1. Dentin treatment of weakened roots with lasers A. R. GIOVANI 1, A. E. SOUZA-GABRIEL 2, S. C. DA SILVA SR. 3, M. SOUSA-NETO 4, Y. SILVA-SOUSA 5, and L. P. VANSAN 3 1 University of Ribeirão Preto, Ribeirão Preto, SP, Brazil/ 2 University of São Paulo FORPUSP, Ribeirão Preto, SP, Brazil ABSTRACT METHODS INTRODUCTION OBJECTIVE CONCLUSIONS REFERENCES E-mail:drgiovani@gmail.com The aim of this study was to evaluate in vitro the effect of 2.940-nm Er:YAG and 980-nm diode lasers in intraradicular dentin regarding the bond strength of composite resin in weakened roots. Roots of 50 maxillary canines were weakened standardizing the radicular walls thickness in 2 mm. The apical 4 mm were filled with AH plus and gutta-percha. For the push-out test, the 40 irradiated roots and the ten remaining roots were divided into five groups (n=10) according to dentin treatment: GI - 37% phosphoric acid, GII - Er:YAG laser; GIII- Er:YAG laser and phosphoric acid, GIV: diode laser and GV- diode laser and phosphoric acid. After treatment, the teeth were restored with composite resin and glass fiber post was cemented. The roots were sectioned transversely (1 mm slices) at cervical, middle and apical thirds. In the first slice of each third it was performed the push-out test in universal testing machine. The second slice was prepared for scanning electron microscopy. The push-out test, it was found significant statistical differences for both factors (treatment and thirds) (p<0.05). The dentin treatments provided dentin bond strength values statistically different in all groups (p<0.05): GI (4.17±2.24), GII (2.98±1.42), GIII (2.33 ± 1.98), GIV (0.53 ± 0.20) and GV (0.73±0.32). The cervical third had the highest values (3.47 ± 2.30), followed by medium (2.23±1.70) and apical (0.72 ± 0.48) (p 0.05). GI, GII and GIII had a favorable adhesive interface with long and numerous tags. GV had gaps at the adhesive interface, and GIV and GV exhibited no tags. The dentin treatment with phosphoric acid remains the best choice for the hybridization of dentin tissue, because both lasers, regardless of the association with phosphoric acid, interfered negatively in the adhesion of composite resin used in the reinforcement of weakened roots. The objective of this study was to evaluate, in vitro, the effect of 2.940 nm Er:YAG and 980 nm diode lasers in intraradicular dentin regarding the bond strength of composite resin in weakened roots. The restoration of endodontically treated teeth with excessive loss of dental structure caused by extensive carie, pulpal pathology and iatrogenic, it should return to the dental element the form and function, providing an appropriate distribution of forces 1, 2. The use of adhesive restorative materials as reinforcement of weakened roots, together with prefabricated post has aided in the rehabilitation of endodontically treated teeth with little dental structure 3. The weakened root with less intraradicular dentin is a less favorable substrate for adhesion of resinous material, due to its density and smaller than the diameter of the dentin tubules near the channel 4. Furthermore, when performing the reinforcement of weakened roots with composite resin, the professional is faced with difficulties, as the surface treatment of dentin, insertion and polymerization of resinous material inside the root canal. Among these factors, treatment of dentin intraradicular deserves mention, because it can interfere in the adhesiveness of the resinous materials 3. Besides the chemicals substances traditionally used for cleaning and treating dentinal root canal such as sodium hypochlorite (NaOCl), ethylenediaminetetraacetic acid (EDTA) and phosphoric acid, which has the ability to increase permeability by 90% of dentinal tubules 5 other means are being researched such as laser irradiation, which can be applied for the treatment of dentinal walls 6. Among the equipments of high potency, the Er:YAG laser deserves prominence, because his wavelength of 2.940 nm coincides with the maximum pick of absorption of the hydroxiypatite, what induces to the process of ablation of the mineralized tissue. 