Restorative Dentistry

Adhesion of a compomer to dental structures

P, F. Abate. DDS^S, M. Bertacchini, DDS*/M, A. Polack, DDS*/R, L. Macchi. DDS,

Abstract The objeclive of tin's stndy was to evalúale the bond sireiiglh ofa compomer lodental enamel, dentin. and cenientiim. Flat surfaces afilíese tlssiie.i were obtainedJrom recently exmicted human leelli. The differenl substrates were either treatedwilh PSA (a primer and adhesive) or acid etched (35% phosphoric add gel) andtreated with PSA. Cylindrical specimens of compomer were then bonded to thesubstrates. Shear bond strength was determined afier a 24-hour immersion in37°C water Significant differences were found between both treatments on enamel,while none were found on denlin or cementum. The use of acid etchani on enamelas a surface-conditioning step previous to priming with PSA allowed a better bondbetween Dyract compomer and that subslrate: acid etching wa.s not particularlyneeded on dentin and cemennim. (Quintessence Int 1997:28:509-512.)

Clinical relevance

Acid etching of enamel could be a usefiil clinicalstep to enhance adhesion when a compomer (Dy-ract) is used as a restorative material.

Introduction

The adhesion of materials to dental structure is arelevant issue in dentistry. The constant and rapidintroduction of new adhesive agents constitutes aproblem for the evaluation and clinical selection ofaspecific product.

The adhesion of restorative materials to enamel withthe use of the acid-etching technique is widelyaccepted by the profession and has become a routinewithin modern dentistry,' This statement cannot beapplied to the interaction of materials to dentin androot cementum. mainly because of the variable andcomplex histologie structures of these tissues.

* Department of Denial Materials. School of Dentislr>: University orBuenos Airei. Buenos Aires, Argenlina.

Reprint requeslb; Dr P. F, Abate. Depürtment of Dental Materials, Schooiof Dentistry. University of Buenos Aires, M, T. de Aivcar 2142, BuenosAires C, P. 1123. Argentina,This slüdy was supported by LIniversity of Buenos Aires Grant 0D021

The development of glass-ionomer cements byWtlson and Kent- in 1969 was impoaant in this area;for the first time, a material with lasting adhesion todental structure was available,^ Glass-ionomer mate-rials adhere to enamel and dentin.•* release fluoride,'-*and prevent secondarj' caries.' New-generation glass-ionomer cements have even better properties: Theycan be light cured because resiti technology is includedin their formulation,^ As a result of the presence ofresins, acid etching of enamel could increase the valuesof adhesion,^

Currently, different products possess these com-binations of characteristics; with the development ofthe so-called compomers. distinction among all mate-rials has become rather conftjsing,̂

On the other hand. Fusayama et al'" demonstratedan improvement in the values of adhesion of restorativeresins to dentin when the dentinal surface waspreviously subjected to acid conditioning. Over theyears, this technique has become known as totaletching because all tooth surfaces arc acid treated.

The mechanical testing of adhesion provides know-ledge, although incomplete, about the adhesive reac-tion of an adhesive material to tooth structure. Evenwhen the most commonly mentioned property of abonding system is its adhesive strength to dentin,' it isstill interesting to know the adhesive possibihties todifferent substrates that new products, such as thecompomers, offer.

Quintessence International Volume 28, Number 8/1997 509

Table I Shear bond strengths (MPa) under thedifferent experimental conditions

Substrate

EnamelDentinCementum

A

Mean (SD)

14.1 (1.9)13.0 (2.9)15.5 (4.0)

B

Mean (SD)

26.1 (4.0)10.7 (2.0)12.5(2.1)

1

(A vsB)

7.64 <1,87 ;1.53 ;

P

Í .001>.O5O>.O5O

A = PSA Primer/Ad ties iveB = Acid condilioning ptus PSA Primer/Atlhesjv

Fig 1 Mean shear bond strengths (MPa) of a compomer tovarious substrates.

Cementum

A; PSA Pmner/AdheaiveB: Acid conditioning + PSA Primer/Adhesive

Compomers need the treatment ofthe tooth surfacewith a solution to condition it and produce adhesion.This might represent the use of a so-called one-stepadhesive.

