Evaluation of alternative alloys to type III gold for use in fixed prosthodontics

Comparative effectiveness of fiber and metal posts in the restoration of endodontically treated teeth: A systematic review with network meta-analysis

STATEMENT OF PROBLEM

Different varieties of fiber and metal intraradicular posts have been used for the restoration of endodontically treated teeth with insufficient sound tooth structure. Evidence on the comparative efficacy of posts in a clinical setting is insufficient to provide clear clinical guidelines and recommendations.

PURPOSE

The purpose of this systematic review with network meta-analysis was to assess the comparative efficacy of fiber and metal posts used for the restoration of endodontically treated teeth.

MATERIAL AND METHODS

A search was conducted for trials published in Medline, Scopus, PubMed, and Cochrane Central Register of Controlled Trials from inception until November 2022. The study was registered with the International Prospective Register of Systematic Reviews (PROSPERO) (CRD42022384340). A network meta-analysis was performed on data from randomized controlled trials that assessed the comparative efficacy of fiber posts and metal posts for the restoration of endodontically treated teeth. Subgroup analyses were performed to compare all the varieties of fiber and metal posts. The types of posts were ranked according to their efficacy using the Surface Under the Cumulative Ranking (SUCRA) system. The Grading of Recommendations, Assessment, Development, and Evaluations (GRADE) approach was used to assess the level of certainty of evidence.

RESULTS

Twenty-five articles were included in the quantitative analysis. Fiber posts (RR=0.15 [95% CI: 0.06, 0.33]) significantly prevented tooth fracture as compared with no posts. Prefabricated carbon fiber posts (RR=0.06 [95% CI: 0, 0.54]) ranked highest followed by custom glass fiber posts (RR=0.15 [95% CI: 0.04, 0.52]) and prefabricated glass fiber posts (RR=0.22 [95% CI: 0.07, 0.62]) in the outcome of tooth fracture. Metal posts (RR=0.24 [95% CI: 0.12, 0.46]) ranked higher than fiber posts (RR=0.39 [95% CI: 0.27, 0.56]) in the outcome of debonding. Custom gold alloy posts (RR=0.12 [95% CI: 0.03, 0.48]), prefabricated gold alloy posts (RR=0.04 [95% CI: 0.00, 0.87]), and prefabricated titanium posts (RR=0.21 [95% CI: 0.10, 0.45]) had higher rankings in the outcome of debonding or loss of retention of a post followed by custom glass fiber posts (RR=0.37 [95% CI: 0.21, 0.63]) and prefabricated glass fiber posts (RR=0.38 [95%CI: 0.25, 0.58]). Prefabricated glass fiber posts (RR=0.40 [95% CI: 0.20, 0.81]) had statistically significant differences in the outcome of secondary caries. The GRADE approach determined a moderate level of certainty of evidence.

CONCLUSIONS

The use of a fiber post when indicated results in reduced risk of tooth fracture as compared with no post. Prefabricated carbon fiber posts, prefabricated glass fiber posts, and custom glass fiber posts reveal a lower risk of tooth fracture. Overall, the use of prefabricated glass fiber posts had a lower risk of tooth fracture, debonding, and secondary caries. However, more trials with longer follow-up periods are recommended to enhance the certainty of evidence.

Customized Post and Cores Fabricated with CAD/CAM Technology: A Literature Review

Post and core restorations are a widely accepted method to restore endodontically treated teeth with compromised tooth structure. The use of computerized technology to fabricate customized post and cores is a simple and quick alternative to conventional methods. A literature search was conducted, and a summary of articles describing fabrication techniques and materials used to fabricate post and cores with computer-aided design and computer-aided manufacturing (CAD/CAM) has been provided. Several techniques have been reported to restore endodontically treated teeth with CAD/CAM post and cores, including direct and indirect methods. Zirconia, composite resin, and hybrid ceramic were the most commonly reported materials. Published reports on CAD/CAM post and core are limited; however, further studies are needed to investigate the long-term outcome of this treatment.

