Erratum: Finite element analysis of the effects of a mouthguard on stress distribution of facial bone and skull under mandibular impacts / 대한치과보철학회지

There has been a mistake, claimed and confirmed by all the authors of Vol 50(1), 2012, p. 1-9 issue, that first author should have been Il-Han Kim instead of Kwan-Tae Noh.

Finite element analysis of the effects of a mouthguard on stress distribution of facial bone and skull under mandibular impacts / 대한치과보철학회지

PURPOSE: The purpose of this study was to investigate the effects of a mouthguard on stress distribution under mandibular impact. MATERIALS AND METHODS: The FEM model of head consisted of skull, maxilla, mandible, articular disc, teeth, and mouthguard. The impact locations on mandible were gnathion, the center of inferior border, and the anterior edge of gonial angle. And the impact directions were vertical, oblique (45degrees), and horizontal. The impact load was 800 N for 0.1 sec. RESULTS: When vertical impact was applied, the similar stress and the distribution pattern was occurred without the relation of the mouthguard use (P>.05). The model with mouthguard was dispersed the stress to the teeth, the facial bone and the skull when the oblique (45degrees) impacts were happened. However, the stress was centralized on the teeth in the model without mouthguard (P<.05). The model with mouthguard was dispersed the stress to the teeth, the facial bone and the skull when the horizontal impacts was occurred. However, the stress was centralized on the teeth without mouthguard (P<.05). For all impact loads, stress concentrated on maxillary anterior teeth in model without mouthguard, on the contrary, the stress was low in the model with mouthguard and distributed broadly on maxillary anterior teeth, facial bone, and skull. CONCLUSION: The mouthguard was less effective at shock absorbing when vertical impact was added. However, it was approved that mouthguard absorbed the shock regarded to the oblique (45degrees) and horizontal impact by dispersing the shock to the broader areas and decreasing the stress.

Finite element analysis of the effects of mouthguard produced by combination of layers of different materials on teeth and jaw / 대한치과보철학회지

PURPOSE: The purpose of this study was to compare the stress distribution of teeth and jaw on load by differentiating property of materials according to each layer of widely used mouthguard. MATERIALS AND METHODS: A Korean adult having normal cranium and mandible was selected to examine. A customized mouthguard was constructed by use of DRUFOMAT plate and DRUFOMAT-TE/-SQ of Dreve Co. according to Signature Mouthguard system. The cranium was scanned by means of computed tomography with 1mm interval. It was modeled with CANTIBio BIONIX/Body Builder program and simulated and interpreted using Alter HyperMesh program. The mouthguard was classified as follows according to the layers. (1) soft guard (Bioplast)(SG) (2) hard guard (Duran)(HG) (3) medium guard (Drufomat)(MG) (4) soft layer + hard layer (SG + HG) (5) hard layer + soft layer (HG + SG) (6) soft layer + hard layer + soft layer (SG + HG + SG) (7) hard layer + soft layer + hard layer (HG + SG + HG) The impact locations on mandible were gnathion, the center of inferior border, and the anterior edge of gonial angle. And the impact directions were oblique (45degrees). The impact load was 800 N for 0.1 sec. The stress distribution was measured at maxillary teeth, TMJ and maxilla. The statistics were conducted using Repeated ANOVA and in case of difference, Duncan test was used as post analysis. RESULTS: In teeth and maxilla, the mouthguard contacting soft layer of mandibular teeth presented lowest stress measure and, in contrast, in condyle, the mouthguard contacting hard layer of mandibular teeth presented lowest stress measure. CONCLUSION: For all impact directions, soft layer + hard layer + soft layer, the mouthguard with three layers which the hard layer is sandwiched between two soft layers, showed relatively even distribution of stress in impact.

