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Laser-induced fluorescence to discriminate between a dental composite resin and tooth

Purpose. Investigation of laser-induced fluorescence of an experimental pigment (Flu) to discriminate between a filling and the tooth and its influence on the material properties of experimental dental composites. Materials and methods. Three experimental composites (EC) were manufactured. The stan- dard contained no Flu, Flu-0.5 contained 0.5%, Flu-1.0 contained 1%. To judge the extent of fluorescence, specimens and fillings placed in natural teeth were irradiated with an infrared laser (980nm, 120mW). Flexural strength, modulus of elasticity, depth of cure, water sorp- tion, solubility, and color (CIE- L * a * b * -values) were measured to investigate the influence of Flu on EC. ANOVA was calculated and the statistical significance was p <0.05. Results. Strong laser-induced green fluorescence was observed so that fillings and tooth structures were clearly discriminated. No influence of Flu on flexural strength and modulus of elasticity occurred. Water sorption and solubility were far below the limits of EN ISO 4049. Increasing Flu concentrations revealed minor but significant reduction of depth of cure, shifts to more white and red and less yellow. Significance. Flu provides laser-induced fluorescence allowing an easy discrimination between fillings and teeth. Flu did not severely influence the material laser tips
1. Introduction Esthetics is of major importance for contemporary restorative dentistry [1–5] . It is a great success that modern resin-based filling materials cannot be differentiated anymore from the hard tooth tissues. Although this is beneficial for the patient, it is problematic for the dentist since it is nearly impossible to see a filling or excess material with the naked eye [6–8] .To be able to discriminate between a cured and uncured esthetic resin-based material and hard tooth tissues when desired is advantageous because it would be possible to.
Furthermore, highly esthetic dental restorations also cause potential problems for forensic dentists who may find the fill- ings difficult to identify and hence include in postmortem odontograms. This has implications for the accuracy of dental identifications, particularly in situations where limited time is available for postmortem identification. Pretty et al. [9] pre- sented “Quantitative Light-induced Fluorescence (QLF)” as a new technique to detect small changes in enamel mineral content. Three publications were found describing experimental composites with fluorescing chemicals or glass fillers [6–8] . Tani et al. [7] used commercial light curing units and formed the exciting light by putting different filters in front of the light guide. Teeth and samples of commercial composites were irradiated and the excitation and fluorescence spec- tra were measured with a fluorescence spectrophotometer. Finally the fluorescence differences of tooth and compos- ite for the different excitation wavelengths were considered. Uo et al. [8] prepared an experimental composite by using an experimental rare-earth oxide-containing fluorescent glass filler. Fluorescence occurred when the material was irradi- ated with a purple LED (383nm) but could only be seen in the dark. Rheinberger et al. [6] described in their inven- tion, the use of certain fluorescing dyes as, for example, derivates of coumarin, phthalimide, fluoranthene, xanthene, thioxanthene, and others. The irradiation was done with com- mercially available light curing devices. The fluorescence was only seen in the dark and when the interfering light of the curing device was cut off with appropriate light filters. All the aforesaid approaches are very awkward and involved con- sidering the necessary material modifications and practical aspects. dental laser handpiece
2. Materials and methods Three experimental resins with the same base formulation ( Table 1 ) were prepared. The experimental fluorescent pig- ment (Flu) was added in an amount of 0.5% (Flu-0.5) and 1.0% (Flu-1.0) to two of these resins ( Table 1 ). The third one did not contain Flu and was considered as the standard. Flu is an inorganic colorless white powder mainly based on sulfides and oxides of Yttrium, Ytterbium and Erbium. Flu provides fluorescence at a wavelength of 980nm when irradi- ated with an infrared laser (120mW, 980nm, RLDH980-120-3, Roithner Laser, Vienna, Austria). A quartz-tungsten halogen curing device (Spectrum 800, Dentsply DeTrey GmbH, Kon- stanz, Germany) with a 10mm diameter light guide was used to polymerize the materials with the constant polymeriza-tion mode. After each series of 10 specimens was cured, the output of the curing device was tested with a radiometer (Optilux radiometer, Kerr-Sybron GmbH, Karlsruhe, Ger- many).  Light  densities  between  480  and  500mWcm − 2 were measured and no decrease in the output could be observed.