Investigation of the effect of sealer activation methods on dentin penetration and bond strength when applied with different root canal filling techniques: CLSM evaluation

The aims of this study were to evaluate the effect of three different root canal sealer activation methods on dentin tubule penetration values and bond strength in root canals filled using different root canal filling techniques and to investigate the correlation between them. 176 maxiller central incisors were used in our study. The standard root lengths of 15 mm were created by removing the crowns of all dental specimens. Root canals were prepared to file X4 with ProTaper Next nikel titanium rotary files. Firstly, all samples divided into 4 equal groups according to the sealer activation method, one of which was the control group: (1. No activation (control), 2. Manual dynamic activation (MDA), 3. Sonic activation (EDDY) and 4. Passive Ultrasonic activation (PUA)). Subsequently, each group was divided into 4 subgroups according to the obturation technique: A. Lateral condensation, B. Single cone, C. Sealer without gutta-percha, D. Continuous wave obturation (Elements) (n=11 for each group). After the root canal obturation was completed, 3 sections of 1mm thickness were obtained for each sample, coronal-middle-apical. First, the dentin tubule penetration percentage, area and depth of the sections were evaluated by confocal laser scanning microscope and then the same sections were subjected to push-out test to examine the bond strength values. One-way ANOVA tests were used for statistical analysis of data, for multiple comparisons Kruskal Wallis test was used and Spearman test was used for correlation between variables. When the data obtained in our study were evaluated; There was no statistically significant change in the penetration percentages of any sealer activation methods compared to the groups filled with lateral condensation (p> 0.05). It was observed that PUA and EDDY caused decrease in sealer penetration area and depth, but only PUA decrease caused a statistical difference (p≤0.05). When the bond strength values were examined, it was seen that PUA and EDDY decreased these values and MDA increased, but these changes were not statistically significant (p> 0.05). In groups filled with single cone technique; no significant change in penetration percentage values could be obtained with sealer activation. When the penetration area, penetration depth and bond strength values were examined, only a significant increase of these values could be observed by manual dynamic activation (p≤0.05), but the changes caused by other activation methods did not create a statistical difference (p> 0.05). EDDY group showed the highest penetration values only in the sealer-filled groups, but no statistical difference was found between any of the groups (p> 0.05). Also; it was observed that all activation groups decreased the bond values but there was a statistically significant difference only in the PUA activated group (p> 0.05). In the root canals filled with continuous wave obturation technique, no sealer activation method showed a statistically significant difference in penetration percentage, area and depth. When the bond strength values were examined, it was observed that PUA and EDDY decreased these values and this decrease made a statistically significant difference. Considering the limitations of this study it can be said that the sealer activation methods effect root canal dentin tubule penetration (percentage, area and depth of penetration) and bond strength values in varying rates. In addition, this effect may show different results when different root canal filling techniques are applied. Manual dynamic activation, which is a simple and inexpensive method that does not require additional equipment, can be preferred, especially in the single-cone technique since it can increase tubular penetration values and bond strength values. In warm gutta-percha technique, sonic and ultrasonic systems can reduce the bond strength values when used with increasing frequency and activation times. Although the bond strength values vary depending on the root canal filling technique, they are independent from dentin tubule penetration values Key words: bond strength, confocal laser scanning microscope, sealer activation, sealer penetration, sonic activation, ultrasonic activation