Dental Research

The effect of dentinal conditioning on light-activatedglass-ionomer cementT. p.c. Sim*/S.K. Sidhu**

This article reports the effeet of condiliomng of denima! surfaces on ihi: sealing capability of ahght-ctiring glass-ionomer restorative material, Fuji I! LC The in vitro evaluation measuredgap formation at the tooth-resioration interface. The control specimens were restored withFuji n LC after dentinal surface treatment with a polyacrylic acid solution, while the experi-mental specimens were restored without pretreatment. The sealing ability of the material todentin was as.sessed by measuring the gap between the restorative material and tooth structure.The comrol group registered a mean marginal gap of 7.75 ¡im, and the experimental groupregistered a mean gap of 10.75 fim. but statistical analysis indicated thai there was no signifi-cant difference between the two groups. Dentinal surface treatment prior to restoration withthe light-curing glass-ionomer cement used in this study resulted in a smaller gap at thedentin-restoration interface, bul this difference was not significant.(Quintessence Int 1994:25:505-508:)

Introduction

Presently, there is exceptional interest regarding glass-ionomer cement (GIC) restorative materials. Sincethey were first described by Wilson and Kent' in 1972,these materials have progressively improved to the cur-rent products. Manufacturers have claimed that thecommon limitations of an earlier generation of glass-ionomer cements have been resolved with the newestclass of similar dental materials, the light-curing GICs.However, it must be demonstrated that these latest ma-terials possess properties identical or superior to thoseof the chemically curing glass-ionomer cements.

* Denial Officer, Singapore Armed Forces, Dental Branch, HQMedical Services, Loe wen Road, Tanglin, Singapore tO24,

** Overseas Visiting Lecturer, Department of Conservative Den-tal Surgery, Floor 25, Llnited Medical and Denial Schools, Guy'sHospilal.London Bridge, London SEt yRT, England,

Address all correspondence to Dr S. K. Sidhu,

Treatment of the dentinal surface prior to placementof glass-ionomer cement restorative material is recom-mended when the chemically cured GICs are used. Abrief, 10-second apphcation of a 10% solution of poly-acrylic acid is an accepted technique.^ The restorativeprotocol recommended by most manufacturers ofglass-ionomer cements includes using polyacrylic acidto alter the smear layer, because it removes gross debrisbut retains "plugs" in the dentinal tubules.-" '̂

However, there is no compelhng clinical evidence toverify that dentinal pretreatment enhances the adhe-sion of glass-ionomer cements.- Although certain stud-ies have demonstrated an improvement in shear bondstrength** and retentive rates of restorations^ after pre-treatment of dentin, other researchers have concludedthat it did not enhance restorative bond strength ofdentin to glass-ionomer cement.*̂

The adhesion between glass-ionomer cement andtooth structure is the result of an ion-enriched layer inthe cement.' Opponents of surface treatment'"'" con-sider conditioning the dentinal surface detrimental tothe development of this ionic exchange layer. Con-versely, proponents claim that leaving the smear layerundisturbed would complicate the development of an

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Dental Research

adhesive layer." This controversy involved the chemi-cally cured materials, and this issue is further compli-cated by the recent emergence of the light-curing GICs,Sparse literature is available to provide information ontheir response and physical properties.

This study evaluated the effect of surface pretreat-ment on a new light-curing glass-ionomer cement res-torative material by measuring the marginal gaps at thetooth-restoration interface. The surface pretreatmentin this study involved dentinai conditioning with poly-acrylic acid to remove the smear layer in dentinai cavitypreparations.

Method and materials

Preparation uf specimens

Extracted, intact, human permanent molars stored inisotonic saline were selected for the study. Flat surfacesof dentin were created on the facial surfaces of theteeth by wet grinding with a grade 600 carborundumpaper. Test cavity preparations were completed on theflattened surfaces of the teeth. The dimensions of eachcavity were a standard 2 mm in diameter and 1.5 mm indepth, A sharp probe was used to ensure that the prep-arations had no pulpal involvement and the marginswere intact and entirely in dentin. The teeth were con-tinually stored in isotonic saline and maintained moistduring cavity preparation. Eighty cavity preparationswere randomly assigned to two groups of 40 specimenseach.

