Influence of Er:YAG laser irradiation distance on the bond strength of a restorative system to enamel

Transcription

1 Journal of Dentistry (2006) 34, Influence of Er:YAG laser irradiation distance on the bond strength of a restorative system to enamel Daniela Thomazatti Chimello-Sousa*, Aline Evangelista de Souza, Michelle Alexandra Chinelatti, Jesus Djalma Pécora, Regina Guenka Palma-Dibb, Silmara Aparecida Milori Corona Faculdade de Odontologia de Ribeirão Preto/USP, Departamento de Odontologia Restauradora, Av. do Café, S/N Monte Alegre, Cep: , Ribeirão Preto-SP, Brazil Received 10 February 2005; received in revised form 18 June 2005; accepted 21 June 2005 KEYWORDS Er: YAG laser; Irradiation distance; Adhesion; Enamel Summary Objectives: The aim of the present study was to investigate in vitro the effect of Er:YAG laser on bonding to enamel, varying the irradiation distance. Method: Tensile bond strength of an adhesive restorative system to non-irradiated and irradiated enamel surfaces was evaluated. Thirty caries-free human third molars were sectioned in mesio-distal direction and embedded in acrylic resin. Enamel was flattened, and a 3-mm-diameter bonding area was demarcated. Specimens were randomly assigned into six groups: groups I V were treated with the Er:YAG laser (80 mj/2 Hz), varying the irradiation distance (11, 12 mm-focused, 14, 16 and 17 mm, respectively), followed by 35% phosphoric acid etching. Control group (VI) received treatment with phosphoric acid alone. Single Bond adhesive system was applied on the conditioned enamel, and composite resin cones, bonded to enamel, were fabricated with Z250. After storage, samples were tested in tensile to failure (50 kgf and 0.5 mm/min). Results: Means in MPa were: I-9.67 (G3.44); II (G2.65); III (G2.22); IV (G3.58); V (G4.52); VI (G3.03). ANOVA and Tukey test revealed statistically significant decrease of bond strength in group I (P!0.05). Groups II IV presented similar results, as did groups IV and V. Control group (VI) yielded the best overall performance (P!0.05). Conclusion: Er:YAG laser irradiation adversely affected adhesion to enamel. However, bond strength was influenced by the irradiation distance, thus being stronger with the increase of distance to the target tissue. Q 2005 Elsevier Ltd. All rights reserved. * Corresponding author. Tel.: C ; fax: C address: dtchimello@yahoo.com.br (D.T. Chimello- Sousa). Introduction The treatment of dental substrate prior to adhesive /$ - see front matter Q 2005 Elsevier Ltd. All rights reserved. doi: /j.jdent

2 246 restorative procedures is an extremely important step of the bonding protocol and accounts for the clinical success of restorations. Great improvement has been achieved after introduction of phosphoric acid etching of enamel, 1 which increased adhesion substantially. Phosphoric acid acts on enamel by selectively dissolving the hydroxyapatite of the prisms, thereby facilitating penetration of the bonding agents and tag formation. 2,3 Nevertheless, a disadvantage attributed to acid conditioning is that demineralisation of enamel surface makes it more permeable and prone to long-term acid attack and caries, especially if the demineralised substrate is not completely filled by resin monomers. 2 In order to overcome this limitation, studies 2,4 have investigated alternative procedures for treatment of enamel surface, such as the erbium:yttrium aluminum garnet (Er:YAG) laser irradiation. The ability of Er:YAG laser to effectively ablate dental hard tissues is ascribed to its 2.94 mm wavelength emission, which is coincident with the main absorption band of water (w3.0 mm) and OH K groups in hydroxyapatite (w2.8 mm). 2,4,5 The incident radiation is highly absorbed by water molecules in the dental hard structures, 6 8 causing sudden heating and water evaporation. The resulting high-stream pressure leads to the occurrence of successive microexplosions with ejection of tissue particles, 6,9,10 which are characteristic of the ablation process and determine the microcraterlike appearance of lased surfaces. 