Showing papers in "Advances in Dental Research in 1992"

Degradability of Dental Ceramics

Abstract: The degradation of dental ceramics generally occurs because of mechanical forces or chemical attack. The possible physiological side-effects of ceramics are their tendency to abrade opposing dental structures, the emission of radiation from radioactive components, the roughening of their surfaces by chemical attack with a corresponding increase in plaque retention, and the release of potentially unsafe concentrations of elements as a result of abrasion and dissolution. The chemical durability of dental ceramics is excellent. With the exception of the excessive exposure to acidulated fluoride, ammonium bifluoride, or hydrofluoric acid, there is little risk of surface degradation of virtually all current dental ceramics. Extensive exposure to acidulated fluoride is a possible problem for individuals with head and/or neck cancer who have received large doses of radiation. Such fluoride treatment is necessary to minimize tooth demineralization when saliva flow rates have been reduced because of radiation exposure to salivary glands. Porcelain surface stains are also lost occasionally when abraded by prophylaxis pastes and/or acidulated fluoride. In each case, the solutes are usually not ingested. Further research that uses standardized testing procedures is needed on the chemical durability of dental ceramics. Accelerated durability tests are desirable to minimize the time required for such measurements. The influence of chemical durability on surface roughness and the subsequent effect of roughness on wear of the ceramic restorations as well as of opposing structures should also be explored on a standardized basis.

Dental composites/glass ionomers: the materials.

Abstract: Most commercial dental composites contain liquid dimethacrylate monomers (including BIS-GMA or variations of it) and silica-containing compositions as inorganic reinforcing filler particles coated with methacrylate-functional silane coupling agents to bond the resin to the filler. They also contain initiators, accelerators, photo-initiators, photosensitizers, polymerization inhibitors, and UV absorbers. Durability is a major problem with posterior composites. The typical life-span of posterior composites is from three to 10 years, with large fillings usually fewer than five years. Polymerization shrinkage and inadequate adhesion to cavity walls are remaining problems. Some pulp irritation can occur if deep restorations are not placed over a protective film. Some have advocated the use of glass-ionomer cement as a lining under resin composite restorations in dentin. The concept of glass-ionomer cements (GICs) was introduced to the dental profession in the early 1970's. Current GICs may contain poly(acrylic acid) or a copolymer. Higher-molecular-weight copolymers may also be used to improve the physical properties of some GICs. Stronger and less-brittle hybrid materials have been produced by the addition of water-soluble compatible polymers to form light-curing GIC formulations. The ion-leachable aluminosilicate glass powder, in an aqueous solution of a polymer or copolymer of acrylic acid, is attacked by the hydrated protons of the acid, causing the release of aluminum and calcium ions. Salt bridges are formed, and a gel matrix surrounds the unreacted glass particles. The matrix is adhesive to mineralized tissues. Provisions must be made for maintenance of the water balance of restorations for the first 24 hours.(ABSTRACT TRUNCATED AT 250 WORDS)

Casting alloys: side-effects.

Abstract: Side-effects from dental materials are a minor problem, but should be recognized. In recent questionnaire surveys about side-effects, the incidence was estimated to be 1:300 in periodontics and 1:2600 in pedodontics. None of these reactions was related to dental casting alloys. In prosthodontics, the incidence was calculated to be about 1:400, and about 27% were related to base-metal alloys for removable partial dentures (cobalt, chromium, nickel) and to noble/gold-based alloys for porcelain-fused-to-metal restorations. The complaints consisted of intra-oral reactions (such as redness, swelling, and pain of the oral mucosa and lips), oral/gingival lichenoid reactions, and a few instances of systemic reactions. In orthodontics, the incidence was 1:100, and most reactions (85%) were related to metal parts of the extra-oral anchorage devices. Even though the extensive use of base-metal alloys has been of major concern to the dental profession, relatively few case reports substantiate this concern. Allergy to gold-based dental restorations has been more commonly reported. Palladium-based alloys have been associated with several cases of stomatitis and oral lichenoid reactions. Palladium allergy seems to occur mainly in patients who are very sensitive to nickel. All casting alloys, except titanium, seem to have a potential for eliciting adverse reactions in individual hypersensitive patients. Tolerance induction may be a possible benefit of the use of intra-orally placed alloys. In non-sensitized individuals, oral antigenic contacts to nickel and chromium may induce tolerance rather than sensitization. A variety of systemic diseases and reactions has been claimed to be caused by dental materials. The claims are generally poorly documented.

