Laser-activated fluoride treatment of enamel as prevention against erosion

Transcription

1 ADRF RESEARCH REPORT Australian Dental Journal 2007;52:(3): Laser-activated fluoride treatment of enamel as prevention against erosion J Vlacic,* IA Meyers, LJ Walsh Abstract Background: Erosion is the loss of dental hard tissues from an acidic challenge, often resulting in exposure of dentinal tubules and hypersensitivity to environmental stimuli. Laser-activated fluoride (LAF) therapy with 488nm laser energy has been shown previously to increase the resistance of human enamel and dentine to acid dissolution. The aims of this study were to investigate the action spectrum of LAF in protecting tooth enamel from softening in response to an erosive challenge, and to examine for any temperature change with the treatment. Materials and Methods: Buccal and lingual surfaces of extracted sound molar and premolar teeth were used to prepare matched pairs of enamel slabs (N=10 per group). After application of 1.23% neutral sodium fluoride gel (12 300ppm F ion), slab surfaces were lased with 488, 514.5, 532, 633, 670, 830 or 1064nm wavelength (energy density 15J/cm -2 ; spot size 5mm), then exposed to an erosive challenge (1.0M HCl for five minutes). The Vicker s hardness number (VHN) was recorded before fluoride gel application and again following the acid challenge. Negative controls did not receive laser exposure. Results: All wavelengths of laser light examined provided a protective LAF effect against softening, compared with the negative control surfaces. Conclusion: From these findings, we conclude that the action spectrum of the LAF effect extends across the visible spectrum, providing protection to dental enamel from an erosive challenge. Key words: Laser, fluoride, erosion, enamel. Abbreviations and acronyms: LAF = laser-activated fluoride; VHN = Vicker s hardness number. (Accepted for publication 1 November 2006.) *Visiting Clinician, School of Dentistry, The University of Queensland, Brisbane. Professor of General Dental Practice, School of Dentistry, The University of Queensland, Brisbane. Professor of Dental Science, School of Dentistry, and Program Director, Centre for Biophotonics and Laser Science, The University of Queensland, Brisbane. INTRODUCTION Dental erosion can be defined as the physical results of a pathologic, chronic, localized loss of dental hard tissues that is chemically etched away from the tooth surface by acid and/or chelation without bacterial involvement. 1 The pathogenesis of erosion is multifactorial, 2 but the fundamental event is etching and progressive and irreversible loss of the enamel surface layer. 3 Acid dissolution of dental enamel (a mixture of carbonated-, hydroxy- and fluor-apatites) can then result in exposure of underlying dentine tubules, leading to hypersensitivity in response to environmental stimuli such as cold foods. 4,5 Preventive strategies for dental erosion are few and with the ageing of the population and greater retention of teeth, dental erosion is becoming a significant clinical concern. 1,3 Sognnaes and Stern 6 were the first to demonstrate increased enamel resistance to demineralization as a result of laser irradiation. Since then numerous studies have examined the process by which laser energy, either alone or in combination with topical fluoride therapies (laser-activated, LAF), increases the resistance of tooth structure to mineral loss from the organic acids involved in dental caries More recently we have shown 25 that this effect is achieved with a broad spectrum of laser light with comparable results to that of the traditional Argon ion laser. With an increase in incidence of dental erosion, and in light of the above findings, it was of interest to determine whether LAF therapy may also offer protective benefits against dental erosion, which typically involves stronger acids such as phosphoric and hydrochloric acids. No previous studies have examined systematically the action spectrum of LAF, using laser wavelengths in the visible and near infrared regions, as protection against dental enamel loss caused by a strong erosive challenge. Accordingly, the aim of the present study was to investigate the effectiveness of seven commonly available laser wavelengths, in terms of the LAF protective effect to an erosive challenge. Additionally, the authors also examined intra-pulpal temperature changes with each of the lasers. As softening of enamel is a key factor that links to its loss, we used microhardness measurements to assess the extent of protection afforded by LAF therapy. Australian Dental Journal 2007;52:3. 175

