Noble Alloys Research Articles

Comparison of the load at failure of soldered and nonsoldered porcelain- fused-to-metal crowns

Statement of problem The application of solder material to metal frameworks could affect the porcelain-to-metal failure load and possibly compromise the longevity of porcelain-fused-to-metal crowns. Purpose This in vitro study assessed the influence of solder on the porcelain failure load between metal and porcelain, using crown-shaped specimens. Material and methods Forty standardized crown patterns were fabricated on a metal die and cast with noble alloy (Protocol). The specimens were divided into test (soldered, n=20) and control (nonsoldered, n=20) groups. A 2-mm–diameter perforation was produced on the buccal surface of the test specimens, 1.5 mm apical to the junction between occlusal and buccal surfaces. The perforation was repaired with high-fusing white ceramic solder material. All castings were finished with aluminum oxide stones and airborne-particle abraded with 50-μm aluminum oxide at 75 psi of pressure. Two layers each of opaque and dentin porcelain were applied on all specimens. All crowns were subjected to a vertical compressive load with a universal testing machine at a crosshead speed of 0.5 mm/min until fracture. The loading apparatus of the device contacted the buccal cusp only. In both control and test groups, 10 crowns were loaded with a stainless steel pin (phase I) whereas the remaining 10 in each group were loaded with a carbon steel pin (phase II). Means of loads at failure were recorded in each group for each pin type and compared (soldered vs nonsoldered) by use of a t test (α=.05). Results Mean failure load for nonsoldered crowns was 349 ± 63 kgf in phase I and 228 ± 49 kgf in phase II. Soldered crowns showed a significantly lower failure load (265 ± 82 kgf [phase I; P<.02] and 154 ± 108 kgf [phase II; P<.04]) and a greater standard deviation. Conclusion Soldered metal-porcelain crown specimens demonstrated a significantly lower load at failure. Within the limits of this study, it was concluded that solder material might negatively affect porcelain-metal crowns.

An in vitro comparison of tensile bond strengths of noble and base metal alloys to enamel

Statement of problem Many different surface treatments have been used to increase the bond strength of noble and base metal alloys to enamel, but only a few have been studied. Purpose The purpose of this in vitro study was to compare the tensile bond strength of a tin-plated noble alloy, an Alloy Primer–treated noble alloy, and an airborne particle–abraded base metal alloy, all bonded to enamel with a phosphate-methacrylate resin luting agent. Material and methods Seventy noncarious molar teeth were extracted, cleaned, and embedded in autopolymerizing acrylic resin with the buccal surface of the teeth exposed. Seventy wax patterns (4-mm diameter × 2-mm thickness) were waxed, invested, and cast—50 with a noble alloy (Argedent 52) and 20 with a base metal alloy (Argeloy N.P.). Twenty of the noble alloy specimens were tin-plated (TP), 20 noble alloy specimens were treated with Alloy Primer (AP), and 20 base metal alloy specimens were airborne particle abraded (AA). All specimens were luted with a phosphate-methacrylate resin luting agent (Panavia F) and stored in 100% humidity at 37°C, half for 24 hours and half for 7 days. Ten noble alloy specimens were tin-plated and stored in water for 48 hours (aged) before cementation and then stored in water for 24 hours after cementation. These specimens were used to test whether there is an advantage to aging the tin-plated surface in water before cementation. All specimens were thermocycled (5° to 55°C) for 500 cycles and then tested for tensile bond strength (TBS), measured in MPa, with a universal testing machine at a crosshead speed of 0.5mm/min. Various castings (n=6 per test group) were randomly selected from each group and inspected under a scanning electronic microscope to determine mode of failure. The mean values and standard deviations of all specimens were calculated for each group. A 2-way analysis of variance (ANOVA) was performed, and multiple pairwise comparisons were then completed with post hoc Tukey test (α=.05). Results The TBS of the tin-plated noble alloy specimens bonded to enamel (24 hours: 9.33 ± 1.31 MPa; 7 days: 11.65 ± 1.55 MPa) was significantly greater than the Alloy Primer noble alloy specimens (24 hours: 6.11 ± 1.01 MPa; 7 days: 5.45 ± 1.22 MPa) ( P < .001). The Alloy Primer noble alloy group showed the lowest TBS compared with the tin-plated noble alloy and airborne particle–abraded base metal alloy group (24 hours: 10.61 ± 1.41 MPa; 7 days: 6.94 ± 1.40 MPa). The tin-plated noble alloy specimens showed greater TBS after storage for 7 days in distilled water compared with storage for 24 hours (24 hours: 9.33 ± 1.31 MPa; 7 days: 11.65 ± 1.55 MPa). Aging the tin-plated noble alloy for 48 hours in 37°C (9.17 ± 1.68 MPa) prior to cementation did not increase the TBS to enamel. The airborne particle–abraded base metal alloy showed significantly lower TBS at the 7-day storage time compared to the 24-hour storage time (24 hours: 10.61 ± 1.41 MPa; 7 days: 6.94 ± 1.40 MPa) ( P < .001). SEM examination of the debonded metal and enamel surfaces showed mixed (adhesive and cohesive) failures for all groups. Conclusion Tin-plating a noble alloy produced the highest bond strength to enamel. Storing the tin-plated noble alloy in 37°C distilled water for 48 hours before cementation did not result in a change in TBS. Using an Alloy Primer with a noble alloy resulted in statistically significant lower TBS than tin-plating.

