SiO2 investment molds.

J Dent Res. 1990 Dec;69(12):1800-5

Authors: Takahashi J, Kimura H, Lautenschlager EP, Chern Lin JH, Moser JB, Greener EH

Pure titanium was cast into five different phosphate-bonded SiO2 investment mold materials (at 350 degrees C) with an argon-arc melting and pressure casting machine. The mesh castability, the fit of the MOD inlay castings, and the Knoop hardness and the micro-structure in cross-sections of castings were examined. The setting and thermal expansion, the compressive strength, and the X-ray diffraction analysis of the investments were also measured. The castability, the fit, and the thickness of the reacted layer differed in degree among these investments, in spite of the same phosphate-bonded SiO2-type investment. A significant correlation was obtained between the thermal expansion (at 350 degrees C) and the casting accuracy.

PMID: 2174447 [PubMed - indexed for MEDLINE]

The effect of casting ring liners on the potential expansion of a gypsum-bonded investment.

J Dent Res. 1988 Nov;67(11):1366-70

Authors: Earnshaw R

Cellulose paper (used wet) and ceramic paper (used dry) are replacing asbestos paper as cushioning ring liners in dental casting. A study was made of the effects of all three of these materials on the setting and subsequent thermal expansion of a gypsum-bonded cristobalite casting investment (W/P = 0.40). Thermal expansion measurements were made on the same specimens that were produced during the setting expansion tests. Control specimens setting against a smooth dry surface showed a total expansion of 1.7%. Specimens setting against dry ceramic liners had similar total expansions, in the range 1.6 to 1.7%. Specimens setting against either of the wet lining materials showed an increased total expansion (in the range 2.2 to 2.3%), by virtue mainly of a large increase in setting expansion. In order for reproducible setting expansion results to be obtained with wet liners, it was necessary to control the amount of absorbed water carefully. Dry asbestos and dry cellulose liners gave higher expansions than pre-wetted ones, since they abstracted water from the mix, reducing its effective W/P ratio (giving a thicker mix), and then functioned as wet liners. These results suggest that, at least as far as potential investment expansion is concerned, wet cellulose liners have an effect similar to that of the traditional wet asbestos liners. Dry ceramic liners give a much lower investment expansion, and when these liners are used, an investment with an increased measured expansion could be an advantage.

PMID: 3053818 [PubMed - indexed for MEDLINE]

Effect of the porosity of the filler aggregates on the setting expansion of investment material.

J Dent Res. 1988 Oct;67(10):1278-83

Authors: Takahashi J, Okazaki M, Kimura H, Haeuchi Y, Kubo F

Twenty experimental phosphate-bonded investments were prepared by the mixing of two types of fillers (spherical glass beads and irregularly shaped silica particles) with five types of filler aggregates of different porosities, and two different ratios of MgO to NH4H2PO4. These investments were mixed with three different liquids, and their setting expansion, time until setting expansion began (induction time), and fluidity were measured under constant experimental conditions. The following results were obtained: (1) The setting expansion was significantly related to bulk porosity of filler aggregates, not to packed porosity, despite variations in type of filler, ratio of MgO to NH4H2PO4 or type of liquid; and (2) the fluidity and the time until setting expansion began were also related to the bulk porosity of the filler aggregates.

PMID: 2844866 [PubMed - indexed for MEDLINE]

Casting metals: reactor response.

Adv Dent Res. 1988 Aug;2(1):44-6

Authors: Tesk JA

PMID: 3248139 [PubMed - indexed for MEDLINE]

An electrochemical and multispectroscopic study of corrosion of Ag-Pd-Cu-Au alloys.

J Dent Res. 1986 Jun;65(6):888-91

Authors: Niemi L, Minni E, Ivaska A

Corrosion of a multi-phase Ag-Pd-Cu-Au-based commercial dental casting alloy and a Cu-Pd-rich and Ag-rich single-phase alloy was studied by open-circuit potential measurements, atomic absorption spectrometry, and electron spectroscopy. The alloys were immersed in an artificial saliva solution for 24 hr while the open-circuit potentials of the alloys were measured. The potentials were found to stabilize at certain levels after a steep rise during the first hours of the experiment. Cu was found to dissolve considerably from the Cu-Pd-rich alloy, with simultaneous enrichment of Pd in the surface layer of the alloy. Ag dissolved slightly from the Ag-rich alloy, but both Cu and Ag were found to dissolve from the multi-phase alloy. Neither Pd nor Au dissolved from any of the alloys studied.

PMID: 3458739 [PubMed - indexed for MEDLINE]

Thermal behavior of the gypsum binder in dental casting investments.

