Dental Materials Fillings Performance

2003;134;463-472 J Am Dent Assoc

ADA COUNCIL ON SCIENTIFIC AFFAIRS Direct and indirect restorative materials

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JADA, Vol. 134, April 2003 463

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P R A C T I C A L S C I E N C E A B S T R A C T

Background. In recent years, dentistryhas benefited from a marked increase in thedevelopment of esthetic materials, includingceramic and plastic compounds. But theadvent of these new materials has not elimi-nated the usefulness of more traditionalrestorative materials such as gold, basemetal alloys and dental amalgam. Overview. This report outlines importantfeatures of direct and indirect restoratives,with an emphasis on the safety and efficacyof each material. Conclusions and Practice Implications. This article was developedto help dentists explain to their patients therelative pros and cons of various materialsused in dental restorations, which includefillings, crowns, bridges and inlays. Theweight of the scientific evidence indicatesthat all of these materials are safe and effec-tive for their intended use. Patients, in con-sultation with their dentists, are free tochoose the most appropriate among them fortheir particular needs.

Direct and indirectrestorative materialsADA COUNCIL ON SCIENTIFIC AFFAIRS

Patients and practitioners have a variety ofoptions when choosing materials and proce-dures for restoring carious lesions or missingteeth. This report outlines important featuresof many of the most popular restorative choices

and is intended as a communication tool for dentists touse in discussing the options available for a particularrestoration with their patients. This is not a comprehen-

sive literature review and, due to spacelimitations, it covers only the most com-monly used restorative materials. Thechoice of material and procedures torestore form, appearance and functionto the dentition is an important healthcare decision that is ultimately made bythe patient after careful consultationwith his or her dentist. It is imperativethat dentists provide this information ina manner that is clear, concise andbased on the best available scientificinformation.

This article is a companion piece tothe chart comparing the important fea-tures of many frequently used restora-tive materials that appeared in theMarch 18, 2002, issue of ADA News1

(Tables 1 and 2). The chart tabulated physical and clin-ical characteristics of the two common categories ofmaterials: direct and indirect. Practitioners might wish

The weight ofthe scientific

evidence indicates that

all of thevarious dental

restorativematerials

are safe andeffective for

their intendeduse.

“Practical Science” is prepared each month by the ADA Council on Scientific Affairs and Divi-sion of Science, in cooperation with The Journal of the American Dental Association. Themission of “Practical Science” is to spotlight what is known, scientifically, about the issuesand challenges facing today’s practicing dentists.

to explain the differences between thetwo categories thus: Direct materialsare those that can be placed directly inthe tooth cavity during a single appoint-ment. Indirect materials are used tofabricate restorations in the dental lab-oratory that then are placed in or on theteeth; placement of indirect materialsgenerally requires two or more visits tocomplete the restoration. Table 3 (page466) lists commonly used direct andindirect materials.

The service life of dental restorativesdepends on a number of patient-, ma-terial- and procedure-related factors.Patient-related factors include the sizeand location of the restoration, chewinghabits and loads, the level of oralhygiene and maintenance, and systemic

Copyright ©2003 American Dental Association. All rights reserved.

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464 JADA, Vol. 134, April 2003

P R A C T I C A L S C I E N C E

TABLE 1

COMPARISON OF DIRECT RESTORATIVE DENTAL MATERIALS. FACTORS AMALGAM RESIN-BASED

COMPOSITE (DIRECT AND INDIRECT)

GLASS IONOMER RESIN-MODIFIEDGLASS IONOMER

A mixture of mer-cury and silver alloypowder that forms ahard solid metalfilling. Self-hard-ening at mouth tem-perature.

Dental fillings andheavily loaded backtooth restorations.

Leakage is mod-erate, but recurrentdecay is no moreprevalent than othermaterials.

Good to excellent inlarge load-bearingrestorations.

Requires removal oftooth structure foradequate retentionand thickness of thefilling.

Tolerant to a widerange of clinicalplacement condi-tions, moderatelytolerant to the pres-ence of moistureduring placement.

Highly resistant towear.

