The Clinical and Legal Mythology of Anti-Amalgam
Michael J. Wahl, D.D.S.
Myth #3: Resin composite restorations last as long as amalgam restorations.
Fact #3: Numerous studies have shown amalgam restorations last longer than resin.
Dickerson stated, “we can all find amalgam that has lasted a long time, but statistically, that is the exception, not the rule.”  In fact, it has been shown in many studies that amalgam restorations generally do last a long time, or at least longer than resin composite restorations. Two independent studies, published in 1971  and 1976 , showed that the median age of an amalgam filling was 10 years.
A 1990 study of the reasons for placement of 2542 tooth-colored restorations showed that the median longevity of a Class II amalgam was about 8 years, but less than 4 years for a resin composite . In fact, for all types of restorations studied (Class I, II, III, and V), the longevity of amalgam exceeded that of composite: “If all the restorations are considered, the longevity of amalgam restorations still exceeds that of resin-based materials by more than 2 years.”  In a 1997 survey of reasons for replacement of failed restorations, the median age was 9 years for amalgam, but only 6 years for resin composite . The median age of amalgams was 12 to 14 years while that of resin composite restorations was 7 to 8 years . In 1998, a study of dentists in general practice in Florida indicated that the median age of a replaced amalgam was 15 years, but that of a composite restoration was only 8 years .
Although several authors have stated that composite’s “clinical superiority” over amalgam is “well-documented” for Class I  and Class V restorations , a 1999 study of the placement or replacement of 9,031 restorations by dentists in the United Kingdom showed that amalgam outlasted composite for Class I, II, and V restorations . A 1995 study of Class II resin composites showed a failure rate of 15% after only five years .
In 1999, Raskin et al reported the results of a 10-year study of posterior composite restorations. Forty-two Class I and 58 Class II resin composite restorations were placed “under highly controlled conditions” by a single operator. Of the 37 restorations available for review after 10 years, 32 had failed. Because some restorations were unavailable for review, the authors estimated a failure rate of 40% to 50% for Class I and Class II resin composite restorations . In 1998, Collins et al reported on 161 Class I and Class II posterior resin composite restorations and 52 high-copper amalgam controls placed by a single operator. After 8 years, the overall failure rate of the composite restorations (13.7%) was more than twice that of the amalgam restorations (5.8%). The main reasons for failure were bulk fractures and secondary caries . A 2000 study of 6,761 replaced restorations showed the median age of replaced amalgam was 10 years, but only 8 years for composite . The median age of replaced amalgam was significantly greater than replaced composite for all restoration types (Class I, II, III, IV, and V).
In 1989, two independent studies reported a 5-year failure rate of 9% for posterior composites [15,16]. In 1992, however, a study reported a 5-year failure rate of 5% (only slightly higher than the amalgams in the same study).  These failure rates are greater than the 2.3% 5-year failure rate Roberson et al. reported in 1989 in a study of about 600 amalgam restorations .
The results would probably be even better for amalgams placed today. New, more conservative preparation techniques (even without amalgam bonding) have been developed [19-21], allowing for smaller, longer lasting, more fracture-resistant amalgam restorations [22-24]. Amalgam bonding, which was not commonly used when the restorations in these studies were placed, has been shown to increase fracture resistance  as much as bonded resin composite . In addition, amalgam bonding has been shown to inhibit caries  and has enabled dentists to make still smaller preparations , and the use of caries-indicating dyes during preparation is commonplace now. Berry et al stated in 1999 that “no clinical studies have shown that the longevity of the current generation of direct-placement posterior composite restorations will equal the longevity of amalgam restorations.” 
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Dr. Wahl practices dentistry in Wilmington, Delaware. This article was originally published as Wahl MJ. Amalgam — resurrection and redemption. Part 2: the medical mythology of anti-amalgam. Quintessence International 2001; 32:696-710, 2001. It is reproduced here with the kind permission of the publisher. The author thanks Drs. J. Rodway Mackert, Ivar A. Mjör, and Fred Eichmiller for reading the manuscript and offering several helpful suggestions.
Dr. Wahl practices dentistry in Wilmington, Delaware. This article was originally published in Quintessence International 32:525-535, 2001 and is reproduced here with the kind permission of Quintessence Publishing Co. The author also thanks Drs. J. Rodway Mackert, Ivar A. Mjör, and Fred Eichmiller for reading the manuscript and offering several helpful suggestions.
This page was posted on November 1, 2002.