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Tooth filling materials Dental amalgams & alternative materials

6. Conclusion on health effects of dental amalgams and their alternatives on users

  • 6.1 What is the scientific evidence linking dental amalgams to health problems?
  • 6.2 How safe are dental amalgams containing mercury?
  • 6.3 How safe are alternative tooth filling materials?

6.1 What is the scientific evidence linking dental amalgams to health problems?

The SCENIHR opinion states:

4. OPINION

We discuss here the general observations that constitute the scientific opinions concerning the safety of dental amalgams and alternative dental restorative materials and then provide answers to the questions posed in the mandate.”

4.1. The scientific and clinical evidence

Dental amalgam remains an effective restorative material and, from the perspectives of longevity, the mechanical performance and economics, may be considered the material of choice for some restorations in posterior teeth, including the replacement therapy for existing amalgam fillings.

However, because dental amalgam is not tooth-coloured nor does it adhere to remaining tooth tissues, its use has been decreasing in recent years and tooth-coloured filling materials have become increasingly more popular. This is consistent with the significant trend towards more minimal intervention techniques in dentistry, especially those that involve materials with adhesive properties.

There is an increasing trend towards non-amalgam restorations, which shows some variations within and between countries, and is emphasized by the significant reduction of training in the placement of dental amalgam restorations and the corresponding increase in training in the use of amalgam alternatives in a growing number of dental schools in European countries.

Independent of risk management decisions, and of the economic considerations in restorative dentistry, a sustained reduction in the use of dental amalgam in oral health care provision is expected across the European Union, the rate of which is dependant on trends in dental education towards the increasing use of alternative materials in place of amalgam and the possible reduced availability of mercury products in general.

Mercury is the major metallic element used in dental amalgam. It is recognized that mercury in general does constitute a toxicological hazard, with reasonably well defined characteristics for the major forms of exposure, involving elemental mercury, organic and inorganic mercury compounds. It is accepted that the reduction in use of mercury in human activity would be beneficial, both for the decrease in indirect human exposure and environmental considerations.

For many decades, going back to the introduction of amalgam into clinical practice over 150 years ago, there has been a debate about the possibility of causal relationships between the use of mercury containing amalgam and a wide variety of adverse systemic health effects. In spite of many studies and investigations into this putative causal link, there is no unequivocal evidence to support this possibility.

It is recognized that some local adverse effects are occasionally seen with dental amalgam fillings, including allergic reactions and an association with clinical features characteristic of lichen planus, but the incidence is low and normally readily managed. There have been claims of causation with respect to a variety of systemic conditions, particularly neurological and psychological/psychiatric effects, including Alzheimer’s, Parkinson Disease, Multiple Sclerosis and also kidney disease. However, several major epidemiological studies have failed to reveal such effects. These studies have included assessments in children and in pregnant and lactating women. It is generally concluded that no increased risks on adverse systemic effects exist, and indeed the most recent studies have failed to find any association between the use of amalgam and neuropsychological development in children. We do not therefore consider that the current use of dental amalgam poses a risk of systemic disease.

The main exposure to mercury in individuals with amalgam restorations occurs during placement or removal of the fillings. Exposure does occur through the lifetime of a restoration, but the rates of mercury release are extremely low. The transient mercury release during placement and removal will result in exposure to the patients and also to the dental personnel. However, this may be minimized by the use of appropriate clinical techniques. In particular it should be noted that the removal of amalgam restorations will increase the exposure of the individual patient to relatively high levels of mercury compared to leaving the amalgam filling intact. Although there is the possibility of some alleviation of subjective symptoms such as burning or dry mouth and taste disturbance, we find no evidence of clinical justification to remove clinically satisfactory amalgam restorations with the exception of those patients which are suspected to have allergic reactions and positive patch tests.

The use of dental amalgam results in environmental exposure to mercury, primarily through its release during amalgam placement and removal, and the handling and disposal of amalgam waste products in general. Improvements in the treatment of waste water from dental clinics and amalgam waste has generally reduced this exposure. A further source of environmental exposure occurs through the burial or cremation of individuals with dental amalgam fillings. It should be noted that a significant increase in amalgam usage occurred between 1950 and 1990 that may result in a rise in environmental exposure over the next few decades as these individuals die.

