Lasers Med Sci (2010) 25:467472 DOI 10.

1007/s10103-009-0656-5

ORIGINAL ARTICLE

Evaluation of mineral content of enamel prepared by erbium, chromium:yttriumscandiumgalliumgarnet laser

Received: 21 February 2008 / Accepted: 9 February 2009 / Published online: 11 March 2009 # Springer-Verlag London Limited 2009

Abstract The aim of this study was to evaluate the mineral content of enamel etched at two different power settings with an erbium, chromium:yttriumscandiumgallium garnet (Er,Cr:YSGG) laser. Buccal, lingual and mesial or distal surfaces of five premolar teeth were cut, and three enamel slabs were obtained from each tooth. Fifteen enamel specimens were divided into three groups (1 W, 2 W and control) of five specimens each and subjected to Er,Cr: YSGG laser. The mean percentage weights of the five elements [calcium (Ca), potassium (K), magnesium (Mg), sodium (Na) and phosphorus (P)] in each slab were measured by inductively coupled plasma-atomic emission spectrometry (ICP-AES). One way analysis of variance (ANOVA) was used to analyze differences among the groups (1 W, 2 W and control). There were no significant differences among the groups (1 W, 2 W and control) for Ca, K, Mg, Na, or P, or for the Ca/P ratio (P>0.05).

Scanning electron microscopy (SEM) photographs indicated that the surface irregularities increased with increased power setting. Laser treatment did not affect the mean percentage weights of Ca, K, Mg, Na, and P, or the Ca/P ratio, in any group. Keywords Calcium/phosphorus ratio . Elemental composition . Enamel . Erbium, chromium:yttrium scandiumgalliumgarnet laser . Inductively coupled plasmaatomic emission spectrometry (ICP-AES) . Laser treatment

Introduction Since the report by Buonocore [1] was published in 1955, different etching methods have been used for direct bonding of attachments in orthodontics. Etching with 37% phosphoric acid is the most widely used [25]. The advantage of etching with phosphoric acid is the high level of bracket bond strength achieved. On the other hand, the loss of mineral crystals, essentially the acid-protecting barrier, is inevitable. Because of this mineral loss, the acid-etched region may be vulnerable to successive acid attacks in the oral environment [2]. Maleic [3, 4] or polyacrylic [5, 6] acids and sandblasting treatment [7, 8] have been used as alternatives to phosphoric acid. In the literature there are recent reports about the use of lasers for enamel etching [915]. Laser treatment of dental hard tissues involves conversion of light energy to thermal energy to resect tissues. In particular, laser treatment of dental enamel causes thermally induced changes within the enamel to a depth of 1020 m, depending on the type of laser used and the energy applied to the enamel surface [9]. Adjustment of the laser power output permits localized melting and ablation of the enamel surface, in effect etching

A. Secilmis (*) Department of Prosthodontics, Faculty of Dentistry, University of Gaziantep, Gaziantep, Turkey e-mail: acarasli@hotmail.com A. Usumez Department of Prosthodontics, Faculty of Dentistry, University of Gaziantep, Gaziantep, Turkey S. Usumez Department of Orthodontics, Faculty of Dentistry, University of Gaziantep, Gaziantep, Turkey G. Berk Dentaform, Ankara, Turkey