The retention of complete crowns prepared with three different tapers and luted with four different cements

Statement of problem The role of adhesive properties of cements on the retentive strength of crowns with different degrees of taper is not clear. Purpose This study evaluated the retention of full crowns prepared with 3 different tapers and cemented with 2 conventional and 2 adhesive resin cements. Material and methods One hundred twenty sound human molar teeth were assigned randomly to 1 of 12 groups, (n=10). The groups represented the 4 cements: zinc phosphate (Fleck’s), a conventional glass ionomer (Ketac-Cem); 2 adhesive resin cements (C&B Metabond and Panavia); and 3 tapers of 6-degrees, 12-degrees, and 24-degrees within each cement. Crowns were cast with a high noble alloy. The 6-degree taper was considered the control within each cement group. Retention was measured (MPa) by separating the metal crowns from the prepared teeth under tension on a universal testing machine. Analysis of variance was used to test the main effects on the retentive strength of full crowns, namely cements, tapers, and failure modes. The Fisher’s multiple comparison test was used to evaluate the source of the differences. The χ 2 analyses were used to examine the relationships between failure types, cements, and tapers. All statistical tests were conducted at α=.05. Results There was a significant difference in the main effect cement ( P<.0001) and taper ( P=.0002). The mean retentive strength values of both Fleck’s and Ketac-Cem were significantly lower than the mean retentive strength values of both C&B Metabond and Panavia ( P<.0001). The retention of crowns prepared with 6-degree taper was not significant from the 12-degree taper ( P=.0666). The difference in retention was significant between the 6-degree taper and the 24-degree taper ( P<.0001) and between12-degree taper and 24-degree taper ( P=.0178). The types of failure were adhesive in the cement (65%), cohesive in the tooth (31%), and assembly failure (fracture of embedding resin) (4%). The type of failure was dependent on the degree of taper ( P<.0001) and on the type of cement ( P<.0042). Conclusion Within the limitations of this study, the retentive values of the adhesive resins at 24-degree taper were 20% higher than the retentive values of the conventional cements at 6-degree taper. The use of resin luting agents yielded retention values that were double the values of zinc phosphate or conventional glass ionomer cement.

The heat-activated solderless passivation (HASP) technique for correcting nonpassive-fitting bars without soldering.

