Diode laser irradiation and fluoride uptake in human teeth.
In most industrial countries, dental caries represents an important oral health problem. Dental caries is a multifactorial disease, which requires appropriate preventive modalities and oral hygiene education [Peterson et al., 2005]. Preventive modalities are mainly represented by a reduction of dietary cariogenic refined carbohydrates, use of improved plaque removal and oral hygiene techniques. In addition, use of systemic and topical fluoride applications [ref from Jack] , placement of pit and fissure sealants, use of fluoride releasing preventive and restorative materials, use of mouth rinses containing antimicrobials such as chlorexidine gluconate are all important.
Fluoride plays a very important role in dental caries prevention and it can arrest the progressive loss of dental enamel, induced by bacterial acid dissolution [Peterson and Lennon, 2004]. Fluoride works through three principal mechanisms:
* improving acid resistance of the enamel,
* enhancing remineralisation of incipient lesions,
* interfering with micro-organisms by inhibiting bacterial metabolism and enzymatic process.
When Fluoride ions (F-) substitute the hydroxyl groups (OH-), hydroxyapatite is transformed to fluorapatite, which is more stable and resistant to acid attack. For this reason, many clinical studies showed considerable caries reductions after fluoride applications [ten Cate and Featherstone, 1991; Helfenstein and Steiner, 1994; van Rijkom et al., 1998].
It is known that dental prevention with fluoride may be performed by systemic or topical applications, producing chemical and physical modifications of enamel surfaces [ten Cate and Featherstone, 1991; Robinson, 2009]. Several studies concluded that the combination of laser and topical fluoridation was more effective for increasing the fluoride uptake by enamel, so reducing its solubility to acids and increasing resistance to caries [Chin-Ying et al., 2004; Santaella et al., 2004; Tepper et al., 2004; Wiegand et al., 2005; Ana et al., 2006; Tagliaferro et al., 2007; Esteves-Oliveira et al., 2009].
According to a study carried out by Stern and Sognnaes  the application of lasers on dental hard tissues creates morphological and structural changes, increasing the acid resistance of the lased enamel and altering the acid resistance and permeability. The extent of these changes is affected by laser parameters (wavelength, energy output, exposure time, modality of laser irradiation emission) and by optical characteristics of the lased tissues (hydration condition, presence of chromophores, absorption coefficient). Since that early research, numerous studies have examined the combination of laser irradiation and topical fluoride application in order to verify if the laser energy could increase the resistance of dental structure to acid demineralisation [Featherstone et al., 1997; Chin-Ying et al., 2004; Tepper et al., 2004].
The combination of different types of lasers with topical fluoride has proven to be more effective than traditional methods, increasing resistance of the enamel to caries and reducing its solubility to acids. Importantly, the use of laser favours the incorporation of fluoride into enamel, not only on its surface as calcium fluoride (CaF2) but also within its crystalline structure [ten Cate, 1999; Featherstone and Fried, 2001; Nammour et al., 2003; Hsu et al., 2004; Villalba Moreno et al., 2007; Vlacic et al., 2007; Bevilacqua et al., 2008; Magalhaes et al 2008]. The aim of this study was to evaluate the treatment of fluoride in combination with diode laser and to investigate laser-induced compositional changes (contents in F-) in enamel after laser irradiation and topical fluoride application.
Materials and methods
A commercial gallium-aluminium-arsenide (GaAIAs) diode laser (KDL-10, KaVo, Biberach, Germany) with a wavelength of 809nm and a power of up to 10W was used, attached to a 400-[micro]m optic conductor fibre as transmission element. The study comprised 20 sound human premolars, extracted for orthodontic reasons. After extraction, the teeth were stored at 4[degrees]C in 0.1% thymol solution for no longer than 60 days. After removal of each root, teeth were randomly assigned to two groups: 1--control/fluoride; 2--diode laser. Teeth were sectioned into two halves longitudinally (disto-mesial) to obtain a total of 40 specimens. The enamel of each specimen was coated with acid-resistant varnish (Nail Polish, Yesensy, Madrid, Spain) with one window of 3x3mm of exposed enamel left.
To perform the different treatments on the same tooth, the two halves of each tooth of group 1 were assigned between:
* Group A--untreated control,
* Group B--amine fluoride gel (Elmex gel, 12500 ppm F, Gaba Int. AG, Basel, Switzerland) application (2 minutes) alone.
The two halves of each tooth of group 2 were assigned between:
* Group C--Elmex gel application immediately followed by diode laser (KDL-10, KaVo, Biberach, Germany) two treatments (20 seconds each) at 2W output,
* Group D--diode laser (KDL-10, KaVo, Biberach, Germany) two treatments (20 seconds each) at 2W output before amine fluoride gel (Elmex gel, 12,500 ppm F, Gaba Int. AG, Basel, Switzerland) application (2 minutes).
