Restoration of Posterior Teeth in Clinical Practice: Evidence Base for Choosing Amalgam Versus Composite

This article reviews the current use of amalgam versus resin composite in posterior restorations and the evidence-base for choosing between these two treatment options. While much research has been published on the issue of the clinical use of amalgam versus resin composite, there are several issues that limit the true evidence-base on the subject. Furthermore, while the majority of published studies on posterior composites would seem to indicate equivalent clinical performance of resin composite to amalgam restorations, the studies that should be weighted much more heavily (randomized controlled trials) do not support the slant of the rest of the literature. As part of an evidence-based approach to private practice, clinicians need to be aware of the levels of evidence in the literature and need to properly inform patients of the true clinical outcomes that are associated with the use of amalgam versus resin composite for posterior restorations, so that patients are themselves making informed decisions about their dental care.

Clinical practice in the twenty-first century

The restoration of posterior teeth with direct restorations in clinical practice has changed significantly over the past 30 years. Prior to 1980, amalgam was clearly the restoration of choice for use in posterior teeth and was preferred by the vast majority of private practitioners. Both the amalgam alloys and the clinical techniques of placement were longstanding, well-established protocols with an outstanding clinical track record. However, a number of issues began to push clinicians to evaluate alternatives to dental amalgam about 30 years ago. There began a cultural shift in dental consumers that placed a higher value on esthetics and natural-appearing restorations. This increased demand for esthetic restorations has grown over 30 years and is strong today. Another change was the increased consideration of the potential health issues associated with mercury in amalgam. Although there has never been a scientific study that directly links the clinical use of amalgam to any health concern, nevertheless it has been shown that mercury does indeed leach out of amalgam restorations and adds to the biologic burden of mercury on the human system, along with mercury doses that are derived from food and air. Finally, increasing concerns about the environmental impact of mercury waste from dental offices have driven some dentists away from the clinical use of amalgam as well.

More dentists began to utilize resin composite for posterior restorations in the 1970s; however, there were clinical issues that limited its use, including wear, color stability, leakage, recurrent caries, and difficulty in placement technique. Even in the 1980s, 89% of practitioners in the United States reported using amalgam as the restoration of choice in their clinical practice. The use of resin composite has changed dramatically since the report by Pink and colleagues. In the past decade, there has been a large shift toward using resin composite for posterior restorations. Today, it is more commonly placed than amalgam restorations. The shift in clinical practice occurred for a number of reasons. First, there is a perception that patients prefer esthetics restorations and that belief is supported by the literature. One study found that a majority of patients prefer a tooth-colored material (composite), even when informed that the clinical longevity will be shorter than that of amalgam. In the same study, dentists more frequently wanted to place the material with better clinical performance. Dentists were more influenced by longevity while patients were more influenced by esthetics. Second, dentists themselves have the perception that materials and bonding systems have significantly improved. Third, continued environmental and health concerns about mercury in dental amalgam have pushed many patients and some practitioners to try and use less amalgam. In some countries there are regulatory controls that limit or eliminate the use of amalgam. Finally, dentists have improved methods of composite placement, which improve contour and proximal contacts. These placement methods (eg, the use of sectional, contoured matrices with bitine rings) are now taught by most dental schools and easily implemented by practitioners. The shift from amalgam dominance in practice to composite has been remarkable.

Evidence base for material of choice for direct posterior restorations

Practitioners have perceived clinical improvements in posterior resin composite restorations and have significantly increased the use of resin composite for posterior applications. But is there a real evidence base for this drastic swing in the use of resin composites in posterior restorations? The use of evidence-based clinical decision making in dentistry is still in its infancy. Most dental practitioners do not rely on high levels of evidence, but rather base clinical decisions on opinion and individual case observations. The gold standard for evidence-base in clinical practice is the randomized, controlled clinical trial or a systematic review based on a number of such trials.

There have been several thorough reviews in the literature comparing the use of amalgam and composite use in direct posterior restorations. A large number of these studies would indicate that resin composite used clinically as a posterior restoration performed equal to or better than amalgam. One thorough recent review of the literature summarized that the yearly failure rate of composite was 0% to 9%, while the yearly failure rate of amalgam was 0% to 7%. Other studies actually show lower failure rates for resin composite than amalgam. However, using an evidence-based approach, one must look at the literature very carefully. A comprehensive electronic and hard copy search was made, using PubMed, the Cochrane Library, and similar resources.

Evidence base for material of choice for direct posterior restorations

Practitioners have perceived clinical improvements in posterior resin composite restorations and have significantly increased the use of resin composite for posterior applications. But is there a real evidence base for this drastic swing in the use of resin composites in posterior restorations? The use of evidence-based clinical decision making in dentistry is still in its infancy. Most dental practitioners do not rely on high levels of evidence, but rather base clinical decisions on opinion and individual case observations. The gold standard for evidence-base in clinical practice is the randomized, controlled clinical trial or a systematic review based on a number of such trials.

There have been several thorough reviews in the literature comparing the use of amalgam and composite use in direct posterior restorations. A large number of these studies would indicate that resin composite used clinically as a posterior restoration performed equal to or better than amalgam. One thorough recent review of the literature summarized that the yearly failure rate of composite was 0% to 9%, while the yearly failure rate of amalgam was 0% to 7%. Other studies actually show lower failure rates for resin composite than amalgam. However, using an evidence-based approach, one must look at the literature very carefully. A comprehensive electronic and hard copy search was made, using PubMed, the Cochrane Library, and similar resources.