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it through a process of continuous vaporization and microexplosions due to vaporization of water trapped within the hydroxyapatite matrix. In general, more material is removed by the microexplosion of entrapped water than by direct vaporization of the hydroxyapatite crystals. However, the degree of surface roughening is dependant upon the system used and the wavelength of the laser [9]. Laser etching is painless and does not involve vibration or heat, making it highly attractive for routine use. Furthermore, laser etching of enamel or dentin has been reported to yield a fractured and uneven surface and open dentin tubules, both apparently ideal for adhesion [16]. The surface produced by laser etching is claimed to be acid resistant as a result of modified calcium-to-phosphorus ratio (Ca/P ratio), reduced carbonate-to-phosphate ratio, and formation of more stable and less acid-soluble compounds, thus reducing susceptibility to acid attack and caries [12, 17, 18]. The erbium, chromium:yttriumscandiumgalliumgarnet (Er,Cr:YSGG) laser, which uses a pulsed-beam system, when used with an airwater spray, has been shown to cut enamel, dentin, cementum, and bone efficiently and cleanly [19, 20]. In a previous study, it was suggested that the Er,Cr:YSGG laser may etch enamel suitably for orthodontic purposes. The authors stated that the mean shear bond strength and enamel surface etching obtained with an Er,Cr:YSGG laser (operated at 1 W or 2 W for 15 s) is comparable to that obtained with acid etching [14]. The alterations in chemical composition may affect the adhesion of dental materials to dental hard tissues [21]. A study on laser etching with the Er,Cr:YSGG laser system reported that laser etching affected compositional structure of the dentin surfaces. The mineral structure of dentin has been measured by inductively coupled plasma-atomic emission spectrometry (ICP-AES) [21]. This technique uses a sample that is passed through argon in a ray fluorescence (RF) field. When the sample is introduced into the plasma, the atoms are excited and emit very stable light of varying wavelengths that permit identification of the elements [22]. The mineral content of dental hard tissues can be measured by scanning electron microscopy (SEM) and energy dispersive spectrometry, with amounts detectable at the parts per million (milligrams per liter) level. However, with ICP-AES it can be detected at the parts per billion (micrograms per liter) level. In addition, multiple elements can be measured at the same time by ICP-AES. The measurements should be repeated for a second element [23]. The aim of this study was to evaluate the compositional changes [in calcium (Ca), potassium (K), magnesium (Mg), sodium (Na) and phosphorus (P)] of the enamel surfaces prepared by Er,Cr:YSGG laser treatment and to compare the Ca/P ratios of the groups, using ICP-AES.

Materials and methods Preparation of the enamel slabs Five, upper, premolars that were free of dental caries or restoration were cleaned with gauze and a fine brush and stored in distilled water at room temperature immediately after extraction. The teeth were then mounted in quadrangular molds with an autopolymerizing acrylic resin (Meliodent, Bayer Dental Ltd., Newbury, UK). To prepare the enamel slabs, we cut buccal, lingual and mesial or distal surfaces of the crowns with a diamond saw under water cooling. Finally, three enamel slabs were obtained from each tooth. Fifteen enamel slabs from five premolars were divided into two test groups and one control group as shown in Fig. 1. The prepared slabs were stored in distilled water at room temperature. The surface areas of the enamel slabs were approximately 9 mm2. Laser treatment An Er,Cr:YSGG dental laser (Waterlase; Biolase Technologies, San Clemente, CA, USA) with a pulse duration of 140 s, a pulse repetition rate of 20 Hz and a power output range of 0 W to 6 W was used for laser etching. The lasers wavelength was 2,780 nm. Laser energy was delivered through a fiberoptic system to a sapphire tip terminal, 6 mm long and 600 m in diameter, using a non-contact mode with power settings of 1 W (pulse energy 50 mJ and 2 W (pulse energy 100 mJ), 80% water and 90% air. The beam was aligned perpendicularly to the enamel at 1.5 mm distance and moved in a sweeping fashion by hand to obtain a homogeneous surface appearance over the entire area of each enamel slab. Energy densities were 17.68 J/cm2 for the 1 W group and 35.36 J/cm2 for the 2 W group. ICP-AES technique The enamel slabs were stored in plates at 70C in a cabinet desiccator (Ventisell, Italy) until they reached a constant weight. That is to say, the specimens were dehydrated. Their weights were recorded with an electronic balance (Electronic Balance AX200, Shimadzu Corporation, Japan). Ten milliliters of nitric acid (HNO3) and 3 ml hydrochloric acid (HCl) were added to the specimens, and the specimens were burned at 180 p.s.i. and 180C in a microwave oven (CEM, Mars 5, USA) until they had dissolved. After calibration of the ICP-AES instrument (Vista AX, Varian, Australia), 2 ml of solution was taken. In this technique, the solutions are carried in a nebulizer with the help of a peristaltic pump. The specimens turn into aerosols and are carried by an argon spray. The aerosols are heated by conduction and radiation and reach approximately 10,000C, at which temperature they are completely atomized. Resonance

