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Adhesive restorations with amalgam: Guidelines for the clinicianA, John G ^ / Luiz Narciso Baratieri- '̂̂ /Sylvio Monteiro, Jr** / André Vicente Ritter*

The adhesive amalgam restoration techmquc combines the good properties of amaigam withtl-ie principies of tooth structure preservation and margined seal inherent to adhesive materials.In spite of lack of longitudinal data, results of early clinical and laboratory tests are encourag-ing. If the present research is substantiated by ciinicai confirmation of their results, bondedamalgam restorations will become routine. The purpose of this articie is to present a briefliterature review on adhesive amalgam restoration and to introduce guidelines for its use.(Quintessence Int 1994;25.-687-695.)

Introduction

Although amalgam is predicted to have a limited rolein future dentistry, amalgam restorations presentlyoceupy a considerable part of the time a practitionerdedicates to his or her patients,' According to a recentsutT/ey conducted in the United States, of the 10,000surveyed dentists, 94% still use amalgam as the mainrestorative material in Class II cavities, with only 6%preferring not to use it.-"'

In spite of the strong appeal of tooth-colored restora-tive materials because of their increasingly improvedproperties and the excellence of their esthetic results,they cannot mateh some of amalgam's advantages:

1, Universally accepted and iess demanding applica-tion technique'"""

2, Controlled and predictable clinical perfonuance'-^'3, Inexpensive'''4, Self-sealing of the margins''^

* Professor of Oral Biology and Pathology, Stale University ofNew York at Stony Brook, School of Dental Medicine. LongIsland, New York 1179Ü.

*" Professor of Operative Deniistry, Federal University of SaniaCatarina, School of Dentistry, Florianópolis, Santa Catarina,Brazil.

*•" Associate Professor of Operative Dentistry, Federal Univer-sity of Santa Catarina,

Address all eorrepondence to Dr Luiz Narciso Baralieri, Riia DomJaime Cámara, Í90, 8S015-120, Florianópolis, Santa Catarina,Brazil,

5, Lesser amount of training and skill required fromthe operator'-'' ^

6, Shorter appointments due to its easy handling pro-cedures,'•''•'However, amalgam has disadvantages, such as its

coior"" and lack of adhesion to tooth structure. Con-cerns about mercury toxicity may limit its use as a res-torative material under specific clinical situations,''Lack of adhesiveness of amalgam to the dental struc-ture requires cavity design with mechanical retention,at the expenseof healthy tooth structure,""" Marginalleakage"''*'-'̂ -'''"'̂ and its potential pathologic conse-quences are serious clinical problems,

Adhesives systems designed to bond amalgam to en-amel and dentin have been introduced in an effort tocompensate for some of the disadvantages presentedby amalgam, particularly marginal microleak-ggg'i,7,i2,T5,i('>,ii; gi^j |.|̂ g need for additional retentive de-vices,''•^'^"-'^ These sytems may obviate the need forprotective bases and strengthen remaining tooth tis-sues weakened by disease and cavity preparation,-""^^

The purpose of the present article is to describe thecurrent status of adhesive restorations with amalgam,offering a guide to the clinician as to when, why, andhow to use the technique.

Literature review

Since Buonocore,̂ "* in 1955, introduced the concept ofadhesive dentistry, a inethod to increase the adhesionof resin materials to enamel, and Fusayama et aP""described an adhesive restorative technique in whichphosphoric acid was used to condition vital detitin.

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much has been written, discussed, studied, and experi-enced in Ihe field of enamel and dentinal adhesives.

Tliere is an obvious ciinieal advantage to having auniversal adhesive system, ie, one Ihat simultaneouslyand suceessfully treats enamel and dentin, for bondingall restorative materials, including amalgam. Such ad-hesive systems should not be for amalgam specificallybut should be appropriate for use with other reslora-tive materials, such as eomposile resins, porcelain, andprecious and nonprecious alloys.

Aiding the retention of amalgam with phosphate ce-ment was advocated in the 1920s and was known as theBaldwern technique. Tlie first reports of experimentsinvolving the use of adhesives under amalgam restora-tions were published in 19S6."-' 'Varga et al ' ' assessedthe bond between amalgam and human enamel as wellas the effect on the marginal seal. They used two differ-ent adhesive resin systems: (I) a bis-GMA phospho-nated ester (Panavia-Ex, Kurary) and (2) a 4-META/MMA-TBB restn (Super-Bond CB, Sun Medi-cal). Shear bond strength values recorded for the 4-META resin were 13.4 ±6.0 MPa after 24 hours in wa-ter and 17.7 ± 4.7 MPa after 30 days in water. Neitherthe 4-META resin nor Panavia-Ex showed evidence ofmarginal leakage. T^e authors concluded that these ad-hesives could enhance the clinical performance ofamalgam restorations.

