• Journal of Dental Rehabilitation and Applied Science
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• v.19 no.4
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• pp.257-268
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• 2003

The purpose of this study was to assess the loading distributing characteristics of implant prosthesis according to position and direction of load, under vertical and inclined loading using FEA analysis. The finite element model was designed according to standard fixture (4.1mm restorative component x 11.5mm length). The crown for mandibular first molar was made using UCLA abutment. Each three-dimensional finite element model was created with the physical properties of the implant and surrounding bone. This study simulated loads of 200N at the central fossa in a vertical direction (loading condition A), 200N at the outside point of the central fossa with resin filling into screw hole in a vertical direction (loading condition B), 200N at the centric usp in a $15^{\circ}$ inward oblique direction (loading condition C), 200N at the in a $30^{\circ}$ inward oblique direction (loading condition D) or 200N at the centric cusp in a $30^{\circ}$ outward oblique direction (loading condition E) individually. Von Mises stresses were recorded and compared in the supporting bone, fixture, and abutment screw. The following results have been made based on this study: 1. Stresses were concentrated mainly at the ridge crest around implant in both vertical and oblique loading but stresses in the cancellous bone were low in both vertical and oblique loading. 2. Bending moments resulting from non-axial loading of dental implants caused stress concentrations on cortical bone. The magnitude of the stress was greater with the oblique loading than with the vertical loading. 3. An offset of the vertical occlusal force in the buccolingual direction relative to the implant axis gave rise to increased bending of the implant. 4. The relative positions of the resultant line of force from occlusal contact and the center of rotation seems to be more important. 5. The magnitude of the stress in the supporting bone, fixture and abutment screw was greater with the outward oblique loading than with the inward oblique loading and was the greatest under loading at the centric cusp in a $30^{\circ}$ outward oblique direction. Conclusively, this study provides evidence that bending moments resulting from non-axial loading of dental implants caused stress concentrations on cortical bone. But it seems to be more important that how long is the distance from center of rotation of the implant itself to the resultant line of force from occlusal contact(leverage). The goal of improving implants should be to avoid bending of the implant.

• The Journal of Korean Academy of Prosthodontics
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• v.44 no.5
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• pp.561-573
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• 2006

Statement of the problem: In cases of low bone level in maxilla followed by extraction due to severe periodontitis or enlarged maxillary sinus, crown-root ratio of implant prosthesis will increase. The prognosis of these cases is not good as expected. Purpose : The purpose is to compare stress distribution due to crown-root ratio and effect of splinting between two implants in maxillary molar area under different loads Material and methods: Using ITI($4.1{\times}10$ mm) implant. two finite element models were made(model S: two parallel implants, model A: one of two is 20 degree inclined). Each model was designed in different crown-root ratio(0.7:1, 1:1, 1.25:1) and set cement type gold crown to make it splinted or non-splinted clinical situations. After that, 300 N force was loaded to each model in four ways.(load 1 : middle of occlusal table, load 2 : middle of buccal cusp, load 3 : middle of lingual cusp, load 4 : horizontal load to middle of buccal cusp), and stress distribution was analyzed. Results: On all occasions, stress was concentrated on neck of implant near cortical bone. In the case of inclined implant, stress was increased compared with parallel implants. Under load 1, 2, 3, stress was not increased even when crown-root ratio increases, but under load 4, when crown-root ratio increases, stress also increased. And more stress was concentrated under load 1 than load 2, 3. When crown-root ratio was same, stress under load 1, 2, 3 decreased when splinting, but under load 4, stress did not really decrease. Conclusion: Under vertical load, stress distribution related to crown-root ratio did not change. But under horizontal load, stress increased as crown-root ratio increases. Under vertical load, splinting decreased stress but under horizontal load, effect of splinting was decreased as condition of implant changes for the worse such as increase of crown-root ratio, inclined implant.