Lasers Med Sci (2010) 25:467472 Fig. 1 Schematic structure of the test groups and method

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beams emitted from stimulated atoms when they return to their basic energy levels are transferred to a detector and pass as emission lines at specific wavelengths. Every element is described according to its different wavelength. Data relating to the quantity of beam passed in emission lines pass from a digitizer and appear separately for each element at a computer display. In this study, each element was measured three times and the means of the measurements were calculated in milligrams per liter (parts per million) by the computer. The levels of five elements (Ca, K, Mg, Na and P) in each specimen were measured by ICP-AES. The mineral contents were calculated as percentage weights. Scanning electron microscopy examinations One specimen from each group was prepared for SEM (Jeol JSM-6400; Jeol Ltd., Tokyo, Japan). After surface treatment, the specimens were sputter coated (Hummer VII SEM Sputtering System, Anatech LTD, Alexandria, VA) with goldpalladium alloy under high vacuum and photomicrographs were taken. Statistical analysis Differences between the groups (1 W, 2 W and control) were statistically analyzed by one way analysis of variance (ANOVA) and Tukeys honestly significant difference (HSD) tests. We compared the groups to verify the
Table 1 Mean percentage weights of the five elements (mean standard deviation) and Ca/P ratio for each group (n=5)

differences at a significance level set at P<0.05, using the statistical program SPSS 11 for Windows. Results The mean percentage weights of the five elements (Ca, K, Mg, Na and P) in the enamel slabs are shown in Table 1 One-way ANOVA showed that there were no significant differences among the groups (1 W, 2 W and control) for Ca, K, Mg, Na, or P, or for the Ca/P ratio (P>0.05). The P values were 0.93, 0.97, 0.97, 0.99, 0.89, 0.88 for Ca, K, Mg, Na, P and Ca/P ratio, respectively. SEM views of the Er,Cr:YSGG laser-treated enamel surfaces are shown in Figs. 2 and 3. The surface treated with 2 W laser was rougher than those of the control and 1 W groups. The rough, crestal appearance of the irradiated enamel surface could be observed in both slabs treated with laser. This appearance was predominant in the slabs that had been laser irradiated at 2 W (Fig. 3). Discussion In this study we evaluated the compositional changes in the enamel surfaces prepared by Er,Cr:YSGG laser irradiation and compared the Ca/P ratios of the groups, using ICP-AES. The mean percentage weights of Ca, Mg, Na, and P and the Ca/P ratio of the groups were not affected by laser irradiation.

Groups 1 W 2 W Control

Ca 3.611.46 3.741.70 3.861.92

K 0.050.01 0.050.01 0.050.00

Mg 0.030.02 0.040.02 0.040.02

Na 0.340.03 0.350.04 0.350.03

P 3.781.12 3.881.28 3.881.39

Ca/P 0.96 0.96 0.99

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Fig. 2 SEM view of enamel surface treated with 1 W laser. 2,000

A rise in temperature in the enamel induces modifications in the enamels structure [2, 24]. Water is lost at 80 120C; protein decomposes at approximately 350400C and completely decomposes above 400C; -tricalcium phosphate (-TCP) forms above 600C with the loss of carbonate; enamel melts above 1,000C in air, and -TCP is converted to -TCP above 1,100C [2, 2528]. The decomposed protein and other organic matrix products melt and swell and probably lead to blockage of the interprismatic and intraprismatic spaces, which act as ion diffusion channels, and eventually result in a decrease of calcium loss [2, 29]. Furthermore, the enamel crystalline structure improves with a decrease in enamel solubility in acid at temperatures of 250C to 400C [2, 27, 30, 31]. Kim et al. [2] stated that no new phases (-TCP) were found after ablation with erbium:yttriumaluminumgarnet (Er:YAG) laser and that this condition could imply that the temperature during the laser treatment may not rise above 600C. Analogously, Er,Cr:YSGG laser ablation is water mediated. Dental enamel consists of between 85% and 95%, by volume, hydroxyapatite, 812%, by volume, water and 2 3%, by volume, organic components [32]. Hydroxyapatite has an absorption maximum close to 2.8 m (OH) and water at 3 m. The application of erbium lasers for good absorption in dental enamel solely for caries prevention presupposes that the energy densities used are below the ablation threshold. It has been stated that the surface is not meant to be ablated or melted; rather, only its structure or chemical composition should be altered [33]. However, in our study, the mean percentage weights of Ca, K, Mg, Na and P and the Ca/P ratio of the groups were not affected by the Er,Cr:YSGG laser treatment. The strongly absorbed laser energy in the enamel is converted to heat that boils water abruptly. The boiled water forms high-pressure steam that leads to the ablation process when the pressure exceeds the ultimate strength of