In 1987, Shimizu et al'* studied the use of an adhesiveliner(Panavia-Ex) to reduce microleakage of amalgamrestorations with or without a giass-ionomer base andfluoride treatment. They concluded thai the use of Pa-navia-Ex as an adhesive was immediately effecttve inreducing microleakage of amalgam restorations. Pana-via used in combination with glass-ionomer cementwas more effective than Panavia alone and Panavia incombination with Ag(NH3)2}- and a glass-ionomer ce-ment was even more effective.

Staninec and HoU'" measured the tensile strength ofamalgam to tooth strueture as well as the microleakageat the amalgam-tissue interface. They reported thatamalgam can adhere to acid-treated enamel and dentinthrough a thin coat of Panavia resin. They obtainedmean tensile strengths of 1,404 psi for enamel and 469psi for the dentin. Less microleakage was observed inamalgam restorations with Panavia than in restorationslined with copal varnish or not lined at all.

Panavia adheres poorly to dentin, which explains theresults obtained.'"*"' Adhesion becomes considerablygreater with Che use of biologically compatible dentinaladhesives.'^'-' Work by Nakabayashi et al'"-'^ showedthe formation of a resin-reinforced dentinal zone, lo-

cated between the cured resin and the dentin. The/one, called the hybrid layer, seems to be responsiblefor inhibiting the marginal microleakage and also forthe high resin-to-dentin adhesion strength.

Since 1977, Fusayama el a l , - " ' have advocated con-ditioning enamel and dentin with phosphoric acid andcoating both wilh a chemically adhesive resin system asthe best treatment for the cavity wall. This approachhas been shown to be biocompalible, to stop marginalleakage, and to improve bond strength to looth struc-ture. This concept is now gainning acceptance byWestern researchers.'''""'

Torii et al"' were able to inhibit in vitro the progres-sion of carious lesions along the amalgam-adhe-s ive- tooth structure margins. Their finding has clinicalimportance, because, according lo Mjör," about 71%of amalgam restorations are replacements, of which58% arcaresul tofsecondary caries. Thus, the employ-ment of an amalgam adhesive might improve the prog-nosis and extend the longevity of amalgam restora-tions.

Staninec ' ' 'comparedtheretentionin vitro of Class IIamalgam restorations mediated either by an adhesiveagent in no-undercut preparations or by conventionalmechanical retention (boxes and grooves). The resto-rations retained in cavities by means of an adhesive hadtwice the resistance to displacement of restorations insimilar eavilies with conventional mechanical reten-iion. This result suggests the possibility that the adhe-sive technique is more conservative.

Eakle et a P ' have recently assessed the effects ofbonded amalgam in relation to resistance of teeth tofracture. They reported thai a tooth restored with abonded amalgam requires a significantly greater loadto fracture than does a tooth restored with amalgamand no adhesive. Using scanning electron microscopy(SEM), they examined the bonded fractured speci-mens and found evidence for mechanical interlockingbetween the adhesive resin and amalgam particles, sug-gesting the existence of a bonding mechanism. Previ-ously, Staninec and Holt '-postulated the existence ofamechanical and ionic adhesion between the etchedloolh surface and the adhesive resin and a mechanicalinterlocking and adhesion mediated by Van der Waalsforces between adhesive resin and amalgam.

The literature is now replete with microleakage andbond strength data for adhesive amalgam restora-tions. "̂ •-"•̂ '•̂ •̂̂ "̂" In contrast, few studies have beenpublished on the use of the adhesive amalgam tech-nique in vivo.^'-^'^'*^'' There are reports of clinical cas-

7z354 jng the technique used and a description

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of the indications. In a longitudinal clinical study, forexample. Lleno et al" followed, for 1 year, 129 amal-gam restorations in 104 patients. They used the 4-META/MMA-TBB system. Mechanical retention notbeing necessary, preparation in most cases was reducedto the removal of carious tissue, without anesthesia.According to the authors, postoperative sensitivity wasnot significant and no failures were reported.

S, It reduces the incidence of marginal fracture, "''''9, It reduces the incidence of recurrent car-

10. it allows definitive restoration of a tooth with abadly broken-down crown in one elinical ses-sion.'-'-'

11. It allows the biologic scaling of the pulpodentinalcomplex,''^'-^

Indications (dinicül applications)

Resin adhesives can offer auxiliary retention, improvethe marginal seal, and protect the pulpal complex in allamalgam restorations, irrespective of the location anddepth.''-''-"'-''•-''""^ '̂ for young, adult, and aged patientsalike. These adhesives have been suggested for repairof restorations, ie. to bond new to old amalgam''"*"' andto seal fatilty margins in new or old amalgam restora-tions. Although these adhesives offer a bond betweenamalgam and tooth structure, use of a well-defined re-sistance form for the amalgam may still be an advan-tage in some elinical instances. Weak walls should notbe left: in such cases, reduction of cusps and reconstruc-tion with amalgam are recommended.

