The CAD/CAM system has been in use in the industry for decades and has been popular in recent years with its use in many areas of dentistry. These systems' numerous advantages over conventional methods, coupled with the ongoing advancement of intraoral scanner technologies, have led to their frequent preference among clinicians. It is well known that the method of rescanning, which is frequently employed in clinical settings to acquire data from previous, can also affect the accuracy of the results. In addition, it has been observed that the efficacy of the rescanning method varies depending on the intraoral scanner utilized.. On the other hand, the "cut-out-rescan" technique is a procedure performed on a prepared tooth that involves cutting and rescanning the tooth based on a previously performed diagnostic scan.Considering this information, the objective of this in vivo study was to assess the accuracy of four different scanners using a cut-out-rescan procedure with a rubber dam isolation. This clinical study was conducted with the approval of a local ethics committee (Protocol number: 09.2024.1000). Informed consent was obtained from each patient. 20 patients with adequate oral health who had daily routine appointments for treatment at Marmara University restorative dentistry department were included in the study. Exclusion criteria for the study were missing premolar and molar teeth (except wisdom teeth) or the presence of amalgam and ceramic restorations that could affect the scanning in the right hemi-arc of the mandible. Using of intra oral scanners was performed by a restorative dentist with 5 years of experience.The patients' mandibular arches were scanned with 4 different intraoral scanners (IOS) (Trios 3, 3Shape; Primescan, Dentsply; Element 5D, iTero; Lumina, iTero) prior to the procedure, and the obtained digital impressions were stored as a standard tessellation language (STL) file. The digital scan had appropriate anatomic references to enable a proper matching with the digital scan taken after teeth preparation. The official scanning strategy and ambient scanning light conditions in the manufacturer's instructions were followed for all scanners. A 15-minute break was taken between the different experimental groups to reduce operator fatigue, and the IOS was calibrated before each experimental scan according to the manufacturer's recommendations.The 2nd premolar, 1st, and 2nd molar teeth were isolated with a rubber dam (medium; Nic Tone, Manufacturera Dental Continental) to be included in the operation field. Clamps were placed on the 2nd premolar and 2nd molar teeth. It was aimed to facilitate the second scanning process by expanding the isolation area to include 3 teeth.

A flowable composite was applied by placing Teflon tape on the occlusal surface of the 1st molar to create a difference in its morphology. In the procedure that simulated the final impression process under rubber dam isolation, the relevant tooth was marked on the initial scan along with the contact areas of the adjacent teeth. The marked area which the to be re-scanned, was trimmed away from the virtual casts. The diameter of the mesh holes was controlled by adjusting the settings of the automatic mesh hole generator in the software program of the IOS. Subsequently, the mesh hole area was rescanned starting on the occlusal surface of the second molar, moving toward the occlusal of the first molar to the occlusal of the second premolar, then the buccal surfaces of the second premolar, followed by the first molar and second molar. The rescanning procedures ended with the lingual surfaces of the second molar, followed by the lingual surfaces of the first molar and second premolar. Following the second scan, the area was re-scanned in high-resolution mode, where higher mesh quality could be achieved. The software of the intraoral scanner automatically fused two different data sets obtained by initial/reference and preparation digital scans. Data about tooth positions, morphologies, rubber dam, and surrounding soft tissues was integrated simultaneously. The obtained final scan was exported as an STL file. The discrepancy examination was achieved using the Oracheck Software (Dentsply Sirona, Germany) program, which allows for a 3D comparison between two digital scans utilizing the best-fit algorithm. The initial/reference and final STL files were imported into the software program and three-dimensional images of the 2nd premolar, 1st molar and 2nd molar teeth were superimposed. Gingiva and rubber dam records were removed from the digital models with the "cutting" and "editing" tools. Deviations between models were obtained and recorded volumetric (mm3) and distance (mm) and analyzed quantitatively. Trueness was defined as the average absolute distance between the initial and the final digital scans.Data were analysed with IBM SPSS v23 and Jamovi software. The conformity of the data to normal distribution was analysed by Shapiro-Wilk test. Since the data by tooth and scanner were not normally distributed, they were analysed by Robust ANOVA using the WALRUS package. Intraoral general evaluations were analysed by Kruskal Wallis test. Multiple comparisons were made with Bonferroni Test. The relationship between quantitative data that did not show normal distribution was analysed by Spearman's rho correlation. Intraobserver agreement was analyzed with intraclass correlation coefficient. Median (minimum-maximum) was used to represent quantitative data. Significance level was taken as p\<0.050.