Evaluation of photopolymer resins for dental prosthetics fabricated via the stereolithography process at different polymerization temperatures. Part II: Dimensional accuracy and fracture load of fixed dental prostheses.

STATEMENT OF PROBLEM: Prostheses printed on a 3-dimensional (3D) printer need to undergo the postpolymerization process, which can increase the working time. However, it has been not suggested for reducing workload and improving the properties of prostheses in dental clinical practice. PURPOSE: The purpose of this in vitro study was to evaluate how the printing temperature impacts the dimensional accuracy and fracture load of 3D printed fixed dental prostheses (FDPs). MATERIAL AND METHODS: Dental prostheses were printed at room temperature (RT), 50°C, and 70°C using a stereolithography 3D printer. Subsequently, after rinsing away residual monomer, the printed parts underwent the green condition (it was not subjected to any postprocessing) and postpolymerization. The mechanical properties of the printed FDPs were determined by loading to fracture (n=6). To evaluate their clinical applicability, the dimensional accuracy and fit of FDPs fabricated at various resin polymerization temperatures were measured (n=6). The 1-way analysis of variance was used to perform statistical comparisons, followed by the Tukey honestly significant difference test (α=.05). RESULTS: The specimens printed at RT and 50°C were better than those printed at 70°C in terms of dimensional accuracy and fit (P<.05). Nonetheless, the dimensional accuracy and fit of the specimens printed at 70°C were clinically acceptable. The fracture load of the 3-unit FDPs depended significantly on the printing temperature. CONCLUSIONS: The dimensional accuracy and fracture load of the 70°C group were acceptable for FDP fabrication. Thus, the temperature of 70°C without postprocessing may help make the procedure more efficient.

Evaluation of photopolymer resins for dental prosthetics fabricated via the stereolithography process at different polymerization temperatures-Part I: Conversion rate and mechanical properties.

STATEMENT OF PROBLEM: Improvement in the mechanical properties of 3-dimensional (3D) printed dental prostheses is necessary to prevent wear caused by an antagonist or fracture. However, how different printing temperatures affect their mechanical properties is unclear. PURPOSE: The purpose of this in vitro study was to evaluate the mechanical properties of 3D printed parts fabricated at different printing temperatures. MATERIAL AND METHODS: Photopolymer specimens were fabricated at 3 different temperatures (room temperature, 50 °C, and 70 °C) using a stereolithography 3D printer. After rinsing to remove the residual monomer, the specimens were divided into 2 groups: with or without postprocessing. The viscosity of the photopolymerization resin was measured while the temperature was increased. Furthermore, the double-bond conversion (DBC) of the printed part was evaluated (n=3). Mechanical properties were investigated via dynamic mechanical analysis (n=1) and tensile testing (n=5). Statistical comparisons were performed via 1-way analysis of variance, followed by the Tukey honestly significant difference test (α=.05). RESULTS: The DBC rates of the green condition group increased from 66.67% to 86.33% with increasing temperature. In addition, these specimens exhibited improved mechanical properties and reduced residual monomer levels. CONCLUSIONS: Specimens fabricated at a temperature of 70 °C exhibited mechanical properties suitable for clinical application.

Feasibility of using an intraoral scanner for a complete arch digital scan, part 2: A comparison of scan strategies.

STATEMENT OF PROBLEM: Various strategies for intraoral scanners (IOSs) can be used to scan the oral cavity. However, research on the scan range that can be clinically is lacking. PURPOSE: The purpose of this in vitro study was to compare the 3-dimensional (3D) distortion of complete arch scans as part of the scan strategy and analyze the clinically recommended scan range. MATERIAL AND METHODS: A computer-aided design (CAD) reference model was obtained with an industrial scanner. A CAD test model was obtained by using 6 IOSs (TRIOS2, TRIOS3, CS3500, CS3600, i500, and Primescan) to apply 2 scan strategies and 2 dental laboratory scanners (DOF and E1) (N=15). All the teeth were segmented in the reference model by using 3D inspection software (Geomagic control X). The 3D analysis was performed by aligning the test model to the reference model and evaluating the root mean square values of all segmented teeth. The Mann-Whitney U-test was performed for a statistical comparison of the 2 scan strategies (α=.05), the Kruskal-Wallis test (α=.05) was used to compare the scanners, and the Mann-Whitney U-test and Bonferroni correction method were used as post hoc tests (α=.0017). RESULTS: The 8 scanners obtained significant differences in the root mean square values of all teeth (P<.001). The root mean square value of IOSs increased from the left maxillary second molar to the right maxillary second molar. The difference in the 2 scan strategies showed different patterns depending on the IOS. CONCLUSIONS: Scan strategy 2 improved the accuracy of the IOSs. TRIOS2 and CS3500 are for single crowns; TRIOS3, CS3600, and i500 are for short-span prostheses; and Primescan is for long-span prostheses.