4 The ablation of tooth structure is achieved, via a thermomechanical interaction 6 and, since the tissue is not completely vaporised, but only disintegrated into fragments, the majority of incident radiation is consumed in the ablation process, leaving very little residual energy for adverse thermal interactions with the pulp tissue and surrounding soft and/or hard structures. 11 The microscopical appearance of lased enamel surfaces depicted the non-selective removal of substrate, which presents with fusion areas of variable extension, and anfractuous pattern. 4,12,14,15 The scarcity, or even the absence of smear layer on the irradiated surfaces constitutes another microscopical finding, becoming possible the visualisation of enamel rods. 4,16,17 Smear layer removal and surface roughening might be favourable factors to monomer infiltration into the substrate, thereby facilitating the adhesion process. 2 On the other hand, some studies 2,12,18,19 have described laser-ablated surfaces as acid-resistant, by the formation of more stable and less soluble compounds. The reduction of solubility could be explained by the alteration of ultra-structure and composition of the substrate due to heating, which might be an adverse factor to the action of acid etching. However, the effect of Er:YAG laser on the target tissues relays on various parameters, including the irradiation distance (the distance between the beam output and the substrate), emission mode, irradiation length, energy, pulse repetition rate (frequency), tissue water content and air/water spray cooling Regarding the Er:YAG laser settings advised for dental treatment, the laser irradiation distance is an important parameter, for being directly related to the laser ablation ability and surface morphology. 9,21,25 Thus, depending on the established irradiation distance, the incident energy on dental surface increases the ablation depth or amplifies the irradiated site. 25,26 In fact, the dispersion of the energy occurs when the active tip is far-off the substrate, causing a little amplification of the spot size (diameter of the beam) and consequently higher is the irradiated area, decreasing the performance of the laser on the tissue. 25 Aoki et al., 26 verified that this dispersion did not cause damage to the adjacent structures of irradiated areas, when low parameter settings of energy and pulse repetition rate were employed. Although some researches 7,27 29 have proved the effectiveness of Er:YAG laser irradiation on the surface treatment of dental enamel, as compared to the traditional acid conditioning, controversial results have been shown, 2,15,30 due probably to the diversity of parameters and methodologies utilised. 9 The described irradiation distances ranged from contact mode to 17 mm working distance, on focused and/or defocused modes. However, there are no reported studies comparing different irradiation distances, with respect to their effect on the adhesion of resin systems to enamel surface. Therefore, the aim of the present work was to investigate in vitro the influence of Er:YAG laser, applied at different irradiation distances, on bond strength of an aesthetic restorative system to enamel. The null hypothesis tested was that there is no difference in the bonding to non-lased and lased enamel, and that the working distance does not influence the adhesion to this substrate. Materials and methods D.T. Chimello-Sousa et al. Thirty caries-free human third molars, extracted within a 6-month period and stored in 0.9% saline solution at 4 8C, were cleaned with scaler and

