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GMS Health Technol Assess. 2008; 4: Doc12.
Published online Nov 13, 2008.
PMCID: PMC3011298
Longevity of dental amalgam in comparison to composite materials
Katja Antony,*1 Dieter Genser,1 Cora Hiebinger,1 and Friederike Windisch1
1Gesundheit Österreich GmbH, Geschäftsbereich ÖBIG, Wien, Österreich
*To whom correspondence should be addressed: Katja Antony, Gesundheit Österreich GmbH, Geschäftsbereich ÖBIG, Stubenring 6, 1010 Wien, Tel.: +43-1-51561-259, E-mail: antony/at/goeg.at
Health political background
Caries is one of the most prevalent diseases worldwide. For (direct) restaurations of carious lesions, tooth-coloured composite materials are increasingly used. The compulsory health insurance pays for composite fillings in front teeth; in posterior teeth, patients have to bear the extra cost.
Scientific background
Amalgam is an alloy of mercury and other metals and has been used in dentistry for more than one hundred and fifty years. Composites consist of a resin matrix and chemically bonded fillers. They have been used for about fifty years in front teeth. Amalgam has a long longevity; the further development of composites has also shown improvements regarding their longevity.
Research questions
This HTA-report aims to evaluate the longevity (failure rate, median survival time (MST), median age) of direct amalgam fillings in comparison to direct composite fillings in permanent teeth from a medical and economical perspective and discusses the ethical, legal and social aspects of using these filling materials.
Methods
The systematic literature search yielded a total of 1,149 abstracts. After a two-step selection process based on defined criteria 25 publications remained to be assessed.
Results
The medical studies report a longer longevity for amalgam fillings than for composite fillings. However, the results of these studies show a large heterogeneity. No publication on the costs or the cost-effectiveness of amalgam and composite fillings exists for Germany. The economic analyses (NL, SWE, GB) report higher costs for composite fillings when longevity is assumed equal (for an observation period of five years) or longer for amalgam compared to composite fillings. These higher costs are due to the higher complexity of placing composite fillings.
Discussion
Due to different study designs and insufficient documentation of study details, a comparison of different studies on longevity of direct amalgam and composite fillings in posterior teeth is difficult. Apart from the difficulties in conducting a randomized, controlled long-term study comparing the longevity of direct fillings, the fact that composites and adhesives used in a study have often already been replaced by the next generation of the product at the time of study publication presents an additional problem. Not only the filling material, but also patient parameters and local, intraoral factors (e. g. localisation of the filling) as well as the treating dentist have an impact on the longevity of dental fillings. In evaluating economic studies, one has to refer to the heterogeneity of data on longevity in the medical evaluation. The only effect parameter used in the studies is longevity, other aspects (e. g. long-term functionality) are only referred to in discussions. Extensive counselling of patients regarding the selection of the appropriate filling material is important.
Conclusions
Amalgam fillings show a longer longevity than composite fillings. Two out of six systematic reviews conclude that the expected survival time of composite fillings can be comparable to amalgam fillings. However, these conclusions are based on the results of short-term studies which usually overestimate the longevity of filling materials. From an economic standpoint, amalgam is the more economic filling material compared to direct composite fillings in posterior teeth when considering longevity as the only result parameter. Other aspects than longevity need to be considered in individually choosing the appropriate dental filling material. For future studies aiming to compare the longevity of amalgam and composite fillings, a sufficient sample size and study period, preferably in the setting of a private dental practice, should be aimed for. An evaluation of the cost-effectiveness of amalgam and composite fillings should take the functionality of teeth over a longer time period into account, as well as patients’ preferences. The rapid development of composite materials and adhesives make short term revisions of these conclusions necessary.
1. Health political background
Caries is one of the most prevalent diseases worldwide. Amalgams have been used in dentistry for more than one hundred and fifty years for the restoration of carious lesions. The advantages of amalgam are its high resistance to wear, its excellent marginal adaptation and its easy processability in combination with a low error-proneness. However, the economic filling material is being rejected by some patients due to aesthetic reasons and individual safety concerns. As an alternative, tooth coloured composite materials are utilised; the improvement of their material properties makes it possible to use them in posterior permanent teeth. The placement of these filling materials takes longer and is therefore associated with higher costs than the placement of amalgam fillings.
The compulsory health insurance pays for tooth-coloured fillings in front teeth. In posterior teeth, higher reimbursements for composite fillings are granted if an amalgam filling is absolutely contra-indicated. Does the patient wish a filling material outside the basic coverage, he has to bear the extra cost, which is the difference between the fee for the chosen filling and the reimbursement for the cheapest comparable plastic filling (according to information of the Medical Advisory Service for Dentists (MDZ), this amounts to 40 to 130 Euro for composite fillings, depending on the size of the cavity and the extent of treatment).
