• Journal of Dental Rehabilitation and Applied Science
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• v.26 no.4
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• pp.433-445
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• 2010

The aim of this study was to evaluate the fixation effect by connecting impression copings and to compare the three types of impression trays which were used in open tray impression technique. Experimental groups used 3 types of impression trays which are custom tray, plastic metal combination tray and polycarbonate stock tray. These three groups were subdivided into splinted and non-splinted impression copings group. The total number of experimental groups was six. 10 specimens were made for each group. We used 1-screw test, observing the specimen on which only one side abutment of reference framework was fixated with 20 Ncm. The gap between implant analogue and abutment of the other side was observed by stereo microscope. It was measured at 6 points in each specimen. Measuring value was selected when same result was revealed 3 times. Recorded data were statistically analyzed. Whether impression copings were splinted or not, there was no significant difference among custom tray group, plastic metal combination tray group, and polycarbonate stock tray group. Significant statistical difference in vertical fit discrepancy was found between splinted and non-splinted impression copings group with custom tray, plastic metal combination tray and polycarbonate stock tray (p<0.05).

• Journal of Dental Rehabilitation and Applied Science
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• v.36 no.4
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• pp.211-221
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• 2020

The typical biomechanical properties of an internal conical connection (ICC) are axial displacement and loss of preload. The axial displacement of an ICC without a vertical stop can cause the loss of preload and a lowered occlusion. The stress of an ICC is concentrated on the contact interface of the abutment and not on the screw, and during placement, it is important to choose a wider coronal wall thickness as much as possible. The ICC should also be placed below the level of the bone crest. During the restoration of an ICC, care should be taken to ensure an appropriate abutment shape and an accurate connection. To get the best clinical results, it is important to select its wall thickness and place it in the appropriate position to restore it adequately.

• The Journal of Korean Academy of Prosthodontics
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• v.46 no.4
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• pp.359-371
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• 2008

Purpose: The purpose of this study was to investigate the stress distribution in mandibular implant overdentures with telescopic crowns compared to bar attachment. Material and methods: Three-dimensional finite element models consisting of the mandibular bone, 4 implants, and primary bar-splinted superstructure or secondary splinted superstructure with telescopic crowns were created. Vertical and oblique loads were directed onto the occlusal areas of the superstructures to simulate the maximal intercuspal contacts and working contacts such as group function occlusion. Maximum stress and stress distribution were analysed in mandibular bone, implant abutments, and superstructures. Results: 1. In comparison of von Mises stress on mandibular bone, telescopic overdenture had a little lower stress values in vertical load and working side load except oblique load. In the mandible, the telescopic overdenture distributed more uniform stress than the bar overdenture. 2. In comparison of von Mises stress on implant abutments, telescopic overdenture had much lower stress values in all load conditions. In implant abutments, the telescopic overdenture distributed stress similar to the bar overdenture. Stress was concentrated on the distal surfaces of the posterior implant abutments in both mandibular overdentures. 3. In comparison of von Mises stress on superstructures, the telescopic overdenture had much more stress values in all load conditions. However, the telescopic overdenture distributed more uniform stress on superstructure than the bar overdenture. In the bar overdenture, stress was concentrated on each cental area of bar structures and connected area between implant abutments and bar structures. Conclusion: In the results of this study, the telescopic overdenture had lower stress values than the bar overdenture in mandibular bone and implant abutments, but more stress values in superstructures. However, if optimal material was selected in making superstructures, the telescopic overdenture was compared to the bar overdenture in stress distribution.

• The Journal of Korean Academy of Prosthodontics
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• v.49 no.3
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• pp.197-205
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• 2011

Purpose: This study was to evaluate the accuracy of the implant torque controller used in dental clinics and to investigate whether it was applied appropriately. Materials and methods: Fifty dentists who work in dental clinics were enrolled in this study. Dental (implant) practice career, experience frequency of implant screw loosening and fracture, education of implant torque controller application and infection control methods were included in the survey. 25 Ncm and 30 Ncm of the tightening torque applied to the implant screw were measured by 50 clinicians. After measuring the torque value by using the torque controller, the torque mean according to where education about the implant torque controller was received was analyzed with independent t-test at the significance level of 0.05. Results: The torque controller used in private dental clinics showed 4.78% error ratio. When 50 dentists applied 25 Ncm to the implant screw was $29.0{\pm}8.4$ Ncm, and that in 30 Ncm was $34.3{\pm}9.1$ Ncm. Statistical significance was found between the group that was educated about implant torque application and the group that was not educated. Conclusion: During the prosthodontic treatment with implant, there was difference between actual applied torsion force and the amount torque controller indicated. Clinicians have to not only be well-informed about the accurate usage method of the torque controller, but also keep and manage the torque controller so as to maintain continuous and accurate torque values. Through this, it is considered to achieve clinical results to minimize problems of screw loosening or fracture.