The fabrication of a cast noble alloy overdenture bar entails a variety of clinical and laboratory steps, each of which can potentially generate distortions that result in the non-passive fit of the finished product. Traditional laboratory procedures to correct the misfit of cast bars entail sectioning the bar, then reconnecting the bar segments by soldering or welding. After such procedures, research has shown that the bar may still not fit passively on the implant abutments in the patient's mouth. In addition, the overall structure of the bar would be weaker at the mended joints. The heat-activated solderless passivation (HASP) technique involves a two-step process of correcting the master cast, then attaching the cast bar to a soldering index and applying heat to relax the metal until the tensile forces of the retention screws pull the bar into a passive fit.

Influences on human internal exposure to environmental platinum.

Different influences on internal exposure to platinum are investigated and for the first time weighted in environmentally exposed subjects as far as individual internal platinum concentrations are concerned. Detailed medical and environmental histories as well as oral cavity status were assessed in 84 dermatological patients, and internal platinum exposure was determined by analyzing platinum in urine using adsorptive voltammetry (AV). Platinum concentrations ranged from <0.9 (detection limit) to 65.5 ng Pt/l urine. Influence of different types and age of alloy restorations and therefore relevance of the exposure pathway due to solubilization of platinum in saliva could be demonstrated. No platinum-related health effects (contact stomatitis, asthma or kidney conditions) were observed. Analysis of covariance showed the number of noble dental alloy restorations (P<0.0001) and to a lesser extent age (P=0.0017) to independently influence internal platinum exposure. Even though spread of environmental platinum has increased, internal platinum exposure is low in subjects without assessable medical or dental devices (usually <4.5 ng/l urine) and not related to adverse health effects. For the first time, detailed individual information on possible exposure pathways to platinum were considered in an analysis of relevant influential factors: Car traffic exposure and dermatological condition showed no association with internal platinum exposure. Uptake from platinum containing noble metal dental alloy restorations (NMDAR) is of greatest relevance, surmounting the influence of each year of lifetime on platinum body load by more than 10-fold.

Self-accommodating martensite plate variants in shape memory CuAlNi alloys

In noble metal copper-based β-phase alloys, which exhibit the shape memory effect, martensitic transformation occurs by lattice invariant shears on close-packed {1 1 0} β planes of the matrix, called the basal plane of the martensite. The parent single crystal undergoes the martensitic transformation on cooling in a self-accommodating manner minimising the total shape change at the advanced stage of the transformation. These alloys are deformed by variant-to-variant transformation when stressed in the martensite state. The reversible shape memory effect is also considered in terms of the correspondence-variants and the formation of each martensite is accompanied by a definite shape deformation. The so-called self-accommodation is achieved by combining suitable correspondence-variants. In a single crystal of the parent phase, 24 martensite variants grouped around six {1 1 0} β planes can be formed at temperatures lower than M s. In the present study, configurations of the martensite variants in CuAlNi alloys have been investigated by an electron microscope technique.

Electrochemical impedance spectroscopy study of high-palladium dental alloys. Part I: behavior at open-circuit potential.

Electrochemical impedance spectroscopy (EIS) was used to study the in vitro corrosion of three representative high-palladium alloys and a gold-palladium alloy for comparison. The corrosion resistances (measured as the charge transfer resistance R(CT) from an equivalent circuit) of the high-palladium alloys and the gold-palladium alloy were comparable in simulated body fluid and oral environments, and under simulated dental plaque. The great similarity in corrosion behavior for the three high-palladium alloys is largely attributed to their substantial palladium content and passivity in the laboratory test media, and possibly to their similar structure at the submicron level. Differences in composition and microstructure at the micron level and greater, including the effects of heat treatment simulating the firing cycles for dental porcelain, do not have noteworthy effects on the in vitro corrosion of the three high-palladium alloys. Good accuracy and convenience of extracting corrosion characteristics from equivalent circuit modeling, along with the capability of providing intrinsic information about the corrosion mechanism, enable EIS to be an excellent alternative method to conventional potentiodynamic polarization for evaluating the corrosion behavior of noble dental alloys.

