Enhancing Photopolymerization and Modeling Kinetic Degradation in Dental Composites

Enhancing Photopolymerization and Modeling Kinetic Degradation in Dental Composites | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Enhancing Photopolymerization and Modeling Kinetic Degradation in Dental Composites Olivier Boyron, Rayenne Latoui, Mohamed Affif Belhani, Djallel Bouzid This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4510299/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 04 Sep, 2024 Read the published version in Journal of Polymer Research → Version 1 posted 5 You are reading this latest preprint version Abstract This study aims to optimize the photopolymerization process of a dental composite in order to increase the degree of conversion and reduce the release of unpolymerized monomers. In addition, it seeks to understand the kinetics of composite degradation under various oral environmental conditions. Optimization of the photopolymerization process is carried out using a Box-Behnken design, exploring factors such as irradiation time, intensity and distance. Infrared spectroscopy is used to evaluate photopolymerization parameters. Release of unpolymerized monomers is quantified using liquid chromatography at different pH levels, incubation media and time. Thermogravimetric analysis is used to study thermal degradation and establish a kinetic model. Optimized conditions for photopolymerization, determined as an irradiation time of 40 seconds, an intensity of 1500 mW cm − 2 , and a distance of 5 mm, lead to a degree of conversion of 61%, reducing the presence of unpolymerized monomers. Chromatographic analysis reveals a pH-dependent release of monomers, with acid saliva showing the highest release. Thermal analysis indicates variable activation energy values depending on ageing conditions, underlining the importance of optimal conversion for increased material strength. This study offers a comprehensive approach to improving the properties of dental resins, providing optimized conditions for light-curing that increase material strength. biocompatible composites photopolymerization Box-Behnken design monomers release degradation kinetics TGA Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 1. Introduction Nanotechnology has emerged as a promising field in restorative dentistry. One notable application of nanotechnology is improving the wear resistance of dental materials through the use of resin containing nanoparticles. [ 1 , 2 ] Nano-composite are actually the only materials used for dental restoration. They serve several requirements in terms of mechanical strength, chemical stability, or even aesthetic quality. However, despite all these advantages, they present a certain toxicity which can affect human health. This toxicity is due to monomers that can be released and reach the saliva, thus entering the organism. [ 3 ] Monomer release is the result of incomplete polymerization of the composite resin, with an average degree of conversion of around 60%. [ 4 ] This low value is due to several factors, including those related to the photopolymerization, such as the light intensity, irradiation time and the distance between the resin and the light. The composite is used in an extreme condition that will favor its bio-degradation. The unpolymerized monomers of the resin matrix, particularly the basic ones like bisphenol A‑glycidyl methacrylate (BisGma), urethane dimethacrylate (UDMA), and ethoxylated bisphenol‑A dimethacrylate (BisEMA), as well as co-monomers such as tetraethyleneglycol dimethacrylate (TEGDMA) and 2‑hydroxyethyl methacrylate (HEMA), are the main cytotoxic substances that are released. [ 5 – 12 ] However, due to the complexity of the oral environment, the studies carried out have never succeeded in simulating in vitro aging of all the factors. [ 13 ] In this work, the influence saliva pH, aging media and oral environment temperature on the aging of the commercial dental composite “ NT Premium Enamel B2” was investigated. Water and saliva are the primary media used to simulate the oral environment. Ferracane et al. [ 14 ] suggest that solvents with properties between those of highly aggressive organic solvents and water are highly indicative of the oral environment. In contrast, the US Food and Drug Administration (FDA) considers a 75% ethanol solution to be a clinically relevant food/oral simulation liquid. Furthermore, Tsitrou et al. [ 15 ] have studied the effect of various extraction media, including culture media, as well as storage times on the elution of monomers from modern dental composites. To predict the degradation of the composite under different conditions, the establishment of a kinetic model is crucial. However, accurate prediction necessitates knowledge of the three kinetic parameters of the model: the activation energy Ea, the pre-exponential factor A, and the kinetic model f(α). Numerous methodologies are available for determining kinetic parameters. The classical method involves developing a suitable kinetic model for the material being studied. However, due to the complexity of composite resins, we opted for an approach that utilises the Sestak-Berggren equation to determine the constants that validate the kinetic model for our specific composite. The purpose of this study was, firstly, to evaluate the effect of photopolymerisation parameters of a dental composite "NT Premium Enamel B2" on monomer conversion using FTIR infrared spectroscopy and Box-Behnken design as a statistical experimental design to analyse the data. Secondly, to quantify the release of unpolymerized monomers from the composite, a degradation test was conducted in artificial saliva under various conditions of pH, incubation media and treatment times using high-performance liquid chromatography (HPLC). Lastly, the thermal degradation of the samples after ageing was studied using thermogravimetric analysis (TGA) which allows the establishment of a degradation kinetic model under different conditions. 2. Experimental section Material Dental composite The selected dental composite, “NT Premium Enamel B2” from coltene brasil, contains 75% inorganic charges, as well as monomers such as Bis-GMA, Bis-EMA, and TEGDMA, a BHT inhibitor, photo initiators, fillers, and dyes. Artificial saliva Artificial saliva was prepared according to the Ringer protocol. [ 17 ] The composition of the saliva is shown in Table 1 . Table 1 Artificial saliva composition. Compounds Concentration [mM] Volume [mL] Na2HPO4 2.4 100 KH2PO4 2.5 100 NaCl 1 100 KHCO3 1.5 100 CaCl2 1.5 100 MgCl2 0.15 100 Citric acid 0.002 6 Dibasic sodium phosphate dihydrate was purchased from Honeywell (Germany), monobasic potassium phosphate, citric acid monohydrate and ethanol were acquired from SIGMA-ALDRICH (Spain), potassium carbonate, calcium chloride, magnesium chloride and sodium chloride were purchased from BIOCHEM (France). HCl from Honeywell (Germany) and NaOH from BIOCHEM (France) were used to adjust the pH to the desired value. Water was purified using a Millipore water purification system. Fourier transform infrared spectroscopy (FTIR) Infrared spectra were recorded using Fourier transform infrared (FTIR) spectrometer from Shimadzu, equipped with a diamond crystal attenuated total reflectance (ATR) accessory. Background and samples were acquired using 40 scans at a spectral resolution of 8 cm -1 from 4000 to 380 cm -1 . Sample films (1 mm thick) were polymerized at room temperature using an ‘Eighteeth curing pen’ LED dental lamp. The degree of conversion was determined by monitoring the decrease of the C = C band associated to the vinyl bonds of the reacting methacrylate during polymerization. [ 18 , 19 ] The amount of double bonds is related to the absorbance of infrared light at the wavenumber of 1636 cm -1 . To reduce errors due to variation in the amounts of sample analysed, an internal standard corresponding to the absorbance of the phenyl group at 1608 cm -1 was also used. The degree of conversion can therefore be calculated from the following equation. [ 20 ] $$DC \left(\%\right)=\left[1-\frac{\left(A1636{cm}^{-1}/A1608{cm}^{-1}\right)polymer}{\left(A1636{cm}^{-1}/A1608{cm}^{-1}\right)monomer}\right]\times 100$$ 1 High-performance liquid chromatography analysis The ULC-20A system from SHIMADZU was used to perform high-performance liquid chromatography (HPLC) analysis. The system was equipped with a VP-ODS C8 column (150 x 4.6 mm with 5µm particle diameter) and coupled with a UV-visible detector operating at ambient temperature. Separation was achieved using a mobile phase composed of 45% acetonitrile and 55% water, with a constant flow rate of 1 mL min -1 . A volume of 25 µL was manually injected using a micro-syringe from Thermo Scientific. The maximum absorption wavelength, previously determined using a benchtop UV-Visible spectrophotometer, was set at 205 nm, corresponding to the TEGDMA absorption. The HPLC chromatogram of TEGDMA monomer at a concentration of 10 ppm eluted at a time of 8.7 min is shown in Fig. 1 . The calibration curve used in this work is shown in Fig. 2 and was established using several solutions with TEGDMA concentrations ranging from 5 mg L -1 to 1000 mg L -1 to calculate its concentration in the composite. Thermogravimetric analysis Thermogravimetric analysis (TGA) was conducted using a Mettler Toledo TGA/DSC. Approximately 10 mg of samples were precisely weighed and placed into 70 µL aluminum oxide crucibles. The samples were heated from 25°C to 600°C at varying heating rates (5, 10, 20°C min -1 ) under a dry nitrogen atmosphere with a flow rate of 30 mL min -1 . 3. Results and discussion 3.1. Influence of photopolymerization parameters This part involves finding a reliable model for maximizing the factors that influence the efficiency of the polymerization process. The aim is to optimize the conversion degree using an experimental design. Box-Behnken design The Box-Behnken design was used to optimize the degree of conversion, which depends on three factors (irradiation time, intensity, distance between sample and light), the design results in a second order model. 