# Temperature Changes in Composite Materials during Photopolymerization
## 4 Discussion  
The research results show that the change of the polymerization time has a great impact on the mechanical properties, such as flexural strength. Furthermore, the increase of the material temperature was influenced by the polymerization time. Hence, the null hypothesis was rejected. The results demonstrated that in our study the average temperature \begin{table}
\begin{tabular}{l l l l l l} \hline \hline
**Response: dt** & & & & & \\ \hline  & Df & Sum Sq & Mean Sq & F value & Pr(\textgreater{}F) \\
**Filler** & 1 & 52.00 & 52.001 & 2.2404 & 0.1371 \\
**Polymerization** & 6 & 66.54 & 11.090 & 1.4778 & 0.3237 \\
**Residuals** & 118 & 2738.89 & 23.211 & & \\ \hline \hline \end{tabular} Mean flexural strengths as measured in each test group were higher than the minimum value for composite materials as per the ISO:4049 standard, i.e., 80 MPa (Figure 3).  
\end{table} 
Table 4: Multiple factor ANOVA test for the time of polymerization and the type of filler. Figure 3: Mean values of flexural strength (MPa) and standard deviations. as measured for all test materials did not exceed 42.0 \({}^{\circ}\)C for Fast-Cure 3 s mode. This value was exceeded for the remaining polymerization modes, reaching a maximum value of 45.8 \({}^{\circ}\)C for Fast-Cure 20 s. This value is particularly important for deep cavities with only a thin layer of dentin separating the composite material from the pulp. High temperatures can cause irreversible damage to pulp tissue, and therefore require endodontic treatment. The study of [PERSON] et al. measured the temperatures following polymerization of bonding systems (N Bond, G-Bond, OptiBond XTR, Clearfil SE, Adper Single Bond 2 and V Bond) on pre-prepared dentin discs obtained from human third molars. The study environment temperature of experiments was 37 \({}^{\circ}\)C. The irradiation time was 20 s, and the minimum and maximum temperature rise growth in all subgroups was 1.7 \({}^{\circ}\)C and 2.8 \({}^{\circ}\)C, respectively. In the case of the 20 s polymerization protocol, no dangerous rise in temperature (5.5 \({}^{\circ}\)C) was obtained for either of the bonding systems tested [16]. Our research findings revealed that the maximum temperature increase for the 20 s mode (Fast-cure, 2 \(\times\) 10 s) was 17.8 \({}^{\circ}\)C, for the Filtek Z550 material, with the lowest of 7.25 \({}^{\circ}\)C for the Essentia Medium Dentin 3 s mode. In our study the initial temperature was maintained at 29 \(\pm\) 1 \({}^{\circ}\)C. The critical pulp temperature values were not exceeded in the case of Fast-cure 3 s mode. [PERSON] et al., in their study, performed on 30 extracted human molars with class I cavities filled using a nano-hybrid material (Filtek Bulk Fill Posterior Restorative (BFP, 3M ESPE)), found the maximum temperature increase during polymerization at 0.625 mm apically from the top and center of the defect. On the basis of their results, the authors concluded that replacing pulsed or soft start modes with continuous irradiation might reduce the risk of damage to the pulp [17]. The authors' research does not confirm this thesis. For the 5 s modes (Fast-cure and Pulse-cure) and 10 s (Fast-cure, Pulse-cure and Step-cure 9 s) temperature rises were similar: \(\pm\)14 \({}^{\circ}\)C (5 s modes) and \(\pm\)15.5 \({}^{\circ}\)C (10 s modes). Another study ([PERSON] et al.) compared the rise in the temperature during polymerization of two materials (SDR, Dentsply and AURA, SDI) polymerized using two lamps (Bluephase G2, Ivoclar Vivadent, and VALO Cordless, Ultradent) in the standard output power mode. An increase of 6 \({}^{\circ}\)C was observed for the Bluephase G2 lamp, as compared to 4 \({}^{\circ}\)C for the VALO Cordless lamp for the light curing adhesive system (20 s mode without microcirculation) [18]. Our study demonstrated that for fast-cure 20 s mode (2 \(\times\) 10 s) the highest temperature increase was 17.8 \({}^{\circ}\)C, in the case of Filtek Z550 material. There was no simulated pulpal microcirculation. On the other hand, [PERSON] et al.