• The Journal of Korean Academy of Prosthodontics
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• v.50 no.1
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• pp.36-43
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• 2012

Purpose: To analyze the stress distribution of the implant and its supporting structures through 3D finite elements analysis for implants with different hexagon heights and to make the assessment of the mechanical stability and the effect of the elements. Materials and methods: Infinite elements modeling with CAD data was designed. The modeling was done as follows; an external connection type ${\phi}4.0mm{\times}11.5mm$ Osstem$^{(R)}$ USII (Osstem Co., Pusan, Korea) implant system was used, the implant was planted in the mandibular first molar region with appropriate prosthetic restoration, the hexagon (implant fixture's external connection) height of 0.0, 0.7, 1.2, and 1.5 mm were applied. ABAQUS 6.4 (ABAQUS, Inc., Providence, USA) was used to calculate the stress value. The force distribution via color distribution on each experimental group's implant fixture and titanium screw was studied based on the equivalent stress (von Mises stress). The maximum stress level of each element (crown, implant screw, implant fixture, cortical bone and cancellous bone) was compared. Results: The hexagonal height of the implant with external connection had an influence on the stress distribution of the fixture, screw and upper prosthesis and the surrounding supporting bone. As the hexagon height increased, the stress was well distributed and there was a decrease in the maximum stress value. If the height of the hexagon reached over 1.2mm, there was no significant influence on the stress distribution. Conclusion: For implants with external connections, a hexagon is vital for stress distribution. As the height of the hexagon increased, the more effective stress distribution was observed.

• Journal of Dental Rehabilitation and Applied Science
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• v.26 no.1
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• pp.39-46
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• 2010

To assess the stress distribution of implant prosthesis induced by intentional misfit using photoelastic model. Stress was measured at the surrounding bone after applying vertical load to the implant. Three implants were placed in each of three photoelastic resin blocks. No misfits were used for the control group, while for the experimental group $100{\mu}m$ misfit after cutting the crown was used. The photoelastic stress analysis was performed. In control group, stress concentration was not shown when the load was not applied, whereas stress concentration was shown only in the loaded part even when load was applied and the stress was distributed in anterior-posterior direction when applying a load in the middle. When intentional misfits were given, stress around the fixture was incurred when tightening the screw even if load was not applied. If the load was applied, stress was concentrated around the implants including areas where the load was applied. In particular, the prosthesis made of UCLA showed more stress concentration as compared with a conical abutment. In the UCLA case, concentration was shown from the apex following through the axis to the cervical area. Prosthesis with misfit makes the stress concentrated though the load was not applied and it induces even more severe stress concentration when the load was applied. This founding demonstrates the importance of the correct prosthesis production.

• Journal of Periodontal and Implant Science
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• v.46 no.6
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• pp.362-371
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• 2016

Purpose: The increasing demand for esthetically pleasing results has contributed to the use of ceramics for dental implant abutments. The aim of this study was to compare the biological response of epithelial tissue cultivated on lithium disilicate ($LS_2$) and zirconium oxide ($ZrO_2$) ceramics. Understanding the relevant physicochemical and mechanical properties of these ceramics will help identify the optimal material for facilitating gingival wound closure. Methods: Both biomaterials were prepared with 2 different surface treatments: raw and polished. Their physicochemical characteristics were analyzed by contact angle measurements, scanning white-light interferometry, and scanning electron microscopy. An organotypic culture was then performed using a chicken epithelium model to simulate peri-implant soft tissue. We measured the contact angle, hydrophobicity, and roughness of the materials as well as the tissue behavior at their surfaces (cell migration and cell adhesion). Results: The best cell migration was observed on $ZrO_2$ ceramic. Cell adhesion was also drastically lower on the polished $ZrO_2$ ceramic than on both the raw and polished $LS_2$. Evaluating various surface topographies of $LS_2$ showed that increasing surface roughness improved cell adhesion, leading to an increase of up to 13%. Conclusions: Our results demonstrate that a biomaterial, here $LS_2$, can be modified using simple surface changes in order to finely modulate soft tissue adhesion. Strong adhesion at the abutment associated with weak migration assists in gingival wound healing. On the same material, polishing can reduce cell adhesion without drastically modifying cell migration. A comparison of $LS_2$ and $ZrO_2$ ceramic showed that $LS_2$ was more conducive to creating varying tissue reactions. Our results can help dental surgeons to choose, especially for esthetic implant abutments, the most appropriate biomaterial as well as the most appropriate surface treatment to use in accordance with specific clinical dental applications.

