• The Journal of Advanced Prosthodontics
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• 제12권3호
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• pp.124-130
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• 2020

PURPOSE. The aim of this in vitro study was to evaluate the effect of sintering procedures on marginal discrepancies of fixed partial metal frameworks fabricated using different sintering-based computer-aided design and computer/aided manufacturing (CAD/CAM) techniques. MATERIALS AND METHODS. Forty resin die models of prepared premolar and molar abutment teeth were fabricated using a three-dimensional (3D) printer and divided into four groups (n = 10) according to the fabrication method of metal frameworks used: HM (via hard milling), SM (via soft metal milling), L25 (via direct metal laser melting [DMLM] with a 25 ㎛ layer thickness), and L50 (via direct DMLM with a 50 ㎛ layer thickness). After the metal frameworks were fabricated and cemented, five vertical marginal discrepancy measurements were recorded in each site (i.e., buccal, facing the pontic, lingual, and facing away from the pontic) of both abutment teeth under a stereomicroscope (×40). Data were statistically analyzed at a significance level of 0.05. RESULTS. No statistically significant differences (P>.05) were found among the four axial sites of metal frameworks fabricated by sintering-based CAD/CAM techniques. The HM and L25 groups showed significantly (P<.001) lower marginal discrepancy values than the SM and L50 groups. CONCLUSION. Marginal discrepancy in the sites facing the pontic was not influenced by the type of sintering procedure. All fabrication methods exhibited clinically acceptable results in terms of marginal discrepancies.

• 대한치과보철학회지
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• 제34권3호
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• pp.501-532
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• 1996

This study investigated the effects of cantilever length, location and load condition on stress distribution developed in the implants, prostheses and supporting tissues. The osseointegrated prostheses with two 10mm Branemark implants at 2nd premolar and 1st molar sites with cantilever extensions at 1st premolar, 2nd and 3rd molar sites were constructed. Under 100N, 200N of vertical and $45^{\circ}$ oblique loads at the cantilever pontics, stress distribution patterns and displacement were analyzed with three dimensional finite element method. The results were as follows : 1. The stress was concentrated at the joint of the cantilever pontic and implant superstructure, the neck of implant and the ridge crest near the cantilever But there was little load transfer to the lower supporting tissues of implants. 2. The implant near the cantilever was displaced inferiorly while the implant far from the cantilever was displaced superiorly. In horizontal direction the implants were displaced to the direction where the loads were applied, except the apexes of the implants. 3. In case of anterior cantilever, the stress and displacement were higher than the prosthesis connected with natural tooth. 4. The stress developed in the posterior cantilevered type was higher than in the anterior cantilevered type. The greastest stress was concentrated at the ridge crest near the posterior cantilever. 5. The longer the cantilever, the more the stress was developed and was concentrated at the joint of the cantilever pontic and implant superstructure. 6. Under oblique load, the stress was concentrated at the necks of implants and the ridge crests, but decreased at the joint of the cantilever pontic and implant superstructure than under vertical load.

• 대한치과보철학회지
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• 제46권3호
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• pp.290-297
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• 2008

