JCDA • www.cda-adc.ca/jcda • November 2005, Vol. 71, No. 10 • 743

Clinical S H O W C A S E

“Clinical Showcase” is a series

of pictorial essays that focus on

the technical art of clinical

dentistry. The section features

step-by-step case demonstrations

of clinical problems encountered

in dental practice. If you would

like to propose a case or

recommend a clinician who

could contribute to this

section, contact editor-in-chief

Dr. John O’Keefe at

jokeefe@cda-adc.ca.

One of the critical goals of adhesivedentistry is to restore the peripheralseal of dentin that is interrupted

when enamel is lost as a result of develop-mental sequelae, trauma, caries or opera-tive intervention such as preparatoryexcision. For coronal lesions the exposedstrata may be bounded by dentin, enamelor both. Manufacturers continue to workvigorously on resin formulations that willrestore this peripheral seal with operativeease and absolute durability.

Enamel BondThe bond between resin and enamel is

generally satisfactory. Most cliniciansreport that it is possible to achieve seem-ingly impeccable margins at the visiblecavosurfaces when restoring posteriorteeth with a direct composite-resin tech-nique. Clinical experience, however,reveals that these resin–tooth interfacesdeteriorate as they age. More pertinently,

in vitro studies have revealed the formi-dable challenge of achieving a predictableseal at the proximal margins when tooth-coloured restorations are used.1

Dentin BondThe bond between resin and dentin

has been more of a challenge, andnumerous generations of resin-bondingagents have been energetically touted asthe ultimate dentin bonding agent.Regrettably, predictability of outcome hasbeen trumped by simplicity of applica-tion; as a result, the newer bonding agentsare certainly simple to use (one bottle;separate etching, priming and rinsing notrequired) but are no better (in fact, theyare far worse) than the 3-bottle systems ofthe 1990s. For dentin bonding, it appearsfar easier to achieve a seal than to main-tain it, and in vivo studies have confirmedthat resin–dentin bonds degrade in theoral cavity.2

Return to the Resin-Modified Glass–IonomerCement Sandwich TechniqueWilliam Liebenberg, BSc, BDS

Figure 1: Preoperative view showslesions approximal to teeth 15 and16. The patient requested a directtooth-coloured restoration.

Figure 2: When restoring 2 approximallesions containing sound marginal ridges, it isprudent to gain access through the tooth thatdisplays the largest lesion radiographically.Accordingly, a pear-shaped diamond FG 830drill (Axis Dental, Irving, Texas) was used topenetrate through the enamel of the secondpremolar.

Figure 3: A stainless steel protective matrix(InterGuard, Ultradent, South Jordan, Utah)was used during removal of the caries to preserve those portions of the adjacent tooththat were sound. A round #6 carbide bur wasused for the bulk of the excision.

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Enamel Protecting DentinSeveral authors have concluded that resin

bonded to enamel protects the resin–dentinbond against degradation.3 It follows from thedata on the bond to enamel and dentin that thereliability of adhesion depends on the periph-eral seal to the enamel.

The ProblemFor a lesion that is entirely bounded by

enamel (i.e., an intra-enamel lesion), pre-serving the dentin seal becomes a matter ofestablishing a lasting interface between theresin and the enamel. Unfortunately, not all

lesions are of this type, and posterior proximallesions commonly have gingival marginsbounded by dentin. The strength and quality ofthe peripheral seal is therefore compromisedand is susceptible to hydrolytic degradation.

The SolutionFor a posterior tooth with a proximal

margin that extends apical to the cemento-enamel junction and for which a direct tooth-coloured restoration is planned, thesolution is the open-sandwich technique. Thistechnique is not new,4 but it deserves to berevisited, given the commercial proclivity

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Figure 7: When a G-Ring (Garrison DentalSolutions, Spring Lake, Mich.) is applied, thecurve of the matrix becomes distorted.Because the position and form of the matrixwill determine the outline of the definitiverestoration, it is important to refine the curveof the matrix before placing the restorativematerial.