3 Er:YAG laser irradiation distance on enamel bond strength 247 water/pumice slurry in dental prophylactic cups. Each tooth was examined under a 20! stereomicroscope (Nikon Inc., Instrument Group, Melville, NY 11747, USA) to discard those with structural defects. Roots were sectioned 2 mm below the cementoenamel junction and crowns were bisected longitudinally in a mesiodistal direction with a water-cooled diamond saw (Minitom, Struers A/S, Copenhagen, DK-2610, Denmark), thus providing 60 halves. Pulpal remains were removed and the surfaces were identified to avoid that both buccal and lingual halves of the same tooth were assigned to the same experimental group. Halves were individually embedded in acrylic resin (JET, Clássico, São Paulo, SP, , Brazil) using PVC rings (2 cm diameter 1 cm high) as molds. After resin polymerisation, the rings were removed and the tooth/ resin blocks were ground in a water-cooled polishing machine (Politriz DP-9U2, Struers A/S, Copenhagen, DK-2610, Denmark) with #400- and #600-grit silicon carbide (SiC) papers (Buehler Ltd, Lake Bluff, Il , USA) to obtain a flat enamel surface, sufficient to the adhesion site delimitation. To demarcate the bonding site, a piece of insulating tape with a 3-mm-diameter central hole, made by means of a modified Ainsworth rubber-dam punch (Duflex S.S. White Artigos Dentários Ltd, Rio de Janeiro, RJ , Brazil), was attached to the specimen surface. This procedure had double aim: to define a fixed test surface, and to ensure that the resin composite cone would be precisely adhered to the treated enamel surface. The 60 specimens were randomly assigned to six groups of equal size (nz10), according to the surface treatment: Er:YAG laser irradiation at distances of 11 mm (Group I), 12 mm (Group II), 14 mm (Group III), 16 mm (Group IV) and 17 mm (Group V), followed by 35% phosphoric acid conditioning (Etching gel, 3M ESPE, St Paul, MN 55144, USA); control group (VI), treated with 35% phosphoric acid solely. The experimental groups are detailed in Table 1. Since it has been demonstrated 15 that application of laser only, i.e. without further acid etching, yielded markedly low bond strength to enamel, groups irradiated with Er:YAG laser alone was not included in our study. The Er:YAG laser device used was the Kavo Key Laser 2 model (Kavo Dental GmbH & Co. KG, Bismarckring 39, Biberach, 88396, Germany), emitting at 2.94 mm wavelength. The parameter settings used were: 80 mj of energy and 2 Hz of pulse repetition rate, providing a J/cm 2 of energy density (fluence) for all the specimens. The laser beam was delivered on non-contact mode, with a fine water mist at 5 ml/min, for 20 s. Laser beam spot size was 0.63 mm and the 2051 handpiece with a removable tip attached to a flexible fibre delivery system was used. The irradiation distance was standardized by using a custom designed apparatus consisting of two parts: a holder to fix the laser handpiece in such a way that the laser beam was delivered perpendicular to the specimen surface, at a constant working distance from the target site; and a semi-adjustable base, on which the plexglass w plate with the fragment attached to it was firmly fixed with wax. Two operators manipulated the apparatus micrometer screws, in such a way that the semi-adjustable base was alternately moved in both right-to-left and forward-to-back directions, thus allowing the laser beam to provide an accurate ablation of the entire enamel site. The irradiation distance was checked with a ruler every sample. For the tested restorative system, the bonding protocol was followed according to manufacturer s instructions. Phosphoric acid was applied for 15 s, followed by rinsing and excess water removal with absorbing paper. Two consecutive coats of Single Bond adhesive system (3M ESPE, St Paul, MN 55144, USA), an ethanol-and-waterbased total-etch single-bottle bonding agent, was applied with disposable tips (Microbrush Corporation, Orlando, FL 32837, USA); the remaining solvent was evaporated with a brief, mild airblast, and the adhesive was light-cured with a Table 1 Enamel bond strength means (MPa) and standard deviations in each experimental group Group Treatment Mean (MPa) I Er:YAG laser (11 mm) C35% phosphoric acid 9.67 (G3.44) d II Er:YAG laser (12 mm) C35% phosphoric acid (G2.65) c III Er:YAG laser (14 mm) C35% phosphoric acid (G2.22) c IV Er:YAG laser (16 mm) C35% phosphoric acid (G3.58) b,c V Er:YAG laser (17 mm) C35% phosphoric acid (G 4.52) b VI 35% Phosphoric acid (control) (G3.03) a The same superscript letters indicate statistical similarity (PO0.05).