Biodegradation of dental composites/glass-ionomer cements.

Abstract: Studies of the degradation processes, types of tests, and measurements and analyses of substances leaching out from resin-based composite materials and glass-ionomer cements are reviewed. For both types of materials, the initial release rate rapidly decreases to a low, but nearly constant, level.For composites, various types of degradation processes have been demonstrated. Elements from filler particles and degradation products from the resin (e.g., formaldehyde) leak out. Many substances are not properly identified. It is, however, difficult for in vitro and in vivo degradation to be compared.For glass ionomers, a total disintegration of a surface layer is observed, together with a slow release of elements from the bulk. Of the elements released, fluoride is the most interesting. Marked differences have been shown between in vitro and in vivo solubility tests.

Biodegradation of restorative metallic systems.

Abstract: Metallic materials utilized for the construction of intra-oral and implant dental restorations include a wide range of relatively pure metals and multicomponent alloys. Basic corrosion and biodegradation properties of these alloys have been studied by both in vitro and in vivo techniques. These property characteristics have been shown to be dependent on composition and metallurgical state, combinations within a construct, surface conditions, mechanical aspects of function, and the local and systemic host environment. The susceptibility of these metallic materials to various forms of biodegradation will be presented, with emphasis on corrosion.

Local and systemic responses to dental composites and glass ionomers.

Abstract: For many years, the dental profession worked mainly with rather inert restorative materials that had a limited contact with vital tissue, and the opportunity for local and systemic complications was minimal However, conditions have changed in recent years where the two leading non-mercury-containing materials, resin composites and glass-ionomer cements, are chemically active compounds and can have detrimental effects on pulp tissue With the advent of light-curing techniques with incremental layering, resin component formulae that were formerly found to be quite irritating to the pulp have become less so with the elimination of the need for matrices and pressure for good adaptation to be gained As experience revealed the deficiencies and dangers of ultraviolet-light-curing techniques, visible-light-curing systems were developed that provided greater depth of cure, a higher degree of polymerization with less shrinkage with incremental layers, and less porosity When glass-ionomer cements (GICs) were first introduced, with just one acid (polyacrylic), pulpal responses were classified as bland With the addition of many more acids to enhance certain characteristics and reduce the setting time, GICs have become more irritating, especially when used as luting agents in areas where the remaining dentin thickness is 05 mm or less Gold foil and amalgam are inert and innocuous restorative materials but require pressure for condensation which creates an exaggerated inflammatory response This presentation emphasizes the pulpal responses and side-effects of these non-mercury-containing restorative materials and how to keep them within an acceptable range of biocompatibility Despite the lack of any substantial appearance of soft tissue and systemic responses to resin composites and GICs, the results of a survey of recent literature are included

Interactions between dental amalgams and the oral environment.

Abstract: Dental amalgam fillings interact in a complex way with the environment in the oral cavity as they are subjected to chemical, biological, mechanical, and thermal forces. These forces change the restoration's appearance and properties, while metal ions, amalgam debris, non-metallic corrosion products, and mercury vapor are released into the oral cavity. The phenomena and conditions that affect the amalgam/environment interaction include the chemistry and biochemistry of the environment, formation of biofilms on the amalgam surfaces, existence of localized corrosion cells, galvanic contacts with other metallic restorations, abrasion during mastication, and synergistic effects of the different forces. Corrosion processes result in a degradation of the functional amalgam properties, while tarnishing reactions cause discoloration. Corrosion degradation of amalgam fillings is due mainly to localized corrosion cells in pores and crevices. Corrosion on occlusal surfaces is accelerated by abrasion during mastication, which removes the protective surface films. The average total amounts of metal species, including mercury, released per day in vivo from a restoration have not been determined. Much of the reported indirect evidence for high mercury release rates is either unreliable or controversial. A more detailed investigation is needed and will require the development of more sophisticated techniques of sampling in vivo, as well as both experimental and theoretical modeling in vitro.