A concept to detect a subgingival finish line using an intraoral optical coherence tomography system: A clinical report.

This clinical report introduces an approach for detecting the supragingival finish line by penetrating the teeth and gingival tissue using optical coherence tomography (OCT) technology. This approach was used in 3 patients who underwent tooth preparation with a subgingival finish line. Consequently, the subgingival finish line, typically challenging to discern clearly in intraoral scans, was identifiable in the OCT image.

Effect of distance between the abutment and the adjacent teeth on intraoral scanning: An in vitro study.

STATEMENT OF PROBLEM: The introduction of intraoral scanners has increased the use of digital technology in dental procedures. However, data on the accuracy of abutment scans according to the distance between the adjacent tooth and the abutment are lacking. PURPOSE: The purpose of this in vitro study was to compare the 3D accuracy of abutment scans according to the distance between the adjacent tooth and the abutment. MATERIAL AND METHODS: A right maxillary first molar was removed and scanned with an industrial 3D scanner, and the image was extracted as a standard tessellation language (STL) file. Six virtual models with 1-mm, 1.5-mm, 2-mm, 2.5-mm, 3-mm, and 3.5-mm spacing between abutment teeth and adjacent teeth were fabricated with an industrial computer-aided design (CAD) software program. Then, 6 master models were fabricated with a 3D printer and copied into dental gypsum. The replicated models (reference models) were scanned 20 times with an intraoral scanner (CS3600); the resulting model was referred to as the CAD test model. The adjacent teeth of the reference models were deleted, and the models were scanned with a laboratory scanner; the resulting model was referred to as the CAD reference model. The CAD reference model was used to measure the scan accuracy in 4 directions (buccal, lingual, mesial, and distal) and 4 areas (occlusal, angle, axial, and margin) by using a 3D inspection software program. The Friedman nonparametric test (α=.05) was used for comparison, and post hoc testing was performed by using the Mann-Whitney U-test and Bonferroni correction method (direction and area variables; α=.0008, distance variable; α=.0003). RESULTS: The buccal, lingual, mesial, and distal directions of the abutment were significantly different according to distance (P<.001). The margin, axial, angle, and occlusal regions of the abutment were also significantly different according to distance (P<.001). CONCLUSIONS: The distance between the abutment teeth and adjacent teeth affected the accuracy of the abutment scan. In intraoral scanning, when the distance between the abutment teeth and the adjacent teeth is more than 1.5 mm, the scan error does not increase, and more accurate scan data can be obtained.

Evaluation of intaglio surface trueness and margin quality of interim crowns in accordance with the build angle of stereolithography apparatus 3-dimensional printing.

