Recast Alloy Research Articles

Comparative in-vitro microscopic evaluation of vertical marginal discrepancy, microhardness, and surface roughness of nickel–chromium in new and recast alloy

Reusing of alloy has become a need of time due to the increasing demand, depletion of resources, and substantial increase in their price. The alloys used require a long-term stay in the oral cavity exposed to a wet environment, so they must have good wear resistance, biocompatibility, and mechanically good strength. In this study, the vertical marginal discrepancy, surface roughness, and microhardness of the new and recast nickel–chromium (base metal) alloys were evaluated. 125 wax patterns were fabricated from a customized stainless steel master die with a heavy chamfer cervical margin divided into 5 groups. Each group had 25 samples. Group A: 25 wax patterns were cast using 100% by weight of new alloy, Group B: the casting was done by using 75% new alloy and 25% alloy by weight, Group C: wax patterns were cast using 50% new alloy and 50% alloy, Group D: 25% new alloy and 75% alloy and Group E: 100% recast alloy. The vertical marginal discrepancy was measured by an analytical scanning microscope, microhardness was tested on a universal testing machine, and surface roughness was on a tester of surface roughness. Castings produced using new alloys were better than those obtained with reused alloys. Alloys can be reused till 50% by weight along with the new alloy and accelerated casting technique can be used to save the lab time to fabricate castings with acceptable vertical marginal discrepancy, microhardness, and surface roughness. This indicated that 50% recasting of (Ni–Cr) can be used as a good alternative for the new alloy from an economical point of view.

Ionic release of dental cobalt-chromium based alloys

Background: Since the 1980s, as the cost of noble metals has increased, more base metal alloys have been used in fixed and removable prostheses. Cobalt-chromium (Co-Cr) alloys are one of the most widely used base metal alloys in the prosthetic dental department and have several clinical uses. Co-Cr alloys are frequently used as having excellent biocompatibility, great strength, good resistance to tarnish, corrosion, and wear, as well as being heat-resistant and non-magnetic.
 Materials and Methods: For the ion release test, seventy specimens of a cobalt-chrome alloy disc with dimensions of 5 mm in diameter and 3 mm in thickness were created. They were divided into five groups, each of which had 14 specimens, based on the manufacturing method as follows: new cast alloy group; selective laser melting group (3D printer specimens); once recast alloy + old selective laser melting group; new cast + once recast alloy group; once recast alloy group.
 Result: The outcomes showed that there were no
 statistically significant differences in ion release in any of the groups examined (P>0.05).
 Conclusion: The production technique and alloy composition have a slight influence on ion release. A positive clinical response is anticipated, since it was found that every group met the ionic release criteria of the international standards.

Bulk Recycling of Ni-Cr-Mo Dental Alloy - A Sustainable Approach

Many dental alloy manufacturers instruct not to recast alloys, but the dental laboratories reuse the casting surplus for economic reasons. It is a controversial topic in dental practice, so the present study attempts to assess the effects of recasting Ni-Cr-Mo alloys. Three sets of alloy pellets were recast. The first set was melted and allowed to solidify. The second and third sets were recast two times and three times, respectively. The elemental composition of all the recast samples was analysed using ED-XRF (Energy Dispersive X-ray Fluorescence) spectrometer. The variation in the chemical composition for the number of recasting was reported. It was observed that the recasting for one time doesn't change the elemental composition to a considerable extent. However, further increase in the number of recasting two and three times, the depletion of the major alloying elements (Ni, Cr, and Mo) was notable. Hence, the current study intends to calculate the exact amount of the depleted elements after each recast. Also, to have a theoretical analysis of the elements necessary for making a master alloy that can be added during the recasting to avoid changes in elemental composition. Moreover, the microstructure of the recast samples was observed using an optical electron microscope (OEM). No drastic variation in the microstructure was observed for the alloy with several melting and solidifying cycles, except for the orientation of the dendritic arm. Furthermore, to confirm the mechanical strength of the recast alloy Vickers microhardness test was conducted. The average microhardness of the base Ni-Cr-Mo alloy was 216 HV, and recasting once does not affect the hardness value. However, the three-time recast alloy showed only a 9% decrement. Finally, it can be concluded that the number of recasting can be as many times provided depleted elements are added in exact proportion after each recast. The current research suggests recycling dental alloys in bulk outside a dental clinic, and a dentist should responsibly segregate different base metal alloys and promote sustainable dentistry.