Brittle, subject tochipping on fillingedges, but good bulkstrength in largerhigh-load restorations.

Early sensitivity to hot and cold possible.

Silver or graymetallic color doesnot mimic toothcolor.

Generally lower;actual cost of fillingsdepends on theirsize.

One.

General Description

Principal Uses

Leakage andRecurrent Decay

Overall Durability

Cavity Preparation Considerations

Clinical Considerations

Resistance toWear

Resistance toFracture

Biocompatibility

Post-PlacementSensitivity

Esthetics

Relative Cost toPatient

Average Number of Visits To Complete

A mixture of sub-micron glass fillerand acrylic thatforms a solid tooth-colored restoration.Self- or light-hardening at mouth temperature.

Esthetic dental fill-ings and veneers.

Leakage low whenproperly bonded tounderlying tooth;recurrent decaydepends on mainte-nance of the tooth-material bond.

Good in small-to-moderate size restorations.

Moderately resistant,but less so thanamalgam.

Moderate resistanceto fracture in high-load restorations.

Occurrence of sensi-tivity highly depen-dent on ability toadequately bond therestoration to theunderlying tooth.

Mimics natural toothcolor and translu-cency, but can besubject to stainingand discolorationover time.

One for direct fill-ings; 2+ for indirectinlays, veneers andcrowns.

Self-hardening mixture offluoride containing glasspowder and organic acidthat forms a solid toothcolored restoration able torelease fluoride.

Leakage is generally low;recurrent decay is com-parable to other directmaterials, fluoride releasemay be beneficial forpatients at high risk fordecay.

Low resistance to fracture.

Low.

Small non–load-bearing fillings, cavity liners andcements for crowns and bridges.

Moderate to good in non–load-bearing restorations;poor in load-bearing.

Adhesive bonding permits removing less tooth structure.

Must be placed in a well-controlled field of operation; very little tolerance topresence of moisture during placement.

High wear when placed on chewing surfaces.

Self- or light-hardening mixture ofsub-micron glass fillerwith fluoride-containing glasspowder and acrylicresin that forms asolid tooth-colored restoration able torelease fluoride.

Leakage is low whenproperly bonded to theunderlying tooth;recurrent decay iscomparable to otherdirect materials; fluo-ride release may bebeneficial for patientsat high risk for decay.

Low to moderateresistance to fracture.

Occurrence of sensi-tivity highly de-pendent on ability toadequately bond therestoration to theunderlying tooth

One.

Well-tolerated with rare occurrences of allergenic response.

Mimics natural tooth color, but lacks natural translucency of enamel.

Moderate; actual cost of fillings depends on their size and technique.

One.

NOTE: The information in this chart is provided to help dentists discuss the attributes of commonly used dental restorative materials with theirpatients. The chart is a simple overview of the subject based on the current dental literature. It is not intended to be comprehensive. Theattributes of a particular restorative material will vary from case to case depending on a number of factors.


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TABLE 2

COMPARISON OF INDIRECT RESTORATIVE DENTAL MATERIALS.FACTORS CERAMIC METAL-CERAMIC CAST-GOLD

(HIGH NOBLE) ALLOYS

Ceramic is fused toan underlying metalstructure to providestrength to a filling,crown or bridge.

Crowns and fixedbridges.

Very strong anddurable.

Including bothceramic and metalcreates a strongerrestoration thanceramic alone; mod-erately aggressivetooth reduction isrequired.

Highly resistant towear, but ceramiccan rapidly wearopposing teeth if itssurface becomesrough.

Ceramic is prone toimpact fracture; themetal has highstrength.

Well tolerated, butsome patients mayshow allergenic sen-sitivity to basemetals.

Ceramic can mimicnatural tooth appear-ance, but metallimits translucency.

Minimum of two;matching esthetics ofteeth may requiremore visits.

Alloy of gold, copper andother metals resulting ina strong, effective filling,crown or bridge.

Inlays, onlays, crownsand fixed bridges.

Well-tolerated.

Alloys of non-noblemetals with silverappearance resultingin high-strengthcrowns and bridges.

