This work aims was to correlate the changes in the optical attenuation coefficients obtained through the OCT technique with the values obtained in Knoop sectional microhardness tests over time in dental human enamel samples irradiated with the Nd: YAG laser and Acid Phosphate Fluoride (APF), aiming the prevention of caries lesions in vitro. After Ethical Committee approval, 160 enamel samples, obtained from 40 human tooth molars, were divided into 4 groups: Control group (where no treatment was performed); Fluoride group (APF - fluoride phosphate acidulated for 4 minutes); Fluoride-Laser group: APF followed by irradiation with Nd:YAG laser (DE = 84.9 J/cm2, contact mode, with the use of carbon paste as photoabsorver); Laser-fluoride group (irradiation with Nd:YAG laser followed by APF). The samples of all groups were subjected to pH cycling during 20 days. On days 5, 10, 15 and 20, 10 samples from each group were removed from the cycling for the Knoop sectional microhardness test. Two samples of each group, at each time, were randomly selected for the analysis with FTIR-ATR (Fourier transform infrared spectroscopy associated with attenuated total reflection technique). The analysis by ATR-FTIR showed changes in the chemical composition of the samples of the irradiated groups in relation to Control and Fluoride group. There was correlation between the values of sectional microhardness tests and the measured optical attenuation coefficient by OCT in irradiated dental enamel, showing that the association between fluoride application and Nd:YAG laser irradiation is an important tool for the prevention of tooth enamel demineralization.
Peri-implantitis is a destructive inflammatory process that affects the tissues that provide support to the dental implant, the bone and gingiva, and can lead to the loss of the implant. Among the treatments of this disease, the irradiation of the contaminated surface with high intensity lasers is considered a promising alternative; Thus, irradiation parameters must be correctly adjusted in order to promote an efficient and safe treatment. This study investigated the temperature changes at the implant-bone interface during simulated implant surface decontamination using an 808nm diode laser. Dental implants were inserted in bovine bone, in which an artificial periimplant bone defect was made. Access holes of 0.5mm diameter were drilled to allow the positioning of four Ktype thermocouples in different regions: T0 Implant-bone interface, T1 inside the implant, T2 In the bone defect, T3 In the apex of the implant. For laser irradiation, an optical fiber was used at a distance of 0.5mm from the implant surface, and the mean output power varied between 0.5 to 3.0W on both pulsed (PW) and continuous (CW) wave modes. Irradiations were performed by 60s, and the temperature rises were registered for a period of 180s. It was observed that the critical threshold of 47ºC was exceeded at T0, T1 e T2 thermocouples when irradiations were performed at 1.0W; for T3 thermocouple, the threshold was exceeded at 3.0W CW mode. For PW mode, the thermocouples T0, T1, T2 had the threshold exceeded at the power of 1,0W and for T3 the threshold was exceeded at 3.0W. Decontamination of implant surfaces using the diode laser did not excessively heat the implant-bone interface within the mean output power ranging from 0.5 to 1.0W; however, the temperature rise is critical when using the mean power of 0.5W CW and 1.0W PW. Thus, using the PW mode up to the power of 1W seems to be a promising parameter for a safe clinical application.
Laser Induced Breakdown Spectroscopy (LIBS) is a technique capable to perform elemental analyses of a variety of samples, independent of matter state. Other spectroscopy techniques may require a destructive and time-consuming sample preparation. On the other hand, LIBS is a less destructive technique with no (or considerably less) sample preparation, using a relatively simple experimental setup. LIBS also provides a multielement analysis into one single spectrum acquisition, applying a Nd:YAG short-pulsed laser to ensure the stoichiometry between the sample and the generated plasma. LIBS have been applied on the study of carious lesions using a Nd:YAG into its fundamental emission at 1064 nm. It was shown that ratio of P/Ca and Zn/Ca can be used to monitor the cariogenic process. Another minor elements, e.g. C and Cu, associated with bacteria biofilm were also measured with the Nd:YAG laser. The fundamental wavelength emission (1064 nm) of Nd:YAG is coincident with a hydroxyapatite transmission window and it may affect the result. In order to address this issue a study used the second harmonic of the Nd:YAG laser at 532 nm. It was show that it is also possible perform LIBS on carious lesion using the Nd:YAG at 532 nm. However, there is not a work direct comparing the LIBS at 532 nm and 1064 nm for carious lesion detection. So, the aim of this work was to investigate the influence of laser wavelength on the LIBS performance for carious lesion detection. In both cases the carious lesion was detected with the advantage of no interference with hydroxyapatite at 532 nm.
Considering the use of high intensity lasers for preventing dental caries, this blind in vitro study evaluated the compositional and fluorescence effects promoted by Nd:YAG laser (λ=1064 nm) when applied for prevention of progression of dentin caries, in association or not with topical application of acidulated phosphate fluoride (APF). Sixty bovine root dentin slabs were prepared and demineralized by 32h in order to create early caries lesions. After, the slabs were distributed into six experimental groups: G1- untreated and not submitted to a pH-cycling model; G2- untreated and submitted to a pH-cycling model; G3- acidulated phosphate fluoride application (APF); G4- Nd:YAG irradiation (84.9 J/cm2, 60 mJ/pulse); G5- treated with Nd:YAG+APF; G6- treated with APF+Nd:YAG. After treatments, the samples of groups G2 to G6 were submitted to a 4-day pH-cycling model in order to simulate the progression of early caries lesions. All samples were characterized by the micro-attenuated total reflection technique of Fourier transformed infrared spectroscopy (μATR-FTIR), using a diamond crystal, and by a fluorescence imaging system (FIS), in which it was used an illuminating system at λ= 405±30 nm. Demineralization promoted reduction in carbonate and phosphate contents, exposing the organic matter; as well, it was observed a significant reduction of fluorescence intensity. Nd:YAG laser promoted additional chemical changes, and increased the fluorescence intensity even with the development of caries lesions. It was concluded that the compositional changes promoted by Nd:YAG, when associated to APF, are responsible for the reduction of demineralization progression observed on root dentin.
