• The Korean Journal of Physiology and Pharmacology
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• v.13 no.3
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• pp.221-227
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• 2009

For successful restoration of visual function by a visual neural prosthesis such as retinal implant, electrical stimulation should evoke neural responses so that the informat.ion on visual input is properly represented. A stimulation strategy, which means a method for generating stimulation waveforms based on visual input, should be developed for this purpose. We proposed to use the decoding of visual input from retinal ganglion cell (RGC) responses for the evaluation of stimulus encoding strategy. This is based on the assumption that reliable encoding of visual information in RGC responses is required to enable successful visual perception. The main purpose of this study was to determine the influence of inter-dependence among stimulated RGCs activities on decoding accuracy. Light intensity variations were decoded from multiunit RGC spike trains using an optimal linear filter. More accurate decoding was possible when different types of RGCs were used together as input. Decoding accuracy was enhanced with independently firing RGCs compared to synchronously firing RGCs. This implies that stimulation of independently-firing RGCs and RGCs of different types may be beneficial for visual function restoration by retinal prosthesis.

• Journal of Information Technology Services
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• v.22 no.5
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• pp.87-98
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• 2023

Traditionally, tooth restoration has been carried out by replicating teeth using plaster-based materials. However, recent technological advances have simplified the production process through the introduction of computer-aided design(CAD) systems. Nevertheless, dental restoration varies among individuals, and the skill level of dental technicians significantly influences the accuracy of the manufacturing process. To address this challenge, this paper proposes an approach to designing personalized tooth restorations using Generative Adversarial Network(GAN), a widely adopted technique in computer vision. The primary objective of this model is to create customized dental prosthesis for each patient by utilizing 3D data of the specific teeth to be treated and their corresponding opposite tooth. To achieve this, the 3D dental data is converted into a depth map format and used as input data for the GAN model. The proposed model leverages the network architecture of Pixel2Style2Pixel, which has demonstrated superior performance compared to existing models for image conversion and dental prosthesis generation. Furthermore, this approach holds promising potential for future advancements in dental and implant production.

• The Journal of Advanced Prosthodontics
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• v.6 no.5
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• pp.361-371
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• 2014

PURPOSE. In case of large horizontal discrepancy of alveolar ridge due to severe resorption, cantilevered crown is usually an unavoidable treatment modality. The purpose of this study was to evaluate the clinical criteria for the placement of the aforementioned implant crown. MATERIALS AND METHODS. The mandible model with 2 mm thick cortical bone and cancellous bone was fabricated from CT cross-section image. An external connection type implant was installed and cantilevered crowns with increasing offset of 3, 4, 5, 6, and 7 mm were connected. Vertical load and $30^{\circ}$ oblique load of 300 N was applied and stress around bone and implant component was analyzed. A total of 14 cases were modeled and finite element analysis was performed using COSMOS Works (Solid works Inc, USA). RESULTS. As for the location of the vertical load, the maximum stress generated on the lingual side of the implant became larger according to the increase of offset distance. When the oblique load was applied at $30^{\circ}$, the maximum stress was generated on the buccal side and its magnitude gradually decreased as the distance of the offset load increased to 5 mm. After that point, the magnitude of implant component's stress increased gradually. CONCLUSION. The results of this study suggest that for the patient with atrophied alveolar ridge following the loss of molar teeth, von-Mises stress on implant components was the lowest under the $30^{\circ}$ oblique load at the 5 mm offset point. Further studies for the various crown height and numbers of occusal points are needed to generalize the conclusion of present study.

• The Journal of the Korean dental association
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• v.54 no.12
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• pp.1024-1034
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• 2016

