• The Journal of Advanced Prosthodontics
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• v.7 no.4
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• pp.294-302
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• 2015

PURPOSE. The purpose of this study was to verify the clinical-feasibility of additive manufacturing by comparing the accuracy of four different manufacturing methods for metal coping: the conventional lost wax technique (CLWT); subtractive methods with wax blank milling (WBM); and two additive methods, multi jet modeling (MJM), and micro-stereolithography (Micro-SLA). MATERIALS AND METHODS. Thirty study models were created using an acrylic model with the maxillary upper right canine, first premolar, and first molar teeth. Based on the scan files from a non-contact blue light scanner (Identica; Medit Co. Ltd., Seoul, Korea), thirty cores were produced using the WBM, MJM, and Micro-SLA methods, respectively, and another thirty frameworks were produced using the CLWT method. To measure the marginal and internal gap, the silicone replica method was adopted, and the silicone images obtained were evaluated using a digital microscope (KH-7700; Hirox, Tokyo, Japan) at 140X magnification. Analyses were performed using two-way analysis of variance (ANOVA) and Tukey post hoc test (${\alpha}=.05$). RESULTS. The mean marginal gaps and internal gaps showed significant differences according to tooth type (P<.001 and P<.001, respectively) and manufacturing method (P<.037 and P<.001, respectively). Micro-SLA did not show any significant difference from CLWT regarding mean marginal gap compared to the WBM and MJM methods. CONCLUSION. The mean values of gaps resulting from the four different manufacturing methods were within a clinically allowable range, and, thus, the clinical use of additive manufacturing methods is acceptable as an alternative to the traditional lost wax-technique and subtractive manufacturing.

• Journal of Periodontal and Implant Science
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• v.47 no.6
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• pp.381-387
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• 2017

Purpose: The aim of this study was to evaluate volumetric and histologic changes in edentulous alveolar ridge areas after ridge preservation using basic fibroblast growth factor-2 (bFGF-2) in combination with collagenated biphasic calcium phosphate (BCP). Methods: The experiments were performed in 6 adult male beagle dogs. The following 3 groups were created: 1) ridge preservation with bFGF-2 and collagenated BCP (experimental group), 2) ridge preservation with collagenated BCP (positive control group), and 3) a negative control group in which no ridge preservation procedure was performed. Volumetric change analysis was performed using an optical scanner and casts. Histological observations were made using light microscopy. Results: After the initial swelling subsided, the magnitude of the volumetric change in the experimental group and positive control group was smaller than in the negative control group. In the experimental group, a distinct trend was observed for the resorption of residual bone and collagen fibers at 4 weeks and for more mature bone and faster healing at 12 weeks. Conclusions: Based on the findings of the present study, bFGF-2 may be considered for use as a therapeutic molecule in ridge preservation procedures.

• The Journal of Advanced Prosthodontics
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• v.10 no.5
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• pp.367-373
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• 2018

PURPOSE. To evaluate the fit of a crown produced based on a 3D printed model and to investigate its clinical applicability. MATERIALS AND METHODS. A master die was fabricated with epoxy. Stone dies were fabricated from conventional impressions (Conventional stone die group: CS, n=10). Digital virtual dies were fabricated by making digital impressions (Digital Virtual die group: VD, n=10). 3D data obtained from the digital impression was used to fabricate 3D printed models (DLP die group: DD, n=10, PolyJet die group: PD, n=10). A total of 40 crowns were fabricated with a milling machine, based on CS, VD, DD and PD. The inner surface of all crowns was superimposed with the master die files by the "Best-fit alignment" method using the analysis software. One-way and 2-way ANOVA were performed to identify significant differences among the groups and areas and their interactive effects (${\alpha}=.05$). Tukey's HSD was used for post-hoc analysis. RESULTS. One-way ANOVA results revealed a significantly higher RMS value in the 3D printed models (DD and PD) than in the CS and DV. The RMS values of PD were the largest among the four groups. Statistically significant differences among groups (P<.001) and between areas (P<.001) were further revealed by 2-way ANOVA. CONCLUSION. Although the fit of crowns fabricated based on the 3D printed models (DD and PD) was inferior to that of crowns prepared with CS and DV, the values of all four groups were within the clinically acceptable range (<$120{\mu}m$).

