The aim of this research is related with the diagnosis of caries by use of a laser. We study the fundamental characterization of the diagnosis method using both fluorescence and Raman scattering spectroscopy. We try to evaluate the possibility of the caries diagnosis using Raman spectroscopy and its clinical application. We focus on the PO34- ion that flows out with the dissolution of hydroxyapatite (HAp), and the fluorescence that increases in connection with caries. The Raman line of P-O vibration is overlapped on the continuous, background spectrum by fluorescence. Consequently, we try to find out the correlation between a healthy part and a carious part by analyzing both fluorescence and Raman spectra. It was found that Raman intensity of HAp at carious lesion was weaker than those of healthy parts and the florescence intensity at the same portions was stronger. We have obtained the feasibility to estimate the degree of caries and health condition by deriving the ratio between Raman and florescence intensity. And the trial measurements in vivo were carried out to verify the availability of the method by using a fiber probe type multi channel Raman spectrometer. The process of remineralization is under researching for the development of preventive medicine.

The variety of optical spectroscopic techniques is used for chemical analysis of normal and carious tissues. Polarization light microscopy, fluorescence spectroscopy/microscopy, Raman and IR spectroscopy/microscopy all provide valuable information on the tooth structure and chemical composition; however, near-IR laser-induced fluorescence measurements proved to be the most efficient indicator of bacterially infected tooth.

Early dental caries result from destruction of the tooth's outer mineral matrix by acid-forming bacteria found in dental plaques. Early caries begin as surface disruptions where minerals are leached from the teeth resulting in regions of decreased mineral matrix integrity. Visually, these early carious regions appear as white spots due to the higher backscattering of incident light. With age these areas may become stained by organic compounds. Optical coherence tomography (OCT) examination of human teeth demonstrates a difference in penetration depth of the OCT signal into the carious region in comparison with sound enamel. However, while OCT demonstrates a structural difference in the enamel in the region of the caries, this technique provides little insight into the source of this difference. Raman spectroscopy provides biochemical measures derived from hydroxyapatite within the enamel as well as information on the crystallinity of the enamel matrix. The differences in the biochemical and morphological features of early caries and intact sound enamel are compared. Histological thin sections confirm the observations by OCT morphological imaging while Raman spectroscopy allows for biochemical identification of carious regions by a non-destructive method. Visual examination and conventional radiographic imaging of the intact tooth are used in clinical assessment prior to optical measurements. The combination of OCT, Raman spectroscopy and thin section histology aid in determining the changes that give rise to the visual white spot lesions.

Previous studies have demonstrated that Polarization Sensitive Optical Coherence Tomography (PS-OCT) can be used to image early dental caries. The purpose of this study was to compare the measured reflectivity of natural caries lesions with the mineral loss measured using digital microradiography. An all polarization-maintaining fiber based PS-OCT system operating at 1310-nm was used to acquire polarization resolved images of natural white spot lesions and pigmented lesions on the smooth surfaces of extracted teeth. There was a strong positive correlation between the increase in the integrated reflectivity in the perpendicular polarization axis of the PS-OCT system and the increase in the integrated mineral loss or lesion severity for both white-spot and pigmented lesions, P <0.001. Therefore, PS-OCT is well-suited to assess the severity of natural caries lesions and resolve the internal structure of early caries lesions for the potential assessment of the lesion activity.

The aim of this study was to investigate the effects of high refractive index liquids on PS-OCT imaging of dental enamel. Several biocompatible agents such as propylene glycol and glycerol that have been proposed or utilized for soft tissue OCT experiments (skin and GI mucosa) were applied to the occlusal surfaces of sound and carious teeth. This study determined that the application of high refractive index liquids increased penetration depth in sound enamel to a greater degree than dried or water moistened samples. The results also demonstrated that image contrast between sound and carious enamel is dependent on the viscosity of the liquid and the degree of porosity of the carious lesion. The use of liquid agents with different viscositites in PS-OCT imaging may help determine the severity and depth of caries lesions in the occlusal pits and fissures.