Patients satisfaction for implant supported overdenture with small diameter implant / 대한치과보철학회지

PURPOSE: In cases when implant supported overdenture is made by using standard size implant, additional procedure such as bone surgery and bone grafting can be required. And it gives burden to doctor and patient in terms of cost. Therefore, it is necessary to find the implant therapy for the edentulous patients in making denture with accordable cost and simple procedure. MATERIALS AND METHODS: Edentulous patients with upper and lower dentures participated in this study. Before the operation, survey about patient's satisfaction to the existing dentures was carried out. Surgical procedures included four small diameter implants installation anterior area and immediate loading. One and three month after the procedure, the same survey about patient's satisfaction was carried out, and radiography was taken. RESULTS: We are doing research to the nine patients. Survival rate is 97.2 percent. The comparison of patient's satisfaction before and after surgery is performed based on oral health impact profile 49. We analyze mainly with masticatory discomfort, retention, aesthetics, social problem, psychological discomfort problems. As a result, satisfaction level is increased at all factors. Retention is the most increased satisfactory factor followed by mastication difficulty, pronunciation, psychological discomfort, social discomfort, aesthetics in order. Marginal bone loss is 0.21 mm at 12 weeks after implant placement. CONCLUSION: This research reveals that the denture supported by mini dental implant increases patient's satisfaction. This study will be continued with more patients for a long time and we are scheduled for taking additional radiography to check whether peri-implant bone resorption occurs or not.

An influence of operator's posture on the shape of prepared tooth surfaces for fixed partial denture / 대한치과보철학회지

PURPOSE: Dentists suffer back, neck and shoulder pain during their careers due to bad operating posture. If dentists have a good operating posture ergonomically, there would be less pain and discomfort in the shoulder and back. Therefore, dentists should learn the Home position which enables dentists to approach a stable posture ergonomically. This study was to compare tooth preparation in the Home position and the Random position, and evaluate the clinical efficacy of the Home position. MATERIALS AND METHODS: Tooth preparation for fixed partial denture was performed on the maxillary left 2nd premolar and maxillary left 2nd molar at the two different operating positions were compared. The amount of occlusal reduction, marginal width, subgingival margin depth, and convergence angle were measured. A T-test was performed separately to compare the results of the Random position and the Home position. RESULTS: 1. The amounts of average thickness of occlusal reduction on fossa were deficient to the ordered ones in the Random position and the Home position (P > .05). 2. The average subgingival margin depth of prepared margin on maxillary left 2nd premolar, maxillary left 2nd molar were excessive in the Random position than in the Home position. On the maxillary left 2nd premolar, there was no statistical difference in the Random position and the Home position except Distal midline, DL line angle, Lingual midline, ML line angle (P .05). 4. Analysis of pearson correlation : In the Random position, the amounts of average thickness of occlusal reduction, the average subgingival margin depth of prepared margin, convergence angle were significantly associated with each other (P < .05). But in the Home position, they were not significantly associated with each other (P < .05). 5. The time needed for preparation in the Home position was faster or equal than that of the Random position as time went on. CONCLUSION: In conclusion, there were no significant differences between Home postion and Random position in measures of occlusal reduction, marginal width, marginal depth, convergence angle. However, preparation time and incidence of damaging adjacent teeth were less in Home position than in Random position. Therefore, if trained properly, Home position which is more ergonomically stable can be adopted for clinical use.

FEM Analysis of the Effects of Mouth guard material properties on the Head and Brain under Mandibular Impact / 대한치과보철학회지

STATEMENT OF PROBLEM & PURPOSE: The purpose of this study was to investigate the effect of a mouth guard material properties on the skull and brain when they were under impact loads on mandible. MATERIAL AND METHODS: Two customized mouth protectors having different material propeerst ieach other were made for a female Korean who had no history of brain trauma, no cerebral diseases, nomal occlusion and natural dentition. The 3D finite element model of human skull and brain scanned by means of computed tomography was constructed. The FEM model of head was composed of 407,825 elements and 82,138 nodes, including skull, brain, maxilla, mandible, articular disc, teeth and mouth guard. The stress concentrations on maxillary teeth, maxilla and skull with two mouth guards were evaluated under oblique impact load of 800N onto mandibular 3 loading points for 0.1sec. And the brain relative displacement was compared in two different mouth guard materials under same condition. RESULT AND CONCLUSION: The results were as follows; 1. In comparison of von Mises stress on maxillary teeth, a soft mouth guard material had significantly lower stress values on measuring point than a hard mouth protector materials (P < .05). 2. In comparison of von Mises stress on maxilla and skull, A soft mouth protector material had significantly lower stress values on measuring point than a hard mouth protector materials (P < .05). 3. For impact loads on mandible, there were more stress concentrated area on maxilla and skull with hard mouth guard than soft with mouth protector. 4. For impact loads on mandible, brain relative displacement had little relation with mouth guard material properties. In results of this study, soft mouth guard materials were superior to hard mouth guard materials for mandible impact loads for prevention of sports injuries. Although the results of this study were not enough to figure out the roles of needed mouth guard material properties for a human head, we got some knowledge of the pattern about stress concentration and distribution on maxilla and skull for impact loads with soft or hard mouth protector. More studies are needed to substantiate the relationship between the mouth guard materials and sports injuries.