Bacterial adhesion of Streptococcus mutans to cobalt chromium recast alloys

Cobalt chromium (CoCr) alloys are utilized to make dental prosthesis. Casting CoCr alloys is a common operation in dentistry laboratories due to its low cost. Casting surplus (metal remaining in the sprue and crucible former) is frequently reused by dental laboratories to reduce and recycle metal waste. However, the quality and safety of these recast alloys require further information. Microbial attachment to the surface of metal prostheses may affect its quality and safety. Biofilm formation on metal surface can cause biocorrosion and secondary infection. The effects of different proportions of recast Cobalt Chromium alloy on the bacterial adhesion are not clear. The purpose of this study was to investigate how recasting affects the Streptococcus mutans (S. mutans) adhesion. Twenty disk-shaped specimens (n= 20, allocated for 5 groups) were prepared from CoCr alloys (Remanium GM; Dentaurum) with different proportions (100% new alloy, 25% recast alloy, 50% recast alloy, 75% recast alloy, and 100% recast alloy). After the immersion of the specimens in bacterial suspension for 24 hours, the number of bacteria that adhere to the specimen’s surface was counted using Colony Forming Units. Data were analyzed with one-way ANOVA (α = 0.05). The bacterial adhesion was significantly affected by the recast alloys (p < 0.05). An increased proportion of CoCr recast alloys showed an increase in S. mutans adhesion to the specimen surface.

The effect of recasting on the Fatigue resistance of Co-Cr alloys

The present study evaluated the effect of recasting cobalt-chromium alloys with the addition of new alloy in different ratios (75% and 50%) on the deflection fatigue resistance using three types of alloys: Wironit (Bego), Remanium (Dentaurum), and Wisil (Wipla). Each alloy was divided into three groups for each test, group I (100% new alloy), group II (75% new alloy +25% recast alloy), and group III (50% new alloy + 50% recast alloy).Fatigue specimens produced were butterfly-shaped and half round at their cross section with 18mm length, 1mm thickness, and 2mm width. For each alloy group, five samples were prepared.The results of this study revealed that recasting with adding 75% new alloy did not significantly affect the fatigue resistance of Wironit and Wisil alloys, while significantly affected that of Remanium. Recasting with the addition of 50% new alloy significantly decreased the fatigue resistance of the three types of alloys.Wironit alloy showed the higher mean values for deflection fatigue resistance compared with Remanium and Wisil alloys.

Evaluation of effect of recasting of nickel-chromium alloy on its castability using different investment materials: An in vitro study.

Castability has been found to be affected by many aspects of the entire casting system. Very few references in dental literature are available regarding recasting of the base metal alloys. To evaluate and compare the castability of fresh and reused nickel-chromium alloy and to evaluate the effect of two brands of investment materials on castability of nickel-chromium alloy. For the experimental purpose of evaluation of the effect of recasting of nickel-chromium alloy on its castability, different percentages of new and casted alloy (Nickel-chromium alloy-(Wirolloy NB, Type 4 (Ni-67%; Cr-25%; Mo-5%; Si-1.5%; Mn, Nb, B, C each <1%) and two commercial brands of investment materials namely, Deguvest Impact (Degudent; Dentsply Germany) and Bellavest SH (Degudent; Dentsply Germany) was used to obtain 30 samples. Castability value was obtained using Whitlock's formula. Student t-test and one way ANOVA using SPSS 20.0 software was done. The results of this study confirm earlier works that demonstrate that there is no significant difference in castability values of new and recast alloys. In addition, it also demonstrated, there was no difference in castability using Deguvest Impact and Bellavest SH investment materials. Within the limitations of the study, it was concluded that there was no significant difference found in castability of different percentage combinations of new and once casted alloy using two investment materials. The addition of new alloy during recasting to maintain the castability of nickel-chromium alloy may therefore not be required.