15 tests (12 tests plus 3 center points) were performed, for each test, three repetitions were carried out. The matrix of tests and their responses are shown in Table 2 . Table 2 Box-Behnken design matrix Test Time a) [s] Distance [mm] Intensity [mW cm − 2 ] DC b) [%] 1 10 0 1450 49.3 2 60 0 1450 63.8 3 10 20 1450 48.6 4 60 20 1450 59.3 5 10 10 600 45.8 6 60 10 600 59.4 7 10 10 2300 52.6 8 60 10 2300 63.9 9 35 0 600 59.2 10 35 20 600 54.9 11 35 0 2300 62.2 12 35 20 2300 59.4 13 35 10 1450 59.3 14 35 10 1450 59.4 15 35 10 1450 59.4 a) Photopolymerization time; b) conversion degree calculated by FTIR spectroscopy with ATR The experimental matrix consists of a Box-Behnken type design with three factors on three levels each, with a central point (the test where all the factors are adjusted to their mean). The time was varied from 10 to 60 s, while the intensity was set from 600 to 2300 mw cm − 2 and the distance was changed from 0 to 20 mm. The analysis of the results was done with Minitab, a response model is established by neglecting interactions of order 3. Eq. 2 represents the model of the conversion rate by the Box-Behnken design. With , t: time of polymerization (s); D: distance between the composite and the light (mm) and I: intensity of the light (mW cm − 2 ). The model shows that the interaction between factors can be neglected as the coefficient value is not significant. This model includes second order terms, proving that certain factors follow a non-linear trend. Figure 3 's main effect diagram shows that the polymerization time follows a second-order curve, while the other factors exhibit a linear behavior. Time is also the main factor with the highest coefficient, it reaches a plate around 40 s. On the other hand, distance is the least significant factor, being inversely proportional to the degree of conversion, while the intensity of the light source is directly proportional. Analysis of variance The analysis of variance (ANOVA) indicates that the model has acceptable correlation coefficients. The critical Fisher factor was obtained using the Fisher table, with F = 147.2, which is significantly higher than its critical value Fc = 2.8. The R 2 and R 2 adjusted value were 99.2 and 98.6, respectively, indicating that the model is therefore valid. Factors optimization The model allowed the selection of factors to maximize the degree of conversion. According to the literature, the achievable conversion degree for composite resins is around 60%. [ 2 ] Values above this rate are considered favorable. The distance factor is found to be less significant, allowing for a distance value of 5 mm to facilitate polymerization in the mouth for the operator. Figure 4 displays the favorable combinations of polymerization time and light source intensity in white area, while the blue area indicates the conversion rate values below 60%. To optimize energy and heat generation, the optimal point is 40 seconds of polymerization time, 5 mm of distance, and an intensity of 1500 mW cm -2 , as determined by the preset intensity of the dental lamp. This composition results in a conversion rate of 61.2%. Figure 5 displays the infrared spectra of the composite at different polymerization time and using the optimum values of intensity and distance obtained by the Box-Benkhen design model, 1500 mw cm -2 and 5 mm respectively. The figure shows the decrease in the elongation vibration peaks of methacrylate double bonds at 1636 cm -1 as a function of polymerization time. 3.2. Analysis of monomer released in saliva This part reports the quantification of TEGDMA released by the resin obtained with the optimized parameters. The purpose of this analysis is to measure the amount of the potentially toxic monomer that may be released into the organism while the composite is in the oral environment. To simulate the aging of resins in an in vitro system, four different media were used. An artificial saliva with three different pH values (acidic pH of 3.5, neutral pH of 7, and basic pH of 10) [ 18 ] and an ethanol/water medium with a 75% v/v ratio were used as two of the media. [ 15 ] The other two media were saliva with different pH values, which were used to simulate changes in pH when consuming different meals. Meanwhile ethanol was used to accelerate the degradation and aging of the composite resin as it is a good solvent for the monomers. The experiment involved three factors: (1) the medium (artificial saliva at three different pH values and ethanol at 75%), (2) the incubation temperature (37°C and 50°C), and (3) the incubation time (1 and 7 days). Preparation of samples Cylindrical specimens of 5 mm diameter and 2 mm thickness of the “NT Premium Enamel B2” resin composite were prepared using a Teflon mold. The composites were compressed in the mold between two glass plates and polymerized at room temperature for 40 s using an “Eighteeth curing pen” LED dental lamp with an intensity of 1500 mW cm -2 at a distance of 5 mm. The polymerized specimens were removed from the mold, and flushed with ethanol. Then, they were immersed in 1 ml of aging medium in a 2 ml capped vial. The vials were subsequently incubated in an oven at the designated temperature for the appropriate length of time. The analysis was conducted using high-performance liquid chromatography (HPLC). Table 3 summarizes the samples prepared, their aging conditions and the results obtained for the samples submitted to different conditions. The study findings suggest that the amount of TEGDMA released is influenced by the type of medium, pH, and incubation temperature. Moreover, the release of TEGDMA is increased with the residence time of the composite in the medium. Table 3 Resin composite aging conditions and HPLC analysis results Sample Medium pH Temperature [°C] Time [days] Mass a [mg] Area b [mV*mV] TEGDMA Concentration c [mg L − 1 ] TEGDMA quantity [µg g − 1 ] Cp1 AS d 7 37 1 69.6 33983 0.5 0.01 Cp2 AS 3.5 37 1 74.9 1633419 26.7 0.35 Cp3 AS 10 37 1 61.3 41939 0.7 0.01 Cp4 AS 7 50 1 46.4 43653 0.7 0.02 Cp5 EtOH/water 7 37 1 62.4 1975042 32.2 0.51 Cp6 AS 7 37 7 66.3 237474 3.8 0.06 Cp7 AS 3.5 37 7 67.3 2660754 43.4 0.64 Cp8 AS 10 37 7 64.9 698364 11.4 0.17 Cp9 AS 7 50 7 68.9 369540 6 0.09 Cp10 EtOH/water 7 37 7 77.8 3690466 60.3 0.77 Cp11 e EtOH/water 7 37 7 67.5 23141306 378.1 5.60 a initial mass of the sample before degradation; b area of the TEGDMA peak obtained by HPLC at 8.6 minutes; c concentration of TEGMA in the sample determined by the calibration curve; d artificial saliva; e unpolymerized sample The Table 3 displays the effect of the degree of conversion on monomer release in saliva. The Cp11 sample un-polymerized had the greatest amount of released TEGDMA. This release represents the dissolution and migration of TEGDMA in artificial saliva. As the conversion degree increased after polymerization, the number of unbound monomers decreased, resulting in a small amount of TEGDMA released in all polymerized samples. The amount of TEGDMA released varies from 0.01 to 0.77 µg g -1 . This indicates that HPLC is a reliable method for determining and quantifying the monomers. Figure 6 shows the amount of TEGDMA measured for each type of medium, demonstrating that the type of aging medium used has a real effect on the release of TEGDMA. As expected, ethanol/water at 75% was the medium with the highest release of TEGDMA. This high release is attributed to the ability of ethanol to be a good solvent for monomers, including TEGDMA. The artificial saliva with acid pH of 3.5 also showed a significant amount of released. The low pH values promote the release of monomers as well as the degradation of composite resins. The neutral medium showed stability during the 7 days of incubation. This stability is less evident during incubation at high temperature. The basic medium, on the other hand, showed stability in the short term, but began to release monomers gradually. 3.3. Modeling of the kinetic release TGA analysis Thermogravimetric analysis provides the mass loss as a function of time and temperature. It was carried out on two samples (Cp10 and Cp7) that have undergone different aging conditions and exhibit the highest TEGDMA release. As a reference, an untreated sample (Cp0) was also analyzed by TGA. These three samples were submitted to three heating rates (5, 10 and 20°C min -1 ). The TGA curves of sample Cp7 for the three heating rates are shown in Fig. 7 . This thermogram displays three degradation zones that are almost similar for all samples. [22] For temperatures below 300°C, the degradation was negligible due to the high thermal resistance of the composite. The main degradation was observed in the temperature range between 300°C and 500°C, where a rapid mass loss occurs due to the degradation of the polymer chains. Above 500°C, the residue is due to the inorganic part of the composite. The heating rate affects the degradation temperature profiles. The higher the heating rate, the more degradation is shifted to high temperatures due to degradation kinetics. For example, at the heating rate of 5°C min -1 the sample reaches 5% degradation at a temperature of 352°C, while the sample at the heating rate of 20°C min -1 does not reach the 5% degradation until reaching a temperature of 393°C. Under the influence of the kinetics of degradation, the exploitation of these different curves allowed the determination of kinetic models. Kinetic model of release The kinetic equation of degradation is equivalent to that of chemical kinetics, expressed as: $$\frac{\varvec{d}\varvec{a}}{\varvec{d}\varvec{t}}=\varvec{K}\varvec{f}\left(\varvec{a}\right)$$ 3 Where, f(α) is the kinetic model, and k is the rate constant obtained by the Arrhenius law: k = \(\varvec{A}\varvec{e}\varvec{x}\varvec{p}(-\frac{{\varvec{E}}_{\varvec{a}}}{\varvec{R}\varvec{T}})\) (4) The variable α represents the mass lost during the thermogravimetry experiment: α = \(\frac{{\varvec{W}}_{\varvec{i}}-{\varvec{W}}_{\varvec{f}}}{{\varvec{W}}_{\varvec{f}}}\) (5) Where W i is the initial mass, and W f is the final mass. Finally, the combination of Equations 3 and 4 results in the following formula: $$\frac{\varvec{d}\varvec{a}}{\varvec{d}\varvec{t}}=\varvec{A}\varvec{e}\varvec{x}\varvec{p}(-\frac{{\varvec{E}}_{\varvec{a}}}{\varvec{R}\varvec{T}})\varvec{f}\left(\varvec{a}\right)$$ 6 Various methodologies can be applied to determine kinetic triplet values. The most common approach is to select a suitable kinetic model from