Search results

Virtually all studies that were located on posterior resin composites and amalgam were either retrospective case series, retrospective epidemiologic studies, or prospective, nonrandomized studies. Retrospective studies on longevity have rated the clinical performance of posterior resin composites very close to amalgam restorations. One prospective trial also found no difference in longevity of amalgam or composite but was based on only 38 subjects. These types of studies are very susceptible to various forms of bias and confounding variables that are impossible to account for. For example, a prospective, nonrandomized study that allows the patient to choose his or her restoration of choice (composite versus amalgam) may be open to a bias as a result of oral hygiene. The group that chooses the esthetic tooth colored restoration may also be a group that generally has higher oral care expectations and lower plaque scores. Such a systematic difference between the test and control subjects may influence the outcome of the study. Such confounding factors, both known and unknown, are presumably compensated for by randomly allocating a sufficiently large number of subjects to test and control sides. Another way to compensate for inter-subject differences is to employ a split-mouth design, in which clinically similar lesions on contralateral teeth are randomly allocated to receive either amalgam or composite. The comparison is thus between the restorations within the mouth of the same patient.

Another study design issue that has recently been questioned is the validity of “university-based” research verses “practice-based” research. The vast majority (virtually all) studies of longevity of composite versus amalgam—particularly prospective studies—have been done in university settings. Restoration locations in these studies follow a strict placement protocol under rubber dam isolation, with no time constraints in placement, and by the most meticulous operators who teach operative dentistry and are detail oriented. Often, the study populations are university faculty, staff, and students with high educational levels and high oral health IQs. An argument being made is that these placement conditions and study subjects are not realistic to what is seen in private practice. As such, new studies of materials, techniques, and longevity are being planned in “practice-based” networks, thereby yielding data that is truly a result of clinical practice in a private practice setting.

In evaluating the evidence-base for posterior composites or amalgam, the vast majority of the literature on the use of amalgam or composite in posterior teeth is very low-level evidence (see the articles “Evidence-based curriculum reform: the Kentucky experience” and “Evidence-based dentistry and the concept of harm” by Thomas and colleagues elsewhere in this issue, which describe the hierarchy of evidence). There are numerous bench-top studies and expert opinion that have evaluated wear, microleakage, marginal integrity, and shrinkage; and while these studies show plausible reasons that these materials will perform well, these studies would not dictate use in private practice. As noted elsewhere in this issue (see the article “Evidence-based dentistry and the concept of harm” by Thomas and colleagues), such information constitutes a very low level of evidence. Likewise, there are many retrospective case reports and case series in the literature evaluating reasons for failure and estimating yearly failure rates; these studies are prone to bias and results of these studies are often conflicting. There are far fewer prospective, controlled studies in the literature on amalgam or composite restorations (level 3 and 4). What is needed to make such clinical decisions are randomized, controlled trials (RCTs) or, preferably, systematic reviews based on multiple RCTs.

A search was undertaken to find trials that might provide a stronger evidentiary basis on which to make a decision between the two materials. PubMed was searched using the keywords composite, amalgam, clinical, and longevity. In this search, results were limited to clinical trials. Two RCTs were identified that directly compared amalgams and composites for posterior restorations. Unfortunately, the study populations in both were children, which ultimately limits the generalizability with regard to an adult population. However, these studies provide the strongest evidence on which to base clinical decisions.

The first of these RCTs is from the New England Children’s Amalgam Trial. The primary outcome that was examined in this study was the safety of mercury-containing amalgam restorations in children. A secondary outcome that was examined was longevity of posterior restorations after 2 to 5 years of follow-up. A total of 534 children (average age 7.9 years old) were randomly assigned to receive posterior amalgam or posterior composites and a total of 1,262 restorations were placed. Replacement of restorations were more frequently needed for the resin composites (14.9%) than for amalgam restoration (10.8%); however, this difference was not statistically significant in the random effects survival mode ( P = 0.45). This study also noted that while replacement rates were similar (14.9% versus 10.8%), the reasons for replacement were quite different. Composites demonstrated more recurrent caries and required repair more often.

The second RCT was also part of a large RCT with the primary outcome measure being the safety of mercury-containing restoratives. This study randomly assigned 472 children (ages 8–12) to receive either amalgam or composite restorations in their posterior teeth. A total of 1,748 restorations were followed for 7 years. Overall, 10.1% of all restorations failed over the 7-year trial (5.6% of amalgams and 14.5% of composites). The 7-year survival rate for amalgams was 94.4%, while the survival rate of composites was 85.5%. This RCT agreed with the other available RCT that recurrent caries was much more common in composites than in amalgams (composite recurrent caries were +12.7%, while amalgam recurrent caries were 3.7%). The relative risk of recurrent caries was 3.5 (95% confidence interval of 2.3–5.1, P <0.0001).

These two randomized, controlled clinical studies demonstrate clearly that amalgam has higher survival than composite for posterior restorations, and there is much more secondary decay associated with resin composite than amalgam in posterior restorations. These two findings should be conveyed to patients who are receiving restorations in their posterior teeth, so that patients can make decisions with their provider that are informed decisions.

As noted previously, these two studies are the strongest evidence now available on this topic. However, the study populations were elementary school children and the results may not be entirely applicable to adults. Trials are needed to assess the longevity of composite and amalgam restorations in a large sample of adult patients. As an aside, it may be worthwhile to evaluate the safety of composite vis-à-vis amalgam restorations. While there have long been concerns about the safety of amalgam because of its mercury content, recently, concerns have been voiced concerning potential health effects of bisphenol A, a component of some composite resins. Future trials will be needed to clarify these issues.

Only gold members can continue reading. Log In or Register to continue

Oct 29, 2016 | Posted by in General Dentistry | Comments Off on Restoration of Posterior Teeth in Clinical Practice: Evidence Base for Choosing Amalgam Versus Composite
Premium Wordpress Themes by UFO Themes