Analysis of Deformation in Ni-Cr Structures with New and Recast Alloys

The present study analyzed new and recast Ni-Cr alloys, regarding the relationship between the applied force and the deformation in cantilevered bar segments, with dimensions of 4.0 mm, 3.5 mm, 3.0 mm in thickness, 4.5 mm width and 15 mm length, on a universal testing machine “EMIC”. The bars in the tests were initially obtained acrylic resin by 4.8 mm wide × 4.3 mm thick × 4 cm long. We obtained 30 bars divided into two groups, with 15 to test new alloys and 15 with alloys recast. The alloy used was Tilite. For the application of the load, the bars were attached to “EMIC” where the active tip of 200 kgf load cell was at a specific point of the bar (15 mm) with a speed of 0.5 mm per minute. The data showed statistically significant differences in relation to alloys and thickness among the bars, and all thicknesses evaluated were different. Thus, it was concluded that there was statistically significant difference between the groups and their variables, and that the alloys recast could be reused at least 1 time, without loss of properties.

Evaluation of Surface Roughness and Tensile Strength of Base Metal Alloys Used for Crown and Bridge on Recasting (Recycling).

Dental casting alloys play a prominent role in the restoration of the partial dentition. Casting alloys have to survive long term in the mouth and also have the combination of structure, molecules, wear resistance and biologic compatibility. According to ADA system casting alloys were divided into three groups (wt%); high noble, Noble and predominantly base metal alloys. To evaluate the mechanical properties such as tensile strength and surface roughness of the new and recast base metal (nickel-chromium) alloys. Recasting of the base metal alloys derived from sprue and button, to make it reusable has been done. A total of 200 test specimens were fabricated using specially fabricated jig of metal and divided into two groups- 100 specimens of new alloy and 100 specimens of recast alloys, which were tested for tensile strength on universal testing machine and surface roughness on surface roughness tester. Tensile strength of new alloy showed no statistically significant difference (p-value>0.05) from recast alloy whereas new alloy had statistically significant surface roughness (Maximum and Average surface roughness) difference (p-value<0.01) as compared to recast alloy. Within the limitations of the study it is concluded that the tensile strength will not be affected by recasting of nickel-chromium alloy whereas surface roughness increases markedly.

Evaluation of the Bond Strength of Ceramic to Nickel- Chromium Alloy with various proportions of Recast Alloy - An Invitro Study.

Aim: The purpose of this study was to evaluate the bond strength and point of failure between ceramic and Nickel-Chromium alloys with various proportions of fresh and recast alloy. Materials and method: Fresh and once recast nickel-chromium alloy were used in various proportions and divided into 5 groups, group A, B, C, D, E with 100%, 75%, 50%, 25% and 0% of fresh alloy respectively with 10 specimens in each group. All the metal specimens were veneered with VMK 95 ceramic and were then subjected to three point bend test and SEM analysis. Results: The values were statistically analyzed using One-way ANOVA and Bonferroni test. One-way ANOVA analysis showed a statistically significant difference (p < 0.001) in metal ceramic bond strength which decreased as the percentage of once recast Nickel-Chromium alloy increased. There was no statistically significant differences between Groups A, B and C but Group D and E showed statistically significant differences when compared with group A. SEM analysis showed, majority of the failure occurred at the metal- ceramic interface. Conclusion: When more than 50% fresh alloy was used in the casting procedure, the bond strength was found to be superior to that when less than 50% of fresh alloy was used. Upto 50% of once recast alloy does not have significant effect on the metal-ceramic bond strength.

Effects of environment on the release of Ni, Cr, Fe, and Co from new and recast Ni-Cr alloy

The addition of previously cast alloy to new alloy for economic reasons may increase the release of elements. The purpose of this study was to analyze the effects of the immersion period, immersion media, and addition of previously cast alloy to new alloy on the release of elements. Disk-shaped specimens were prepared from a Ni-Cr alloy (Ni: 61 wt%, Cr: 26 wt%, Mo: 11 wt%, Si: 1.5 wt%, Fe, Ce, Al, and Co <1 wt%) (Remanium CS; Dentaurum) with new alloy (group N) and 50% new/50% recast alloy (group R). After the immersion of the specimens in both NaCl (pH 4) and artificial saliva (pH 6.7) for 3, 7, 14, 30, and 60 days, the release of ions was determined by using atomic absorption spectrometry. Data were analyzed with a 3-way ANOVA (α=.001). The release of Ni was significantly affected by the immersion period, of Ni and Cr by the alloy and media (P<.01), and of Fe by the alloy (P<.01). Ion release from the recast alloy in artificial saliva was 109.71 for Ni, 6.49 for Cr, 223.22 for Fe, and 29.90 μg/L for Co. The release of Co in NaCl was below the detection limit in both groups. The release of Ni in NaCl and artificial saliva increased with the length of the immersion period in both groups. The release of Cr and Fe was higher in artificial saliva than in NaCl in group R, regardless of the immersion period. The release of Co in NaCl was below the detection limit in both groups.

