Luciano Bachmann

To simulate light propagation in human skin irradiated with laser sources emitting at 660 nm, 830 nm, and 904 nm, using different beam diameters and divergences, in order to characterize the internal fluence rate distribution profiles within the tissue. Monte Carlo simulations were performed using the GPU-accelerated MCX platform. Optical properties (absorption and reduced scattering coefficients) were experimentally obtained from human skin samples and incorporated into a three-dimensional voxel-based model. Laser parameters, including output power, beam radius, and divergence, were experimentally characterized and used as input for simulations. The effects of wavelength, beam divergence, and source radius on axial and spatial fluence rate distribution were quantitatively evaluated under controlled power conditions. All wavelengths exhibited exponential attenuation with comparable depth-dependent behavior within the first millimeters of tissue. Beam radius significantly modulated surface peak fluence rate and central-axis magnitude at depth under constant total power. In contrast, real divergence values typical of commercial devices produced minimal changes in axial fluence under contact-mode conditions, whereas large theoretical divergence angles markedly reduced fluence retention and increased lateral spread. Among the investigated variables, beam radius exerted the strongest influence on subsurface fluence magnitude under constant power, whereas wavelengths within the therapeutic window (660–904 nm) showed comparable attenuation behavior in superficial tissue. Realistic divergence values typical of commercial devices minimally affected axial fluence under contact-mode conditions, while larger angular spreads significantly reduced central-axis fluence retention.

This study evaluated whether an experimental chitosan hydrogel loaded with amine-functionalized nanohydroxyapatite could reduce dentin demineralization and promote remineralization in an in vitro GERD model. A total of 176 bovine dentin specimens were initially eroded with hydrochloric acid and distributed into four treatment groups: untreated control, chitosan gel, experimental hydrogel, and 4% TiF4 varnish, with or without abrasion. The specimens were then exposed to liquid or gaseous hydrochloric acid for 6 days. Remineralization intensity and depth were assessed by swept-source OCT, surface morphology by scanning electron microscopy, and chemical changes by µ-Ramam spectroscopy.OCT showed that the experimental hydrogel produced the highest brightness and greatest mineralized depth, reaching 320–333 µm under gaseous HCl and 255–280 µm under liquid HCl, whereas the untreated control showed the lowest depth values (143–170 µm). TiF4 varnish provided the strongest surface protection, while the experimental hydrogel showed the best depth- related remineralization. Liquid hydrochloric acid caused more severe demineralization than gaseous acid, and abrasion intensified mineral loss, especially in untreated dentin. Morphological analysis showed narrower dentinal tubules and a thin deposited surface layer in the experimental hydrogel and chitosan groups, and the experimental hydrogel also showed stronger phosphate-related Raman bands under liquid acid challenge. However, none of the treatments preserved the organic matrix at the level of sound dentin. Within the limitations of this in vitro study, the experimental hydrogel and TiF4 varnish showed promising but distinct protective effects against dentin erosion: the hydrogel favored deeper remineralization, whereas TiF4 provided stronger superficial protection.

Objective. To evaluate whether pulse oximeters cleared under older U.S. Food and Drug Administration (FDA) standards remain accurate in ICU patients under newer draft guidance, to assess their performance against different regulatory metrics, and to investigate whether skin tone or LED spectral characteristics could be associated with measurement bias. Approach. In this prospective ICU study, three regulatory-cleared pulse oximeters were compared against arterial blood gas analysis. Skin pigmentation was characterized using the Individual Typology Angle (ITA°), and differential bias was estimated following FDA recommendations. Red and infrared LED emissions were measured using a fibre-optic spectrometer, and Gaussian models were used to extract peak wavelengths. Main Results. Two low-cost devices demonstrated large mean bias, wide limits of agreement (LoA), and poor correlation with arterial blood gas (ABG), failing both 2013 FDA guidance (accuracy root mean square, ARMS ≤ 3%) and updated FDA accuracy requirements. The clinical bedside monitor showed lower bias and minimal pigmentation-related differential error, though still above the proposed ARMS threshold. All devices remained inside the 2017 ISO Standard (ARMS ≤ 4%). Spectral analysis revealed that the most accurate device used a longer infrared peak and a slightly shorter red peak, a combination that could influence separation at key hemoglobin absorption wavelengths and potentially reduce melanin-related interference. Significance. These findings indicate that some oximeters cleared under older standards may underperform in ICU patients when assessed against newer accuracy proposals, underscoring the importance of reevaluating device performance as guidance evolves.