4 248 D.T. Chimello-Sousa et al. Fig. 1 Specimen schematic illustration and bond strength testing. (A) Inverted resin composite cone adhered to the delimited dentin site; (B) Apparatus used for tensile bond testing. visible light-curing unit (XL 3000, 3M ESPE, St Paul, MN 55144, USA), with a light output not less than 450 mw/cm 2, for 10 s. After the bonding protocol was completed, specimens were individually fixed in a metallic clamping device (developed at the Houston Biomaterials Research Centre and manufactured at the Precision Workshop at Ribeirão Preto School of Dentistry of University of São Paulo, Brazil), keeping enamel surface parallel to a flat base. A split bisected polytetrafluoroethylene jig was positioned on the tooth/resin block surface, thus providing an inverted conical cavity with the smaller diameter coincident with the demarcated 3-mm-diameter bonding site. A hybrid composite resin (Z250, 3M ESPE, St Paul, MN 55144, USA) was inserted into the jig in three increments, each polymerised for 40 s. The resin increments provided enough material to saturate the treated-surfaces. As the matrix cavity was filled, the specimen was removed from the clamping device and the matrix was opened, leaving adhered to the demarcated enamel surface an inverted resin composite cone with a 6 mm diameter tapering to a 3 mm diameter and 4 mm high. After 24-h storage in distilled water at 37 8C, the cone-shaped composite/acrylic resin block was placed into an apparatus with an internal taper, corresponding to the resin cones shape. This configuration was loaded in tension, using a universal testing machine (Mod. MEM 2000, EMIC Ltda, São José dos Pinhais, PR , Brazil), at a crosshead speed of 0.5 mm/min and a 50 kgf load cell until fracture. A schematic illustration of the specimen and details about the bond test apparatus are presented in Fig. 1. Bond strengths were recorded in kgf and converted into MPa. Means and standard deviations were calculated, and data were analysed by ANOVA, with surface treatment as independent variable. Multiple comparisons were done using Tukey test at 0.05 significance level. Fractured specimens were observed with a 40! stereomicroscope (Nikon Inc. Instrument Group, Melville, NY 11747, USA) to assess the failure modes, which were classified as adhesive, cohesive or mixed. Adhesive failure was considered the one at the specimen/adhesive interface; cohesive failure if occurred in the material or the substrate, with no damage to the interface, and mixed failure was the one involving at the same time the interface and the material or the substrate. Results Means and standard deviations of the bond strength data are presented in Table 1. One-way analysis of variance showed statistically significant difference (P!0.01) between the highest and the lowest values. Multiple comparisons of the data revealed that the control group had the highest bond strength mean (P!0.05). The 11-mm irradiation distance showed the lowest bond strength mean (P!0.05). Bond strength means recorded in the 12, 14 and 16- mm groups were statistically similar among them (PO0.05). Likewise, statistically significant difference was not observed between the 16 and 17-mm groups (PO0.05).

5 Er:YAG laser irradiation distance on enamel bond strength 249 The analysis of the bonding sites after tensile strength test revealed that, for the Er:YAG-lased fractured specimens, a mixed-failure mode (simultaneously cohesive of the material and adhesive) was predominantly observed. Cohesive failures (of the material or the substrate) were recorded in 40% of specimens in the 11 and 12-mm groups, 20% in the 14 and 17-mm groups, 30% in the 16-mm group and 60% of specimens in the control group (Fig. 2). Discussion Fig. 2 Failure types (%). The outcomes of the present research seem to corroborate the assumption that the Er:YAG laser irradiation, regardless of the working distance, affects adversely the bonding to enamel. Our results disclosed that the application of Er: YAG laser at the tested irradiation distances, before phosphoric acid, etching did not yield the same bonding ability as that provided by acid conditioning alone, which was the most effective enamel surface treatment for the tested restorative system. Similar results were reported in other studies, 2,4,15 in which the working distances for the Erbium laser were described as contact mode and association of defocused and focused modes, and the bond strength of different adhesive systems to laser-treated enamel was tested to failure in tensile and microtensile. A possible explanation for the lower bond strength observed in the Er:YAG laser-irradiated groups is that the heating generated by laser irradiation increases the resistance of dental enamel to demineralisation by acids. 