Crowns, fixed bridgesand partial dentures.

Well tolerated, but some patients mayshow allergenic sensi-tivity to base metals.

BASE METAL ALLOYS (NON-NOBLE)

The commonly used methods used for placement provide a good seal againstleakage. The incidence of recurrent decay is similar to other restorative procedures.

High corrosion resistance prevents tarnishing; highstrength and toughness resist fracture and wear.

The relative high strength of metals in thin sectionsrequires the least amount of healthy tooth structureremoval.

These are multiple-step procedures requiring highly accurate clinical and laboratory processing. Most restorations require multiple appointments and laboratory fabrication.

Resistant to wear and gentle to opposing teeth.

Highly resistant to fracture.

High thermal conductivity may result in early post-placement discomfort from hot and cold.

Metal colors do not mimic natural teeth.

Higher; requires at least two office visits and laboratory services.

Minimum of two.

General Description

Principal Uses

Leakage andRecurrent Decay

Durability

Cavity Preparation Considerations

Clinical Considerations

Resistance toWear

Resistance toFracture

Biocompatibility

Post-Placement Sensitivity

Esthetics

Relative Cost toPatient

Average Numberof Visits To Complete

Porcelain, ceramicor glass-like fillingsand crowns.

Inlays, onlays,crowns and esthetic veneers.

Sealing abilitydepends on materials, under-lying tooth structureand procedure usedfor placement.

Brittle material,may fracture underheavy biting loads.Strength dependsgreatly on quality ofbond to underlyingtooth structure.

Because strengthdepends on ad-equate ceramicthickness, itrequires moreaggressive toothreduction duringpreparation.

Highly resistant towear, but ceramiccan rapidly wearopposing teeth if itssurface becomesrough.

Prone to fracturewhen placed undertension or onimpact.

Well-tolerated.

Low thermal con-ductivity reducesthe likelihood of dis-comfort from hotand cold.

Color and translu-cency mimic naturaltooth appearance.

Higher; requires atleast two office visitsand laboratory services.

Minimum of two;matching estheticsof teeth may requiremore visits.

Sensitivity, if present, is usually not material-specific.


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conditions that can changethe amount of saliva andits chemistry. Material-related factors includestrength, wear resistance,tolerance to water, dimen-sional stability and colorstability. Added to this areprocedural factors gener-ally encountered in makingand placing a restoration,such as the size and depthof the cavity, the ability to prevent contaminatingthe cavity surface with saliva and blood, and theability to access the tooth and tooth surfaceneeding restoring. Because each restoration hasunique circumstances that profoundly affect itslifetime, this article does not attempt to discuss orpredict longevity of service for any of these mate-rials. Dentists need to consider all of these factorsand discuss them with patients for them to makethe best informed decision.

DIRECT RESTORATIVE MATERIALS

Dental amalgam. A modern amalgam restora-tion is an alloy composed of mercury, silver, tinand copper along with other metallic elementsadded to improve physical and mechanical prop-erties. A unique aspect of the amalgam restora-tion is that it starts out as a pastelike mixture ofmetals and, within a few minutes after place-ment, hardens in the mouth by a series of chem-ical reactions to form a stable metallic alloy. Themercury is transformed from the metallic liquidstate into a solid and stable intermetallic compound.

Amalgam is especially suitable for Class I andII restorations in teeth that encounter heavychewing forces. Class II restorations tend to belarge with extensive tooth-material interfaceareas. These present a potential for leakage oforal fluids around the margins of the tooth-fillinginterface, increasing the risk for recurrent caries.However, amalgam has been reported to becapable of sealing the tooth-restoration marginswith corrosion products that accumulate withtime. Since it is metallic in composition, amalgamis unable to mimic the color or translucency ofnatural teeth, and its silver-gray color limits itsuse on anterior teeth.

Advantages of amalgam restorations over otherdirect-placement materials include resistance towear; tolerance to a wide range of clinical place-

ment conditions, especially wet fields; and excel-lent load-bearing properties.2-4 Amalgam’s resis-tance to wear is superior to that of resin-basedcomposites, especially for areas in direct andheavy contact with opposing teeth. This is duelargely to amalgam’s ability to adapt throughdeformation under load.

