Effect of zinc in two non-gamma-2 dental amalgam systems

Dental amalgam: An update

Dental amalgam has served as an excellent and versatile restorative material for many years, despite periods of controversy. The authors review its history, summarize the evidence with regard to its performance and offer predictions for the future of this material. The PubMed database was used initially; the reference list for dental amalgam featured 8641 articles and 13 publications dealing with recent advances in dental amalgam. A forward search was undertaken on selected articles and using some author names. For the present, amalgam should remain the material of choice for economic direct restoration of posterior teeth. When esthetic concerns are paramount, tooth-colored materials, placed meticulously, can provide an acceptable alternative. All alternative restorative materials and procedures, however, have certain limitations.

Amalgam at the new millennium

Dental amalgam has served as an excellent and versatile restorative material for many years, despite periods of controversy. The authors review its history, summarize the evidence in regard to its performance and offer predictions for the future of this material. For the present, amalgam should remain the material of choice for economical direct restoration of posterior teeth. When esthetic concerns are paramount, tooth-colored materials, placed meticulously, can provide an acceptable alternative.

Almost two centuries with amalgam: where are we today?

Amalgam has provided valuable and comparatively inexpensive service to patients for a longer time than any other restorative material. Despite the excitement surrounding the use of each new restorative material, each has a shortcoming that amalgam hasn't.

Dental amalgam: the materials

The goal of this presentation is to describe the material as it is used clinically, explain why small quantities of Hg can be released, and suggest ideas for amalgams that do not release mercury. A set amalgam is a dynamic material that undergoes many microstructural changes during clinical use, related to both the elevated temperature and corrosion-prone environment in the mouth and mechanical forces applied to the restoration. Amalgams can be divided roughly into two groups by their copper content: low Cu (traditional) and high Cu. High-Cu amalgams generally perform better clinically, but all amalgams corrode to some extent in the mouth. Some corrosion is deemed to be a positive factor, because corrosion product deposition reduces leakage at the margins of restorations; that is, the restorations are partly self-sealing. One of the reasons cited for the improved clinical performance of high-Cu amalgams over low-Cu amalgams is that the corrosion-prone phase, gamma 2, is nearly eliminated in high-Cu amalgams. Future research should involve improvements in the clinical performance of dental amalgams, studies of the mercury release from various types of amalgams and the toxic potential of this exposure, and the development of new amalgam systems that reduce the mercury exposure. Although the longevity of modern amalgams is impressive, it is important for their stability to be increased both clinically and microstructurally. An amalgam should be developed with a stable microstructure that, once set, would not change during clinical use. Microstructural changes lead to clinical deterioration. A stable system would not corrode, and the matrix transformation gamma 1 to beta 1 would be prohibited.(ABSTRACT TRUNCATED AT 250 WORDS)

Corrosion behavior and microhardness of three amalgams

The marginal microhardness of three different types of amalgam was tested after 2 months' immersion in an aqueous solution of NaCl (85 mM) and phosphates (Na2HPO4 100 mM and NaH2PO4 100 mM). Amalgams immersed in distilled water were used as controls. The microhardness tests were conducted at a distance of 50 micron from the margins and at the bulk of each specimen. The solutions were analyzed for Sn, Cu, Zn, Ag, and Hg by means of atomic absorption spectrophotometry (AAS). A statistically significant reduction in the marginal microhardness after immersion in the test solution was found for the conventional and the high-Cu single composition amalgam but not for the high-Cu blended amalgam. SEM-examination of cross-sections of the amalgams revealed small areas of subsurface grain boundary corrosion, no deeper than 10 micron for all the amalgams. The SEM-examination of the specimens and AAS analysis of the solutions indicated that the reduction in marginal microhardness was attributed mainly to corrosion of the Cu-rich phases for the high-Cu single composition amalgam and to corrosion of the gamma 2 phase for the conventional amalgam. The phosphates reduced the corrosion of the amalgams in the presence of NaCl. It is concluded that the marginal strength of dental amalgams in a corrosive environment is largely dependent upon their corrosion resistance.

