A clinical, radiographie, and scanning electronmicroscopic evaluation of adhesive restorationson carious dentin in primary teeth

Cecilia C. C. Ribeiro, DDS, MS'/Luiz N. Baratieri, DDS, MS, PhD'VJorge Perâigâo, DMD, MS, PhD""7Naira M. M. Baratieri, DDS, MS, PhD""*/André V. Ritter, DDS***"

Objective: The purpose ot this project was to evaluate the performance of a dentin adhesive system oncarious and noncarious primary dentin in vivo. Method and materials: Fcrty-eight primary molars withcarious iesions were randomly assigned to 2 different treatments: group 1 (control, n = 24)—Ail identifi-able, irreversibiy infected dentin was removed prior to the appiication of the bonding agent and restorativematerial: group 2 (experimental, n = 24)—irreversibiy infected dentin was partiatiy removed prior to the ap-piication of the bonding agent and restorative materiai. The ccntroi and experimental teeth were clinicallymonitored every 3 months and evaiuated 12 months after restoration. The teeth were extracted arcund thetime of extoiiation and processed tor scanning electron microscopy Results: Retention rate, marginal in-tegrity, and pulpal symptoms were identicai in both groups. Radiographicaiiy, the radiolucent area associ-ated with the expérimentai restorations did not increase with time in 75% of the cases. For the controlgroup, the adhesive system formed a hybrid layer in the experimental group, there was morphologic evi-dence ot the formation ot an acid-resistant "altered hybrid layer." An acid-resistant tissue, resulting fromthe interdiffusion of adhesive resin within the area of carious dentin. was observed adjacent to and underthe altered hybrid layer Ct:>nclusion: Application of an adhesive restorative system to irreversibiy infecteddentin did not affect the ciinical performance of the restoration. (Quintessence Int 1999;30:591 -599)

Key words: caries, dentin bonding agent, primary tooth, resin composite

CLINICAL RELEVANCE: In primary teeth containingresidual irreversibiy infected dentin, tbe dentin hybridiza-tion technique may prevent further deterioration ot the at-fected tissues and perform as a clinically acceptableshort-term restorative procedure.

•Assistant Protessor, Department of Pedodontics, Fédérai University ofMarantiao. School of Oeritistry Sao Luis, Maranhäo, Brazil.

" Professor and Chairman, DepartmenI ol Operative Dentistry, Schoolol Dentistry, Federal university ol Santa Catarina, Florianópolis, SantaCatarina. Brazil.

*"• Associate Professor, Department of Operative Dentistry, Sohooi ofDentistry, University of North Carolina at Chapei Hill, Chapel Hill,Norlh Carolina.

" " Professor, Department of Oral Radiology, School of Dentistry, FederalUniversity of Santa Catarina, Fioiianópolis, Santa Catarina. BrazrI.

Atjxiliary Professor, DepartmenI of Operative Dentistry, School ofDentistry, Federal University of Santa Catarina, Fiorianópolis, SaniaCatarina, Brazil; Graduate Student. Department of Operative Dentistryand Dental Research Center, School of Dentistry, University of NorthCarolina at Chapel Hill, Chapel Hdl, North Carolina.

Reprint requests: Dr Jorge Perdiglo. Associate Professor, DepartmenI ofOperative Dentistry, Sohooi of Dentistry, University of North Carolina atChapei Hill, CB #7450 Bratjer H ali. Room 306, Chapel Hill, North Carolina37699-7450. E-mail. jorge_perdigao@ de ntistry.unc.edu

Complete removal of irreversibly infected dentin isof paramotint importance ¡n restorative dentistry.

However, clinical methods available for the identifica-tion of this substrate are empirical (color and hardnessof the dentin) and controversial (caries-detecting solu-tions and dyes). It is frequently assumed that bacteriaoften are left in the preparations and become en-trapped under the restorations.'"'' Clinical, radio-graphic, and bactériologie research has shown thatcarious lesions can be arrested if the margins of therestoration remain sealed.'"''