Dental Transillumination (DT) is a technique for imaging internal structures of teeth by detecting infrared radiation
transmitted throughout the specimens. It was successfully used to detect caries even considering dental enamel and
dentin scatter infrared radiation strongly. Literature reports enamel’s scattering coefficient is 10 to 30 times lower than
dentin; this explain why DT is useful for imaging pathologies in dental enamel, but does not disable its using for imaging
dental structures or pathologies inside the dentin. There was no conclusive data in the literature about the limitations of
using DT to access biomedical information of dentin.
The goal in this study was to present an application of DT to imaging internal structures of dentin. Slices of tooth were
confectioned varying the thickness of groups from 0.5 mm up to 2,5 mm. For imaging a FPA InGaAs camera Xeva 1.7-
320 (900-1700 nm; Xenics, Inc., Belgium) and a 3W lamp-based broadband light source (Ocean Optics, Inc., USA) was
used; bandpass optical filters at 1000±10 nm, 1100±10 nm, 1200±10 nm and 1300±50 nm spectral region were also applied to spectral selection. Images were captured for different camera exposure times and finally a computational processing was applied. The best results revealed the viability to imaging dent in tissue with thickness up to 2,5 mm without a filter (900-1700nm spectral range). After these results a pilot experiment of using DT to detect the pulp
chamber of an incisive human tooth was made. New data showed the viability to imaging the pulp chamber of specimen.
The diagnosis of dental caries at an early stage enables the implementation of conservative treatments based
on dental preservation. Several diagnostic methods have been developed, like visual-tactile and radiographic
are the most commons but are limited for this application. The Optical Coherence Tomography is a technique
that provides information of optical properties of enamel, which may change due to the decay process. The
objective of this study was to evaluate the ability of OCT to detect different stages of demineralization of tooth
enamel during the development of artificial caries lesions, taking as a reference standard for comparison
sectional microhardness testing. Different stages of caries lesions were simulated using the pH cycling model
suggested Feathestone and modified by Argenta. The samples were exposed to 0 (control group), 5, 10, 15,
20 and 25 days at a daily regimen of three hours demineralization followed by remineralization during 20
hours. It was used an OCT system with at 930nm. Sectional images were generated in all lesion region. The
results obtained from the OCT technique presented similar behavior to microhardness, except for the group
25 days, due to inability to perform indentations reading in areas of more intense demineralization. A linear
relationship was observed between the OCT and microhardness techniques for detection of demineralization
in enamel. This relationship will allow the use of OCT technique in quantitative assessment of mineral loss
and for the evaluation of incipient caries lesions.
The use of laser for bone cutting can be more advantageous than the use of drill. However, for a safe clinical application,
it is necessary to know the effects of laser irradiation on bone tissues. In this study, the Fourier Transform Infrared
spectroscopy (FTIR) was used to verify the molecular and compositional changes promoted by laser irradiation on bone
tissue. Bone slabs were obtained from rabbit's tibia and analyzed using ATR-FTIR. After the initial analysis, the samples
were irradiated using a pulsed Er,Cr:YSGG laser (2780nm), and analyzed one more time. In order to verify changes due
to laser irradiation, the area under phosphate (1300-900cm-1), amides (1680-1200cm-1), water (3600-2400cm-1), and
carbonate (around 870cm-1 and between 1600-1300cm-1) bands were calculated, and normalized by phosphate band area
(1300-900cm-1). It was observed that Er,Cr:YSGG irradiation promoted a significant decrease in the content of water
and amides I and III at irradiated bone, evidencing that laser procedure caused an evaporation of the organic content and
changed the collagen structure, suggesting that these changes may interfere with the healing process. In this way, these
changes should be considered in a clinical application of laser irradiation in surgeries.
This study investigated the compositional and crystallographic changes on enamel when irradiated by Er,Cr:YSGG (λ=2.7μm, 8.5J/cm2) or Nd:YAG (λ=1064nm, 84.9J/cm2 associated with black coating), its resistance to demineralization when irradiation is associated with fluoride (APF-gel), and CaF2-like material formation and retention. Sample surfaces were analyzed by ATR-FTIR (4000-650cm-1, 4cm-1) resolution. Irradiation with Er,Cr:YSGG laser promoted a significant decrease on carbonate content of enamel. After
Nd:YAG irradiation, it was observed a significant decrease of carbonate and amides I and II. X-ray diffraction showed that both laser irradiations promoted formation of α-tricalcium phosphate and tetracalcium phosphate, and a significant increase on the crystal growth of the enamel apatite (ANOVA, p<0.05 was used for all analysis). These changes can explain the improved resistance of enamel to demineralization observed in the second part of the study, in which 240 enamel slices were divided in 8 groups, received 4 min of professional fluoride gel (APF-gel 1.23%F-) applied before or after irradiation. After treatments, the formation of calcium fluoride (CaF2) was determined. The remaining slabs of each group were submitted to a 10-day pH-cycling
model and, subsequently, enamel demineralization was evaluated by cross-sectional microhardness. Both lasers significantly reduced enamel demineralization (ANOVA, p<0.05), and the previous APF-gel application followed by laser showed the higher reduction of enamel demineralization. CaF2 formed before pH-cycling was
significantly higher in groups were APF was associated with laser irradiation. After demineralization, these groups also presented higher CaF2 retention in respect to isolated treatments (only APF or only laser), suggesting its anticaries potential.
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