2. Scientific background
Caries is a multifactorial disease, which can lead to the deterioration of enamel and dentin due to the interaction of plaque (biofilm) and the surface of the tooth. Among others, amalgam and composite materials are used as filling materials for carious lesions. Amalgam is an alloy of mercury and other metals, which has been used for more than one hundred and fifty years. Composites are synthetic filling materials that are composed of a resin matrix and chemically bonded fillers. They have been used for about fifty years in front teeth. Amalgam has a long longevity. As the development of composites has also shown improvements regarding their longevity a comparison of the current literature seems meaningful.
3. Research questions
This report aims to answer the following research questions:
  • What is the longevity (failure rate, median survival time (MST), median age) of direct amalgam fillings compared to direct composite fillings in permanent teeth?
  • What is the cost-effectiveness of direct amalgam fillings compared to direct composite fillings?
  • What are the ethical, legal and social aspects that have to be considered when using amalgam or composite materials for direct fillings?
4. Methods
This HTA-report was prepared by applying the methods of a systematic literature review. The systematic literature search (DIMDI-HTA-superbase as well as HTA- and Cochrane-databases; March 2007) yielded 1,149 abstracts. Following a two-part selection process according to standard, predefined criteria, 21 medical and five economic publications were included in the assessment. Relevant texts regarding ethical (eleven articles) and legal (two articles) aspects were also used.
5. Results
Systematic reviews point out that only few long-term data exist. However, short-term studies (? 5 years) often overestimate the longevity of filling materials and give a distorted image. The setting (controlled study at a university; general dental practice) has an impact on the results. Therefore, a meaningful comparison of different study results is only possible when an evaluation of the filling materials under similar conditions is ensured. The fact that the documentation of the majority of studies is incomplete is also criticised.
A systematic review of 2007 evaluates the longevity of fillings in posterior teeth in studies published between 1996 and 2006. The review is focused on amalgam, however, the longevity of composites is mentioned for comparison. In longitudinal studies, the MST for amalgam is reported to range between 11.4 and one hundred and fifty years under ideal conditions at dental education centres and between 7.1 and 44.7 years in private dental practices. For composites, MST between 8.0 and 44.4 years are reported under ideal conditions. Only one longitudinal study has been conducted in the setting of a general dental practice; this study reports a MST of 16 years for composites in posterior teeth (observation period: 17 years). However, the relatively low failure rate of 5% after ten years rapidly increases to 40% after 15 and 72% after 17 years. In studies with a shorter observation period, MST for cavities of class I and II of 9.1 and 19.2 years are reported for composites. Another review of 2003 provides an overview of prospective clinical studies on direct composite fillings in posterior teeth. The studies included were published between 1996 and 2002. The observation periods of studies range from one to 17 years, failure rates vary between 0 and 45%. The impact of the length of the observation period on the failure rate is highly significant and confirms that short-term studies have a tendency to overestimate the longevity of fillings. It is concluded that the expected survival time of correctly placed composite fillings can be comparable to amalgam fillings, but that overall, the longevity of amalgam is higher than that of composite fillings in posterior, as well as in front teeth for most observation periods that are longer than three to five years. A review of 2004 also reports annual failure rates for amalgam fillings of between 0 and 7.4% for observation periods of up to 20 years. Annual failure rates for composite fillings are reported to be 0 to 9%. In older studies, annual failure rates are significantly higher than in studies published since 1990. Also, failure rates in cross-sectional studies are considerably higher than those in longitudinal studies. In controlled longitudinal studies published between 1990 and 2003, the median annual failure rate for amalgam fillings in class II cavities (2.0% (0 to 7.4%)) is similar to that of composite fillings (1.7% (0 to 7.0%)). An earlier review of the same authors’ group draws the same conclusions. A British HTA-report of 2001 was prepared following the guidelines of the NHS Centre for Reviews and Dissemination. The probability of survival for amalgam fillings is reported to be ?85% after five years and ?80% after ten years. In the majority of studies on composites, the probability of survival of fillings is ?80% after five years and ?75% after ten years. The authors state that most studies were conducted in a dental clinic or another institutional setting. Especially studies on composite fillings mostly evaluate small sample sizes; a lot of the studies showing particularly low longevity were conducted in the 1980s or early 1990s. A systematic review of 1999 was conducted according to the guidelines of the NHS Centre for Reviews and Dissemination and the Cochrane Collaboration and evaluates class I and II filings in studies having an observation period of at least five years. The MST ranges between five and 23 years for amalgam fillings. For composite fillings, a MST of 17 years is reported; other authors state that after ten years, 72% of amalgam and 56% of composite fillings were still functional.