2 Table 1. Laser equipment and parameters Configuration Model and manufacturer Wavelength Power Exposure Power density (nm) (mw) time (sec) (mw/cm 2 ) Argon ion gas laser Sabre R Series Argon ion gas laser Sabre R Series KTP (Frequency doubled Nd:YAG) Nuvolase Smartbleach, ARC, Belgium InGaAsP diode laser SaveDent, Denfotex, UK InGaAs diode laser Omnilase, Laserdyne, Australia GaAs diode laser Omnilase, Laserdyne, Australia Nd:YAG dlase300, Sunrise Technologies, USA MATERIALS AND METHODS (a) Erosion challenge Enamel slabs were prepared from sound human molar and premolar teeth that had been extracted for orthodontic reasons, from a population without access to naturally or artificially fluoridated water. After debridement of gingival soft tissue remnants and prophylaxis with a fluoride-free paste, the lingual and buccal surfaces of the teeth were sectioned into slabs using a diamond saw. Each slab was then divided into two halves to provide matched pairs. The surfaces of the slabs were polished with 1200 grit silicon carbide paper, and the prepared samples stored in a humidor at room temperature until used. The surfaces were allocated randomly into treatment groups (N=10 per group as determined with power analysis). The baseline Vicker s hardness number (VHN) of each surface was determined using a mini-load hardness tester (Ernst Leitz). The test and control surfaces of every slab in every group were measured twice to determine an average. To ensure protection from fluoride exposure, the control half of the surfaces were coated with a clear nail varnish, and then covered with an opaque shield to prevent exposure to laser light. The test sides were covered with 100µL of 1.23% neutral sodium fluoride gel (Colgate NeutraFluor, ppm F ion) followed immediately by laser activation (spot size 5mm; energy density 15J/cm 2 ; as per Table 1). Table 1 specifies the various parameters used with each laser, such as wavelength, power, exposure time and power density. The energy density of 15J/cm 2 was used since this was shown to be the optimal value in previous studies. 7-10,12,25 As laser tips varied between different lasers the authors determined the vertical distance at which the 5mm spot size could be attained for each laser unit. Once all the individual vertical dimensions were determined each laser tip was mounted in a secure holder at the determined height ensuring the desired 5mm spot size. All lasers were used in continuous wave mode except the Nd:YAG laser, which could only be operated in free-running pulsed mode. A single laser exposure was used for all lasers, except for the KTP laser, for which the exposure was divided into two portions (30 seconds prior to fluoride application and 30 seconds after fluoride application), according to the protocol provided by the manufacturer. Immediately after laser treatment, the fluoride gel was rinsed from the enamel surfaces with deionized water, the protective varnish on the control side dissolved using acetone, and the surfaces rinsed with deionized water. The surfaces were then subjected to an acid challenge (1.0M hydrochloric acid for 5 minutes) to provide an erosive (corrosive) challenge sufficient to cause softening of the unprotected enamel. The VHN of both test and control surfaces, of every enamel slab, was then re-measured twice to determine an average measurement. (b) Temperature changes Temperature changes occurring during LAF treatment at the level of the dental pulp with each of the laser wavelengths used were also assessed. Sound extracted human premolar teeth underwent soft tissue debridement and a fluoride-free prophylaxis. Using a diamond saw the teeth were vertically sectioned in half and residues of the pulp tissue removed. To provide stability during testing the roots of the teeth were vertically mounted in plaster blocks up to their middle third. Temperature changes were measured using a miniature K-type thermocouple 0.5mm in diameter, which was placed in the pulp chamber of the tooth against the dentine immediately opposite the point of irradiation. The thermocouple was coated with silicone heatsink compound and was fixed firmly into place using miniature orthodontic separator elastic bands. Temperature measurements were recorded using a digital thermometer attached to a computer using an analogue-to-digital converter. RESULTS (a) Erosion challenge (i) Control groups The control slabs subjected to the erosion challenge without protection from LAF therapy demonstrated a Table 2. Reduction in Vicker s hardness values for the 7 control groups Laser type Wavelength (nm) Probability value Argon Argon KTP InGaAsP diode laser InGaAs diode laser GaAs diode laser Nd:YAG P values shown are for 1-tailed test. 176 Australian Dental Journal 2007;52:3.