Recently, it was documented that the combined treatment of fluoride and laser can induce an even greater increase in caries resistance than laser or fluoride treatment alone. However, the real mechanisms remained unclear. The aim of our present pilot study is to characterize the crystallographic changes in the human enamel treated with fluoride (F), laser (L), and combined fluoride-laser (LF) therapies using Micro-XRD and Micro-FTIR, so as to elucidate the true mechanisms of the combined effects of fluoride and Er:YAG laser on human enamel. Three sound human teeth were selected and 3 windows were created on each tooth surface. The 3 windows were later subjected to the F or L or LF treatment, respectively. The Micro-XRD patterns for the 9 windows were recorded before and after the treatments. Three sections from another 3 sound human teeth were selected for Micro-FTIR investigation and 3 windows were created on the cut surface of each section. The 3 windows were later subjected to the F or L or LF treatment, respectively. The FTIR patterns for the 9 windows were recorded before and after the treatments. The results revealed that both the LF and L treatments caused the contraction in the a-aixs and the improvement in the enamel crystallinity. Though the difference in the a-axis contraction between the LF and L-treated windows was not very significant (0.006Å), this crystallographic change might suggest more than 34% decrease in the enamel solubility. In conclusion, both the L and LF therapies may improve the crystalline stability and thus acid resistance of human enamel.

Background and Objective: The surface modification of root dentin by mid-infrared (MIR) pulsed-laser irradiation is a potential candidate for non-invasive treatment to prevent root surface caries. The purpose of this study is to compare the relative acid resistance of root dentin treated with an MIR Free Electron Laser emitting at between 9.0 μm and 9.7 μm. Study Design/Materials and Methods: The average power density was varied over the range 7.5-51.5 W/cm2. After irradiation, the samples were immersed in a 0.1 M lactic acid solution. Acid resistance was estimated as the quantity of Ca dissolved in the solution after immersion times (tim) of 1-22 h. Results: The acid resistance of all samples increased markedly, but only until tim = ~3 h. It did not depend significantly on the laser parameters used. Conclusion: The surface modification of root dentin leads to improved acid resistance, but this only persists for a few hours and therefore represents a poor treatment for root surface caries.

Several prior studies have shown that pretreatment of dental enamel by specific carbon dioxide laser conditions inhibited subsequent acid dissolution of the outer several μm of dental enamel. An initial low dissolution rate was followed by a return to the non-irradiated control dissolution rate from deeper regions. The aim of the present study was to examine the dissolution profiles following irradiation using 60 pulses per spot rather than the previously used 10 or 25. Bovine enamel blocks were irradiated at a wavelength of 9.6 μm at either 20 or 60 pulses per spot with a 20 μs pulse duration carbon dioxide laser using overlapping spots, and a fluence of 1.0 J/cm². Dissolution profiles were measured in acetate buffer, versus non-irradiated controls. The higher number of pulses per spot produced a similar initial low dissolution rate, but the effect was deeper than with 20 pulses per spot. Supported by NIH/NIDCR grant DE 09958.

The Er:YAG laser at 2940 nm has been proposed for use in dental cavity preparation and removal of carious enamel and dentin. The purpose of the present study was to determine the effect of the Er:YAG laser ablation in treating dental caries after a period from 5 to 11 years. For this study, 133 cavities were chosen, and for their reparation of it the three restorative materials were used. Baseline examination was made in the following intervals: one week, 1 year, and from 5 to 11 years after cavity preparation and placement of filling material. Clinical assessments were carried out in accordance with the US Public Health Service System. The follow-up included: the marginal ridge, marginal adaptation, anatomic form, caries, color match, cavo surface margin discoloration, surface smoothness, and postoperative sensitivity. Er:YAG laser ablation is an excellent method for treating frontal teeth, i.e., incisors, canines, premolars, and initial occlusal caries of molars. However, visual control of non-contact therapy is necessary. Er:YAG laser ablation is safe, and it strongly reduces pain. The laser treatment markedly decreases the unpleasant sound and vibration.