A Study on the Stress Distribution of Tooth/Implant Connected with Konus Telescope Denture Using 3-Dimensional Finite Element Method / 대한치과보철학회지

PURPOSE: For decades dental implants have been used widely in the field of prosthetic dentistry. However there is confusion when establishing treatment plans in cases where some teeth are remained but an insufficient number of implants can be used due to limited anatomical status and ecomomical problems. Many clinicians have tried to connect natural teeth and implants, and it still has controversy. But, there have been few studies on mechanical analysis of connecting natural teeth and implants with konus telescopic removable partial dentures. The purpose of this study was to analyze the stress distribution of prosthesis, abutment and alveolar bone when teeth and implants were connected with the konus telescopic denture, by means of 3-dimensional finite element analysis. MATERIAL AND METHODS: The assumption of this study was that there were 2 mandibular canine (11 mm in length, 4 mm in diameter) and 2 implants(10 mm in length, 4 mm in diameter) which are located in the second premolar region. The mandible, teeth, implants, abutments, and connectors are modeled, and analyzed with the commercial software, ANSYS Version 8.1(Swanson, Inc., USA). The control group used implants instead of natural teeth. 21038 elements, 23544 nodes were used in experimental group and 107595 elements, 21963 nodes were used in control group, Stress distribution was evaluated under 150 N vertical load on 3 experimental conditions - between teeth and implants (Load case 1), posterior to implants (Load case 2), between natural teeth (Load case 3). RESULTS: 1. In all load cases, higher von mises stress value was observed in the experimental group. 2. Maximum von miss stress observed in all load cases and all locations were as follows ; a. 929.44 Mpa in the experimental group, 640.044 Mpa in the control group in outer crown and connector - The experimental group showed 1.45 times high value compared with the control group. b. 145,051 Mpa in the experimental group, 142.338 Mpa in the control group in abutment - The experimental group showed 1.02times high value compared with the control group. c. 32.489 Mpa in the experimental group, 25.765 Mpa in the control group in alveolar bone - The experimental group showed 1.26times higher value compared with the control group. 3. All maximum von mises stress was observed in load case 2, and maxim von mises stress in alveolar bone was 32.489 Mpa at which implant failure cannot occur. 4. If maximum von mises stress is compared between two groups, the value of the experimental group is 1.02 times higher than the control group in abutment, 1.26 times higher than the control group in alveolar bone. CONCLUSION: If natural teeth and implants are connected with the konus telescopic denture, maximum stress will be similar in abutment, 1.26 times higher in alveolar bone than the control group. With this result, there may be possible to make to avoid konus telescopic dentures where natural teeth and implants exist together.

A study of sagittal condylar inclination and occlusal plane inclination of two semiadjustablearticulators with different reference plane / 대한치과보철학회지