Ceramometal Bond Strength Analysis using New and Recast Nonprecious Alloys with Three Different Ceramics

ABSTRACT Objectives This study is undertaken to evaluate the dependence of bond strength of 100% fresh nonprecious alloy and the combination of 50% recast (used) alloy and 50% fresh alloy with three different veneering ceramic material. Materials and methods To evaluate the shear bond strength between new and recast alloy nonprecious Ni-Cr alloy (System KN®, Adentatec, Germany) was used with three different commercially available ceramics. A total of 60 samples were prepared and divided in two groups depending on the new or recast alloy. The 30 specimens of new alloy (group A) and 30 specimens of recast alloy (group B) were fabricated. Each group was again divided into three subgroups of 10 specimens for ceramic veneering Vita VMK-95 [V], IPS Classic [I] and Noritake [N] as veneering ceramic materials. Thus, six subgroups were formed as groups AV, AI, AN, BV, BI and BN. Groups AV and BV were veneered with Vita Ceramics, Groups AI and BI were veneered with IPS Classic (Ivoclar) and Groups AN and BN were veneered with Noritake. Then, shear bond strength between new and recast alloy was analyzed for each type of ceramics using MTS machine. Results The bond strength between new [group A] and recast alloy [group B] using three different veneering ceramics were evaluated. It was found that the new or the fresh alloy had highest shear bond strength than the recast alloy. Statistically, it was found that there was significant difference in bond strength between the new and recast alloys, when same type of ceramics was compared. When comparing ceramics, the Noritake group had highest bond strength, while other groups, that is, Vita and Ivoclar had comparatively low bond strength. Conclusion From this study, conclusion can be drawn that the use of 50% recast alloy shows reduction in bond strength values. Therefore, the use of recast alloy should not exceed more than 50%, as it would compromise the properties of alloy and the efficacy of bond strength between ceramic and alloy. How to cite this article Gosavi S, Wadkar A, Gosavi SY. Ceramometal Bond Strength Analysis using New and Recast Nonprecious Alloys with Three Different Ceramics. Int J Prosthodont Restor Dent 2013;3(1):14-20.

Effect of alloy recasting on the color of opaque porcelain applied on different dental alloy systems

The effect of different proportions of recast dental alloys on the color of overlying opaque porcelain (OP) is unknown. The purpose of this study was to compare the color of OP applied on 2 different proportions (50% and 100%) of recast alloys with the color of commercially available shade tabs of OP. Six different metal alloy systems (2 base: Metalloy CC, Cr-Co [B-MCC]; Heraenium NA, Ni-Cr [B-HNA]; 3 noble: Cerapall 2, Pd-Au [N-CP2]; Triumph, Pd-Ag [N-T]; V-Deltaloy, Au-Pd [N-VD]; and 1 high-noble: V-Gnathos Plus, Au-Pt [HN-GP]) were selected for the fabrication of disk-shaped specimens (10 mm in diameter, 1 mm in thickness). Each alloy was divided into 2 subgroups: 50% new alloy with 50% recast alloy (n=3) and 100% recast alloy (n=3). OP (B1) was applied (0.1 mm) to all specimens. The color coordinates (L*, a*, b*) of each specimen and the corresponding commercially available OP shade tab (control) were measured with a spectroradiometer, and color differences between specimens and control group were calculated. Data were statistically analyzed (2-way ANOVA, Ryan-Einot-Gabriel-Welsch multiple range test, α=.05). For each alloy, ΔL*(L(control)(-)L(recastalloy)) values for the 2 subgroups were not statistically different from each other. The Δa* and Δb* of different proportions of N-CP2, B-HNA, N-VD, and HN-GP were not statistically different within the alloys. However, the a* values of 100% recast N-T and B-MCC were significantly closer to the a* values of the control group, and the b* values of 50% recast B-MCC were significantly closer to the b* values of the control group (P<.05). Delta E(control-recast) alloy values for different proportions of alloys were not statistically different. However, color differences did not meet the criterion of clinical acceptability (ΔE=3.46). According to the results of this study, the different proportions (50% and 100%) of recast alloys used have similar effects on the color of OP. Differences between the final color of OP on the recast alloys used and the color of OP shade guide tabs did not meet the criterion of clinical acceptability considered in this study.