J Dent Res. 1986 Jun;65(6):877-84

Authors: Mori T

This study examined the thermal behavior of cast gypsum specimens, with and without additives, by means of simultaneous differential thermal analysis-thermogravimetry (DTA-TG) and dilatometry. Specimens were prepared from wet-calcined hemihydrates (Hydrocal and Densite). The additives studied were boric acid (H3BO3) and sodium chloride (NaCl), and these were added to the hemihydrate powders in concentrations of 2 wt% (in the case of H3BO3) and 0.5 wt% (in the case of NaCl). A large shrinkage was observed in the range of 300 to 500 degrees C, and this was greatly reduced when either H3BO3 or NaCl was present. The dehydration of gypsum (calcium sulfate dihydrate) was not completed until the initial stage of this large shrinkage was reached, but the phase transition of calcium sulfate anhydrite (III-CaSO4 to II-CaSO4) was the major cause for the large shrinkage. This phase transition occurred over a much wider temperature range than that suggested by the DTA-TG results. Dehydration conditions similar to those employed in wet calcination of gypsum appeared to be produced under atmospheric pressure when NaCl was present.

PMID: 3458738 [PubMed - indexed for MEDLINE]

A technique for characterizing casting behavior of dental alloys.

J Dent Res. 1985 Feb;64(2):134-8

Authors: Hinman RW, Tesk JA, Whitlock RP, Parry EE, Durkowski JS

A technique for characterizing casting behavior of dental alloys has been developed and tested. The method employs easily reproducible specimen patterns and uses equipment and procedures generally available in dental prosthetic laboratories. A castability value is arrived at by counting complete segments of a cast alloy grid. Test results indicate that the castability evaluation procedure described can be a valuable aid in the laboratory for both selecting and using dental materials for producing cast restorations. The test method would also appear useful for the evaluation of products and techniques during research and development. An absolute minimum for the castability value determined relative to clinical and laboratory efficacy has yet to be established.

PMID: 3855884 [PubMed - indexed for MEDLINE]

The structure of a commercial dental Ag-Pd-Cu-Au casting alloy.

J Dent Res. 1984 Feb;63(2):149-54

Authors: Niemi L, Her&#xF8; H

The structure of a commercial dental Ag-Pd-Cu-Au casting alloy has been studied by microprobe and X-ray diffraction analyses after various heat treatments. The composition of phases in equilibrium was established. After being annealed at 400 degrees C, 500 degrees C, and 600 degrees C for seven wk, the alloy consisted of three phases: a Cu- and Pd-rich fee phase (alpha 1) with alpha = 0.372nm, a Ag-rich matrix (alpha 2) with alpha = 0.399nm, and an ordered CsCl-type bcc PdCu phase with alpha = 0.296nm. The PdCu phase was not observed above 600 degrees C, and the proportion of the alpha 1 phase decreased sharply above 700 degrees C. After being annealed at 900 degrees C, the alloy matrix was partly decomposed at the Cu-enriched grain boundaries. The decomposed areas grew into the grain interior during subsequent precipitation hardening. No segregation of Au was detected after casting, and the element was evenly distributed throughout the alloy structure after all heat treatments.

PMID: 6582096 [PubMed - indexed for MEDLINE]

Polarization-corrosion behavior of commercial gold- and silver-base casting alloys in Fusayama solution.

J Dent Res. 1983 Dec;62(12):1221-5

Authors: Johnson DL, Rinne VW, Bleich LL

Based on polarization measurements, high Au alloys are highly corrosion-resistant and exhibit the lowest corrosion rates; intermediate Au, Ag, and Pd alloys with Cu are passive but exhibit higher corrosion rates. Twenty weight percent (w/o) In-Ag alloys exhibit active corrosion behavior at potentials only 100 mV noble to the corrosion potential.

PMID: 6361084 [PubMed - indexed for MEDLINE]

Estimation of solidification time during casting by use of a heat transfer model.

J Dent Res. 1982 Oct;61(10):1188-91

Authors: Okazaki M, Takahashi J, Kimura H, Ida K

Time-dependent temperature profiles in dental casting molds were analyzed by an unsteady heat conduction model. The thermal conductivity and initial temperature of the mold greatly affected the heat transfer in the mold. The thermal conductivities of gypsum- and phosphate-bonded investments at high temperatures were accurately measured by means of the hot wire method. From the data obtained, the solidification times of Ag, Ag alloy, and Co-Cr alloy were calculated and compared with the experimental results.

PMID: 6749926 [PubMed - indexed for MEDLINE]

Effects of phase transformations of silicas and calcium sulfates on the compressive strength of gypsum-bonded investments at high temperatures.