Oxidation behavior of surface-modified titanium for titanium-ceramic restorations

STATEMENT OF PROBLEM

Titanium-ceramic bonding is an unsolved problem for the current use of titanium-ceramic restorations.

PURPOSE

The purpose of the study was to characterize oxide formation on titanium surfaces at porcelain sintering temperatures and to determine the effect of chromium coating methods on titanium oxide formation.

MATERIAL AND METHODS

Sputter coating and electroplating methods of chromium application were compared and combined.

RESULTS

Porous, weak titanium oxide formation on uncoated samples was demonstrated at porcelain sintering temperatures. Groups with chromium coating as an oxygen diffusion barrier exhibited lower oxidation rates, except samples coated by sputtering alone. Temperature effect was found to have the greatest significance on titanium oxidation rate. The overall lowest oxidation rate was located in the group that had chromium coating by the combined coating method and was oxidized at 750 degrees C.

CONCLUSION

The electroplating method requires further investigation and development so that a uniform chromium layer can be deposited on titanium.

Use of plastic bar molded casting in the modification of variably expanding investment to compensate for casting shrinkage of nickel-chromium alloy

Trial plastic bar molded castings were compared for accuracy with cast crowns by means of a nickel-chromium alloy, which was used to establish the liquid density of variably expanding investments. The plastic bars were invested to evaluate the change of expansion rate in a wide range of six liquid densities from 0% to 100%, and the distances between the sections were measured before and after casting. Wax crowns were cast to obtain a more detailed relation around 0% expansion at seven liquid densities, and the gaps between the base of the die and the margin of the crown were measured before and after casting. The expansion rates of both castings were calculated and thus were proportional to the liquid density; both regression curves indicated high correlation coefficients. As a result of the statistics of the Student's t-test, the difference between the two methods was not significant. The trial plastic bar was useful in establishing the variably expanding investment for precise casting of artificial crowns.

Corrosion investigation of two materials for implant supraconstructions coupled to a titanium implant

The corrosion of two materials for implant supraconstructions, a carbon fiber/PMMA composite and a silver-palladium alloy, was investigated in vitro, the materials being galvanically coupled to a titanium implant. Corrosion current and pH of the electrolyte were monitored, and corrosion products were identified by powder X-ray diffraction. The carbon composite and the silver-palladium per se did not corrode, whereas a silver-palladium specimen brazed with the recommended brazing alloy corroded unmistakably, yielding copper-containing corrosion products. The action of local corrosion cells around the brazed joint is considered, and it is concluded that the two materials seem well suited for implant supraconstructions, provided that brazing the silver-palladium can be avoided. Considering the clinical relevance of the experimental model used, it is concluded that the model is likely to predict a lower corrosion susceptibility than the one found in vivo.

Veterans Administration Cooperative Studies Project No. 147. Part IX: A comparison of the mechanical properties of several alternative metal ceramic alloys cast in clinical and research laboratories

Comparison of mechanical properties of five metal ceramic alloys cast in clinical and research laboratories resulted in significant differences. Tested alloys included one Au-Pd (control), one Pd-Ag, and three Ni-Cr. Mechanical properties included strength, elongation, and microhardness. Tensile bars were torch cast simultaneously with restorations in the clinical laboratory and induction cast by using a preformed design in the research laboratory. Mechanical properties of most alloys showed larger variations when cast in the clinical laboratory. In the clinical laboratory the Au-Pd alloy showed significantly higher values for all properties. One Ni-Cr alloy was not significantly affected by environment for all properties. The remaining alloys were significantly affected for some properties by environment. The different laboratories had no greater or lesser effect on the base metals as a group than on the noble metals. Variation in handling, spruing, casting, and specimen size may account for some of the differences between laboratories.

Palladium-silver alloys: a review of the literature

Since their introduction in 1973, the use of palladium-silver alloys has increased significantly and they now comprise a substantial part of the noble metal ceramic alloy sales in North America. Literature regarding various properties of this alloy system is presented with particular emphasis on castability, fit, and porcelain discoloration.