the existing ones. The majority of these models are derived from the modified version of the empirical equation of Sestak-Beggren, refer to Eq. 7, by adjusting the constants c, n, and m. This technique is referred to as "model fitting". [20] f(α) = c(1-α) nαm (7) Combining the Eq. 7 of Sestak-Beggren model with the kinetic Eq. 6 yields the following relation: ln ( \(\frac{\frac{\varvec{d}\varvec{a}}{\varvec{d}\varvec{t}}}{{\left(1-\varvec{\alpha }\right)}^{\mathbf{n}}{\varvec{\alpha }}^{\mathbf{m}}}\) ) = lncA - \(\frac{{\varvec{E}}_{\varvec{a}}}{\varvec{R}}\frac{1}{\varvec{T}}\) (8) The Eq. 8 can be expressed as a linear function of the form y = b-ax, with x = 1/T . The equation for this model requires the determination of the values of α, t and T, which can be obtained from TGA measurements. However, the values of the constants n and m are still unknown. To determine them, a MATLAB program was used to optimize the correlation coefficient (r) of Eq. 8, with the aim of finding the values of n and m that produce a Pearson correlation coefficient closest to 1. [ 20 , 21 ] The straight-line regression of the degradation data ( Fig. 8 ) obtained by ATG on the 3 samples and at different speeds was used to determine the values of the constants. These data, given in Table 4 , were finally exploited to measure the activation energies for each sample. Triangles depict the raw TGA data and the line displays the corresponding calculated regression. Table 4 Calculated values of constants obtained by fitting the model Sample Heating rate [°C min − 1 ] n a) m a) r b) Ea [Kj mol − 1 ] Cp0 c 20 10 5 -0.8 -5.5 1.7 1.7 1.2 2.3 0.97 0.95 0.96 113 119 65 Cp7 20 10 5 -5.7 -20.4 -12.2 2 1.9 1.8 0.97 0.96 0.95 106 109 72 Cp10 20 10 5 -49.9 -29.3 -19.2 1.2 1.8 2.0 0.95 0.95 0.95 221 111 85 constants of Sestak-Beggren determined by MATLAB; b) Pearson correlation coefficient; c) untreated sample Given the correlation coefficients greater than 0.95 (Table 4 ), the validity of the kinetic model is confirmed for the n and m values determined. The n and m values have a variability depending on the samples and heating rates, which shows that the kinetic model does not have a constant equation with fixed coefficients. This feature highlights the advantage of using this method to determine variable coefficients, adapted to our conditions, compared with the application of pre-existing models. Concerning the activation energies, it can be seen that for high heating rates (10 and 20°C min -1 ), the activation energy values are close. They are significantly higher than the values obtained at a heating rate of 5°C min -1 . This result suggests that excessive heating rates do not allow the system to reach a correct equilibrium and affect the Ea measurements. Consequently, we considered the data obtained at 5°C min -1 to determine the coefficients n and m and subsequently the activation energy. The activation energies of the three samples determined at a heating rate of 5°C min -1 are quite similar. Sample Cp0, which was not subjected to conditions that could degrade the resin, shows a lower activation energy, proving the presence of residual monomers in the resin and facilitating its degradation. In contrast, sample Cp10, which was exposed to the most favorable conditions for the release of monomer (as shown in Table 3 ), has the highest activation energy, meaning that it will require more energy to degrade. Sample Cp7, which has a monomer release rate between the two samples (as shown in Table 3 's HPLC measurement), exhibits an intermediate activation energy. Finally, these study on activation energy highlights the importance of achieving an optimum photopolymerization conversion to increase the activation energy of the sample, thereby improving its resistance to usage conditions. In addition to its health implications, the reduced presence of residual monomer in the resin contributes to a longer material lifetime. 4. Conclusion The relevance and originality of this study lies in its comprehensive approach, from the optimization of the dental composite photopolymerization process to the understanding of its degradation kinetics in the practical usage environment. The Box-Behnken experimental design was revealed to be useful to optimize the polymerization process to increase the degree of conversion. The identified optimization conditions include a photopolymerization time of 40 seconds, an irradiation intensity of 1500 mW cm -2 and a distance of 5 mm. These conditions lead to a degree of conversion of 61%. Reducing the amount of unpolymerized monomers increases the material's biostability and longevity. HPLC analysis was used to estimate the amount of TEGDMA that could be released into the body from a commercial dental composite exposed to different environments. This work revealed that the highest release was observed in acidic saliva, while the basic medium showed short-term stability. In the neutral medium, the resin exhibited stability over the 7-day incubation period. The degradation kinetics were determined using a modeling method to obtain the various kinetic parameters, including the activation energy Ea. The optimized model demonstrated that the total activation energy is influenced by the heating rate and differs according to the type of aging environment. This energy tends to increase when unpolymerized monomers have been released from the matrix resin. This work, and in particular the kinetic study, has highlighted the importance of optimum conversion of the photopolymerization to increase the activation energy of the sample. This improvement plays a crucial role in strengthening the material against the challenges posed by real-life conditions. In addition, the reduced presence of residual monomers not only has health implications, but also contributes substantially to extending the overall life of the material. Declarations Funding This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Funding The authors report no conflicts of interest and no financial support for this study. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgments The authors would like to thank Franck Collas of Mettler Toledo for his help with thermal analysis. Disclosure The authors declare that no generative AI and AI-assisted technologies were used in the writing process, and we take full responsibility for the content of publication. References Biomedical Engineering: Materials, Technology, and Applications, Wiley-VCH, 2022. ISBN: 9783527347469 Abedini, F., Ebrahimi, M., Roozbehani, A. H., Domb, A. J., Hosseinkhani, H. (2018). Overview on natural hydrophilic polysaccharide polymers in drug delivery. Polym. Adv. Technol. 29(12), 2564-2573. DOI: 10.1002/pat.4375 Ngokwey, I. L. (2017). Libération des monomères par les résines composites en odontologie conservatrice : données actuelles. Anusavice, K. J., Shen, C., Rawls, H. R. 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Boyron","email":"data:image/png;base64,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","orcid":"https://orcid.org/0000-0002-0386-5814","institution":"CNRS","correspondingAuthor":true,"prefix":"","firstName":"Olivier","middleName":"","lastName":"Boyron","suffix":""},{"id":315009935,"identity":"f643c92c-1c09-4b1b-a407-7b31fe155180","order_by":1,"name":"Rayenne Latoui","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Rayenne","middleName":"","lastName":"Latoui","suffix":""},{"id":315009936,"identity":"491e73fb-00f0-4ae3-83bf-e2de4bd0073b","order_by":2,"name":"Mohamed Affif Belhani","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Mohamed","middleName":"Affif","lastName":"Belhani","suffix":""},{"id":315009937,"identity":"4d385d54-3fb7-47ea-a7e5-702c3afc7e61","order_by":3,"name":"Djallel Bouzid","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Djallel","middleName":"","lastName":"Bouzid","suffix":""}],"badges":[],"createdAt":"2024-05-31 16:51:25","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4510299/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4510299/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s10965-024-04116-y","type":"published","date":"2024-09-04T16:05:03+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":59518665,"identity":"58eded88-5020-4ba7-abbe-098d3aa4faae","added_by":"auto","created_at":"2024-07-02 18:34:17","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":47008,"visible":true,"origin":"","legend":"\u003cp\u003eHPLC Chromatogram of TEGDMA monomer\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;t\u003csub\u003eM\u003c/sub\u003e:dead time; t\u003csub\u003eR\u003c/sub\u003e(TEGDMA): retention time of TEGDMA monomer\u003c/p\u003e","description":"","filename":"Fig1.png","url":"https://assets-eu.researchsquare.com/files/rs-4510299/v1/22b5c0eac47ebb8022068c7b.png"},{"id":59518669,"identity":"e83fec6e-c4bf-4398-99a1-f21dc23dd530","added_by":"auto","created_at":"2024-07-02 18:34:18","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":21272,"visible":true,"origin":"","legend":"\u003cp\u003eCalibration curve of TEGDMA monomer\u003c/p\u003e","description":"","filename":"Fig2.png","url":"https://assets-eu.researchsquare.com/files/rs-4510299/v1/6ff2280461714c56e5f74d30.png"},{"id":59518666,"identity":"ca33c7d6-560c-40c8-9303-4fa1ff6ff1f6","added_by":"auto","created_at":"2024-07-02 18:34:18","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":41877,"visible":true,"origin":"","legend":"\u003cp\u003eThe main effect diagram obtained by Minitab\u003c/p\u003e","description":"","filename":"Fig3.png","url":"https://assets-eu.researchsquare.com/files/rs-4510299/v1/fa87847b96a9721eac035c93.png"},{"id":59518667,"identity":"81b84658-c88d-4f43-94ce-18604f5782bc","added_by":"auto","created_at":"2024-07-02 18:34:18","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":53221,"visible":true,"origin":"","legend":"\u003cp\u003eOverlay conversion degree contours obtained by Minitab software\u003c/p\u003e","description":"","filename":"Fig4.png","url":"https://assets-eu.researchsquare.com/files/rs-4510299/v1/3bae9ef2e0669d99eef6b562.png"},{"id":59519071,"identity":"4489bc08-7bf9-48ae-9efc-782217be9fa7","added_by":"auto","created_at":"2024-07-02 18:42:18","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":392122,"visible":true,"origin":"","legend":"\u003cp\u003eInfrared spectra of the composite at different time of photopolymerization at intensity =1500 mW cm\u003csup\u003e-2 \u003c/sup\u003eand distance = 5 mm\u0026nbsp;\u003c/p\u003e","description":"","filename":"Fig5.png","url":"https://assets-eu.researchsquare.com/files/rs-4510299/v1/70498d68ad1f754e40c13e09.png"},{"id":59518672,"identity":"beb564a0-906a-45f3-8770-f793c6eddaa0","added_by":"auto","created_at":"2024-07-02 18:34:18","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":31860,"visible":true,"origin":"","legend":"\u003cp\u003eQuantity of TEGDMA released classified by media type after 1 day and after 7 days\u003c/p\u003e","description":"","filename":"Fig6.png","url":"https://assets-eu.researchsquare.com/files/rs-4510299/v1/737884fc48ce293721f04531.png"},{"id":59519070,"identity":"89cd8bd9-77fd-4707-9d5d-c4e11ca9dd3c","added_by":"auto","created_at":"2024-07-02 18:42:18","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":22256,"visible":true,"origin":"","legend":"\u003cp\u003eTGA degradation curves of the sample CP7, at 5, 10 and 20 °C min\u003csup\u003e-1\u003c/sup\u003e.