J Dent Res. 1982 Sep;61(9):1077-82

Authors: Ohno H, Nakano S, Miyakawa O, Watanabe K, Shiokawa N

The effects of transformations of silicas and calcium sulfates on high temperature compressive strength were investigated in commercial and experimental investment materials containing fused quartz as silica. The strength is only slightly affected by the alpha leads to beta transformation of cristobalite and not by the quartz alpha leads to beta transformation. The state of the calcium sulfates is the main factor influencing variations in the strength at a particular temperature.

PMID: 6302149 [PubMed - indexed for MEDLINE]

Wetting effects of surface treatments on inlay wax-investment combinations.

J Dent Res. 1981 Nov;60(11):1858-60

Authors: Morrison JT, Duncanson MG, Shillingburg HT

Gypsum-bonded and phosphate-bonded investments were applied to wax surfaces which were untreated, treated by buffing with cotton moistened with a die lubricant containing organic solvent, or treatment with a wax pattern cleaner. Contact angles between the investment material and wax surfaces were measured and compared. The treatment of a wax pattern with a surface tension reducing agent significantly increases the degree of wetting by both gypsum- and phosphate-bonded investments.

PMID: 6945325 [PubMed - indexed for MEDLINE]

Cytotoxicity of Pd-Co dental casting ferromagnetic alloys.

J Dent Res. 1981 Aug;60(8):1403-9

Authors: Kawata Y, Shiota M, Tsutsui H, Yoshida Y, Sasaki H, Kinouchi Y

PMID: 6942004 [PubMed - indexed for MEDLINE]

Decomposition of gypsum bonded investments.

J Dent Res. 1981 Aug;60(8):1418-23

Authors: Matsuya S, Yamane M

Decomposition of gypsum bonded investments was investigated by means of TG-DTA and X-ray diffraction. The decomposition began at about 900 degrees C and led to the formation of CaSiO3 as a major product and Ca2SiO4 as a minor one. CaO was not formed during the decomposition of any of the investments. The decomposition process followed Jander's equation, [1-(1-alpha)1/3]2 = kt, and the Ca2+ ion diffusion in CaSiO3 was concluded to be a rate-determining step.

PMID: 6265514 [PubMed - indexed for MEDLINE]

Correlation between macroscopic porosity location and liquid metal pressure in centrifugal casting technique.

J Dent Res. 1981 Jan;60(1):59-66

Authors: Vaidyanathan TK, Schulman A, Nielsen JP, Shalita S

Radiographic analysis of uniform cylindrical castings fabricated by the centrifugal casting technique has revealed that the macroscopic porosity is dependent on the location of the sprue attachment to the casting. This is attributed to the significant pressure gradient associated with the centrifugal casting technique. The pressure gradient results in different heat transfer rates at portions of the castings near and away from the free surface of the button. Consequently, the macroscopic porosity is invariably at portions of the casting close to the free surface of the button. In addition, some optimized sprue-reservoir combinations could be predicted and proved, based on this pressure gradient concept.

PMID: 7002971 [PubMed - indexed for MEDLINE]

Pd-Co dental casting ferromagnetic alloys.

J Dent Res. 1981 Jan;60(1):50-8

Authors: Kinouchi Y, Ushita T, Tsutsui H, Yoshida Y, Sasaki H, Miyazaki T

Three kinds of Pd-Co alloys have been newly developed. Their magnetic and physical properties and corrosion resistances have been examined. As a result, it was found that they are available as the dental casting ferromagnetic alloy which can be used in combination with Sm-Co magnets, overcoming such problems as non-castability and brittleness.

PMID: 6934191 [PubMed - indexed for MEDLINE]

Setting and thermal reactions of phosphate investments.

J Dent Res. 1980 Sep;59(9):1478-85

Authors: Neiman R, Sarma AC

The setting reactions and thermal degradation of the phosphate binders are interpreted from the DTA and X-ray diffraction data. Setting takes place through complex formation of (NH4Mg PO4.6H2O)n, excess reactants, and water. Dehydration and thermal reactions lead to a sequence of reactions forming (NH4MgPO4.H2O)n, (Mg2P2O7)n, Mg2P2O7, and Mg3(PO4)2.

PMID: 6931124 [PubMed - indexed for MEDLINE]

Casting accuracy of nickel-chromium alloys: marginal discrepancies.

J Dent Res. 1980 Jul;59(7):1164

Authors: Duncan JD

PMID: 6929811 [PubMed - indexed for MEDLINE]

An explanation for the water distribution in a hygroscopic expansion technique.

J Dent Res. 1980 Jun;59(6):1048-54

Authors: Consani S, Ruhnke LA

The water distribution in a controlled water addition technique was investigated using a Liquid Scintillation Counter. The mix water arrangement varied in different sections of the investment mass. The water distribution seemed to be the result of the influence of added water and a sprue base.

PMID: 6989872 [PubMed - indexed for MEDLINE]

Castability of low gold content alloys.