We present finite element models of human dental enamel that account for water-pores known to exist in this material, and use them to assess the influence of these pores on the temperature and stress profiles during and after single Er:YAG (2.9 micrometer) and CO₂ (10.6 micrometer) laser pulses of duration 0.35 microsec. Our results indicate that the temperature maximum is reached at the water-pores at the end of the laser pulse; this maximum seems to be independent of pore size for the CO₂ laser but appears to be strongly dependent of pore size for the Er:YAG laser. The pressure reached at the water pore seems to be directly related to the temperature at the pore and it is significantly higher that the stress levels reached throughout the modelled structure, which indicates that water pores should play a significant role in the ablation mechanisms, even before water vaporization takes place. These results suggest that researchers conducting enamel ablation by Er:YAG lasers - or other lasers with wavelengths for which the absorption coefficients of the mineral and the water differ significantly - may want to select their samples and analyse their results taking into account factors that may alter the degree of mineralization of a tooth, such as age or type of tooth.

In order to achieve esthetic dental restorations, there should be no visible difference between restorative material and treated teeth. This requires a match of the optical properties of both restorative material and natural teeth. These optical properties are determined by absorption and scattering of light emerging not only on the surface but also inside the material. Investigating different dental composites in several shades, a method has been developed to calculate the optical parameters absorption coefficient μa, scattering coefficient μs, anisotropy factor g and reduced scattering coefficient μs'. The method includes sample preparation and measurements of transmittance and reflectance in an integrating sphere spectrometer, followed by inverse Monte Carlo simulations. Determination of optical properties is more precise and comprehensive than with the previously used Kubelka Munk theory because scattering can be looked at separated into pure scattering with the scattering coefficient μs and its direction with the anisotropy factor g. Moreover the use of the inverse Monte Carlo simulation not only minimizes systematic errors and considers the scattering phase function, but also takes into account the measuring geometry. The compilation of a data pool of optical parameters now enables the application of further calculation models as a basis for optimization of the composition of new materials. For example, a prediction of the general color impression for multiple layers can be carried out as well as the calculation of the wavelength dependent penetration depths of light with regard to photo polymerization. Further applications are possible in the area of laser ablation.

Photo-cured dental composites are widely used in dental practices to restore teeth due to the esthetic appearance of the composites and the ability to cure in situ. However, their complex optical characteristics make it difficult to understand the light transport within the composites and to predict the depth of cure. Our previous work showed that the absorption and scattering coefficients of the composite changed after the composite was cured. The static Monte Carlo simulation showed that the penetration of radiant exposures differed significantly for cured and uncured optical properties. This means that a dynamic model is required for accurate prediction of radiant exposure in the composites. The purpose of this study was to develop and verify a dynamic Monte Carlo (DMC) model simulating light propagation in dental composites that have dynamic optical properties while photons are absorbed. The composite was divided into many small cubes, each of which had its own scattering and absorption coefficients. As light passed through the composite, the light was scattered and absorbed. The amount of light absorbed in each cube was calculated using Beer's Law and was used to determine the next optical properties in that cube. Finally, the predicted total reflectance and transmittance as well as the optical property during curing were verified numerically and experimentally. Our results showed that the model predicted values agreed with the theoretical values within 1% difference. The DMC model results are comparable with experimental results within 5% differences.

A fundamental understanding of how near-IR light propagates through sound and carious dental hard tissues is essential for the development of clinically useful optical diagnostic systems, since image contrast is based on changes in the optical properties of these tissues upon demineralization. The optical properties of enamel can be quantitatively described by defining the optical constants, the absorption and scattering coefficients, and the scattering phase function. Our aim was to measure the optical scattering properties of natural enamel caries. Near-IR attenuation measurements and angular-resolved goniometer measurements coupled with Monte Carlo simulations were used to determine the optical properties of natural lesions. An ultra-high resolution digital microradiography system was used to quantify the lesion severity by measurement of the relative mineral loss for comparison with optical scattering measurements. Natural demineralization increases the scattering coefficient more than two orders of magnitude at 1310-nm and the scattering is highly forward directed.

The effectiveness of Bacteriotoxic light therapy (BTL) in many respects depends on the right choice of the photo sensitizer and used parameters of laser radiation. Experimental studies in vitro have revealed the presence of correlation dependence between the photo sensitizer Radachlorine, energy density, irradiation duration executed with low energy diode laser and the number of viable bacterial cells causing the development of inflammatory affection of oral cavity. BTL in parameters defined in the experiments develops bactericidal action on pathogenic microflora of oral cavity.