The general reduction in the use of dental amalgam in clinical practice has been coincident with an increasing use of alternative restorative materials, usually referred to as tooth-coloured materials, principally composites, cements and their hybrids. We note that these materials, which may be very complex chemically, are not without certain clinical limitations and toxicological hazards. They frequently contain a variety of organic substances and they undergo chemical reactions within the tooth cavity and adjacent soft tissues during placement.

It should not be assumed that non-mercury containing alternatives are free from any concerns about adverse effects. With respect to dental composite restorative materials and hybrid systems that incorporate polymerisable resins, it is known that some of the monomers involved in their intra-oral placement and polymerisation are highly cytotoxic to pulp and gingival cells in vitro. There is clear evidence that some of these substances are mutagenic in vitro although it is far from clear whether this has any clinical significance. Some of these substances are irritants when used by themselves in various situations and the occupational hazards associated with their use are similar to those hazards found in the printing and automotive industries. Allergies to a few of these substances have been reported, both in patients and in dental personnel.

It is noted that there are very limited scientific data available concerning exposure of patients and dental personnel to those substances that are used in alternative restorative materials. It is recognised that such data are very difficult to obtain.

These alternative materials have now been in clinical use for well over thirty years, initially in anterior teeth and more recently also for restorations in posterior teeth. This use has revealed little evidence of clinically significant adverse events, even taking into account the fact that the quality of evidence concerning clinical outcomes is limited, with a reliance on case reports. It is also important to note that the commercially available materials have either changed substantially or been improved considerably during this time, with reduced bioavailability of harmful components through improved polymerisation processes.

As a separate issue, it should be borne in mind that these photo-polymerisable systems require activation and that the powerful light sources now used for this purpose may constitute an additional risk for adverse effects, both to patients and dental personnel. Eye protection is extremely important.

We note that the full chemical specification of these alternative restorative materials is not always divulged and it may be difficult to ascertain exactly what they contain. As a result, there is limited toxicological data publicly available for these materials. All dental restorative materials are defined as medical devices according to EU-Directive 93/42/EEC. They are surgically invasive medical devices intended for long-term use which according to rule 8 defines them as class 2b medical devices. However, the directive has a derogation clause which states that when such medical devices are used in teeth they will be in class 2a. As such when regulatory approval is sought from a notified body it is not necessary to reveal a design dossier including a risk analysis and therefore the chemical specification does not have to be revealed. In view of the lack of information on the toxicity of the constituents of the alternatives and relevant exposure data it is not possible to provide a scientifically sound statement on the safety of these materials.

As a general principle, the relative risks and benefits of using dental amalgam or the various alternatives should be explained to patients to assist them to make informed decisions. This may have implications concerning the provision of product information. In view of the controversial nature of this subject, which has existed for very many years, it would also be beneficial for the community in general to be better informed of the recognized benefits and risks.

It is noted that indirect restorative techniques, involving the use of gold alloys and ceramics may also be used when direct restorations are contra-indicated. Their use, which is both time-consuming and expensive, has remained at a comparatively low level in recent years. This use is not seen as a health concern.

Source & ©: SCENIHR,  The safety of dental amalgam and alternative dental restoration materials for patients and users (2008), 4.0 Opinion, p.52

6.2 How safe are dental amalgams containing mercury?

The SCENIHR opinion states:

4.2. Human Safety of Dental Amalgam

4.2.1. Is there scientific evidence that supports a link between amalgam and allergic reactions, neurological disorders or other health disorders?

With respect to allergic reactions, many metals in close contact with the skin or mucosal surfaces can be the cause of contact dermatitis and equivalent conditions, and mercury is no exception. Oral lichen planus is sometimes associated with dental amalgam restorations, and one of the possible causes is allergy to constituents of dental amalgam. Whilst the incidence is low, it is recognised that many of the patients affected will show a positive skin patch test for either amalgam or mercury, and removal of restorations from patients with such conditions and positive patch tests often results in the alleviation of symptoms.

