4. Discussion
SMEAR LAYER
The present study aimed to evaluate the effectiveness of an Er:YAG laser protocol used to activate EDTA using different shapes of laser tips (flat and tapered) for different periods (10 and 20 s) for two cycles when and to compare it with the current common ultrasonic activation protocol. Three different parameters were analyzed using SEM images, these included the smear layer removal, count of exposed tubules, and count of remaining debris at the apical third.The overall result of the current study shows that the least effective laser group was observed for Laser 4, where LAI was applied using a tapered fiber tip for 20 s. Both smear layer removal and debris removal were significantly lower than in the control group (PUI); this again can be interpreted by the model of the photoacoustic streaming that results from using that shape of fiber tip for that specific time. Based on this interpretation, other factors may play a role in the photoacoustic streaming model and the outcome of LAI. Some of the factors to be considered are the size, shape, and length of the root canal.De Groot, et al. [A study was done by De Moor et al. [In our study, the temperature changes on the outer root surface during activation induced by an Er:YAG laser utilizing 17% EDTA solution were measured on the outer root surface. The results showed that the temperature change was not more than 4 °C, and that the average temperature range was 23.2–27.1 °C. Kreisler et al. [This is an in vitro study where the experiment’s conditions may not represent the real clinical conditions; therefore, the results should be extrapolated carefully. First, the mechanism of LAI action contains generating waves and bubbles that traveled into the irrigant and is followed by the implosion of irrigant bubbles. The interaction between the original waves and the waves that are reflected from the canal walls may differ according to the size of the prepared root canal. The root canals in this study were prepared to a standard volume using a rotary file system. This means, that the LAI results found in this study may differ if applied to other canals that were prepared using different files. Second, the change in the distance between the laser tip and the apical third may also result in different findings for the same reason. The distance of the 12 mm applied in this study may not be applicable for all teeth that need root canal treatment. Lastly, the results might differ with other rotary file systems; therefore, further studies are desirable to thoroughly evaluate the efficiency of laser-activated irrigation (LAI) while keeping these limitations in mind.