• Journal of Technologic Dentistry
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• v.45 no.4
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• pp.118-123
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• 2023

Purpose: This study proposes measures needed to implement a job-based national practical exam for dental technicians. Methods: For this study, a survey was conducted targeting 244 currently employed individuals. The current national practical test for dental technicians was divided into directions for the job-based practical test, subjects that need improvement among the current practical test subjects, items that need to be reflected in the practical test evaluation for each subject, and subjects that need to be added to the practical test. It comprised ten questions (Cronbach's α=0.801). Results: The following results were obtained. Satisfaction with the current practical test was lower than average. Future improvement should focus on job-based evaluation. The dental ceramic lab technology subject needs to be reorganized urgently, and the tasks that require evaluation for each subject are different. Moreover, if evaluation subjects are added in the future, the introduction of assessment for dental CAD/CAM (computer-aided design/computer-aided manufacturing) subjects was found to be the most urgent. Conclusion: In this study, the most necessary tasks of the current national practical examination for dental technicians were evaluated and the content needed for future reorganization was investigated. Future tests should be expanded to evaluate critical job areas. Furthermore, it is necessary to open new courses in fields such as CAD/CAM, as they are in high demand in the workplace.

• The Journal of Korean Academy of Prosthodontics
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• v.54 no.3
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• pp.193-202
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• 2016

Purpose: This study was performed in order to assess the effect of the surface treatment methods and the use of bonding agent on the shear bond strength (SBS) between the aged CAD-CAM (computer aided design-computer aided manufacturing) hybrid materials and added composite resin. Materials and methods: LAVA Ultimate (LU) and VITA ENAMIC (VE) specimens were age treated by submerging in a $37^{\circ}C$ water bath filled with artificial saliva (Xerova solution) for 30 days. The surface was ground with #220 SiC paper then the specimens were divided into 9 groups according to the combination of the surface treatment (no treatment, grinding, air abrasion with aluminum oxide, HF acid) and bonding agents (no bonding, Adper Single Bond 2, Single Bond Universal). Each group had 10 specimens. Specimens were repaired (added) using composite resin (Filtek Z250), then all the specimens were stored for 7 days in room temperature distilled water. SBS was measured and the fractured surfaces were observed with a scanning electron microscope (SEM). One-way ANOVA and Scheffe test were used for statistical analysis (${\alpha}=.05$). Results: Mostly groups with bonding agent treatment showed higher SBS than groups without bonding agent. Among the groups without bonding agent the groups with aluminum oxide treatment showed higher SBS. However there was no significant difference between groups except two subgroups within LU group, which revealed a significant increase of SBS when Single Bond Universal was used on the ground LU specimen. Conclusion: The use of bonding agent when repairing an aged LAVA Ultimate restoration is recommended.

• Journal of Technologic Dentistry
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• v.35 no.1
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• pp.29-35
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• 2013

Purpose: The purpose of this study was to evaluate the validity of digital models fabricated by dental scannable stone. Methods: Twenty same cases of stone models(maxillary full arch) were manufactured. Intercanine distance, intermolar distance, two dental arch lengths(right, left), two diagonal of dental arch lengths(right, left) were measured for comparison. Each of ten stone models were measured by digital vernier calipers and scanned by dental scanner. Ten digital models were measured by CAD program. The mean(SDs) values were compared by a Mann-Whitney U test(${\alpha}$=0.05). Results: No statistically significant differences between the two groups were found at intermolar distance, dental arch length(right)(p>0.05). However, intercanine distance, dental arch length(left) and two diagonal of dental arch lengths(right, left) were statistically significant(p<0.05). Conclusion: Stone models fabricated by dental scannable stone showed larger than digital models.