Dental Amalgam— Environmental Aspects:

Abstract: Increasing knowledge about the risk of toxic effects caused by anthropogenic mercury accumulation in ecosystems has resulted in a growing pressure for reduction of the discharge of mercury waste. Consequently, the mercury waste problems of dental clinics have been given increased attention, and restrictions on handling and discharge of contaminated waste have been established in several countries. Major amalgam particles from trituration surplus of those produced during the carving and burnishing of new amalgam restorations are generally collected in coarse filters and sold for refinement. Minor amalgam particles released by production of new fillings or by removal of old restorations partly sediment in tubes and drains. The remaining particles are carried with the waste water stream to the local purifying plant. In Scandinavia, the industrial discharge of mercury-contaminated waste water has been reduced to a minimum. According to recent investigations, dental clinics appear to be responsible for the major amount of mercury collected in the sludge generated in purifying plants. If threshold values for heavy metal content, including mercury, are exceeded, the sludge is not allowed to be recycled as fertilizer. Installation of an approved amalgam-separating apparatus in dental clinics is now mandatory in several countries--for example, Switzerland, Germany, Sweden, and Denmark. Approval of amalgam separators is based on national testing programs, including clinical or laboratory tests demanding 95-99% separating efficiency.

Problems and Benefits Associated With Restorative Materials: Side-Effects and Long-Term Cost:

Abstract: The paper reviews data on biological side-effects of dental materials on patients and also on personnel who routinely handle the materials. The incidence of adverse effects is low-in one study indicated to be 1:700 for all types of treatments. For individual types of materials, it will be significantly lower, and for restorative materials, probably in the 1 : 10,000 to 1:20,000 range. Allergic reactions are the most common type of adverse effect of dental materials. Lichenoid reactions on the oral mucous membrane adjacent to amalgam restorations are the most frequently encountered side-effects for a specific group of restorative materials.Cost analyses were based on reports of longevity of different restorations and the cost of restorations at the time of placement. Amalgam restorative therapy was more cost-effective than composite restorations and gold castings.

Oral mucosa and skin reactions related to amalgam.

Abstract: Documented cases of oral mucosa and skin affections related to amalgam restorations are rare, although the exact incidence is unknown. Lesions of the oral mucosa may be due to specific immunologic or non-specific toxic reactions toward products generated from restorations. The immunologic reaction most probably involved in mucosal affections related to amalgam is the delayed or cell-mediated (type IV) reaction. Such reactions are seen in contact allergy, and the term "contact lesions of the oral mucosa" has been used. There is a much lower tendency of sensitization through mucous membranes than through skin, and it is questionable whether mercury released from amalgam restorations is able to sensitize a patient.A chronic toxic reaction may be established due to repeated or constant influence to toxic agents in low concentrations over long periods. Such reactions are most frequently localized to the contact zone with the toxic agent. Chronic toxic reactions may possibly be seen in areas of the oral mucosa ...

Toxicology versus allergy in restorative dentistry.

Abstract: The frequency of side-effects among dental patients is very low and is seen mostly as mild allergic reactions. Among the dental staff, contact allergic eczema is occasionally seen, induced by certain metals and various organic materials.

Principles of risk assessment.

Abstract: _ This review discusses the basic principles of risk assessment as used in general toxicology and in monitoring side-effects of therapeutic treatments. It also outlines how these principles may apply to assessment of biological reactions to dental restorative materials. Mercury exposure from amalgam fillings is used as an example. The calculations performed are intended only as illustrations, and many other factors must be taken into account. Thus, the calculations are not intended as the last word in risk assessment of amalgam fillings.

Casting alloys: the materials and "The Clinical Effects".

Abstract: This manuscript is published as part of the proceedings of the NIH Technology Assessment Conference on Effects and Sideeffects of Dental Restorative Materials, August 26-28,1991, National Institutes of Health, Bethesda, Maryland, and did not undergo the customary journal peer-review process. I t is estimated that 96% of adults in the United States between the ages of 18 and 65 have one or more carious or filled teeth, with an average of almost 10 decayed or filled teeth for each adult (Miller etal, 1987). The best treatment for carious teeth, to prevent loss and restore masticatory function, often involves the use of cast dental restorations. This paper will discuss the chemical compositions of noble and base metal dental alloys and, based on 72-month data from a 10-year clinical study (Morris etal., 1986), will summarize the clinical behavior of alloys with "representative formulations". "Noble" refers to metals with marked resistance to oxidation and chemical reaction. Silver is not considered noble in the context of dental casting alloys. "Precious" refers to an economic value. The American Dental Association has stated that "semi-precious" has no meaning in dentistry because no definition has been agreed on (ADA, 1984). "Base metal" refers to metal elements that are chemically reactive to their environment (Phillips, 1991).