STATEMENT OF PROBLEM & PURPOSE: Articulators are very important for education and overall clinical situation in the field of prosthodontics, however preexisting articulators are designed and built based on maxillofacial structures and mean values of mandibular movement of Western people. Purpose of this research is to find out a adequate basis for applicating these articulators, presently used for clinical education, for Korean. MATERIAL AND METHODS: 59 Korean adults (41 males, 18 females), aged between 24 to 41, where selected for this study. Two pairs of both maxillary and mandibular models were made for each examinee. These models where attached to both KaVo PROTARevo 7 and Hanau Modular semiadjustable articulators by using facebow transfer, than sagittal condylar inclination, occlusal plane inclination and position of mandibular on the articulator where measured. RESULT AND CONCLUSION: 1. Mean sagittal condylar inclination for KaVo PROTAR semiadjustable articulator was 33.75degree (standard deviation 12.46degree) meanwhile Hanau Modular semiadjustable articulator showed 40.72degree (standard deviation 12.09degree) for mean sagittal condylar inclination. 2. Mean occlusal plane inclination for KaVo PROTAR semiadjustable articulator was -2.76degree (standard deviation 3.63degree) meanwhile Hanau Modular semiadjustable articulator showed 11.87degree (standard deviation 3.63degree) for mean occlusal plane inclination. 3. On the average center of the mandibular dentition were in the range of 5 to 7 mm of the central position of the articulator. Both anterior and posterior dentition were positioned at the center of the articulator vernacularly for KaVo PROTAR semiadjustable articulators, meantime for Hanau Modular semiadjustable articulator, anterior dentition was positioned 5 mm downwards and 3mm upwards for posterior dentition from vertically central position of the articulator.

The survey on oral health and maxillofacial trauma incidence of the sports players in Korea / 대한치과보철학회지

STATEMENT OF PROBLEM: In spite of increasing sports injury, there was no collected data on the rate and type of dental injuries for athletes in Korea. PURPOSE: The purpose of this study was to investigate the occurrence of maxillofacial injuries and attitude of college sports player in Korea towards mouthguard. MATERIAL AND METHODS: Total 617 athletes answered a series of questionnaire concerning their sports injury and using mouthguard. RESULTS: 1. 81%(502) of athletes had, playing or training a sports, suffered an injury. Female athletes suffered an injury more than male athletes(p<0.05). Contact sports athletes were injured more than non contact sports athletes(p<0.05). 2. 335 athletes(54.8%) had suffered maxillofacial injuries while playing or training. 81.8% of athletes suffered an maxillofacial injury in contact sports(p<0.05). 3. Laceration of oral area, wrick in neck, fracture or avulsion on upper incisors, concussion, TMJ injury, fracture or avulsion on lower incisors, fracture or avulsion on lower molars were frequently injured area. 4. 67.2% of athletes answered that mouthguard could prevent sports injury especially high in contact sports(p<0.05). But only 39.1% of athletes required mouthguard while playing. 44.6% of athletes showed their intention of using mouthguard. CONCLUSION: This study shows that the incidence of maxillofacial injuries is very high while the actual use of mouthguard is very low. To prevent sports injury, a dentist must inform sports players and coaches of accurate information about mouthguard so that they can use it well. A dentist also has to provide them with better mouthguard on the basis of user's complaint.

3D finite element analysis of overdenture stability and stress distribution on mandibular implant-retained overdenture / 대한치과보철학회지

STATEMENT OF PROBLEM: Recently there are on an increasing trend of using implants -especially in edentulous mandible of severly alveolar bone recessed. PURPOSE: The aim of this study was to analyze the displacement and stress distribution of various mandibular implant-retained overdenture models supported by two implants in interforaminal region under the occlusion scheme load. MATERIAL AND METHOD: FEA models were made by the 3D scanning of the edentulous mandibular dentiform. The three models were named as Model M1, M2, and M3 according to the position of implants: M1, Lt. incisor area, M2, Canine area, and M3, 1st Premolar area. Inter-implant angulation model was named as M4. Conventional complete denture was named M5 and used as a control group. Ball implant and Gold matrice were used as a retentive anchors. The occlusion type loads were applied horizontally over each tooth. RESULTS: 1. In mandibular implant retained overdenture Canine Protected Occlusion type load resulted in higher levels of stress to the implants and female matrices than other types of loads. 2. The overdenture model, M1, with implants in lateral incisor areas resulted in lower stress concentration to the implants and female matrices than other models. 3. In mandibular implant retained overdenture the stresses of the implant and female matrice were lower in mesially inclined implant than these of parallel installed implant. CONCLUSION: Lateral incisor areas could be the best site for the implants in mandibular implant-retained overdenture. The mandibular implant retained overdenture models mentioned above showed to the lowest stress to the implants and female matrices.