With respect to all other putative links between dental amalgam and health disorders in recipients of amalgam restorations, there is no scientific evidence to support such links. It is accepted that elemental mercury does have a specific toxicological profile and that the presence of amalgam restorations in an individual is likely to lead to raised blood and urine mercury levels. However these raised levels appear to be lower than those necessary to cause adverse effects in general, and the overwhelming clinical and epidemiological evidence does not support any causal link between mercury and any of the diseases that have been suggested as being associated with dental amalgam. This analysis has taken into account the possibilities of effects within the urinary, neurological, reproductive and immune systems and also associations with psychological conditions.

4.2.2. Is the use of dental amalgam safe for patients and users, i.e. dental health professionals? Are certain populations particularly at risk, e.g. pregnant women or children?

In the light of the above comments we conclude that dental amalgam is a safe material to use in restorative dentistry with respect to patients. Dental health is an extremely important component of general health care and the benefits of amalgam to individuals presenting with dental caries far outweigh the very low level of risk associated with allergies. With respect to populations at risk, there is a lack of information about effects in pregnant women. There is no evidence to suggest that pre-existing amalgam restorations pose any risk as far as the health of such women and the developing foetus is concerned, and certainly any removal of restorations during this time would present a greater exposure to mercury. As with any other medical or pharmaceutical intervention, however, caution should be exercised when considering the placement of any dental restorative material in pregnant women. There is no evidence that infants or children are at risk of adverse effects arising from the use of dental amalgam, the most recent studies failing to find any association between the use of amalgam and neuropsychological development in children. We emphasise that we find no evidence of clinical justification to remove clinically satisfactory amalgam restorations on the grounds of patient safety, with the exception of those patients which have a positive patch test and local alterations of the oral mucosa or systemic allergic reactions. It should be noted that the removal of amalgam restorations will result in an acute relatively high exposure of the individual patient to mercury, compared to leaving the amalgam filling intact.

As far as dental personnel are concerned, it is recognised that they may be at greater risk with respect to mercury exposure than the general population. However, the incidence of reported adverse effects is very low and this possibility has decreased substantially with improvements to dental amalgam delivery and amalgam hygiene practices in general.

Source & ©: SCENIHR,  The safety of dental amalgam and alternative dental restoration materials for patients and users (2008), 4.2 Human safety of Dental Amalgam, p.54

6.3 How safe are alternative tooth filling materials?

The SCENIHR opinion states:

4.3. Human Safety of Alternatives

4.3.1. Is there scientific evidence that supports a link between alternative materials and allergic reactions, neurological disorders or other health disorders?

Far less information is available concerning exposure, toxicity and clinical outcomes for alternative materials compared with dental amalgam. The materials themselves are far more complex chemically and there are no simple surrogates as markers for either exposure or toxicity, equivalent to the mercury in amalgams.

There is some evidence that certain of the low molecular weight substances used in the preparation of these alternatives are associated with local allergic reactions, although the incidence is very low.

There is no evidence that there is any association between these materials as used clinically and any neurological disorders or any other health disorders.

4.3.2. Is the use of alternative dental restoration treatment safe for patients and dental health professionals? Are certain populations particularly at risk, e.g. pregnant women or children?

Although there are well recognised cytotoxicity and mutagenicity profiles for some of the chemical substances used in alternative materials, there is no evidence of any adverse clinical effects associated with such substances, apart from a very low incidence of allergies. Notwithstanding the observation that complete chemical compositions and risk analyses do not have to be revealed during the regulatory approval process so that some uncertainties may exist, these materials can be considered safe for patients. Since there is no evidence of any systemic bioavailability of these substances in the body, there would be no expectation that any particular population would be at risk. Again, as with any other medical or pharmaceutical intervention caution should be exercised when considering the placement of any dental restorative material in pregnant women. We do emphasise, however, that data is sparse and the continuing evolution of these materials suggests that caution should be exercised before new variations are introduced into the market.

As far as dental personnel are concerned, again there is evidence of limited numbers of cases of allergies to these materials. The pervasiveness of some of the low molecular weight species throughout dental clinics should be noted.

4.4. Oral Health and Safety - In view of the specific properties of dental amalgam and alternatives when used for dental restorative treatment, is dental health equally ensured by dental amalgam and alternatives?