\u003c/p\u003e","description":"","filename":"Fig7.png","url":"https://assets-eu.researchsquare.com/files/rs-4510299/v1/a03ad5a50695fcbeb356f240.png"},{"id":59518670,"identity":"81274760-9d6a-4e4e-b13f-e6d254276fa2","added_by":"auto","created_at":"2024-07-02 18:34:18","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":318577,"visible":true,"origin":"","legend":"\u003cp\u003eEstablishment of the kinetic model for samples Cp0, Cp7 and Cp10\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eTriangles depict the raw TGA data and the line displays the corresponding calculated regression.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"Fig8.png","url":"https://assets-eu.researchsquare.com/files/rs-4510299/v1/988f8947f1d2ac132bc17bf4.png"},{"id":64185748,"identity":"4170bb6d-1b13-4da5-a3e9-c04111fa6037","added_by":"auto","created_at":"2024-09-09 16:21:37","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1533584,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4510299/v1/6c8f2086-b7f0-437f-a740-18f9e12f564e.pdf"},{"id":59519072,"identity":"fd7be440-5457-4920-aba4-3b84abd3c0ac","added_by":"auto","created_at":"2024-07-02 18:42:18","extension":"tif","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":6023426,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eGraphical abstract\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"GraphicalabstractJournalofPolymerResearch.tif","url":"https://assets-eu.researchsquare.com/files/rs-4510299/v1/64f7fab516eb6a624c07d255.tif"}],"financialInterests":"","formattedTitle":"Enhancing Photopolymerization and Modeling Kinetic Degradation in Dental Composites","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eNanotechnology has emerged as a promising field in restorative dentistry. One notable application of nanotechnology is improving the wear resistance of dental materials through the use of resin containing nanoparticles. \u003csup\u003e[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eNano-composite are actually the only materials used for dental restoration. They serve several requirements in terms of mechanical strength, chemical stability, or even aesthetic quality. However, despite all these advantages, they present a certain toxicity which can affect human health. This toxicity is due to monomers that can be released and reach the saliva, thus entering the organism.\u003csup\u003e[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]\u003c/sup\u003e Monomer release is the result of incomplete polymerization of the composite resin, with an average degree of conversion of around 60%.\u003csup\u003e[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]\u003c/sup\u003e This low value is due to several factors, including those related to the photopolymerization, such as the light intensity, irradiation time and the distance between the resin and the light.\u003c/p\u003e \u003cp\u003eThe composite is used in an extreme condition that will favor its bio-degradation. The unpolymerized monomers of the resin matrix, particularly the basic ones like bisphenol A‑glycidyl methacrylate (BisGma), urethane dimethacrylate (UDMA), and ethoxylated bisphenol‑A dimethacrylate (BisEMA), as well as co-monomers such as tetraethyleneglycol dimethacrylate (TEGDMA) and 2‑hydroxyethyl methacrylate (HEMA), are the main cytotoxic substances that are released.\u003csup\u003e[\u003cspan additionalcitationids=\"CR6 CR7 CR8 CR9 CR10 CR11\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]\u003c/sup\u003e However, due to the complexity of the oral environment, the studies carried out have never succeeded in simulating in vitro aging of all the factors.\u003csup\u003e[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eIn this work, the influence saliva pH, aging media and oral environment temperature on the aging of the commercial dental composite \u003cb\u003e\u0026ldquo;\u003c/b\u003eNT Premium Enamel B2\u0026rdquo; was investigated. Water and saliva are the primary media used to simulate the oral environment.\u003c/p\u003e \u003cp\u003eFerracane et al. \u003csup\u003e[\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]\u003c/sup\u003e suggest that solvents with properties between those of highly aggressive organic solvents and water are highly indicative of the oral environment. In contrast, the US Food and Drug Administration (FDA) considers a 75% ethanol solution to be a clinically relevant food/oral simulation liquid. Furthermore, Tsitrou et al. \u003csup\u003e[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]\u003c/sup\u003e have studied the effect of various extraction media, including culture media, as well as storage times on the elution of monomers from modern dental composites.\u003c/p\u003e \u003cp\u003eTo predict the degradation of the composite under different conditions, the establishment of a kinetic model is crucial. However, accurate prediction necessitates knowledge of the three kinetic parameters of the model: the activation energy Ea, the pre-exponential factor A, and the kinetic model f(α). Numerous methodologies are available for determining kinetic parameters. The classical method involves developing a suitable kinetic model for the material being studied. However, due to the complexity of composite resins, we opted for an approach that utilises the Sestak-Berggren equation to determine the constants that validate the kinetic model for our specific composite.\u003c/p\u003e \u003cp\u003eThe purpose of this study was, firstly, to evaluate the effect of photopolymerisation parameters of a dental composite \"NT Premium Enamel B2\" on monomer conversion using FTIR infrared spectroscopy and Box-Behnken design as a statistical experimental design to analyse the data. Secondly, to quantify the release of unpolymerized monomers from the composite, a degradation test was conducted in artificial saliva under various conditions of pH, incubation media and treatment times using high-performance liquid chromatography (HPLC). Lastly, the thermal degradation of the samples after ageing was studied using thermogravimetric analysis (TGA) which allows the establishment of a degradation kinetic model under different conditions.\u003c/p\u003e"},{"header":"2. Experimental section","content":"\u003cp\u003e\u003cstrong\u003eMaterial\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eDental composite\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThe selected dental composite, \u0026ldquo;NT Premium Enamel B2\u0026rdquo; from coltene brasil, contains 75% inorganic charges, as well as monomers such as Bis-GMA, Bis-EMA, and TEGDMA, a BHT inhibitor, photo initiators, fillers, and dyes.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eArtificial saliva\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eArtificial saliva was prepared according to the Ringer protocol.\u003csup\u003e[\u003cspan\u003e17\u003c/span\u003e]\u003c/sup\u003e The composition of the saliva is shown in Table \u003cspan\u003e1\u003c/span\u003e.\u003c/p\u003e\n\u003cdiv\u003e\u0026nbsp;\u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv\u003eTable 1\u003c/div\u003e\n \u003cdiv\u003e\n \u003cp\u003eArtificial saliva composition.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCompounds\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eConcentration\u003c/p\u003e\n \u003cp\u003e[mM]\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eVolume\u003c/p\u003e\n \u003cp\u003e[mL]\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNa2HPO4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e100\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eKH2PO4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e100\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNaCl\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e100\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eKHCO3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e100\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCaCl2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e100\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eMgCl2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e100\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCitric acid\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.002\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eDibasic sodium phosphate dihydrate was purchased from Honeywell (Germany), monobasic potassium phosphate, citric acid monohydrate and ethanol were acquired from SIGMA-ALDRICH (Spain), potassium carbonate, calcium chloride, magnesium chloride and sodium chloride were purchased from BIOCHEM (France). HCl from Honeywell (Germany) and NaOH from BIOCHEM (France) were used to adjust the pH to the desired value. Water was purified using a Millipore water purification system.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFourier transform infrared spectroscopy (FTIR)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eInfrared spectra were recorded using Fourier transform infrared (FTIR) spectrometer from Shimadzu, equipped with a diamond crystal attenuated total reflectance (ATR) accessory. Background and samples were acquired using 40 scans at a spectral resolution of 8 cm\u003csup\u003e-1\u003c/sup\u003e from 4000 to 380 cm\u003csup\u003e-1\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eSample films (1 mm thick) were polymerized at room temperature using an \u0026lsquo;Eighteeth curing pen\u0026rsquo; LED dental lamp.