STATEMENT OF PROBLEM: Studies on the intaglio surface trueness and margin quality of interim crowns fabricated using stereolithography apparatus (SLA) 3D printing depending on the type of tooth and the build angle are lacking. PURPOSE: The purpose of this in vitro study was to evaluate the effects of intaglio surface trueness and margin quality in accordance with the type of tooth and the build angles of interim crowns fabricated by SLA 3D printing. MATERIAL AND METHODS: A definitive cast was digitized for computer-aided design (CAD) reference model (CRM) production, and the interim crown was designed by using a CAD software program and saved as a standard tessellation language (STL) file. For CAD test model (CTM) production, 3D printing was performed in accordance with the type of tooth (maxillary central incisor, first premolar, and first molar) and the build angles (90, 120, 135, 150, 180, 210, 225, 240, and 270 degrees) (n=17). The intaglio surface of the printed interim crown was digitized. CRM and CTM used 3D inspection software to analyze the intaglio surface superimposition and root mean square (RMS). In addition, a grading system was developed to evaluate the margin quality, which was assessed visually. Statistical analysis was performed using 1-way ANOVA, 2-way ANOVA, and the Tukey honestly significant difference post hoc test (α=.05). RESULTS: The RMS value showed significant differences in the various types of tooth as per the build angles (P<.001). The central incisor and first premolar showed the lowest RMS value at 180 degrees, and the first molar showed the lowest RMS value at 210 degrees. The margin quality was significantly different as per the build angle in the central incisor and the first molar (P<.05). The worst margin quality observed in all teeth was at 180 degrees. CONCLUSIONS: In 3D printing, the build angle affected the intaglio surface trueness of the interim crown. The recommended build angle for interim crowns fabricated using 3D printing is between 150 and 210 degrees. The tooth type affected the margin quality according to the build angle, except in the case of first premolars.

Effect of finish line locations of tooth preparation on the accuracy of intraoral scanners.

AIM: The purpose of this study was to compare the accuracy of intraoral scanning on a tooth model according to four finish line conditions (supragingival, equigingival, subgingival, and subgingival with gingival cord). MATERIALS AND METHODS: To simulate the clinical situation, the abutment was fabricated using ceramic materials. A pigment was added to the transparent orthodontic silicone to create a translucent gingiva. A CAD reference model (CRM) was obtained using a contact scanner. Finish lines on the tooth preparation were placed at the subgingival (0.5 mm below the level of the gingiva), equigingival, and supragingival (0.5 mm above the level of the gingiva) locations. In addition, a gingival cord was packed into the gingival sulcus below the subgingival finish line. A CAD test model (CTM) was obtained using two types of intraoral scanners (IOSs), i500 (Medit) and EZIS PO (DDS; N = 20 per locations). CRM and CTM were superimposed and analyzed using 3D analysis software. In the statistical analysis, the comparison of accuracy according to the finish line locations was confirmed by one-way ANOVA (α = 0.05). The differences between the groups were analyzed using the Tukey HSD post-hoc test. RESULT: There was a significant difference in the accuracy of intraoral scanning according to the finish line locations of the tooth preparations (P < 0.001). The equigingival and subgingival finish lines showed poor accuracy. The use of gingival cords significantly improved the accuracy (P < 0.05). There were significant differences between the two types of IOSs, with the i500 showing better accuracy than the EZIS PO (P < 0.001). CONCLUSION: Supragingival finish lines or the use of gingival displacement cords is recommended for clinically acceptable accuracy (< 100 µm) of the marginal region captured with an IOS.

Comparison of Intaglio Surface Adjustment in the Oral Cavity for Lithium Disilicate Crowns Fabricated Using Different Scanners.

PURPOSE: A clinical study to evaluate the intraoral adjustment of crowns fabricated using different scanners. MATERIALS AND METHODS: A total of 15 patients requiring single ceramic crowns were recruited. Impressions were made according to four protocols: a conventional approach and using three intraoral scanners (IOSs) (CS3600 (Carestream Dental, Atlanta, GA), i500 (Medit, Seoul, Republic of Korea), and EZIS PO (DDS, Seoul, Republic of Korea)). Four crowns per patient were fabricated using lithium disilicate ceramic. An experienced dentist performed the internal adjustment in the oral cavity. Three-dimensional analysis was conducted using an inspection software program (Geomagic Control X; 3D Systems, Rock Hill, SC). Statistical analysis was conducted using one-way analysis of variance and Tukey's honest significance difference tests (α = 0.05). RESULTS: A significant difference was observed in the intraoral adjustment among the conventional approach and the three IOSs (F = 213.7, p < 0.001). Crowns fabricated by conventional impressions (20.1 ± 1.4 µm) displayed better three-dimensional conformity before and after intraoral adjustment than IOS groups (29.6 ± 4.3 µm) (p < 0.001). CONCLUSIONS: Crowns fabricated using conventional impressions required fewer intraoral adjustments of the intaglio surface than those fabricated using IOSs.

Prediction of learning curves of 2 dental CAD software programs, part 2: Differences in learning effects by type of dental personnel.