Purpose. The purpose of this study was to compare the type and frequency of prosthetic complications associated with attachment types for implant overdenture. Material and methods. In this retrospective study, 38 patients (mean age, 63.5 years) have been treated with implant overdentures from 2007 to 2014. Ten patients received a bar-clip attachment. Eleven patients had received a milled bar with Locator attachment. Seventeen patients had received a Locator attachment. The mean follow-up period was 36.9 months (range, 15-83 months). The type and frequency of prosthetic complications was recorded. The frequency was analyzed to determine the statistical difference among the 3 different attachments by using one-way ANOVA (${\alpha}=.05$) and Bonferroni post hoc method at a 5% level of significance. Results. The total number of prosthetic complications was higher in the bar-clip attachment (55 events) than in the milled bar with Locator attachment (39 events) and the Locator attachment (34 events). There were no statistically significant differences, and the most common prosthetic complication was the loss of retention. In the bar-clip attachment group, the average frequency of prosthetic complications was 3.0 events per prosthesis during the first year. In the milled bar with Locator attachment and Locator attachment groups, the average frequencies were 1.45 events and 2.35 events, respectively. Statistically significant differences were observed in the frequency of the complication. (p = .043) Conclusions. Compared to the bar-clip attachment, implant overdentures that use milled bars with the Locator attachment have a significantly lower incidence of prosthetic complications in the first year of follow-up after placement.

• The Journal of Korean Academy of Prosthodontics
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• v.29 no.2
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• pp.1-16
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• 1991

In order to see the possible effect of the functional load-bearing after osseointegration of the titanium root form implant in dog a histologic study was conducted. One side of lower jaw was surgically prepared edentulousness and titanium implants were inserted. Some implants were functionally loaded through fixed detachable prosthesis and some are isolated and unloaded. The dog was sacrificed four months later and bone sections with implants were processed for histologic evaluation and the results were as follows ; (1) The bone to implant interface after four months of load bearing presented no mobility and no marginal bone loss radiographically and histologically. (2) The interface zone between compact bone and implant revealed a direct bone to implant contact and in some areas marrow tissue contacts were examined at the light microscopic level. (3) At the ultrastructural level the interface of surrounding compact bone matrix and implant, three types of superficial layers were found ; one with moderate electron dense amorphous granular substance layer, other with high electron dense fine granular substance layer, and another type of amorphous granular substance covered with high electron dense line of minute granules. (4) The osteoblasts in the marrow tissue neighboring implants and osteocytes in compact bone showed typical normal characteristics and in the marrow tissues some of lymphocytes and mast cells were observed. (5) The abscence of abnormal tissue reactions at a cellular level indicates a high degree of biocompatibility for the experimental titanium implant and basically no difference was found between functionally loaded and unloaded implants.

• Journal of Dental Anesthesia and Pain Medicine
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• v.17 no.3
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• pp.205-213
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• 2017

Background: This study retrospectively investigated outcomes following dental implantation in patients with special needs who required general anesthesia to enable treatment. Method: Patients underwent implant treatment under general anesthesia at the Clinic for the Disabled in Seoul National University Dental Hospital between January 2004 and June 2017. The study analyzed medical records and radiographs. Implant survival rates were calculated by applying criteria for success or failure. Results: Of 19 patients in the study, 8 were males and 11 were females, with a mean age of 32.9 years. The patients included 11 with mental retardation, 3 with autism, 2 with cerebral palsy, 2 with schizophrenia, and 1 with a brain disorder; 2 patients also had seizure disorders. All were incapable of oral self-care due to serious cognitive impairment and could not cooperate with normal dental treatment. A total of 27 rounds of general anesthesia and 1 round of intravenous sedation were performed for implant surgery. Implant placement was performed in 3 patients whose prosthesis records could not be found, while 3 other patients had less than 1 year of follow-up after prosthetic treatment. When the criteria for implant success or failure were applied in 13 remaining patients, 3 implant failures occurred in 59 total treatments. The cumulative survival rate of implants over an average of 43.3 months (15-116 months) was 94.9%. Conclusion: For patients with severe cognitive impairment who are incapable of oral self-care, implant treatment under general anesthesia showed a favorable prognosis.

• The Journal of Korean Academy of Prosthodontics
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• v.45 no.3
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• pp.354-361
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• 2007

Statement of Problems. The precision of fit between the bearing surfaces of implant abutments and the prosthesis framework has been considered fundamental to implant prosthodontic protocol. Purpose. The study aimed to investigate the effect of laboratory procedure on the dimensional accuracy of cast implant bars. Material and methods Thirty implant bars were fabricated on a metal master model. The gap distances were measured at the right implant abutment replica-gold cylinder interface after casting procedure. The bar length data of precasting and postcasting state were collected and analyzed. Results. The mean gap distance found after casting was $106.3{\mu}m$ for buccal side, $122.1{\mu}m$ for distal side and $117.1{\mu}m$ for the lingual side. The mean bar length was $17964.7{\mu}m$ at precasting measurement, $17891.6{\mu}m$ at postcasting measurement. The mean change of bar length was $-73.1{\mu}m$. Conclusion. Even though the techniques used in this study strictly followed the guidelines established in the literature, the 30 cast implant bars evaluated all yielded gap distances that were beyond acceptable accuracy. There was a statistically significant difference between precasting and postcasting bar length (P<0.01). There was a decreasing tendency in bar length after casting procedure. It was necessary to correct this dimensional change from laboratory procedure by some corrective methods.

