## 4 Discussion
On the other hand, despite having different molecules in their organic matrices and different filler types and loading, micro-hybrid Filtek Z250 and ormocer Admira showed similar DCs in this study, which is in agreement with the study of [PERSON] et al. (2005), who recorded that ormocer Admira had similar results with the packable and hybrid RBCs [12]. It was explained in this situation that Admira contains a resin system with inorganic-organic copolymers, and this more rigid matrix of Admira with high molecular weight molecules may be the cause of high DC values. [PERSON] et al. (2002) reported that LED LCUs produce a narrow light spectrum closer to the CQ excitation peak, leading to a higher DC even at low power density [15]. Therefore, the clinician must know the emission spectrum of the light emitted from the LCU so that they can match the light to the RBC. In cases when CQ is used as a photoinitiator, the second-generation LED LCU, which has a narrow spectrum output (450-490) and appropriate intensity (>300 mw/cm\({}^{2}\)), can adequately polymerize RBCs. However, some manufacturers use a smaller amount of CQ in RBCs to lessen the undesirable yellowing color of CQ and to obtain a whiter or more translucent color in RBCs [6]. On the other hand, some RBCs use additional photoinitiators, known as co-initiators, although this is not always stated in the manufacturer's data sheets [41]. Unlike CQ, the absorption peak of these compounds is in the UV-A region (<410 nm) and extends slightly into the visible light spectrum. Since shorter wavelengths are required for the excitation of co-initiators in RBCs, the co-initiator probably cannot receive sufficient irradiation in the deepest regions and does not contribute to the polymerization reaction of RBCs containing co-initiators in case an LED LCU is used [17; 19]. The manufacturers state that the packable Filtek P60, micro-hybrid Filtek Z250, and armocer Admira used in this study contain only CQ as the photoinitiator and are without co-initiators. No finding was found for whether hybrid Tetric Ceram and flowable Tetric Flow contain co-initiators, either alone or synergistically with CQ. It has been reported that LED curing may be less effective in RBCs where initiators are present that absorb outside the relatively narrow emission of the LED LCU [15]. Thus, if an LED LCU is used for polymerization, the dental RBC should be carefully selected. Lower DC values were obtained by hybrid Tetric Ceram and flowable Tetric Flow than other RBCs placed with the three techniques in this study; therefore, it has been thought that these RBCs might contain co-initiators that absorb outside the relatively narrow emission range of the LED LCU. This situation might decrease the polymerization efficiency of the LCU. As long as manufacturers do not state all of the photoinitiator combinations in their products, the efficiency of second-generation LED LCUs in some RBCs will not be predictable [41]. Similarly, the data assessed by the handmade photoluminescence system conflict with data based on the manufacturer's information about the LED LCU used in this study. While the light intensity of the LED LCU determined by the photoluminescence system was found to be 229.153 mW/cm\({}^{2}\) at 458.595 nm, the light intensity of the LED (Ledmax 1055) stated by the manufacturers was 1350-1500 mW/cm\({}^{2}\) at 470 nm. [PERSON] and [PERSON] (2003) stated that there was no lower bound for irradiance and suggested that low-intensity curing with an LED LCU can be preferred for RBCs [42]. Lower outputs of LCUs are advantageous clinically, as less heat is transmitted to the tooth and adjacent tissues [37]. A slower polymerization curing regime may allow stress relaxation to occur during polymerization, with longer molecular chains and high flow characteristics [42]. The lower heat generated in RBC fillings is important for pulal vitality, influences the stress setup, and prevents postoperative sensitivity [9; 37; 42].