STATEMENT OF PROBLEM: Dental computer-aided design (CAD) software programs are essential elements of the digital workflow. Therefore, it is necessary to study the learning effect of dental CAD software programs for efficient use. PURPOSE: The purpose of this in vitro study was to predict the learning curve of dental CAD software programs according to dental personnel by using the Wright model and to investigate the tendency of dental personnel to reduce working time according to repeated learning. MATERIAL AND METHODS: A total of 36 participants were recruited, including an equal number of dentists, dental technicians, and dental students (12 each). A custom abutment design was evaluated by using exocad CAD and Deltanine CAD software programs. The design was carried out in the following order: 4 steps repeated 3 times each. This study applied the formula of the Wright model to predict 500 repetitive times. In the statistical analysis, 3-repetition and 500-repetition times were analyzed with the Kruskal-Wallis H test and Friedman test (α=.05), and a post hoc comparison was performed by using the Mann-Whitney U-test and Bonferroni correction method (α=.017). RESULTS: Three repetitions resulted in shorter working time in the dental technician group. The 3-repetition time decreased statistically for all dental personnel (P<.001). The time for 500 repetitions showed a statistically significant difference according to the type of dental personnel (P=.036), but no significant difference was found after the fourth iteration (fifth iteration: P=.076). Furthermore, the estimated time of 500 iterations decreased statistically significantly from the first to the 500th iteration (P<.001). CONCLUSIONS: All dental personnel showed learning effects of dental CAD software programs. Although the dental technician group initially showed less working time, after initial learning, the same learning effect appeared, regardless of the type of dental personnel.

A method to evaluate the accuracy of dental implant placement without postoperative radiography after computer-guided implant surgery: A dental technique.

This technique allows evaluation of the accuracy of a dental implant's position after computer-guided surgery without postoperative radiography. Once the scanned implant and scan body file were prepared, the position of the placed implant was verified by using a computer-guided implant software program instead of radiography, thus reducing radiation exposure.

Displacement of Customized Abutments Designed on a Working Cast and in the Oral Cavity: A Comparative In Vivo Study.

PURPOSE: To compare abutment displacement between the virtual, customized abutment that was designed on a cast and the customized abutment prepared in the oral cavity. MATERIALS AND METHODS: Eleven patients were selected for a single posterior implant prosthetic treatment. The impression was obtained using the closed tray impression method with a vinyl polysiloxane material using a custom tray. The standard tessellation language files of the customized abutment that was designed using the computer-aided design system and acquired with an intraoral scanner in the oral cavity were superimposed and analyzed for distance and angle displacement using the three-dimensional inspection analysis program (Geomagic Control X). In the statistical analysis, distance and angle displacement values were analyzed with the Kruskal-Wallis H test (α = 0.05), and a post hoc comparison was performed using the Mann-Whitney U-test and Bonferroni correction method. RESULTS: The mean distance and angle displacement of the 15 customized abutments were 89.52 ± 66.86 µm and 0.83 ± 1.21°, respectively. There were significant differences in distance displacement (p < 0.001), and angle displacement (p < 0.001) among the 15 customized abutments, and there were no significant differences in angle displacement along the 4 directions (p = 0.735). CONCLUSIONS: The displacement values of the customized abutments evaluated in the oral cavity differed significantly from patient to patient.

Prediction of the learning curves of 2 dental CAD software programs.

STATEMENT OF PROBLEM: Dental clinical procedures are being replaced by digital workflows. Therefore, the time necessary to learn dental computer-aided design (CAD) software to achieve a change in the digital workflow should be evaluated. PURPOSE: The purpose of this study was to predict the learning curve according to the type of dental CAD software with the Wright model and to determine the rate of improvement in the learner's working time with iterative learning. MATERIAL AND METHODS: A total of 40 participants with various degrees of experience with dental computer-aided design and computer-aided manufacturing (CAD-CAM) systems were recruited. The 4 specified steps of a custom abutment design were performed with 3DSystem CAD software (Daesung) and exocad DentalCAD (exocad GmbH) software and were repeated 3 times in stages. The times were analyzed with repeated-measures 1-factor and 2-factor analyses. The learning time for 300 design iterations was estimated by applying the Wright model formula, and the 300-repetition times were analyzed with the Mann-Whitney U test (α=.05). RESULTS: exocad had a longer mean learning time than the 3DSystem. The overall change with repeated learning was significantly different (P<.001), and all differences were found in the first to third iterations. Software-dependent differences were also observed (P=.005). The Mann-Whitney U test also revealed a significant difference between the 2 software programs (P=.015), but no significant difference was found after the 56th iteration (57th iteration: P=.051). CONCLUSIONS: As the time reduction patterns for iterative learning differ depending on the type of CAD software, the learning curves may differ according to the type of software. As the operator's skill increased through iterative learning, the differences in learning times between the software programs gradually disappeared.