• Journal of Technologic Dentistry
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• v.41 no.3
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• pp.211-217
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• 2019

Purpose: The purpose of this study is to evaluate the repeated measurement stability of scans related to dentition type. Methods: A normal model and the crowding and diastema models are also duplicated using duplicating silicon. After that, a plaster model is made using a plaster-type plaster on the duplicate mold, and each model is scanned 5 times by using an extraoral scanner. The gingival part and molar part were deleted from the 3D STL file data obtained through scanning. Using the 3D stl file obtained in this way, data is nested between model groups. Thereafter, RMS values obtained were compared and evaluated. The normality test of the data was performed for the statistical application of repeated measurements with dentition type, and the normality was satisfied. Therefore, the one-way ANOVA test, which is a parametric statistical method, was applied, and post-tests were processed by the Scheffe method. Results: The average size of each RMS in the Normal, Diastema, and Crowding groups was Normal> Crowding> Diastema. However, the standard deviation was in the order of Crowding> Normal> Diastema. The average value of each data is as follows. Diastema model was the smallest ($5.51{\pm}0.55{\mu}m$), followed by the crowding model ($12.30{\pm}2.50{\mu}m$). The normal model showed the maximum error ($13.23{\pm}1.06{\mu}m$). Conclusion: There was a statistically significant difference in the repeatability of the scanning measurements according to the dentition type. Therefore, you should be more careful when scanning the normal intense or crowded dentition than scanning the interdental lining. However, this error value was within the range of applicable errors for all clinical cases.

• The Journal of Advanced Prosthodontics
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• v.14 no.1
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• pp.22-31
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• 2022

PURPOSE. The purpose of this study was to investigate the misfit and screw preload at the implant abutment connection of implant supported fixed dental prosthesis with cantilever (ICFDP) manufactured using different digital manufacturing techniques and to compare the screw preload before and after cyclic loading. MATERIALS AND METHODS. Mandibular jaw model with four intra-foraminal implants was scanned using digital scanner. Stereolithography file was used to design a framework with nonengaging (NE) abutments and 10 mm cantilever distal to one terminal implant. Five frameworks were constructed using combined digital-conventional techniques (CAD-cast), and five frameworks were constructed using three-dimensional printing (3DP). Additional CAD-cast framework was constructed in a way that ensures passive fit (PF) to use as control. Scanning electron microscope (SEM) measured the implant abutment connection misfit. Sixty screws were used on the corresponding frameworks. Screws were torqued and pre-cyclic loading reverse torque value (RTV) was recorded. Frameworks were subjected to 200,000 loading cycles with a loading point 9 mm from the center of terminal implants adjacent to the cantilever and post-cyclic loading RTVs were recorded. RESULTS. Microscopic readings showed significant differences between frameworks. PF demonstrated the lowest measurements of 16.04 (2.6) ㎛ while CAD-cast demonstrated the highest measurements of 29.2 (3.1) ㎛. In all groups, RTVs were significantly lower than the applied torque. Post-cyclic loading RTV was significantly lower than pre-cyclic loading RTV in PF and 3DP frameworks. Differences in RTVs between the three manufacturing techniques were insignificant. CONCLUSION. Although CAD-cast and three-dimensionally printed (3DP) both produce frameworks with clinically acceptable misfit, 3DP might not be the technique of choice for maintaining screw's preload stability under an aggressive loading situation.

• Journal of Technologic Dentistry
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• v.46 no.2
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• pp.36-41
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• 2024

Purpose: This study aimed to generate virtual mandibular left first molar teeth using deep convolutional generative adversarial networks (DCGANs) and analyze their matching accuracy with actual tooth morphology to propose a new paradigm for using medical data. Methods: Occlusal surface images of the mandibular left first molar scanned using a dental model scanner were analyzed using DCGANs. Overall, 100 training sets comprising 50 original and 50 background-removed images were created, thus generating 1,000 virtual teeth. These virtual teeth were classified based on the number of cusps and occlusal surface ratio, and subsequently, were analyzed for consistency by expert dental technicians over three rounds of examination. Statistical analysis was conducted using IBM SPSS Statistics ver. 23.0 (IBM), including intraclass correlation coefficient for intrarater reliability, one-way ANOVA, and Tukey's post-hoc analysis. Results: Virtual mandibular left first molars exhibited high consistency in the occlusal surface ratio but varied in other criteria. Moreover, consistency was the highest in the occlusal buccal lingual criteria at 91.9%, whereas discrepancies were observed most in the occusal buccal cusp criteria at 85.5%. Significant differences were observed among all groups (p<0.05). Conclusion: Based on the classification of the virtually generated left mandibular first molar according to several criteria, DCGANs can generate virtual data highly similar to real data. Thus, subsequent research in the dental field, including the development of improved neural network structures, is necessary.

• The Journal of Advanced Prosthodontics
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• v.6 no.1
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• pp.1-7
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• 2014

PURPOSE. The accuracy of a gypsum model (GM), which was taken using a conventional silicone impression technique, was compared with that of a polyurethane model (PM), which was taken using an iTero$^{TM}$ digital impression system. MATERIALS AND METHODS. The maxillary first molar artificial tooth was selected as the reference tooth. The GMs were fabricated through a silicone impression of a reference tooth, and PMs were fabricated by a digital impression (n=9, in each group). The reference tooth and experimental models were scanned using a 3 shape convince$^{TM}$ scan system. Each GM and PM image was superimposed on the registered reference model (RM) and 2D images were obtained. The discrepancies of the points registered on the superimposed images were measured and defined as GM-RM group and PM-RM group. Statistical analysis was performed using a Student's T-test (${\alpha}=0.05$). RESULTS. A comparison of the absolute value of the discrepancy revealed a significant difference between the two groups only at the occlusal surface. The GM group showed a smaller mean discrepancy than the PM group. Significant differences in the GM-RM group and PM-RM group were observed in the margins (point a and f), mesial mid-axial wall (point b) and occlusal surfaces (point c and d). CONCLUSION. Under the conditions examined, the digitally fabricated polyurethane model showed a tendency for a reduced size in the margin than the reference tooth. The conventional gypsum model showed a smaller discrepancy on the occlusal surface than the polyurethane model.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.11
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• pp.693-700
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• 2020

