## 4 Discussion  
In endodontic procedures, minimally invasive access cavity approaches, minimally invasive instrumentation and shaping, activation and agitation of irrigation solutions with different methods, and pressureless canal filling methods are all used for minimally invasive treatment purposes [22; 23]. Many studies in the literature have emphasized the importance of preserving healthy tooth structure, especially pericervical dentin, using conservative endodontic cavities [13; 17; 24; 25]. In agreement with the results of this study, [PERSON] et al. revealed that CAC preserved more healthy dentin and pericervical dentin in comparison with TAC after root canal preparation using Wave One Gold and TruNatomy files [25]. Pericervical dentin is dentin located 4 mm coronal and 4 mm apical to the cementoenamel junction. Preservation of pericervical dentin, especially in the molar area, plays a critical role in the longstanding optimal functioning of the teeth [24]. Ni-Ti instrument systems, which increase shaping efficiency and shorten the working time, have created a revolutionary change by raising endodontic treatments to a new level. Two different Ni-Ti systems were used in this study. Due to the findings of [PERSON] et al. [26], the files used in studies must have similar apical diameters and tapers to compare morpho-geometric changes after root canal preparation. Parallel to this, in the present study, root canal preparations with OR and PU were made by selecting files with 25 apical diameters and similar tapers. OR and PU are files that have been introduced to the market by manufacturers for minimally invasive root canal shaping purposes and were therefore used in this study. At the time this manuscript was written, a single study on OR was found in the literature review. [PERSON] et al. [15] evaluated the amount of debris extruding apically after root canal preparation with OR in curved canals. Today, reciprocation is presented as a safe and viable alternative to traditional continuous rotational motion. In addition, previous studies have reported that systems operating with reciprocal motion have a 0.13-0.26% lower incidence of fracture than systems with rotation [27; 28]. On the other hand, there are two main topics for which the reciprocal movement is criticized. The first is that reciprocating instruments are more likely to promote the development or propagation of dentinal microcracks than conventional fully rotating rotary systems, while the other is likely to cause debris accumulation during preparation and the extrusion of debris from the apex [29]. In the present study, no significant difference was found in terms of volume change in the samples as a result of the preparation made with OR and PU in teeth with traditional and conservative access cavities (\(p>0.05\)). According to this result, the type of access cavity does not have any effect on the volume change as in the study of [PERSON] et al. [30]. [PERSON] et al. did not find any effect of traditional and conservative access cavities on volume change after canal preparation in a similar study on upper molars [18]. According to these results, the nature of a cavity as a traditional or conservative access cavity does not affect the volume change in the root canals because of root canal preparation and agrees with the results obtained in this study. No statistically significant difference was found among groups in terms of the change in surface area (\(p>0.05\)). From the perspective of the two different types of access cavities