Lasers in Surgery and Medicine 36:351–355 (2005)

Tensile Bond Strength of a Flowable Composite Resin toEr:YAG-Laser-Treated Dentin

Juliana Donadio-Moura, MSD,1 Sheila Gouw-Soares, PhD,2 Patricia M. de Freitas, MSD,3

Ricardo S. Navarro, MSD,4 Lynn G. Powell, PhD,5 and Carlos de P. Eduardo, PhD6*

1School of Dentistry, University of Sao Paulo (USP), Sao Paulo, SP 05508-900, Brazil2Institute of Energetic and Nuclear Research (IPEN), Sao Paulo, SP 05508-900, Brazil3Department of Restorative Dentistry, School of Dentistry, University of Sao Paulo (USP), Sao Paulo, SP 05508-900,Brazil4Department of Orthodontics and Pediatric Dentistry, School of Dentistry, University of Sao Paulo (USP), Sao Paulo,SP 05508-900, Brazil5School of Medicine, University of Utah, Salt Lake City 84132-2801 Utah6Department of Restorative Dentistry, School of Dentistry, University of Sao Paulo (USP), Sao Paulo, SP 05508-900,Brazil

Background and Objectives: This in vitro studyevaluated the influence of a flowable composite resin(FCR) on the tensile bond strength of resin to dentintreated with the Er:YAG Laser (L) and diamond bur (DB).Study Design/Materials and Methods: Ninety dentinsurfaces obtained from 45 third molars were ground andrandomly divided into six groups (n¼ 15): G1–DB, G2–DBþFCR, G3–L (100 mJ, 10 Hz, 37.04 J/cm2), G4–L(100 mJ, 10 Hz, 37.04 J/cm2)þFCR, G5–L (250 mJ, 2 Hz,92.60 J/cm2), andG6–L (250mJ, 2Hz, 92.60 J/cm2)þFCR.After surface etching with 37% phosphoric acid and theapplication of an adhesive system, inverted conical speci-mens were prepared with a hybrid composite resin. Ingroups G2, G4, and G6 a FCR was placed before the hybridcomposite resin. After 24 hours-storage in distilled water,the tensile test was performed in a universal testingmachine (0.5 mm/minute, 500 N).Results: Data were submitted to Kruskal Wallis test(P¼ 0.01). The mean bond strength values (MPa�SD)were: G1–13.54 (�2.99), G2–14.67 (�2.32), G3–9.49(�3.09), G4–14.60 (�2.76), G5–8.97 (�3.89), and G6–13.02 (�2.18). Groups G1 and G2 presented the highestbond strength values, which were statistically similar tothose of G4 and G6. The groups treated with laser andwithout theFCR (G3 andG5) showed the lowest shear bondstrength values.Conclusions: FCR can increase the adhesion to dentintreated with Er:YAG laser within different parameters.Lasers Surg. Med. 36:351–355, 2005.� 2005 Wiley-Liss, Inc.

Key words: adhesion; dentin; Er:YAG laser; flowableresin; tensile bond strength

INTRODUCTION

During the last few years, the demand for estheticprocedures and for preserving healthy tooth structure,has lead to the development and improvement of adhesive

materials that can fulfill their function of bonding toenamel and dentin. These procedures were originallydeveloped to act on the tooth substrate prepared byconventional techniques. However, new investigationspoint to alternative tools that could better prepare thedentin surface for future bonding procedures. Among theseinnovations for dentin surface treatment, the use of lasershas been widely disseminated.

Described as a safe and effective tool for the removal ofdental hard tissues [1], Er:YAG laser works at a wave-length of 2.94 mm,which coincideswith the absorption peakof water and hydroxiapatite [1–3] and can ablate theenamel anddentin effectively. Somestudieshavepointed tothe feasibility of using anEr:YAG laser in conjunction witha water spray to remove hard dental tissues without com-promising the laser cutting efficiency. With a fine watermist, the temperature can be suppressed and the irradia-tion can be performed with no damage to the pulp [4–7].

The cavities prepared with Er:YAG laser do not presenta smooth surface; their surfaces have opened dentinaltubules without smear layer production and microscopi-cally rough surfaces [2,8,9]. These dentin characteristicsare expected to favor resin bonding, so that most of thesecavities are filled with adhesive materials.

