Optimizing the Pharmacological and Optical Dosimetry for Photodynamic Therapy with Methylene Blue and Nanoliposomal Benzoporphyrin on Pancreatic Cancer Spheroids

Photodynamic therapy (PDT) is a cancer treatment that relies on the remote-controlled activation of photocatalytic dyes (photosensitizers) in cancer tissues. To effectively treat cancer, a variety of pharmacological and optical parameters require optimization, which are dependent on the photosensitizer type. As most photosensitizers are hydrophobic molecules, nanoliposomes are frequently used to increase the biocompatibility of these therapeutics. However, as nanoliposomes can influence the therapeutic performance of photosensitizers, the most suitable treatment parameters need to be elucidated. Here, we evaluate the efficacy of PDT on spheroid cultures of PANC-1 and MIA PaCa-2 pancreatic cancer cells. Two strategies to photosensitize the pancreatic microtumors were selected, based on either nanoliposomal benzoporphyrin derivative (BPD), or non-liposomal methylene blue (MB). Using a comprehensive image-based assay, our findings show that the PDT efficacy manifests in distinct manners for each photosensitizer. Moreover, the efficacy of each photosensitizer is differentially influenced by the photosensitizer dose, the light dose (radiant exposure or fluence in J/cm2), and the dose rate (fluence rate in mW/cm2). Taken together, our findings illustrate that the most suitable light dosimetry for PDT strongly depends on the selected photosensitization strategy. The PDT dose parameters should therefore always be carefully optimized for different models of cancer.

Dual-Light Photodynamic Therapy Effectively Eliminates Streptococcus Oralis Biofilms

Purpose: During cancer treatment, oral mucositis due to radiotherapy or chemotherapy often leads to disruption of the oral mucosa, enabling microbes to invade bloodstream. Viridans streptococcal species are part of the healthy oral microbiota but can be frequently isolated from the blood of neutropenic patients. We have previously shown the antibacterial efficacy of dual-light, the combination of antibacterial blue light (aBL) and indocyanine green photodynamic therapy (aPDT). Methods: Here, we investigated the dual-light antibacterial action against four-day Streptococcus oralis biofilm. In addition, while keeping the total radiant exposure constant at 100J/cm2, we investigated the effect of changing the different relative light energies of aBL and aPDT to the antibacterial potential. Results: The dual-light had a significant antibacterial effect in all the tested combinations. Conclusion: Dual-light can be used as an effective disinfectant against S. oralis biofilm.

Applicability of Exposure Reciprocity Law for Fast Polymerization of Restorative Composites Containing Various Photoinitiating Systems

SUMMARY Objectives: The exposure reciprocity law (ERL) has been used to calculate the optimal irradiation time of dental composites. This study examined the applicability of ERL for fast polymerization of restorative composites containing various photoinitiating systems using a high-power multi-peak light-emitting diode (LED) lamp. Methods: Three commercial composites differing in photoinitiating systems were tested: Filtek Ultimate Universal Restorative (FU) with a camphorquinone-amine (CQ-A) photoinitiating system, Tetric EvoCeram (TEC) with CQ-A and (2,4,6-trimethylbenzoyl)phosphine oxide (TPO), and Estelite Σ Quick (ESQ) with CQ and a radical amplified photopolymerization (RAP) initiator. Specimens 2-mm thick were polymerized using a high-power multipeak LED lamp (Valo) at 3 pairs of radiant exposures (referred to as low, moderate, and high) ranging from 15.8–26.7 J/cm2. They were achieved by different combinations of irradiation time (5–20 seconds) and irradiance (1300–2980 mW/cm2) as determined with a calibrated spectrometer. Knoop microhardness was measured 1, 24, and 168 hours after polymerization on specimen top (irradiated) and bottom surfaces to characterize the degree of polymerization. The results were statistically analyzed using a three-way analysis of variance and Tukey’s post hoc tests, α = 0.05. Results: Microhardness increased with radiant exposure and except for ESQ, top-surface microhardness was significantly higher than that on bottom surfaces. Combinations of high irradiance and short irradiation time significantly increased the top-surface microhardness of TEC at low and moderate radiant exposures, and the bottom-surface microhardness of FU at a low radiant exposure. In contrast, the microhardness of ESQ on both surfaces at high radiant exposure increased significantly when low irradiance and long irradiation time were used. With all tested composites, bottom-surface microhardness obtained at low radiant exposure was below 80% of the maximum top-surface microhardness, indicating insufficient polymerization. Conclusion: Combinations of irradiance and irradiation time had a significant effect on microhardness, which was affected by photoinitiators and the optical properties of composites as well as spectral characteristics of the polymerization lamp. Therefore, ERL cannot be universally applied for the calculation of optimal composite irradiation time. Despite high irradiance, fast polymerization led to insufficient bottom-surface microhardness, suggesting the necessity to also characterize the degree of polymerization on the bottom surfaces of composite increments when assessing the validity of ERL.