The effect of sprue attachment design on castability and porosity

Sprue attachment design is an important and controversial variable that can affect casting characteristics of castability and porosity. Four sprue attachment designs--straight, flared, abrupt constriction, and gradual constriction--were investigated. Standardized wax copings simulating complete veneer metal ceramic crowns with knife-edge margins were sculpted on refractory investment dies, sprued, invested, and cast with Olympia alloy. The specimens were embedded, sectioned, and polished. Castability was analyzed by measuring the width of the cast meniscus of the margins. The margin widths of the flared and the straight sprue attachment groups were significantly less than the abrupt or gradual constriction attachment group (p less than 0.05). Photomicrographs revealed discernible differences in the relative quantity and location of porosity in the sprue-coping junctions. The straight and flared sprue attachment groups were less porous than the abrupt or gradual constriction groups (p less than 0.01). Flared and straight sprue attachments optimized castability and minimized porosity.

Casting metals in dentistry: past--present--future

This article deals mainly with the development of dental casting techniques and formulation of the different groups of alloys used in the fabrication of ceramo-metal restorations.

It is recognized that in order for the quality of dental cast restorations to be improved, having alloys with the proper composition is not enough. Biocompatibility, good mechanical and physical properties, longevity of the restoration, compatibility with porcelain, and a simple manipulative technique are as important. Researchers have contributed to different aspects of dental castings and have made cast restorations what they are today. Unfortunately, much of the original basic research has been overlooked by present investigators, who have duplicated studies conducted in the past without realizing that the study had already been performed and the research had been published. The main reason for this is that abstracts of articles published prior to 1975 are not available through a library computer-search system. To obtain copies of articles published prior to 1975, one has to search the literature to know where they were published. This article provides references for much of the past work in this area. Also, dental libraries do not carry copies of U.S. patents. This places the majority of researchers located at dental schools at a disadvantage. They are not familiar with what the patents claim, what is taught, and why certain elements are added or eliminated from alloys and investment materials. This article also provides the numbers of many U.S. patents. By having the patent number, one can obtain the text of the patent from the U.S. Patent Office in Washington, DC.

Since esthetics plays an important role in today's society, emphasis will be given only to alloys designed for fabrication of ceramo-metal restorations. Many ceramo-metal alloys are available today, and they are classified differently by different individuals. In this article, classification will be based on the major components of these alloys, as well as on a chronological introduction of one group leading to the development of the next group. Based on this, one can classify these alloys into six major groups. Chemical composition, properties, and the developers of these alloys, along with their U.S. patents, are given.

Recently, two types of all-ceramic restorations have been introduced. The main advantage of the all-ceramic restoration is its superior esthetic quality compared with that of ceramo-metal restorations. Their main disadvantages are low strength and ductility. Their strength, however, is sufficient for single-unit restorations, but not for bridgework. The use of titanium for dental restorations has also been studied, and it has been found to be suitable.

Future Studies - Future work should be devoted to the following: (1) the development of stronger and more ductile ceramic materials: (2) further study of the promising palladium alloys from the noble metal group and titanium alloys from the base metal group; (3) the development of easier and less-time-consuming techniques for the fabrication of dental appliances; (4) the development of a powder technique rather than a cast technique for future fabrication methods; and (5) the development of new laboratory equipment, e.g., a single sintering oven capable of sintering both ceramic and metallic particles, which would be accepted if the powder technique is developed.

Evaluating six sprue designs used in making high-palladium alloy castings

Six different sprue designs were studied to determine which, if any, could be used to produce more complete castings with a high-palladium alloy. A standardized mesh test pattern was used to ensure objective measurements and accurate evaluations of the spruing techniques. This study of problems usually encountered when casting high-palladium alloys found that: Differing sprue designs effect significant differences in obtaining complete castings (p less than .05) as indicated in the ANOVA. The connection between the casting and the sprue should be constricted to improve castability of high-palladium alloys. Although this spruing technique may be used in different sprue designs to improve the quality of castings, further research seems indicated.