Juliana Donadio-Moura is a Trainee at the Special Laboratoryof Lasers in Dentistry; Sheila Gouw-Soares, an AssistantProfessor of the Professional Master Course of Lasers inDentistry; Patricia M. de Freitas and Ricardo S. Navarro, arethe Graduate Student (PhD); Lynn G. Powell, a Professor,Assistant Dean for Dental Education; and Carlos de P. Eduardo,a Full-time Professor.

Contract grant sponsor: FAPESP; Contract grant number: 97/10823-0; Contract grant sponsor: IVOCLAR/VIVADENT (Brazil).

*Correspondence to: Dr. Carlos de P. Eduardo, PhD, Departa-mento de Dentistica/Faculdade de Odontologia de Sao Paulo–USPAv. Prof. Lineu Prestes, 2227 Cidade Universitaria, Butanta SaoPaulo, SP 05508-900, Brazil. E-mail: cpeduard@usp.br

Accepted 10 February 2005Published online 11 April 2005 in Wiley InterScience(www.interscience.wiley.com).DOI 10.1002/lsm.20176

� 2005 Wiley-Liss, Inc.

Some in vitro studies reported that bond strength toEr:YAG-laser-treated dentin is lower than that of dentinthat had not been laser treated [10–13]. In order to achievegreater bonding results, some authors have evaluated theuse of different surface treatments and irradiation para-meters [11–13].Recently, a new class of low-viscosity resin composites,

called flowable composites, was introduced in the marketand these are widely used by professionals. Some of theircharacteristics are: low viscosity [14], low elasticitymodulus [14–16], and easy application [17]. Despite itsability to reduce dentinal cervical sensitivity [18], this newadhesive material has been reported to provide betteradaptation to dentin [15,17]. At present, little is knownabout the use of low-viscosity composite resin to increasethe adhesion of hybrid composite resin to laser-treateddentin [13,19]. It is expected that this restorative materialassociated to an adequate adhesive system [13], can show asuperior adaptation to the irregularities of the laser treateddentin.This study aimed to determine whether the use of a

flowable composite resin (FCR) on dentin treated withEr:YAG laser affects the tensile bond strength betweendentin and composite resin.

MATERIALS AND METHODS

Specimen Preparation

This study protocol was reviewed and approved by theEthical Committee of the University of Sao Paulo. Forty-five recently extracted third molar teeth were cleaned andstored in distilledwater (378C�1) up to the beginning of theexperiment (1 month). The crowns were removed approxi-mately to the cementoenamel junction and were long-itudinally sectioned with a double-faced diamond disk (KGSorensen, Baruevi, SP, Brazil) used in a low-speed micro-tome (LABC UT 1010/Extec Enfield, CT, USA). Twosamples were obtained from each tooth. Samples withstains or cracks, observed under a stereomicroscope used at30� (Meiji Techno EMZ series, Saitoma, Japan), were dis-carded. Ninety crowns were embedded individually in aself-curing polyester resin (Uceflex UC 2120, RedeleaseProdutos, Brazil) in a polypropylene ring mould 2.0 cm indiameter, so that the external surface of the crown (enamelfrom the buccal or lingual surfaces) was exposed, and thenleft to polymerize.

Preparation of the Dentin Surfaceand Laser Irradiation

After the polyester resin polymerization, the sampleswere ground in a water-cooled polishing machine (PolitrizEcomet 3/Buehler) with 120, 240, and 400-grit siliconcarbide paper (Struers Company, Ballerup, Denmark) toremove the overlying enamel and to provide uniformsuperficial dentin surfaces. After that, the dentin surfaceof each sample was polished with a 600-grit silicon carbidepaper and immediately washed with an ultrasonic systemin order to remove the smear layer.The dentin specimens were randomly assigned to six

groups (n¼ 15), as shown in Table 1. The samples fromG1 and G2 were not submitted to laser irradiation andwere considered as positive and negative controls, respec-tively. A round diamond bur (DB) (#1012, KG Sorensen) ina high-speed drill, under air-water spray, was used toprepare the dentin surface of the samples from groups G1and G2.The samples from the experimental groups G3, G4, G5,