• The Journal of Korean Academy of Prosthodontics
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• v.58 no.4
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• pp.321-327
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• 2020

Purpose: The purpose of this study was to measure and compare the strain value exerted on the cervical area using different screw tightening protocols in implant-supported, screw-retained 3-unit prostheses. Materials and methods: Strain gauges were attached to four implants: two external and two internal. Thereafter, two study model were designed each type using acrylic resin. CAD-CAM was used to design hex and nonhex abutments for each group (EH, ENH, IH, and INH group) and Screw-cement-retained prostheses were also designed using a nonprecious base metal. Abutment was fixed with 10 Ncm torque, and the prosthesis was cemented. Screws were fixed with 30 Ncm torque using different three protocols. After 5 min, the strain gauge level was measured, and group analysis was performed (α=.05). Results: External group showed significantly lower strain values than internal group and the EH group showed significantly lower strain values than the ENH group (P<.05). There was no difference in strain value based on the types of screw tightening protocols in same group (P>.05). The IH group exhibited significantly higher strain values than the INH group and the IH group showed a significant difference in strain values based on the types of screw tightening protocols used (P<.05). Conclusion: There was no significant effect on the external type in the implant-supported, screw-retained prostheses. However, strain values were high in the internal type, and the types of screw tightening protocol significantly affected these implants.

• Journal of the Korean Academy of Esthetic Dentistry
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• v.22 no.1
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• pp.30-46
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• 2013

Porcelain fused to metal crown has been used mostly over the last 50 years for restorations in dentistry. However, the patients' awareness of aesthetic aspect, biocompatibility and the problems such as an allergy to metals led to the growing interest in the 'metal free restoration'. In particular, the price of the precious metals that have been mainly used to date has risen drastically, which made them impossible to play their role as oral restorative materials anymore, and in addition, the PFM restoration has intrinsic problems of chipping and fracture. Therefore, the CAD/CAM has been drawing more attention than ever due to the popular needs for the material that is more aesthetic and stronger for restoration of the molar implant. Considerations in carrying out the full zirconia restoration are as follows: 1) strength, 2) combination work, 3) light penetrability, 4) treatment of cracks, 5) the color reproducibility of the block, 6) the abrasivity of antagonistic tooth, 7) low temperature degradation. In this presentation, the color reproducibility of the block will be discussed. One of the biggest reasons for avoiding the full zirconia restoration is that it is difficult to reproduce the natural color compared to the conventional PFM restoration. Thus, many clinicians show reluctance due to the exposure of the ugly block when the coloring on the surface is removed after occlusal adjustment. From the experience of using blocks by Zirkonzahn for more than 4 years, it is considered that these problems can be addressed to some degrees. Accordingly, how to make restorations that are well in harmony with surrounding prosthesis or natural teeth will be discussed.

• The Journal of Korean Academy of Prosthodontics
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• v.51 no.1
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• pp.47-51
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• 2013

With the introduction of dental implants, restoration of missing teeth with conventional fixed or removable partial dentures is being replaced with implants. Especially, with young patients, not only longevity but also esthetic factors need to be considered. Implant restorations provide long-term success functionally but, esthetic complications such as, marginal exposure due to gingival recession, loss of the papilla and dark color of metal abutments may occur. Recently, zirconia restorations with CAD/CAM technology provide functional, biocompatible and esthetic restorations possible. All-ceramic restorations using the pressed ceramic technique show better fracture toughness values than those of the conventional porcelain veneering technique. Pressed ceramic technique creates the veneer design in wax and the lost wax technique is used to create the restoration. The final contour of the restoration may be controlled during wax-up. A 22-year old female patient was restored with dental implants and zirconia restorations using the pressed ceramic technique presenting short-term but optimistic prognosis.

• Journal of Dental Rehabilitation and Applied Science
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• v.32 no.4
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• pp.351-357
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• 2016

Rehabilitation of maxillectomy patients is challenging. The maxillary defects need to functional restoration because of mastication, speech, swallowing problems. The goal of making obturator is to restore maxillary defects and give patients comfortable, esthetic prosthesis. This case report presents acquired masticatory and esthetic results and improved retention resulting from the pharyngeal obturator prosthesis using implant.