\u003c/p\u003e\n\u003cp\u003eThe degree of conversion was determined by monitoring the decrease of the C\u0026thinsp;=\u0026thinsp;C band associated to the vinyl bonds of the reacting methacrylate during polymerization. \u003csup\u003e[\u003cspan\u003e18\u003c/span\u003e, \u003cspan\u003e19\u003c/span\u003e]\u003c/sup\u003e The amount of double bonds is related to the absorbance of infrared light at the wavenumber of 1636 cm\u003csup\u003e-1\u003c/sup\u003e. To reduce errors due to variation in the amounts of sample analysed, an internal standard corresponding to the absorbance of the phenyl group at 1608 cm\u003csup\u003e-1\u003c/sup\u003e was also used. The degree of conversion can therefore be calculated from the following equation. \u003csup\u003e[\u003cspan\u003e20\u003c/span\u003e]\u003c/sup\u003e\u003c/p\u003e\n\u003cdiv id=\"Equ1\"\u003e\n \u003cdiv id=\"FileID_Equ1\" name=\"EquationSource\"\u003e$$DC \\left(\\%\\right)=\\left[1-\\frac{\\left(A1636{cm}^{-1}/A1608{cm}^{-1}\\right)polymer}{\\left(A1636{cm}^{-1}/A1608{cm}^{-1}\\right)monomer}\\right]\\times 100$$\u003c/div\u003e\n \u003cdiv\u003e1\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003e\u003cstrong\u003eHigh-performance liquid chromatography analysis\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe ULC-20A system from SHIMADZU was used to perform high-performance liquid chromatography (HPLC) analysis. The system was equipped with a VP-ODS C8 column (150 x 4.6 mm with 5\u0026micro;m particle diameter) and coupled with a UV-visible detector operating at ambient temperature. Separation was achieved using a mobile phase composed of 45% acetonitrile and 55% water, with a constant flow rate of 1 mL min\u003csup\u003e-1\u003c/sup\u003e. A volume of 25 \u0026micro;L was manually injected using a micro-syringe from Thermo Scientific. The maximum absorption wavelength, previously determined using a benchtop UV-Visible spectrophotometer, was set at 205 nm, corresponding to the TEGDMA absorption. The HPLC chromatogram of TEGDMA monomer at a concentration of 10 ppm eluted at a time of 8.7 min is shown in Fig. \u003cspan\u003e1\u003c/span\u003e.\u003c/p\u003e\n\u003cp\u003eThe calibration curve used in this work is shown in Fig. \u003cspan\u003e2\u003c/span\u003e and was established using several solutions with TEGDMA concentrations ranging from 5 mg L\u003csup\u003e-1\u003c/sup\u003e to 1000 mg L\u003csup\u003e-1\u003c/sup\u003e to calculate its concentration in the composite.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eThermogravimetric analysis\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThermogravimetric analysis (TGA) was conducted using a Mettler Toledo TGA/DSC. Approximately 10 mg of samples were precisely weighed and placed into 70 \u0026micro;L aluminum oxide crucibles. The samples were heated from 25\u0026deg;C to 600\u0026deg;C at varying heating rates (5, 10, 20\u0026deg;C min\u003csup\u003e-1\u003c/sup\u003e) under a dry nitrogen atmosphere with a flow rate of 30 mL min\u003csup\u003e-1\u003c/sup\u003e.\u003c/p\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec4\"\u003e\n \u003ch2\u003e3.1. Influence of photopolymerization parameters\u003c/h2\u003e\n \u003cp\u003eThis part involves finding a reliable model for maximizing the factors that influence the efficiency of the polymerization process. The aim is to optimize the conversion degree using an experimental design.\u003c/p\u003e\n \u003cp\u003e\u003cem\u003eBox-Behnken design\u003c/em\u003e\u003c/p\u003e\n \u003cp\u003eThe Box-Behnken design was used to optimize the degree of conversion, which depends on three factors (irradiation time, intensity, distance between sample and light), the design results in a second order model. 15 tests (12 tests plus 3 center points) were performed, for each test, three repetitions were carried out. The matrix of tests and their responses are shown in Table \u003cspan\u003e2\u003c/span\u003e.\u003c/p\u003e\n \u003cdiv\u003e\n \u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv\u003eTable 2\u003c/div\u003e\n \u003cdiv\u003e\n \u003cp\u003eBox-Behnken design matrix\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"5\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eTest\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eTime\u003csup\u003ea)\u003c/sup\u003e [s]\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eDistance [mm]\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eIntensity\u003c/p\u003e\n \u003cp\u003e[mW cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e]\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eDC\u003csup\u003eb)\u003c/sup\u003e [%]\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1450\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e49.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1450\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e63.8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1450\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e48.6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1450\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e59.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e600\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e45.8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e600\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e59.4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2300\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e52.6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2300\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e63.9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e600\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e59.2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e600\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e54.9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2300\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e62.2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2300\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e59.4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1450\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e59.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1450\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e59.4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1450\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e59.4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003ctfoot\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"5\"\u003e\u003csup\u003ea)\u003c/sup\u003ePhotopolymerization time; \u003csup\u003eb)\u003c/sup\u003econversion degree calculated by FTIR spectroscopy with ATR\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tfoot\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003eThe experimental matrix consists of a Box-Behnken type design with three factors on three levels each, with a central point (the test where all the factors are adjusted to their mean). The time was varied from 10 to 60 s, while the intensity was set from 600 to 2300 mw cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e and the distance was changed from 0 to 20 mm.\u003c/p\u003e\n \u003cp\u003eThe analysis of the results was done with Minitab, a response model is established by neglecting interactions of order 3. \u003cstrong\u003eEq.\u0026nbsp;2\u003c/strong\u003e represents the model of the conversion rate by the Box-Behnken design.\u003c/p\u003e\n \u003cdiv id=\"Equa\"\u003e\n \u003cdiv id=\"FileID_Equa\" name=\"EquationSource\"\u003e\u003cimg src=\"https://myfiles.space/user_files/122228_c8a1650c59388082/122228_custom_files/img1719909476.png\"\u003e\u003cbr\u003e\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003e\u003cem\u003eWith\u003c/em\u003e, \u003cem\u003et: time of polymerization (s); D: distance between the composite and the light (mm) and I: intensity of the light (mW cm\u003c/em\u003e\u003csup\u003e\u003cem\u003e\u0026minus;\u0026thinsp;2\u003c/em\u003e\u003c/sup\u003e\u003cem\u003e).\u003c/em\u003e\u003c/p\u003e\n \u003cp\u003eThe model shows that the interaction between factors can be neglected as the coefficient value is not significant.\u003c/p\u003e\n \u003cp\u003eThis model includes second order terms, proving that certain factors follow a non-linear trend. Figure \u003cspan\u003e3\u003c/span\u003e\u0026apos;s main effect diagram shows that the polymerization time follows a second-order curve, while the other factors exhibit a linear behavior. Time is also the main factor with the highest coefficient, it reaches a plate around 40 s. On the other hand, distance is the least significant factor, being inversely proportional to the degree of conversion, while the intensity of the light source is directly proportional.\u003c/p\u003e\n \u003cp\u003e\u003cem\u003eAnalysis of variance\u003c/em\u003e\u003c/p\u003e\n \u003cp\u003eThe analysis of variance (ANOVA) indicates that the model has acceptable correlation coefficients.\u003c/p\u003e\n \u003cp\u003eThe critical Fisher factor was obtained using the Fisher table, with F\u0026thinsp;=\u0026thinsp;147.2, which is significantly higher than its critical value Fc\u0026thinsp;=\u0026thinsp;2.8. The R\u003csup\u003e2\u003c/sup\u003e and R\u003csup\u003e2\u003c/sup\u003e adjusted value were 99.2 and 98.6, respectively, indicating that the model is therefore valid.\u003c/p\u003e\n \u003cp\u003e\u003cem\u003eFactors optimization\u003c/em\u003e\u003c/p\u003e\n \u003cp\u003eThe model allowed the selection of factors to maximize the degree of conversion. According to the literature, the achievable conversion degree for composite resins is around 60%.\u003csup\u003e[\u003cspan\u003e2\u003c/span\u003e]\u003c/sup\u003e Values above this rate are considered favorable.