and G6 were then irradiated with the Er:YAG laser (KeyLaser II, KaVo, Biberach, Germany) emitting photons at awavelength of 2.94 mm. The output power and repetitionrate of this equipment range from 60 to 500 mJ and 1 to15 Hz, respectively. The beam diameter at the focal areafor the handpiece #2051 (non contact) was 0.63 mm. Thehandpiece #2051 was positioned 12 mm from the dentinsurface. The samples were irradiated with the energydepicted in the equipment display and corresponded to theenergy delivered from the handpiece. The energy densityused for the laser irradiation on groups G3/G4 and G5/G6was 37.04 J/cm2 and 92.60 J/cm2, respectively. The hand-piece was positioned perpendicular to the dentin surfaceand the samples were irradiated scanning once in eachdirection, horizontally and vertically, in order to promotehomogeneous irradiation and to cover the entire samplearea. The irradiation was performed with a water-cooledspray (5.0 ml/minute).

Bonding Procedures

In order to demarcate the dentin bonding area, a piece ofinsulating tape with a 2-mm diameter central hole wasattached to the specimen surface. After the surfacetreatment, the samples were submitted to the bondingprocedures. The materials with their compositions, speci-

TABLE 1. Experimental Groups

Experimental groups

Groups Laser de Er:YAG DB PA Primerþ bond Flowable composite

G1 — þ þ þ �G2 — þ þ þ þG3 100 mJ, 10 Hz � þ þ �G4 100 mJ, 10 Hz � þ þ þG5 250 mJ, 2 Hz � þ þ �G6 250 mJ, 2 Hz � þ þ þDB, diamond bur at high speed drill; PA, 37% phosphoric acid.

352 DONADIO-MOURA ET AL.

fications, and manufacturers are listed in Table 2. Thebonding and restorative procedures strictly followed themanufacturer’s instructions. Prior to the use of a bondingagent, the dentin was etched with 37% phosphoric acid(Total Etch1, IVOCLAR-VIVADENT, Schaan, Liechten-stein) for 10 seconds. After that, the surface was rinsed for15 seconds and gently air dried for 5 seconds. The bondingsystem used was the excite system (IVOCLAR-VIVA-DENT), according to the manufacturer instructions.Immediately after the use of a bonding agent, a thin layer

of the tested FCR (Tetric Flow/IVOCLAR-VIVADENT)wasplaced onto the dentin disks from groups G2, G4, and G6with disposable brush tips and light cured for 20 seconds.

Tensile Bond Strength

After the bonding procedures, all samples (G1–G6) wereindividually fixed in a metallic clamping device, keepingthe dentin surface parallel to a flat base. A split bisectedpolytetrafluoro-ethylene jig was positioned on the samplesurface, thus providing an inverted conical cavity with thesmaller diameter coinciding with the delimited 2-mmdiameter bonding site. A hybrid light-cured compositeresin (Tetric Ceram/IVOCLAR-VIVADENT) was insertedinto the jig in three increments (1.5 mm thick), eachpolymerized for 40 seconds. As the cavity was filled, thesample was removed from the metallic device, leaving aninverted cone with 4-mm diameter tapering to a 2-mmdiameter and 4.5 mm high adhering to the delimited area.After 24hours storage indistilledwaterat 378C, the cone-

shaped samples were submitted to the tensile bondstrength evaluation, using a universal testing machine(Mini Instron 4442), running at a cross-head speed of0.5 mm/minute and a 500 N load cell until fracture.

RESULTS

Statistical analysis was made by a parametric methodusing the one-way analysis of variance (ANOVA) andKruskal–Wallis test (a¼ 1%). Mean tensile bond strengthsand standard deviations are shown in Table 3. Meansvaried in a range from 8.97 to 14.67 MPa.The one-way ANOVA revealed statistically significant

difference in tensile bond strengthwithin the experimentalgroups. The Kruskal–Wallis test showed that there was nostatistically significant difference between the non-irra-diated groups (G1 and G2) and the laser-treated dentinrestored with a FCR (G4 and G6). The lowest TBS values

were obtained with dentin irradiated with the Er:YAGlaser,without theuse of aFCR (groupsG3andG5withTBSof 9.49 and 8.97 MPa, respectively).