the tooth. During the ablation process, water evaporates explosively within the tooth particles. The ablated materials and their successive recoil force create craters on the surface. The irradiated surface becomes flaky, with an irregularly serrated and microfissured morphology [2]. In this study, SEM views of the irradiated surfaces achieved with the Er, Cr:YSGG laser system showed that the surface irregularities and exposed enamel prisms increased with increasing power setting. There was no evidence of denaturing or disruption of enamel structure resulting from irradiation. The Ca and P present in hydroxyapatite crystals are the major inorganic components of dental hard tissue. The Ca/P ratio of hydroxyapatite in dental hard tissues implies the basic composition of dental hard tissue surfaces, depending on the crystal type, availability of Ca, the anatomical location, and the technique of determination [23, 34, 35]. It has been reported that some chemical agents caused alterations in the chemical structure of human enamel and changed the Ca/P ratio of the enamel [36]. In our study there was no significant alteration in the Ca/P ratio in the Er,Cr:YSGG laser-treated groups. The mechanism of the increased acid resistance of enamel after laser irradiation has been explained by the enamelss decreased permeability and solubility. Erbium lasers, such as Er:YAG and Er,Cr:YSGG, and carbon dioxide (CO2) have been used for the prevention of enamel demineralization [2, 24, 33, 3739]. Kim et al. [2] found that phosphoric acid-etched specimens had the highest Ca and P dissolution and that Er:YAG laser-ablated specimens had the lowest dissolution. They stated that the improved crystalline structure might be related to the decrease in the enamels solubility in an acidic environment. The mineral loss occurred from the subsurface in the unlased specimens, whereas it occurred from the surface in the laser-ablated specimens, probably as a result of the improved crystallinity and the blocking effect of the organic matrix.