Results of in vivo experiments have shown the maximum effectiveness of combined use of photo sensitizer 0,1% gel Radachlorine simultaneously with continuous and super pulse low energy irradiation of the diode laser with energy density 400 J/cm², and power 1W. Given parameters have lead to complete elimination of Streptococcus pyogenes from inflammation foci in oral cavity of experimental animals.

Dental enamel manifests high transparency in the near-IR. Previous work demonstrated that near-IR light at 1310-nm is ideally suited for the transillumination of interproximal dental caries (dental decay in between teeth) [1]. However, most new dental decay occurs in the pits and fissures of the occlusal (biting) surfaces of posterior teeth. These caries lesions cannot be detected by x-rays during the early stages of decay due to the overlapping topography of the crown of the tooth. In this study, a near-IR imaging system operating at 1310-nm was used to acquire occlusal images by launching the near-IR light into the buccal surface of the tooth just above the gingival margin (gum-line). The near-IR light diffuses through the highly scattering dentin providing uniform back illumination of the enamel of the crowns allowing imaging of the occlusal surfaces. The near-IR images show high contrast between sound and demineralized areas. Demineralization (decay) can be easily differentiated from stains and pigmentation. Moreover, the high transparency of the enamel enables imaging at greater depth for the detection of subsurface decay hidden under the enamel. These early images suggest that the near-IR offers significant advantages over conventional visual, tactile and radiographic caries detection methods.

Last year we demonstrated that thermal damage to dentin could be minimized by using Q-switched Er:YSGG laser pulses shorter than the thermal relaxation time of the deposited laser energy in conjunction with a layer of water added to the tissue surface before ablation. This resulted in significantly higher bond strengths of composite resin to laser treated dentin surfaces. Unfortunately, Q-switched erbium laser pulses cause strong acoustic effects and sound waves that are potentially irritating to the clinician and patient. The objective of this study was to investigate the influence of slightly longer Er:YAG laser pulses that avoid the undesirable acoustic effects on the bond strength of composite to laser prepared dentin surfaces. The surfaces of human dentin samples were irradiated by Er:YAG lasers operating with pulse durations of 0.5-μs, 20-μs, and 200-μs. A motion control system and a pressurized spray system incorporating a microprocessor controlled pulsed nozzle for water delivery, were used to ensure uniform treatment of the entire surface. Shear bond testing was used to evaluate the adhesive strength in order to assess the suitability of laser treated surfaces for bonding. High bond strengths with minimal peripheral thermal damage were achieved using 20-30μs Er:YAG laser pulses.

FT-Raman spectroscopy was used to investigate the influence of the Er:YAG laser irradiation into the human dentin structure. Polished dentin disks with 4mm thickness from six third molars were irradiated with Er:YAG laser. The dentin disks were prepared by polishing through a series of SiO2 papers with water and cleaned by ultrasonic system. Four pretreatment were performed. The disks were etched with 37% phosphoric acid for 15 s (control group), Er:YAG laser 80mJ, 3Hz, and 30s. (Group I), Er:YAG laser 120mJ, 3Hz, 30s. (Group II) and Er:YAG laser 180mJ, 3Hz, and 30s. (Group III). The FT-Raman spectra obtained from normal and treated dentin were analyzed. Attention was paid to the inorganic and organic dentin component (961, 2941cm-1). FT-Raman spectroscopy showed that the mineral and organic content were less affected by the acid etching and by the Er:YAG laser irradiation with 80mJ. Pulse energies of 120 and 180mJ showed to produce more reduction in the organic and inorganic content associated with more reduction in the peak areas at 961 and 2941cm-1. FT-Raman spectroscopy provided information of dentin chemical constituents with non-chemical sampling preparation.

Autofluorescence of healthy and inflamed human pulpal tissues was observed by confocal laser microscopy. In this preliminary study, photodynamic diagnosis (PDD) was applied to diagnose pulpal disease. The ability to accurately diagnose pulpal pathology prior to pulpectomy would be very beneficial. Clinically, however, we are unable to perform biopsy to detect pathological changes. Therefore, this study was performed using healthy, acutely and chronically inflamed human pulpal tissues to detect pathological changes in pulpal tissues. Following excision, pulpal tissues were rapidly frozen and standard cryosections were prepared. Autofluorescence of pulpal tissues was observed using a confocal laser microscope to examine whether there were any differences in autofluorescence intensities between healthy and inflamed pulpal tissues. Several combinations of excitation and detection wavelengths were tested to observe autofluorescence from pulpal tissues; the excitation wavelengths ranged from 488nm to 633nm, and the detection wavelengths were longer than 505 nm. Autofluorescence was detected in both healthy and inflamed groups. With this technique, it may be possible to diagnose pulpal pathology without biopsy, and might be applicable to photodynamic diagnosis (PDD) and photodynamic therapy (PDT) in root canal treatment.