STATEMENT OF PROBLEM: Implant-supported fixed cantilever prostheses are influenced by various biomechanical factors. The information that shows the effect of implant number and position of cantilever on stress in the supporting bone is limited. PURPOSE: The purpose of this study was to investigate the effect of implant number variation and the effect of 2 different cantilever types on stress distribution in the supporting bone, using 3-dimensional finite element analysis. MATERIAL AND METHODS: A 3-D FE model of a mandibular section of bone with a missing second premolar, first molar, and second molar was developed. $4.1{\times}10$ mm screw-type dental implant was selected. 4.0 mm height solid abutments were fixed over all implant fixtures. Type III gold alloy was selected for implant-supported fixed prostheses. For mesial cantilever test, model 1-1 which has three $4.1{\times}10$ mm implants and fixed prosthesis with no pontic, model 1-2 which has two $4.1{\times}10$ mm implants and fixed prosthesis with a central pontic and model 1-3 which has two $4.1{\times}10$ mm implants and fixed prosthesis with mesial cantilever were simulated. And then, 155N oblique force was applied to the buccal cusp of second premolar. For distal cantilever test, model 2-1 which has three $4.1{\times}10$ mm implants and fixed prosthesis with no pontic, model 2-2 which has two $4.1{\times}10$ mm implants and fixed prosthesis with a central pontic and model 2-3 which has two $4.1{\times}10$ mm implants and fixed prosthesis with distal cantilever were simulated. And then, 206N oblique force was applied to the buccal cusp of second premolar. The implant and superstructure were simulated in finite element software(Pro/Engineer wildfire 2.0). The stress values were observed with the maximum von Mises stresses. RESULTS: Among the models without a cantilever, model 1-1 and 2-1 which had three implants, showed lower stress than model 1-2 and 2-2 which had two implants. Although model 2-1 was applied with 206N, it showed lower stress than model 1-2 which was applied with 155N. In models that implant positions of models were same, the amount of applied occlusal load largely influenced the maximum von Mises stress. Model 1-1, 1-2 and 1-3, which were loaded with 155N, showed less stress than corresponding model 2-1, 2-2 and 2- 3 which were loaded with 206N. For the same number of implants, the existence of a cantilever induced the obvious increase of maximum stress. Model 1-3 and 2-3 which had a cantilever, showed much higher stress than the others which had no cantilever. In all models, the von Mises stresses were concentrated at the cortical bone around the cervical region of the implants. Meanwhile, in model 1-1, 1-2 and 1-3, which were loaded on second premolar position, the first premolar participated in stress distribution. First premolars of model 2-1, 2-2 and 2-3 did not participate in stress distribution. CONCLUSION: 1. The more implants supported, the less stress was induced, regardless of applied occlusal loads. 2. The maximum von Mises stress in the bone of the implant-supported three unit fixed dental prosthesis with a mesial cantilever was 1.38 times that with a central pontic. The maximum von Mises stress in the bone of the implant-supported three-unit fixed dental prosthesis with a distal cantilever was 1.59 times that with a central pontic. 3. A distal cantilever induced larger stress in the bone than a mesial cantilever. 4. A adjacent tooth which contacts implant-supported fixed prosthesis participated in the stress distribution.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• 제34권2호
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• pp.166-179
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• 2008

Excessive concentration of stress which is occurred in occlusion around the implant in case of the implant supported fixed partial denture has been known to be the main cause of the crestal bone destruction. Therefore, it is essential to evaluate the stress analysis on supporting tissue to get higher success rates of implant. The purpose of this study was to evaluate the effects of stress distribution and deformation in 3 different types of three-unit fixed partial denture sup-ported by two implants, using a three dimensional finite element analysis in a three dimensional model of a whole mandible. A mechanical model of an edentulous mandible was generated from 3D scan, assuming two implants were placed in the left premolars area. According to the position of pontic, the experiments groups were divided into three types. Type I had a pontic in the middle position between two implants, type II in the anterior posi-tion, and type III in the posterior position. A 100-N axial load was applied to sites such as the central fossa of anterior and posterior implant abutment, central fossa of pontic, the connector of pontic or the connector between two implants, the mandibular boundary conditions were modeled considering the real geometry of its four-masticatory muscular supporting system. The results obtained from this study were as follows; 1. The mandible deformed in a way that the condyles converged medially in all types under muscular actions. In comparison with types, the deformations in the type II and type III were greater by 2-2.5 times than in the type I regardless of the loading location. 2. The values of von Mises stresses in cortical and cancellous bone were relatively stable in all types, but slightly increased as the loading position was changed more posteriorly. 3. In comparison with type I, the values of von Mises stress in the implant increased by 73% in Type II and by 77% in Type III when the load was applied anterior and posterior respectively, but when the load was applied to the middle, the values were similar in all types. 4. When the load was applied to the centric fossa of pontic, the values of von Mises stress were nearly $30{\sim}35%$ higher in the type III than type I or II in the cortical and cancellous bone. Also, in the implant, the values of von Mises stress of the type II or III were $160{\sim}170%$ higher than in the type I. 5. When the load was applied to the centric fossa of implant abutment, the values of von Mises stress in the cortical and cancellous bone were relatively $20{\sim}25%$ higher in the type III than in the other types, but in the implant they were 40-45% higher in the type I or II than in the type III. According to the results of this study, musculature modeling is important to the finite element analysis for stress distribution and deformation as the muscular action causes stress concentration. And the type I model is the most stable from a view of biomechanics. Type II is also a clinically accept-able design when the implant is stiff sufficiently and mandibular deformation is considered. Considering the high values of von Mises stress in the cortical bone, type III is not thought as an useful design.