DISCUSSION

The results of the present study suggest that the use ofa FCR can increase the adhesion of a hybrid compositeresin to dentin treated with Er:YAG laser within differentparameters.

Flowable composite were created by retaining thesame small particle size of traditional hybrid composites,but reducing the filler content and allowing the increasedresin to reduce the viscosity of the mixture [15,16]. Theflowability of low-viscosity composite resins is achievedmainly by increasing the proportion of monomer in thecomposite formulation [16]. These characteristics areexpected to reduce the shrinkage stress generated duringthe placement of a composite restoration andmay preservethe integrity of the adhesive interface [20]. However, theapplication of a lightly filled resin at the margin of arestoration may lead to increased wear of this region andcan compromise the quality of the bonding margins [20].Clinically, FCRs are expected to be applied to all the cavitywalls, excluding the cavity margins. In the present study,the FCR was applied to the dentin surface in order topromote a thin layer capable of reducing stress shrinkage.

Considering the decrease in the filler content, FCRsare claimed to increase adhesion to dentin, since itsmonomer content can better integrate to the one presentin the adhesive system and result in a more homogeneouslayer with demineralized dentin tubules penetrated by theadhesive materials.

TABLE 2. Restorative Systems Used and Their Compositions, Specifications, and Manufacturers

Material Composition Manufacturer

Adhesive system, excite Phosphonic acid, HEMA, dimethacrylates, alcohol IVOCLAR VIVADENT

Flowable composite, tetric flow BIS-GMA, triethylene glycoldimethacrylate,

urethandimethacrylate

IVOCLAR VIVADENT

Hybrid composite resin, tetric ceram Monomer matrix: Bis-GMA, urethane dimethacrylate,

triethylene glycol dimethacrylate (20.2% weight);

inorganic fillers: barium glass, ytterbium trifluoride,

Ba-Al-fluorosilicate glass, and silicon dioxide,

spheroid mixed oxide (79.0% weight)

IVOCLAR VIVADENT

TABLE 3. Tensile Bond Strength Data (Means�SD

in MPa) of the Dentin Submitted to Different

Restorative Treatments

Groups Treatment TBS

G1 DB 13.54� 2.99 a

G2 DBþFC 14.67� 2.32 a

G3 L (100 mJ/10 Hz) 9.49� 3.09 b

G4 L (100 mJ/10 Hz)þFC 14.60� 2.76 a

G5 L (250 mJ/2 Hz) 8.97� 3.89 b

G6 L (250 mJ/2 Hz)þFC 13.02� 2.18 a

Same letters indicate statistical similarity (P¼ 0.01).

TENSILE BOND STRENGTH OF A FLOWABLE COMPOSITE RESIN 353

The infiltration of the resin into the surrounding de-mineralized dentin is important for achieving a favorableresin bonding, since it attaches to and integrates with theresin tags [21]. This may possibly justify the findings ofthe present study. When using the FCR (G2, G4, and G6),the tensile bond strength was higher than that of the othergroups, except for G1. The result of groupG1was expected,because dentin preparation with DB leads to the formationof a smear layer that can be removed by surface etching[22]. After the acid etching, both the intertubular andperitubular dentin can be demineralized and contribute tothe interdiffusion of the adhesive system. Therefore, theuse of aFCR on cavities preparedwithDBwas not shown toenhance bonding quality.Er:YAG laser presents a great interaction with the hard

dental tissues and is able to produce a dentin surfacewithout smear layer, with a microretentive pattern,revealing tubule openings [1,2,19]. This characteristic issupposed to improve the bond strength of resins to dentin[19,23]. However, some studies have reported the increaseof tooth acid resistance after the laser treatment. Conse-quently, the collagen matrix may not be totally exposed bythe 37% phosphoric acid, mainly in the peritubular region[12], and adhesion to composite resin can be compromisedby the lack of resin infiltration into the demineralizeddentin [21].The laser-treated dentin with the flowable composite