3 Fig 1. Data for 488nm (Argon ion gas laser) control and treatment groups. Data sets for each slab are, in sequence, control slabs at baseline, control slabs after erosion challenge (showing softening), test slabs at baseline and test slabs after LAF treatment and erosion. The same sequence is used in the subsequent figures. Fig 4. Data for 633nm (InGaAsP diode laser) control and treatment groups. Please see Fig 1 caption for details. Fig 2. Data for 514.4nm (Argon ion gas laser) control and treatment groups. Please see Fig 1 caption for details. Fig 5. Data for 670nm (InGaAs diode laser) control and treatment groups. Please see Fig 1 caption for details. Fig 3. Data for 532nm (KTP laser) control and treatment groups. Please see Fig 1 caption for details. statistically significant reduction in hardness (Table 2, Figs 1 7), using the one sample paired t-test. The data sets were normally distributed. (ii) Treatment groups All of the LAF treatment groups showed a protective effect, with a statistically significant increase in VHN Fig 6. Data for 830nm (GaAs diode laser) control and treatment groups. Please see Fig 1 caption for details. from their baseline values (Table 3, Figs 1 7). The assumption of normality had to be met on the basis of the skewness normality, the kurtosis normality and omnibus normality. For 488nm, 532nm, 670nm and 830nm groups the normality was accepted and a one sample paired t-test was used for analysis of each group. For the 514nm, 633nm and 1064nm groups the normality was not met, and the data were analysed with the Wilcoxon Signed-Rank Test for Differences in Australian Dental Journal 2007;52:3. 177

4 Table 5. Intra-pulpal temperature changes during LAF therapy Wavelength Median temperature Minimum and maximum (nm) change temperature range ( C) Fig 7. Data for 1064nm (Nd:YAG) control and treatment groups. Please see Fig 1 caption for details. Table 3. Increase in Vicker s hardness values for the 7 treatment groups Laser type Wavelength (nm) Probability value Argon Argon KTP InGaAsP diode laser InGaAs diode laser GaAs diode laser Nd:YAG P values shown are for 1-tailed test. Medians. A value of =0.05 was used as the level for significance. As normality assumptions were not met by all groups a non-parametric test, Kruskal-Wallis Multiple Comparison Z-Value test, was used to compare the effectiveness of all of the wavelengths against each other. The mean effect of the 633nm laser was significantly different to the means of the 488nm and the 830nm, respectively (Table 4). Although both the 488nm laser and the 830nm laser were significantly different to the 633nm laser, they were not significantly different from each other. (b) Temperature change Data for temperature changes are shown in Table 5. With the Argon ion and Nd:YAG lasers, a small increase in the intra-pulpal temperature was noted, while with the KTP and diode lasers, a small decrease in intra-pulpal temperature was recorded. All temperature changes seen were considerably less than the accepted threshold value of 5.5 C for pulpal injury. DISCUSSION The pathogenesis of erosion is multifactorial in nature 2 and is influenced by intrinsic factors and extrinsic factors. 26,27 Brought on by etching and progressive and irreversible loss of the enamel surface layer, 3 the softened tooth structure is easily removed with mechanical stimuli 28 such as normal chewing and toothbrushing. Numerous studies have investigated the erosive potential of different substances and the influence of aetiological and physiological factors on the location and severity of erosion. 44,45 Factors such as protection by saliva and pellicle are known to influence the location of erosion lesions, 44,47,48 while the severity of the condition is affected by medical conditions including gastro-oesophageal reflux Preventive strategies for dental erosion are few, and for this reason greater efforts are required to address the increasing clinical problems posed by dental erosion. 1,3,49 The present study examined the success of LAF therapy using seven different laser wavelengths for conferring protection to tooth structure from an artificial erosion-like challenge. The results of this study build upon previous work which showed that laser energy in combination with topical fluoride therapies can increase the resistance of tooth structure to mineral loss from the organic acids involved in dental caries. 7-21,25 In this study, hydrochloric acid was used to simulate the strong acidic challenge encountered with gastro-oesophageal reflux. The findings show that irradiation of enamel with LAF therapy confers protection to the tooth structure from a strong erosive challenge. This protective effect was achieved with a wide spectrum of both visible and near- Table 4. Kruskal-Wallis Multiple Comparison Z-Value test Variable Argon ion gas Argon ion gas InGaAsP InGaAs GaAs KTP (488nm) (514.5nm) diode laser diode laser diode lase Nd:YAG Argon ion gas (488nm) * Argon ion gas (514.5nm) KTP InGaAsP diode laser * * InGaAs diode laser GaAs diode laser * Nd:YAG *Medians significantly differ if the z-value is > Australian Dental Journal 2007;52:3.