Ideally, amalgam should be placed in a clean,dry field. Often, cavity location or patient man-agement considerations make this impossible,and amalgam is the only direct material currentlyavailable that can be used to provide a service-able restoration under these conditions.5 Theinability to keep a clean, dry cavity preparationoccurs most frequently in very young patients, indeep cavities under the gingival margin or veryfar back in the mouth. In these very challengingsituations, amalgam can provide a satisfactoryand very serviceable restoration.

Safety of dental amalgam. Amalgam has beenused successfully as a restorative material sincethe middle of the 19th century.6-8 Despite its longhistory of success, the safety of this material hasbeen questioned periodically owing to the pres-ence of mercury in its composition. Nevertheless,virtually every major health organization respon-sible for protecting public health in the UnitedStates (such as the National Institute of Dentaland Craniofacial Research, the Centers for Dis-ease Control and Prevention and the U.S. Foodand Drug Administration9) and abroad (such asthe World Health Organization and FederationDentaire International) have declared dentalamalgam as safe and effective.

Very small quantities of elemental mercuryvapor (less than one-half of the estimated naturaldaily exposure) can be released from amalgamrestorations during chewing.10 The possibility oflocalized allergic reactions to amalgam is recog-nized.9 A recent study reported that immediatehypersensitivity to amalgam is relatively infre-



TABLE 3

CATEGORIES OF MODERN RESTORATIVE MATERIALS.DIRECT INDIRECT

All-Ceramic (Porcelain)

Metal-Ceramic

Cast-Gold (High Noble) Alloys

Base Metal (Non-noble) Alloys

Amalgam

Resin-based Composites (Direct and Indirect)

Glass Ionomers

Resin-Modified Ionomers


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fillings to the tooth. Shrinkage of the compositeon curing can induce stress on therestoration/tooth bond, resulting in strain orbending of the tooth and in rare instances frac-ture. Failure of the tooth/composite bond also canbe a source of early postoperative sensitivity.Recent improvements in composites and theadhesives used to place composites have mini-mized the occurrence of these adverse events.

Composite restorative materials are rarelyplaced without the use of an adhesive. The cavitypreparation is cleaned, etched with phosphoricacid or similar etchant and impregnated with abonding resin to adhere mechanically to the

microporosities created by etchingthe dentin and enamel. Bondingresins typically contain low–molec-ular-weight resin monomers, andsome of these have been implicatedin allergic reactions. Sensitizationto compounds such as hydroxyethylmethacrylate have been reported,but the problem is actually morecommon among dentists than it isamong patients.16 Frequent expo-sure to these resins have been

reported to cause allergic dermatitis on the fin-gertips of clinicians who have had repeated directcontact with these unreacted monomers.18

Another safety concern regarding resin-basedcomposites arose in the mid-1990s, when someresearchers claimed to have detected the presenceof bisphenol A, which is known to have an estro-genic potential, in the saliva of patients whorecently had received pit-and-fissure sealants.19

The presence of bisphenol A in the dentalsealants in this study was thought to have origi-nated from the breakdown of bisphenol A glycidyl dimethacrylate, or Bis-GMA, a monomercommonly used in composite and sealant formula-tions. Two recent studies disputed this con-tention. A study published in 2000 demonstratedthat a small amount of bisphenol A could bedetected in saliva immediately after placement ofa particular pit-and-fissure sealant, but this pres-ence was very transient and no detectable levelwas measured in the blood of these patients.20 Theauthors of this study concluded that the suspi-cions of sealants’ potential for estrogenicity wasunfounded. A second study, published in 2001,demonstrated that the bisphenol A measured inthese clinical trials19,20 most likely was derivedfrom the enzymatic cleavage of a different

quent.11 A 1986 review of the literature spanninga time frame of 1905 to 1986 turned up only 41cases of amalgam allergy.12 Considering the hun-dreds of millions of amalgams that were placedover this period, amalgam allergy can be consid-ered very rare.

