High Noble Alloy Research Articles

The effect of a resin-based sealer on crown retention for three types of cement

<h2>Abstract</h2><h3>Statement of problem</h3> In an effort to control postoperative sensitivity, dentin sealers are being applied following crown preparation with little knowledge of how crown retention might be affected. A previous study demonstrated no adverse effect when using a glutaraldehyde-based sealer, and existing studies have shown conflicting results for resin-based products. <h3>Purpose</h3> This study determined if a resin sealer applied to prepared dentin affected retention of cemented castings when using 3 common types of luting agents. <h3>Material and methods</h3> Extracted human molars (n=55) were prepared with a flat occlusal, 20-degree taper, and 4-mm axial length. The axial surface area of each preparation was determined and specimens were distributed equally among groups (n=11). A 2-step, single-bottle adhesive system (One Step) was used to seal dentin following tooth preparation. Sealer was not used on the control specimens except for the modified-resin cement (Resinomer) specimens that required use of adhesive with cementation. Using ceramometal high noble alloy (Olympia), a casting was produced for each specimen and cemented with a seating force of 20 Kg using either zinc phosphate (Fleck's), glass ionomer (Ketac-Cem) or modified-resin cement (Resinomer) with the single-bottle adhesive. Castings were thermal cycled at 5°C and 55°C for 2500 cycles; then removed along the path of insertion using a universal testing machine at 0.5 mm/min. A single-factor ANOVA was used with α=.05. The nature of failure was also recorded and the data analyzed with a chi-square test. <h3>Results</h3> Mean dislodgment stresses for unsealed and sealed conditions were 3.7 ± 1.0 and 2.2 ± 0.8 MPa for zinc phosphate; 2.7 ± 1.2 and 4.2 ± 0.9 MPa for glass ionomer, respectively (<i>P</i><.001). Retentive stress of castings cemented with modified-resin cement was 6.4 ± 1.7 MPa. With resin sealer in combination with zinc phosphate, cement resided totally on castings in 82% of the situations and was on both surfaces without sealer. The tooth failed before casting dislodgent in 9 of 11 specimens cemented with modified-resin cement. <h3>Conclusions</h3> Resin sealer decreased casting retentive stress by 42% when used with zinc phosphate. However, sealer use resulted in 55% increased retention when used with glass ionomer. The modified-resin cement produced the highest mean dislodgment stress, nearly always exceeding the strength of the tooth.

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.

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)

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.)

Shear bond strength of techniques for bonding esthetic veneers to metal

Statement of problem. New composites with improved qualities have been introduced to the dental profession as alternatives to porcelain. There is concern about the strength and reliability of new metal-resin bonding systems when these composites are used as esthetic veneers over metal frameworks. Purpose. This in vitro study compared the shear bond strength of 2 metal-resin bonding techniques with the bond strength of conventional porcelain fused-to-metal (PFM). Effects of water storage and thermocycling were also evaluated. Material and methods. Ninety disks, cast in a medium gold, high noble PFM alloy, were divided equally into 6 groups, and received 3 treatments for veneering: conventional feldspathic porcelain on 1 group, and a composite (Artglass) bonded to the metal, using 2 metal-resin bonding techniques. Specimens were tested in shear, half of them after a 24-hour dry storage at room temperature and the rest after 10-day storage in normal saline solution at 37°C and thermocycling. Fractured specimens were evaluated under ×10 magnification to determine the nature of failure. Statistical analysis was performed with 2-factor analysis of variance (ANOVA). Results. Mean shear bond strength values before and after wet storage and thermocycling were 29.66 and 22.91 MPa for the PFM group; 21.43 and 17.92 MPa for the Siloc group; and 19.34 and 15.64 for the etched group, respectively. The PFM group exhibited significantly higher bond strength values compared with the other 2 groups ( P <.001). All groups showed a significant decrease in bond strength values after wet storage and thermocycling ( P <.001). Conclusion. Wet storage and thermocycling caused a significant decrease in shear bond strength of all specimens. Shear bond strength of conventional feldspathic PFM was significantly higher than that of the 2 metal-resin bonding techniques tested. The 2 latter techniques did not reveal any statistically significant differences. (J Prosthet Dent 1999;82:608-14.)