\u003c/p\u003e\n \u003cp\u003eThe distance factor is found to be less significant, allowing for a distance value of 5 mm to facilitate polymerization in the mouth for the operator. Figure \u003cspan\u003e4\u003c/span\u003e displays the favorable combinations of polymerization time and light source intensity in white area, while the blue area indicates the conversion rate values below 60%. To optimize energy and heat generation, the optimal point is 40 seconds of polymerization time, 5 mm of distance, and an intensity of 1500 mW cm\u003csup\u003e-2\u003c/sup\u003e, as determined by the preset intensity of the dental lamp. This composition results in a conversion rate of 61.2%.\u003c/p\u003e\n \u003cp\u003eFigure \u003cspan\u003e5\u003c/span\u003e displays the infrared spectra of the composite at different polymerization time and using the optimum values of intensity and distance obtained by the Box-Benkhen design model, 1500 mw cm\u003csup\u003e-2\u003c/sup\u003e and 5 mm respectively. The figure shows the decrease in the elongation vibration peaks of methacrylate double bonds at 1636 cm\u003csup\u003e-1\u003c/sup\u003e as a function of polymerization time.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec5\"\u003e\n \u003ch2\u003e3.2. Analysis of monomer released in saliva\u003c/h2\u003e\n \u003cp\u003eThis part reports the quantification of TEGDMA released by the resin obtained with the optimized parameters. The purpose of this analysis is to measure the amount of the potentially toxic monomer that may be released into the organism while the composite is in the oral environment.\u003c/p\u003e\n \u003cp\u003eTo simulate the aging of resins in an in vitro system, four different media were used. An artificial saliva with three different pH values (acidic pH of 3.5, neutral pH of 7, and basic pH of 10)\u003csup\u003e[\u003cspan\u003e18\u003c/span\u003e]\u003c/sup\u003e and an ethanol/water medium with a 75% v/v ratio were used as two of the media.\u003csup\u003e[\u003cspan\u003e15\u003c/span\u003e]\u003c/sup\u003e The other two media were saliva with different pH values, which were used to simulate changes in pH when consuming different meals. Meanwhile ethanol was used to accelerate the degradation and aging of the composite resin as it is a good solvent for the monomers.\u003c/p\u003e\n \u003cp\u003eThe experiment involved three factors: (1) the medium (artificial saliva at three different pH values and ethanol at 75%), (2) the incubation temperature (37\u0026deg;C and 50\u0026deg;C), and (3) the incubation time (1 and 7 days).\u003c/p\u003e\n \u003cp\u003e\u003cem\u003ePreparation of samples\u003c/em\u003e\u003c/p\u003e\n \u003cp\u003eCylindrical specimens of 5 mm diameter and 2 mm thickness of the \u0026ldquo;NT Premium Enamel B2\u0026rdquo; resin composite were prepared using a Teflon mold. The composites were compressed in the mold between two glass plates and polymerized at room temperature for 40 s using an \u0026ldquo;Eighteeth curing pen\u0026rdquo; LED dental lamp with an intensity of 1500 mW cm\u003csup\u003e-2\u003c/sup\u003e at a distance of 5 mm.\u003c/p\u003e\n \u003cp\u003eThe polymerized specimens were removed from the mold, and flushed with ethanol. Then, they were immersed in 1 ml of aging medium in a 2 ml capped vial. The vials were subsequently incubated in an oven at the designated temperature for the appropriate length of time.\u003c/p\u003e\n \u003cp\u003eThe analysis was conducted using high-performance liquid chromatography (HPLC). Table \u003cspan\u003e3\u003c/span\u003e summarizes the samples prepared, their aging conditions and the results obtained for the samples submitted to different conditions.\u003c/p\u003e\n \u003cp\u003eThe study findings suggest that the amount of TEGDMA released is influenced by the type of medium, pH, and incubation temperature. Moreover, the release of TEGDMA is increased with the residence time of the composite in the medium.\u003c/p\u003e\n \u003cdiv\u003e\n \u003ctable id=\"Tab3\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv\u003eTable 3\u003c/div\u003e\n \u003cdiv\u003e\n \u003cp\u003eResin composite aging conditions and HPLC analysis results\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"9\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSample\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMedium\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003epH\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eTemperature\u003c/p\u003e\n \u003cp\u003e[\u0026deg;C]\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eTime [days]\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMass\u003csup\u003ea\u003c/sup\u003e [mg]\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eArea\u003csup\u003eb\u003c/sup\u003e [mV*mV]\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eTEGDMA Concentration\u003csup\u003ec\u003c/sup\u003e [mg L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e]\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eTEGDMA quantity [\u0026micro;g g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e]\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCp1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAS\u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e37\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e69.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e33983\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCp2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e37\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e74.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1633419\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e26.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.35\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCp3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e37\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e61.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e41939\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCp4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e46.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e43653\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.02\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCp5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eEtOH/water\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e37\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e62.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1975042\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e32.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.51\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCp6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e37\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e66.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e237474\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.06\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCp7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e37\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e67.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2660754\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e43.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.64\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCp8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e37\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e64.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e698364\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e11.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.17\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCp9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e68.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e369540\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.09\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCp10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eEtOH/water\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e37\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e77.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3690466\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e60.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.77\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCp11\u003csup\u003ee\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eEtOH/water\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e37\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e67.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e23141306\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e378.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.60\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003ctfoot\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"9\"\u003e\u003csup\u003ea\u003c/sup\u003einitial mass of the sample before degradation; \u003csup\u003eb\u003c/sup\u003earea of the TEGDMA peak obtained by HPLC at 8.6 minutes; \u003csup\u003ec\u003c/sup\u003econcentration of TEGMA in the sample determined by the calibration curve; \u003csup\u003ed\u003c/sup\u003eartificial saliva;\u003csup\u003ee\u003c/sup\u003eunpolymerized sample\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tfoot\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003eThe Table \u003cspan\u003e3\u003c/span\u003e displays the effect of the degree of conversion on monomer release in saliva. The Cp11 sample un-polymerized had the greatest amount of released TEGDMA. This release represents the dissolution and migration of TEGDMA in artificial saliva. As the conversion degree increased after polymerization, the number of unbound monomers decreased, resulting in a small amount of TEGDMA released in all polymerized samples.\u003c/p\u003e\n \u003cp\u003eThe amount of TEGDMA released varies from 0.01 to 0.77 \u0026micro;g g\u003csup\u003e-1\u003c/sup\u003e. This indicates that HPLC is a reliable method for determining and quantifying the monomers. Figure \u003cspan\u003e6\u003c/span\u003e shows the amount of TEGDMA measured for each type of medium, demonstrating that the type of aging medium used has a real effect on the release of TEGDMA.\u003c/p\u003e\n \u003cp\u003eAs expected, ethanol/water at 75% was the medium with the highest release of TEGDMA. This high release is attributed to the ability of ethanol to be a good solvent for monomers, including TEGDMA. The artificial saliva with acid pH of 3.5 also showed a significant amount of released. The low pH values promote the release of monomers as well as the degradation of composite resins.