Efficacy of dental amalgam. Until the advent ofresin-based composites in the late 1960s,amalgam was the restorative material of choicefor all but the most esthetically demanding resto-rations. For example, the total number ofamalgam restorations placed in 1979 in theUnited States was estimated to be 157 million.13

That number had declined to about 66 million in1999. The relative number ofamalgam restorations placed wassurpassed by resin-based compositerestorations in the late 1990s, andthe use of amalgam continues todecline at a fairly constant rate.This decline can be attributed toseveral factors, including theincrease in the demand for estheticrestorations, the reduction in dentalcaries and its severity, improve-ments in composite technology andimproved training and experience of the clinicianin the placement of composite restorations.

Resin-based composites. Composite restora-tive materials are complex blends of polymeriz-able resins mixed with glass powder fillers. Tobond the glass filler particles to the plastic resinmatrix, the filler particles are coated with silane,an adhesive coupling molecule. Other additivesalso are included in composite formulations toenhance radiographic opacity for better diagnosticidentification, to facilitate curing and to adjustviscosity for better handling. Color and translu-cency of dental composites are modified to mimicthe color and translucency of teeth, making themthe most esthetic direct filling material available.

Safety of resin-based composites. Like otherrestorative materials currently approved for usein dentistry, resin-based composites are consid-ered safe. Allergic reactions to resin-based com-posites have been noted in a very small number ofpeople.14-16 Postoperative tooth sensitivity afterthe use of composite materials is not uncommon,but it usually is transient and related to leakagenext to the margins of the filling or, occasionally,to mechanical stress placed on the tooth as thefilling material cures.17 Highly effective bondingresins are used to provide adhesion of composite



Like other restorativematerials currentlyapproved for use in

dentistry, resin-basedcomposites are considered safe.


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monomer—bisphenol A dimethacrylate, or Bis-DMA—and not from the suspected breakdown ofBis-GMA.21 The majority of composites andsealants currently used do not contain Bis-DMA.Therefore, current resin-based composite ma-terials generally are regarded as safe and effec-tive when placed properly.

Effectiveness of resin-based composites. Theseesthetic materials originally were designed andintended for anterior restorations only. As theirpopularity increased and the materials were fur-ther improved, their use expanded into nearly allclasses and types of dental restorations. Today,composites are commonly used for anterior resto-rations and also used extensively for small- tomoderate-sized posterior fillings in teeth withoutsevere chewing loads. While they generally arenot as strong or durable as metals, resin-basedcomposites have shown promise of improvementin durability and length of service in clinicalstudies of their performance in Class I and ClassII restorations.

An important factor in the placement of resin-based composites is adequate field control. Com-posite restorations cannot be placed successfullyin a cavity that is contaminated by blood orsaliva. Cavity contamination results in failure toachieve adhesion between the filling and thetooth and subsequent leakage at this interface.

Direct versus indirect composites. Curingshrinkage can be prevented partially by fabri-cating and curing the bulk of the restoration out-side the mouth. Heat and pressure also can helpimprove the degree of cure in the restoration. Forthese reasons, indirect composite restorations fab-ricated in a dental laboratory were developed,attempting to improve the overall durability ofthe filling. However, indirect composites mayrequire a second appointment for placement.While some improvement in properties could beachieved, clinical evidence indicates that directcomposite restorations carefully fabricated fromquality materials probably are as serviceable asthe indirect laboratory-fabricated equivalents.22,23

Glass ionomers. Glass ionomers are tooth-colored filling materials that can be used torestore cavities with low load-bearing require-ments. They are supplied as a powder-liquidsystem composed of an acid-soluble glass powderand liquid polyacrylic acid. On mixing, the acidreacts with the surface of the glass powder,forming a hard matrix that surrounds the unre-acted portion of the glass powder. The resulting

structure is much like a dental composite in thatit has acceptable esthetics, except for the ten-dency of ionomers to appear opaque when com-pared with natural tooth enamel.

