Dental Research

Comparison of the effect of insertion techniques of a resin compositeon dentinal adaptation of two visible light-cured bases: Directevaluation versus a replica techniqueTezer Ulusu*/Nurban Tulunoglu

Abstract This scanning electron microscopic study evaiuated the adaptation of two visiblelight-cured bases. Calclmol LC and lonoseal, to the denlinal surface after the useof various techniques to insert the resin eomposite material. Twenr\--eight Class Icavities were prepared and restored in four groups: seven Calcimol LC and resincomposite plaeed with a bulk or an Incremental technique: and ¡onoseal and resincomposite placed with a bulk or an incremental technique. The specimens weresectioned longitudinally through the center ofthe restoration and an impressionwas made with apoly(viny! siloxane) impression material. When the tooth surfacesand the impressions tnadefrom these surfaces wei-e compared in the scanning electronmicroscope, extra gaps on tooth surfaces were observed that were not apparent in theimpressions. These extra gaps probably resulted from desiccation oftissue.<i: thus,the observation of replicas was useful to eliminate the inclusion of false" gaps inthe analysis. The results indicated that there tvas no substantial differencebetween Calcimol LC and ¡onoseal base materials placed under resin compositeinserted wiih an incremental technique. (Quintessence lnt !996;27.63-6S.)

Clinical relevance

These results show that the use of an hicrementaltechnique with visible light-cured calcium hydroxideadapted better to dentin of primary teeth. In theseSEM studies of gap formation between two materials,the combination of direct examination with replicatechnique will give more accurate resuits than willdirect examination alone.

Introduction

Restorations often require au intermediary base oflining material to alleviate postoperative hypersen-sitivit>' and to provide protection ofthe pulp.' How-

* Professor. Department of Ped odontic s. Gazi University. Faculty ofDentistry. Ankara, Turkey.

•" Assistant Professor. Department of Pedodontics. Gazi University.Faculty ofDentistry. Ankara. Turkey.

Reprint requests: Dr Nurhan Oztac, Gazi Universitesi, Di^hekimligiFakültesi, Pedodonti Anabilim Dali. Fmek-Ankara, Turkiye 06510.

ever, the properties of each specific lining materialconfer advantages and disadvantages.-

Both calcium hydroxide and glass-ionomer cementhave become lining materials of choice: calciumhydroxide because of its ease of handling and itsexcellent pulpal response, and giass-ionomer cementbecause of its ability to adhere to tooth structure, itspotential to be etched and reliably bonded, and itsapparent ability to reduce postoperative sensitivitywhen used as a base under posterior resin com-posites.^"''

Prisma visible light-cured (VLC) Dycal has beenshown to have significant improvements in severalphysical properties.''•' This material consists of adispersion of calcium hydroxide and barium sulfate ina urethane d i met h aery I ate resin and is activated byvisible light. Several advantages attend this formula-tion,''-^ not tlie ieast of which is its chemical bond withresin restorative materials.'"

Research and development efforts for glass-ionomercements are curreutly directed toward eliminating thedisadvantages of working and seUing tie by incorporat-ing light-curing technology, while preserving tbe

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Uiusj et al

Table I Restorative treatments for 28 Class 1 cavity preparations

No. ofteeth

7

7

7

7

Base

Calcimol LC

Calcimol LC

lonoseal

Ionoseal

Etching time

60 s (enamel)

60 s (enamel)

60 s (enamel)20 s (glass-ionomer base)

60 s (enamel)20 s (glass-ionomer base)

Restoration

Clearfil(incremental technique)

Clearfil(bulk technique)

Clearfil(incremental technique)

Clearfil(bulk technique)

important benefits of fluoride release and dentinalbonding.'

As filled polymers, light-cured lining materials mayundergo volumetric change during polymerization.Such dimensional changes have been reported to havean effect on the adaptation of resin and its relationshipwith the tissue to which it is applied.'"

Recent studies have shown that gaps of different sizeand number may occur between VLC lining materialsand tissue. The size and number of the gaps depend onthe type of restoration, the technique of placement,and the methods of sectioning and examination.•'"

The method used in the present study was developedby Gwinnett.'-'" who reported that poly(vinyl siloxane)impression materials can accurately reproduce therelationship between restoration and tissue.

The purpose of this study was to examine theadaptation ofa visible light-cured calcium hydroxide(Calcimol LC, VOCO) and a resin-modified (visiblelight-cured) glass-ionomer cement (Ionoseal. VOCO)to dentinal surfaces prepared with high-speed dia-mond burs and the effects of various resin compositeinsertion techniques in vitro. The study was alsodesigned to determine whether gaps observed withVEC calcium hydroxide and VEC glass-ionomercement were real or artifacts of the impressiontechnique.