Influence of recasting different types of dental alloys on gingival fibroblast cytotoxicity

Surplus alloy from the initial casting is commonly reused with the addition of new alloy. This recasting procedure could affect the cytotoxicity of dental alloys. The purpose of this in vitro study was to evaluate the effect of repeated casting of high-noble and base metal alloys on gingival fibroblast cytotoxicity. Disk-shaped specimens (5 × 2 mm, n=60) of a high-noble (Au-Pt) and 2 base metal (Ni-Cr and Cr-Co, n=20) alloys were prepared with 100% new alloy and 50%, 65%, and 100% once recast alloy. The elemental composition of specimens was analyzed with X-ray energy-dispersive spectroscopy. Five specimens from each group were conditioned in saline with 3% fetal bovine serum albumin. The conditioning media were analyzed for elemental release with atomic absorption spectroscopy. Cytotoxic effects were assessed on human gingival fibroblast with a 3-(4.5-dimethylthiazol-2-yl)-2.5-diphenyl tetrazolium bromide (MTT) colorimetric assay. The data were analyzed with 1-way and 2-way ANOVA and Tukey's HSD multiple comparison test (α-=.05). Elemental compositions of Co-Cr and Au-Pt alloys were significantly different among casting protocols. Elemental release of Co-Cr and Ni-Cr alloys was significantly different between new and recast specimens (P<.001). Nickel release increased with recast alloy addition. The 2-way ANOVA showed a significant effect of the casting procedure (P<.001) alloy group (P<.001) and their interaction for cytotoxicity (P<.001). The Ni-Cr alloy groups with 65% and 100% recast alloy had lower cellular activity than all other specimens (P<.001). The results of this study indicated that alloys containing nickel have increased cytotoxic effects and that composition of the alloys affected the cytotoxicity. Furthermore, recasting nickel-containing alloys with 65% surplus metal addition significantly increased the cytotoxic activity.

Effect of Surface Treatment on Elemental Composition of Recast NiCr Alloy

Objective: The aim of this study was to compare the effects of different surface treatments on the elemental composition stability of as-received and recast types of NiCr casting alloys. Material and Methods: Six commercial NiCr dental casting alloys (Kera N, Nodelco, Bellabond, Wiron 99, Metaplus VK, and Tritech D) were used in this study. Seventy-two specimens (12 × 12 × 1.2 mm) were produced using the lost-wax casting process. Three casting protocols were established in relation to the proportion of as-received and recast alloys: Group A (100% as-received metal), Group B (50 wt% new metal, 50 wt% once-recast metal), and Group C (100% once-recast metal). Two specimens in every group received two different surface treatments: sandblasting with 110 μmm Al2O3 or oxidation firing. An elemental analysis was performed with x-ray energy-dispersive spectroscopy. Results were subjected to one-way analysis of variance and Tukey HSD tests. Results: The elemental composition was significantly different in the casting groups and treatment groups (p < 0.05). The lowest mean weight percentage Ni value was recorded for Group C and the highest for Group A. Aluminum-oxide sandblasting of the alloy surface reduced the mean weight percentage for Cr. Conclusion: Recasting metal alloys may adversely affect surface quality.

An Invitro Analysis of Elemental Release and Cytotoxicity of Recast Nickel–Chromium Dental Casting Alloys