Shear bond strengths of 2 intraoral porcelain repair systems to porcelain or metal substrates

Statement of Problem. When clinical fractures of the ceramic veneer on ceramometal can be repaired, the need for remake can be eliminated or postponed. A number of ceramic repair materials are available; bond strength data would be useful for predicting the success of a given repair system. Purpose. This in vitro study evaluated shear bond strengths of 2 porcelain repair systems intended for intraoral bonding of resin to porcelain and metal. Material and Methods. Sixty cylindrical specimens were fabricated with feldspathic porcelain and/or a high noble alloy: 20 porcelain (P), 20 porcelain and metal (PM), and 20 metal (M). Specimens were divided into subgroups of 10, and resin composite cylinders were bonded with 1 of 2 systems: CoJet-System (CJ) or Ceramic Repair (CR). Bonded specimens were stored in 37°C distilled water for 24 hours before being thermocycled at 5°C to 55°C for 300 cycles with a 30-second dwell time. The specimens then were stored for an additional 8 days before being subjected to shear force in a universal testing machine at a crosshead speed of 5 mm/min. Stress at failure was calculated in MPa, and mode of failure was recorded. Analysis of variance (ANOVA) was applied to the data. Comparisons between substrates were made with the Duncan multiple range test (P <.05), and differences between the 2 repair systems within like substrate groups were examined with the Student t test. Results. Bonding groups exhibited the following values in megapascals: PM-CR = 19.3 ± 4.1; PM-CJ = 25.0 ± 3.1; M-CR = 14.3 ± 4.9; M-CJ = 23.0 ± 2.3; P-CR = 18.3 ± 4.2; P-CJ = 22.4 ± 5.6. The ANOVA results showed significant differences between the CJ and CR groups. The Student t test revealed that the mean data for the CJ groups were significantly higher than for the CR groups (P <.05). The Duncan multiple range test demonstrated significant differences between the PM and M groups (P <.05) for the CR system only. Conclusion. Under the conditions of this study, CJ achieved significantly higher bond strengths to PM and M substrates. Significant differences in strength were found between PM and M, but only within the CR system. (J Prosthet Dent 2001;86:526-31.)

Bond strength of binary titanium alloys to porcelain

The purpose of this study was to investigate the bond strength between porcelain and experimental cast titanium alloys. Eleven binary titanium alloys were examined: Ti–Cr (15, 20, 25 wt%), Ti–Pd (15, 20, 25 wt%), Ti–Ag (10, 15, 20 wt%), and Ti–Cu (5, 10 wt%). As controls, the bond strengths for commercially pure titanium (KS-50, Kobelco, Japan) and a high noble gold alloy (KIK, Ishifuku, Japan) were also examined. Castings were made using a centrifugal casting unit (Ticast Super R, Selec Co., Japan). Commercial porcelain for titanium (TITAN, Noritake, Japan) was applied to cast specimens. The bond strengths were evaluated using a three-point bend test according to ISO 9693 . Since the elastic modulus value is needed to evaluate the bond strength, the modulus was measured for each alloy using a three-point bend test. Results were analyzed using one-way ANOVA/S-N–K test ( α=0.05). Although the elastic moduli of the Ti–Pd alloys were significantly lower than those of other alloys ( p=0.0001), there was a significant difference in bond strength only between the Ti–25Pd and Ti–15Ag alloys ( p=0.009). The strengths determined for all the experimental alloys ranged from 29.4 to 37.2 MPa, which are above the minimum value required by the ISO specification (25 MPa).

The influence of intracrevicular crown margins on gingival health: Preliminary findings

