## 4 Discussion
The smear layer in the dentin tubules was removed with the acid applied after preparation and the tubule mouths became open. The adhesive applied afterwards penetrated the tubules and created a strong bond. During rupture, there was some rupture from the tubule walls along with the resin. In the SEM image taken from a sample from the control group, the tubule mouths seen as blocked with resin cement show cohesive rupture from within the resin cement (Figure 3). When Figure 3c is examined, the tubule mouths are seen as blocked with resin cement. During rupture, cohesive rupture occurred from within the resin cement. In the clearly observed tubules, the test paste may have penetrated the tubules due to its hydrophilic properties and prevented the adhesive from entering the tubule. It is thought that this is the reason why the bond strength was significantly lower in the contamination group. For the infiltration of a monomer into dentinal tubules, etching is crucial. A phosphoric acid concentration of 35% is enough to remove the smear layer and open the dentinal tubules. Different etching techniques, such as single-, two-step, or three-step procedures, have been described in the literature. Although there is a tendency to simplify bonding procedures for ease of use, more favourable and reliable adhesion in the long term can be achieved with three-step total-etch adhesives [16; 18]. It has been strongly recommended to use the total-etch technique if IDS is to be planned [1]. Thus, the total etching protocol was followed in the current study according to the manufacturer's instructions. In clinical practice, in order to clean the residual cement more easily, we polymerize the resin cement for 3 s at 450 mW/cm in the first step. After the residual cement is cleaned, we complete the polymerization process from four directions. Since this study was planned to simulate the clinic, the same application was made to the study samples. However, this situation may cause our bond strength values to decrease. The application of a Weibull analysis is strongly suggested for strength data of brittle materials. The Weibull modulus of Group A was higher than those of both Groups B and C. The higher Weibull modulus indicates less spread of the data and less variability among the measurements. However, a lower Weibull modulus for Group C indicated a wider distribution compared to the other groups. The R\({}^{2}\) value for Group C was higher than for Groups A and B. A higher R\({}^{2}\) represents a more precise fit of each data point on the equation line. Although Group C had a relatively lower Weibull modulus, each measurement fit on the line better. The sample size of each group in this study was ten; however, it has been recommended that a sample size of thirty should be used when Weibull analysis is conducted [25]. However, several studies were conducted on fewer than 30 specimens, and Weibull analysis was used [26; 27]. Although a smaller sample size yielded enough data to analyze the Weibull modulus, it is a limitation of the current study. SEM-EDS analyses showed that cleaning procedures were unable to remove the try-in pastes entirely (Figure 5). Remnants of try-in pastes in and around openings of dental tubules prevent the penetration of DBA and decrease the bond strength values. The importance of the application of DBA to freshly cut and etched dentin before any contamination has been pointed out [1]. IDS increased the penetration of DBA into dental tubules and guaranteed the formation of resin tags, thereby improving bond strength [28; 29; 30]. Group B showed statistically higher bond strength values than Group C in the current study [1; 5]. The application of DBA immediately after dentin exposure prevented the obstruction of dentin tubules by try-in pastes. In this in vitro study, shear bond strength values were obtained in sample groups where IDS and DDS applications were made. The obtained values indicate that dental clinicians can perform IDS applications safely.