Improper Light Curing of Bulkfill Composite Drives Surface Changes and Increases S. mutans Biofilm Growth as a Pathway for Higher Risk of Recurrent Caries around Restorations

How dentists cure a resin-based material has deleterious effects on the material’s properties and its interaction with surrounding dental tissues. Biofilm accumulation has been implicated in the pathogenesis of carious lesions around dental restorations, with its composition manifesting expressed dysbiosis in patients suffering from dental caries. To evaluate the influence of varying radiant exposure on the degree of conversion (DC%), Streptococcus mutans biofilm growth, and surface roughness of bulk-fill composites under different light-curing conditions. Two light-curing units (LCU) at 600 and 1000 mW/cm2 were used to simulate curing conditions with different angulations (∢20° and ∢35°) or 2 mm-distance displacements of the LCU tip. The radiant exposure (RE) was assessed, and the composites were analyzed for DC%. Biofilm formation was induced over the bulk-fill composites and analyzed via colony-forming units counting and scanning electron microscopy (SEM). The surface roughness was analyzed via a profilometer and SEM after biofilm formation. Curing conditions with different angulation or displacement decreased RE compared to the “optimal condition”. The moderately (∢35°) angulated LCU tip and low (600 mW/cm2) radiant emittance significantly reduced the DC% (p < 0.05). The difference in DC% between the top and bottom of the composites ranged from 8 to 11% for 600 mW/cm2 and 10 to 20% for 1000 mW/cm2. Greater S. mutans biofilm and surface changes were found in composites with non-optimal RE delivery (e.g., tip displacement and angulation) (p < 0.05). Inadequate polymerization of bulk-fill composites was associated with more biofilm accumulation and surface topography changes. Overall, non-optimally performed curing procedures reduced the amount of delivered RE, which led to low DC%, more biofilm formation, and higher surface roughness. The improper light-curing of bulk-fill composites compromises their physicochemical and biological properties, which could lead to inferior clinical performance and reduced restorative treatments’ longevity.

Dynamic OCT Signal Loss for Determining RPE Radiant Exposure Damage Thresholds in Microsecond Laser Microsurgery

Optical microsurgery of the retinal pigment epithelium (RPE) requires reliable real-time dosimetry to prevent unwanted overexposure of the neuroretina. The system used in this experiment implements optical coherence tomography (OCT) to detect the intentional elimination of RPE cells. We evaluated the performance of OCT dosimetry in terms of its ability to detect RPE cell damage caused by microsecond laser pulses of varying duration. Therefore, ex-vivo porcine RPE choroid sclera explants were embedded in an artificial eye and exposed to single laser pulses of 2–20 µs duration (wavelength: 532 nm, exposure area: 120 × 120 µm2, intensity modulation factor: 1.3). Simultaneously, time-resolved OCT M-scans were recorded (central wavelength: 870 nm, scan rate: 33 kHz). Post-irradiation, RPE cell damage was quantified using a calcein-AM viability assay and compared with an OCT-dosimetry algorithm. The results of our experiments show that the OCT-based analysis successfully predicts RPE cell damage. At its optimal operating point, the algorithm achieved a sensitivity of 89% and specificity of 94% for pulses of 6 µs duration and demonstrated the ability to precisely control radiant exposure of a wide range of pulse durations towards selective real-time laser microsurgery.