Advantages

The amalgam adhesive restoration technique offers ad-vantages over nonadhcsive treatment alternatives:1. It is a treatment option for extensively carious pos-

terior teeth, with a lower cost than either cast metalrestorations or metal-ceramic crowns.'' '

2. It allows the use of amalgam in teeth with low gingi-vo-occlusal height (unlike conventional amaigam,amalgam with pins, amalgapin, inlays, onlays, andcomplete cast crown restorations),

3. It permits more conservative cavity preparationsbecause it does nof always require additional me-chanical retention''-'-'''-' (unlike conventional amal-gam, amalgam with pins, amalgapin, inlays, onlays,complete cast crown restorations),

4. It eliminates the use of retention pins and their in-herent risks, eg. periodontal perforation and pulpalexposure,''-"'''

5 It reduces marginal leakage to a mini-

6, It reinforces tooth structure weakened by carles andcavity preparation.''''"" '•'

7, It reduces the incidence of postoperative sensitivity,commonly observed with amalgam restora-jiQ„^_7.21.23,55

Limitations and disadvantages

The adhesive amalgam technique also has some limita-tions and disadvantages:

1. It increases the time taken to perform a convention-al amalgam restoration and may be technique sensi-tive.-'

2. It requires practioners to adapt to the new tech-nique.-'

3. It increases the cost of the amalgam restoration.-'4. It makes the use of amalgam seem feasible in situa-

tions where it wonld not be indicated, such for largerestorations involving working cusps."

5. It has not been in use long enough to allow a properevaluation ofits clinical performance.'" '-"'-'"-̂ '-̂ ^

Technique

Bonding amalgam to tooth structure with a partial- ortotal-etch technique and placement of a resin adhesiveis making the traditional amalgam cavily preparationobsolete. Cavity preparations for bonded amalgam res-torations may, however, still require an adequate formof resistance. Fragile cusps and walls should be reducedand protected with amalgam. For wide and cotnplexcavities, the lack of clinical data should temper thedentist's enthusiasm for establishing retention with theadhesive only. In such cases, we believe it to be of fun-damental importance to establish some mechanical re-tention in the remaining dental tissue. However, eom-bining pins with adhesive may be contraindicated'''' be-cause catastrophic tooth failure has been observed inlaboratory tests,

l"he technique for employing these adhesives variesslightly among the different brands: however, the clini-cian must always follow a logical and previously estab-lished sequence. The various steps in handling theamalgam are basically identical to those followed for itstraditional usage.

Figures la to II and 2a to 2f illustrate the procedurefor placement of a bonded amalgam restoration.

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Fig la The vital mandibular left first molar has a large carious lesion. The buccal cusps are undermined.

Fig 1 b The linguai aspect reveals the undermined buccaicusps.

Fig 1 c A smooth, icw-speed round bur is used to removecarious tissue.

Fig Id Fragüe buccal cusps have not been sacriiiced dur-ing cavity preparation. Note the presence of pigmentedbuccai fissures, A wooden wedge is protecting Ihe inter-proximal rubber dam.

Figle Enamei and vitai dentin are etched with a 10%phosphoric acid gel (All-Etch, Ali-Bond 2 system - BiscoDental). The pigmented fissures are aiso being elched. After15 seconds of total etching, the acid gei is removed with anair-water spray.

Fig If The vitai dentin and enamel are dried with absor-bent paper (wet adhesion]. Drying can aiso be performedwith air jets.

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Fig Ig After drying, conditioned enamel has a dull whiteappearance. The dentin is still siightly wet.

Fig 1 h Three coats ot adhesive primer (Primer A + PrimerB, Aii-Bond 2 system) have been applied. The shiny aspectis caused by hydrophilic resin incorporated in the pfimef.

Fig 1 i The dentin-enamei bonding agent is applied with adisposable brush (All-Bond Liner F),

Fig 1j Amaigam is condensed into the cavity before theautocuring bonding agent is polymerized.

Fig 1 k The restoration is carved. Fig 11 The restorations are finished and poiished. Tooth 37has been restored with the same system.

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Fig 2a The mandibular left first molar bas been endodonti-cally treated and has completely undermined cusps.

Fig 2b The lingual view reveals the presence of caries andundermined buccal cusps.