Research on the interaction of dentirt bondingagents (DBAs) with dentin has focused primarily ontheir in vitro performance, with the assumption thatDBAs behave similarly in vital teeth. Chnical trials onDBAs have reported satisfactory results regardingretention rate, postoperative sensitivity, and preserva-tion of tooth vitality.'""' Ultrastructural observationsof the "hybrid-layer" or "resin-dentin interdiffusionzone" created in vivo are usually performed shortlyafter the materials have been applied to the sub-strate.^"-' For this hybridization technique to be clini-cally acceptable, the interface mtist remain sealed andintact. Additionally, that interface must be able toresist thermal and occiusai stresses that occur in the

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oral cavity. Consequently, it is of great relevance tostudy the hybrid layer after it has heen exposed tointraoral conditions.

The purpose of the present research project was toevaluate-clinically, radiographieally, and microscopi-cally-the performance of a DBA applied to cariousand noncarious primary dentin in vivo. The null hypo-thesis tested in this study was that the application of aDBA on irreversibly-infected dentin would not affectthe clinical performance of the restoration.

METHOD AND MATERIALS

Sample and inclusion criteria

Thirty-eight children (18 boys and 20 girls), with agesranging from 7 to 11 years oid, participated in thisstudy. The ethics committee of the Federal Universityof Santa Catarina, School of Dentistry, approved theuse of human subjects according to the terms presentedin the protocol. The parents or guardians responsiblefor the child were informed of the details of the studyand signed an informed consent form authorizing thechild's participation in the study. Inclusion was basedon fulfillment of the following criteria:

Patient1. In good health2. At least one primary molar with caries3. Available for clinical examination every 3 months

for at least 1 year

Carious tooth1, Vital primary molar due to exfoliate in approxi-

mately 1 year2, Without clinical symptoms of irreversible pulpitis3, Without radiographie signs suggesting pulpal

and/or periapical abnormalities4, Physiologic root résorption process initiated or

expected within 1 year

Lesion1, Involve dentin clinically and radiographicaily2, At least 2 mm wide (faciolingually)3, Located on occlusal or proximo-occlusal surface in

a primary molar4, All margins in enamel5, No pulpal exposure expected during cavity prepa-

ration

Periapical radiographs were taken at baseline toevaluate the extent of the lesion and to check the degreeof physioiogic résorption of the roots, as well as the re-lationship of the primary tooth to its successor, Forly-eight teeth qualified and were selected for the study.

Cavity preparation

After the patient was anesthetized with 1,8 mL of 3%Citancst {ASTRA} and the area was cleaned withpumice and water, the shade of the restorative com-posite was selected. Rubber dam was applied, andthe preparation was initiated. Th¡- .oeth were ran-domly assigned to 1 of 2 clinical procedures (n = 24),The same number of Class I and CLi s II lesionswere assigned to each group (12 for each treatmentgroup).

Group 1 (control). Access to the lesion was ob-tained with a No, 329 carbide bur used at high speedunder copious water cooling, A caries-detectingsolution {Vide Carie, INODOiVI) was used accordingto manufacturer's instructions. All identified irre-versibly infected dentin was removed with a No, 2low-speed round bur. The preparation was consid-ered finished when stained dentin was no longer visi-ble in the cavity.

Group 2 (experimental). Access to the lesion wasobtained as in group 1. All the margins were left inenamel without clinical signs of caries. Carious dentinwas thoroughly removed from the dentinoenamel¡unction, while the carious dentin from the pulpal andaxial walls was only removed superficially with a No,2 round bur running at low speed. Visibly moist andsoft carious infected dentin was intentionally left inthe cavity, except at the dentinoenamel and enamelmargins.

Restorative procedures

Enamel and dentin were conditioned with lC/o maleicacid (Scotchbond Multi-Purpose Etchant, 3M Dental)for 15 seconds and rinsed with air-water spray for 10seconds. The cavity was blot dried and the primer andadhesive of the Scotchbond Multi-Purpose adhesivesystem (3M Dental) were apphed in accordance withmanufacturer's instructions.

All cavities were restored with ZIOO restorativematerial (3M Dental). The composite was applied in 2increments; each increment was iight cured for 40 sec-onds with a Demetron 401 (Demetron/Kerr) curinglight. The intensity of the light, which was monitoredwith a Curing Radiometer (Demetron/ Kerr), re-mained in excess of 450 mW/cml

The restorations were finished and polished withUltradent Carbides (Ultradent Products) and Sof-LexXT disks (3M Dental). Periapical radiographs of therestored teeth were taken at this appointment andapproximately 1 year after the restorations wereplaced.