Fig. 3 SEM view of enamel surface treated with 2 W laser. 2,000

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471 11. Martnez-Insua A, Da Silva Dominguez L, Rivera FG, Santana-Penn UA (2000) Differences in bonding to acid-etched or Er:YAG-lasertreated enamel and dentin surfaces. J Prosthet Dent 84:280288. doi:10.1067/mpr.2000.108600 12. Usumez S, Orhan M, Usumez A (2002) Laser etching of enamel for direct bonding with an Er,Cr:YSGG hydrokinetic laser system. Am J Orthod Dentofacial Orthop 122:649656. doi:10.1067/ mod.2002.127294 13. Lee BS, Hsieh TT, Lee YL, Lan WH, Hsu YJ, Wen PH, Lin CP (2003) Bond strengths of orthodontic bracket after acid-etched, Er:YAG laser-irradiated and combined treatment on enamel surface. Angle Orthod 73:565570 14. Basaran G, Ozer T, Berk N, Hamamci O (2007) Etching enamel for orthodontics with an erbium, chromium:yttrium-scandiumgallium-garnet laser system. Angle Orthod 77:117123. doi:10.2319/120605-426R.1 15. Souza-Zaroni WC, Chinelatti MA, Delfino CS, Pcora JD, Palma-Dibb RG, Corona SA (2008) Adhesion of a self-etching system to dental substrate prepared by Er:YAG laser or air abrasion. J Biomed Mater Res B Appl Biomater 86B:321329. doi:10.1002/jbm.b.31020 16. Visuri SR, Gilbert JL, Wright DD, Wigdor HA, Walsh JT (1996) Shear strength of composite bonded to Er:YAG laser-prepared dentin. J Dent Res 75:599605 17. Fowler BO, Kuroda S (1986) Changes in heated and in laser irradiated human tooth enamel and their probable effects on solubility. Calcif Tissue Int 38:197208. doi:10.1007/ BF02556711 18. Keller U, Hibst R (1990) Ultrastructural changes of enamel and dentin following Er:YAG laser radiation on teeth. Proc SPIE 1200:408415. doi:10.1117/12.17486 19. Eversole LR, Rizoiu IM (1995) Preliminary investigations on the utility of an erbium, chromium YSGG laser. J Calif Dent Assoc 23:4147 20. Eversole LR, Rizoiu I, Kimmel AI (1997) Pulpal response to cavity preparation by an erbium, chromium: YSGG laser-powered hydrokinetic system. J Am Dent Assoc 128:10991106 21. Secilmis A, Altintas S, Usumez A, Berk G (2008) Evaluation of mineral content of dentin prepared by erbium, chromium:yttrium scandium gallium garnet laser. Lasers Med Sci 23:421425. doi:10.1007/s10103-007-0498-y 22. Deutsch AS, Cohen BI, Musikant BL (2003) Inductively coupled plasma-emission spectroscopy and atomic absorption for the use of elemental analysis of a root canal after lasing with a holmium: YAG laser. J Endod 29:404406. doi:10.1097/00004770200306000-00006 23. Ari H, Erdemir A (2005) Effect of endodontic irrigation solutions on mineral content of root canal dentin using ICP-AES technique. J Endod 31:187189 24. Liu JF, Liu Y, Stephen HC (2006) Optimal Er:YAG laser energy for preventing enamel demineralization. J Dent 34:6266. doi:10.1016/j.jdent.2005.03.005 25. Fowler BO, Moreno EC, Brown WE (1966) Infrared spectra of hydroxyapatite, octacalcium phosphate and pyrolyzed octacalcium phosphate. Arch Oral Biol 11:477492. doi:10.1016/0003-9969 (66)90154-3 26. Corcia JT, Moody WE (1974) Thermal analysis of human dental enamel. J Dent Res 53:571580 27. Holcomb DW, Young RA (1980) Thermal decomposition of human tooth enamel. Calcif Tissue Int 31:189201. doi:10.1007/ BF02407181 28. Kuroda S, Fowler BO (1984) Compositional, structural, and phase changes in in vitro laser-irradiated human tooth enamel. Calcif Tissue Int 36:361369. doi:10.1007/BF02405347 29. Sato K (1983) Relation between acid dissolution and histological alteration of heated tooth enamel. Caries Res 17:490495

Within the limitation of this study it was found that Er, Cr:YSGG laser treatment of enamel at 1 W and 2 W power settings did not significantly affect the mean percentage weights of elements. Therefore, taking advantage of laserinduced caries resistance through an altered Ca/P ratio seems questionable in dental practice.

Conclusion ICP-AES was used to evaluate the compositional changes [in calcium (Ca), potassium (K), magnesium (Mg), sodium (Na) and phosphorus (P)] of the enamel surfaces prepared by Er,Cr:YSGG laser treatment. Within the limitations of this study, the following conclusions were drawn: 1. Laser treatment did not affect the mean percentage weights of Ca, K, Mg, Na, and P, or the Ca/P ratio, in any group. 2. For the laser-treated groups, SEM photographs indicated that the surface irregularities increased with increased power setting.