7,8 Depending on the used parameters, the Er:YAG laser can propitiate irregular surface and with cracks 9, to remove smear layer and to open dentinal tubules 9 and to expose collagen fibers 10 that could promote retention for the composite resin 10 and cements resinous. 11 The diode 980 nm laser has also been indicated in the dentistry treatment, especially in the endodontically area, owed mainly this antimicrobial activity. 4,12 The dentin irradiated presents modifications that can interfere with the performance of resin materials such as removing the smear layer that altered permeability of the surface and affect the bond strength of resin materials, opening the dentinal tubules and fusion. However, the literature is sparse on studies that relate the adhesiveness of resin materials in weakened roots, especially when the dentin walls are treated with laser. 1.The dentin treatment with phosphoric acid remains the best choice for the hybridization of dentin tissue,. 2.The lasers Er:YAG 2.940 nm and diode 980 nm regardless of the association with phosphoric acid, interfered negatively in the adhesion of composite resin used in the reinforcement of weakened roots. Prepare of specimens = 50 Maxillary Canines Human The ANOVA analisys demonstrated significant differences among the factors in study (treatment and thirds) and their interactions (p <0.05). The dentin treatments provided medium values of resistance adhesive, statistical different amongst themselves (Tabela1). The weakened roots that received the treatment with phosphoric acid presented the superior values adhesiveness to the dentine (4,17±2,24) and they were statistical different (p<0.05) of the other groups (Table I). In relation to the thirds, the cervical presented the superior values, following for the medium and apical (p <0,05) (Table II). In the interaction of the factors, it was verified that the superior values of the union resistance of the resin to the wall of the radicular channel was with the use of the phosphoric acid in the cervical third of the root statistical different from the others (p 0.05). The other groups presented intermediate medium values (Table III). RESULTS 1 - Giovani AR, Vansan LP, Sousa-Neto MD, Paulino SM: Dent In vitro fracture resistance of glass-fiber and cast metal posts with different lengths. J Prosthet Dent. 2009 Mar, 101(3):183-8. 2 - Hatta M, Shinya A, Vallittu PK, Shinya A, Lassila LV. 2011. High volume individual fiber post versus low volume fiber post: the fracture load of the restored tooth. J Dent. 2010 Jan, 39(1):65- 71. 3 - Teixeira CS, Silva-Sousa YT, Sousa-Neto MD. Bond strength of fiber posts to weakened roots after resin restoration with different light-curing times. J Endod. 2009 Jul, 35(7):1034-1039. 4 - Mjör IA, Smith MR, Ferrari M, Mannocci F. The structure of dentine in the apical region of human teeth. Int Endod J. 2001 Ju,l 34(5):346-353. 5 - Malkoc MA, Taşdemir ST, Ozturk AN, Ozturk B, Berk G. Effects of laser and acid etching and air abrasion on mineral content of dentin. Laser Med Sci. 2011 Jan, 26(1): 21-27. 6 - Alfredo E, Silva, SRC, Ozório JEV, Sousa-Neto MD, Brugnera-Junior A, Silva-Sousa, YTC. Bond strength of AH Plus and Epiphany sealers on root dentine irradiated with 980 nm diode laser. Int Endod J. 2008 Sep, 41(9):733-740. 7 - Coluzzi DJ, Goldstein AJ. Lasers in Dentistry – An Overview. Dent. Today. 2004 Apr;23(4):120-7. 