This study compared the accuracy and reliability of definitive casts fabricated from a digital impression and conventional impression technique. A master model with the prepared upper full-arch tooth was used. Samples of ten plaster models and ten polyurethane models were duplicated using a selected standard master model. Six linear measurements were recorded between the landmarks, directly on each of the stone models and the polyurethane models on two occasions by a double examiner. The Wilcoxon signed-rank test, interclass correlation coefficient (ICC), measurement error (MSE), and limit of agreement (LoA) were used for statistical analysis. The ICC ranged from 0.76 to 0.99 when comparing the stone models and polyurethane models. The mean difference between the stone models and polyurethane models ranged from 0.09mm to 0.20mm, suggesting that stone models might be slightly larger than polyurethane models. Based on this study, the accuracy of the polyurethane models in evaluating the performance of an oral scanner and subtractive technology was acceptable. Further studies will be needed on patient subjects under clinical conditions that may involve missing or malpositioned teeth and fixed dental prostheses because this study was limited to use a standard master model and duplicated sample models in a laboratory setting.

• Journal of Dental Rehabilitation and Applied Science
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• v.31 no.4
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• pp.316-328
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• 2015

Purpose: The objects of this study was to evaluate the accuracy of the dental stone casts made from alginate impressions according to storage condition and stone pouring time. Materials and Methods: Each of upper and lower impressions of dental model was taken. The dental stone models were made immediately, 10, 30, 60, 180, 360 minutes after the impressions were taken at each storage condition. 3D models were constructed by scanning the stone model using 3D laser scanner. With Reference points, positioned on digital models, linear measurements of the dimensional change were compared by 3D metrology software, 3D average models were made and superimposition to identify the specific site of dimensional change and to measure surface deviation (mm). Results: Dental stone models which were made immediately after taking the impression showed the smallest linear dimensional change. As the stone pouring time was prolonged, the linear dimensional change was increased. More than 180 minutes after impression taking, linear dimensional change and surface distortion increased in the posterior molar region, regardless of the storage condition. Conclusion: For the optimum accuracy of the dental stone casts, alginate impression should be poured as soon as possible. If there were a need for storing, a humidor with 100% relative humidity must be used and be stored less than 180 minutes to fabricate the accurate dental model.

• Journal of Korean Dental Science
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• v.12 no.1
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• pp.13-19
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• 2019

Purpose: The aim of this study was to compare the flexural strength of provisional fixed dental prostheses which was three-dimensional (3D) printed by several build directions. Materials and Methods: A metal jig with two abutment teeth and pontic space in the middle was fabricated. This jig was scanned with a desktop scanner and provisional restoration was designed on dental computer-aided design program. On the preprocessing software, the build angles of the restorations were arranged at $0^{\circ}$, $30^{\circ}$, $45^{\circ}$, $60^{\circ}$, and $90^{\circ}$ and support was added and resultant structure was sliced to a thickness of $100{\mu}m$. Processed restorations were printed with digital light processing type 3D printer using poly methyl meta acrylate-based resin. After washing and post-curing, compressive loading was applied at a speed of 1 mm/min on a metal jig fixed to a universal testing machine. The maximum pressure at which fracture occurred was measured. For the statistical analysis, build direction was set as the independent variable and fracture strength as the dependent variable. One-way analysis of variance and Tukey's post hoc analysis was conducted to compare fracture strength among groups (${\alpha}=0.05$). Result: The mean flexural strength of provisional restoration 3D printed with the build direction of $0^{\circ}$ was $1,053{\pm}168N$; it was $1,183{\pm}188N$ at $30^{\circ}$, $1,178{\pm}81N$ at $45^{\circ}$, $1,166{\pm}133N$ at $60^{\circ}$, and $949{\pm}170N$ at $90^{\circ}$. The group with a build direction of $90^{\circ}$ showed significantly lower flexural strength than other groups (P<0.05). The flexural strength was significantly higher when the build direction was $30^{\circ}$ than when it was $90^{\circ}$ (P<0.01). Conclusion: Among the build directions $0^{\circ}$, $30^{\circ}$, $45^{\circ}$, $60^{\circ}$, and $90^{\circ}$ set for 3D printing of fixed dental prosthesis, an orientation of $30^{\circ}$ is recommended as an effective build direction for 3D printing.