Variations of this material incorporate metalpowders, such as the alloy powder also used inamalgam, or involve the sintering of silver withthe glass powder in an attempt to improvestrength and wear resistance. The polyacrylicacid also has been freeze-dried and incorporatedinto the glass powder, requiring only the additionof water to react and set. Residual acid in themixed material promotes an ionic bond to toothstructure, adhesively bonding the material to thetooth. The glass powder has a natural rich fluo-ride content that has been credited with pro-viding a cavity-inhibiting environment to protectthe tooth from decay.24 Although widely quoted,this protective effect of fluoride in glass ionomershas come under scrutiny in recent years, as there has been little clinical evidence of its effectiveness.25

Safety of glass ionomers. Glass-ionomer ma-terials have proven to be safe with little potentialfor soft-tissue irritation or other adverseresponses. Postoperative sensitivity of glassionomer material is low and most often isattributed to the placement technique ratherthan to a direct reaction to the material.26

Effectiveness of glass ionomers. Modern glass-ionomer materials often are used to restore non-carious erosion or abrasion defects that develop inthe tooth near the gumline. They also are used forpediatric restorations, for which service longevityrequirements are low. Glass ionomers also fre-quently are used as cavity liners or bases, pro-viding protection to the underlying tooth pulp indeep fillings. The tooth color of the materialallows for an esthetic restoration, but naturalappearance suffers since the material lackstranslucency. In addition, glass ionomers havebeen used as pit-and-fissure sealants. However,the high viscosity of these materials and theirrapid chemical setting restricts their use to widefissures and patients with a high risk of devel-oping caries.27 Glass-ionomer materials also havefunctioned well as cements for crowns andbridges.

The materials are sensitive to both moisturecontamination and desiccation during the settingreaction. These factors make glass ionomers arather technique-sensitive material to place prop-erly and one that requires good control of mois-




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ture and contamination within the cavity. Resin-modified glass ionomers. Resin-

modified glass ionomers are similar to conven-tional glass ionomers but have better propertiesand handling characteristics.28 Acrylic resins sim-ilar to those used in resin-based composites areadded to the material to reduce sensitivity to thesetting environment and to provide the ability forthe material to be rapidly cured (hardened).Resin-modified glass ionomers (sometimes called“hybrid ionomers”) have two curing systems,light-curing and self-curing. The light-curingsystem enables the material to be cured ondemand with a visible light-curing unit. Themechanical properties of resin-modified glassionomers are similar to those of conventionalionomers, thus preventing them from servingeffectively in permanent load-bearing restora-tions. They are tooth-colored and have a slightlybetter enamel-mimicking translucency than thatof conventional glass ionomers.

Safety of resin-modified glass ionomers. Resin-modified glass ionomers are well-tolerated whenproperly placed.27 However, the addition of theacrylic monomers slightly increases the potentialfor irritation or allergenic response when com-pared with conventional glass ionomers withoutresins. These materials are not indicated forpatients who have a demonstrated allergenicresponse to resin-based composites.

Effectiveness of resin-modified glass ionomers.The clinical uses of resin-modified glass ionomersare the same as those of conventional glassionomers. Unlike conventional glass ionomers,which suffer from short working and long settingtimes, the working and setting times of thesematerials are under better control by the dentist.This removes some of the technique sensitivityfrom this material, making it easier to achieve asuccessful restoration. For this reason, resin-modified glass ionomers have largely replacedconventional glass ionomers for most indications.In addition, the improved translucency results ina better esthetic match to natural tooth enamel.

INDIRECT RESTORATIVE MATERIALS

All indirect restorations require a cement for theprepared teeth to retain them. The cement canhave a large influence on the performance andbiocompatibility of the overall restoration. Twobroad categories of available cements are water-based cements and resin-based cements. Fromthese two categories, a dentist has a wide variety

of materials with different working characteris-tics and properties from which to choose. Thechoice often depends on the type of materialselected for the indirect restoration and the clin-ical requirements, such as setting characteristics,film thickness, setting rates and adhesion to theunderlying tooth.