Raman spectroscopy of oral tissues is a promising tool for in vivo diagnosis of oral pathologies, due to the high chemical and structural information content of Raman spectra. However, measurements on biological tissues are usually hindered by low level signals and by the presence of interfering noise and background components due to light diffusion or fluorescence processes. Numerical methods can be used in data analysis, in order to overcome these problems. In this work the wavelet multicomponent decomposition approach has been tested in a series of micro-Raman measurements performed on “in vitro” animal tissue samples. The experimental set-up was mainly composed by a He-Ne laser and a monochromator equipped with a liquid nitrogen cooled CCD equipped with a grating of 1800 grooves/mm. The laser light was focused on the sample surface by means of a 50 X optical objective. The resulting spectra were analysed using a wavelet software package and the contribution of different vibration modes have been singled out. In particular, the C=C stretching mode, and the CH2 bending mode of amide I and amide III and tyrosine contributions were present. The validity of wavelet approach in the data treatment has been also successfully tested on aspirin.

Enamel components are related to enamel caries susceptibility, thus, non-destructive techniques to be used in selecting homogeneous dental enamel have been studied. This study aimed to determine the enamel components that make it more susceptible to in vitro demineralization. Fourier transform Raman Spectroscopy (FTRS) was used to verify the relative amounts of organic material and enamel mineral before and after being submitted to an 8-day pH cycling model. FTRS was performed in 30 enamel slabs, which were subsequently demineralized; next, the slabs were again analyzed by FTRS. The cross-section microhardness was performed for mineral loss (ΔZ) quantification. Slabs that presented the greatest differences in the caries development pattern, considering the ΔZ mean obtained (ΔZ=1,510.1±623.4; n=30), were selected in order to constitute 2 groups with statistically different ΔZ values, more demineralized group (MDG) and less demineralized group (LDG), which had ΔZ=2,368.9±421.7a and ΔZ=909.2±229.2b (n=8), respectively. The differences between both MDG and LDG, regarding enamel components (phosphate, carbonate and organic matrix) determined by FTRS before and after pHC, were accessed by t test (significance level=0.05). The results showed that all groups presented fewer carbonate and organic contents after demineralization. LDG showed no difference in phosphate content before and after pHC. Before pHC, MDG carbonate content was statistically greater than the one found in LDG. The presence of a correspondent calcium fluoride band was not observed in enamel spectrum. In conclusion, only carbonate quantity influenced enamel susceptibility to in vitro demineralization and FT-RAMAN is an appropriate technique to select homogeneous enamel samples.

The purpose of this study was to evaluate the morphological changes in cavities made by Er:YAG laser (2.94μm)(KaVo KEY 3)(LELO-FOUSP) and high-speed drill. Cavities were made on the buccal and lingual surfaces of 27 human molars (Banco de Dentes-FOUSP), using different laser parameters (n=3): G1-15Hz/160mJ enamel/ 6Hz/200mJ dentin; G2-15Hz/180mJ enamel/ 6Hz/200mJ dentin; G3-15Hz/160mJ enamel/ 6Hz/250mJ dentin; G4-15Hz/180mJ enamel/ 6Hz/250mJ dentin; G5-15Hz/180mJ enamel/ 10Hz/180mJ dentin; G6-15Hz/160mJ enamel/ 10Hz/180mJ dentin; G7-15Hz/160mJ enamel/ 10Hz/160mJ dentin; G8-15Hz/180mJ enamel/ 10Hz/160mJ dentin and G9-high-speed drill. Samples were fixed (2.5% glutaraldhyde, 12h, 4°C), dehydrated (25-100% ethanol), dried to a critical point and sputter-coated with gold for analysis under SEM. All laser parameters used showed no evidence of thermal damage and signs of burning and melting, Er:YAG laser ablated dental hard tissues, showing enamel prisms, like scales, dentin surface without smear layer and opened dentinal tubules. It was concluded that Er:YAG laser parameters were effective for ablation of hard tissues, promoting morphological changes in irradiated tissues, creating an irregular and microretentive morphological pattern.