Effect of pH on element release from dental casting alloys

Statement of problem. Dental casting alloys are subjected to transient acidity in the oral environment, yet most studies have not investigated the effects of these transient environments on elemental release from alloys. Elemental release is important because it plays a significant role in alloy biocompatibility. Purpose. It was hypothesized that acidic environments would increase elemental release from dental alloys during exposure and after the acidic environment was removed. This hypothesis was based on the known increase in release of nickel from nickel-based alloys in an acidic environment. Material and methods. High-noble, noble, and base metal casting alloys were exposed for 30 minutes to solutions with pH ranging from 1 to 7. Elemental release of representative elements was measured by means of atomic absorption spectrometry during the exposure and in the week after the exposure. This release was compared with elemental release in the week before the exposure. Results. High-noble and noble alloys were resistant to acidic environments. A pH of 4 did not increase elemental release during or after exposure. A pH 1 environment slightly elevated release of Ag, Cu, and Pd in some alloys. However, a Ni-based alloy released large amounts of Ni during the acidic exposure of pH 1 or 4, and more importantly, in the week after the exposure as well. Increased time of exposure to acid did not alter elemental release from noble or high-noble alloys, but markedly increased release from the Ni-based alloy. Conclusions. Transient exposure of casting alloys to an acidic oral environment is likely to significantly increase elemental release from Ni-based alloys, but not from high-noble or noble alloys. (J Prosthet Dent 1998;80:691-8.)

Influence of metals on IL-6 release in vitro

Certain dental alloys have been claimed to cause gingival and periodontal inflammation. However, little information is available on the molecules mediating the mechanism of such an effect. Recently, a three-dimensional cell culture system consisting of human fibroblasts and keratinocytes has been introduced for evaluating the irritancy of cosmetic products, including the analysis of inflammatory mediators. In the present study the influence of pure metals and a high noble dental cast alloy upon cell viability and the synthesis of the proinflammatory mediator interleukin-6 was recorded in this in vitro skin equivalent model. The cultures were exposed to test specimens fabricated from copper, nickel, cobalt, zinc, palladium, tin, indium, a high noble cast alloy and a dental ceramic. Cell vitality was reduced after a 24 h exposure to copper (14–25% of untreated controls), cobalt (60%), zinc (63%), indium (85%), nickel (87%), and the heat treated and not heat treated high noble cast alloy (87%/90%). Dental ceramic, palladium and tin did not influence cell viability. Increased IL-6 levels were observed in cultures exposed to copper (5–19-fold compared to untreated controls), zinc (16-fold), cobalt (12-fold), nickel (10-fold) and palladium (4-fold). Other materials tested produced IL-6 levels comparable to those of untreated controls. Our findings suggest that metal ions are involved in proinflammatory activity at low toxicity and non-toxic levels as assessed by different biological endpoints.

Marginal fit and surface roughness of crowns made with an accelerated casting technique

Statement of problem. Conventional investing and casting techniques following the manufacturers’ recommendations are time-consuming. Accelerated casting techniques have been reported, but their accuracy has not been adequately studied for complete crown castings. Purpose. This study evaluated the marginal fit and surface roughness of complete crowns made with a conventional and an accelerated casting technique. Materials and methods. Part I of the study determined the mean time interval required for each investment to reach its maximum exothermic setting reaction temperature. Part II determined the marginal discrepancy of standardized complete crowns cast in a high noble metal ceramic alloy, with the use of four phosphate-bonded investments. A conventional technique (as recommended by the manufacturer) was compared with an accelerated technique that used 13- to 17-minute bench set time (as determined in part I for each investment) and 15-minute wax elimination cycle in a 815°C (1500°F) preheated furnace. Part III evaluated the surface roughness of castings made with the same techniques as in part II. Results. For the marginal discrepancy and surface roughness, crowns fabricated with the accelerated casting technique were not significantly ( P>0.05) different from those fabricated with the conventional technique. Conclusion. The accelerated casting technique described in this study could be a vital alternative to the time-consuming conventional techniques. (J Prosthet Dent 1998;80:337-45.)