Method and materials

A total of 28 Class I cavities were prepared on theocciusal surtace of freshly extracted maxillary andmandibular primary molars. The cavities were cut witha No. 56 tungsten carbide bur in a high-speed turbineand with abundant air-water spray. All cavities were

prepared by the same operator to a depth of 0.5 mmbelow the dentinoenamel junction. The teeth wererestored as described in Table 1.

Tlie placement of Calcimol LC was carried out bythe same operator for 14 teeth. When Calcimol LC wasplaced on the pulpal floor, it tended to form a meniscuscurve and leave an apparent deficieny on the pulpalfloor, as reported by McConnell et al.'' Therefore, asecond layer of Calcimol LC was placed. Each layerwas cured for 20 seconds, according to the manufactu-rer's directions. The cavosurface enamel was thenetched. An etching gel containing 37% phosphoricacid was applied for 60 seconds. This was followed by30-second washing and 30-second dr>'ing processes.

Ionoseal was placed by the same operator in anothergroup of 14 cavities and was cured for 20 seconds. Thecavosurface enamel was etched with the same acid gelfor 60 seconds. However, the Ionosea! material wasonly etched for 20 seconds and then washed for 30seconds and dried for 30 seconds.

The dentinal bonding material wab applied with asable hairbrush, as recommended by the manufacturer,and the excess material was removed with an airsyringe. The resin composite restorative material(Clearfil, Kuraray) was placed either in bulk (oneincrement) or in a two-occlusal incremental technique.Each increment was cured for 20 seconds. All specimenswere embedded in acrylic resin.

The specimens were stored in 37°C distilled waterfor 24 hours. Following the storage period, thespecimens were sectioned longitudinally through thecenter of the restoration with a diamond blade(Isomet, Beuhler). Tlie specimens were treated for 10seconds with 31% phosphoric acid to remove the

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Ulusu et al

Fig 1 The impressions accurately reproduced the rela-tionship between the liner and the dentin. In the same areas,continuous gaps on the impressions (A) and tooth surface(B) are noticeable between the liner and the dentinal floor otthe preparation.

Fig 2 The meniscus eftect is lessened (arrows) becausetwo coats of VLC Calcimol have been placed on the pulpalfloor

smear layer that resulted from the sectioning pro-cedure. They were thoroughly rinsed with water for 20seconds and were dried carefully with air spray.

Impressions, for which the teeth were dried briefiyto minimize desiccation, were taken one at a time.Permagum (ESPE) light-bodied poly(vinyl siioxane)impression material was mixed and applied to the cuttooth surface. A flat toothpick was used to tamp thefluid material into the region of the restoration.

After it had set, the impression was removed,trimmed, and mounted on an aluminum stub. Both theimpressions and the sectioned tooth surface were driedwith high-vacuum SEM until no moisture remained.Completion was indicated by a larnp. which turned offwhen the drying procedure was completed sufficiently.AH the specimens were coated with gold-palladiumand examined with a scanning electron microscope(SEM) (Jeoi JSM 5400). The SEM observations wererecorded on film.

Results

The relationship between liner and dentin was accu-rately reproduced by the impression material (Fig I ).When gaps were present, the material penetrated intothem to produce a thin fiash or wall, characterizing thesite, width, and extent of the gaps.

When two coats ofVLC Calcimoi were piaced onthe pulpal fioor, the material tended to pool intointernal line angles. As the width of the lining material

at the central region increased, the meniscus effect wasreduced (Fig 2).

In the group in which Calcimol LC was used andthe restorative material was placed with an incrementaltechnique, both the sectioned tooth surface andimpressions revealed good adaptation between thetooth and calcium hydroxide at the cavity fioor (Figs3a and 3b). In some areas, discontinuous gaps in therange of 5 p.m wide were observed on tooth surfacesand impressions. Both showed areas along the axialwall with a few discontinuous gaps (of less than 5 pm).

In the group in which Calcimol LC was used andthe restorative resin material was placed with a bulktechnique, tooth surfaces and impressions revealedseveral continuous or discontinuous gaps approx-imately 5 to 10 |im wide at the cavity fioor (Fig 4).Also, several discontinuous gaps of less than 5 imwere tioted on the axial walls.

In the group in which lonoseal was used and therestorative material was placed with an incrementaltechnique, tooth section surfaces and impressions bothshowed a good adaptation of the liner at the cavityfloor and lateral wails of the preparations (Figs 5a and5b). A few discontinuous gaps of less than 5 [imweteobserved only at the axial walls of the preparations(Figs 6a and 6b).

In the group in which lonoseal was used under therestorative resin placed with a bulk technique, someimpressions revealed a good adaptation at the cavityfloor and discontinuous gaps (approximately 5 ¡am

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UlüSu et ai

Fig 3a The adaptation between VLC Caicimoi and the Fig 3b impression of the same area,dentinal floor of the preparation.

Fig 4 A gap is evident between the cavity fiocr and VLCCaicimoi (leit). impression of the same area inght).