Recasting of the casting alloys affects the composition and elemental release which may have cytotoxic effect different from the pure alloy in the surrounding tissues. An Invitro study was conducted to investigate the elemental release and their cytotoxic effects from commercially available Ni-Cr dental casting alloys, commonly used for fabricating fixed partial dentures. Three Ni-Cr alloys [Wiron 99(A), Ceramet (B), and Hi Nickel CB (C)] were tested. Alloy specimens (disks 3×5mm) were casted and grouped as follows: Group I (A(1)/B(1)/C(1)): 100% pure alloy; Group II (A(2)/B(2)/C(2)): 50% new with 50% recast; and Group III (A(3)/B(3)/C(3)): 100% recast. Disks of each alloy type from each group were transferred to Dulbecco's modified eagle medium and left for 3days at 37°C in an atmosphere of 5% CO(2). Ni, Cr, Co, Cu and Mo elemental release from metal alloys into culture medium was investigated using Inductively Coupled Plasma Mass Spectrometry. Cytotoxicity was tested using mouse fibroblast cells and MTT Assay. Controls consisted of 6 wells containing cells with no alloy specimens. Data were analyzed by two-way analysis of variance followed by t-test. The total amount of elements released in parts per billion for various casting groups were Group I, A(1)-6.572, B(1)-6.732, C(1)-8.407; Group II, A(2)-22.046, B(2)-26.450, C(2)-29.189; Group III, A(3)-84.554, B(3)-88.359, C(3)-92.264. More amounts of elements were released in Hi Nickel CB than Ceramet and Wiron 99 in all the three test groups. Percentage of viable cells from MTT analysis were Group I, A(1)-62.342, B(1)-61.322 C(1)-60.593, Group II, A(2)-58.699, B(2)-56.494, C(2)-52.688, Group III, A(3)-53.101, B(3)-52.195, C(3)-47.586. The viable cells present in the culture media were more in Wiron 99 than Ceramet and Hi Nickel CB. Elemental release increased with amount of recast alloy. Amongst the three alloys tested Hi Nickel CB had significantly higher elements released compared to Ceramet and Wiron 99 in 100% pure alloys, 50% recast and 100% recast alloys. Wiron 99 showed least element release in 100% pure alloy, 50% recast and 100% recast specimens. 100% pure alloys of all three alloys are less cytotoxic, but their cytotoxicity is more on 50% and 100% re-casted alloys. Out of all three variations of casting Wiron 99 was least cytotoxic, followed by Ceramet and Hi Nickel CB. Recasting of alloys significantly increased the elements released and their cytotoxicity.

Corrosion Behavior of As‐Received and Previously Cast Type III Gold Alloy

The rationale for using gold alloys is based largely upon their alleged ability to resist corrosion, but little information is available to determine the corrosion behavior of recast alloys. This study characterized the elemental composition of as-received and recast type III gold alloy and examined the in vitro corrosion behavior in two media using a potentiodynamic polarization technique. Seventy-eight disk-shaped specimens were prepared from a type III gold alloy under three casting protocols according to the proportion of as-received and recast gold alloy (n = 26). (1) Group as received (100% as-received metal), (2) group 50% to 50% (50% wt. new metal, 50% wt. once recast metal), and (3) group recast (100% once recast metal). The surface structures of 20 specimens from each group were examined under scanning electron microscopy, and their elemental compositions were determined using X-ray energy-dispersive spectroscopy. Further, the potentiodynamic cyclic polarization between -1000 and +1000 mV (SCE) were performed for six specimens from each casting protocol in 0.09% NaCl solution (n = 3) and Fusayama artificial saliva (n = 3) at 37 degrees C. Zero-current potential and corrosion current density were determined. The data were analyzed with 1-way ANOVA and the Ryan-Einot-Gabriel-Welsch multiple-range test t (alpha= 0.05). Elemental composition was significantly different among the casting groups (p < 0.001). The mean weight percentage values were 72.4 to 75.7% Au, 4.5 to 7.0% Pd, 10.7 to 11.1% Ag, 7.8 to 8.4% Cu, and 1.0 to 1.4% Zn. The mean values for Zero-current potential and corrosion current density for all casting protocols were not significant (p > 0.05); however, the difference between the electrolytes was significant (p < 0.001). Fusayama artificial saliva seemed to offer the most corrosive environment. Type III gold alloy in any casting protocol retained passivity under electrochemical conditions similar to the oral environment. Moreover, high-gold type III alloys from reputable manufacturers and recasting protocol tested should produce acceptable corrosion-resistant castings.