Two primary studies of 2007 compare failure rates of fillings in children. In one of the studies, the replacement rate for composites after five years is 21.9% and for amalgam 15.9% (p=0,61). For both materials, the necessity to replace a filling increases with the number of fillings per patient (p<0,001). Although no difference was shown between replacement rates for amalgam and composite fillings during the observation period, the authors assume that differences will become significant over time. In the second study, the survival rate of amalgam fillings after seven years was higher than that for composite fillings (85.5%) as well.
A longitudinal study of 2003 evaluates extensive fillings in a longitudinal study in 428 patients. All teeth included in the study have been previously restored, 60% are endodontically treated. During the study period, two different amalgams and three different composites are used. Until 2000, the fillings are evaluated at least every four years. Composites are used almost exclusively in premolars. A Kaplan-Meier survival analysis shows a MST of 12.8 years for amalgam and 7.8 years for composite fillings. The overall ten-year survival rate is reported to be 60% for amalgams and 50% for composites. In an earlier study at least four class I or II fillings are placed per patient (using amalgam and three different composites) and tracked for eight years. 90.6% of the fillings are placed in molars, 9.4% in premolars. After eight years, 13.7% of the 161 composite fillings and three (5.8%) of the 52 amalgam fillings have lost their functionality.
Three retrospective studies analyse data of patient records. In one of these studies of 2005, the survival time of amalgam fillings ranges from 60% to 72% after five years and from 43% to 58% after ten years depending on their size and complexity. For composite fillings in front teeth and non-load-bearing posterior teeth, the survival time is 58% after five years and 43% after ten years. Another study evaluates class I and II fillings that have been placed between 1990 and 1997 in premolars and molars. Between 1990 and 1994, amalgam is used relatively more frequently for larger fillings and composite for smaller fillings. After 1994, amalgam is hardly used. For amalgam, a survival rate of 89.6% after five and 79.2% after ten years, for composites, a survival rate of 91.7% after five and 82.2% after ten years is reported. Hawthorne und Smales (1997) include only patients, who have been coming to control visits on a regular basis for more than twelve years. During the observation period, 1,728 amalgam (mostly cavities class I and II) and 458 composite fillings (mostly cavities class III, IV and V) are placed. The MST for amalgam is calculated to be 22.5 years, for composites it is 16.7 years.
In several studies, data is collected through surveys sent to private dental offices and walk-in clinics; the median age for amalgam fillings is reported to be six to 15 years, for composites four to eight years.
Only a few studies are available on economic aspects of tooth fillings. No publication on costs and cost-effectiveness of amalgam and composite fillings has been found for Germany during the search period of the present report. In three publications, cost-effectiveness for amalgam and composite fillings is calculated for Great Britain (GB), the Netherlands (NL) and Sweden (SWE), two publications deal with the long term costs of amalgam and composite fillings (GB and SWE).
A British HTA-report of 2001 uses a model calculation to calculate the cost-effectiveness of amalgam and composite fillings for GB. Using survival times arising from a systematic literature review and surveyed costs (questionnaire regarding treatment times, hourly rates and material costs) the authors calculate the expected costs for a five or ten-year period for amalgam and composite fillings. The costs of composite fillings are 1.5- or three times higher than those for amalgam fillings for the five and ten-year periods, respectively. The authors point out that the economic analysis does not consider all influencing factors (e. g. work environment, overhead costs), costs for patients and their preferences regarding the material (e. g. aesthetic demands, safety concerns).
An article of the NL (1999) deals with the cost-effectiveness of composite and amalgam fillings (regarding replacement of existing class II fillings) from the perspective of dentistry. They exclusively regard treatment times for the treatment steps as costs, the longevity is observed over five years in a separate randomized controlled trial (RCT). During the study period no relevant differences in effectiveness of the materials are determined. Treatment times for placing amalgam fillings are consistently lower than those for placing composite fillings. The authors conclude that, bearing in mind the limitations of the study, amalgam is the material of choice from the perspective of dentistry due to lower time resources needed and equal effectiveness (five-year consideration).
Two publications by a Swedish group calculate direct costs (rates and co-payment of patients) for amalgam and composite fillings. In both publications, longevity is assessed by means of MST in studies conducted in Nordic countries; it is stated to be 9.3 years for amalgam and 4.7 years for composite class II fillings. In one text, the authors calculate the costs of amalgam and composite fillings in class II cavities per theoretical functional year of the filling from the perspective of the publicly funded health care system, patients, as well as total costs (in public dental centres). It has to be considered that amalgam fillings are not being paid for by the publicly funded health care system (Försäkringskassan) in Sweden since 1999 due to environmental considerations. Amalgam is the more cost-effective filling material for class II cavities from all three perspectives. Based on these results, the authors calculate theoretical long term treatment costs (for a period of ten years) of direct class II composite and amalgam fillings in a further publication. The average long term costs for amalgam fillings are – independent of the selected discount rates – lower than those for composite fillings (class II cavities). This holds true from the perspective of and of the publicly funded health care system. The relation of total patients costs for amalgam and composite fillings is 0.5 to 1.0. The authors emphasise that patient preferences have not been considered in their calculations.