Fig 2c A phosphoric add gel is applied for 15 seconds toenamel, dentin, and the glass-ionomer base.

Fig 2e The dentin-enamel bonding agenl is applied to en-amel, dentin, and glass-ionomer base witb a brusb. Amal-gam must be condensed in the cavity before the adhesive ispolymerized.

Fig 2d After 15 seconds, the etching gel is removed withan air-water spray, the tooth is dried, and Ihe matrix (AutoMatrix, Caulk/Dentsply¡ is positioned and stabiiized withwooden wedges. Note the while-opaque appearance of theetched enamel.

Fig 2f The restoration is finished and polished.

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Discussion

Several questions retnain unanswered:

1. Would the benefits offered by amalgam adhesivesbe sufficient to compensate for their limitations anddisadvantages'?

2. Are these benefits going to be maintatned clinicallyover time?

3. Are amalgam adhesives indispensable for a clinical-ly acceptable amalgam restoration?

The theoretical priticiple, based on laboratory work,isveryattractive, as laboratory tests have shown. A res-torative technique capable of combining ihe best prop-erties of amalgam and the principles of conservativepreparation and marginal seal inherent to adhesive ma-terials would provide an ideal restoration for posteriorteeth," except for the poor esthetic results achievedwith amalgam. The technique, nevertheless, is lackingciinieal evaluation through well-conducted, compara-tive studies capable of establishing its long-term advan-tages over the conventional technique.'-'^

Chnieal performance and follow-up of one or moreadhesive restoratiotis of amalgam' -" are not sufficient10 encourage the unrestrained use of the techniquebecause sueeess as well as failure of these restorationscan depend on factors other than the adhesive. Suchfactors as cavity preparation,''•'"•'•''-"' the type of alloyused,"'*-̂ "̂*''' amalgam condensation,''"' occlusion,'*"^and the patient's dietary and hygienic habits''**'*•*'''must all enter into the evaluation.

Postopeative sensitivity is commonly reported withamalgam restorations,'" but we now have as a matter ofclinical record several hundred restorations, large andconventional in vital teeth, that had no liner (only aflu-oride application) and ehcited no postoperative sensi-tivity. Studies now confirm'̂ ^™ that the infiltration ofhacteria into the tooth-restoration interface, ratherthan the amalgam restoration itself, is the cause of post-operative pain." The provision of a sealed restorationinterface affords protection to the pulpodentinal com-plex, eliminating pathologic consequences. Dtsinfec-tion of the cavity preparation should be consideredroutine. Commercially available disinfecting agents donot interfere with the bond to dentin'- and are quitecompatible with the wet bonding procedure describedby Kanca.''

The relationship between adhesive and denlin is nowwell doeumented,-^--''^"'^''"'" and mechanical entrap-ment of resin in the amalgam has been suggested"-'^'^^

as the bonding mechanism. Our studies offer morpho-logic evidence of this; however, although this may pro-vide the primary mechanism, we cannot discount othermechanisms, such as sulphone-amalgam interactions,that could occur with products such as Liner F (BiscoDental).

It is important that materials, before being put to use,are extensively tested and evaluated in the laboratory,particuiariy under simulated conditions found in theoral environment. However, there is no greater reco-gnition for a restorative material or technique than thelong-term clinical confirmation of its efficiency. Suchwould be the case with amalgam which, in spite of itshistorical dental significance, can still rival modern ma-terials and can be used as a comparison standard in la-boratory and clinical tests.*-''"•''""

It has been documented that the majority of replace-ments of amalgam restorations are due to recurrentcaries. However, it is also a fact that the diagnosis of re-current caries and the need to replace a restoration areindividual decisions based on poorly determined prin-ciples.'''̂ "'' Diagnosis is often difficult and tinged witherror. A large number of amalgam restorations mayhave been replaced unnecessarily,*^" when a simple re-finishing or seahng of the margins would have suf-fi ce d,̂ "''̂ '-*'̂

Conclusion

In the future, amalgam adhesives will have a significantand increasing role to play in the daily restorative tasksof clinicians. Ifthe highly favorable trends indicated bypresent research are substantiated through clinicaltesting, bonded amalgam restorattons will become rou-tine. Preservation of loolh structure, low placementcosts, and reduced chair time will continue to makeamalgam the material of choice for tnany patients. Ad-hesively retained amalgam restorations will probablyovercome some ofthe shortcomings exhibited by amal-gam when it is placed in a conventional manner. Tlierestorative procedure for amalgarn in posterior teethwill become simplified while it offers biological, func-tional, and mechanical advantages.

Acknowledgments

The authors would like to acknowledge the valuatilc help they re-ceived from Dr Mauro José Pintarelli and Dr Claudia Irene Weso-loski.

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