Dental amalgam: the materials

Abstract: 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)

Side-effects: mercury contribution to body burden from dental amalgam.

Abstract: The purpose of this paper is to examine and report on studies that relate mercury levels in human tissues to the presence of dental amalgams, giving special attention to autopsy studies. Until recently, there have been few published studies examining the relationship between dental amalgams and tissue mercury levels. Improved and highly sensitive tissue analysis techniques have made it possible to measure elements in the concentration range of parts per billion. The fact that mercury can be absorbed and reach toxic levels in human tissues makes any and all exposure to that element of scientific interest. Dental amalgams have long been believed to be of little significance as contributors to the overall body burden of mercury, because the elemental form of mercury is rapidly consumed in the setting reaction of the restoration. Studies showing measurable elemental mercury vapor release from dental amalgams have raised renewed concern about amalgam safety. Mercury vapor absorption occurs through the lungs, with about 80% of the inhaled vapor being absorbed by the lungs and rapidly entering the bloodstream. Following distribution by blood circulation, mercury can enter and remain in certain tissues for longer periods of time, since the half-life of excretion is prolonged. Two of the primary target organs of concern are the central nervous system and kidneys.

Dental composites/glass ionomers: clinical reports.

Abstract: Composites and glass ionomers have not been extensively tested in clinical trials for biological safety. Most clinical evaluations have looked at other factors, such as retention, wear, or color. The primary evaluation criterion used in clinical trials is post-operative sensitivity. Sensitivity does not seem to have any correlation to pulpal inflammation. Inflammation can be the result of mechanical, thermal, chemical, and bacterial insults. It is complicated for individual contributions to be separated in short-term studies. General usage of these materials over about 20 years indicates a high benefit-to-risk ratio. Despite some complaints of sensitivity with some glass-ionomer compositions, both composites and glass ionomers are relatively trouble-free. There is no evidence of short-term or long-term risk. Toxicological studies have focused almost exclusively on pulpal reactions. Systemic reactions have not been closely examined, although there is no suspicion of any problems after virtually billions of procedures in the United States. New glass-ionomer cements are similar to contemporary composite formulations. Continued development of these materials may ultimately produce an amalgam replacement material that is economically and philosophically desirable to general dentists.

Side-effects of dental ceramics.

Abstract: Evaluation of side-effects to low-dose exposure of any agent is difficult, especially if the agent exhibits a low toxicity. The most common way to approach such evaluation is to define special groups which are exposed more than others. Studies of such risk groups may facilitate interpretation of information related to those exposed to a low dose. For dental materials, dentists, dental assistants, and laboratory technicians represent typical risk groups. In addition to receiving dental treatments and having restorations like anyone else, they handle the materials in their daily work. The exposure to the materials occurs more frequently and at a higher dose for these groups than for the patient receiving dental treatment. Thus, the possibilities for side-effects are greater. Some materials are handled more closely by laboratory technicians than by other members of the dental team, e.g., dental ceramics.

Statement: effects and side-effects of dental restorative materials.

Abstract: T he incidence of tooth decay has been declining steadily among American children in recent years, but there remains a substantial demand in this country for dental restorative materials. More than 200 million restorations are placed each year. The most commonly used dental restorative material is silver amalgam, followed by tooth-colored plastic composite materials, various cements, alloys, porcelain, and other ceramics. Selection of the most appropriate material depends on the extent of the cavity or defect in the tooth, the condition of the mouth, whether the restoration will be visible, and cost factors. The effectiveness of currently used materials in the restoration of tooth function is established, especially for amalgams, casting alloys, ceramics, composites, and glass ionomers. Once placed, dental restorative materials are in prolonged contact with living tissues. Although they are made as strong and inert as possible, fillings may deteriorate or break, and minute amounts of component substances may be released into the mouth. The possibility of adverse health effects from exposure to mercury from dental amalgam has kindled concern among some members of the public. The issue has also been debated in the scientific community. This conference was convened to evaluate and compare the data on the effectiveness and sideeffects of currently used dental restorative materials. It was sponsored by the National Institute of Dental Research (NIDR) and the National Institutes of Health's Office of Medical Applications of Research and held in Bethesda, Maryland, August 26-28,1991. Members of a scientific panel and a large audience heard and discussed a series of reports by experts on various aspects of this subject. The panel then weighed the scientific evidence and responded to the following five questions:

Dental Ceramics: the State of the Science:

Abstract: This review covers the properties of dental ceramics. Castable systems, bioactive glass, PMF systems, CAD/CAM, and ceramic brackets in orthodontics are briefly discussed. Many of the advances made between 1960 and 1975 were directed toward the understanding, controlling, and developing of new ceramic processes. New and deeper understanding of the structure of non-crystalline solids, structural imperfections, sintering physics, and other physical phenomena related to the melting and solidification processes has brought ceramics from the near-total art form process of the mid-century to the status of a highly sophisticated science it enjoyed in the 1980's.

Dental amalgam and mercury vapor release.

Abstract: Dental diseases are among the most common ailments, and dentists in the United States spend over 50% of their time in dental practice rebuilding carious, malformed, and traumatically injured teeth. It is logical, therefore, that the majority of the dental school curriculum is devoted to the diagnosis, prevention, and treatment of teeth with anomalies. Dentists have several choices of materials they can use to accomplish the task of rebuilding teeth. Besides amalgam, they have ceramic materials, resin composites, base-metal and noble casting alloys, and glass-ionomer cements to use to restore the posterior dentition. Each of these restorative materials has advantages and disadvantages, and the clinical judgment as to when a particular material should be used is given a high priority in dental education. Amalgam is the most widely used of these restorative materials, with 92% of dentists listing it as the material of choice in the posterior of the mouth (Clinical Research Associates, 1990). Dentists have been placing amalgams for over 150 years in the US. They placed 150 million last year, which represents over 75 tons of amalgam alloy. The reasons that dentists use this restorative material so frequently are its durability, ease of manipulation, and low cost. Numerous clinical studies have been conducted on the serviceability of amalgam. Most of these have been on the old, low-copper alloys, and results indicate that they last from 8 to 15 years (Bailit et al., 1979; Osborne et al., 1980; Qvist et al., 1986). In the past 20 years, vast improvements have been made in amalgams with the development of the high-copper systems.(ABSTRACT TRUNCATED AT 250 WORDS)

Teratological aspects of dental amalgam.

Abstract: The teratogenic effect is determined by four factors: (1) the agent, (2) the dose, (3) the stage of embryonic development, and (4) the genetic constitution of the embryo. The first two factors are of particular interest and warrant further comment. It should be emphasized that the mercury released from dental amalgam is mainly metallic mercury vapor. The dose of mercury vapor from dental amalgam fillings in the order of 5 ug/day is very low compared with the doses in a teratological study and is not likely to exceed the threshold necessary for a teratogenic effect to occur.The concentration of the teratogen at the target tissue is determined not only by the degree of placental transfer but also by other factors, such as the distribution within the maternal organism, the affinity to the fetal liver and blood, the hematocrit value, and the passage through the ductus venosus. These factors might help to explain toxicological mechanisms and species differences and have to be considered if the results of anima...

Documented clinical side-effects to dental amalgam.

Abstract: Since all dental restorative materials are foreign substances, their potential for producing adverse health effects is determined by their relative toxicity and bioavailability, as well as by host susceptibility. Adverse health effects to dental restoratives may be local in the oral cavity or systemic, depending on the ability of released components to enter the body and, if so, on their rate of absorption. The medical scientific community is now in general agreement that patients with dental amalgam fillings are chronically exposed to mercury, that the average daily absorption of mercury from dental amalgam is from 3 to 17 micrograms per day, and that the amalgam mercury absorption averages 1.25-6.5 times the average mercury absorption from dietary sources (World Health Organization, 1991). The health significance of this chronic mercury exposure is now being investigated by several medical research groups.

Future needs for dental restorative materials.

Abstract: While the population of the United States increases from 250 to 310 million people, the number in older age groups will increase dramatically from 28 million to about 64 million. Tooth retention has improved remarkably in the 65-74 age groups, from 7.4 in 1962 to 17.9 in 1986. While younger age groups will require less treatment due to decline in dental caries, older age groups appear to require more treatment than did similar age cohorts in previous generations. Hence, the need for restorative procedures by the United States population will be on an upward trend for the next decade or two.