Feasibility of using an intraoral scanner for a complete-arch digital scan.

STATEMENT OF PROBLEM: The introduction of intraoral scanners has increased the use of digital technology in dental procedures. However, research on the extent of clinically recommended scans is lacking. PURPOSE: The purpose of this in vitro study was to compare 3D arch distortion according to the distance from the tooth at the beginning of a complete-arch scan made using an intraoral scanner. MATERIAL AND METHODS: An industrial scanner was used to digitize a master model for a computer-aided design (CAD) reference model. In addition, the master model was digitized using 4 intraoral scanners (TRIOS2, TRIOS3, CS3500, and CS3600) and 1 dental laboratory scanner (FREEDOM HD) to make the CAD test model (N=20). The scanned teeth were divided using an inspection software program (Geomagic control X), and overlapping and 3D analyses of the CAD reference model and CAD test model were performed. The presence or absence of normal distribution in the root mean square (RMS) values of all divided teeth was assessed and evaluated with the Kruskal-Wallis test (α=.05), and post hoc comparison was performed using the Mann-Whitney U-test and Bonferroni correction method (α=.005). RESULTS: The overall RMS value was significantly different for all scanners (P<.001). The dental laboratory scanner showed the lowest value (47.5 ±1.6 µm), whereas TRIOS2 showed the highest value (343.4 ±56.4 µm). TRIOS3 (9.6 ±1.2 µm) showed the best trueness in those teeth where the scan started. However, the larger the scan range, the lower the RMS value difference between TRIOS3 and CS3500. The RMS values of the dental laboratory scanners were higher than those of the intraoral scanners in the narrow scan range. CS3600 showed an RMS value less than or equal to that of the dental laboratory scanner at 5 teeth scan ranges. However, the wider the scan range, the lower the RMS values of all the intraoral scanners. CONCLUSIONS: Current complete-arch scanning is not sufficiently accurate for fabricating fixed prostheses. However, intraoral scanners are useful for short scans, such as those for single (TRIOS2, TRIOS3, and CS3500) or short-span prostheses (CS3600).

Feasibility of images acquired using smartphone camera for marginal and internal fit of fixed dental prosthesis: comparison and correlation study.

This study aimed to measure marginal and internal fit using images captured with both an optical microscope and a smartphone camera, comparing the fit measurement performance of these devices and analyzing their correlation. Working casts (with 10 posterior and 10 anterior teeth) created to fabricate fixed dental prostheses were used. These working casts were scanned using a desktop scanner (E1) to design an interim crown, and the designed interim crown was fabricated using a three-dimensional (3D) printer. Utilizing the silicone replica technique, the fabricated interim crown replicated the fit, which was then captured using both an optical microscope and a smartphone camera. The captured images were used to measure the marginal and internal fit according to the imaging device. Intraclass correlation coefficients (ICC) were used for reliability analysis according to the imaging device. Furthermore, the Wilcoxon signed-rank test was adopted for the comparative evaluation of the marginal and internal fit between the imaging devices (α = 0.05). The measurement results of the marginal and internal fit according to the optical microscope and smartphone camera did exhibit a significant difference (P < 0.05). The ICC between the two devices showed an "excellent" agreement of over 0.9 at all measurement points (P < 0.001). A smartphone camera could be used to obtain images for evaluating the marginal and internal fit.

Effect of the Inter-Tooth Distance and Proximal Axial Wall Height of Prepared Teeth on the Scanning Accuracy of Intraoral Scanners.