11,31,32,33 In this respect, it has been reported that some chemical alterations occur in enamel due to the crystals liquefaction. 5,31,34 During the quick dental tissue cooling there is an increase of the hydroxyapatite crystals, 34 which present with reduction of carbonate content, 18 and formation of pyrophosphate 12,18 and metaphosphate, 12,19 which have been described as more stable and less soluble components, thus reducing dental susceptibility to acid attack. 2,11 In addition, studies 17,18,34,35 demonstrated that Er:YAG laser irradiation obliterates enamel micropores, thus blocking the intra and interprismatic spaces, restricting resin interdiffusion into the enamel surface. Therefore, it seems feasible to speculate that phosphoric acid conditioning after laser irradiation would be insufficient to effectively remove the laser-altered layer and produce an etching pattern similar to that created by phosphoric acid alone. These differences could account for the higher acid resistance of laser-irradiated substrate as compared to acid-etched substrate. 33 Acid etching provides suitable substrate for adhesion, since it removes the smear layer and creates a uniform microretentive pattern, 17 due to the selective dissolution and removal of hydroxyapatite crystals. This aspect is a favourable condition to deep penetration of adhesive agents into the microporosity network, thus forming resin tags upon light curing. 2 Likewise, laser-treated substrates could be receptive for a certain degree of monomer infiltration, due to absence of smear layer and microretentive pattern. 4,17,21 However, the micromorphology of laser-irradiated enamel exhibits less regular and less homogenous aspect, with subsurface fissures resulted from heat generated during irradiation, 2 which might be adverse factors for the bonding process. Marked differences at the interface between Er:YAG-lased or acidetched enamel and adhesive were reported by Ceballos et al. 32 According to these authors, no gap was found in acid-etched enamel specimens, and resin tags were visible. On the other hand, laser irradiated samples, whether acid etched or not, presented with gaps and no mechanical interlocking. Among the lased groups, the irradiation of enamel at the defocused working distances of 16 and 17 mm yielded the highest bond strength means. Er:YAG laser ablation on focused mode (12 mm) showed similar results as those recorded for the groups in which the laser beam was delivered on defocused mode at 14 and 16-mm irradiation distances. The shortest working distance (11 mm) resulted in the lowest bond strength means, thereby suggesting that alterations in the adhesion to enamel might be distance-dependent rather than focalisation-dependent. Supporting this finding, it has been reported 36 that the greater the irradiation distance, the lesser the surface alterations in depth. Diverging in some aspects to our results, Keller and Hibst 4 described differences in enamel surface morphology when applying Er:YAG laser in defocused or focused mode, with the

6 250 presence of more homogeneous cratter pattern after defocused irradiation. In addition, these authors achieved higher bond strength means when associating the two application modes (defocused followed by focused mode), as compared to laser beam defocalisation alone. Visuri et al., 22 observed that bond strength decreased when acidetching was applied after laser treatment in focused mode. Other study 25 has advocated that the working irradiation distance higher than 15 mm reduces dental tissue ablation. However, an appropriate comparison of the results obtained in this study is difficult due to the lack of works reporting the laser irradiation distance and the variability of parameters and methodologies described in the available literature. As regards the types of failure observed in the fractured specimens, a cohesive-failure pattern (into the material or the substrate) was predominantly observed in the non-lased group, indicating that the adhesive interface was preserved. In contrast, failure mode in the lased groups was mostly mixed, which may be attributed to the fact that the Er:YAG laser beam does not provide a uniform, homogeneous etching pattern, leaving non-lased areas between pulses, 4,14 in which bonding to enamel is expected to be stronger. Mixed failure for the acid-etched specimens and adhesive failure for lased specimens irradiated on focused mode were reported by Keller and Hibst. 