\u003c/p\u003e\n \u003cp\u003eThe neutral medium showed stability during the 7 days of incubation. This stability is less evident during incubation at high temperature. The basic medium, on the other hand, showed stability in the short term, but began to release monomers gradually.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec6\"\u003e\n \u003ch2\u003e3.3. Modeling of the kinetic release\u003c/h2\u003e\n \u003cp\u003e\u003cem\u003eTGA analysis\u003c/em\u003e\u003c/p\u003e\n \u003cp\u003eThermogravimetric analysis provides the mass loss as a function of time and temperature. It was carried out on two samples (Cp10 and Cp7) that have undergone different aging conditions and exhibit the highest TEGDMA release. As a reference, an untreated sample (Cp0) was also analyzed by TGA. These three samples were submitted to three heating rates (5, 10 and 20\u0026deg;C min\u003csup\u003e-1\u003c/sup\u003e).\u003c/p\u003e\n \u003cp\u003eThe TGA curves of sample Cp7 for the three heating rates are shown in Fig. \u003cspan\u003e7\u003c/span\u003e. This thermogram displays three degradation zones that are almost similar for all samples.\u003csup\u003e[22]\u003c/sup\u003e For temperatures below 300\u0026deg;C, the degradation was negligible due to the high thermal resistance of the composite. The main degradation was observed in the temperature range between 300\u0026deg;C and 500\u0026deg;C, where a rapid mass loss occurs due to the degradation of the polymer chains. Above 500\u0026deg;C, the residue is due to the inorganic part of the composite.\u003c/p\u003e\n \u003cp\u003eThe heating rate affects the degradation temperature profiles. The higher the heating rate, the more degradation is shifted to high temperatures due to degradation kinetics. For example, at the heating rate of 5\u0026deg;C min\u003csup\u003e-1\u003c/sup\u003e the sample reaches 5% degradation at a temperature of 352\u0026deg;C, while the sample at the heating rate of 20\u0026deg;C min\u003csup\u003e-1\u003c/sup\u003e does not reach the 5% degradation until reaching a temperature of 393\u0026deg;C.\u003c/p\u003e\n \u003cp\u003eUnder the influence of the kinetics of degradation, the exploitation of these different curves allowed the determination of kinetic models.\u003c/p\u003e\n \u003cp\u003e\u003cem\u003eKinetic model of release\u003c/em\u003e\u003c/p\u003e\n \u003cp\u003eThe kinetic equation of degradation is equivalent to that of chemical kinetics, expressed as:\u003c/p\u003e\n \u003cdiv id=\"Equ2\"\u003e\n \u003cdiv id=\"FileID_Equ2\" name=\"EquationSource\"\u003e$$\\frac{\\varvec{d}\\varvec{a}}{\\varvec{d}\\varvec{t}}=\\varvec{K}\\varvec{f}\\left(\\varvec{a}\\right)$$\u003c/div\u003e\n \u003cdiv\u003e3\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003eWhere, f(\u0026alpha;) is the kinetic model, and k is the rate constant obtained by the Arrhenius law:\u003c/p\u003e\n \u003cp\u003ek \u003cstrong\u003e=\u003c/strong\u003e\u003cspan\u003e\u003cspan\u003e\\(\\varvec{A}\\varvec{e}\\varvec{x}\\varvec{p}(-\\frac{{\\varvec{E}}_{\\varvec{a}}}{\\varvec{R}\\varvec{T}})\\)\u003c/span\u003e\u003c/span\u003e (4)\u003c/p\u003e\n \u003cp\u003eThe variable \u0026alpha; represents the mass lost during the thermogravimetry experiment:\u003c/p\u003e\n \u003cp\u003e\u0026alpha; \u003cstrong\u003e=\u003c/strong\u003e \u003cspan\u003e\u003cspan\u003e\\(\\frac{{\\varvec{W}}_{\\varvec{i}}-{\\varvec{W}}_{\\varvec{f}}}{{\\varvec{W}}_{\\varvec{f}}}\\)\u003c/span\u003e\u003c/span\u003e (5)\u003c/p\u003e\n \u003cp\u003eWhere W\u003csub\u003ei\u003c/sub\u003e is the initial mass, and W\u003csub\u003ef\u003c/sub\u003e is the final mass. Finally, the combination of Equations \u003cspan\u003e3\u003c/span\u003e and 4 results in the following formula:\u003c/p\u003e\n \u003cdiv id=\"Equ3\"\u003e\n \u003cdiv id=\"FileID_Equ3\" name=\"EquationSource\"\u003e$$\\frac{\\varvec{d}\\varvec{a}}{\\varvec{d}\\varvec{t}}=\\varvec{A}\\varvec{e}\\varvec{x}\\varvec{p}(-\\frac{{\\varvec{E}}_{\\varvec{a}}}{\\varvec{R}\\varvec{T}})\\varvec{f}\\left(\\varvec{a}\\right)$$\u003c/div\u003e\n \u003cdiv\u003e6\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003eVarious methodologies can be applied to determine kinetic triplet values. The most common approach is to select a suitable kinetic model from the existing ones. The majority of these models are derived from the modified version of the empirical equation of Sestak-Beggren, refer to Eq.\u0026nbsp;7, by adjusting the constants c, n, and m. This technique is referred to as \u0026quot;model fitting\u0026quot;. [20]\u003c/p\u003e\n \u003cp\u003ef(\u0026alpha;)\u0026thinsp;=\u0026thinsp;c(1-\u0026alpha;) n\u0026alpha;m (7)\u003c/p\u003e\n \u003cp\u003eCombining the Eq. 7 of Sestak-Beggren model with the kinetic Eq. \u003cspan\u003e6\u003c/span\u003e yields the following relation:\u003c/p\u003e\n \u003cp\u003eln \u003cstrong\u003e(\u003c/strong\u003e\u003cspan\u003e\u003cspan\u003e\\(\\frac{\\frac{\\varvec{d}\\varvec{a}}{\\varvec{d}\\varvec{t}}}{{\\left(1-\\varvec{\\alpha }\\right)}^{\\mathbf{n}}{\\varvec{\\alpha }}^{\\mathbf{m}}}\\)\u003c/span\u003e\u003c/span\u003e\u003cstrong\u003e)\u0026thinsp;=\u003c/strong\u003e\u0026thinsp;lncA\u003cstrong\u003e-\u003c/strong\u003e \u003cspan\u003e\u003cspan\u003e\\(\\frac{{\\varvec{E}}_{\\varvec{a}}}{\\varvec{R}}\\frac{1}{\\varvec{T}}\\)\u003c/span\u003e\u003c/span\u003e (8)\u003c/p\u003e\n \u003cp\u003eThe Eq.\u0026nbsp;8 can be expressed as a linear function of the form y\u0026thinsp;=\u0026thinsp;b-ax, with x\u0026thinsp;=\u0026thinsp;1/T .\u003c/p\u003e\n \u003cp\u003eThe equation for this model requires the determination of the values of \u0026alpha;, t and T, which can be obtained from TGA measurements. However, the values of the constants n and m are still unknown. To determine them, a MATLAB program was used to optimize the correlation coefficient (r) of Eq. 8, with the aim of finding the values of n and m that produce a Pearson correlation coefficient closest to 1. \u003csup\u003e[\u003cspan\u003e20\u003c/span\u003e, \u003cspan\u003e21\u003c/span\u003e]\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eThe straight-line regression of the degradation data \u003cstrong\u003e(\u003c/strong\u003eFig. \u003cspan\u003e8\u003c/span\u003e\u003cstrong\u003e)\u003c/strong\u003e obtained by ATG on the 3 samples and at different speeds was used to determine the values of the constants. These data, given in Table \u003cspan\u003e4\u003c/span\u003e, were finally exploited to measure the activation energies for each sample.\u003c/p\u003e\n \u003cp\u003e\u003cem\u003eTriangles depict the raw TGA data and the line displays the corresponding calculated regression.\u003c/em\u003e\u003c/p\u003e\n \u003cdiv\u003e\n \u003ctable id=\"Tab4\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv\u003eTable 4\u003c/div\u003e\n \u003cdiv\u003e\n \u003cp\u003eCalculated values of constants obtained by fitting the model\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"6\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSample\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eHeating rate [\u0026deg;C min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e]\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003en\u003csup\u003ea)\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003em\u003csup\u003ea)\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003er \u003csup\u003eb)\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eEa\u003c/p\u003e\n \u003cp\u003e[Kj mol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e]\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCp0\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-0.8\u003c/p\u003e\n \u003cp\u003e-5.5\u003c/p\u003e\n \u003cp\u003e1.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.7\u003c/p\u003e\n \u003cp\u003e1.2\u003c/p\u003e\n \u003cp\u003e2.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.97\u003c/p\u003e\n \u003cp\u003e0.95\u003c/p\u003e\n \u003cp\u003e0.96\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e113\u003c/p\u003e\n \u003cp\u003e119\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e65\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCp7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-5.7\u003c/p\u003e\n \u003cp\u003e-20.4\u003c/p\u003e\n \u003cp\u003e-12.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003cp\u003e1.9\u003c/p\u003e\n \u003cp\u003e1.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.97\u003c/p\u003e\n \u003cp\u003e0.96\u003c/p\u003e\n \u003cp\u003e0.95\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e106\u003c/p\u003e\n \u003cp\u003e109\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e72\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCp10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-49.9\u003c/p\u003e\n \u003cp\u003e-29.3\u003c/p\u003e\n \u003cp\u003e-19.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.2\u003c/p\u003e\n \u003cp\u003e1.8\u003c/p\u003e\n \u003cp\u003e2.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.95\u003c/p\u003e\n \u003cp\u003e0.95\u003c/p\u003e\n \u003cp\u003e0.95\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e221\u003c/p\u003e\n \u003cp\u003e111\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e85\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003e\u003cspan\u003e\u003cem\u003econstants of Sestak-Beggren determined by MATLAB;\u003c/em\u003e \u003csup\u003e\u003cem\u003eb)\u003c/em\u003e\u003c/sup\u003e\u003cem\u003ePearson correlation coefficient;\u003c/em\u003e \u003csup\u003e\u003cem\u003ec)\u003c/em\u003e\u003c/sup\u003e\u003cem\u003euntreated sample\u003c/em\u003e\u003cbr\u003e\u003c/span\u003e\u003c/p\u003e\n \u003cp\u003eGiven the correlation coefficients greater than 0.95 (Table \u003cspan\u003e4\u003c/span\u003e), the validity of the kinetic model is confirmed for the n and m values determined. The n and m values have a variability depending on the samples and heating rates, which shows that the kinetic model does not have a constant equation with fixed coefficients. This feature highlights the advantage of using this method to determine variable coefficients, adapted to our conditions, compared with the application of pre-existing models.