This study aimed to analyze the effect of the height of the proximal axial wall of the prepared tooth and the distance between the adjacent tooth and the prepared tooth on the scan accuracy of intraoral scanners. Ten working casts with maxillary first molars prepared to receive zirconia crowns were randomly obtained from a dental clinic. Each of the 10 casts was scanned using two intraoral scanners (i700; MEDIT and CS3600; Carestream; computer-aided design [CAD] test model, CTM; N = 15 per working cast) 15 times per scanner. Individual dies of the prepared teeth were fabricated, and high-precision scan data were acquired using a laboratory scanner (CAD reference model, CRM; N = 1). CTMs were aligned relative to the prepared tooth of CRMs by using three-dimensional inspection software (Ver 2018.1.0; Control X; 3D Systems). Data were statistically analyzed using an independent t-test and one-way analysis of variance for between-group comparisons (α = 0.05). The inaccuracy in the proximal regions (mesial or distal) of the prepared tooth was higher than that in the buccal and lingual regions (p < 0.05). The scan accuracy was not correlated with the variables when the distance between the adjacent tooth and the prepared tooth was ≥2.0 mm and the height of the proximal axial wall of the prepared tooth was <3.0 mm (p > 0.05). Therefore, an excellent scan accuracy can be obtained using an intraoral scanner when the distance between the adjacent tooth and the prepared tooth is ≥2.0 mm and the proximal axial wall height of the prepared tooth is <3.0 mm.

A depth-resolved quantitative evaluation method for non-carious cervical lesions treatment with optical coherence tomography.

OBJECTIVES: The aim of this study is prognostic assessment of surface smoothness and the presence of internal bubbles after treatment of non-cancerous cervical lesions (NCCLs) using optical coherence tomography (OCT). METHODS: After treatment with NCCLs, cross-sectional images of the lesion parts of the sample were non-invasively acquired and analyzed. The surface smoothness between tooth and resin, resin and cemento-enamel junction, and the presence bubble inside resin was confirmed. In addition, using an algorithm that distinguishes between resin and dental structure based on OCT cross-sectional images, we quantitatively analyzed the amount of resin used in treating NCCLs and acquired 3D images. RESULTS: The inner structure of the resin in each sample was checked, and the presence of bubbles was confirmed. In addition, the resin sections were separated from the tomographic images acquired by OCT to visualize 3D images. The volume of resin used in the treatment part of each NCCLs samples was quantitatively analyzed as 3.7216 ∼ 14.889 mm3. CONCLUSIONS: OCT is able to measure not only the surface abrasion provided by existing intraoral scanner, but also the size and depth location of interal bubbles, which is distinctive advantage of our method. Based on our results, OCT is a significant tool for qualitative and quantitative analysis of dental NCCLs treatment before and after treatment. CLINICAL SIGNIFICANCE: The study used OCT, a non-destructive diagnostic, to reveal the structure of the resin and the location and size of bubbles after NCCLs treatment. These findings could be golden standard in determining the prognosis of NCCLs treatment.

How does the consecutive use of intraoral scanners affect musculoskeletal health? A preliminary clinical study.

BACKGROUND: Minimizing muscle strain and reducing the risk of musculoskeletal disorders associated with intraoral scanner (IOS) usage require ergonomic awareness, device selection, and workplace adjustments in dental practice. This preliminary clinical study aimed to simulate intraoral scanning tasks using wired and wireless IOSs and assess muscle activation and fatigue for both types. MATERIALS AND METHODS: Fourteen participants performed intraoral scanning tasks using wired and wireless IOSs (i700; MEDIT), with weights of 280 g and 328 g, respectively. The same computer system and software conditions were maintained for both groups (N = 14 per IOS group). Electrodes were placed on arm, neck, and shoulder muscles, and maximal voluntary contraction (MVC) was measured. Surface electromyography (EMG) was performed during the simulation, and EMG values were normalized using MVC. The root mean square EMG (%MVC) and muscle fatigue (%) values were calculated. Statistical comparisons were performed using the Mann-Whitney U and Friedman tests, with the Bonferroni adjustment for multiple comparisons (α = 0.05). RESULTS: Arm (flexor digitorum superficialis) and neck muscles (left sternocleidomastoid and left splenius capitis) showed significantly higher EMG values with wireless IOS (P < 0.05). The neck (left sternocleidomastoid and right levator scapulae) and shoulder muscles (right trapezius descendens) demonstrated significantly higher muscle fatigue with wireless IOS (P < 0.05). CONCLUSIONS: The consecutive use of heavier wireless IOS may increase the risk of muscle activation and fatigue in certain muscles, which may have clinical implications for dentists in terms of ergonomics and musculoskeletal health.