A study on the difference of the sagittal condylar guidance by semi-adjustable articulator and axiograph / 대한치과보철학회지

STATEMENT OF PROBLEM: In the Protar articulator, the models are almost parallel with the Camper's plane. The ultrasonic-based ARCUSdigma system is basis for the determination of dynamic function parameters with so-called "articulator related registration". PURPOSE: The purpose of this study was to compare the sagittal condylar guidance angles found by use of the wax protrusive records in a semi-adjustable articulator(KaVo Protar 7) with those found by use of the Axiograph(ARCUSdigma). 83 volunteers with intact dentition participated in this study after obtainment of informed consent. MATERIAL AND METHOD: The sagittal condylar guidance angles were measured and estimated statistically by semi-articulator and Axiograph. All the readings were in degrees. No control was used in this project. To test whether there was a significant difference between the 2 independent samples, paired t-test and Kruskal-Wallis test were carried out(p=.05). RESULTS: 1. The mean results for the wax protrusive records were as follow: right side (32.65 degrees, SD 16.48); left side (33.27 degrees, SD 17.49). 2. The mean results for the Axiograph were as follow: right side (32.26 degrees, SD 7.00); left side (33.07 degrees, SD 7.58). 3. There was no statistical difference on the wax protrusive records and Axiograph(p>0.05). CONCLUSION: Both methods of wax protrusive records and Axiograph are clinically acceptable for measuring the sagittal condylar guidance angles in semi-adjustable articulators.

Flexural strength of implant fixed prosthesis using fiber reinforced composite / 대한치과보철학회지

STATEMENT OF PROBLEM: Use of fiber composite technology as well as development of nonmetal implant prosthesis solved many problems due to metal alloy substructure such as corrosion, toxicity, difficult casting, expensiveness and esthetic limit. After clinical and laboratory test, we could find out that fiber-reinforced composite prostheses have good mechanical properties and FRC can make metal-free implant prostheses successful. PURPOSE: The purpose of this study is to evaluate the flexural strength of implant fixed prosthesis using fiber reinforced composite. MATERIAL AND METHODS: 2-implant fixture were placed in second premolar and second molar area in edentulous mandibular model, and their abutments were placed, and bridge prostheses using gold, PFG, Tescera, and Targis Vectris were fabricated. Tescera was made in 5 different designs with different supplements. Group I was composed by 3 bars with diameter 1.0mm and 5 meshes, 2 bars and 5 meshes for Group II, 1 bar and 5 meshes for Group III, and only 5 meshes were used for Group IV. And Group V is composed by only 3 bars. Resin (Tescera) facing was made to buccal part of pontic of gold bridge. All of gold and PFG bridges were made on one model, 5 Targis Vectris bridges were also made on one model, and 25 Tescera bridges were made on 3 models. Each bridge was attached to the test model by temporary cement and shallow depression was formed near central fossa of the bridge pontic to let 5 mm metal ball not move. Flexual strength was marked in graph by INSTRON. RESULTS: The results of the study are as follows. The initial crack strength was the highest on PFG, and in order of gold bridge, Tescera I, Tescera II, Targis vectris, Tescera IV, Tescera III, and Tescera V. The maximum strength was the highest on gold bridge, and in order of PFG, Tescera I, Tescera IV, Tescera II, Targis vectris, Tescera III, and Tescera V. CONCLUSIONS: The following conclusions were drawn from the results of this study. 1. Flextural strength of implant prosthesis using fiber reinforced composite was higher than average posterior occlusal force. 2. In initial crack strength, Tescera I was stronger than Tescera V, and weaker than PFG. 3. Kinds and number of auxillary components had an effect on maximum strength, and maximum strength was increased as number of auxillary components increased. 4. Maximum strength of Tescera I was higher than Targis vectris, and lower than PFG.