Specimens in both control and experimental groupswere restored with a light-curing glass-ionomer cementrestorative material, Fuji II LC (GC International),handled according to the instructions of the manufac-turer. The specimens in the control group (group 1)were subjected to dentinai surface treatment prior torestoration with the glass-ionomer cement. The wallsand floor of each cavity in this group were pretreatedwith a polyaciylic acid solution (Dentin Conditioner,GC International), The conditioner was applied with ascrubbing motion for 20 seconds, as recommended bythe manufacturer, and each cavity preparation wasrinsed thoroughly with oil-free compressed air. Thespecimens were subsequently restored with Fuji II LCin one increment. The surface of the restoration was se-cured against a clear matrix for 30 seconds and curedwith an Elipar Visio-Light system (ESPE). The dentinof the teeth in the experimental group (group 2) wasnot treated before restoration, but the specimens were

otherwise restored in the same manner as the controlgroup. Immediately after light curing, the control andexperimental specimens were finished and polishedwith tungsten-carbide burs and a series of coarse- tofine-grit disks (Sof-Lex disks, 3M Dental) used withwater spray.

The specimens were then subjected to thermocy-cling. The regimen consisted of 3,000 cycles betweentemperature baths of 5 °C ± 2 "C and 55 "C ± 2 °C,with a dwell time of 30 seconds in each bath and a 5-sec-ond transfer time between baths. The specimens werethen immersed and stored in a 0.5 % basic fuchsin dyesolution for 24 hours at 37 °C to facilitate measurementof the marginal gaps.

Measurement of marginal gap

The margins of all cavity preparations were examinedmicroscopically, and four approximately equidistantpoints along the circumference of each circular cavitywere designated for measurement. The four gaps foreach restoration were examined, measured and re-corded, using an optical microscope (Olympus BHMmicroscope) connected to a micrometer with a digitalcounter (Olympus OSM, No, 602002), The mean mar-ginal gap for each specimen was calculated by deter-mining the average of the measurements at the four dif-ferent points. The mean marginal gap of each group ofspecimens was computed by dividing the sum of the av-erage gap values by the number of specimens.

Results

F.xamination of the tooth-restoration interface of con-trol and experimental specimens indicated that a mea-surable gap was common at each of the measurementsites. The control-group specimens (group 1) registereda mean marginal gap of 7,75 |j.m (SD = 1,34 [im), whilespecimens in group 2 recorded a mean gap of 10,75 |im(SD = 1.42 |j.m). However, statistical evaluation usingStudent's r test revealed that there was no significantdifference between the control and experimentalgroups (i = 2,22) at P<,005.

Discussion

One factor essential to the longevity of a restoration isthe sealing of the cavity. Marginal gaps between resto-rative materials and tooth structure are common,'^ buta great deal of effort is expended to reduce the micro-leakage. Marginal gap formation may result from the

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Dental Research

setting shrinkage of a restorative material, so active re-search is presently beitig conducted on the new light-curing glass-ionomer cements because of their un-known properties and handling protocol.

This study examined the effecl of retnoving the den-tinal smear layer on the seal of a new light-cured glass-ionotner cement. Although the procedures were stan-dardized in this sttidy, the smear layer was not quanti-fied because the procedure was arduous and unreli-able. U is not inconceivable though that the quantity ofthe original smear layer would have an effect on the in-timacy between the restorative material and dentin.However, the extensive number of specimens and re-cordings, including the random sampling of the treat-ment or control groups, should attenuate spurious ef-fects.

Treatment of dentinal surfaces with acid removes thesmear layer,'^ widens tubular orifices, and increaseswetness of the exposed dentinal surface.''''^ Propo-nents of retaining the smear layer consider the seaUngof dentinal tubules and reduction in permeability desir-able,"" while other researchers advocate its removal be-cause it compromises adhesion and can he a focus forbacteria and toxin.'^ Nevertheless, it has been sug-gested that smear layer removal is critical for the devel-opment of an adhesive layer in chemically curing glass-ionomer cement.^ It is not apparent if the same mecha-nism of adhesion occurs with the light-curing materialsand whether identical principles could be applied di-rectly. In the absence of information on newer dentalmaterials, it may be prudent to apply the same condi-tioning unless it is overtly objectionable. Clinical expe-rience has emphasized the desirabihty of subjecting thefreshly prepared cavity to more than washing with wa-ter,̂ This investigation suggested that omitting the con-ditioning resulted in no advantage, at least in reducingmarginal gaps. Hence the clinical significance of thisstudy shotild be to support the inclusion of dentinalconditioning in the restorative procedure.