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Clinical evaluation methods

All restorations were examined by the same operator24 hours, 3, 6, 9 months, and 1 year after theywere placed. The following evaluation criteria wereapplied.

Retention, A modification of fhe criteria introducedby Houpt et aF- was used as follows: Score 0, 1. or 2was assigned when there was no loss of the restora-tion, partial loss of the restoration, or total loss of therestoration, respectively.

Marginal integrity. Marginal adaptation was evalu-ated directly by visual inspection after the restoredteeth eíLfoliated, le, at least 1 year after the restorationshad been placed. The US Public Health Service crite-ria used by Ryge and Snyder ^ were applied, using thefollowing scoring system: An Alfa rating was assignedwhen the margin was undetectable with an explorer;Bravo was assigned when marginal deficiencies werecaught by an explorer going both ways, but therestoration would still he clinically acceptable; andCharlie was assigned when the marginal deficiencieswere clinically unacceptable and demanded replace-ment of the restoration.

Ciinicai findings. A specific patient form was usedto record clinical findings (signs and/or symptoms)suggesting pulpal injury and/or any other problemwith the restoration. Pain or discomfort reported bythe patients or their parents was also recorded on thisform. If a restoration had to be removed, it was con-sidered a failure.

Radiographie evaluation methods

One investigator (NMMB) subjectively comparedthe baseline periapica! radiographs {24 hours afterthe restorations had been placed) with the 1-yearperiapical radiographs, to determine ii there wasprogression of the radiolucent area in the experi-mental group (group 2}. Percentages of the occluso-pulpal or occlusogingival extent of tbe lesions werecalculated on the baseline and 1-year periapicalradiographs.

Scanning eiectron microscopic evaiuation

Forty teeth (20 from each group} were recovered 1year after the restorations were placed. The specimenswere sectioned, processed, and evaluated under scan-ning electron microscope (SEM) (JSM 6300, JEOL),using the methodology described by Perdigao et al. ''Preparation included surface décalcification in 6 N ofhydrochloric acid for 30 seconds, followed by depro-teinization with 2% sodium hypochlorite for 10 min-utes to remove the exposed organic material,^*

RESULTS

Figures 1 and 2 show a representative clinical sequenceof 2 restorations in the experimental group (with resid-ual carious dentin). Figures 3 and 4 show 2 pairs ofperiapical radiographs at baseline and 1-year recall.

Ail restorations were retained at 1 year (retentionscore 0), One tooth from the control group wasexcluded from the study because of pulpal necrosisand fistulization.

For marginal integrity, 95.7% of the restorations inthe control group and lOO.OO/o of the restorations inthe experimental group received the score Alfa. In thecontrol group, 4.5% of the restorations received thescore Bravo.

After 1 year, 11 of 24 restorations of the experimen-tal group (45.8''/o) exhibited regression of the radioiu-cency associated with the restoration. In 6 restorations(25,0%), there was progression of the radiolucent area.In the remaining 7 restorations (29.20/0). the radiolu-cent area remained unchanged.

Under the SEM, in the experimental group, theresidual carious dentin appeared as a dark bandbecause of its low mineral content (Figs 5a and 5b). Inall specimens from the experimental group, a non-tubular or partially tubular dentin was observed (Fig5b), An acid-resistant, "altered hybrid layer" wasobserved within this carious dentin area (Figs 5b to5d). The area underneath the altered hybrid layer,about 400 pm below the resin-dentin interface,showed a conventional hybrid layer with complete im-pregnation of resin into dentin.

For the control group (complete removal of cariousdentin), a typical hybrid layer and resin tag formationwere observed for all the interfaces of the restorations.Figures 6a to 6c show representative images of theseinterfaces.

DiSCUSSION

Research has shown that caries can be arrested undersealed restorations,^"'"-"' which has been confirmedby the present investigation. All restorations in theexperimental group (partial caries removal) wereretained and presented good marginal integrity at the1-year recall. Neither clinical symptoms, such as spon-taneous or elicited sensitivity, nor clinical and radio-graphic signs indicating degeneration of pulp tissuewere present during the 1-year iollow-up period.