Figure 8: A thin burnishing instrument isinserted between the lingual surface of thepremolar and the matrix and is manipulatedto pull the matrix out of the proximal con-vexity. The instrument is then inserted to theproximal depth, and a burnishing action isused to re-form the matrix to an ideal physiological curve.

Figure 9: It is time well spent toadjust the matrix by applying burnishing actions on both sidesuntil the ideal curve is attained. It is far more time consuming (and destructive to the restorative interface) to attempt to changethe proximal contour once thecomposite resin has been polymerized.

Figure 6: A curved AutoMatrixretainerless band (Dentsply,Woodbridge, Ont.) is placed in a cir-cumferential position, and a wedge isput into place before the separatingring is applied. The separating ringwill provide interproximal separation,and the wedge will affect matrixadaptation as it is pressed into theproximal space along the gingivalmargin.

Figure 5: A wooden wedge is inserted insuch a way that it depresses the interproximaltissue, revealing the extent of the decay.Round burs are then used to remove thedecay; the wooden wedge serves as a buttress to limit the action of the bur duringrefinement of the margin.

Figure 4: Intraoperative view of cariesremoval. The depth of the premolar lesion hasapproached the cementoenamel junction, andthe molar has a substantial rim of enamelalong the gingival margin.

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toward simplification and the inability ofmany of the newer materials to bond reliablyand permanently to the diverse and compro-mised dentin substrates that cliniciansencounter in clinical practice. Traditionally,the filler of the “sandwich” was a glass–ionomer cement, but resin-modified glass–ionomer cements (RMGIC) have superiormechanical properties and bonding strengthto dentin.5 A previous study investigating thedurability and cariostatic effect of a modifiedopen-sandwich restoration using an RMGICconcluded that it had acceptable durability for the extensive restorations evaluated.6

Furthermore, the open-sandwich techniqueallows the least amount of microleakage of thevarious direct restorative options currentlyavailable.7

The TechniqueAfter removal of the caries and placement

of the matrix, the tooth is conditioned withpolyacrylic acid according to the manufac-turer’s directions. A single gingival incrementof RMGIC is applied by syringe and is allowedto cure or is subjected to light polymerization.The restoration is then completed with com-posite resin (Figs. 1 to 21).

Figure 10: A 10% polyacrylic acid isapplied to remove the smear layer inpreparation for application of thesandwich layer of the resin-modifiedglass–ionomer cement (RMGIC).

Figure 11: A Fuji II LC (GC America, Alsip, Ill.)RMGIC is extruded into position. An effort ismade to apply the RMGIC as accurately aspossible to avoid placing it on the occlusalcavosurface margins.

Figure 12: Once the RMGIC has been poly-merized, the entire cavity is etched with phos-phoric acid in preparation for the compositeresin restoration. The etchant can come intocontact with the RMGIC without deleteriousaffect on the bond to the overlying compositeresin.

Figure 14: The first increment of compositeresin shade A1. The separating ring has beenremoved to accommodate a slight verticalmovement of the matrix so that the margincan be slightly overextended.

Figure 15: The final occlusal increment isshaped into the correct occlusal form usingfine composite instruments such as theFlexichange line (Dentsply). Note that noattempt was made to round the distal mar-ginal ridge before polymerization.

Figure 13: The author prefers a min-imum of 4 consecutive coatings ofadhesive resin on dentin when usingtotal-etch adhesives such as SingleBond (3M ESPE, St. Paul, Minn.). Thissimple change in the bonding tech-nique can improve the strength ofthe resin–dentin bond and reducenano-leakage.8

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Lessons to be LearnedThe case illustrated here was specifically chosen to

demonstrate how the immediate marginal integrity(Fig. 21) will invariably deteriorate with time (Fig. 22).Studies have confirmed that the visible margins have lowerleakage scores than those of the proximal gingival margins,which validates the additional effort involved in performingthe sandwich technique. Currently available dentin bondingagents can maintain the peripheral seal that is integral to alladhesive procedures only if the seal is bounded by enamel. Itis therefore recommended that the sandwich technique be therestoration of choice when proximal gingival margins extendbeyond the cementoenamel junction. C

References1. Brunton PA, Kassir A, Dashti M, Setcos JC. Effect of different application andpolymerization techniques on the microleakage of proximal resin compositerestorations in vitro. Oper Dent 2004; 29(1):54–9.