(G4andG6) presented thehighest bond strength, similar tothe results obtained with the control groups (G1 and G2).The finding that the combination of laser and flowablecomposite were equal to the DB suggests that flowablecomposite seems to be the help for achieving high bondstrength values of resin to irradiated dentin. Although,Er:YAG laser can increase dentin acid resistance andcreate a dentin surface without peritubular dentin demi-neralization [13], the use of a FCR seems to revert theseadverse effects by better adapting to the irregularities ofthe laser treated dentin surface due to its flowability.Furthermore, in the present study the decrease in the

energy applied and the increase of the repetition rate (G4)was shown to present similar tensile bond strength valuescompared to the group with higher energy (G6), with theadvantage of decreasing the possibility of temperaturedamage to the pulp when using water cooling. An in vitrostudy conducted by Glockner et al. (1998) [4] revealed notemperature increase when using laser with water cooling,while the use of a high-speed handpiece can lead to tem-perature rises of over 608C. Gouw-Soares et al. (2001) [24]showed temperature increases of less than 38C in cavitypreparations with energy density of 108.28 J/cm2 andconcluded that these parameters are safe and effective forclinical application. Therefore, the dentin treatment withthe energy densities evaluated in the present study can beconsidered a safe and effective alternative for cavitypreparation.Despite the possibility of ablating dental hard tissue

and increasing the adhesion of composite resin to dentinwithout damage to the pulpal tissue [19], another impor-tant characteristic of laser treatment is its antimicrobial

property [25–27]. Even if there is no difference between theirradiated and non-irradiated dentin with respect to itsbond strength, the cavities prepared with the laser deviceare expected to undergo microbial reduction in the infecteddentin.Even when the current effectiveness of the convention-

ally prepareddentinwithDBs is acknowledged, the conceptof laser-treated dentin is promising and deserves increas-ing attention in the future. Further studies should beconducted in order to elucidate the interaction of differentrestorativematerialswith laser-treateddentinandbring tolight a new pattern of interaction for bonding to Er:YAGirradiated dentin.

ACKNOWLEDGMENTS

The authors thank the Special Laboratory of Lasers inDentistry (LELO) and the International CooperationCommittee (CCInt) of the University of Sao Paulo (Brazil).This studywas suported byFAPESP(Grant no. 97/10823-0)and by IVOCLAR/VIVADENT (Brazil) who supplied thematerials investigated free of charge.

REFERENCES

1. Hibst R, Keller U. Experimental studies of the application ofEr:YAG laser on dental hard substances: I. Light microscopicand SEM investigations. Lasers Surg Med 1989;9:338–344.

2. Keller U, Hibst R. Experimental studies of the application ofEr:YAG laser on dental hard substances: II. Light miscro-scopic and SEM investigations. Lasers Surg Med 1989;9:345–351.

3. Paghdiwala AF, Vaidyanathan M, Paghdiwala MF. Evalua-tion of Erbium:YAG laser radiation of hard dental tissues:Analysis of temperature changes, depth of cuts and struc-tural effects. Scann Microscop 1993;7:989–997.

4. Glockner K, Rumpler J, Ebeleseder K, Stadtler P. Intrapulpaltemperature during preparation with the Er:YAG lasercompared to the conventional bur: An in vitro study. J ClinLaser Med Surg 1998;16:153–157.

5. Takamori K. A histopathological and immunohistochemicalstudy of dental pulp and pulpal nerve fibers in rats after thecavity preparation using Er:YAG laser. J Endod 2000;6:95–99.

6. Jayawardena JA, Kato J, Loriya K, Takagi Y. Pulpalresponse to exposure with Er:YAG laser. Oral Med OralSurg Oral Pathol 2001;91:222–229.

7. Nair PNR, Baltensperger MM, Luder HU, Eyrich GKH.Pulpal response to Er:YAG laser drilling of dentin in healthyhuman third molars. Lasers Surg Med 2003;32:203–209.

8. Aoki A, Ishikawa I, Yamada T, Otsuki M, Watanabe H,Tagami J, Ando Y, Yamamoto H. Comparison betweenEr:YAG laser and conventional technique for root cariestreatment in vitro. J Dent Res 1998;77:1704–1714.