Effect of a mouthguard on stress distribution in teeth, maxilla and mandible for maxilla and mandibular impact using finite element analysis / 대한치과보철학회지

STATEMENT OF PROBLEM: The use of mouthguard is important as the leisure life is popular today. PURPOSE: The purpose of this study is to investigate the effect of a mouthguard on stress distribution in teeth, maxilla and mandible for maxilla impact. MATERIAL AND METHODS: The 3-dimensional finite element model was based on a CT scan film of an average korean adult when the subject is using a customized mouthguard which was made with the Signature Mouthguard system of Dreve. The load was applied to the upper central incisor cervical area parellel impact force for 0.1sec(L1), The Von-mises stress analysis with a mouthguard and without a mouthguard was compared. RESULTS: The results of this study were as follows: 1. Without the mouthguard, stress was concentrated on teeth and alveolar bone in all load conditions. 2. With the mouthguard, maximum stress value was decreased and stress was dispersed in all load conditions. 3. Stress extinction with the mouthguard was faster than without the mouthguard in all load conditions. CONCLUSION: We acknowledged that the mouthguard has a stress buffer effect as the maximum stress value was decreased and stress was dispersed when impact force was applied.

Finite element analysis on maxillary molar implant under different C/R ratio / 대한치과보철학회지

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 x 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.

Spectrophotometric analysis of the influence of zirconia core on the color of ceramic / 대한치과보철학회지

STATEMENT OF PROBLEM: Problem of matching the appearance of porcelain restorations with the patient's natural dentition has always been a concern to dental clinicians. Recently, demands for esthetics, even in restorations requiring strength, has brought a revolution to dentistry and increased use of zirconia. Among the various factors, shade and translucency of the core can significantly affect the overall esthetics of the restoration and should be considered when selecting an all-ceramic system. PURPOSE: The purpose of this study was to spectrophotometrically evaluate the influence of different zirconia systems and core thickness on the final shade of all-ceramic restorations using the CIEL*a*b* system. MATERIAL AND METHODS: Core specimens (n = 20 per group) of In-Ceram Alumina, In-Ceram Zirconia, Digident CAD/CAM Zirconia, Cercon Zirconia were fabricated 20mm in diameter. 10 specimens of each group were fabricated at core thickness of 0.5mm and 0.7mm. These core specimens were veneered with shade A1 and A3 porcelain of the recommended manufacturer. CIEL*a*b* coordinates were recorded for each specimen with a spectrophotometer (Model CM-2600d, Minolta, Japan). Color differences were calculated using the equation delta E*=[(delta L*)2+(delta a*)2+(delta b*)2]1/2. RESULTS: 1. Specimens of core thickness 0.5mm and 0.7mm did not exhibit clinically perceived color difference. 2. Regarding shade reproducibility, In-Ceram Alumina and In-Ceram Zirconia showed significant difference within each group. 3. Cercon Zirconia group showed the highest L* value and Digident Zirconia group showed lowest a* and b* value. 4. Generally, the shade difference between materials was higher in the A3 shade group than in the A1 shade group. CONCLUSION: Within the limitations of this study, there was no color difference after increase in core thickness and every all-ceramic system has color characteristics that clinicians have to consider when selecting materials. Also, manufacturers of different porcelain systems must make every effort to achieve color reproducibility.

Dimensional change and flexural strength in complete dentures fabricated by injection molding and conventional compression processing / 대한치과보철학회지

STATEMENT OF PROBLEM: Fracture and dimensional change of an acrylic resin denture are a rather common occurrence. PURPOSE: The purpose of this study was to compare differences in dimensional changes and flexural strength of separate maxillary complete dentures after immediate deflasking by injection molding and conventional compression processing. MATERIAL AND METHOD: To evaluate dimensional stability, the maxillary dentures were fabricated by using different materials and methods. Lucitone 199(Dentsply Trubyte, york, pennsylvania, USA) and Vertex(Dentimex, zeist, Netherlands) were used as materials. Compression and injection packing methods were used as processing methods. The impression surface of the dentures was measured by 3D Scanning System(PERCEPTRON, USA) and overlapped original impression surface of the master cast. To evaluate flexural strength, resin specimens were made according to the different materials, powder/liquid ratio and processing methods. Flexural strength of the complete resin specimens (64mm*10mm*3.3mm) were measured by INSTRON 467.(INSTRON, England) The data was analyzed by ANOVA, t-test and Tukey test.(p<.05 level of significance) RESULT: The results were as follows: 1. There was no significant differences between master model and denture base for each group in overall dimensional changes. 2. Palatal area was more stable than flange or alveolar area in dimensional stability. but, there was no significant differences among each area. 3. Materials and power/liquid ratio had an effect on flexural strength.(p<.05) Especially materials was most effective.(p<.05) 4. Lucitone 199(powder/liquid ratio followed by manufacturer's direction) showed higher flexural strength than Vertex. CONCLUSION: Dimensional stability or flexural strength are affected by materials rather than packing techniques.