• The Journal of Advanced Prosthodontics
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• v.4 no.2
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• pp.61-71
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• 2012

PURPOSE. To compare the changes in the occlusal vertical dimension, activity of masseter muscles and biting force after insertion of immediate denture constructed with conventional, tooth-supported and Implant-supported immediate mandibular complete denture. MATERIALS AND METHODS. Patients were selected and treatment was carried out with all the three different concepts i.e, immediate denture constructed with conventional (Group A), tooth-supported (Group B) and Implant-supported (Group C) immediate mandibular complete dentures. Parameters of evaluation and comparison were occlusal vertical dimension measured by radiograph (at three different time intervals), Masseter muscle electromyographic (EMG) measurement by EMG analysis (at three different positions of jaws) and bite force measured by force transducer (at two different time intervals). The obtained data were statistically analyzed by using ANOVA-F test at 5% level of significance. If the F test was significant, Least Significant Difference test was performed to test further significant differences between variables. RESULTS. Comparison between mean differences in occlusal vertical dimension for tested groups showed that it was only statistically significant at 1 year after immediate dentures insertion. Comparison between mean differences in wavelet packet coefficients of the electromyographic signals of masseter muscles for tested groups was not significant at rest position, but significant at initial contact position and maximum voluntary clench position. Comparison between mean differences in maximum biting force for tested groups was not statistically significant at 5% level of significance. CONCLUSION. Immediate complete overdentures whether tooth or implant supported prosthesis is recommended than totally mucosal supported prosthesis.

• Journal of Periodontal and Implant Science
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• v.41 no.2
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• pp.86-91
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• 2011

Purpose: The aim of this study was to analyze the short-term predictability and reliability of Astra Tech implants according to the demographical distribution of patients and condition of implant sites and location of implants. Methods: Among patients treated with Astra Tech implant (Astra Tech AB) in the Department of Periodontology at the Dental Hospital of Yonsei University of College of Dentisry and K Dental Clinic from May 2004 to March 2009, 195 implants in 98 patients which had been restored more than 6 months ago were reviewed in this study. Following data were reviewed from patient charts and implants success rate was examined: 1) patient type and implant location, 2) bone status at the implant site, 3) diameter and length of the placed implants, 4) presence or absence of bone augmentation and types of the augmentation. Results: The results from this study are as follows: 1) most implants were placed in the molar area, especially 1st molar area of maxilla, 2) most implants were placed at $D_2$ and $D_3$ bone type, 3) most implants were placed in areas of B and C bone quantity, 4) autogenous and alloplastic bone graft and artificial membrane were used for placement of 74 implants. Conclusions: Short-term survival rate of Astra Tech implants was 100%.

• The Journal of Korean Academy of Prosthodontics
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• v.32 no.1
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• pp.120-147
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• 1994

This study was performed for the purpose of evaluating the stress distribution around threaded type implants, cylindrical type implants and teeth connected with rigid or non-rigid connector. The stress distribution around the surrounding bone was analyzed by three-dimensional photoelastic method. Twelve mandibular photoelastic epoxy resin models and a circular polariscope were used to record the isochromatic fringes. After the stress distribution around the implant and tooth was observed, the results were as follows ; 1. In threaded type implants, stress concentrated patterns were observed at the neck either vertical or 25 degree lateral force. 2. The stress concentrated patterns were observed at the tooth apical portion and neck portions of the implant and tooth when a threaded implant was connected with the tooth by either a rigid or non-rigid connector. More force was generated at the tooth neck portion by a rigid connector and more force at the implant neck portion by a non-rigid connector. 3. The stress concentrated patterns were observed at the apical portion of the implant and tooth when a cylindrical type ,implant was connected with the tooth either by a rigid or non-rigid connector. More force was generated at the tooth apical portion by a rigid connector and more force at the neck portion of the tooth and implant by a non-rigid connector. 4. The stress around the tooth was more equally distributed in a threaded type implant than in a cylindrical implant when the tooth was connected with either a rigid or non-rigid connector. 5. The stress around a threaded type implant was progressively more equally distributed in the following order : 1) when used a single implant, 2) a non-rigid connection with the implant and tooth, 3) a rigid connection with the implant and tooth, 4) a rigid connection with two implant fixtures.