9. Burnnet LH, Conceicao EM, Pelino JEP, Eduardo CP.Comparative study of influence on tensile bond strength ofa composite to dentin using Er:YAG laser, air abrasion, or airturbine for preparation of cavities. J Clin Laser Med Surg2001;19:199–202.

10. Kataumi M, Nakajima M, Yamada T, Tagami J. Tensile bondstrength and SEM evaluation of Er:YAG laser irradiateddentin using dentin adhesive. Dent Mat J 1998;17:125–138.

11. Eguro T, Maeda T, Otsuki M, Nishimura Y, Katsuumi I,Tanaka H. Adhesion of Er:YAG laser-irradiated dentin andcomposite resins: Application of various treatments onirradiated surface. Lasers Surg Med 2002;30:267–272.

12. Ramos RP, Chinelatti MA, Chimello DT, Borsatto MC,Pecora JD, Palma-Dibb RG. Bonding of self-etching and

354 DONADIO-MOURA ET AL.

total-etch systems to Er:YAG laser-irradiated dentin. Tensilebond strength and scanning electron microscopy. Braz Dent J2004;15:SI9–SI20.

13. Souza AE, Corona SAM, Palma-Dibb RG, Borsatto MC,Pecora JD. Influence of Er:YAG laser on tensile bondstrength of a self-etching system and a flowable resin indifferent dentin depths. J Dent 2004;32:269–275.

14. Prager MC. Using flowable composites in direct posteriorrestorations. Dent Today 1997;16:62–69.

15. Bayne SC, Thompson JY, Swift EJ, Jr., Stamatiades P,Wilkerson M. A characterization of first generation flowablecomposites. J Am Dent Assoc 1998;129:567–577.

16. Labella R, Lambrechts P, Van Meerbeek B, Vanherle G.Polymerization shrinkage and elasticity of flowable compo-sites and filled adhesives. Dent Mat 1999;15:128–137.

17. Murchison DF, Charlton DG, Moore WS. Comparative radio-pacity of flowable resin composites. Quintessence Int 1999;30:179–184.

18. Stafan D, Schulman A, Calamia J. Clinical effectiveness of aclass V flowable composite resin system. Comp Cont EducDent 1999;20:16.

19. Goncalves M, Corona SAM, Borsatto MC, Silva PCG, PecoraJD. Tensile bond strength of dentin-resinous system inter-faces conditioned with Er:YAG laser irradiation. J Clin LaserSurg Med 2002;20:89–93.

20. Choi KK, Condon JR, Ferracane JL. The effects of adhesivethickness on polymerization contraction stress of composite.J Dent Res 2000;79:812–817.

21. Nakabayashi N, Kojima K, Masuhara E. The promotion ofadhesion by the infiltration of monomers into tooth sub-strates. J Biomed Mater Res 1982;16:265–273.

22. Sano H, et al. Tensile properties of mineralized and deminera-lized human and bovine dentin. J Dent Res 1994;73:1205–1211.

23. Visuri SR, Gilbert JL, Wright DD, Wigdor HA, Walsh JT.Shear strength of composite bonded to Er:YAG laser-prepared dentin. J Dent Res 1996;74:599–605.

24. Gouw-Soares S, Pelino JEP, Haypek P, Bachmann L,Eduardo CP. Temperature rise in cavities prepared in vitroby Er:YAG Laser. J Oral Laser Appl 2001;1:119–123.

25. Mehl A, Folwaczny M, Haffner C, Hickel R. Bactericidaleffects of 2.94 microns Er:YAG-laser irradiation in dentalroot canals. J Endod 1999;25:490–493.

26. Schoop U, Moritz A, Kluger W, Patruta S, Goharkhay K,SperrW,Wernisch J, Gattringer R,Mrass P, Georgopoulos A.The Er:YAG laser in endodontics: Results of an in vitro study.Lasers Surg Med 2002;30:360–364.

27. Perin FM, Franca SC, Silva-Souza YT, Alfredo E, Saquy PC,Estrela C, Souza-Neto MD. Evaluation of Er:YAG laserirradiation versus 1% sodium hypochlorite irrigation for rootcanal disinfection. Aust Endod J 2004;30:20–22.

TENSILE BOND STRENGTH OF A FLOWABLE COMPOSITE RESIN 355