\u003c/p\u003e\n \u003cp\u003eConcerning the activation energies, it can be seen that for high heating rates (10 and 20\u0026deg;C min\u003csup\u003e-1\u003c/sup\u003e), the activation energy values are close. They are significantly higher than the values obtained at a heating rate of 5\u0026deg;C min\u003csup\u003e-1\u003c/sup\u003e. This result suggests that excessive heating rates do not allow the system to reach a correct equilibrium and affect the Ea measurements. Consequently, we considered the data obtained at 5\u0026deg;C min\u003csup\u003e-1\u003c/sup\u003e to determine the coefficients n and m and subsequently the activation energy.\u003c/p\u003e\n \u003cp\u003eThe activation energies of the three samples determined at a heating rate of 5\u0026deg;C min\u003csup\u003e-1\u003c/sup\u003e are quite similar. Sample Cp0, which was not subjected to conditions that could degrade the resin, shows a lower activation energy, proving the presence of residual monomers in the resin and facilitating its degradation. In contrast, sample Cp10, which was exposed to the most favorable conditions for the release of monomer (as shown in Table \u003cspan\u003e3\u003c/span\u003e), has the highest activation energy, meaning that it will require more energy to degrade. Sample Cp7, which has a monomer release rate between the two samples (as shown in Table \u003cspan\u003e3\u003c/span\u003e\u0026apos;s HPLC measurement), exhibits an intermediate activation energy.\u003c/p\u003e\n \u003cp\u003eFinally, these study on activation energy highlights the importance of achieving an optimum photopolymerization conversion to increase the activation energy of the sample, thereby improving its resistance to usage conditions. In addition to its health implications, the reduced presence of residual monomer in the resin contributes to a longer material lifetime.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eThe relevance and originality of this study lies in its comprehensive approach, from the optimization of the dental composite photopolymerization process to the understanding of its degradation kinetics in the practical usage environment.\u003c/p\u003e \u003cp\u003eThe Box-Behnken experimental design was revealed to be useful to optimize the polymerization process to increase the degree of conversion. The identified optimization conditions include a photopolymerization time of 40 seconds, an irradiation intensity of 1500 mW cm\u003csup\u003e-2\u003c/sup\u003e and a distance of 5 mm. These conditions lead to a degree of conversion of 61%. Reducing the amount of unpolymerized monomers increases the material's biostability and longevity.\u003c/p\u003e \u003cp\u003eHPLC analysis was used to estimate the amount of TEGDMA that could be released into the body from a commercial dental composite exposed to different environments. This work revealed that the highest release was observed in acidic saliva, while the basic medium showed short-term stability. In the neutral medium, the resin exhibited stability over the 7-day incubation period.\u003c/p\u003e \u003cp\u003eThe degradation kinetics were determined using a modeling method to obtain the various kinetic parameters, including the activation energy Ea. The optimized model demonstrated that the total activation energy is influenced by the heating rate and differs according to the type of aging environment. This energy tends to increase when unpolymerized monomers have been released from the matrix resin.\u003c/p\u003e \u003cp\u003eThis work, and in particular the kinetic study, has highlighted the importance of optimum conversion of the photopolymerization to increase the activation energy of the sample. This improvement plays a crucial role in strengthening the material against the challenges posed by real-life conditions. In addition, the reduced presence of residual monomers not only has health implications, but also contributes substantially to extending the overall life of the material.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eFunding\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Funding The authors report no conflicts of interest and no financial support for this study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDeclaration of Competing Interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors would like to thank Franck Collas of Mettler Toledo for his help with thermal analysis.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDisclosure\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that no generative AI and AI-assisted technologies were used in the writing process, and we take full responsibility for the content of publication.\u003c/p\u003e\n"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eBiomedical Engineering: Materials, Technology, and Applications, Wiley-VCH, 2022. 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(2014). Effect of extraction media and storage time on the elution of monomers from four contemporary resin composite materials. Toxicology international, 21(1), 89. DOI: 10.4103/0971-6580.128811\u003c/li\u003e\n\u003cli\u003eBenhamada, M., Bouzid, D., Saouli, O., Boyron, O. (2015). The effects of hydrothermal ageing characterized by SEC on the degradation kinetic of polycarbonate calculated through TGA. Chem. Eng. Trans., 43, 1183-1188. DOI: 10.3303/CET1543198\u003c/li\u003e\n\u003cli\u003eMohammed, I., Alwahab, Z. N. (2018). A comparison of the effect of artificial saliva with different pH values on surface roughness of veneering ceramic to metal and zirconia substructure (in vitro study). World J. Pharm. Res., 7(17), 107. DOI: 10.20959/wjpr201817-13326.\u003c/li\u003e\n\u003cli\u003eRastelli, A. N. S., Jacomassi, D. P., Bagnato, V. S. (2008). Degree of conversion and temperature increase of a composite resin light cured with an argon laser and blue LED. Laser Physics, 18, 1570-1575. DOI: 10.1134/S1054660X0812030X\u003c/li\u003e\n\u003cli\u003eRuyter, I. E., Svendsen, S. A. (1978). Remaining methacrylate groups in Composite restorative materials. Acta Odontol Scand, 36, 75-82. DOI: 10.3109/00016357809027569\u003c/li\u003e\n\u003cli\u003eRuyter, I. E., Gyorosi, P. P. (1976). An Infrared Spectroscopic Study of Sealants, Scand J Dent Res, 84, 396-400. DOI: 10.1111/j.1600-0722.1976.tb00512.x\u003c/li\u003e\n\u003cli\u003eBenhamada, M. (2015). Etude de la migration du Bisph\u0026eacute;nol A des mat\u0026eacute;riaux plastiques alimentaires. PhD thesis, Constantine 3, Algeria.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"journal-of-polymer-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jpol","sideBox":"Learn more about [Journal of Polymer Research](https://www.springer.com/journal/10965)","snPcode":"10965","submissionUrl":"https://www.editorialmanager.com/jpol/","title":"Journal of Polymer Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"biocompatible composites, photopolymerization, Box-Behnken design, monomers release, degradation kinetics, TGA","lastPublishedDoi":"10.21203/rs.3.rs-4510299/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4510299/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study aims to optimize the photopolymerization process of a dental composite in order to increase the degree of conversion and reduce the release of unpolymerized monomers. In addition, it seeks to understand the kinetics of composite degradation under various oral environmental conditions.\u003c/p\u003e \u003cp\u003eOptimization of the photopolymerization process is carried out using a Box-Behnken design, exploring factors such as irradiation time, intensity and distance. Infrared spectroscopy is used to evaluate photopolymerization parameters. Release of unpolymerized monomers is quantified using liquid chromatography at different pH levels, incubation media and time. Thermogravimetric analysis is used to study thermal degradation and establish a kinetic model.\u003c/p\u003e \u003cp\u003eOptimized conditions for photopolymerization, determined as an irradiation time of 40 seconds, an intensity of 1500 mW cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, and a distance of 5 mm, lead to a degree of conversion of 61%, reducing the presence of unpolymerized monomers. Chromatographic analysis reveals a pH-dependent release of monomers, with acid saliva showing the highest release. Thermal analysis indicates variable activation energy values depending on ageing conditions, underlining the importance of optimal conversion for increased material strength.\u003c/p\u003e \u003cp\u003eThis study offers a comprehensive approach to improving the properties of dental resins, providing optimized conditions for light-curing that increase material strength.\u003c/p\u003e","manuscriptTitle":"Enhancing Photopolymerization and Modeling Kinetic Degradation in Dental Composites","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-07-02 18:34:13","doi":"10.21203/rs.3.rs-4510299/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2024-06-16T19:29:04+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-06-16T12:24:22+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Journal of Polymer Research","date":"2024-06-04T15:42:24+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-06-03T00:07:53+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Polymer Research","date":"2024-05-31T12:51:11+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-polymer-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jpol","sideBox":"Learn more about [Journal of Polymer Research](https://www.springer.com/journal/10965)","snPcode":"10965","submissionUrl":"https://www.editorialmanager.com/jpol/","title":"Journal of Polymer Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"97adb301-ff7b-45a9-aa7c-94bf158994b6","owner":[],"postedDate":"July 2nd, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-09-09T16:10:27+00:00","versionOfRecord":{"articleIdentity":"rs-4510299","link":"https://doi.org/10.1007/s10965-024-04116-y","journal":{"identity":"journal-of-polymer-research","isVorOnly":false,"title":"Journal of Polymer Research"},"publishedOn":"2024-09-04 16:05:03","publishedOnDateReadable":"September 4th, 2024"},"versionCreatedAt":"2024-07-02 18:34:13","video":"","vorDoi":"10.1007/s10965-024-04116-y","vorDoiUrl":"https://doi.org/10.1007/s10965-024-04116-y","workflowStages":[]},"version":"v1","identity":"rs-4510299","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4510299","identity":"rs-4510299","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}