8 - Scaini F, Souza-Gabriel AE, Alfredo A, Cruz-Filho AM. Temperature Variation on the external root surface during intracanal Er:YAG laser irrariadtion. Photomed Laser Surg. 2008 Oct;26(5):413- 17. 9 - Souza-Gabriel AE, Chinelatti MA, Borsatto MC, Pecora JD, Palma-Dibb RG, Corona SA. Effect of Er:YAG laser irradiation distance on superficial dentin morphology. Am J Dent. 2006 Aug;19(4):217-21. 10 - Carvalho RC, De Freitas PM, Otsuki M, De Eduardo CP, Tagami J. Micro-shear bond strength of Er:YAG-laser-treated dentin. Lasers Med Sci. 2008 Apr;23(2):117-24. 11 - Haragushiku GA, Sousa-Neto MD, Silva-Sousa YTC, Alfredo E, Silva SC, Silva RG. Adhesion of Endodontic Sealers to Human Root Dentine Submitted to Different Surface Treatments. Photomed Laser Surg. 2010 Jun;28(3):405-10. 12 - Gutknecht N, Franzen R, Schippers M, Lampert F. Bactericidal effect of a 980-nm Diode laser in the root canal wall dentin of bovine teeth. J. Clin. Laser Med. Surg. 2004 Feb; 22(1): 9-13. #3547 Specimens (n=50) Specimens (n=50) Group II Laser Er:YAG 2.940 nm (10 Hz, 500 mJ, 16 s) Group II Laser Er:YAG 2.940 nm (10 Hz, 500 mJ, 16 s) Group III Laser Er:YAG 2.940 nm (10 Hz, 500 mJ, 16 s) and Phosphoric acid 37% Group III Laser Er:YAG 2.940 nm (10 Hz, 500 mJ, 16 s) and Phosphoric acid 37% Group I Phosphoric acid 37% Group I Phosphoric acid 37% Group IV Laser Diodo 980 nm (1,5W, continues waves) and Phosphoric acid 37 Group IV Laser Diodo 980 nm (1,5W, continues waves) and Phosphoric acid 37 Group IV Laser Diodo 980 nm (1,5W, contínuos waves Group IV Laser Diodo 980 nm (1,5W, contínuos waves Fig. 1 – Maxillary Canines Human (n=50). Fig. 2 – Root section (work lenght =15mm). Fig. 3 – drills used to flare root. Fig. 4 – Rotary cutting instrument (Profile.06 Taper Series 29). Fig. 5 – Instrumentation (work lenght =15mm). Fig. 6 – Obturation AH Plus sealer. Fig. 7 – A) Opus 20 (Opus20, OpusDent, Tel-Aviv, Israel) and B) Tip of sapphire of the laser Er:YAG. Fig. 9 – A) Laser of diode 980 nm (SIROlaser 2.2 - Dental SIRONA, Bensheim, Germany) used for the irradiation of the specimens and B) Tip with flexible fiberoptic of 200 µm of diameter. Fig. 8 – Materials used for the root reinforcement. Dentin TreatmentMeans± DP Acid4,17 ± Er: YAG2,98 ± 1,42 b Er:YAG +Acid2,33 ± 1,98 c Diodo 980 nm0,53 ± 0,20 e Diodo 980 nm + Acid0,73 ± 0,32 d Table I - Medium values and standard deviations of the displacement of the composed resin after the different dentin treatments. ThirdsMeans ± DP Cervical3,47 ± Médio2,23 ± 1,70 b Apical0,72 ± 0,48 c Table II - Medium values and standard deviations of the displacement of the composed resin after the different dentin treatments, in the different thirds.. Treatments Thirds CervicalMediumApical Acid(6,41 ± 0,19) a(4,88 ± 0,47) b(1,20 ± 0,10) e Er:YAG(4,50 ± 0,46) b(3,10 ± 0,33) c(1,24 ± 0,08) e Er:YAG +Acid(4,74 ± 0,29) b(2,21 ± 0,11) d(0,01 ± 0,00) g Diodo 980 nm(0,52 ± 0,06) f(0,32 ± 0,04) g(0,72 ± 0,18) f Diodo 980 nm + Acid(1,12 ± 0,18) e(0,64 ± 0,02) f(0,42 ± 0,05) f Table III - Medium of the adhesive resistance (MPa) and standard deviations of the dentin treatments in the different thirds of the weakened roots. * Different letters indicate significant statistical difference. Critical value of Tukey = 0.161 (p <0.05). * Different letters indicate significant statistical difference. Critical value of Tukey = 0,.07 (p <0.05). * Different letters indicate significant statistical difference. Critical value of Tukey = 0,347 (p <0.05). Fig. 10 – Machine of cuts Isomet 1000 (Buehler, Lake Forest, IL, USA). Fig. 11 – Specimen sectioned into 2 mm. Fig. 12 – Specimen sectioned: 1 slice – push-out and 2 slice – MEV. Fig. 13 – Universal Testing Machine Instron 4444. Fig. 14 – Specimen positioned in the base of the Machine during the test.