The main aim of the study was to implement the most reliable method of measuring the degrees of conversion during photopolymerization of dental fillings. Contrary to the methods used so far, the method is based only on comparison with the monomer absorbance spectrum without reference bands. Another aim of the study was to prepare a comparative analysis of the polymerization kinetics of dental resins under various light sources and different environmental conditions (irradiance, light dose, temperature), with estimation of the degrees of conversion (DC) of the resins being the main metric. HRi Universal Enamel (UE2) and HRi Universal Dentine (UD2) were examined under two different types of light sources used in dentistry, LED and halogen. DC was measured by Fourier transform infrared spectroscopy (FTIR) in transmission mode from 5 s up to 7 days. Spectra were recorded from the parallel optical layers of samples that were placed between the KBr crystals. The results are expressed by the changes in the absorbance spectrum during the polymerization and the calculated conversion rates. The results of each experiment were averaged from three separate measurements of three samples, during which the samples were illuminated under identical conditions. The data were analyzed by performing ANOVA test comparisons between sample groups at the significance level α = 0.05. The degree of conversion of the UD2 resin was higher than that of UE2 for each experimental condition, but there was no statistically significant difference between the DC of those materials (p > 0.05). There was statistically significant difference (p < 0.01) in the DC caused by LED and halogen light sources producing the same light doses (38 J/cm2). This was the result of different features of light transmission to the filler in the resin composite. The efficacy of the LED source is twice as high as that of the halogen light source. Maximal DC without any other differences in conditions, such as resin type or light source, reached around 70% for temperatures of 22–37 °C. For 37 °C, this took 24 h, which is a contrast to the 7 days it took for 23 °C. The influences of different conditions and factors on reaction kinetics are only strong in the early and the rapid stage of conversion. The optimal time of irradiance using either light source is 20 s for a monolayer, and its thickness should not exceed 2 mm.

Introduction. Composite materials are currently most commonly used to reconstruct tooth tissues. During the polymerization, it results in marginal leakage between filling and hard dental tissues. Marginal leakage causes bacterial microleakage which leads to the discoloration of restoration margin and secondary caries. Intensive development of new technologies focus on elaborate processes decreasing the risk of microleakage appearance. Aim. The purpose of this in vitro study was to estimate marginal leakage degree in composite restorations which were polymerized with different kinds of lamps. Material and methods. 35 extracted human permanent molars were used in the study. Calibrated cavities on interproximal surfaces (class 2.2 acc. Mount and Hume classification) were prepared. Teeth were divided into 5 groups. Cavities were filled with composite materialaccording to the manufacturer’s instructionsusing different kinds of polymerizationlamps: halogen (floodlight) lamp, high intensity LED lamp and LED lamp with three working modes. Marginal leakage was evaluated by estimating a dye penetration and SEM images registration. Quantitative analysis of marginal gap was also performed. Results. In samples analysis with optical microscope and stereo microscope the dye penetration and marginal gap was not observed. Only scanning electron microscope with back-scatter detector has revealed the marginal leakage. the largest marginal leakage was observed in case of high intensity led lamp– FlashMax(1.60 μm), and the smallest for LED lamp – pulse and increasing modes(0.96 μm and 0.98 μm, respectively). Marginal leakage was not observed in samples polymerized with continuous mode of LED lamp. Conclusions. The results of this study suggest that the increase in light intensity of the polymerization lamp significantly shortens the exposure time, which is clinically advantageous, but excessive light intensity can cause severe systolic tensions leading to a marginal leakage.