The high retention rate observed in this study forboth experimental and control groups is In agreementwith the clinical findings by Van Meerbeek et al,''Using the Scotchbond Multi-Purpose system, theyfound 98% retention in cervical noncarious lesions

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Fig la Case 1. Preoperative view of tooth Fig 1b Le:. i.-i ..-M-i i.juai anesthesia and Fig 1c Appearance after partiai removal of75 (K), which has an extensive carious iesion. piacemeni ol rubber Jam. carious dentin with a No. 2 round bur used

at lew speed.

Fig I d Appiicalion of primer and adhe- Fig Ie Resin composite appiied in incre- Fig I f Restoration after finishing with car-s'^6' ments and iight cured. bide finishing burs and aluminum oxide

disiis.

Fig Ig Restoration at the 1-year recali. Fig Ih Extracted tooth, sectioned in two and processed for SEMobservation.

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Fig 2a Case 2 Preoperalive view ot Tooth 65 (J), winjch Fig 2b Etchiiiig ot -.tie substrate with 10% maieic acid afterhas a carious iesion in Itie occiusai aspect parliai rernovai ot canouE lissue.

Fig 2c Apoiication ot 1 coat oí primer and appiioation ot Fig 2d immediafeiy postoperstive appearance ot theadliesive in a uniform layer. restoration.

Fig 2e Restoration at the 1-year recaii. Fig 2f Extracted tootti, sectioned in two and processed for SEMobservation.

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Fig 3a Baseline bitewing radiograph showing a restoration onthe occiusai aspect of tooth 65 (J¡ in the experimental group (withresiduai carious dentin). (Arrow) Radiolucency.

Fig 3b Bitewing radiograph 17 months after the piacement. Thesize of the radioluoenoy (arrow) has not increased over time.

Fig 4a Basei.ne bitewing rad'ograph of another restoration(mesio-occiusaij on tooth 65 (J) in the experimental group {withresiduai carious dentin)

Fig 4b Bitewing radiograph 11 months after piacement. Thelesion IS smaliei than it was at baseiine.

Fig 5a General SEM view of a restoration in the experimentalgroup. This tooth is the same shown in clinical case 2 (Figs 2ato 2e). (A) Adhesive; (D) denlin: (E) enamei; (P) pulp chamber;(Z) restoration. 'Areas of carious dentin hybridised by Ihe adhe-sive system.

Fig 5b Cioser view of the field within the egg-shaped area in Fig5a. An extensive altered tiybrid iayer (') connects the resin-dentininterface to the conventionai hybrid iayer (arrowheads). This weil-defined conventionai hybrid iayer ensures the transition to itie zoneot unaffected dentin ¡D). Zone of resin-infilirated, partially lubularcarious dentin (long arrows). (A¡ Adhesive; (Z) restoration

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Fig 5c Closer view of field shown within Ihe small circle in Fig 5band within the egg-shaped area in Fig 5a, Zone of resln-infiiirated,partially tubular carious dentin (long arrows). (H) Conventionai hy-brid layer, 'Altered nybrid layer.

Fig 5d Closer view of field confined by the circle in Fig 5bA well-defined conventional hybnd layer ¡H) is making the transi-tion to unaffected dentin |D), (T) Resin tags. 'Area of hybndizedoarious dentin.

Fig 6a Restoration from the control grojp (without residual cari-ous dentin], (A) Adhesive; (D] dentin; (E) enamel, (P) pulp cham-ber; (Z) restoration

Fig 6b Resin-dantin interface, showing the adhesive (A¡. thehybrid layer (H], and resin tags (T), Dentin (D) is visible in thebackground

Fig 6e Resin-dentin interface of the axial wall, showing resintags (T] running parallel to ttie interface, Circies enclose thespherical partióles of Z100. (A) Adhesive; (D) dentih: (H) conven-tional hybrid layer, (Z) restoration.