The effect of metal surface treatment on the shear bond strengths of base and noble metals bonded to enamel

Adhesive resin luting agents provide a way for bonding metal surfaces to teeth through a combination of micromechanical retention to the rough metal surface and chemical adherence to metal oxides. The purpose of this study was to measure the effect of metal alloy surface treatments that would produce different textures and oxide layers on the shear bond strength of three alloys luted to etched enamel with one adhesive resin luting agent (Panavia). After a simulated porcelain firing sequence, high noble (Olympia), noble (Jelstar), and base metal (Rexillium III) alloy specimens were subjected to one of the following treatments: (1) sandblasting and simulated glazing, (2) simulated glazing only, (3) simulated glazing and sandblasting, or (4) simulated glazing, sandblasting, and tin plating. The specimens were bonded to extracted teeth and subjected to shear testing after water storage for 2 weeks, thermocycling for 500 cycles, and water storage for an additional 2 weeks. Data were analyzed with a two-way analysis of variance (α = 0.05). The base metal specimens and the tin-plated high noble and noble metal specimen groups exhibited similar mean shear bond strengths that were greater than the other groups. Those high noble and noble metal alloys sandblasted after simulated porcelain firing cycles and before the simulated glaze cycle exhibited nonsignificant increases in shear bond strengths compared with the groups that were either sandblasted after the simulated glaze cycle or not sandblasted at all.

The Periotest method: implant-supported framework precision of fit evaluation.

In this study, the Periotest instrument was used to measure the precision of fit between cast high noble-metal frameworks and the supporting implants in a patient-simulation model. Three framework conditions and three implant-location variables were used to evaluate the rigidity of the assembly as measured by the Periotest method. The framework variables were (1) one-piece castings (OPC); (2) sectioned-soldered inaccurate castings (SSIC); and (3) sectioned-soldered accurate castings (SSAC). The implant-location variables were right anterior (RA), center (C), and left anterior (LA). The patient simulation model used consisted of three self-tapping Branemark implants in a reasonable arch curvature in bovine bone. Three working casts were fabricated from the patient-simulation model using polyvinyl siloxane and tapered impression copings. From the working casts, three sets of three frameworks were fabricated as OPCs, SSICs, and SSACs using type 3 high noble alloy. The SSICs were fabricated with a quantitative misfit of 101.6 microns at the facial surface, between the abutment-to-gold cylinder interface at the C implant location. Periotest value (PTV) measurements were made at the midfacial surface of the frameworks directly above each abutment-to-gold cylinder interface. Three measurements were made for each test condition. The data were analyzed to compare framework condition(s) and implant location(s) using ANOVA and Fisher's Protected Least Significant Difference Comparison Test. The ANOVA showed that significant differences exist between the mean PTV data for framework condition and for implant location (p < .01). Significant differences were shown between the mean PTV data for the SSAC assemblies and the OPC and SSIC assemblies. The SSICs displayed a more positive (+) mean PTV than the OPCs. The OPC assemblies had a more positive mean PTV than the SSAC assemblies. The mean PTV data for the SSAC assemblies had a significantly different PTV (p < .01) than the other two framework condition assemblies. The OPC and the SSIC assemblies had PTVs that were not significantly different. The C implant location was significantly different from the RA and the LA implant locations (p < .01). The RA and the LA implant locations were not significantly different from each other. The C implant location always demonstrated the most positive mean PTV regardless of the framework condition being tested. The Periotest instrument quantified differences in the precision of fit between three framework conditions. The SSAC assemblies were significantly more rigid than the OPC and SSIC assemblies. The OPC and SSIC assemblies' mean PTVs were not significantly different. The mean PTVs for the C implant location and the RA and LA implant locations were significantly different (p < .01). The mean PTVs of the RA and LA implant locations were not significantly different. The implant-location PTVs followed the same rank order for all three framework conditions. The procedures used to fabricate a more precise fit between the framework and the supporting implants is influenced by the skill of the clinician and technician.