4 Although Er:YAG laser has been pointed out as a promising technology in dentistry, due to its reported benefits, such as increase in resistance to de-remineralisation process, there is still much to be investigated on the effect of lasing on tooth structure, mainly as regards to the adhesive interface micromorphology and the alterations in substrate compounds, under different laser parameters, seeking to achieve optimal irradiation conditions. Moreover, further in vitro and in vivo researches on the action of acid etching in lased surfaces are mandatory to justify the use of such protocol for caries prevention in clinical practice, and assess the longevity of restorations under the real oral conditions. Conclusion Based on the findings of this research, and within the limitations of an in vitro study, it may be concluded that laser irradiation distance influenced the bonding process, thereby rejecting the null hypothesis. Our results indicated that the greater the distance between the beam output and the target tissue, the higher the bond strength of the restorative system. Therefore, it can be suggested that, when choosing an Er:YAG laser device for treatment of enamel surface before acid etching, with the aim of benefiting from its possible effects in dental substrate, one should preferably utilise the defocused mode with a 17 mm irradiation distance to achieve more acceptable bonding. Acknowledgements The authors gratefully acknowledge CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico), grant n /2002-8, for financial support. References D.T. Chimello-Sousa et al. 1. Buonocore MG. A simple method of increasing the adhesion of acrylic filling materials to enamel surfaces. Journal of Dental Research 1955;34: MartÚnez-Insua A, Dominguez LS, Rivera FG, Santana- PenÚn UA. Differences in bonding to acid-etched or Er: YAG-laser-treated enamel and dentin surfaces. Journal of Prosthetic Dentistry 2000;84: Van Meerbeek B, Vargas M, Inoue S, Yoshida Y, Peumans M, Lambrechts P, et al. Adhesives and cements to promote preservation dentistry. Operative Dentistry 2001;6: Keller U, Hibst R. Effects of Er:YAG laser on enamel bonding of composite materials. In: Lasers in Orthopaedic, dental and vetinary medicine II p Apel C, Meister J, Schmitt N, Gräber HG, Gutknecht N. Calcium solubility of dental enamel following sub-ablative Er:YAG and Er:YSGG laser irradiation in vitro. Lasers in Surgery and Medicine 2002;30: Hibst R, Keller U. Experimental studies of the application of the Er:YAG laser on dental hard substances. I. Measurement of the ablation rate. Lasers in Surgery and Medicine 1989;9: Kumazaki M. Removal of hard dental tissue (cavity preparation) with the Er:YAG laser. In: The 6th International Congress on Lasers in Dentistry. Hawaii, USA: Mauí; 1998, p Armengol V, Jean A, Rohanizadeh R, Hamel H. Scanning electron microscopic analysis of diseased and healthy dental hard tissues after Er:YAG laser irradiation: in vitro study. Journal of Endodontics 1999;25: Keller U, Hibst R. Experimental studies of the application of the Er:YAG laser on dental hard substances. II. Light microscopic and SEM investigations. Lasers in Surgery and Medicine 1989;9: Hossain M, Nakamura Y, Yamada Y, Kimura Y, Nakamura G, Matsumoto K. Ablation depths and morphological changes in human enamel and dentin after Er:YAG laser irradiation with or without water mist. Journal of Clinical Laser Medicine and Surgery 1999;17: Hossain M, Nakamura Y, Kimura Y, Yamada Y, Ito M, Matsumoto K. Caries-preventive effect of Er:YAG laser irradiation with or without water mist. Journal of Clinical Laser Medicine and Surgery 2000;18:61 5.

