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.

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.

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.

Clinical evaluation of the fit of lithium disilicate crowns fabricated with three different CAD-CAM systems.

STATEMENT OF PROBLEM: The fit and performance of prostheses fabricated using various computer-aided design and computer-aided manufacturing (CAD-CAM) systems have been evaluated. However, most studies were conducted in vitro, and relatively few have addressed gingival parameters and prosthesis fit under clinical conditions. PURPOSE: This clinical study aimed to compare the fit of lithium disilicate crowns produced using 3 CAD-CAM systems and evaluate clinical results up to 6 months after delivery. MATERIAL AND METHODS: Forty participants requiring a single crown were recruited. Three monolithic lithium disilicate crowns were fabricated per participant by using 3 different CAD-CAM systems (intraoral scanners, CAD software, and milling machines): CEREC group (CEREC Bluecam, CEREC AC, CEREC MC); EZIS group (EZIS PO, EZIS VR, EZIS HM); and TRIOS group (TRIOS 3, EXO-CAD, ARUM-4X). The fit of the prostheses was assessed via a silicone replica technique, and the most acceptable crown was delivered; 12 were selected from the CEREC group, 16 from the EZIS group, and 12 from the TRIOS group. Follow-up clinical examinations were performed at 1, 3, and 6 months after delivery. The Kruskal-Wallis test with the post hoc Mann-Whitney U test was conducted to analyze significant differences in crown fit and periodontal conditions among the groups (α=.05). RESULTS: The marginal gap of the CEREC group was significantly higher than that of the EZIS group, and the occlusal gap of the EZIS group was significantly lower than those of the CEREC and TRIOS groups (P<.05). Probing depth, bleeding index, and plaque index showed no intergroup differences at 6 months (P>.05). CONCLUSIONS: The lithium disilicate crowns of all groups showed clinically acceptable fit. No significant differences were found among the groups in terms of periodontal conditions after 6 months.

Non-Invasive Optical Coherence Tomography Data-Based Quantitative Algorithm for the Assessment of Residual Adhesive on Bracket-Removed Dental Surface.

The aim of this study was to quantitatively assess the residual adhesive on orthodontic ceramic bracket-removed dental surface. In orthodontic process, ceramic bracket was repeated debonding physically, then the adhesive remained on the dental surface. The residual adhesive caused a lack of adhesive strength between dental and ceramic bracket. Since commonly used adhesive in orthodontics is translucent, residual adhesive is hard to be detected with conventional microscopes. Therefore, 1310 nm center wavelength swept-source OCT system based on laboratory customized image processing algorithm was used for the precise detection of residual adhesive on tooth surface. The algorithm separates residual adhesive from dental surface by comparing the height of adjacent B-scan images, while providing color-scaled images emphasizing the thickness information of residual adhesive. Finally, the acquired results were compared with microscopic and adhesive remnant index scoring gold standards, while the comparison confirmed the potential merits and the improvements of the proposed method over gold standards.

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 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.

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).

Fit of interim crowns fabricated using photopolymer-jetting 3D printing.

STATEMENT OF PROBLEM: The fit of interim crowns fabricated using 3-dimensional (3D) printing is unknown. PURPOSE: The purpose of this in vitro study was to evaluate the fit of interim crowns fabricated using photopolymer-jetting 3D printing and to compare it with that of milling and compression molding methods. MATERIAL AND METHODS: Twelve study models were fabricated by making an impression of a metal master model of the mandibular first molar. On each study model, interim crowns (N=36) were fabricated using compression molding (molding group, n=12), milling (milling group, n=12), and 3D polymer-jetting methods. The crowns were prepared as follows: molding group, overimpression technique; milling group, a 5-axis dental milling machine; and polymer-jetting group using a 3D printer. The fit of interim crowns was evaluated in the proximal, marginal, internal axial, and internal occlusal regions by using the image-superimposition and silicone-replica techniques. The Mann-Whitney U test and Kruskal-Wallis tests were used to compare the results among groups (α=.05). RESULTS: Compared with the molding group, the milling and polymer-jetting groups showed more accurate results in the proximal and marginal regions (P<.001). In the axial regions, even though the mean discrepancy was smallest in the molding group, the data showed large deviations. In the occlusal region, the polymer-jetting group was the most accurate, and compared with the other groups, the milling group showed larger internal discrepancies (P<.001). CONCLUSIONS: Polymer-jet 3D printing significantly enhanced the fit of interim crowns, particularly in the occlusal region.