Statement of problem. The effect on gingival tissue of various crown materials in combination with different abutment biomaterials should be investigated. Purpose. This in vivo study determined the gingival health and subgingival levels of periodontal inflammation-associated bacteria adjacent to various crown and abutment material combinations. Material and methods. Patients in the study received 1 of 5 treatments: an all-ceramic crown luted to a natural tooth, a metal-ceramic (titanium) crown luted to natural tooth, a metal-ceramic (high noble alloy) crown luted to natural tooth, an all-ceramic crown luted to a titanium implant abutment, or a metal-ceramic (high noble alloy) crown luted to a titanium implant abutment. Plaque was collected at least 6 months after luting by paper point from the gingival sulcus of each crown and an adjacent unrestored (control) tooth. DNA probe analysis was performed to determine the levels of Porphyromonas gingivalis, Prevotella intermedia, and Actinobacillus actinomycetemcomitans. In addition, plaque, gingival redness, swelling, and bleeding scores were recorded with use of the California Dental Association scale. Statistical analysis was used to determine the effect of restoration/abutment type on levels of the bacterial species and clinical parameters pertaining to gingival health. Results. None of the sulci sampled contained detectable levels of the 3 bacteria. Plaque levels and gingival redness, swelling, and bleeding scores were low. All treatment groups had similar soft tissue response as measured by gingival redness, swelling, and bleeding. Plaque scores from all-ceramic crown/implant abutment sites were higher than plaque scores from all-ceramic crown/natural tooth sites. However, differences between experimental and control sites within the same treatment group were not observed (P>.05) with any of the 4 clinical measures. Conclusion. In patients with suitable oral hygiene, tooth-supported and implant-supported crowns with intracrevicular margins were not predisposed to unfavorable gingival and microbial responses. (J Prosthet Dent 2001;85:461-5)

Properties of opaque resin composite containing coated and silanized titanium dioxide.

Titanium dioxide (TiO2) is mainly used as a pigment in opaque resin composites for application to the surface of a metal framework. The hypothesis in this paper is that particles of silica/alumina (SiO2/Al2O3)-coated TiO2 treated with a silane coupling agent could bond effectively with resin monomers of opaque resin composites. Untreated TiO2 was used as the control filler. Compressive and flexural strength specimens were prepared by the heat-curing method, because these bulk specimens could not be made by the typical photo-curing method. The treated composite had significantly higher compressive and flexural strengths than the untreated composite after 6 months' immersion in water. Scanning electron microscopy of the fractured composite surfaces showed an interface failure between TiO2 and resin for the untreated composite and cohesive failure within the resin for the treated composite after 6 months' immersion. The light-activated opaque resin composite containing treated TiO2 exhibited significantly higher bond strength to a noble dental alloy after 5000 thermal cycles than that containing untreated TiO2. Thus, silanized SiO2/Al2O3-coated TiO2 appears to be clinically useful as a filler of opaque resin composites.

Evolution of nanoporosity in dealloying.

Dealloying is a common corrosion process during which an alloy is 'parted' by the selective dissolution of the most electrochemically active of its elements. This process results in the formation of a nanoporous sponge composed almost entirely of the more noble alloy constituents. Although considerable attention has been devoted to the morphological aspects of the dealloying process, its underlying physical mechanism has remained unclear. Here we propose a continuum model that is fully consistent with experiments and theoretical simulations of alloy dissolution, and demonstrate that nanoporosity in metals is due to an intrinsic dynamical pattern formation process. That is, pores form because the more noble atoms are chemically driven to aggregate into two-dimensional clusters by a phase separation process (spinodal decomposition) at the solid-electrolyte interface, and the surface area continuously increases owing to etching. Together, these processes evolve porosity with a characteristic length scale predicted by our continuum model. We expect that chemically tailored nanoporous gold made by dealloying Ag-Au should be suitable for sensor applications, particularly in a biomaterials context.

Electrooxidation of acetals for direct hydrocarbon fuel cell applications

Some acetals (e.g., methylal, ethylal and 1,3-dioxolane) were oxidized in different supporting electrolytes and on various electrodes, including oxide-based electrodes dispersed onto carbon powder. The electrooxidation of ethylal and 1,3-dioxolane was demonstrated for the first time. The fuel that exhibited the lower overvoltage from the electrooxidation curve was deduced. Then, from an analysis of the reaction products from long-term anodic experiments, the electrode reactions were deduced. It was shown that the anodic polarization of the electrooxidation of acetals in an acid medium is lower than that of methanol. Thus, acetals seem to be better fuels for fuel cell applications than methanol. It was also shown that ethylal and 1,3-dioxolane are oxidised more easily than methylal for fuel cell applications. Volcano behaviour was obtained for the plot of direct oxidation current density vs metal radius for various single noble metal electrodes. The highest current density was obtained with the Pt-based electrode. Similar behaviour was obtained with electrodes based on noble binary platinum alloys, where the electrooxidation current density increases with the difference in metal radius in each alloy (ΔR). Thus, the alloys that give the highest |ΔR|, e.g. Pt–Ru and Pt–Sn, exhibit the best electrooxidation current density.