• The Journal of Advanced Prosthodontics
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• v.4 no.4
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• pp.197-203
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• 2012

PURPOSE. The aim of this systematic review was to address treatment outcome according to attachment systems for mandibular implant overdentures in terms of implant survival rate, prosthetic maintenance and complications, and patient satisfaction. MATERIALS AND METHODS. A systematic literature search was conducted using PubMed and hand searching of relevant journals considering inclusion and exclusion criteria. Clinical trial studies on mandibular implant overdentures until August, 2010 were selected if more than one type of overdenture attachment was reported. Twenty four studies from 1098 studies were finally included and the data on implant survival rate, prosthetic maintenance and complications, patient satisfaction were analyzed relative to attachment systems. RESULTS. Four studies presented implant survival rates (95.8 - 97.5% for bar, 96.2 - 100% for ball, 91.7% for magnet) according to attachment system. Ten other studies presented an implant survival rate ranging from 93.3% to 100% without respect to the attachment groups. Common prosthetic maintenance and complications were replacement of an assay for magnet attachments, and activation of a matrix or clip for ball or bar attachments. Prosthetic maintenance and complications most commonly occurred in the magnet groups. Conflicting findings were found on the rate of prosthetic maintenance and complications comparing ball and bar attachments. Most studies showed no significant differences in patient satisfaction depending upon attachment systems. CONCLUSION. The implant survival rate of mandibular overdentures seemed to be high regardless attachment systems. The prosthetic maintenance and complications may be influenced by attachment systems. However patient satisfaction may be independent of the attachment system.

• Journal of Technologic Dentistry
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• v.43 no.2
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• pp.42-47
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• 2021

Purpose: The purpose of this study was to evaluate the stability of abutment screws used with the zirconia fixture-based implant system and compare them with those used with the existing titanium fixture system via the finite element method. Methods: A single implant-supported restoration was designed for the finite element analysis. A universal analysis program was used to set 8 occlusal points along the direction to the long axis of the implant, and an occlusal load of 700 N was applied. Results: In all models (Zir and Ti-fixture model), the screw threads presented with the highest von Mises stress (VMS) values, whereas the head and end presented with the lowest VMS values. The VMS of the screw used in the zirconia-fixture model was 5.97% lower than that used in the titanium-fixture model (261.258 vs. 276.911 MPa, respectively) despite statistical significance. Furthermore, the zirconia fixture (352.912 MPa) had a higher stress value (8.42%) than the titanium fixture (332.331 MPa). In a completely tightened titanium fixture implant system, the stress was concentrated in the implant-abutment connection interface, the zirconia fixture presented with a stable stress distribution. Conclusion: Although the zirconia fixture demonstrated a high VMS value, owing to the stiffness and elasticity coefficients of the material, the stress generated in the abutment screws was similar in all models. In conclusion, the zirconia fixture-based implant system presented with a more stable stress distribution in the abutment screws than the titanium fixture-based implant system.

• Journal of Dental Rehabilitation and Applied Science
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• v.38 no.2
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• pp.110-119
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• 2022

When restoration for partially edentulous patients, abutments are not always in favorable positions for making removable partial dentures. Because of these situations, patients are sometimes unsatisfied with the stability and support of their removable partial prostheses. In this regard, removable partial denture using a few implant surveyed crown prostheses can be a good alternative. It can be expected to increase stability and support of removable partial dentures by strategically placing a small number of implants and restoring with implant-supported surveyed crowns. In these cases, the patients who had unilateral residual teeth on mandible were treated with two implant surveyed crowns in the tactical place to have bilateral distribution. After definitive removable partial prosthesis, the patients showed satisfaction with the masticatory function and comfort of using removable dentures.