• 대한치과보철학회지
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• 제31권2호
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• pp.271-300
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• 1993

The purpose of this study was to analyze the stress distribution at supporting bone according to the types of connection modality between implant and tooth in the superstrcture. This investigation evaluated the stress patterns in a photoelastic model produced by three different types of dental implants such as Branemark, Steri-Oss, IMZ and resin tooth using the techniques of quasi three dimensional photoelasticity. The teeth-supported bridge had a first molar pontic supported by second premolar and second molar as a control group. The implant and toothsupported bridge had a first molar pontic supported by second premolar and implant posterior retainer as an experimental group. Prostheses were mechanically connected to an adjacent second premolar by the rigid of nonrigid connection, Nonrigid connection used an attachment placed between the tooth-supported and fixture-supported component. The female(keyway) of attachment was placed on the distal end of the retainer supported by the tooth ; the male(Key) of attachment connected to the osseointegrated bridge was engaged into the keyway. All prostheses were casted in the same nonprecious alloy and were cemented and screwed on their respective abutments and implants. 16㎏ of vertical loads on central fossae of second premolar, first molar pontic, implant of second molar were applied respectively and 6.5㎏ of inclined load on middle buccal surface of first molar pontic was applied. The results were as follows : 1. Under the vertical load on the central fossa of first mloar pontic, the stress developed at the apex of tooth of implat was more uniformly distributed in the case of nonrigid connection than in the case of rigid connection. 2. Under the vertical load on the central fossa of first molar pontic, the stress developed around the cervical area of tooth of implant was larger in the case of rigid connection than in the case of nonrigid connection because the bending moment was more occured in the case of rigid connection than in the case of nonrigid connection. 3. Stress was more restricted to the loaded side of nonrigid connection than to that of rigid connection 4. Under the inclined load. The set screw loosening of implant was more easily occured in the case of nonrigid connection than in the case of rigid connection due to torque moment. 5. In the case of Branemark implant, the stress concentration in second premolar was larger and the stress developed around the cervical area of implant was lower than any other cases under the vertical load, because Branemark implant with the flexible gold screw was showed in incline toward second premolar by a bending moment. 6. The stress developed around the apex of tooth or implant was more uniformly distributed in the case of Steri-Oss implant with stiff screw than in the case of Branemark implant under the vertical load. But, the stress developed around the cervical area of the Steri-Oss implant was larger than that of any other implants because bending moment was occured by vertical migration of second premolar. 7. The stress distribution in the case of IMZ implant was similar to the case of natural teeth under small vertical load. But, the residual stress around the implant was showed to occurdue to deformation of IMC and sinking of screw under larger vertical load.

• 대한치과보철학회:학술대회논문집
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• 대한치과보철학회 2001년도 추계학술대회
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• pp.39-39
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• 2001

• 대한치과기공학회지
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• 제24권1호
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• pp.127-138
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• 2002

There are some cases that dental prosthesis does not operate as properly as expected in oral mouth. The reasons are such as a distortion of the mandibular, a fault of impression taking system or an extrusion of remaining teeth. One of dental prostheses to consider in the situations is the attachment which connects segment bridge. Active discussions are managed on theoretical side of this field but few on clinical side of it, which must be considered first. Accordingly I'd like to suggest a theoretical background for connect attachment of fixed segmented bridge. 1. As a bridge gets longer, burden on dental ligament is increased and the hardness of a bridge is lessened. 2. The flexibility of a bridge increases in ratio to 3 multiplication of the length and decreases in ratio to 3 multiplication of the width of occlusal surface and base of pontic. 3. Precision rest is needed to cope with the shake of teeth and the difference of axis direction among abutments. 4. Female part of the precision rest should be on middle abutment distal and male one on mesial of pontic. 5. Segmented attachment can be efficiently used to cope with long span bridgework and also in case that one piece casting can't be done because of slant of abutment.