Micromotion and dynamic fatigue properties of the dental implant–abutment interface

Statement of problem. Clinical loading may result in micromotion and metal fatigue in apparently stable implant screw joints. This micromotion may contribute to tissue inflammation and prosthesis failure.Purpose. This study investigated dental implant screw joint micromotion and dynamic fatigue as a function of varied preload torque applied to abutment screws when tested under simulated clinical loading.Material and methods. Fifteen noble alloy single-tooth implant restorations, each containing a hexed UCLA-style gold cylinder, were randomly assigned to 3 preload groups (16, 32, and 48 N·cm). Each group consisted of 5 implants (each 3.75 × 15 mm) and 5 square gold alloy abutment screws. A mechanical testing machine applied a compressive cyclic sine wave load between 20 and 130 N at 6 Hz to a contact point on each implant crown. A liquid metal strain gauge recorded the micromotion of the screw joint interface after 100, 500, 1,000, 5,000, 10,000, 50,000, and 100,000 cycles. Baseline data at 0 N·cm were collected before the application of the specified preload torque.Results. The 16 N·cm group exhibited greater micromotion (P<.001) than both the 32 and 48 N·cm groups at all cycle intervals (2-way ANOVA, Tukey HSD). Micromotion of the implant-abutment interface remained constant (P=.99) for each of the preload groups through 105 cycles.Conclusion. Under the loading parameters of this study, no measurable fatigue of the implant–abutment interface occurred. However, dental implant screw joints tightened to lower preload values exhibited significantly greater micromotion at the implant–abutment interface. (J Prosthet Dent 2001;85:47-52.)

Tensile bond strength of resin‐modified glass‐ionomer cement to microabraded and silica‐coated or tin‐plated high noble ceramic alloy

The purpose of this study was to evaluate the influence of alloy surface microabrasion, silica coating, or microabrasion plus tin plating on the tensile bond strengths between a resin-modified glass-ionomer luting cement and a high-noble alloy. Bond strength between the microabraded alloy specimens and conventional glass-ionomer cement or resin cement were included for comparison. One hundred twenty uniform size, disk-shaped specimens were cast in a noble metal alloy and divided into 6 groups (n = 10 pairs/group). The metal surfaces of the specimens in each group were treated and cemented as follows. Group 1: No surface treatment (as cast, control), cemented with a resin-modified glass-ionomer cement. Group 2: Microabrasion with 50-microm aluminum oxide particles, resin-modified glass-ionomer cement. Group 3: A laboratory microabrasion and silica coating system, resin-modified glass-ionomer cement. Group 4: Microabrasion and tin-plating, resin-modified glass-ionomer cement. Group 5: Microabrasion only, conventional glass-ionomer cement. Group 6: Microabrasion and tin-plating, conventional resin cement. The uniaxial tensile bond strength for each specimen pair was determined using an Instron Universal Testing Machine (Instron Corp, Canton, MA). Results were analyzed using a one-way analysis of variance (alpha = 0.05) and a Tukey post-hoc analysis. Mean bond strength: Group 1: 3.6 (+/- 1.5) MPa. Group 2: 4.2 (+/-0.5) MPa. Group 3: 6.7 (+/- 0.9) MPa. Group 4: 10.6 (+/- 1.8) MPa. Group 5: 1.1 (+/- 0.4) MPa. Group 6: 14.6 (+/- 2.3) MPa. Group 6 was significantly stronger than Group 4. The bond strength of specimens cemented with the resin-modified glass-ionomer cement using microabrasion and tin-plating (Group 4) was significantly stronger than all other groups except the resin cement with microabrasion and tin-plating (Group 6). Microabraded and tin-plated alloy specimens luted with the resin-modified glass-ionomer cement resulted in the greatest mean tensile strengths for the resin-modified glass-ionomer cement groups. This strength was 73% of the mean tensile strength of microabraded specimens luted with resin cement.