Comparison of shear bond strengths of two resin luting systems for a base and a high noble metal alloy bonded to enamel

Researchers are investigating the use of noble metals for the fabrication of resin-bonded prostheses because of concerns about health hazards of nickel and beryllium in base metal alloys. Tin-plating has been advocated to improve the bond of resin luting agents to noble metal alloys. Some manufacturers have suggested that tin-plating is unnecessary to bond noble metal alloys to etched enamel with their products. In this study, Rexillium base metal and Olympia noble metal alloy specimens were bonded to extracted human teeth with the use of two resin luting agents (F21 and Panavia OP). One third of the noble metal specimens were tin-plated, one third were oxidized, and one third were oxidized and sandblasted. Each of the bonded specimens were thermocycled and subjected to a shear force until bond failure. The base metal specimens bonded with Panavia OP luting agent exhibited the greatest mean shear bond strengths. The tin-plating surface treatment significantly increased the mean shear bond strengths of Olympia noble metal specimens.

Retentive strength, disintegration, and marginal quality of luting cements

This study evaluated the retention of complete crowns by using five different methods of cementation. Complete crowns were prepared with standardized dimensions on extracted human molars. Metal crowns were cast with a high noble gold ceramic alloy and were cemented with zinc phosphate cement, glass ionomer cement, composite resin cement, composite resin cement with a dentinal bonding agent, and adhesive resin cement. The retention was measured by subjecting the specimens to tensile load until fracture occurred. The disintegration was measured according to American Dental Association Specification No. 8, and the condition of the cements at the margins of crowns was analyzed by use of a scanning electron microscope. Kruskal-Wallis one-way analysis of variance revealed statistically significant differences between the mean retentive strengths. The retention of the zinc phosphate and the glass ionomer groups was significantly different from that of the adhesive resin group. The retention of the adhesive resin cement was 65% greater than the retention of the composite resin and the composite resin/dentinal bonding agent group, but the Mann-Whitney Wilcoxon rank sum test did not depict this difference as significant. The mean ± SD of the disintegration for the zinc phosphate, the glass ionomer cement, and the composite resin cement was 0.025 ± 0.013, 0.023 ± 0.011, and 0.017 ± 0.001, respectively. The scanning electron microscope analysis of the margins revealed that the composite resin cement was almost intact, the zinc phosphate was subjected to limited disintegration, and the glass ionomer displayed the worst marginal integrity.

Resin-bonded prostheses for posterior teeth

This study evaluated fixed partial dentures bonded with resin to dentin on posterior teeth with minimal tooth preparation. The patients included were missing at least one premolar or first molar. The abutment teeth next to the modification spaces were moderately restored with MOD or class II restorations on most of the teeth. A total of 20 patients with 23 fixed partial dentures were included in the study. After removal of existing restorations, the abutment teeth were prepared to eliminate undercuts on the perimeter of the preparations. Undercut areas within the preparation were not filled but were blocked out later in the laboratory. The fixed partial dentures employed inlays as retainers for a metal ceramic pontic. The metal framework was cast in a high noble gold alloy. The areas of the retainers to be bonded were treated with the Kulzer Silicoater method. Immediately before cementation, enamel was etched and exposed dentin was treated with Gluma. Kerr's resin bonded bridge cement was used for cementation. Patients were recalled after periods of 1 week, 1 month, 6 months, 1 year, 2 years, and 4 years for evaluation. None of the restorations lost retention and no major adverse effects were observed in the 4-year follow-up period.

Bond strengths of high-palladium content alloys

Palladium-based alloys have had a significant import on the fabrication of ceramometal restorations. This article compares the bond strengths of four palladium-based alloys with that of a high-noble alloy. Tests were designed to closely represent clinical situations. Bond strengths of the palladium alloys compared favorably with the high-noble metals; palladium alloys containing up to 2% gold were the best.