5 infrared wavelengths of laser energy with all showing a statistically significant increase in the enamel hardness. Several physico-chemical changes have been suggested to occur during LAF treatment, including deposition of calcium fluoride, 50 formation of microspaces in the dental hard tissue, 22,23 formation of tri-calcium phosphate, 24 and phase transformation of hydroxyapatite to fluorapatite. 20 The latter is more resistant to both strong (corrosive/erosive) acids as well as to weaker acids than the carbonated hydroxyapatite predominantly found in dental enamel. Tagomori and Morioka 21 have reported the enhanced uptake of fluoride after laser irradiation, while Goodman and Kaufman 51 found that laser irradiation of enamel results in superficial melting or dissolution of crystals, followed by cooling and recrystallization and incorporation of fluoride to form less soluble fluorapatite. Partial conversion of the enamel surface to fluorapatite would explain the hindrance in softening of the enamel found in our study. It must be recognized that the conditions used did not allow for any protective action of salivary buffers that may be encountered in the oral cavity. An additional point of interest is that in the present study, there was an erosion-protection effect in the visible green region. In contrast, a previous investigation using a caries-like challenge found that the 514.5nm wavelength offered little benefit, 8 which may reflect the difference in experimental model systems used. Thermal changes within enamel can explain the effects of the CO 2 laser, 24 but do not appear to be as apparent with the visible laser wavelengths. The present results suggest that minimal thermal events occur with LAF when undertaken at an energy density of 15J/cm 2. The study of Zach and Cohen 52 defined the temperature thresholds at which irreversible or reversible pulp damage occurred. Temperature rises above 5.5 C resulted in an unacceptable degree of pulpal necrosis. Below this temperature only mild and reversible pulpitis occurred, while below 2.5 C no histological changes to the pulpal tissue could be seen. Across the various laser treatment groups, temperature changes at the level of the dental pulp were generally less than 1.5 C, and thus no deleterious effects would be expected clinically. However, as these measurements were conducted on teeth sectioned in half, the situation in vivo may show changes of lesser magnitude due to increased heatsinking from dentine and the cooling effect of blood flow. CONCLUSION From these laboratory findings, it appears that there is a protective effect of LAF on dental enamel erosion. The action spectrum for this effect is relatively wide, and extends across the visible and near-infrared regions of the spectrum. Such changes may have clinical benefits in terms of improved protection to enamel for patients who are exposed to periodic erosive challenges from endogenous or exogenous acids. ACKNOWLEDGEMENTS The authors thank Dr Paul Meredith, Dr Steven Cooper and Professor Helena Rubinsztein-Dunlop for assistance with the argon ion laser segment of the study. This study was supported in part by the National Health and Medical Research Council of Australia and the Australian Dental Research Foundation Inc. REFERENCES 1. ten Cate JM, Imfeld T. Dental erosion, summary. Eur J Oral Sci 1996;104: Moss SJ. Dental erosion. Int Dent J 1998;48: McIntyre JM. Erosion. Aust Prosthodont J 1992;6: Cox CF. Etiology and treatment of root hypersensitivity. Am J Dent 1994;7: Bissada NF. Symptomatology and clinical features of hypersensitive teeth. Arch Oral Biol 1994;39 