Prediction of learning curves of wired and wireless intraoral scanners.

This clinical study aimed to predict the learning curve of wireless and wired intraoral scanners (IOSs) and to compare the reduction patterns of working time. Overall, 14 participants were enrolled in the study. The intraoral scanning procedure was repeated four times, each using wireless and wired IOSs (i700; MEDIT). The work time from the first to the 600th iterations was predicted using the Wright model. Regarding statistical analysis, the Mann-Whitney U-test was performed for comparison between wireless and wired IOSs and between groups with and without an IOS usage experience, and the Friedman test was performed to evaluate the time reduction (α = 0.05). There was a significant difference between wireless and wired IOSs in the first (P = 0.008) and the third (P = 0.035) iterations. Moreover, the time for 600 iterations was statistically significantly different between wireless and wired IOSs (P < 0.05); however, there was no significant difference after the sixth iteration (e.g., seventh iteration: P = 0.062). In wireless IOS, no significant difference was found between participants with and without an IOS usage experience after the 34th iteration (P = 0.053). The difference in the learning effect between wireless and wired IOSs can be overcome by initial learning; however, an IOS usage experience can affect the learning time of wireless IOSs.

Does an ergonomic dentist stool design have a positive impact on musculoskeletal health during intraoral scans and tooth preparation?

PURPOSE: This study aimed to evaluate the effects of an ergonomic dentist stool design on muscle activity and fatigue in dentists. MATERIALS AND METHODS: Fourteen dentists were recruited, and electrodes were attached to the arm, neck, and shoulder muscles of these dentists according to the Surface ElectroMyoGraphy for the Non-Invasive Assessment of Muscles protocol. After measuring the maximal voluntary contraction, eight-channel surface electromyography was performed during simulations of two dental procedures (intraoral scanning and tooth preparation) while the dentists were using two types of dentist stools. Furthermore, muscle activity and fatigue were determined based on the eight-channel surface electromyography data, and ergonomic risk levels were evaluated according to the muscle activity. The Shapiro-Wilk test was used to confirm that all data were normally distributed, and the Mann-Whitney U test was used to compare the two types of dentist stools (α = 0.05). RESULTS: There was a significant difference between the conventional and ergonomically designed dentist stools in terms of the activity of trapezius descendens muscle (p < 0.05). Notably, the activity of the trapezius descendens muscle was lesser when the dentists used ergonomically designed dentist stools than when they used a conventional dentist stool. The activity of all muscles, except for the sternocleidomastoid, indicated moderate ergonomic risk. CONCLUSION: A dentist stool that enables dentists to maintain ergonomic posture should be used to prevent musculoskeletal disorders.

Dental diagnosis for inlay restoration using an intraoral optical coherence tomography system: A case report.

PATIENTS: The patient was a 32-year-old man who underwent amalgam restoration of the mandibular right second molar. An amalgam restoration fracture was diagnosed by intraoral optical coherence tomography (OCT), and pulp exposure was examined during cavity preparation. Subsequently, a definitive ceramic restoration was fabricated, and the marginal fit in the oral cavity was evaluated using the OCT system. DISCUSSION: The existing OCT system cannot acquire images inside the oral cavity because of the large probe size. However, the proposed intraoral OCT system can access the prostheses in the mandibular right second molar. Therefore, dental diagnosis for restoration treatment with dental prosthesis fracture, marginal gap, and pulp exposure after tooth preparation is possible using the proposed intraoral OCT system. CONCLUSIONS: The use of the intraoral OCT system improved dental diagnosis by allowing the dentist to confirm quantitative values through cross-sectional images, rather than that by determining a treatment plan after visual dental diagnosis.