The objective of this research was to evaluate theadhesive bond strength of a compomer to dentalenamel, dentin. and cementum under different circum-stances.

Method and materials

A compomer product (Dyract, Dentsply) was used.Recently extracted human teeth that had been kept indistilled water after decontamination with chlorinesolutions were selected for the experitnent. Sixteenmaxillar>' incisors with rather flat buccal surfaces wereused to obtain enamel specimens and 16 third molarswere used for dentin. Flat dentina! surfaces wereobtained by grinding the molars, under water, 2 mmbeyond the dentinoenamel junction. Sixteen molarswith relatively smooth-surfaced roots were selected fortesting adhesion to root cementum. Enamel stirfacesand dentin specimens were then finished with abrasivepaper (0, 00, and 000 grit) under water. The cementumsurfaces were cleaned with a brush and flour ofpumice.

All of the specimens were mounted in self-curingresin, and their surfaces were treated as follows:

1. In group A, PSA (Primer and adhesive, Dentsply)was applied according to the manufacturer's in-

structions. The specimens were cleaned with flourof pumice on a brush used at low speed. The PSAwas applied for 30 seconds and rubbed for 10seconds. A second layer of PSA was then appliedfor 30 seconds and rubbed for 10 seconds.

2. In group B, a phosphoric acid gel (3M Dental) wasapplied for 20 seconds, rinsed, and dried before thePSA was applied as in the other group.

Following these treatments, cylindrical 4. l-inm-diameter specimens of cotnpomer (A3 shade) wereattached to the surfaces. The paste that is provided bythe matiufacturer was injected within a translucentmold using a Centrix-type syringe, and the materialwas light activated for 90 seconds with an appropriatedevice (Visilux II. 3M Dental).

After the specimens had been subjected to 24 hoursof immersion in 37°C distilled water, the shear bondstrength between the compomer and the tooth surfaceswas determined with a universal testing machine(Instron) with a crosshead speed of I mni/min. A f-test was used to statistically analyze differences betweenthe results obtained on each surface in the two groups.

Results

Mean bond strengths are shown in Table 1 and Fig 1.The only significant difference between the two groupswas found for the enamel surfaces. The highest bondstrengths were found on enamel that had beenpreviously acid conditioned. They were significantly

510 Quintessence International Volume 28, Number S/1997

Abate et al

higher ( P < .00] ) than were those obtained with justthe use ofthe PSA.

No statistically significant ditierences were foundwhen bond strengths of dentin and root cementumwere analyzed. The mean values were slightly lowerwhen acid conditioning was used.

Discussion

Dyract is a material that has some characteristics ofresin composites and some of glass-ionomer cements.It is handled similarly to composites, but it can beconsidered neither a composite nor a glass-ionomermaterial. Some of these new products have beendescribed as "fiuoride-releasing resins" or "polyacid-modit'icd composites."-'" We believe that this is themost appropriate designation for Dyract because inprevious research'- it was shown that this materialdoes not harden in the absence of light curing. It is.therefore, a material that contains certain componentsofthe glass-ionomer cements but not in the levels thatare needed to promote the acid base setting reaction'that identifies a cement.

The components of the primer/adhesive that isprovided with the product (PSA) are similar to thoseof current adhesive systems for resin composites. Inaddition, the manufacturer of Dyract has developed anadhesive system for resin composites ( Prime and Bond2.0) that has only minor differences with the PSAsystem. Even when they are single-component systems,two separate steps have to be followed for their use.

If an adequate clinical performance is proved, thesesimplified adhesive systems will allow a simplificationof restorative procedures. One of the aims of thedevelopment of compomers was to provide a materialwith enough bond strength to tooth structure withoutthe need for previous acid treatment of the surface.However, the manufacturer suggests acid etching as anoptional step in the instructions that are included withthe product.

The principle behind the use of PSA was probablyto obtain good adhesive behavior with a singleconditioning substance (trying to imitate the proce-dures in the use of restorative glass-ionomer cements).Basically PSA includes three monomers: one that ishydrophilic (phosphonated penta-acrylate ester) andtwo that are hydrophobic (triethylene glycol dimeth-acrylate and an elastomeric resin).

