The performance of bonded vs. pin-retained complex amalgam restorations

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The performance of bonded vs. pin-retained complex amalgam restorations
J.B. SUMMITT, D.D.S., M.S., J.O. BURGESS, D.D.S., M.S., T.G. BERRY, D.D.S., M.A., J.W. ROBBINS, D.D.S., M.A., J.W. OSBORNE, D.D.S., M.S.D. and C.W. HAVEMAN, D.D.S., M.S.
JADA

© 2001 American Dental Association

A five-year clinical evaluation

ABSTRACT

Background. The authors compared the clinical performance of complex amalgam restorations, replacing at least one cusp—retained either mechanically with self-threading pins or bonded—with a filled, 4-methacryloxyethyl trimellitate anhydride, or 4-META, –based resin designed for amalgam bonding.

Methods. The authors placed 60 amalgam restorations (28 pin-retained and 32 bonded), each restoration replacing at least one cusp. They used self-threading stainless steel pins in the pin-retained group and a filled, 4-META–based bonding resin in the bonded group. For both groups, the authors left in place any retention form remaining after removal of an old restoration but did not enhance it.

Results. At four years, six restorations had failed. At five years, of the 40 restorations available for evaluation, three had failed, for a total of nine failed restorations; seven of those were pin-retained and two were bonded. Using the Fisher exact test to compare the groups at five years, the authors found no significant difference in failure rate, marginal adaptation, marginal discoloration, secondary caries, tooth sensitivity or tooth vitality.

Conclusions. At five years, there was no difference in the performance of pin-retained amalgam restorations and bonded amalgam restorations. This study will be continued for at least a sixth year.

Clinical Implications. Bonding with a filled, 4-META–based bonding resin appears to be a satisfactory method of retaining large amalgam restorations replacing cusps.

For years, dentists have used mechanical resistance features such as threaded pins,1,2 boxes,3 amalgapins4 and slots5 to provide retention and resistance for complex amalgam restorations replacing cusps.6 Although these mechanical features have served well, each comes with its associated risk.6,7 These risks could be avoided if these features could be replaced by noninvasive means of providing retention and resistance for the restoration.8

In 1989, Parkell introduced a 4-methacryloxyethyl trimellitate anhydride, or 4-META, –based amalgam bonding system to U.S. dentistry. Other companies since have developed amalgam bonding systems or have altered existing products to allow their use for amalgam bonding. Many in vitro studies have evaluated the adhesive and cavity-sealing capabilities of these materials.9–13

The bonding of amalgam restorations appears to be a viable alternative to mechanical retention of restorations.

In amalgam bonding, the mechanism by which the bonding resin attaches to tooth structure is identical to the mechanism by which resin-based composite attaches to dentin and enamel. The attachment of the bonding resin to the amalgam, however, is quite different from that of bonding resin to resin-based composite. The amalgam-to-resin attachment is entirely mechanical rather than chemical. Unset amalgam is condensed into the bonding resin on the tooth surface before it polymerizes, thus incorporating fingers of resin into the amalgam at the interface.14

The mechanical attachment of amalgam to the bonding resin is enhanced by the incorporation of filler particles, either organic or inorganic, into the resin.15–18 A probable reason for this improvement in attachment is that the filled bonding resin is more viscous during condensation of the amalgam, and this provides improved penetration of bonding resin into the amalgam for increased mechanical retention.

In vitro studies have demonstrated that the resistance to a shearing load created by amalgam bonding can be equal to or greater than resistance provided by mechanical features such as pins.15,19,20 Other studies have revealed that Amalgambond Plus (Parkell), with its polymethyl methacrylate filler, provides one of the strongest bonds of amalgam to tooth structure.15,17,18,20–22

In vitro studies have demonstrated that the resistance to a shearing load created by amalgam bonding can be equal to or greater than resistance provided by mechanical features such as pins.

Several clinical studies of bonded amalgam restorations have been reported. Mahler and colleagues23,24 reported no difference between bonded and nonbonded Class II amalgam restorations in tooth sensitivity two weeks after insertion or in marginal fracture after one year23 or three years.24 Belcher and Stewart25 compared the clinical success of complex amalgam restorations retained with pins against that of restorations retained with Amalgambond Plus, both with and without filler powder. At two years, all restorations in all three groups were retained with minimal sensitivity, good marginal adaptation and no recurrent caries. Staninec and colleagues26 reported two-year success of bonded amalgam restorations in primary teeth. An in vivo study by Smales and Wetherell27 evaluated 366 bonded amalgam restorations using five bonding materials. Cuspal coverage was accomplished in 178 of the 366 restorations. They reported a 98.6 percent success rate at up to five years.27

We undertook a clinical study to compare the failure rates, marginal adaptation, marginal discoloration, secondary caries rates, sensitivity and tooth vitality of bonded and pin-retained complex amalgam restorations. In this article, we report the results after five years.

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