The results of this study indicated that omission ofdentinal pretreatment with polyacrylic acid did not sig-nificantly reduce the marginal contraction gap forma-tion. The mean marginal gap was actually greater in theuntreated than in the treated group. However, cautionmust be exercised in the interpretation of these results.These results are relevant only to cut surfaces and can-not he directly related to surfaces covered with an or-ganic pelhcle that occurs in cervical abrasion or ero-sion. This study agreed with recent publications onchemically cured materials** that confirmed the remov-al of the smear layer with polyacrylic acid did not im-

prove the dentin-glass-ionomer cement restorativebond.

This study is important because many dentists arefacing decisions regarding the selection of glass-iono-mer cements for restorative procedures. New productscan be marketed aggressively without sufficient dataconcerning their physical properties. This article, basedon the laboratory response of one product, suppliessome information on this new product. However, thisstudy is of limited scope because it is only applicable toone commercially available light-curing glass-ionomercement restorative material; it was the only such mate-rial available at the time the study was conducted. Thefindings should not be extrapolated to other similarmaterials in this category. Further research is war-ranted to study the various materials and conditionersnow available. Carefully controlled clinical trials andlonghudinal studies are also required to evaluate newmaterials comprehensively.

Summary

A laboratory study was conducted to evaluate marginalgaps in light-cured glass-ionomer cement restorationsplaced in preparations with or without dentinal condi-tioning.

1. The light-curing glass-ionomer cement restorativematerial in this study did not always provide a seal atthe margins of dentinal cavity preparations.

2. Measurable gaps were common at the tooth-resto-ration interface, in restorations with or without den-tinal conditioning.

3. Dentinal surfaces conditioned with polyacrylic acidhad a smaller mean marginal gap than did thosewithout conditioning.

4. However, this reduction in marginal gap formationwas not statistically significant.

References1. Wilson AD, Kent BE. A new trattslucent cement for dentistry,

BrDent.l1972;132:133-135,

2. Mount GJ. Adhesion of glass-ionomer in the clitiical etiviron-ment. Opcr Dent 1991 ;16:141-148.

3. Barakat MM, Powers JM, Yamaguchi R. Parameters that affectthe in vitro bonding of glass-ionomer cetrtent liners to dentin.J Dent Res 1988;67:1161-1163,

4. Aboush YEY, Jenkins CBG. An evaluation of the bonding ofglass-iortomer restorations to den title and enatnel, Br Dent J1986;161:175-184.

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5. Berry EA III. von der Lehr WN, Herrin HK. Dentin surfacetreatments for the removal of smear layer; an SEM study. J AmDem Assoc 1987;115;65-66.

6. Powis DR, FollcrasT, Mcrson SA. Wilson AD. Improved adhe-sion of a glass ionomer cement to dentin and enamel. J DtnlRes 1982:61; 1416-1422.

7. Ngo H, Earl A. Mount GJ, Glass-ionomer cements; A 12-month evaluation. J Prosthet Dent 1986:55;203-205.

8. Hewlett ER, Caputo AA. Wrobel DC. Glass-ionomer bondstrength and treatment of dentin with polyacrylic acid. J Pros-lhelDentl991;ñf>;767-772.

9. Wilson AD, Prosser HJ, Powis DM. Mechanism of adhesion ofpolyelectrolyte cements to hydrosyapatitc. J Dent Res1983;62:59O-592,

1Ü. Beech DR. Solomon A, Bernier R. Bond strength of polycar-boxylic acid cetnents to treated dentin. Dent Mater1985;1; 154-157,

11. WhiteGJ, Beech DR, TyasMJ. Dentin stnear layer; An asset ora liability for bonding? Dent Mater 1989:5:379-383.

12. Saltzbi:rg DS, Ceravolo FJ, Holstein F, Groom G, Gottsegen R.Scanning electron microscope study of the junction betweenrestorations and gingival cavosnrface margins. J Prosthet Dem

13. Newman SM, Porter H. Dentin pretreatment effects on denii-nal bonding [abstract 38], J Dent Res 1986:65:174.

14. Joynl RB, Davis EL. Wieczkowski JRG. Yu XY. Dentin bond-ing agents and tbe smear layer. Oper Dent l991;l(i;IK6-iyi.

15. G winnett A l Smear layer: Morphological considerations. OperDent 1984;(siippl3|;3-12.

Ifi. Van Dijken JWV. The effect of cavity pretreatment proceduresan dentin bonding; A four-year clinical evaluation. J ProsthetDent I99O;64:148-152.

17. Bowcn RL. Adhesive bonding of various materials to hardtooth tissues—Solubility of dentinal smear layer in dilute acidbuffers. Int DenI J 1978;2K:97-107. D

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