Influence of recasting palladium-silver alloy on the fit of crowns with different marginal configurations

Dental laboratories may occasionally recast previously cast dental alloy to produce a prosthesis, but this process may have a negative influence on marginal adaptation. The aim of this study was to evaluate the cervical and internal fit of complete metal crowns that were cast and recast using palladium-silver alloy and 3 different marginal configurations: straight shoulder, 20-degree bevel shoulder, and 45-degree chamfer. Thirty aluminum dies were made, 10 for each marginal configuration. Each group of 10 was further divided into 2 subgroups (n=5), according to the alloy (Pors-on 4) casting history. The dies were waxed using a cylindrical metal matrix to standardize the thickness of the walls. The wax patterns were invested in a phosphate-bonded investment (Deguvest) and cast after heating in an oven (EDG), according to the manufacturer's instruction. The alloy was melted with an oxygen-gas heat source and cooled to room temperature after casting. Afterwards, the specimens were seated on the dies with a static load of 9 kgf for 1 minute. The marginal discrepancy was measured with a metric microscope, using a digital micrometer. All the measurements were done by the same operator. Each crown-die interface was measured 3 times on each of the 4 diametrically opposite points, for a total of 12 measurements for each specimen. Specimens were longitudinally sectioned to obtain 2 hemi-sections for internal discrepancy measurements, measured at 3 points: 1 in the center of the occlusal wall and 2 at each center of each axial wall. Three measurements were made for each point, for a total of 9 measurements per specimen. The results were submitted to parametric statistical 3-way analysis of variance followed by Tukey-Kramer HSD post hoc analysis (alpha=.05). The new alloy provided significantly better adaptation (P<.001) than the recast alloy for both marginal and internal discrepancy measurements. Marginal designs did not shown any statistical differences when the new metal was used. For recast metal, the straight shoulder showed significantly better adaptation (P<.001) than the 20-degree bevel shoulder and the 45-degree chamfered configurations, which were statistically similar to each other. The results of this study suggest that recasting procedures for crown fabrication should not be used with the palladium-silver alloy tested.

Dispersoids in Al–Li AA8090 series alloys

Chemical composition data of Al3Zr-type dispersoids obtained using the EDAX attached to the transmission electron microscopes in three commercial AA8090 series Al–Li alloys demonstrated the incorporation of Ti in these dispersoids. The extrapolation technique led to the composition of dispersoids to be Al3(Zr0.92Ti0.08). No dispersoids were found other than Al3Zr-type in these alloys although one of the alloys contained Mn. Appearance of Mn-rich dispersoids in one of the re-cast alloys which contained Mn showed that the solubility of Mn in Al is significantly influenced by the Li concentration in Al–Li alloy systems.

Observation of dynamic thermal processes induced by α-particle impact on sapphire

The effect of different proportions of recast dental alloys on the color of overlying opaque porcelain (OP) is unknown.The purpose of this study was to compare the color of OP applied on 2 different proportions (50% and 100%) of recast alloys with the color of commercially available shade tabs of OP.Six different metal alloy systems (2 base: Metalloy CC, Cr-Co [B-MCC]; Heraenium NA, Ni-Cr [B-HNA]; 3 noble: Cerapall 2, Pd-Au [N-CP2]; Triumph, Pd-Ag [N-T]; V-Deltaloy, Au-Pd [N-VD]; and 1 high-noble: V-Gnathos Plus, Au-Pt [HN-GP]) were selected for the fabrication of disk-shaped specimens (10 mm in diameter, 1 mm in thickness). Each alloy was divided into 2 subgroups: 50% new alloy with 50% recast alloy (n=3) and 100% recast alloy (n=3). OP (B1) was applied (0.1 mm) to all specimens. The color coordinates (L*, a*, b*) of each specimen and the corresponding commercially available OP shade tab (control) were measured with a spectroradiometer, and color differences between specimens and control group were calculated. Data were statistically analyzed (2-way ANOVA, Ryan-Einot-Gabriel-Welsch multiple range test, α=.05).For each alloy, ΔL*(Lcontrol−Lrecastalloy) values for the 2 subgroups were not statistically different from each other. The Δa* and Δb* of different proportions of N-CP2, B-HNA, N-VD, and HN-GP were not statistically different within the alloys. However, the a* values of 100% recast N-T and B-MCC were significantly closer to the a* values of the control group, and the b* values of 50% recast B-MCC were significantly closer to the b* values of the control group (P<.05). Delta Econtrol-recast alloy values for different proportions of alloys were not statistically different. However, color differences did not meet the criterion of clinical acceptability (ΔE=3.46).According to the results of this study, the different proportions (50% and 100%) of recast alloys used have similar effects on the color of OP. Differences between the final color of OP on the recast alloys used and the color of OP shade guide tabs did not meet the criterion of clinical acceptability considered in this study.