• 대한치과보철학회지
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• 제43권2호
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• pp.204-217
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• 2005

Purpose. The purpose of this study was to analyze stress distribution of all ceramic posterior fixed partial denture using a three dimensional finite element method. Material and method. A three dimensional finite element model was created to demonstrate all-ceramic posterior fixed partial denture and then this computer model measured the stress distribution of the all ceramic bridges which has a ceramic core materials such as Zirconia, IPS Empress. 2. In-Ceram zirconia, Metal-Ceramic. Also the stress distribution was examined according to loading sites when force was applied to sites such as the central area of second premolar the mesial connector of pontic, the central fossa of pontic, the distal connector of pontic, and the central fossa of second molar. Results. 1. In all the materials of the core in this study, von Mises stress indicated that the stress increased as force was applied to loaded sites, just at those points, on the connector, and the margin in the area adjacent to the connectors. 2. The maximum principal stress was much higher in the lower part of the connectors than in any other region. 3. As the load was applied to the different locations, the research showed a consistent increase of stress in the lower connectors. The maximum value of the von Mises stress was two or three times greater when the load was applied directly to the connectors rather than indirectly through another stressed region. 4. In the case of In-Ceram zirconia, the stress in lower connectors was the highest of all the reference points, the stress showed 75% of all the maximum stress. Ziconia showed 72%, Metal Ceramic 67% and IPS Empress 2 50%. 5. In the case of Ziconia, the stress was well dispersed in each reference point that the stress differences were smaller when compared to In-Cream ziconia.

• 대한치과보철학회지
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• 제39권5호
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• pp.526-546
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• 2001

Fiber-reinforced composite(FRC) was developed as a structural component for dental appliances such as prosthodontic framework. FRC provides the potential for fabrication of a metal-free, excellent esthetic prostheses. It has demonstrated success as a result of its simple fabrication, natural colour, and marginal integrity, and fracture resistance of veneering composite resin and the FRC material. Although it has lots of merits, clinical and objective data are insufficient. The purpose of this study was to evaluate the fracture strength and the marginal fitness of fiber reinforced composite bridge in the posterior region for clinical application. Sixteen bridges of each group. $Targis/Vectris^{(R)}$, $Sculpture-Fibrekor^{(R)}$, and In-Ceram, were fabricated. All specimens were cemented with Panavia 21 to the master dies. Strength evaluation was accomplished by a universal testing machine (Instron). The marginal fitness was measured by using the stereoscope (${\times}50$). The results were as follows. : 1. The fracture strength according to the materials was significantly decreased in order In-Ceram($238.81{\pm}82$), Targis Vectris($176.25{\pm}18.93$), Sculpture-Fibrekor($120.35{\pm}20.08$) bridges. 2. FRC resin bridges were not completely fractured, while In-Ceram bridges were completely fractured in the pontic joint. 3. The marginal accuracy was significantly decreased in order Targis/Vectris ($60.71{\mu}m$), Sculpture-Fibrekor($73.10{\mu}m$) In-ceram Bridge ($83.81{\mu}m$). 4. The fitness of occlusal sites had a lower value than the marginal sites(P<0.001), and the marginal gaps of inner site of the pontic were greater than that of outer sites of the pontic. Fiber reinforced composite bridges are new, esthetic prosthesis and can be clinically used in anterior regions and short span bridges. However, caution must be exercised when extrapolating laboratory data to the clinical situation because there are no long term clinical data regarding the overall success of the FRC.

• 대한심미치과학회지
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• 제7권1호
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• pp.32-40
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• 1998

Alveolar ridge augmentation and preservation techniques designed to reconstruct deformed alveolar ridge now occupy a major role in esthetic dentistry. Previously, deformed alveolar ridges were filled with plastic materials(porcelain or resin) of prosthesis to restore ridge contours, which resulted in larger teeth and food impaction under the pontic base. So, prostheses of this type were unacceptable and really detectable when patients smiled. But nowadays, alveolar ridge augmentation procedures enable the dentists to provide patients with fixed prostheses that are esthetic. The development of guided tissue regeneration technique and materials also have made a major impact on extending the scope of therapeutic horizons in dentistry.