The Ability of Dental Practitioners to Light-Cure Simulated Restorations

Clinical Relevance Using a patient simulator, dental professionals were tested to determine their ability to light-polymerize simulated restorations in their dental practice. After receiving specific instructions and training using the simulator, their ability to deliver sufficient light to polymerize restorations was significantly and substantially improved. SUMMARY Objectives: To determine the ability of dental professionals to deliver a radiant exposure of at least six J/cm2 in 10 seconds to simulated restorations. Methods and Materials: The study initially examined 113 light-emitting-diode (LED) light polymerization units (LPUs) used in dental offices to determine if they could deliver at least 6 J/cm2 radiant exposure (RE) in 10s. This assessment was completed by using a laboratory-grade light measuring device (checkMARC, BlueLight Analytics, Halifax, NS, Canada). The participating dental professionals whose LPUs could deliver 6 J/cm2 then used their own LPU to light-cure simulated anterior and posterior restorations in the MARC Patient Simulator (BlueLight Analytics). They then received specific instructions and were retested using the same LPUs. Data were statistically analyzed with a series of one-way analysis of variance (ANOVA), two-way ANOVA, paired-samples t-tests, Fisher post hoc multiple comparison tests, and McNemar tests with a preset alpha of 0.05 (SPSS Inc). Results: Ten (8.8%) LPUs could not deliver the required RE to the checkMARC in 10s and were eliminated from the study. For the anterior restoration, most dental practitioners (87.3%) could deliver at least 6 J/cm2 before instructions. After receiving additional light-curing instructions, only two (1.9%) participants were unable to deliver 6 J/cm2 to the anterior location. At the posterior location, only 55.3% (57) participants could deliver at least 6 J/cm2 before the instructions. After receiving these instructions, an additional 32 participants delivered at least 6 J/cm2. Overall, after receiving instructions on how to use the LPU correctly, the participants improved the amount of RE they delivered to anterior and posterior restorations by 22.5% and 30%, respectively. Conclusion: This study revealed that at the baseline, 44.7% of participating dental professionals failed to deliver 6 J/cm2 in 10s to the posterior simulated restoration when using their own LPU.

Minimum Radiant Exposure and Irradiance for Triggering Adequate Polymerization of a Photo-Polymerized Resin Cement

This study aimed to establish the minimum radiant exposure and irradiance to trigger an adequate polymerization of a photo-polymerized resin cement. In total, 220 disc-shaped specimens (diameter of 10 mm and thickness of 0.1 mm) were fabricated using a photo-polymerized resin cement (Variolink N-transparent, Ivoclar Vivadent). To investigate the minimum radiant exposure, the specimens were polymerized with radiant exposures of 1, 2, 3, 4, 5, 6, and 18 J/cm2 (n = 20). During polymerization, the irradiance was maintained at 200 mW/cm2. To investigate the minimum irradiance, the specimens were polymerized with irradiances of 50, 100, 150, and 200 mW/cm2 (n = 20). During polymerization, the radiant exposure was maintained at the previously determined minimum radiant exposure. The Vickers microhardness (HV) and degree of conversion (DC) of the carbon double bond of the specimens were measured to determine the degree of polymerization of the specimens. The results were analyzed using one-way analysis of variance (ANOVA) and Tukey’s test (p < 0.05). In the investigation of the minimum radiant exposure, the HV and DC of the specimens polymerized with a radiant exposure from 1 to 5 J/cm2 were significantly lower than those with 18 J/cm2 (all p < 0.05). However, no significant difference in HV and DC was found between the specimens polymerized with 6 J/cm2 and 18 J/cm2 (p > 0.05). In the investigation of the minimum irradiance, the specimens polymerized with an irradiance of 50 mW/cm2 had significantly lower HV and DC than the specimens polymerized with an irradiance of 200 mW/cm2 (p < 0.05). However, no significant difference in the HV and DC was found among the specimens cured with irradiances of 100, 150, and 200 mW/cm2 (p > 0.05). In conclusion, the minimum radiant exposure and irradiance to trigger an adequate polymerization of the light-cured resin cement were 6 J/cm2 and 100 mW/cm2, respectively.

