Evaluation of the accuracy of different intraoral scanning techniques under rubber-dam isolation: An invitro study

Background: The application of rubber dam during intraoral scanning provides the ideal conditions for scanning including operative field clarity, moisture reduction, gingival retraction, and isolation from saliva, blood, and tongue. Aim of the study: The purpose of this study was to evaluate the accuracy of intraoral scanning under rubber dam isolation using cut and lock techniques. Materials and methods: A lower first molar in mandibular typodont was prepared for indirect onlay restoration. The reference typodont was then digitized as a reference model using a desktop scanner (MD-1D0410, Medit, South Korea) to obtain a reference standard tessellation language (STL). Thirty digital scanning procedures were performed on the reference model using IOS (i7oo wireless, Medit, South Korea) with three different scanning techniques as follows: Group I: scans were done for the full arch without rubber dam (No-RD) and 10 STL _G1 files were exported (control group), G roup II: scans were done under RD with cut technique (RD-C), where a digital scan was done for the full arch of the typodont first. Then, the prepared area was cut using the software tool and then rescanned again after applying the rubber dam. The procedure was repeated till 10 STL _G2 files were exported. Group III: scans were done under rubber dam isolation using lock technique (RD-L), where a digital scan was done for the prepared area first under rubber dam with at least one tooth distal and one tooth mesial to the prepared tooth. Then the prepared area was locked and then a complete arch scan was completed after removal of the rubber dam and repeated till 10 STL _G3 files were exported.The digital scans were imported to a reverse engineering software program (Geomagic Control X; 3D Systems) to calculate the 3D deviation and assess scanning accuracy using the root mean square (RMS) error, calculated in terms of two regions of interest, one including the full arch dentition (Dentition Area-DA) extending from the distal of the right second molar till the distal of the left second molar, and another area of the onlay preparation surface (Preparation Area-PA). Results: For DA trueness, Group I, with a mean of 60.58 ± 13.19 µm, showed significantly lower error values than both Group II (90.00 ± 13.86 µm) and Group III (84.08 ± 10.99 µm). However, no significant difference was found between Group II and Group III (p = 0.982). When examining DA precision, Group I (57.68 ± 13.60 µm) again demonstrated significantly lower error values compared to Group II (89.71 ± 12.15 µm) and Group III (79.53 ± 10.85 µm). For PA measurements, Group I (43.45 ± 16.45 µm) showed better trueness than Group II (58.33 ± 18.88 µm) and Group III (53.43 ± 19.74 µm), but no significant difference was observed among the groups (p = 0.251). Also, Group I exhibited higher precision (41.24 ± 17.42 µm) compared to Group II (64.35 ± 18.40 µm), with a p value of 0.017, while no significant difference was found between Group II and Group III (p = 0.704). Conclusion: Rubber dam isolation was shown to negatively influence the overall accuracy of intraoral scanning when compared to scans without isolation. However, both the cut and lock techniques produced results within clinically acceptable thresholds, with the lock technique demonstrating superior reliability over the cut technique, particularly in single indirect restorations. These findings suggest that while optimal accuracy is achieved without rubber dam isolation, the lock technique provides a clinically viable alternative when isolation is required. Clinical Implications : In cases which require rubber dam isolation, scanning using the lock technique provides greater accuracy and reliability than the commonly used cut technique. Although full-arch scans without isolation remain the most accurate, the lock technique yields clinically acceptable results for single-tooth restorations, offering clinicians a practical and predictable alternative in situations where isolation is essential.