Phosphonated penta-acrylate ester (patented byDentsply and also included in some other of its

products) would be responsible for the bonding tocalcium in tooth structures.

It is worth mentioning that Dyract is intended to bea self-adhesive material because it includes a monomerfor its organic phase that has COOH groups I tetracar-boxylbutane acid). Again this would be a way topromote in Dyract the adhesive behavior of glass-ionomer materials.

The elastomeric resin could have heen included tocreate an elastic adhesive area that would act as a bufferto withstand the stresses that could be induced in theinterface.

Completing the composition, the PSA has anorganic solvent (acetone) that could enhance thewetting of the surfaces by the adhesive and theinfiltration ofthe resin within the dentin. The so-calledhybrid layer would thus be efficiently obtained, as it iswith most modern composite adhesive systems.

A photoinitiator is also included to allow rapidpolymerization when light activation is carried out.

The manufacturer suggests as an optional step theuse of acid treatment before the placement ofthe PSAand Dyract; the results obtained showed significantdifferences when enamel was the dental surface understudy. These results coincide with those obtained byCortes et al̂ in a similar study. This would mean thatthe well-known conditions that are created on enamelby the acid are also beneficial for the adhesion ofthecompomer material.

Similar results were not found on dentin or rootcementum. It seems that the effect of the PSA inaddition to the availability of COOH groups in theDyract monomers are enough to ensure adequate bondstrengths without the need for previous acid con-ditioning of these surfaces.

Conclusion

The use of phosphoric acid to condition enamel beforethe use ofthe PSA adhesive is to be recommendedbecause it promotes a higher bond strength of Dyractto enamel. Similar treatment is not needed in the caseof dentin and root cementum.

References

1. Swift EJ, Perdigao J.Heymann HO, Bonding to enamel and dentin:A brief story and state of tlie art. 1995. Quintesíence lnl 1995;26i95-IIO.

2. Wilson AD. Kenl BE. The glass-ionomer cement, a new translucentcemenl for deniisiry. J Appl Chem Biineclinol 1971;2I ;3I.3.

Quintessence International Volume 28, Number 8/1997 511

Abate et al

3, McLean JW, Nicholson JW, Wilson AD, Proposed nomenclature Torglass-ionomers dental cements leditoriall. Quintessence tnt 1994:25:587-589.

4. Powis DR, FollerasT, Merson SA, Wilson AD. Improved adhesionof a glass ionomer cement to dentin and enamel. J Dent ResI982:61:i4l6-I422,

5. DeSchepper EJ, Berry UA, Callletau JG.Tate Wll, f-luoride releasefrom light-cured liners. Am J Dent 1990:3:97- 100.

6. Swift EJ, Bailey SJ. Hansen SE. Fluoride release from fast settingglass ionomer restorative materials. Am J Dent 1990:3:101-104.

7, Arcoria CJ, Fisher MA. Wagner MJ, Microleakage in alloy-glassionomer lined amalgam restorations after thermocycling. J OralRehabil 1991:18:9-14,

8, Cortes O, Garcia-Godoy K Boj JR, Bond strength of resin-reinforced glass ionomer cemenis after enamel elching. Am J Dent1993;6:299-3Ü1,

MA, Fortin D. Depth of cure ofDent Mater 1995:11:196-200,

9. Swift EJ. Pawlus MA, Vairesin-modified glass ionomi

10. Fusayama T, Nakamura M, Kurosaki N, Iwaku M, Non-pressureadhesion of a new adhesive restorative resin. J Dent Res 1979:58:1364-1370.

11. Burgess J, Norimg B, Summit J, Resin ionomer restorative matc-rials-The new generation. In: Hunt P (ed). Glass Ionomers: TheNext Generation, Proceedings of the 2iid Imernational SymposiumofGlass Ionomers, Philadelphia: International Symposia in Deniist-ry. 1994:75-86.

12. Abate PF Polack MA, Macchi RL. Barcoll hardness of resin-modified glass ionomers and compomers. Quintessence Int 1997;28:345-348, Ö

512

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