All-ceramic. Dental ceramic materials areused to fabricate lifelike restorations. Ceramic’stranslucency and toothlike color contribute tohighly esthetic restorations. Ceramic is a veryhard and strong material capable of sustainingbiting forces but, being a brittle glasslike ma-terial, can fracture when subjected to extremeforces or sharp impact. Because of the naturalhardness of ceramic, these restorations are highlyresistant to wear. However, if they are not highlypolished and smooth, they rapidly can wearopposing restorations or natural teeth. Over theyears, laboratory-fabricated all-ceramic restora-tions have become very popular owing to theirexcellent esthetic properties, high strength andexcellent biocompatibility.

Safety of ceramic materials. These materialsare composed largely of fused natural oxides.Their glasslike properties render them very inert,and they tend to be highly biocompatible andwell-tolerated.29,30 However, all-ceramic restora-tions rely on technique-sensitive resin-basedcements and adhesives to hold them in place andto seal the tooth against leakage. Rare allergiesor sensitivities to the resin components of thecements and adhesives can occur. There are a fewnonresin cements that can be used with all-ceramic restorations, but they may reduce theoverall strength of the restoration owing to theirlack of adhesion to the ceramic and the tooth.

Effectiveness of ceramic restorations. Dentalceramics are indicated for crowns, inlays, onlaysand veneers in areas where the highest level ofesthetics is desired. Although ceramic is a natu-rally strong material, crowns on posterior teethcomposed entirely of ceramic have lower successrates than those of metallic restorations becauseof the material’s brittleness.31 The low fractureresistance of all-ceramic restorations also limitsthem primarily to single-tooth restorations.

Ceramic veneer restorations replace a verythin layer of enamel on the front of teeth toimprove the appearance or color of the teeth.These restorations are only approximately 0.5millimeter in thickness, but because they arebonded to the underlying tooth with resin-based




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cements and adhesives, they have proven to bevery durable. All-ceramic crowns, inlays andonlays can be similarly bonded to teeth toimprove their strength and performance. A prop-erly constructed and bonded all-ceramic restora-tion can provide many years of service with verylittle change in color or appearance.

Metal-ceramic. The technology for effectivelybonding porcelain to dental metal alloys wasdeveloped in 1962 in an attempt to improve thestrength and durability of these restorations.32,33

These restorations are made by thermallybonding dental porcelains to an underlying metalframework that has been cast to fit the tooth orbridge preparation. The high supportive strengthof the underlying metal allowsmetal-ceramic restorations to pro-vide full coverage of posterior teethand to be used for multiple-toothbridges. The natural tooth color ofceramic masks the unnaturalappearance of the underlying metalto provide excellent toothlike colorand appearance.

Safety of metal-ceramic restora-tions. These restorations generally are well-tolerated except for the moderately rare incidenceof allergy to the metal portion of the restoration.High-noble alloys are better tolerated than thebase alloy metals when used for these restora-tions. For this reason, the proper choice of metalbecomes an important consideration when usingthis option.

Another clinical consideration when choosing ametal-ceramic restoration is the additionalamount of tooth reduction necessary to accommo-date the proper thickness of metal and ceramicneeded to fabricate the crown. Care also must betaken to achieve a smooth ceramic surface toreduce the potential for excessively wearingopposing teeth. Metal-ceramic restorations generally do not rely on adhesion to the tooth forstrength and can be cemented with a wide variety of dental cements. The resin-basedcements, in rare occasions, may induce allergiesand sensitivities.

Effectiveness of metal-ceramic restorations. Thelongevity of a metal-ceramic crown or bridge issomewhat less than that of an all-metal restora-tion because of ceramic’s potential to fail. Theopacity of the underlying metal tends to renderthe restoration somewhat less lifelike than theall-ceramic restoration. However, a skilled techni-

cian can overcome this drawback to some degree. The metal-ceramic restoration cannot provide

the high level of esthetics achievable with an all-ceramic restoration, but it can provide muchbetter durability for posterior restorations. Veryhigh-strength metal alloys also can be used tofabricate larger multiple-tooth bridges using thisoption. Metal-ceramic restorations provide a verydurable, long-lasting option for the restoration ofposterior teeth or teeth with a great deal of struc-tural damage.