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with enamel margins and 96% retention for the le-sions without enamel margins after 3 years. In spite ofthis high retention rate, Van Meerbeek et al" reportedmarginal staining in 10% of the restorations after 1year, which increased to 30% after 3 years. The mar-ginal staining was associated with minor defects onthe enamel margins, which may have been a result oftreating tbe enamel with maleic acid. This weak or-ganic acid may not result in the same etching patternachieved with the regular 37.5% phosphoric acid etch-ing agent.

The lC'/o maleic acid conditioner was used in thepresent clinical investigation because it was marketedin the Scotcbbond Multi-Purpose kit at the time theproject was initiated. Although one investigation re-ported that sealant retention rate may not be affectedwith the use of either 10% maleic acid or 'M.5''''D phos-phoric acid,-^ other studies have reported lowerenamei bond strengths when enamel was etched witblOOo maleic acid.-"-' Because 37.5% phosphoric acid isconsidered more effective than 10% maleic acid, it canbe assumed that the use of the former would not haveimpaired the results of this investigation.

Radiographie evaluation of intentionally sealed car-ious lesions showed that the size of the radioiucencyassociated with some of the experimental sealedrestorations diminished affer 1 year."'"' ' Mertz-Fairhurst et al,' using direct measurement, reported a19-|jm mean regression in lesion depth 1 year aftercarious lesions had been sealed. These data, added tothe results of the present investigation, show that it ispossible to arrest carious lesions without complete re-moval of all compromised dentin. One possible expla-nation for this fact is the remineralization of the inner,nondeteriorated dentin layer described by Fusayamaet al. ' Another explanation may be the bactericidal ef-fects of acid etching and of the adhesive monomersused in bonding.

For the experimental group, the altered hybrid layerwas determined to be acid resistant, because it wassubmitted to the hydrochioric acid and sodiumhypochlorite challenge without dissolving. The hybridlayer has been considered the major bonding mecha-nism for the new generation of adhesive systems.' -'-'By forming both a conventional and an altered hybridlayer, the bonds might have been very reliable in tbeexperimental group. The area underneath the alteredhybrid layer showed a conventional hybrid iayer withcomplete impregnation of resin into dentin. The for-mation of a conventional hybrid layer 400 jim belowthe resin-dentin interface may have occurred becausemaleic acid is a low-viscosity etchant, able to pene-trate within the residual carious dentin and reach un-affected dentin. This etched, unaffected dentin wasthen hybridized by the application of fhe primer and

adhesive, suggesting that the progression of fhe cari-ous lesion was arrested in the experimental group.

For the control group, the SEM observationsshowed that tbe bybrid layer and tag formation oc-curred as described in other in vitro studies and insbort-term clinical studies, " '' ^

in vitro bond strength studies comparing sound andcarious dentin have shown bighcr values for normaldentin.^"-" However, in the present investigation, thepresence of carious dentin under the adhesive restora-tions did not impair the clinical performance of fherestorations after 1 year. It should he noted, however,that the cavosurface margin was located in enamel,which is known to result in a better seal than dentinmargins.''•^•'

CONCLUSION

This study failed to reject the null hypothesisadvanced. The application of an adhesive restorativesystem on irreversibly infected dentin did not affectthe clinical performance of the restoration:

1. Class I and Class II posterior resin compositerestorations in primary molars had a 100% reten-tion rate after 1 year, regardless of the complete-ness of the removal of carious tissue from fhe pul-pal and axial walls.

2. The marginai integrity (observed after the teethwere extracted) was clinically acceptable in ailgroups,

3. The residual carious tissue under the restorationsdid not elicit clinically detectable pulpal alter-ations.

4. The radiographie observations revealed that45.8% of the scaled carious lesions underwent anincrease in radiopacity, while 29.2% remainedstable.

5. After 1 year of clinical use, the specimens pro-cessed for SEM presented hybrid layer formationand resin tag penetration comparahie to tboseobserved in short-term studies,

6. The application of the Scolchbond Multi-Purposeadbesive system on carious dentin resulted in an al-tered hybrid layer that was without any signs ofdemineralization that could suggest progression ofthe lesion.

ACKNOWLEDGMENTS

We Ihaiik Ms M. Manuela Lopes, al the University of North CarolinaElectron Mii;roseopy Laboratory, for helpful assistance with proc:e6s-ing the SEM negatives.

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