Tensile bond strength of resin-modified glass-ionomer cement to microabraded and silica-coated or tin-plated high noble ceramic alloy

Tensile bond strength of resin-modified glass-ionomer cement to microabraded and silica-coated or tin-plated high noble ceramic alloy

Comparison of the tensile bond strength of high-noble, noble, and base metal alloys bonded to enamel

Statement of problem. Although the bond strengths of various resin composite luting materials have been reported in the literature, the evaluation of these systems with various cast alloys of different compositions has not been competely clarified. Purpose. To evaluate the tensile bond strength of sandblasted high-noble, noble, and base metal alloys bonded to etched enamel by 2 different bonding agents of different chemical composition: Panavia-Ex (BIS-GMA) and Super-Bond (4-META acrylic). Material and methods. Flat enamel surfaces were prepared on buccal surfaces of 60 extracted noncarious human incisors. Teeth were divided into 3 groups of 20 each. Twenty circular disks of 5 mm diameter were prepared for casting for each group. Group I was cast with a high-noble, group II with a noble, and group III with a base metal alloy. The surfaces of the disks were sandblasted with 250 μm Al2O3. Ten disks of each group were bonded to exposed enamel surfaces with Super-Bond and 10 disks with Panavia-Ex as recommended by the manufacturer. The tensile bond strength was measured with an Instron universal testing machine with a crosshead speed of 0.5 mm/min until failure occurred. Results. Two-way ANOVA was used to evaluate the results. The differences in bond strengths of Super-Bond and Panavia-Ex with different alloys were not significant. The highest bond strengths were obtained in base metal alloys, followed by noble and high-noble alloys. These results were significant. Conclusion. Panavia-Ex and Super-Bond exhibited comparable tensile bond strengths. For both luting agents, the highest bond strengths were achieved with base metal alloys and the lowest with high-noble alloys. (J Prosthet Dent 2000;84:561-6.)

Effect of a new metal primer on the bond strength between a resin cement and two high-noble alloys

Statement of problem. With the development of new adhesive resin cements, the question of surface treatment of noble metal castings with primers has become an important issue. Purpose. This study compared the tensile bond strength and its durability of a new metal primer (Alloy Primer, Kuraray) to 2 noble metal alloys (Au-Ag-Cu-Pt and Au-Pt-Pd-Ag-In). Material and methods. Sixty cast disk specimens of each alloy were polished, grit blasted with 50 μm Al2O3, and ultrasonically cleaned in 96% isopropanol. Then, they were either nonprimed or primed only with the Alloy Primer or Alloy Primer combined with ED Primer (Kuraray). Plexiglas tubes filled with self-curing composite resin (Clearfil FII, Kuraray) were bonded to the metal samples with the use of an alignment apparatus and a self-curing luting cement (Panavia 21 Ex). The samples were stored in water, either for 3 days with no thermal cycling or for 150 days with 37,500 thermal cycles. After the different storage conditions, the tensile bond strengths of the specimens were determined. Results. The mean bond strengths increased over storage time for all groups, except for the grit-blasted Au-Pt-Pd-Ag-In group. However, only in the grit-blasted and the primed groups for the Au-Ag-Cu-Pt alloy was this increase significantly different (P<.01). After 150 days of storage, the mean bond strength to Au-Ag-Cu-Pt alloy was 38.8 MPa without priming, whereas it was 40.6 to 40.8 MPa with the use of the primers. After the same time, the mean bond strength to the Au-Pt-Pd-Ag-In alloy was 20.6 MPa without priming, whereas it was 31.9 to 37.8 MPa with the use of the primers. When comparing the different bonding methods and different storage times for the alloys, the superiority of the usage of both primers in combination was determined. Conclusion. The tested Alloy Primer significantly improved the bond strength of the dental adhesive resin cement (Panavia 21 Ex) to noble alloys. However, this effect depended on the alloy composition and was much greater for the Au-Pt-Pd-Ag-In alloy than for the Au-Ag-Cu-Pt alloy. (J Prosthet Dent 2000;84:554-60.)