Shear bond strength of porcelain to a new millable alloy and a conventional castable alloy.

STATEMENT OF PROBLEM: A recently introduced presintered cobalt-chromium (Co-Cr) alloy for metal ceramic restorations can be efficiently processed with computer-aided design/computer-aided manufacturing (CAD/CAM) techniques. However, little or no reliable study data are available regarding the bonding ability of porcelain to milled Co-Cr alloys. PURPOSE: The purpose of this study was to evaluate the shear bond strength of veneering porcelain to the presintered Co-Cr alloy and to a conventional castable alloy. MATERIAL AND METHODS: Ninety-six cylindrical cores (6.8 mm in diameter, 9 mm in height) were made of millable alloy (Ceramill Sintron) and castable alloy (4-all) by means of CAD/CAM or casting, 48 cores for each alloy. Four types of veneering porcelain were fired or pressed to the cores; these specimens had dimensions of 4×4×3 mm. After firing, the specimens were put in resin molds, fixed in a universal testing machine, and subjected to a shear force test. Loading was applied to each specimen through the attached crosshead at a constant drive speed of 0.5 mm/min until fracture occurred. Shear bond strengths (MPa) were calculated by dividing the maximum failure force over the cross-sectional area of each specimen. Failure patterns of the specimens were also investigated and characterized as adhesive, cohesive, or mixed. One-way ANOVA and the Duncan post hoc test were used to analyze statistically significant differences between groups (α=.05). RESULTS: The means of the shear bond strengths of (millable) Ceramill Sintron were similar to or higher than those of (castable) 4-all cores. The shear bond strength was significantly lower for Press-To-Metal veneer than for the other fired veneers in the test (P<.001). The pattern of failure in most specimens was mixed, except for Press-To-Metal veneer, where cohesive failure occurred. CONCLUSIONS: The bonding ability of the traditional castable alloy was similar to that of the presintered millable Co-Cr alloy.

Radiopacity for Contemporary Luting Cements Using Digital Radiography under Various Exposure Conditions.

PURPOSE: This study examined the radiopacity of contemporary luting cements using direct digital radiography under a range of exposure conditions. MATERIALS AND METHODS: Disc specimens (N = 80, n = 10 per group, ø5 mm × 1 mm) were prepared from 8 resin-based luting cements (BisCem Clearfil SA Luting, Duolink, Maxcem Elite Multilink Speed, Panavia F 2.0, RelyX Unicem Clicker, V-link). The specimens were radiographed using a charge-coupled device sensor along with an 11-step aluminum step wedge (1.5-mm incremental steps) and 1-mm-thick tooth cut using five tube voltage/exposure time setups (60 kVp, 0.10/0.08 seconds; 70 kVp, 0.10/0.08/0.06 seconds) at 4 mA and 30 cm. The radiopacity of the specimens was compared with that of the aluminum step wedge and human enamel and dentin using NIH ImageJ software (available at http://rsb.info.nih.gov/ij/). A linear regression model for the aluminum step wedge was constructed, and the data were analyzed by ANOVA and Duncan post hoc test. RESULTS: Maxcem Elite (5.142 to 5.441) showed the highest radiopacity of all materials, followed in order by Multilink Speed (3.731 to 3.396) and V-link (2.763 to 3.103). The radiopacity of Panavia F 2.0 (2.025 to 2.429), BisCem (1.825 to 2.218), Clearfil SA Luting (1.692 to 2.145), Duolink (1.707 to 1.993), and RelyX Unicem Clicker (1.586 to 1.979) were between enamel (2.117 to 2.330) and dentin (1.302 to 1.685). The radiopacity of 70 kVp conditions was higher than that of the 60 kVp conditions. CONCLUSIONS: The radiopacities of the tested luting materials were greater than those of dentin or aluminum, satisfying the criteria of the International Organization for Standardization, and they differed significantly from each other in the exposure setups.

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.