Purpose: The aim of this study was to compare the effect of rotary (air-driven, electric-driven) and oscillating (piezoelectric ultrasonic) handpieces on the quality of crown preparation, marginal integrity, and internal adaptation of monolithic zirconia crowns. Materials and Methods: Seventy-two standardized premolar preparations were performed using the air-driven handpiece with a guide pin-ended tapered fissure diamond bur on a modified dental surveyor. The finishing process utilized three handpiece types (n = 24/group) with fine/superfine diamond burs under controlled force with a fixed number of rotations and controlled advancement time. Marginal/internal adaptation was evaluated via the triple-scan technique; defects (marginal, axial, and occlusal) were quantified based on predefined criteria through the inspection of the Standard Tessellation Language (STL) file. Results: One-way ANOVA with Tukey HSD and Kruskal–Wallis with Dunn–Bonferroni tests were utilized. The marginal gap showed no significant differences (p > 0.05, η² = 0.04). The electric handpiece outperformed the ultrasonic (p = 0.023, η² = 0.105) in internal adaptation, while the air-driven showed no differences (p > 0.05). The ultrasonic handpiece produced fewer marginal defects than the air-driven (p = 0.039, ε² = 0.132), but more axial defects (median 9 vs. 6, p = 0.014, ε² = 0.168) than the electric handpiece and occlusal defects (5 vs. 3, 4 p = 0.007, p = 0.015, ε² = 0.227) than rotary handpieces. The air-driven handpiece exhibited comparable defect numbers to the electric handpiece without statistical significance (p > 0.05). Conclusions: Handpiece selection had a small effect on marginal adaptation but more pronounced effects on overall defect formations and internal adaptation. The ultrasonic handpiece’s decreased marginal defects but variable axial/occlusal results reveal technological constraints, whereas rotary handpieces’ consistency reflects their operator-dependent nature.

Background: Direct composite veneers for multiple anterior diastemas still present a challenge for a predictable palatal contour and controlled interproximal emergence profiles for interproximal emergence. Conventional matrices are not positionally stable and do not allow for morphological control, thereby leading to a technique-dependent procedure with the risk of inter-tooth asymmetry. Purpose: To present a dual matrix technique using liquid dam stabilization and a pull-through interproximal contouring while placing direct composite veneers in multiple anterior diastemas. Technique and case description: A 22-year-old female patient presented with bilateral peri-central diastemas (between teeth 12–11 and 21–22) and required a full aesthetic rehabilitation. The 2D-Digital Smile Design template was helpful for treatment planning. Composite veneers were placed on teeth 15 to 25. The isolation was performed using a rubber dam, and a palatal shell was fabricated using a transparent matrix modified extraorally and stabilized using liquid dam material. A pre-curved celluloid matrix was pulled from the facial to the palatal surface to form the interproximal forms and contact points. Composite resin was placed incrementally in dentin and enamel layers. The 10 restorations were evaluated at baseline (one week after the procedure) and at 12 months by both the modified United States Public Health Service (USPHS) and Fédération Dentaire Internationale (FDI) clinical performance grading criteria. Results: All restorations showed Alpha (USPHS)/FDI Score 1 criteria for all parameters examined at baseline. Marginal integrity, marginal adaptation, surface texture, color match, postoperative sensitivity, secondary caries, and tooth integrity were all Alpha/FDI Score 1 at the 12-month follow-up. Mild staining was found at three interproximal sites (15%) and marginal discoloration at one restoration (10%) (Bravo/FDI Score 2–3). Two restorations (20%) had a modest loss in surface luster, and one restoration (10%) had mild gingival marginal redness (both Bravo/FDI Score 2). One restoration had a localized incisal chip graded Bravo (USPHS)/FDI Score 3, which was successfully corrected chairside. No secondary caries or other biological problems were noted. Conclusions: The dual-matrix technique is a conservative single-visit procedure for the closure of anterior diastemas that can improve morphological control and reduce technique sensitivity. Concurrent use of USPHS and FDI criteria enabled comprehensive exploration and direct comparison with current studies.