• The Journal of Korean Academy of Prosthodontics
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• v.31 no.1
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• pp.87-99
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• 1993

Many studies have been reported on the successful replacement of missing teeth with osseointegrated dental Implants. However, little research has been carried out on the bio-mechanical aspect of the stress on the surrounding bone of the free-standing type of dental implant prostheses. This experimental study was aimed to analyze the stress distribution pattern on the supporting tissues depending upon the position of osseointegrated implants supporting fixed bridges. In the cases of unilateral partially edentulous mandible (the 2nd premolar and the 1st and 2nd molars missing), two osseointegrated implants were placed at the 2nd premolar and 2nd molar sites (Model A) , the 1st and 2nd molar sites (Model B, Anterior cantilevered type), the 2nd premolar and 1st molar sites (Model C, Posterior cantilevered type). Chewing forces of dentate patients and denture wearer were applied vertically on the 2nd premolar, the 1st molar, and the 2nd molar of each model. A 3-Unit fixed partial denture was constructed at each model and cantilevered extension parts were involved in Model B and Model C. Two dimensional finite element analysis was undertaken. The commercial software (Super SAP) for IBM 16 bit personal computer was utilized. The results were as follows : 1. The magnitude of applied load influenced on the total value of stresses, but did not in-fluence on the pattern of stress distribution. 2. The magnitude of stress developed from the supporting tissues were in order of Model C,Model A,Model B. 3. High stresses were concentrated on the cervical and apical portion of the implant/bone interface. 4. A difference of the stress magnitude on the implant/bone interface between mesial and distal implant was most prominant in Model C and in order of Model A and Model B. 5. The stresses developed in Model A were evenly distributed throughout both implants. 6. The stresses concentrated on the cervical portion of cantilevered side were higher in the posterior cantilevered type than in the anterior cantilevered type.

• Archives of Plastic Surgery
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• v.45 no.5
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• pp.484-489
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• 2018

Large and ptotic breast reconstruction in patients who are not candidates for a transverse rectus abdominalis myocutaneous flap and revision surgery for the contralateral breast remains challenging. We developed a novel breast reconstruction technique using a latissimus dorsi myocutaneous (LD m-c) flap set at the posterior aspect of the reconstructed breast, combined with an anatomical silicone breast implant (SBI), following tissue expander surgery. We performed the proposed technique in four patients, in whom the weight of the resected tissue during mastectomy was >500 g and the depth of the inframammary fold (IMF) was >3 cm. After over-expansion of the lower portion of the skin envelope by a tissue expander, the LD m-c flap was transferred to cover the lower portion of the breast defect and to achieve a ptotic contour, with the skin paddle set at the posterior aspect of the reconstructed breast. An SBI was then placed in the rest of the breast defect after setting the LD m-c flap. No major complications were observed during the follow-up period. The proposed technique resulted in symmetrical and aesthetically satisfactory breasts with deep IMFs, which allowed proper fitting of the brassiere, following large and ptotic breast reconstruction.

• The Journal of Korean Academy of Prosthodontics
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• v.39 no.1
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• pp.71-83
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• 2001