The effect of magnetism(Neodymium magnet) on bone formation around titanium implants inserted into the tibia of rabbit / 대한치과보철학회지

STATEMENT OF PROBLEM: There are many articles that showed that the magnetism affected the bone formation around titanium implant. It means that a proper magnetism made the osseointegration improved around the implant. So after additional research on the other effect of magnetism on bone formation in implant therapy, we can conclude its possibility of clinical application on implant treatment. PURPOSE: The purposes of this study were to find out the intensity of magnetic field where magnetism in the titanium implant specimen inserted into the bone could affect the bone formation, and to discover the possibility of clinical application in the areas of dental implants and bone grafts. MATERIAL AND METHOD: Ten adult male rabbits(mean BW 2Kg) were used in this study. Titanium implant specimens were surgically implanted on the mesial side of the tibia of rabbits. Neodymium magnets(Magnedisc 500, Aichi Steel Corp. Japan) were placed into the implants of experimental group except control group, just after placement of the titanium implants. At 2, 4 and 8 weeks after the surgery, the animals were sacrificed, specimens were obtained and stained with Hematoxylin-Eosin for light microscopic evaluation and histomorphometric analysis. CONCLUSION: The results were as follows: 1. In radiographic findings, increased radiopacity downward from crestal bone was observed along the titanium implant specimen at experimental period passed by 2,4, and 8 weeks in both control and experimental group. 2. In histoiogic findings, increased new bone formation was shown in both control and experimental group through the experiment performed for 2,4, and 8 weeks. More new bone formation and bone remodeling were shown in experimental group. 3. In histomorphometric analysis, the bone contact ratios were 11.9% for control group and 38.5% for experimental group(p<0.05).

The change of bone formation according to magnetic intensity of magnet placed into titanium implant specimens / 대한치과보철학회지

PURPOSE: The purposes of this investigation were to discover the possibility of clinical application in the areas of dental implants and bone grafts by investigating the bone formation histologically around specimen which was depending on the intensity of magnetic field of neodymium magnet inside of the specimens. MATERIAL AND METHOD: 1. Measurement of magnetic intensity - placed the magnet inside of the specimen, and measured the intensity of magnetic field around the 1st thread and 3rd thread of specimen 20 times by using a Gaussmeter(Kanetec Co., Japan). 2. Surgical Procedure - Male rabbit was anesthetised by constant amount of Ketamine (0.25ml/kg) and Rompun (0.25ml/kg). After incising the flat part of tibia, and planted the specimens of titanium implant, control group was stitched without magnet, while experimental groups were placed a magnedisc 500(Aichi Steel Co., Japan) or magnedisc 800(Aichi Steel Co., Japan) into it, fixed by pattern resin and stitched. 3. Management after the surgery. - In order to prevent it from the infection of bacteria and for antiinflammation, Gentamycin and Ketopro were injected during 1 week from operation day, and dressed with potadine. 4. Preparation of histomorphometric analysis - At 2, 4 and 8 weeks after the surgery, the animals were sacrificed by excessed Ketamine, and then, specimens were obtained including the operated part and some parts of tibia, and fixed it to 10% of PBS buffer solution. After embedding specimens in Technovit 1200 and B.P solution, made a H-E stain. Samples width was 75micrometer. In histological findings through the optical microscope and using Kappa image base program(Olympus Co. Japan), the bone contact ratio and bone area ratio of each parts of specimens were measured and analyzed. 5. Statistical analysis Statistical analysis was accomplished with Mann Whitney U-test. RESULTS AND CONCLUSION: 1. In histomorphometricl findings, increased new bone formation was shown in both control and experimental groups through the experiment performed for 2, 4, and 8 weeks. After 4 weeks, more osteoblasts and osteoclasts with significant bone remodeling were shown in experimental groups. 2. In histomorphometric analysis, the bone contact ratios were 38.5% for experimental group 1, 29.5% for experimental group 2 and 11.9% for control group. Experimental groups were higher than control group(p<0.05)(Fig. 6, Table IV). The bone area ratios were 60.9% for experimental group 2, 46.4% for experimental group 1 and 36.0 % for control group. There was no significantly ststistical difference between experimental groups and control group(p<0.05)(Fig. 8, Table VII) 3. In comparision of the bone contact ratios at each measurement sites according to magnetic ntensity, experimental group 2(5.6mT) was higher than control group at the 1st thread (p<0.05) and experimental group 1(1.8mT) was higher than control group at the 3rd thread(p<0.05)(Fig. 7, Table V, VI). 4. In comparision of the bone area ratios at each measurement sites according to magnetic intensity, experimental group 2(5.6mT) was higher than control group and experimental group 1(4.0mT) at the 1st thread(p<0.1) and experimental group 2(4.4mT) was higher than experimental group 1(1.8mT) at the 3rd thread(p<0.1)(Fig. 9, Table IX, X). Experiment group 2 was largest, followed by experiment group1 and control group at the 3rd thread of implant. There was a significant difference at the 1st thread of control group and experiment group 2. and at 1st thread and 3rd thread of experiment group 1 and 2, and not at control group experiment group 1.(p<0.1)

