Impact of optical fiber-based photo-activation on dental composite polymerization

OBJECTIVES

The study aimed to introduce a novel two-step optical fiber-based photo-activation of dental resin-based composites (RBCs) for reducing polymerization shrinkage stress (PSS).

METHODS

Proposed protocol design - in the first step, two flexible plastic optical fibers connected to a dental light curing unit (LCU), were used as light guides inserted into the filling to initiate low-irradiance polymerization from within; in the second step, fibers were extracted and remaining voids were filled with RBC, followed by conventional high-irradiance curing to finalize polymerization. Three bulk-fill RBCs were tested (Beautifil-Bulk Restorative, Filtek Bulk-fill Posterior, Tetric PowerFill) using tooth cavity models. Three non-invasive examination techniques were employed: Digital Holographic Interferometry, Infrared Thermography, and Raman spectroscopy for monitoring model deformation, RBC temperature change, and degree of conversion (DC), respectively. A control group (for each examined RBC) underwent conventional photo-activation.

RESULTS

The experimental protocol significantly reduced model deformation by 15 - 35 %, accompanied by an 18 - 54 % reduction in RBC temperature change, emphasizing the impact of thermal shrinkage on PSS. Real-time measurements of deformation and temperature provided indirect insights into reaction dynamics and illuminated potential mechanisms underlying PSS reduction. After a 24-hour dark-storage period, DC outcomes comparable to conventional curing were observed, affirming the clinical applicability of the method.

CONCLUSIONS

Protocol involving the use of two 1.5 mm fibers in the first step (300 mW/cm2 x 10 s), followed by a second conventional curing step (1000 mW/cm2 x 10 s), is recommended to achieve the desired PSS reduction, while maintaining adequate DC and ensuring efficient clinical application.

CLINICAL SIGNIFICANCE

Obtained PSS reduction offers promise in potentially improving the performance of composite restorations. Additionally, leveraging the flexibility of optical fibers improves light guide approach for restorations on posterior teeth. Meanwhile, implementation in clinical practice is easily achievable by coupling the fibers with commercial dental LCUs using the provided plastic adapter.

Structure and dielectric properties of (1-x)Bi0.5Na0.5TiO3-xBaTiO3 piezoceramics prepared using hydrothermally synthesized powders

The influence of different processing parameters and various Ba2+ addition (up to 10 mol%) on the structure and dielectric properties of Bi0.5Na0.5TiO3-BaTiO3 (BNT-BT) ceramics was investigated. The powders were hydrothermally synthesized in the alkaline environment at 180°C for different time periods. X-ray diffraction confirmed the presence of dominant rhombohedral Bi0.5Na0.5TiO3 phase and a small amount of secondary pyrochlore Bi2Ti2O7 phase in the pure BNT powders. In addition, one-dimensional Na2Ti2O7 structure was also observed in the powder hydrothermally treated for a long time (i.e. 48 h). The amount of secondary pyrochlore phase in the BNT-BT powders increases with the increase of Ba2+ content. The synthesized powders were pressed into pellets and finally sintered at various temperatures up to 1150°C. High density (more than 90%TD) was obtained in all BNT-BT sintered samples. Optimal sintering parameters were chosen in order to obtain dense ceramics with the optimal phase composition. The temperature dependence of dielectric properties for the BNT-BT ceramics was also studied. Relaxor behaviour of BNT-based ceramics and broad transition peaks are evident in all samples. Dielectric constant up to 400 as well as an acceptable low dielectric loss at temperatures lower than 200°C were obtained in BNT-BT ceramics.

Performances and Biosensing Mechanisms of Interdigitated Capacitive Sensors Based on the Hetero-mixture of SnO2 and In2O3

This study aims to discuss the synthesis and fabrication of SnO₂-In₂O₃-based thick-films and their biosensing applications. The structural characterization of SnO₂-In₂O₃ nanocomposites was performed using X-ray diffraction, Raman spectroscopy and transmission electron microscopy. Furthermore, the screen-printing technology was used in the fabrication of conductive electrodes to form an interdigitated capacitive structure, and the sensor layer based on the mixture of SnO₂ and In₂O₃. Moreover, the sensing performance of the developed structure was tested using Pseudomonas aeruginosa (P. aeruginosa) and Staphylococcus aureus (S. aureus) bacteria. In addition, the validation of sensing characteristics was performed by electrochemical impedance spectroscopic and self-resonant frequency analysis. Finally, the sensing properties were analyzed for two consecutive days, and changes in both P. aeruginosa and S. aureus pathogens growing media were also studied.