Suppl:31S-32S. 6. Sognnaes RF, Stern RH. Laser effect on resistance of human dental enamel to demineralization in vitro. J South Calif Dent Assoc 1965;33: Anderson JR, Ellis RW, Blankenau RJ, Beiraghi SM, Westerman GH. Caries resistance in enamel by laser irradiation and topical fluoride treatment. J Clin Laser Med Surg 2000;18: Westerman GH, Flaitz CM, Powell GL, Hicks MJ. Enamel caries initiation and progression after argon laser irradiation: in vitro argon laser systems comparison. J Clin Laser Med Surg 2002;20: Flaitz CM, Hicks MJ, Westerman GH, Berg JH, Blankenau RJ, Powell GL. Argon laser irradiation and acidulated phosphate fluoride treatment in caries-like lesion formation in enamel: an in vitro study. Pediatr Dent 1995;17: Hicks MJ, Flaitz CM, Westerman GH, Berg JH, Blankenau RL, Powell GL. Caries-like lesion initiation and progression in sound enamel following argon laser irradiation: an in vitro study. ASDC J Dent Child 1993;60: Lee CQ, Lemire DH, Jr., Cobb CM. Effects of CO 2 laser irradiation on tooth-root cementum. Gen Dent 1997;45: Blankenau RJ, Powell G, Ellis RW, Westerman GH. In vivo caries-like lesion prevention with argon laser: pilot study. J Clin Laser Med Surg 1999;17: Hicks MJ, Flaitz CM, Westerman GH, Blankenau RJ, Powell GL. Root caries in vitro after low fluence argon laser and fluoride treatment. Compend Contin Educ Dent 1997;18: , 550, 552; quiz Westerman GH, Hicks MJ, Flaitz CM, Blankenau RJ, Powell GL, Berg JH. Argon laser irradiation in root surface caries: in vitro study examines laser s effects. J Am Dent Assoc 1994;125: Stern RH, Sognnaes RF. Laser inhibition of dental caries suggested by first tests in vivo. J Am Dent Assoc 1972;85: Stern RH, Vahl J, Sognnaes RF. Lased enamel: ultrastructural observations of pulsed carbon dioxide laser effects. J Dent Res 1972;51: Nelson DG, Shariati M, Glena R, Shields CP, Featherstone JD. Effect of pulsed low energy infrared laser irradiation on artificial caries-like lesion formation. Caries Res 1986;20: Fox JL, Yu D, Otsuka M, Higuchi WI, Wong J, Powell G. Combined effects of laser irradiation and chemical inhibitors on the dissolution of dental enamel. Caries Res 1992;26: Hicks MJ, Flaitz CM, Westerman GH, Blankenau RJ, Powell GL, Berg JH. Enamel caries initiation and progression following low fluence (energy) argon laser and fluoride treatment. J Clin Pediatr Dent 1995;20: Meurman JH, Hemmerle J, Voegel JC, Rauhamaa-Makinen R, Luomanen M. Transformation of hydroxyapatite to fluorapatite by irradiation with high-energy CO 2 laser. Caries Res 1997;31: Australian Dental Journal 2007;52:3. 179

6 21. Tagomori S, Morioka T. Combined effects of laser and fluoride on acid resistance of human dental enamel. Caries Res 1989;23: Fowler BO, Kuroda S. Changes in heated and in laser-irradiated human tooth enamel and their probable effects on solubility. Calcif Tissue Int 1986;38: Oho T, Morioka T. A possible mechanism of acquired acid resistance of human dental enamel by laser irradiation. Caries Res 1990;24: Aminzadeh A, Shahabi S, Walsh LJ. Raman spectroscopic studies of CO 2 laser-irradiated human dental enamel. Spectrochim Acta A Mol Biomol Spectrosc 1999;55A: Vlacic J, Meyers IA, Kim J, Walsh LJ. Laser-activated fluoride treatment of enamel against an artificial caries challenge: comparison of five wavelengths. Aust Dent J 2007;52: Zero DT. Etiology of dental erosion extrinsic factors. Eur J Oral Sci 1996;104: Sheutzel P. Etiology of dental erosion intrinsic factors. Eur J Oral Sci 1996;104: Eisenburger M, Shellis RP, Addy M. Comparative study of wear of enamel induced by alternating and simultaneous