7 Er:YAG laser irradiation distance on enamel bond strength Eguro T, Maeda T, Tanabe M, Otsuki M, Tanaka H. Adhesion of composite resins to enamel irradiated by the Er:YAG laser: application of the ultrasonic scaler on irradiated surface. Lasers in Surgery and Medicine 2001;28: Matson JR, Matson E, Navarro RS, Bocangel JS, Jaeger RG, Eduardo CP. Er:YAG laser effects on enamel occlusal fissures: an in vitro study. Journal of Clinical Laser Medicine and Surgery 2002;20: Corona SAM, Borsatto MC, Palma-Dibb RG, Ramos RP, Brugnera Jr A, PÕcor JD. Microleakage of class V resin composite restorations after bur, air-abrasion or Er:YAG laser preparation. Operative Dentistry 2001;26: De Munck J, Van Meerbeek B, Yudhira R, Lambrechts P, Vanherle G. Micro-tensile bond strength of two adhesives to Erbium:YAG-lased vs. Bur-cut enamel and dentin. European Journal of Journal Sciences 2002;110: Hossain M, Yamada Y, Nakamura Y, Murakami Y, Tamaki K, Matsumoto K. A study on surface roughness and microleakage test in cavities prepared by Er:YAG laser irradiation and etched bur cavities. Lasers in Medical Science 2003;18: Trajtenberg CP, Pereira PNR, Powers JM. Resin bond strength and micromorphology of human teeth prepared with an Erbium:YAG laser. American Journal of Dentistry 2004;17: Rohanizadeh R, LeGeros RZ, Fan D, Jean A, Daculsi G. Ultrastructural properties of laser-irradiated and heattreated dentin. Journal of Dental Research 1999;78: Hirota F, Furumoto K. A hypothesis for acquired acid resistance afforded by the laser irradiation. In: The 8th International Congress on Lasers in Dentistry, Yokohama, Japan; 2002, p Burkes EJ, Hoke J, Gomes E, Wolbarsht M. Wet versus dry enamel ablation by Er:YAG laser. Journal of Prosthetic Dentistry 1992;67: Li Z, Code JE, Willem P, Van De Merwe WP. Er:YAG laser ablation of the enamel and dentin of human teeth: determination of ablation rates at various fluences and pulse repetition rates. Lasers in Surgery and Medicine 1992; 12: Visuri SR, Gilbert JL, Wright DD, Wigdor HA, Walsh Jr JT. Shear strength of composite bonded to Er:YAG laserprepared dentin. Journal of Dental Research 1996;75: Glockner K, Rumpler J, Ebeleseder K, Städtler P. Intrapulpal temperature during preparation with Er:YAG laser compared to conventional burr: an in vitro study. Journal of Clinical Laser Medicine and Surgery 1998;16: Kataumi M, Nakajima M, Yamada T, Tagami J. Tensile bond strength and SEM evaluation of Er:YAG laser irradiated dentin using dentin adhesive. Dental Materials Journal 1998; 17: Coluzzi DJ. An overview of laser wavelengths used in dentistry. Dental Clinical of North American 2000;44: Aoki A, Yoshino T, Ohno J, Bando K, Oda S, Watanabe H, Ishikawa I. The effects of mis-irradiation of the Er:YAG laser on soft and bone tissues. In: 5th Congress of International Society for Lasers in Dentistry; 1996, P Moritz A, Schoop U, Goharkhay K, Szakacs S, Sperr W, Schweidler E, et al. Procedures for enamel and dentin conditioning: a comparison of conventional and innovative methods. Journal of Esthetic Dentistry 1998;10: Lee BS, Hsieh TT, Lee YL, Lan WH, Hsu YJ, Wen PH, et al. Bond strengths of orthodontic bracket after acid-etched, Er: YAG laser-irradiated and combined treatment on enamel surface. The Angle Orthodontist 2003;73: Staninec M, Xie J, Le CQ, Fried D. Influence of an optically thick water layer on the bond-strength of composite resin to dental enamel after IR laser ablation. Lasers in Surgery and Medicine 2003;33: Gonc alves M, Corona SAM, Pécora JD, Palma-Dibb RG. Influence of the frequency of Er:YAG laser on the bond strength of dental enamel. Journal of Clinical Laser Medicine and Surgery 2003;21: Arimoto N, Suzaki A, Katada H, Senda A. Acid resistance in lased dentin. In: The 6th International Congress on Lasers in Dentistry, Mauli, Hawaii, USA: Mauí; 1998, p Ceballos L, Osorio R, Toledano M, Marshall GW. Microleakage of composite restorations after acid or Er:YAG laser cavity treatments. Dental Materials 2001;17: Ceballos L, Toledano M, Osorio R, García-Godoy F, Flaitz C, Hicks J. ER:YAG laser pretreatment effect on in vitro secondary caries formation around composite restorations. American Journal of Dentistry 2001;14: Ying D, Chuah GK, Hsu CY. Effect of Er:YAG laser and organic matrix on porosity changes in human enamel. Journal of Dentistry 2004;32: Senda A, Suzaki A, Arimoto N, Irinoda M, Gomi A. Effect of Er:YAG laser irradiation on bovine enamel. Journal of Dental Research 1998;77(AADR Abstracts):280 [Abstract n. 1393]. 36. Yamamoto A, Shinoki T, Kataoka K, Okagami Y. Hard tissue breaking efficacy and possibilities for reducing pain by defocus irradiation of Er:YAG laser. In: The 6th International Congress on Lasers in Dentistry. Hawaii, USA: Mauí; 1998, p.106.