The aim of this study was to evaluate the tensile strength of different adhesive systems to primary tooth dentin prepared by high-speed drill and Er:YAG laser (2.94μm). Buccal surfaces of 38 primary canines were ground and flattened with sand paper disks (#120-600 grit) and distributed into five groups (n=15): G1: diamond bur in high-speed drill (HD)+ 35% phosphoric acid (PA)+Single Bond (SB); G2: HD+self-etching One Up Bond F (OUB);G3: Er:YAG laser (KaVo 3- LELO-FOUSP)(4Hz, 80mJ, 25,72J/cm2) (L)+PA+SB, G4: L+SB, G5: L+OUB. The inverted truncated cone samples built with Z-100 composite resin after storage in water (37°C/24h) were submitted to tensile bond strength test on Mini Instron 4442 (0.5mm/min, 500N). The data were analyzed with ANOVA and Tukey Test (p<0.05). The mean (MPa) were: G1-3.18(±1.24); G2-1.79(±0.73); G3-3.17(±0.44); G4-8.29(±1.86); G5-7.11(±2.07). The data analyzed with ANOVA and Tukey Test showed that Laser associated with PA+SB, SB or OUB lead to increased bonding values when compared to HD+PA+SB and HD+OUB (p=0.000), L+SB showed higher values than L+PA+SB and L+OUB (p=0.0311). Er:YAG laser radiation promoted significant increase of bond strength of different adhesive systems evaluated in the dentin of primary teeth.

Cervical microleakage was evaluated in sealed root canals previously treated with Er:YAG and Nd:YAG lasers. Ninety-two single-rooted maxillary human canines were prepared with the crown-down technique and irrigated with distilled and deionized water. The samples were distributed randomly into 9 groups of 10 teeth each. One tooth was used as a positive control and one as a negative control. In group I, 1.2 ml of EDTAC was applied during 5 min. In groups II to V, radicular dentine was irradiated with Er:YAG laser (Opus 20, Opus Dent, Israel) at the following parameters: 200 mJ and 8 Hz, 200 mJ and 16 Hz, 400 mJ and 8 Hz, or 400 mJ and 16Hz, respectively, for 60 s. In groups VI to IX, radicular dentine was irradiated with Nd:YAG laser (Fotona Medical Lasers, Slovenia) at 10 Hz and 1 W, 10 Hz and 2 W, 15 Hz and 1 W, or 15 Hz and 2 W, respectively, for 60 s. The canals were then sealed by the lateral condensation technique with an epoxy resin-based sealer. The roots were immersed in India ink for 15 days and then cleared to visualize the level of cervical microleakage with a measurement microscope. The results were evaluated by the Kruskal-Wallis test, which showed no statistical significance (p>0.01) for parameter variations of the Er:YAG laser when compared to the control group. However, the increase in frequency and potency for Nd:YAG laser decreased the microleakage when compared to the control group.

The uniformity of laser treated hard tissue surfaces depends on the laser beam quality and the degree of spatial overlap between adjacent laser pulses. Since the surface roughness or surface topography is expected to influence adhesion, our aim in this study was to assess the influence of the surface topography on the adhesion of composite to both enamel and dentin treated at the optimal conditions for the efficient ablation of those tissues with the Er:YAG laser. Human dentin and bovine enamel samples were uniformly irradiated by an Er:YAG laser operating with a pulse duration of 20-30-μs. The laser pulses were 300-μm in diameter with the laser operating in a single TEM00 transverse mode, and the distance between laser spots was varied from 50-200-μm. A motion control system and a pressurized spray system incorporating a microprocessor controlled pulsed nozzle for water delivery, were used to ensure uniform treatment of the entire surface. Shear bond testing was used to evaluate the adhesive strength in order to assess the suitability of laser treated surfaces for bonding. The effect of the degree of overlap of adjacent laser pulses on the surface roughness and the shear bond strength of composite to enamel and dentin is reported.