The purpose of this study was to evaluate muscle activation and fatigue in the operator during tooth preparation and intraoral scanning by simulating these tasks in two types of dental unit chair systems (UCS). Six participants were recruited, and the above tasks were simulated. Electrodes were placed on the skin over five types of muscles (arm, neck, and shoulder muscles), and the maximal voluntary contraction (MVC) was measured. Electromyography (EMG) was assessed during the simulation, and EMG values were normalized using MVC. The root mean square (RMS) EMG (%MVC) and muscle fatigue (%) were calculated. Owing to a lack of normal distribution of the data, Mann–Whitney U test and Kruskal–Wallis H test were performed for statistical comparison, and Bonferroni adjustment was performed for multiple comparisons (α = 0.05). There was no significant difference in RMS EMG between the two types of dental UCS (intraoral scanning, p = 0.237; tooth preparation, p = 0.543). Moreover, the RMS EMG and muscle fatigue were not significantly different between the two tasks (p > 0.05). There was significant muscle fatigue after the intraoral scanner use was simulated thrice (p < 0.001). It is necessary to refrain from performing continuous intraoral scanning and tooth preparation and to take appropriate rest to reduce the incidence of musculoskeletal disorders in dentists in clinical settings.

This study aims to evaluate the effects of printing temperature and post-curing duration on double-bond conversion (DBC), mechanical properties, and fabrication reproducibility of three dental photopolymer resins used for fixed dental prostheses (FDPs), denture bases, and direct clear aligners. Specimens were fabricated using stereolithography and masked stereolithography three-dimensional (3D) printers at room temperature (RT, 28 °C) and 50 °C, then subjected to six post-curing durations: 0, 60, 120, 180, 240, and 600 s. DBC was measured using Fourier transform infrared spectroscopy, and tensile strength was measured using tensile testing. Furthermore, fabrication reproducibility for clinical applicability was analyzed using root mean square deviations from 3D scanning. Printing at 50 °C significantly improved the DBC, tensile strength, and fabrication reproducibility of FDP and denture base resins compared to printing at RT, enabling shorter post-curing times (p < 0.001). Clearer aligner resin specimens printed at 50 °C and post-cured for 120 s exhibited the highest fabrication reproducibility (p < 0.001), while tensile strength did not differ significantly from that of RT specimens post-cured for 240 s (p > 0.05). These findings suggest that optimizing printing temperature and post-curing time enhances the mechanical properties and fabrication reproducibility of 3D-printed dental materials.

This in vitro study evaluated the internal surface trueness and the marginal and internal fit of interim crowns fabricated from intraoral scanner (IOS; i500, MEDIT, Seoul, Republic of Korea) data, considering variations in subgingival finish line depth and the use of gingival retraction. A right maxillary first molar was prepared using a milled ceramic abutment, with subgingival finish line depths set at 0, 0.25, 0.50, 0.75, and 1.00 mm from the gingival crest. All specimens were scanned with an IOS, both with and without gingival retraction. Interim crowns were designed from the scan data and produced via three-dimensional (3D) printing. Internal surface trueness was measured using 3D inspection software (Geomagic Control X version 2022.0.0; 3D Systems, Rock Hill, SC, USA), while marginal and internal fit were assessed with the silicone replica technique. Data were analyzed using the Mann–Whitney U test and Kruskal–Wallis H test (α = 0.05). In the absence of gingival retraction, internal surface trueness and crown fit decreased significantly with increasing finish line depth (p < 0.05). At a 1.00 mm depth without retraction, internal trueness reached 100.1 ± 44.5 µm and marginal fit was 189.1 ± 42.2 µm, both exceeding clinical thresholds. With gingival retraction, trueness and fit remained stable across all depths (p > 0.05). At 1.0 mm depth, trueness was 82.0 ± 61.8 µm and marginal fit was 95.2 ± 22.9 µm, both within clinically acceptable limits. A significant correlation was observed between marginal trueness and overall fit when retraction was not performed (p < 0.05). These results demonstrate that increasing subgingival finish line depth can significantly reduce intraoral scanning accuracy, resulting in suboptimal interim crown adaptation when gingival retraction is omitted. To achieve clinically acceptable internal trueness and marginal fit, gingival displacement with a retraction cord is recommended during intraoral scanning for subgingival prosthesis fabrication.

This study aimed to evaluate the effect of pixel offset adjustments in digital light processing (DLP) three-dimensional (3D) printing on the marginal and internal fit and surface trueness of zirconia crowns. Zirconia crowns were designed using dental computer-aided design software (Dentbird; Imagoworks) and fabricated with a vat photopolymerization DLP 3D printer (TD6+; 3D Controls) under three pixel offset conditions (−1, 0, and 1). Pixel offset refers to the controlled modification of the outermost pixels in the XY plane during printing to compensate for potential dimensional inaccuracies. The marginal and internal fit was assessed using a triple-scan protocol and quantified using root mean square (RMS) values. Surface trueness was evaluated by measuring RMS, positive and negative errors between the designed and fabricated crowns. Statistical analyses included one-way ANOVA and Pearson correlation analysis (α = 0.05). The Pixel offset had a significant effect on fit accuracy and surface trueness (p < 0.05). Higher pixel offsets increased marginal discrepancies (p = 0.004), with the marginal gap exceeding 120 µm at a pixel offset of 1 (114.5 ± 14.6 µm), while a pixel offset of −1 (85.5 ± 18.6 µm) remained within acceptable limits (p = 0.003). Surface trueness worsened with increasing pixel offset, showing greater positive errors (p < 0.001). Optimizing pixel offset in DLP 3D printing is crucial to ensuring clinically acceptable zirconia crowns. Improper settings may increase marginal discrepancies and surface errors, compromising restoration accuracy.