Operative Dentistry

The co-cured, light-activated glass-ionomer cernen-compositeresin restorationGeoffrey M. Knight*

The simultaneous curing ofunpolymerized composite resin and inactivated light-curingglass-ionomer cement appears to offer a number of clinical improvements to the laminatedglass-ionomer cement-composite resin restoration. The observation that composite resincures before the glass-ionomer cement suggests that the polymerization shrinkage ofthe resinmay be taken up by the uncured glass-ionomer cement, reducing the internal stress ofthe res-toration. A procedure is described for the placement of this type of laminate restoration thatreduces both technique sensitivity and placement time, by eliminating a number ofthe stepsrequired for a conventional "sandwich" restoration. The apparent clinical success of this tech-nique indicates the need for laboratory testing to evaluate the potential of this procedure.(Quintessence Int, ¡994;25:97-¡0ú.)

Introduction

Light-curing glass-ionomer cements have made a rapidand significant impact on the practice of restorativedentistry since their introduction early in 1992. Notonly has the light-curing component of these materialsimproved dentists' productivity, but the reported im-provements in clinical properties have also extendedtheir clinical applications.' -

Unlike traditional glass-ionomer cements, the newmaterials do not require protection from moisture con-tamination after initiation of the light-curing compo-nent of setting. They have improved physical proper-ties over conventional glass-ionomer cements, even ifallowed to set without light activation, yet they retainthe many clinical benefits of this material. The majordisadvantage ofthe light-curing glass-ionomer cementsis the current lack of clinical research to determinetheir performance over time.̂

Private Practice, 20 Carpenter Street, Brighton, Victoria, 3186,Australia.

The development of composite resins over the pastthree decades has produced a clinical material with es-thetic properties approaching those of natural teethand a wear resistance clinically close to that of dentaiamalgam."* Composite resin has the ability to bond mi-cromechanical ly to dental enamel and to maintain thisbond in the oral environment over long periods,̂ ^ Uti-fortunately. research has not been able to overcome thepolymerization shrinkage of resins that continues to re-quire critical consideration during the clinical app h ca-tions of this material. Furthermore, there is no long-term clinical evidence demonstrating that compositeresin has an ability to bond to dentin, and compositeresin does not offer fluoride release provided by glass-ionomer cements.''

The long-term clinical success observed with glass-ionomer cements"'̂ may be enhanced by the "sandwichrestoration," in which dentin is replaced with glass-ion-omer cement and enamel with composite resin.' Theresulting restoration overcomes many of the shortcom-ings of both glass-ionomer cements and resins; its clini-cal performance over time contradicts criticism of theprocedure.'" The technique is, however, time consum-ing and may he subjeet to failure at the cement-resininterfaee if the set glass-ionomer cement has notreached sufficient maturity before it is etched."

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Operative Dentistry

Í T

This paper investigates a technique of simultane-ously curing light-activating glass-ionomer cement andcomposite resin to enhance the physical properties ofthe resulting restoration.

The concept of co-curing

The idea of eo-euring emerged after the accidental par-tial curing of specimens of light-activating glass-iono-mer cement and composite resin located together on aglass slab. While 2 seconds of curing hardened the resinsurface, the glass-ionomer cement remained a viscouspaste that was easily indented with a plastie instrument.

It is postulated that during co-curing, as the resin ac-tivates before the glass-ionomer eement, the dimen-sional changes caused by the polymerization shrinkageof the resin may be taken up by the uncured glass-iono-mer cement, eliminating many of the internal stresseswithin the restoration and reducing the likelihood ofmarginal leakage.'- Furthermore, this technique elimi-nates a number of the steps required for the traditionalsandwich procedure, thus reducing technique sensitiv-ity and increasing the efficiency of the placement tech-nique.

The technique described below has been used as aroutine clinical procedure for more than 16 months,Gompared to the sandwich restoration, there Is a sub-stantial reduction in the time required for placementarid all observations to date indicate a similar, if notsuperior, clinical performance.

Clinical technique

The restoration of a tooth requires isolation of the cav-ity from the oral environment. Rubber dam is a usefultool to achieve this but is not essential for a successfuloutcome.