combinations of abrasion and erosion in vitro. Caries Res 2003;37: Hughes JA, West NX, Parker DM, Newcombe RG, Addy M. Development and evaluation of a low erosive blackcurrant juice drink in vitro and in situ. 1. Comparison with orange juice. J Dent 1999;27: Hunter ML, West NX, Hughes JA, Newcombe RG, Addy M. Relative susceptibility of deciduous and permanent dental hard tissues to erosion by a low ph fruit drink in vitro. J Dent 2000;28: Bartlett DW, Coward PY. Comparison of the erosive potential of gastric juice and a carbonated drink in vitro. J Oral Rehabil 2001;28: Mok TB, McIntyre J, Hunt D. Dental erosion: in vitro model of wine assessor s erosion. Aust Dent J 2001;46: Gray A, Ferguson MM, Wall JG. Wine tasting and dental erosion. Case report. Aust Dent J 1998;43: Hunter ML, West NX, Hughes JA, Newcombe RG, Addy M. Erosion of deciduous and permanent dental hard tissue in the oral environment. J Dent 2000;28: Milosevic A, Kelly MJ, McLean AN. Sports supplement drinks and dental health in competitive swimmers and cyclists. Br Dent J 1997;182: Wiktorsson AM, Zimmerman M, Angmar-Mansson B. Erosive tooth wear: prevalence and severity in Swedish winetasters. Eur J Oral Sci 1997;105: Meurman JH, Harkonen M, Naveri H, et al. Experimental sports drinks with minimal dental erosion effect. Scand J Dent Res 1990;98: Eisenburger M, Addy M. Evaluation of ph and erosion time on demineralisation. Clin Oral Investig 2001;5: Rees JS, Davis FJ. An in vitro assessment of the erosive potential of some designer drinks. Eur J Prosthodont Restor Dent 2000;8: Lussi A, Kohler N, Zero D, Schaffner M, Megert B. A comparison of the erosive potential of different beverages in primary and permanent teeth using an in vitro model. Eur J Oral Sci 2000;108: West NX, Hughes JA, Addy M. Erosion of dentine and enamel in vitro by dietary acids: the effect of temperature, acid character, concentration and exposure time. J Oral Rehabil 2000;27: West NX, Hughes JA, Addy M. The effect of ph on the erosion of dentine and enamel by dietary acids in vitro. J Oral Rehabil 2001;28: Hughes JA, West NX, Parker DM, van den Braak MH, Addy M. Effects of ph and concentration of citric, malic and lactic acids on enamel, in vitro. J Dent 2000;28: Jarvinen V, Rytomaa I, Meurman JH. Location of dental erosion in a referred population. Caries Res 1992;26: Lussi AR, Schaffner M, Hotz P, Suter P. Dental erosion in a population of Swiss adults. Community Dent Oral Epidemiol 1991;19: Luo Y, Zeng XJ, Du MQ, Bedi R. The prevalence of dental erosion in preschool children in China. J Dent 2005;33: Dugmore CR, Rock WP. The prevalence of tooth erosion in 12- year-old children. Br Dent J 2004;196: Moazzez R, Bartlett D, Anggiansah A. Dental erosion, gastrooesophageal reflux disease and saliva: how are they related? J Dent 2004;32: Nunn JH. Prevalence of dental erosion and the implications for oral health. Eur J Oral Sci 1996;104: Westerman GH, Hicks MJ, Flaitz CM, Blankenau RJ, Powell GL. Combined effects of acidulated phosphate fluoride and argon laser on sound root surface morphology: an in vitro scanning electron microscopy study. J Clin Laser Med Surg 1999;17: Goodman BD, Kaufman HW. Effects of an argon laser on the crystalline properties and rate of dissolution in acid of tooth enamel in the presence of sodium fluoride. J Dent Res 1977;56: Zach L, Cohen G. Pulp response to externally applied heat. Oral Surg Oral Med Oral Pathol 1965;19: Address for correspondence/reprints: Dr Jelena Vlacic School of Dentistry The University of Queensland 200 Turbot Street Brisbane, Queensland j_vlacic@hotmail.com 180 Australian Dental Journal 2007;52:3.