2. Hashimoto M, Ohno H, Kaga M, Endo K, Sano H, Oguchi H. In vivo degrada-tion of resin-dentin bonds in humans over 1 to 3 years. J Dent Res 2000;79(6):1385–91.

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Figure 19: A BiTine ring (Dentsply Caulk) andanatomically precontoured Palodent matrix(Dentsply Caulk) were used to restore theproximal border of the first molar. The sand-wich technique was not needed here, as therewas a rim of enamel circumferential to thelesion.

Figure 20: The matrix is reflected alongsidethe premolar to allow protective access forfinishing the axial surfaces of the molar withthe disk. The reflected matrix prevents inad-vertent gouging of the proximally restoredtooth.

Figure 21: Completed restorationsdisplay the appropriate physiologicalcontours. The interfacial(resin–enamel) marginal fidelity is a consequence of the meticulous finishing sequence.

Figure 16: The band is disconnected, andexcess composite along the axial margins isremoved with finishing disks. The disks areinserted laterally into the proximal space andare used to cut back the excess marginalheight.

Figure 17: The tip of an Enhance polishingpoint (Dentsply Caulk, Milford, Del.) is usedto reduce the marginal ridge along the inte-rior to maintain physiological roundnessocclusally.

Figure 18: Completed RMGIC sand-wich restoration on the premolar. Notethe absence of sharp angles and themarginal ridge created by the disk (usedon the external surface) and polishingpoint (used on the internal surface).

Figure 22: Postoperative view of the restora-tions 26 months later. In spite of meticulousattention to detail, close examination reveals aslight loss of marginal integrity along theenamel–resin margin. Overall, however, thephysiological form has been maintained.

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3. De Munck J, Van Meerbeek B, Yoshida Y, Inoue S, Vargas M, Suzuki K, andother. Four-year water degradation of total-etch adhesives bonded to dentin.J Dent Res 2003; 82(2):136–40.

4. Suzuki M, Jordan RE. Glass ionomer-composite sandwich technique. J AmDent Assoc 1990; 120(1):55–7.

5. Pereira LC, Nunes MC, Dibb RG, Powers JM, Roulet JF, Navarro MF.Mechanical properties and bond strength of glass-ionomer cements. J AdhesDent 2002; 4(1):73–80.

6. Andersson-Wenckert IE, van Dijken JW, Kieri C. Durability of extensive Class II open-sandwich restorations with a resin-modified glass ionomer cementafter 6 years. Am J Dent 2004; 17(1):43–50.

7. Loguercio AD, Alessandra R, Mazzocco KC, Dias AL, Busato AL, Singer Jda M,and other. Microleakage in class II composite resin restorations: total bondingand open sandwich technique. J Adhes Dent 2002; 4(2):137–44.

8. Hashimoto M, Sano H, Yoshida E, Hori M, Kaga M, Oguchi H, and other.Effects of multiple adhesive coatings on dentin bonding. Oper Dent 2004;29(4):416–23.

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Dr. Liebenberg maintains a general practice in Vancouver,British Columbia.

Correspondence to: Dr. William Liebenberg, 201-2609 Westview Dr., NorthVancouver, BC V7N4M2. E-mail: wliebenb@direct.ca.

The author has no declared financial interests in any company manufac-turing the types of products mentioned in this article.

Dr. Liebenberg will be one of thepresenters at the Ontario DentalAssociation Annual Spring Meetingin 2006. His full-day session, titled“Posterior Restorative Excellence: A Potpourri of ProceduralInnovations,” will take place onSaturday, April 8.

THE AUTHOR