It is difficult to make direct comparisons between dental amalgam and the alternative materials since they are not used in the same way. Dental health can be adequately ensured by both types of material. All the materials are considered safe to use and they are all associated with very low rates of local adverse effects with no evidence of systemic disease. There is, obviously, a greater level of aesthetic appeal with those alternatives that are tooth coloured compared to the metallic amalgam. Furthermore, the use of these alternatives allows the use of minimally interventional adhesive techniques. In clinical practice, amalgams usually require more extensive cavity preparation, with the removal of more tooth substance, than is necessary with the adhesive alternative systems. The composite resins, cements and various hybrids are associated with more minimally invasive operative techniques, and this trend in dental practice is seen to be very important and valuable as far as patients are concerned, being consistent with the general principles of contemporary dentistry. It is true, nevertheless that on a historical basis amalgam restorations have in general been found to last longer, as restorations using alternatives have had a higher incidence of secondary caries. This may change with continuing improvements to the alternative materials. Patients in general have had needed more frequent interventions when treated with alternatives, but each intervention involves much less tooth removal than required for amalgam restorations. Although the alternative materials were originally introduced for the restoration of anterior teeth, primarily with small and moderate size initial lesions, in recent years their use has extended towards lesions of all sizes in posterior teeth. Dental amalgam may still be used for large lesions, and for the replacement of failed existing amalgam restorations, especially those associated with secondary caries. It is recognised that there are alternative indirect restorative materials, including gold alloys and ceramics, which are used in situations where direct restorative treatments are contra-indicated.

As a general principle, the relative risks and benefits of using dental amalgam or the various alternatives should be explained to patients to assist them to make informed decisions. This may have implications concerning the provision of product information. In view of the controversial nature of this subject, which has existed for very many years, it would also be beneficial for the community in general to be better informed of the recognized benefits and risks.

Finally, independent of risk management decisions and of the economic considerations in restorative dentistry, a reduction in the use of dental amalgam in oral health care provision is expected across the European Union. The rate at which this takes place is dependent on the trends in dental education towards the increasing use of alternative materials in place of amalgam, and the possible reduced availability of mercury products in general. This is a process that can be readily managed by the dental profession with no detriment to patient oral health. In view of the opinions expressed above, we see no advantages to carrying out further research on any aspects of the safety of dental amalgam restorations. The lack of data on the toxicity, exposure and health effects of the alternative materials does imply, however, that more experimental, clinical and epidemiological research is required to guarantee patient safety in the future.

5. Comments received from the Public Consultation

Information about the public consultation has been broadly communicated to national authorities, international organisations, and other stakeholders. The relevant web site was opened for comments on 14 January 2008 and the deadline for submission was 22 February 2008. In total, 26 contributions were received from which 14 were from organisations and 12 from individuals. Of the organisations, 6 were non governmental, 4 public authorities and 4 other institutions, including dental associations.

In evaluating the responses from the consultation, submitted material has only been considered for revision of the opinion if

  1. it is directly referring to the content of the report and relating to the issues that the report addresses,
  2. it contains specific comments and suggestions on the scientific basis of the opinion,
  3. it refers to peer-reviewed literature published in English, the working language of the SCENIHR and the working group,
  4. it has the potential to add to the preliminary opinion of SCENIHR.

Each submission which meets these criteria has been carefully considered by the Working Group. Overall, many of the comments were of good quality. The scientific rationale of the report has been revised to take account of relevant comments. The literature has been updated with relevant publications. The Opinion, however, remained essentially unchanged, but was, in certain respects, clarified by the amendments to the scientific rationale.

Epidemiological studies on dental amalgam do not indicate that this material induces systemic adverse effects in patients, other than the recognised local irritation and allergic responses. However, it is recognised that very occasionally an individual may have unexplained atypical physical or other reactions attributed to mercury.

As indicated in the opinion, the information on adverse effects on alternatives is limited. During the public consultation, limited additional information became available regarding the alternative restorative materials.

6. MINORITY OPINION

None

Source & ©: SCENIHR,  The safety of dental amalgam and alternative dental restoration materials for patients and users (2008), 4.3 Human Safety of Alternatives, p.55


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