Research on dental amalgam: 1982-1986

This paper is a five-year review of selected research papers on dental amalgam which were published during the years 1982 through 1986. Papers presented at scientific dental meetings are also included. During the past five years, clarification of amalgam metallurgy has been made, and a few innovative modifications have been recommended. The addition of palladium, indium, and selenium to dental amalgam has been suggested, but commercial applications have yet to be made. The mechanical property of creep has been studied more extensively, while the applicability of fracture toughness tests has been examined. More work has been done on the microleakage of amalgam restorations, with certain alloy factors showing an influence on this problem. Most in vitro investigations on the use of cavity varnish or resin films beneath amalgam restorations show reduced microleakage. Additionally, many electrochemical investigations were conducted. A most significant finding was that amalgam does not appear to break down in vivo as much as in vitro tests would indicate, the buffering action of saliva being protective in this regard. The marginal fracture evaluation of clinical amalgam restorations is still being used as a major clinical performance criterion, and measuring techniques for this failure mode have been improved. Measurements of metallic ion loss from amalgam were made with instruments of high sensitivity, but no evidence has been found to associate this loss with any disease entity. The rare presence of an allergy to mercury appears to be the only contra-indication for the use of amalgam as a dental restoration. Further research on dental amalgam can lead to improved clinical performance of this most useful restorative material.

Dental amalgam: reactor response

Dental amalgam continues to be an important restorative material; both fundamental and applied research should be encouraged. The criteria for replacement of amalgam restorations should be re-examined to determine if the integrity of the margins should continue to receive the dominant research interest.

In the studies of mechanical properties, first attempts have been made to apply fracture mechanics analysis to dental amalgam. The heterogeneous structure and time-dependent strain of dental amalgam will have to be considered in future studies. More attention should be given to the effects of zinc, which has been shown to improve resistance to marginal fracture.

The corrosion properties have been studied in depth, but there are some important unanswered questions. The pathways of corrosion attack in high-copper amalgams and the kinetics of attack in amalgams of different composition should be examined. Biocompatibility of dental amalgam has recently received renewed interest and will have to be examined in more detail. The clinical significance of the release of metallic elements from restorations is generally unknown.

Dental amalgam faces strong competition from non-metallic restorative materials. Future research should be more strongly focused on the critical issues. The involvement of scientists from related disciplines should be encouraged, and no effort should be made to restrict the talent pool by a centralization of resources.

Report of Committee on Scientific Investigation of the American Academy of Restorative Dentistry

A few personal points seem appropriate in summary. It is axiomatic that while research solves problems, it also creates them. As an example, it is an accepted fact that dentistry more than any other profession has made serious inroads into putting itself out of business through research. Each year this report takes note of the reduction in dental caries in children, which has thus triggered a change in the nature of general practice. Be this as it may, it is well to acknowledge that major dental diseases are not disappearing, but their patterns in the population are changing, accompanied by an expansion of other services. Despite the optimistic picture painted earlier in this report, it is grossly premature to acclaim the elimination of caries, and thereby a significant segment of restorative dentistry. Of course the younger age groups have been the major beneficiaries of caries reduction. As the child ages from 9 to 16 years, the percentage of mouths free of caries drops by one half. In addition, the disease pattern in the adult population is being altered because of a longer life span and loss of fewer teeth. Unquestionably what we will, and are already seeing, is not an elimination of restorative dentistry but a different target and changes in procedures because of new materials, therapy, and expanded scope of services. There is yet another subtle change in the trend of dental research and it deals with the reduction in the number of dental schools worldwide and smaller class sizes in those schools. Dental research thereby suffers because of the traditional link between education and research. Thus the potential pool of researchers becomes smaller and research monies for training programs for dental investigators, particularly in clinical research, decreases. This year a surprising number of articles are concerned with manpower as it relates to research priorities. So, it is indeed a time that both the profession and the scientific community find filled with controversy and frustration. Yet never has there been a time that offers more in challenges and rewards.