Impact of COVID-19 Lockdown on Sun Exposure of UK Office Workers

The impact of lockdown due to the COVID-19 pandemic in April–June 2020 on UV exposure of office workers was assessed using an online survey on time spent outdoors and environmental data for different locations in the UK. Without the need for commuting and with the flexibility of homeworking, weekday time spent outdoors was higher in the 2020 lockdown than in the same period in 2017. The weekday erythema effective radiant exposure was higher in 2020 due to an additional 45 min outdoors in the late afternoon that was not observed in 2017 and high UV levels due to extremely sunny weather in spring. The lockdown did not impact the frequency of time spent outdoors around midday, which was still governed by work commitments, and at the weekends, no difference between 2020 and 2017 was observed. In 2020, responders felt that time outdoors was very important for their health and well-being.

Light Transmittance and Depth of Cure of a Bulk Fill Composite Based on the Exposure Reciprocity Law

The objective of this study was to evaluate the effect of the exposure reciprocity law of a multi-wave light-emitting diode (LED) on the light transmittance (LT), depth of cure (DOC) and degree of conversion in-depth (DC) of a bulk fill composite. A bulk fill composite (EvoCeram® bulk fill, Ivoclar Vivadent) was photoactivated using the multi-wave LED (VALO™ Cordless, Ultradent). The LED was previously characterized using a spectrophotometer to standardize the time of exposure when using the Standard or Xtra-Power modes with the same radiant exposure of 20J/cm2. LT was evaluated through samples of the bulk fill composite every millimeter till 4 mm in-depth. DOC was evaluated according to the ISO 4049. DC of the central longitudinal cross-section from each sample of the DOC test was mapped using FT-NIR microscopy. Data were statistically analyzed according to the experimental design (α=0.05; ß=0.2). The radiant exposure in the violet wavelength range for Standard and Xtra-Power was 4.5 and 5.0 J/cm2, respectively; for the blue wavelength range the radiant exposure for Standard and Xtra-Power was 15.5 and 15.0 J/cm2, respectively. There was no statistical difference in the DOC using Standard or Xtra-Power light-curing modes, but the DOC was lower than the claimed by the manufacturer (4 mm). The DC was not significantly affected by the light-curing mode up to 4 mm in depth (p>0.05). According to exposure reciprocity law, the reduction in exposure time using the same radiant exposure did not affect the depth of cure of the bulk fill composite.

Influence of radiant exposure values from two third generation LED curing units on polymerization profile and microhardness of orthodontic composite under ceramic and metallic brackets

ABSTRACT Introduction: Third generation of LED light curing units might be used in short exposure periods for orthodontic brackets bonding. Objective: This study evaluated the effect of the different radiant exposure (RE) values: Manufacturers’ instructions (MI), ½ MI, 1/4 MI and Turbo mode. Two third-generation LED curing units were used: VALO® and Bluephase 20i® . The degree of conversion (DC) and Vickers hardness (VHN) of an orthodontic composite (OC) (Transbond XT) under metallic (MB) or ceramic brackets (CB) were measured. Methods: OC was applied to the bracket base, which was then placed over an attenuated total reflectance (ATR) table coupled to an infrared light spectroscope, or to a glass surface for the VHN analysis. The specimens were light-cured and DC values were calculated. The VHN was obtained in a microhardness tester. The data were analyzed with 2-way ANOVA followed by Tukey’s post-hoc test (pre-set α=0.05). Linear regression analysis evaluated the relationship between RE values and dependent variables. Results: CB allowed higher DC and VHN values than MB (p< 0.001). No significant difference was noted among groups when CB were used. For MB, MI groups showed the highest DC and VHN values. A significant, but weak relationship was found between delivered RE values and dependent variables. Conclusions: The decrease in RE values from third generation LED CU did not jeopardize the DC values when CB were used, but can compromise DC and VHN values when MB are used.