• The Journal of Korean Academy of Prosthodontics
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• v.45 no.6
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• pp.717-723
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• 2007

Statement of problem. Unreasonable distal cantilevered implant-supported prosthesis can mask functional problems of reconstruction temporarily, but it can cause serious strain and stress around its supported implant and surrounding alveolar bone. Purpose. The purpose of this study was to evaluate strain of implants supporting distal cantilevered fixed prosthesis with two different cantilevered length under distal cantilevered static load. Material and methods. A partially edentulous mandibular test model was fabricated with auto-polymerizing resin (POLYUROCK; Metalor technologies, Stuttgart, Swiss) and artificial denture teeth (Endura; Shofu inc., Kyoto, Japan). Two implants-supported 5-unit screw-retained cantilevered fixed prosthesis was made using standard methods with Type III gold alloy (Harmony C&B55; Ivoclar-vivadent, Liechtenstein, Germany) for superstructure and reinforced hard resin (Tescera; Ivoclar-vivadent, Liechtenstein, Germany) for occlusal material. Two strain gauges (KFG-1-120-C1-11L1M2R; KYOWA electronic instruments, Tokyo, Japan) were then attached to the mesial and the distal surface of each standard abutment with adhesive (M-bond 200; Tokuyama, Tokyo, Japan). Total four strain gauges were attached to test model and connected to dynamic signal conditioning strain amplifier (CTA1000; Curiotech inc., Paju, Korea). The stepped $20{\sim}100$ N in 25 N increments, cantilevered static load 8mm apart (Group I) or 16mm apart (Group II), were applied using digital push-pull gauge (Push-Pull Scale & Digital Force Gauge, Axis inc., Seoul, Korea). Each step was performed ten times and every strain signal was monitored and recorded. Results. In case of Group I, the strain values were surveyed by $80.7{\sim}353.8{\mu}m$ in Ch1, $7.5{\sim}47.9{\mu}m/m$ in Ch2, $45.7{\sim}278.6{\mu}m/m$ in Ch3 and $-212.2{\sim}718.7{\mu}m/m$ in Ch4 depending on increasing cantilevered static load. On the other hand, the strain values of Group II were surveyed by $149.9{\sim}612.8{\mu}m/m$ in Ch1, $26.0{\sim}168.5{\mu}m/m$ in Ch2, $114.3{\sim}632.3{\mu}m/m$ in Ch3, and $-323.2{\sim}-894.7{\mu}m/m$ in Ch4. Conclusion. A comparative statistical analysis using paired sample t-test about Group I Vs Group II under distal cantilevered load shows that there are statistical significant differences for all 4 channels (P<0.05).

• Journal of Periodontal and Implant Science
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• v.38 no.2
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• pp.135-142
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• 2008

Purpose: Numerous studies have shown that crestal bone resorption around the implant was related to the location of the implant abutment junction(IAJ). Recently it was hypothesized that platform switching termed the inward horizontal repositioning of the IAJ might limit bone resorption around the implants. The purpose of this clinical study was to evaluate the effect of platform switching on crestal bone resorption. Materials and Methods: The crestal bone loss of 65 external hex implants in 26 patients were radiographically measured at crown placement and follow-up examinations. 23 standard implants(non-platform switching group, NP) were connected with the matching abutments and 42 wide implants(platform switching group, PS) were connected with the 1 mm smaller diameter abutments. Results: There was significant difference of crestal bone loss between NP group and PS group. For implants in the NP group, mean crestal bone loss was $1.18{\pm}0.68\;mm$ at crown placement and $1.42{\pm}0.41\;mm$ at follow-up. The meal bone loss in PS group was $0.47{\pm}0.52\;mm$ at crown placement and $0.60{\pm}0.65\;mm$ at follow-up. When the crestal bone changes according to placement depths of implants were compared, subcrestal position of IAJ had a significantly less bone loss in PS group, but it was not in NP group. Conclusion: Within the limits of the present study, it was concluded that platform switching technique might decrease crestal bone loss around the implants. Additionally, when the IAJ of implant was placed 1 mm deeper in the alveolar bone, the effect of platform switching on bone loss was enhanced.

• The Journal of Korean Academy of Prosthodontics
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• v.59 no.3
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• pp.359-369
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• 2021

Implant prostheses and removable partial dentures are mainly used as treatment methods for partial edentulous patients who have lost a number of teeth. The implant-assisted removable partial denture (IARPD) is strategically selected. The defect in maxillofacial structure due to osteomyelitis, a type of facial bone infection, causes dysfunction such as mastication, swallowing, and pronunciation, as well as social and psychological effects, so a removable restoration is required to restore the supporting tissue. Design of abutment and partial dentures is an essential factor in the success of treatment. In this case, IARPD, which has superior retention and stability compared to traditional removable partial dentures, can have a good prognosis. In a partial edentulous patient with bone defects due to osteomyelitis treatment, the stability of the denture was secured with IARPD restoration. Moreover, maintenance problem that may occur in the future was minimized by providing an appropriate denture design and occlusal scheme through several provisional restorations. This case can be expected to have a favorable prognosis in the long term.