This study aimed to evaluate the effects of different endodontic irrigation protocols on irrigant diffusion, dentin microhardness, and dentinal collagen organization. Bovine dentin specimens were irrigated with 2.5% sodium hypochlorite (NaOCl), 2% chlorhexidine (CHX), or 0.9% saline solution (SS) and subdivided according to the irrigation protocol as follows: conventional irrigation (CI), passive ultrasonic irrigation (PUI), Easy Clean activation (EC), and prolonged contact without activation. Irrigant diffusion within dentin was evaluated by optical coherence tomography (OCT), and dentin microhardness was measured using Knoop microhardness testing before and after the irrigation protocols. Dentinal collagen organization was assessed by Picrosirius Red staining under polarized light microscopy. Data were analyzed using nonparametric tests with a significance level of 5%. OCT analysis showed no significant differences in irrigant diffusion among NaOCl and CHX across the irrigation protocols tested (p>0.05). Dentin microhardness values did not differ significantly before and after irrigation for any solution or protocol tested (p > 0.05). Picrosirius Red analysis showed no significant differences in total birefringent area among groups (p>0.05). However, prolonged exposure to chlorhexidine resulted in significant differences in the distribution of collagen fiber birefringence for yellow, red, and green fibers compared with other irrigation protocols (p < 0.05). The irrigation protocols evaluated did not affect dentin microhardness or irrigant diffusion, but influenced dentinal collagen organization and surface morphology in an irrigant- and exposure time-dependent manner.

BACKGROUND: Photobiomodulation therapy (PBMT) has been extensively researched for tissue repair, pain relief, and muscle recovery. However, melanin, a primary skin chromophore, can impede photon penetration into darker skin, potentially diminishing the efficacy of PBMT. Despite this, clinical protocols and guidelines seldom account for skin pigmentation when setting parameters, possibly exacerbating racial disparities in healthcare. OBJECTIVE: To examine the effect of melanin on the efficacy of PBMT and highlight the necessity for personalized strategies that account for skin pigmentation. DESIGN AND SETTING: Short communication conducted at the Universidade de São Paulo (USP), Ribeirão Preto, São Paulo. METHODS: A narrative review of PBMT mechanisms, light–tissue interactions, and the impact of melanin absorption on treatment outcomes was conducted. RESULTS: The clinical outcomes of PBMT depend on the technical parameters (wavelength, energy, and dose) and skin pigmentation. Darker skin tones with higher melanin content may lead to reduced photon penetration effectiveness. However, most studies and protocols do not consider this variable. Only a few clinical trials have categorized outcomes by skin tone, exposing a notable knowledge gap. CONCLUSION: Melanin plays a crucial role in PBMT response, and overlooking skin pigmentation in research and clinical practice could perpetuate disparities. Enhanced and tailored protocols are essential to optimize PBMT outcomes among diverse populations.

Objectives This study aimed to evaluate the effects of different irrigation protocols on the removal of mono- and multispecies biofilms, as well as on chemical alterations induced in superficial dentin. Materials and methods Specimens were divided into two groups according to the irrigating solution used: sodium hypochlorite (NaOCl 2.5%) or saline solution (SS 0.9%), and were subjected to agitation using either passive ultrasonic irrigation or EasyClean. The chemical composition of dentin discs was assessed by attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR), based on the Amide III/Phosphate and Carbonate/Phosphate ratios at three time points: baseline, after conventional irrigation, and after agitation. In parallel, E. faecalis, E. faecalis + S. oralis, and E. faecalis + C. albicans biofilms were grown on bovine dentin blocks and subjected to the same irrigation protocols. Cell viability was quantified by confocal laser scanning microscopy following Live/Dead staining. Data were analyzed using Kruskal–Wallis, Dunn, and Wilcoxon tests (α < 0.05). Results The Amide III/Phosphate ratio was significantly reduced in the NaOCl groups after agitation (p < 0.05), while changes in the Carbonate/Phosphate ratio were observed only in the SS groups when compared to NaOCl (p < 0.05). From a microbiological perspective, both activation methods with NaOCl significantly reduced cell viability, particularly ultrasonic activation in monospecies biofilms and EasyClean in multispecies biofilms (p < 0.05). Conclusion Based on the results and the methodology applied, it can be concluded that NaOCl activation with either ultrasonic irrigation or EasyClean is effective for disinfection, although it promotes chemical changes in dentin. Clinical relevance This study analyzes the impact of irrigation protocols on biofilm removal and dentin composition. NaOCl activation was effective in reducing microbial viability but promoted chemical changes in dentin, highlighting the need to balance disinfection and structural preservation in endodontic practice.

Accessing skin tone has gained significant relevance in recent decades, mainly due to the increased use of images for diagnostics and cosmetology. Color categorization methods like the Individual Typology Angle and the Monk scale have been used to mitigate this bias. In this study, we present a comprehensive evaluation of the correlation between these two scales through Monte Carlo computational simulation. Results indicate the Monk palette provides better segmentation for darker skin tones, but does not represent real human skin tones at the lighter end of the spectrum.