Another publication of 1997 estimates the long-term (60 years) relative treatment costs for cavities with different filling materials (GB). Longevity for amalgam and composite fillings is assumed to be six and three years for large restorations (MOD) and eight and four years for small (one-surface) fillings. Costs are determined using rates of the National Health Service and private fees. Amalgam is by far the more cost-effective alternative for one-surface fillings as well as extensive fillings (MOD). The authors emphasise that their calculations constitute a theoretical approach as fillings cannot be replaced indefinitely.
6. Discussion
A comparison of studies by different authors on the longevity of direct amalgam and composite fillings in permanent teeth is difficult due to different study designs and insufficient documentation of study details. Longevity of amalgam fillings is still longer than that of composite fillings. Two out of six systematic reviews conclude that the expected survival time of composite fillings can be comparable to amalgam fillings. However, these conclusions are based on the results of short-term studies which usually overestimate the longevity of filling materials. Even if an improvement of the longevity of composites – through improved material properties – may be achieved in the future, the necessity for a more complex placement technique compared to amalgam will probably remain. Apart from the difficulties in conducting a randomized, controlled long-term study comparing the longevity of direct fillings, the fact that the composition of composites and adhesives used in a study has often been changed at the time of study publication or they have been replaced by a next generation product presents an additional problem. However, longevity of fillings not only depends on the materials used, but also on patient parameters and local, intraoral factors (e. g. localisation of filling, cavity size), as well as on the dentist placing the filling. Insofar, a sufficient sample size and study period, preferably in the setting of a private dental practice, should be aimed for in future studies comparing the longevity of amalgam and composite fillings. Furthermore, a complete documentation of the material evaluated, the way fillings are placed, as well as of effect modifiers is necessary to make data more comparable. As the experience and skilfulness of dentists is important especially for placing composite fillings, and the knowledge of the properties of adhesives plays an important role as well, continuing education of dentists that keeps pace with the development of materials is necessary.
The quality of economic studies results from the quality of data regarding evidence and costs, among others; here it has to be referred to the determination of the effect parameter “functional years”. Assuming a longer longevity for amalgam fillings compared to composite fillings the economic analyses show higher costs of composite fillings due to the higher complexity of placing the filling. In the three available analyses, longevity is considered during a limited time period as effect parameter, other aspects are only considered in the discussion. Amalgam and composite fillings cannot be replaced indefinitely (loss of tooth substance); therefore, a long term examination considering patient preferences as well would be meaningful.
From an ethical and legal perspective, informing the patients about possible treatment options and their advantages and disadvantages are particularly important. Apart from the functionality, tolerability and longevity of different filling materials, the experience of the dentist in using these materials should be discussed during counselling. The aesthetical point of view also has to be considered in the selection of a filling material.
7. Conclusions/Recommendations
Amalgam fillings show a higher longevity than composite fillings. Two out of six systematic reviews conclude that the expected survival time of composite fillings can be comparable to amalgam fillings. However, these conclusions are based on the results of short-term studies which usually overestimate the longevity of filling materials. Even if an improvement of the longevity of composites – through improved material properties – may be achieved in the future, the necessity for a more complex placement technique compared to amalgam will probably remain. Taking longevity into consideration as the only result parameter, amalgam is the more cost-effective filling material compared to direct composite fillings in posterior teeth from an economic perspective.
These conclusions are based on available literature, however, due to the large heterogeneity of study results it is afflicted with some uncertainties.
Apart from the longevity of amalgam, other aspects, such as (individual) safety concerns, environmental protection, aesthetic demands, or the long term possibility of replacing fillings need to be considered when selecting the appropriate filling material.
Future studies comparing the longevity of amalgam and composite fillings should aim for a sufficient sample size and study period, preferably in the setting of a private dental practice. In order to allow for a direct comparison of filling materials, longevity of both materials should be evaluated in comparable teeth and cavities in the same patients. A complete representation of data is important for transparency and comparability.
Assessment of the cost-effectiveness of amalgam and composite fillings should consider the functionality of teeth over a longer time period and the possibility of replacing fillings (loss of tooth substance).
The rapid development of composite materials and adhesives make short term revisions of these conclusions necessary.
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