The purpose of this study was to compare the effects of various surface treatments by measuring removal torque on bone healing around titanium implants. 40 Screw-shaped cp titanium implants with length of 4mm, outer diameter of 3.75mm, and pitch-height of 0.5mm were used Group 1 was left as machined(control), Group 2 was blasted with $50{\mu}m\;Al_2O_3$, group 3 was blasted and etched in etching solution($NH_4OH : H_2O_2:H_2O= 1 : 1 : 5$) at $90^{\circ}C$ for 1 minute group 4 was blasted and oxidated under pure oxygen at $800^{\circ}C$. The implant surface roughness was analyzed with SEM and CLSM(Confocal Laser Scanning Microscope) and implants were placed in proximal tibial metaphysis of 10 New Zealand White rabbits. After 3 months of healing period, removal torque of each implant was measured to compare bone healing around implant. The results obtained were as follows 1. In SEM view, blasting increased the roughness of the surface, but etching of that rough surface decreased the roughness due to the removal of the tip of the peak. Oxidation also decreased the roughness due to formation of needle-like oxide grains on the implant surface. 2. The Sa value from CLSM was least in the machined group($0.47{\mu}m$), greatest in blasted group($1.25{\mu}m$), and the value decreased after etching($0.91{\mu}m$) and oxidation($0.94{\mu}m$). 3. The removal torque of etched group(24.5Ncm) was greater than that of machined group(16.7Ncm) (P<0.05), and was greatest in the oxidated group(40.3Ncm) and the blasted group(34.7Ncm).

• Journal of Periodontal and Implant Science
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• v.53 no.2
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• pp.157-169
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• 2023

Purpose: The aim of this study was to evaluate the impact of polydeoxyribonucleotide (PDRN) on histologic outcomes when implant placement and lateral sinus floor elevation are performed simultaneously. Methods: Three bimaxillary premolars (P2, P3, and P4) were extracted from 4 beagle dogs 2 months before lateral sinus floor elevation. After lateral elevation of the sinus membrane, each sinus was allocated to either the test or control group. Sinuses underwent either 1) collagenated synthetic bone graft with PDRN following lateral sinus floor elevation (test group) or 2) collagenated synthetic bone graft without PDRN after lateral sinus floor elevation (control group). Eight weeks after the surgical procedure, all animals were euthanised for a histologic and histomorphometric assessment. Augmented height (AH), protruding height (PH), and bone-to-implant contact in pristine (BIC_p) and augmented (BIC_a) bone were measured. The composition of the augmented area, which was divided into 3 areas of interest located in coronal, middle and apical areas (AOI_C, AOI_M, and AOI_A), was calculated with 3 parameters: the area percentage of new bone (pNB), residual bone graft particle (pRBP), and fibrovascular connective tissue (pFVT). Results: AH, PH, BIC_p, BIC_a total, BIC_a coronal, and BIC_a middle values were not significantly different between sinuses in the control and test groups (all P>0.05). The BIC_a apical of sinuses in the test group (76.7%±9.3%) showed statistically higher values than those of sinuses in the control group (55.6%±22.1%) (P=0.038). pNB, pRBP, and pFVT showed statistically significant differences between the 2 groups in AOI_A (P=0.038, P=0.028, and P=0.007, respectively). pNB, pRBP, and pFVT in AOI_C and AOI_M were not significantly different between samples in the control and test groups (all P>0.05). Conclusions: The histologic findings revealed that lateral sinus floor elevation with PDRN might improve early new bone formation and enable higher bone-to-implant contact.

• Proceedings of the KOSOMBE Conference
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• v.1998 no.11
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• pp.231-232
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• 1998

The purpose of this study was to examine whether the precipitation of calcium phosphate on titanium surface was affected by surface modification. To improve the bone conductivity, of titanium, samples were devided into 4 groups. Group 1 was immersed in 5M-NaOH solution at $60^{\circ}C$ for 24 hours. Group 2 was immersed in 5M-NaOH solution at $60^{\circ}C $ for 24 hours and heat-treated at $600^{\circ}C$ for 1 hour. Group 3 was anodized in Hanks' solution at 1V, $25^{\circ}C$ for 1 hour. Group 4 was anodized in Hanks' solution at 5V, $80^{\circ}C$ for 5 minutes. And then, all specimens were immersed in the MEM Eagle's medium whose composition was similar to that of extracellular fluid for 30 days. The precipitation of the calcium phosphate on implant surface was increased by the immersion in the NaOH solution, and more highly accelerated by heat treatment at $600^{\circ}C$. The precipitation of the calcium phosphate on titanium implant was increased with the treatment of the anodic oxidation in Hanks' solution at 5V, $80^{\circ}C$.