Figure 1 shows a carious lesion on the occlusal sur-face of a maxillary permanent first molar. After appli-cation of a rubber dam, caries is removed and the re-maining occlusal fissures are lightly prepared with a 12-bladed tungsten carbide bur (Fig 2), Preparing the oc-clusal fissures incorporates the benefits described inthe preventive resin restoration.' '

The preparation is etched for 10 seconds with 37%phosphoric aeid (Fig 3), flushed with water, and driedwith oil-free air. Phosphoric acid is used on the eavo-surfaces to etch the enamel and remove the smear layerfrom the dentin. Because the etching of enamel is afunction of concentration and time,'"' the brief lO-sec-ond exposure of the acid to dentin enabled little more

than removal of the ,smear layer. While fuliitv investi-gations may establish superior protocols fm ;:'Lpanngtooth surfaces prior to restoration placement ¡ l¡o tech-nique described in this paper has performi-ü satisfac-torily at a clinical level and eliminates the need lor mul-tiple tooth-conditioning procedures,

A small increment of capsulated Fuji 1! LG glass-ion-omer eement (GC Gorp) is next placed at the base ofthe preparation and cured for 20 seconds, Gapsulatedglass-ionomer cements assure optimal liquid-powderratios and facilitate placement tif the restorative mate-rial. The glass-ionomer eement should fill the cavity upto the dentinoenamel junction (Fig 4), Larger prepara-tions requiring a glass-ionomer base thicker than 3 mmmust be cured incrementally. The remaining prepara-tion and occlusal surface are covered wilh a thin layerof glass-ionomer cement, A plastic instrument is usedto place a small plug of resin into the center of the un-cured glass-ionomer cement (Fig 5). The resin is pud-dled toward the periphery of the cavity and over the oc-elusal fissures with a ball-ended burnisher, so that theglass-ionomer cement is displaced to the margins of thepreparation (Fig 6). The glass-ionomer cement and res-in are cured simultaneously for 20 seconds.

The restoration is then reduced with a high-speed,pear-shaped stone, used under a water spray to preventheat dehydration of the yet chemically unset glass-ion-omer cement. After removal of the dam, the oeelusionis ehecked with articulating paper (Fig 7) and finalpolishing is completed with a mounted rubber point(Fig 8), Five months following placement, the restora-tion has successfully restored the carious lesion andsealed the remaining occlusal surfaees (Fig 9),

Conclusions

Tlie co-curing technique described in this paper hasbeen in routine elinical use over a 16-month period,Tlie fewer clinical steps required for this procedurecompared to a conventional sandwich laminate reduceboth the technique sensitivity and the time required forplacement. Observations of this restoration indicatethat it has a clinical performance similar, if not superi-or, to that of resin and resin laminate restorations.

Further investigations of this technique are requiredto establish whether the clinical performance observedto date can be substantiated by laboratory testing.

98 Quintessence International Volume 25, Number 2/1994

Operative Dentistry

Fig 1 A Class I carious lesion is present on the occiusalsurface of a maxiiiary permanent first molar.

Fig 2 The occiusal fissures are iightiy prepared with a 12-bladed tungsten carbide bur to open the fissures slightly tofaciiitate seaiing ofthe remaining occlusai surface.

Fig 3 The preparation is etched with 37% phosphoric acidfor 10 seconds.

Fig 4 A small increment of capsulated, iight-activated,giass-icnomer cement is placed at the base of the prepara-tion and cured for 20 seconds. The glass-ionomer cementshould fill the preparation up to the dentinoenamei junction.

Fig 5 Inactivated g I ass-i on o mer cement is placed overthe occlusai surface and a small plug of resin is piaced onthe surface.

Fig 6 The resin is then puddled toward the margins of thepreparation with a ball burnisher.

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Fig 7 After the restoration has been cured and contoured,Ihe occlusion is checked for prematurities with articulatingpaper.

Fig 8 Final polishing of the restoration is completed with amounted rubber point.

Fig 9 Five months after placement, the restoration is virtu-aiiy invisibie within the occlusal surface.

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