Enamel surfaces of groups C and D were laser-treated at a standard distance of 4mm, moving the fibreoptic in a uniform way over the fluoride-treated window for the corresponding time period. After treatment, specimens were stored in 1 M KOH solution at room temperature for 24 hours. Teeth were then triple rinsed (10 minutes each) with distilled water.
Fluoride chemical analysis. The fluoride uptake of superficial enamel was evaluated in specimens of each group by means of a fluoride ion-selective electrode (9609BNWP, Thermo Fisher Scientific, Boston, USA). Specimens were etched with 10 of 2M HCl for 10 secs. The liquid was then collected using paper points, subsequently transferred to a solution of 5 ml of water and 0.5 ml of TISAB III (Total Ionic Strength Adjustment Buffer--Thermo Fisher Scientific, Boston, USA) to measure the fluoride content using the fluoride electrode connected to a pH meter (Orion 420A, Thermo Fisher Scientific, Boston, USA). The electrical potential measurements (mV) read by the electrode were compared with a reference curve obtained using NaF standards (Thermo Fisher Scientific, Boston, USA). The temperature of solutions during the measurement was 21-23[degrees]C. The results were expressed in mg/l.
Fluoride chemical analysis. The chemical analyses performed using the fluoride ion-selective electrode showed that the mean amount + SD of fluoride uptake of teeth of group A was 1.55 [+ or -] 0.89 mg/l. Mean fluoride uptake increased sevenfold after fluoride gel treatment: 10.51 [+ or -] 3.38 mg/l for group B, up to 15 times after gel and laser treatment: 23.62 [+ or -] 3.58 mg/l for group C and was 22.7 [+ or -] 4.60 mg/l for group D (diode laser before fluoride application). The Kruskal Wallis test indicated a statistically significant effect of fluoridation with all three treatments (p<0.001). The SNK multiple comparison test indicated a statistically significant increase of fluoride uptake before and after all treatments, and also a statistically significant difference for laser treatment versus fluoride gel (Table 1).
According to the studies on laser and fluoride application, our results highlight that laser treatment increases the deposition of fluoride on the enamel surface, and it enhances the formation of apatitic fluoride [Ana et al., 2006]. These increases were significantly greater than those achieved by conventional topical fluoride and suggest that, related to the surface enamel layer, diode laser increases fluoride uptake when irradiated through topical fluoride application. In the literature, similar findings were reported when different laser wavelengths (C[O.sub.2], Argon, and Nd-Yag lasers) were applied on enamel surfaces during topical fluoride programs. Nevertheless, it is not possible to make comparisons with these different lasers, because the diode laser used had a lower coefficient of absorption by enamel [Haider et al., 1999; Hossain et al., 2002; Nammour et al., 2003; Hicks et al., 2004; Santaella et al., 2004; Villalba Moreno et al., 2007; Vlacic et al., 2007; Bevilacqua et al., 2008; Magalhaes et al 2008; Steiner-Oliveira et al., 2008].
Oho and Morioko  proposed a mechanism of fluoride uptake in laser treated enamel in that thermal effects of laser irradiation can produce surface alterations (such as increased roughness of the dental surface) and promote the retention and the incorporation of fluoride in enamel [Leamy et al., 1998]. This effect could explain the results of our research in which the laser treated groups resulted in a greater fluoride uptake compared with the group treated with fluoride alone. However, there was no significant difference between the groups lased before or after topical fluoridation gel. Probably, this is due to saliva, which plays an important role in fluoride exchange with enamel.
The topical fluoridation-diode laser combination seems to be a promising preventive measure for dental caries and it may be useful for the effective and immediate fluoridation of teeth.
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M.C. Vitale *, D. Zaffe **, A.R. Botticell ***, C. Caprioglio ****
Depts. of * Paediatric Dentistry, *** Human Pathology, School of Dentistry, University of Pavia, ** Biomedical Sciences, University of Modena and Reggio Emilia, **** Consultant in Pavia. Italy.
Postal address: Prox M.C. Vitale. Dept. of Paediatric Dentistry Faculty of Dentistry, University of Pavia, 2 Piazzale Golgi 27100 Pavia, Italy.
Table 1. Statistical significance in an evaluation of fluoride uptake by human dental enamel with and without use of a diode laser by post hoc Student-Newman-Keuls (SNK) multiple comparison test. Groups B C D A (Control) X X X B (Fluoride gel) - X X C (Laser after F-gel) - - - D (Laser before F-gel) X - - X = significant at p<0.05
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|Author:||Vitale, M.C.; Zaffe, D.; Botticell, A.R.; Caprioglio, C.|
|Publication:||European Archives of Paediatric Dentistry|
|Date:||Apr 1, 2011|
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