The effect of solder and laser weld on corrosion of dental alloys / 대한치과보철학회지

STATEMENT OF PROBLEM: Intraoral corrosion not only affects the esthetic and function of metallic dental restoration, but also has biologic consequences as well. Therefore, corrosion is considered a primary factor when choosing the dental alloy and laboratory technique. PURPOSE: The objective of this study was to compare the effects of solder and laser weld on corrosion. MATERIAL AND METHODS: Test specimens were made of 2 types of gold alloys, Co-Cr and Ni-Cr alloy and fabricated 3 methods, respectively: as cast, solder, and laser weld. For the analysis of corroding properties, potentiodynamic polarization test and immersion test conducted. The potentiodynamic polarization scan curve were recorded in 0.9% NaCl solution(pH 7) using Potentiostat/Galvanostat Model 273A. All specimens were exposed to 0.9% NaCl solution(pH 2.3) during 14 days. Elemental release into corrosive solution was measured by atomic emission spectrometry. Differences in corrosion potential and mass release were determined using ANOVA. RESULTS AND CONCLUSION: Through analyses of the data, following results were obtained. 1. In Pontor MPF and Wiron 99, corrosion potential of the solder group was statistically lower than as cast and laser weld group(p0.05). In Jel-Bios 10 and Wirobond, there was no difference of corrosion potential according to joining methods(p>0.05). 2. In all tested alloys, the amount of released metallic ion was greatest in the solder group(p0.05). 3. In scanning electron microscopic examination, except soldered Wiron 99 specimens, it is impossible to discriminate the corrosive property of solder and laser weld. 4. Under the this experimental circumstances, laser weld appears superior to the solder when corrosion is considered.

A novel 3D scan method to quantify teeth wear / 대한치과보철학회지

STATEMENT OF PROBLEM: Tooth wear is physiological phenomenon. Ninety-seven percent of normal people have tooth wear and about 7% has pathologic teeth wear. If we know the amount of tooth surface loss caused by pathologic tooth wear, we may restore it ideally. PURPOSE: Recently, measurement of tooth wear by using 3D scan has been increasing. Therefore, we need to know how accurate 3D scan is. Past accuracy test on 3D scan was about linear change, but as we know that tooth wear is volume change. Thus, the purpose of this study is to know how accurate 3D scan is. MATERIAL AND METHODS: For accuracy test of 3D scanner, volume values measured by 3D scanner and micro-balance were compared. For test I, preliminary, 3 ball samples and 3 circular cones were made with pattern resin. For test II, 10 teeth shape rubber samples were used. RESULTS AND CONCLUSION: 1. The result of the accuracy test on 3D scan with 3 ball samples and 3 circular cones made of pattern resin has no significant difference(p<0.05). 2. The result of the accuracy test on 3D scan with 10 samples of tooth shape rubber has no significant difference(p<0.05). As a result, we may concluded the analysis of quantifying tooth wear used by 3D scan is useful in the clinic.