Cytotoxicity of dental alloys, metals, and ceramics assessed by Millipore filter, agar overlay, and MTT tests

Statement of Problem: Biocompatibility of dental materials is dependent on the release of elements from the materials. In addition, the composition, pretreatment, and handling of the materials influence the element release. Purpose: This study evaluated the cytotoxicity of dental alloys, metals, and ceramics, with specific emphasis on the effects of altering the composition and the pretreatment. Material and Methods: By using cells from a mouse fibroblast cell line and the agar overlay test, Millipore filter test, and MTT test, cytotoxicity of various metals, metal alloys, and ceramics for dental restoration were studied. Effects of altering the composition of a high noble gold alloy and of pretreatment of a ceramic-bonding alloy were also studied. In addition, the release of elements into the cell culture medium by the materials studied was measured using an inductively coupled plasma optical emission spectrophotometer. The results of the MTT test were analyzed statistically using ANOVA and Scheffé test at a significance level of P <.05. Results: Specimens manufactured from materials intended for dental restorations and handled in accordance with the manufacturers’ instructions were ranked from “noncytotoxic” to “mildly cytotoxic” according to the agar overlay and Millipore filter tests. For the MTT test, no significant differences were observed between these materials and controls, with the exception of JS C-gold and unalloyed titanium. The modified materials were ranked from “mildly cytotoxic” to “moderately cytotoxic” in the agar overlay and Millipore filter tests and from “noncytotoxic” to “moderately cytotoxic” in the MTT test. Thus, cytotoxicity was related to the alloy composition and treatment. The release of Cu and Zn seemed to be important for the cytotoxic effect. Conclusion: Alterations in the composition and the pretreatment can greatly influence the cytotoxicity, and the results stress the importance of carefully following the manufacturers’ instructions when handling dental materials. (J Prosthet Dent 2000;84:229-36.)

Effect of ring liner and casting ring temperature on the dimension of cast posts

Statement of Problem: If a post does not fit passively, binding with the radicular tooth structure occurs, possibly increasing the risk for root fracture. Therefore, it is necessary to fabricate slightly undersized cast posts to allow for passive fit and cement placement. Shrinkage of the mold cavity may be a desired effect during the casting of posts. Purpose: This study evaluated the influence of: (1) a cellulose ring liner, and (2) a lower casting temperature of the metal ring, on the dimensions of a cast post. Material and Methods: Eighty plastic posts were divided in 4 equal groups (group 1, 815°C, liner; group 2, 815°C, no liner; group 3, 600°C, liner; and group 4, 600°C, no liner), invested in phosphate-bonded investment and cast with a noble alloy. Posts were measured at 2 locations, the tip and base, before and after casting. Results: Investing in a lined metal ring and using a casting ring temperature of 815°C (group 1) resulted in markedly oversized posts (tip: +25.8 μm; base: +20.3 μm). The absence of the cellulose liner in the casting ring (group 2) decreased the expansion of the investment producing slightly oversized castings (tip: +9.75 μm; base: +4.52 μm). Lined rings that were heated to a final temperature of 600°C (group 3) produced posts that were oversized (tip: +16.65 μm; base: +11.05 μm). Final casting ring temperature of 600°C and the absence of a cellulose liner (group 4) resulted in posts slightly undersized (tip: –4.1 μm; base: –2.2 μm). Conclusion: The use of 2 casting ring temperatures (815°C or 600°C) and the influence of a ring liner were investigated. Decreasing the casting ring temperature from 815°C to 600°C and the absence of a ring liner significantly decreased the dimensions of a cast post. (J Prosthet Dent 2000;84:32-7.)