References
1. Buonocore MG (1955) A simple method of increasing the adhesion of acrylic filling materials to enamel surfaces. J Dent Res 34:849853 2. Kim JH, Kwon OW, Kim HI, Kwon YH (2006) Acid resistance of erbium-doped yttrium aluminum garnet laser-treated and phosphoric acid-etched enamels. Angle Orthod 76:10521056. doi:10.2319/ 11405-398 3. Urabe H, Rossouw PE, Titley KC, Yamin C (1999) Combinations of etchants, composite resins, and bracket systems: an important choice in orthodontic bonding procedures. Angle Orthod 69:267275 4. Bishara SE, Gordan VV, VonWald L, Olson ME (1998) Effect of an acidic primer on shear bond strength of orthodontic brackets. Am J Orthod Dentofacial Orthop 114:243247. doi:10.1016/ S0889-5406(98)70205-7 5. Bishara SE, Vonwald L, Laffoon JF, Jakobsen JR (2000) Effect of altering the type of enamel conditioner on the shear bond strength of a resin-reinforced glass ionomer adhesive. Am J Orthod Dentofacial Orthop 118:288294. doi:10.1067/mod.2000.104903 6. Bishara SE, Ostby AW, Laffoon J, Warren JJ (2007) A selfconditioner for resin-modified glass ionomers in bonding orthodontic brackets. Angle Orthod 77:711715. doi:10.2319/070606-280.1 7. Chung K, Hsu B, Berry T, Hsieh T (2001) Effect of sandblasting on the bond strength of the bondable molar tube bracket. J Oral Rehabil 28:418424. doi:10.1046/j.1365-2842.2001.00678.x 8. Sargison AE, McCabe JF, Millett DT (1999) A laboratory investigation to compare enamel preparation by sandblasting or acid etching prior to bracket bonding. Br J Orthod 26:141146. doi:10.1093/ortho/26.2.141 9. Von Fraunhofer JA, Allen DJ, Orbell GM (1993) Laser etching of enamel for direct bonding. Angle Orthod 63:7376 10. Obata A, Tsumura T, Niwa K, Ashizawa Y, Deguchi T, Ito M (1999) Super pulse CO2 laser for bracket bonding and debonding. Eur J Orthod 21:193198. doi:10.1093/ejo/21.2.193

472 30. Fowler B, Kuroda S (1986) Changes in heated and in laserirradiated human tooth enamel and their probable effects on solubility. Calcif Tissue Int 38:197208. doi:10.1007/ BF02556711 31. Oho T, Morioka TA (1990) Possible mechanism of acquired acid resistance of human dental enamel by laser irradiation. Caries Res 24:8692 32. Schrder HE (1992) Orale stukturbiologie. Thieme, Stuttgart 33. Apel C, Meister J, Schmitt N, Grber HG, Gutknecht N (2002) Calcium solubility of dental enamel following sub-ablative Er: YAG and Er:YSGG laser irradiation in vitro. Lasers Surg Med 30:337341. doi:10.1002/lsm.10058 34. Cohen M, Garnick JJ, Ringle RD, Hanes PJ, Thompson WO (1992) Calcium and phosphorus content of root exposed to the oral environment. J Clin Periodontol 19:268273. doi:10.1111/ j.1600-051X.1992.tb00465.x

Lasers Med Sci (2010) 25:467472 35. Grayson W, Marsall JR (1993) Dentin: microstructure and characterization. Quintessence Int 24:606617 36. Rotstein I, Dankner E, Goldman A, Heling I, Stabholz A, Zalkind M (1996) Histochemical analysis of dental hard tissues following bleaching. J Endod 22:2326. doi:10.1016/S0099-2399(96)80231-7 37. Stern RH, Sognnaes RF, Goodman F (1966) Laser effect on in vitro enamel permeability and solubility. J Am Dent Assoc 73:838843 38. Fried D, Featherstone JD, Le CQ, Fan K (2006) Dissolution studies of bovine dental enamel surfaces modified by high-speed scanning ablation with a lambda=9.3-microm TEA CO2 laser. Lasers Surg Med 38:837845. doi:10.1002/lsm.20385 39. Bevilcqua FM, Zezell DM, Magnani R, da Ana PA, Eduardo Cde P (2008) Fluoride uptake and acid resistance of enamel irradiated with Er:YAG laser. Lasers Med Sci 23:141147. doi:10.1007/ s10103-007-0466-6