• The Journal of Advanced Prosthodontics
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• v.13 no.4
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• pp.237-245
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• 2021

PURPOSE. This study aimed to compare the microshear bond strength (µSBS) of dual-cure resin cement in CAD-CAM zirconia after different cleaning techniques. MATERIALS AND METHODS. Fifty discs of zirconia-based ceramic from Ivoclar Vivadent were embedded in acrylic resin. The discs were divided into five groups according to the cleaning methods used: Group 1: drying with spraying + sandblasting with Al₂O₃; Group 2: washed with water and dried with spraying + sandblasting with Al₂O₃;Group 3: washed with distilled water and dried with spraying + sandblasting with Al₂O₃ + zirconium oxide (Ivoclean); Group 4: washed with distilled water and dried with spraying + sandblasting with Al₂O₃ + potassium hydroxide (Zirclean); and Group 5: washed with distilled water and dried with spraying + sandblasting with Al₂O₃ + 1% NaClO. All of the groups were contaminated with artificial saliva for 1 minute and then cleaned. Statistical analyses were performed using ANOVA and Tukey's tests. RESULTS. There were statistically significant differences among all groups for µSBS (P < .05). The group treated with zirconium oxide (Group 3) showed the highest µSBS (18.75 ± 0.23 MPa). CONCLUSION. When applied to zirconia, the cleaning methods affected the bonding with resin cement differently.

• The Journal of Advanced Prosthodontics
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• v.14 no.6
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• pp.335-345
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• 2022

PURPOSE. This in vitro study aimed to evaluate the surface characteristics of a full veneer crown fabricated chairside (CS) from a (Y, Nb)-TZP zirconia block in response to conventional zirconia grinding and polishing. MATERIALS AND METHODS. Zirconia crowns (n = 40) were first prepared and divided into two groups of materials: Labside (LS) and CS, after which each specimen went through a five-step grinding and polishing procedure. Following each surface treatment, surface characteristics were analyzed using confocal laser microscopy (CLSM), average surface roughness (Ra) values were processed from the profile data through Gaussian filtering, and X-ray diffraction pattern analysis was performed to evaluate the monoclinic (M) phase content. Then, a representative specimen was selected for field-emission scanning electron microscopy (FE-SEM), followed by a final analysis of the roughness and X-ray diffraction of the specimens using the independent t-test and repeated measures analysis of variance (RM-ANOVA). RESULTS. In every group, polishing significantly reduced the Ra values (P < .001). There was no significant difference in Ra between the polished state CS and LS. Furthermore, CLSM and FE-SEM investigations revealed that even though grain exposure was visible in CS specimens throughout the as-delivered and ground states, the exposure was reduced after polishing. Moreover, while no phase transformation was visible in the LS, phase transformation was visible in CS after every surface treatment, with the M phase content of the CS group showing a significant reduction after polishing (P < .001). CONCLUSION. Within the limits of this study, clinically acceptable level of surface finishing of (Y, Nb)-TZP can be achieved after conventional zirconia polishing sequence.

• The Journal of Korean Academy of Prosthodontics
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• v.60 no.4
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• pp.313-319
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• 2022

Complete dentures are one of the most basic treatment methods for the treatment of edentulous patients. The manufacturing process of traditional complete dentures goes through the steps of taking primary impressions, secondary impressions, jaw relation record, trying in wax denture, and final denture insertion. Multiple visits and complex manufacturing procedures are required, and errors may occur in each step. With the development of digital technology, manufacturing steps have been reduced by introducing digital technology to the denture treatment process. In the process of manufacturing dentures by introducing a digital process, a more precise work is possible using Computer-Aided Design, and it is possible to shorten the period of labor and reduce the number of visits. In this case, the anterior teeth arrangement of the patient's existing dentures was transferred to the final dentures using a digital method. After taking impression, try-in dentures were digitally fabricated and tried in the oral cavity to evaluate their retention in the oral cavity. Final dentures were manufactured by milling process. The number of visits was reduced, satisfactory retention and stability of dentures were obtained, and aesthetic recovery was achieved.