J Dent Res. 1980 May;59(5):824-30

Authors: Howard WS, Newman SM, Nunez LJ

A test pattern composed of 14 gauge sprue wax and various gauges of nylon lines was constructed, and used to differentiate the castability of several alloys. The castability of seven commercial low gold content alloys for porcelain fused to metal restorations was compared. Five commercial low gold content yellow alloys for full cast restorations were compared to each other and to a Type III certified control.

PMID: 6988479 [PubMed - indexed for MEDLINE]

Evaluating dimensional accuracy of stone models.

J Dent Res. 1979 Apr;58(4):1352-7

Authors: Hosoda H, Ohsawa M

An optical feeler measuring technique was introduced for evaluating the dimensional accuracy of indirect stone models. It presents the following advantages being able to measure the diameter of specimens in detail at various heights, indicating good reproducibility of the data; and hardly injuring the surface of the stone casts.

PMID: 285105 [PubMed - indexed for MEDLINE]

The chloride corrosion of low-gold casting alloys.

J Dent Res. 1979 Feb;58(2):568-75

Authors: Sarkar NK, Fuys RA, Stanford JW

Potentiodynamic polarization measurements have indicated that the so-called 'low-gold' casting alloys are characterized by decreased chloride corrosion resistance, when compared with ADA Type III and Type IV gold alloys. This decrease in chloride corrosion resistance results apparently from the presence of Ag-rich microsegregations with a possible minor contribution from Cu-rich segregations or precipitates.

PMID: 283085 [PubMed - indexed for MEDLINE]

Neutronographic investigation of wax elimination from high-temperature investment molds.

J Dent Res. 1977 Apr;56(4):448-9

Authors: Walsh JF

PMID: 323320 [PubMed - indexed for MEDLINE]

Automated centrifuge for pour resins.

J Dent Res. 1975 Jul-Aug;54(4):909

Authors: Winkler S, Puengphob R, Tsao DH

PMID: 1099139 [PubMed - indexed for MEDLINE]

Potential applications of certain nickel-titanium (nitinol) alloys.

J Dent Res. 1975 Jan-Feb;54(1):89-96

Authors: Civjan S, Huget EF, DeSimon LB

The mechanical behavior ("shape memory") associated with martensitic solid-state transformation in nearly equiatomic Ni-Ti alloy (55-Nitinol) has been studied. Potential dental and medical applications for 55-Nitinol (55% Ni, 1.5% Co, balance Ti, by weight) and for 60-Nitinol (60% Ni, by weight) have been suggested.

PMID: 1053778 [PubMed - indexed for MEDLINE]

Adhesive refractory protective coating for investment casting.

J Dent Res. 1974 Sep-Oct;53(5):1181-8

Authors: Mabie CP

PMID: 4609112 [PubMed - indexed for MEDLINE]

Petrographic study of the refractory performance of high-fusing dental alloy investments. II. Silica-bonded investments.

J Dent Res. 1973 Jul-Aug;52(4):758-73

Authors: Mabie CP

PMID: 4352582 [PubMed - indexed for MEDLINE]

Adsorption of water on tooth components and related materials.

J Dent Res. 1973 Mar-Apr;52(2):271-80

Authors: Loebenstein WV

PMID: 4511309 [PubMed - indexed for MEDLINE]

Petrographic study of the refractory performance of high-fusing dental alloy investments. I. High-fired, phosphate-bonded investments.

J Dent Res. 1973 Jan-Feb;52(1):96-110

Authors: Mabie CP

PMID: 4345760 [PubMed - indexed for MEDLINE]

Thermal dimensional changes of a critobalite investment.

J Dent Res. 1968 Nov-Dec;47(6):1185

Authors: Kono A, Kobori K, Fusayama T

PMID: 5249054 [PubMed - indexed for MEDLINE]

Strength properties of waxes at various temperatures and their practical application.

J Dent Res. 1967 Jan-Feb;46(1):300-5

Authors: Craig RG, Eick JD, Peyton FA

PMID: 5226403 [PubMed - indexed for MEDLINE]

Heating rate of a gypsum investment related to crack formation.

J Dent Res. 1966 Sep-Oct;45(5):1419-23

Authors: Kono A, Hosoda H, Fusayama T

PMID: 5225313 [PubMed - indexed for MEDLINE]

Reaction of cobalt-chromium casting alloy with investment.

J Dent Res. 1966 Sep-Oct;45(5):1516-28

Authors: Allan FC, Asgar K

PMID: 4289122 [PubMed - indexed for MEDLINE]

The behavior and measurement of hygroscopic expansion of dental casting investment.

J Dent Res. 1954 Aug;33(4):519-30

Authors: ASGARZADEH K, MAHLER DB, PEYTON FA

PMID: 13184041 [PubMed - indexed for MEDLINE]