Evaluation of the castability of four different alternative alloys by measuring the marginal sharpness

The castability of two low-gold and two silver-palladium alloys was evaluated, using a Type III gold alloy as reference. Six castings from each alloy were subjected to a castability test, in which the marginal sharpness of simulated crowns--that is, the edge diameter--was used to assess the castability. The mean crown edge diameters of the silver-palladium alloys were three to four times the corresponding diameters of the gold-based alloys. The differences between these two groups were statistically significant. It is concluded that the castability of the low-gold alloys studied was comparable to that of the Type III alloy, whereas the silver-palladium alloys studied had a castability that may result in technical and clinical problems.

Precious and noble-based casting alloys

Some medium-gold and midrange gold alloys are satisfactory substitutes for Type III alloys, but tarnish may occur. Considering all factors, Type III alloys remain unparalleled as fixed restorative alloys. Some medium-gold and midrange gold metal-ceramic alloys are superior to their high-gold counterparts and are the choice for metal-ceramic restorations.

Castability of crown and bridge alloys

A special saucer-shaped wax pattern was designed to evaluate the castability of five casting machines and four casting alloys. The casting machines used included one broken arm unit, one induction unit, one resistance unit, and two vacuum air pressure units. The alloys included one base metal alloy, two high-fusing noble metal alloys, and one type III gold alloy. Results of analysis of variance showed that at the 95% confidence level there was a significant difference among casting machines and alloys, the casting machines had a stronger effect on castability. No attempt was made to evaluate the fit quality of the castings with regard to surface roughness or porosity.

Evaluation of an improved centrifugal casting machine

A Type III gold alloy, a silver-palladium alloy, and a base metal alloy were cast in two different centrifugal casting machines. With the number of complete cast mesh squares as an indicator of castability, the Airspin casting machine produced superior castings with all three alloys. The base metal alloy produced the greatest number of complete squares with both casting machines.

Preliminary observations on clinical use of a base metal casting alloy

A study was conducted to develop a laboratory technique and to evaluate the clinical efficacy of a base metal casting alloy. Slight modification of recommended investing procedures is required to produce consistently well-fitting castings with the test alloy. After 12 months of clinical service, the test alloy did not differ from the control alloy in tarnish, untoward gingival response, resistance to abrasion, or tooth sensitivity.

An 18-month clinical evaluation of semiprecious and nonprecious alloy restorations

SEM studies indicate that the control alloy, Minigold, WLW, and Litecast metals presented similar results in relation to marginal fit when proper techniques are followed. Clinical evaluation based on the criteria of gingival irritation, patient sensitivity, and abrasion demonstrated no statistically significant differences between the casting alloys tested and the control. The control alloy had significantly fewer restorations with tarnish and corrosion than either WLW or Litecast. There was no significant difference between the control alloy and Minigold in terms of tarnish and corrosion.

A base metal alloy for ceramo-metal restorations

Research of the existing scientific literature and examination of multiple porcelain/metal samples indicate that Ni/Cr is not only compatible with veneering porcelain but, indeed, can probably be the basis for superior ceramo-metal restorations.

Effect of investment on casting high-fusing alloys

A definite interaction in castability was found between the three different phosphate-bonded investments and four different alloys tested in this study. 1. Casting completeness of all alloys, as measured by the length of test specimens, was affected by the investment. The high-gold content alloy, SMG II, yielded the most complete castings of all combinations teted when invested with Ceramigold. Of the nonprecious alloys, Biobond CB combined with Ceramigold II resulted in the longest samples. 2. The surface quality of Jelbon and SMG II castings was good, regardless of the investment used. Wiron S and Biobond CB varied in surface quality with different investments, Ceramigold II giving the smoothest castings. 3. All alloys, especially the nonprecious ones, should be tested for compatability with different investments before asserting their qualities or lack of qualities for clinical use.

Evaluation of three variables affecting the casting of base metal alloys

All the vented samples with sprue widths of 2 mm or more were defect free, whereas the corresponding unvented samples had extensive voids and porosity in all but one casting. All castings with a sprue width of 1 mm were defective regardless of whether or not vents were used. The thickness of the investment above the pattern had no effect on casting results.