Cast-gold (high noble metal) alloys. One ofthe most serviceable dental restorations availableis the cast-gold (high noble metal) restoration.Gold alloys provide a strong, biocompatible, long-

lasting option with a long history ofoutstanding service to dentistry.The relative high strength of cast-gold alloys allows for a minimalreduction of tooth structure toachieve adequate thickness for therestoration. The long survival timeand the low wear of both the resto-ration and opposing natural toothstructure establish cast gold as the

standard by which other dental materials aremeasured.

Safety of cast-gold alloys. By their nature,noble metals are chemically nonreactive withlittle potential for adverse biological response.Allergenic reaction to gold is rare, but it can occurin the form of localized inflammation.34 Non-noblemetals are added to improve the strength of cast-gold alloys, and these additions tend to reduce thenoble nature of the alloy. However, even at noblemetal content below 75 percent, these alloys gen-erally are well-tolerated.

The high strength and toughness exhibited bythese metals allows for the fabrication of thinnerrestorations, thus reducing the amount of toothreduction required during preparation. Cast-goldalloys also can be cemented with practically anyeffective cement, providing the dentist a widevariety from which to choose. Cast-gold alloysstill are considered the standard against whichother restorative materials are compared clini-cally in terms of fit, biocompatibility and clinicalservice.35

Effectiveness of cast-gold alloys. Noble alloysare used to fabricate inlays, onlays, crowns andbridges. Longevity is difficult to measure becauseof the many human factors that affect an indi-vidual restoration, but it generally is agreed that



One of the most serviceable dental

restorations availableis the cast-gold

restoration.


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cast-gold alloy restorations have a typical servicelifetime of 20 years or more.35 These restorationsowe their longevity to a high resistance tomechanical failure, excellent fit to the toothpreparation and resistance to recurrent decay.The largest disadvantage of cast-gold alloys is theinability to match natural tooth color. However,small restorations often can be conservativelyplaced in locations in which little or no metal canbe seen under normal conditions.

Base metal casting alloys. Base metal, ornon-noble, alloys were developed to provide amore economical alternative to cast-gold alloys.These alloys generally are composed of nickel,chromium and cobalt. Base metal alloys can beprecision-cast into crowns and bridges or intolarger frameworks for removable partial dentures.

Safety of base metal casting alloys. Nickel isrecognized as a common metal contact allergen;as much as 14 percent of the general U.S. popula-tion has been reported to be sensitive to themetal.37 Despite this high level of sensitivity,allergic reactions in the oral cavity generally arenot as severe as those manifested on the skin andare not nearly as common.38,39 Many people whocannot tolerate jewelry containing nickel can tol-erate dental restorations containing nickel. Yet,allergies to nickel in the oral cavity are known,and the use of nickel-based alloys is contraindi-cated for use in patients with a known nickelallergy.40

Effectiveness of base metal casting alloys. Thebase metal alloys serve as effective materials forcrown-and-bridge restorations. The higher stiff-ness of these materials results in less flexurethan that which occurs in gold alloys. This isespecially important when ceramic is fused to thesurface or when long spans are required betweensupporting teeth. Also, base metal alloys aremuch lighter in weight than comparable goldalloys. This is important for larger castings suchas partial denture frameworks. Base metal resto-rations also can be cemented using a wide varietyof cements.

On the negative side, base metal alloys areabout three times harder than gold, which makesadjustments for fit or balanced bite more difficult.

CONCLUSION

Advances in modern dental materials providepatients and practitioners a number of choicesfrom which to create more pleasing and natural-

looking restorations. This article has presentedmany of these options, along with their indica-tions for use and possible safety concerns. On thebasis of current knowledge from laboratory andclinical studies, the choices discussed in thisreport, when placed properly, can provide thepatient, in almost all cases, with a safe and effec-tive treatment in the repair of missing, worn,damaged or decayed teeth. ■

Address reprint requests to the ADA Council on Scientific Affairs,211 E. Chicago Ave., 4th Floor, Chicago, Ill. 60611.

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Dental Materials Fillings Performance

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