Fig 5a No gap formation is evident between the axiai waiiand lonoseal.

Fig 5b On ttie repiicated suriace, adaptation of lonosealto the dentinal surface is shown to be good in the samearea.

wide), while some tooth surfaces revealed fracturelines along the cavity floor and continuous gaps ofmore than 10 |im wide (Figs 7a and 7b).

In all groups, the observation of some tooth sectionsrevealed fracture lines lying along the proximal wallsand the floor of the cavity. The impression surfaces ofthese tooth sections did not reveal these fracture lines(Figs 8a and 8b). In addition, fewer gaps wereapparent on the impression surfaces than on the toothsurfaces.

Discussion

The results of this study indicated that the most reliableadaptation of the resin composite restoration to thecavity walls was obtained when the resin was incre-mentally inserted and resin-modiñed glass-ionomer

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et al

Fig 6a A smali, discominuous gap (arrow) is presentbetween the axial wall and lonoseal. Fig 6b in Ihe impression, a small, discontinuous gap

(arrow) is evident between ionoseal and the axial wail in thesame area.

Fig 7a A contradion gap ot greater than 10 j,tm is present Fig 7b Impression of the same area,between lonoseal and the denlinal floor ot the preparation.

An extra gap is present on the tooth surface (arrow)but does not exist in the impression ot that surface (Fig 8b),

Fig 8b The second gap is not evident in the impression.

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Ulusu et al

cement or VLC calcium hydroxide was used as basematerial. Tiie insertion technique of the restorativematerial appears to have a direct influence on thedentinal adaptation of VLC lining material.'•"'-

These materials are placed on the cavity floor as aresin base, allowing them to make a chemical bondwith the overlying resin composite restorative mate-¡gl .i.s.9.1.1.14 ^j^y polymerization shrinkage occurring

in this overlying restorative material could puil thelining material off" the cavity floor and wails."" It hasbeen shown that the maximal shrinkage occurs whenthe bulk insertion technique is used. The results of thisstudy supported the suggestion that resin compositesshould be piaced with an incremental technique.

McConneli et al'' reported that VLC calciumhydroxide lining material tends to form a meniscuscurve and leave an apparent deficiency on the pulpallloor. resulting in a thin central film of liner on thefloor ofthe preparation. They suggested placement ofa second layer of liner if a deficiency occurs, but didnot indicate the number of specimens used in theirstudy. On the other hand, a tight junction betweenVLC calcium hydroxide and dentin can be obtained iftwo coats are applied as recommended by Gwinnett etal,"' Therefore, in the present study, a second layer ofVLC calcium hydroxide was placed in all of thespecimens.

McConneli et al also compared different basematerials with diiferent restorative materials and tech-niques. Tliey used poly(vinyl siioxane) impressions toobserve the adaptation of only a glass-ionomer cementto tooth. Their observations ofthe other groups (VLCDycal ) were made directly on the tooth surfaces. Theyreported that they observed good adaptation in thespecimens in which resin composite was placed on theglass-ionomer cement base, regardless of whether thebulk or incrementai technique was used. When VLCDycal was used as liner, they observed 10 p,m-widegaps. The authors emphasized that their resultsrequired confirmation."*

Gwinnett et al'" reported that gaps probably arecreated as a result of tissue desiccation and theaccompanying volumetric change occurs in the prep-aration of tissue specimens for scanning electronmicroscopy. In the present study, both tooth surfacesand poly(vinyl siloxane ) impression material surfaceswere observed in SEM. The resuits were found to be inagreement with the findings of Gwinnett et al.'"

In some tooth sections, the observed gaps weresignificant; however, the impressions made from thesame tooth sections revealed no gaps. This findingdemonstrates the usefulness of the impression tech-nique in eliminating false conclusions generated by theshrinkage that results from tissue desiccation.

Summary

This present study revealed no substantial differencesin dentinal adaptation between calcium hydroxide orglass-ionomer cement base materials when resin com-posite was placed over them in an incrementaltechnique. Gaps may be exaggerated when the toothsurface is evaiuated directly by SEM; the replicatechnique seems to give more accurate resuits.

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9. Straffon LH, Corpron RL, Bruner FW. Daprai F. Twenlyfour-month clinical trial of visible light-activated cavity liner in youngpermanent teeth. J Dent Child 1991 ;S8:124-128.

10. Gwinnett AJ. The adaptation of visible light cured calcium hydrox-ide liner to dentin. Quintessence lnt I988;I9:111-115.

11. Coli P, Brännström M. The marginal adaptation of four differentbonding agents in Class II composite resin restorations applied inbulk or in two increments. Quintessence lnt 1993;24:5S3-59I.

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13. Mitra SB. Adhesion to dentin and physical properties of a light-Cured glüss-ionomer liner/base. J Dent Res l99O;7O;72-74.

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