A strain gauge analysis of implant-supported cantilevered fixed prosthesis under distal static load / 대한치과보철학회지

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

Stress analysis on the different clasps of the removable partial denture by three-dimensional finite element method / 대한치과보철학회지

STATEMENT OF PROBLEM: In the partially edentulous patients, removable partial dentures have been working as a important treatment modality. Clasps, a kind of direct retainers, received some amount of stresses during the insertion and removal of partial denture on the abutment tooth. PURPOSE: The study is to investigate stresses of the different clasps. MATERIAL AND METHODS: In order to investigate the degree of stresses, maxillary partial edentulism (Kennedy Class II, modification 1) was assumed and removable partial dentures were designed on it with three kinds of metallic materials; cobalt-chromium alloy, type IV gold alloy and commercially pure (c.p.) titanium. Aker's clasp was applied on the left second molar, RPA (mesial rest-proximal plate-Aker's) clasp was on the left first premolar and wrought wire clasp was on the right first premolar. Three dimensional, non-linear, dynamic finite element analysis method was run to solve this process. RESULTS: 1. Cobalt-chromium alloy had the highest von Mises stress value and c.p. titanium had the lowest one irrespective of the types of clasps. 2. In the Aker's clasps, stress on the retentive tips was shown shortly after the appearance of stresses of the middle and minor connector areas. These time lag was much shorter in the RPA clasps than in the Aker's clasp. 3. In general, retentive tips of wrought wire clasps had much less amount of stress than other clasps. CONCLUSION: The amount of stress was the highest in the RPA clasp and the lowest in the wrought wire clasp, in general.

Resonance frequency analysis of impl-ants with anodized surface oxides / 대한치과보철학회지

The present experimental study was designed to address two issues. The first was to investigate whether oxidation voltage of titanium implants influenced bone tissue responses after an in vivo implantation. The second aim was to investigate secondary stability change after 1 to 3months period. Screw-shaped implants with a wide range of oxide properties were prepared by electrochemical oxidation methods, where the oxide thickness varied in the range of 3-15micrometer. The micro structure revealed pore sizes of 1-3micrometer, the crystal structures of the titanium oxide were amorphous, anatase and a mixture of anatase and rutile type. Bone tissue responses were evaluated by resonance frequency measurements that were undertaken 1 to 3months after insertion in the rabbit tibia. It was concluded that no statistical difference of RFA values was found between the groups, RFA gains after 1month and 3months were calculated.

The study on the removal torque of the diamond like carbon coated titanium abutment screws / 대한치과보철학회지

STATEMENT OF PROBLEM: Implant screw loosening remains a problem in implant prosthodontics. Some abutment screws with treated surfaces were introduced to prevent screw loosening and to increase preload. DLC(Diamond Like Carbon) film has similar properties on hardness, wear resistance, chemical stability, biocompatibility as real diamond materials. PURPOSE: The purpose of this study was to investigate the effect of lubricant layer on abutment screw and to discriminate more effective method between soft lubricant and hard lubricant to prevent screw loosening. MATERIAL AND METHOD: In this study, 1mum thickness DLC was used as protective, lubricating layer of titanium screws and 3 times removal torque was measured on the abutment screws to investigate the difference in 10 coated and 10 non-coated abutment screws. RESULTS: The results indicated that the implants with DLC coating group were not more resistant to the applied force in screw loosening. At 32Ncm, the 3 times removal torque in DLC group were 27.7+/-2.89, 25.85+/-2.35 and 26.2+/-2.57. The removal torque in no-coated abutment screws were 27.85+/-4.23, 27.35+/-2.81 and 27.9+/-2.31, respectively. CONCLUSION: The lubricant layer used in this study was Diamond Like Carbon(DLC) and it have a properties of hard and stable layer. The DLC coating layer was hard enough to prevent distortion of screws in the repeated unscrewing procedure in clinical situation. The reduced friction coefficient in hard DLC layer was not effective to prevent screw loosening.

Response of osteoblast-like cells on titanium surface treatment / 대한치과보철학회지

Statement of problem. Titanium is the most important material for biomedical and dental implants because of their high corrosion resistance and good biocompatibility. These beneficial properties are due to a protective passive oxide film that spontaneously forms on the surface. Purpose. The purpose of this study was to evaluate the responses of osteoblast-like cells on different surface treatments on Ti discs. Material and Methods. Group 1 represented the machined surface with no treatment. Group 2 surfaces were sandblasted with 50microm Al2O3 under 5 kgf/cm2 of pressure. Groups 3 and 4 were sandblasted under the same conditions. The samples were treated on a titanium oxide surface with reactive sputter depositioning and thermal oxidation at 600degree C (Group 3) and 800degree C (Group 4) for one hour in an oxygen environment. The chemical composition and microtopography were analyzed by XRD, XPS, SEM and optical interferometer. The stability of TiO2 layer was studied by potentiodynamic curve. To evaluate cell response, osteoblast extracted from femoral bone marrow of young adult rat were cultured for cell attachment, proliferation and morphology on each titanium discs. Results and Conclusion. The results were as follows : 1.Surface roughness values were, from the lowest to the highest, machined group, 800degree C thermal oxidation group, 600degree C thermal oxidation group and blasted group. The Ra value of blasted group was significantly higher than that of 800degree C thermal oxidation group (P=0.003), which was not different from that of 600degree C thermal oxidation group (P0.05). 3. The level of cell proliferation showed no difference among the groups after one day, three days, and seven days (P>0.05). 4. The morphology and arrangement of the cells varied with surface roughness of the discs.

Color stability of current prosthetic composites under accelerated aging and Immersion in a coffee solution / 대한치과보철학회지

The color stability of current prosthetic composites is unknown, even though the quality of com-posite materials has been improving. This study examined the intrinsic color stability of various current prosthetic resins (ceramic-polymers) after an accelerated aging process and the extrinsic color stability after immersion in a coffee solution. By comparing the amount of dis-coloration after aging with that without aging, the effect of the accelerated aging process on external discoloration could be evaluated. Three current prosthetic composites (Artglass, Targis, Sculpture), one light polymerized direct composite (Z100) and one dental porcelain control (Ceramco) were assessed. The col-or changes (delta E) of all the specimens were determined using the CIE L*a*b* color order system with a reflected spectrophotometer. The results were as follows: 1. The prosthetic composite materials subjected to the accelerated aging test showed no sig-nificant difference in color changes (p> .05). 2. In the coffee solution immersion test after the aging process, the color changes of the Targis and Artglass groups were not different from that of the Z100 group, which showed the highest color change. 3. In the immersion only test, a significantly high color change was observed in the sculpture glazing group. 4. The aging process influenced on the color changes more in the Targis, Artglass and Z100 groups than in the Sculpture and Ceramco groups.

Cytotoxicity Of Denture Base Resins / 대한치과보철학회지

The purpose of this study was to investigate the cytotoxicity and mutagenicity of denture ase resins. According to manufacturer's instructions, resin specimens were made. Group 1: heat-polymerizing acrylic resin (Luciton 199(R)). Group 2: heat-polymerizing acrylic resin containing polyhedraloligosilsesquioxane(POSS esin). Group 3: auto-polymerizing acrylic resin (Repair Acrylic(R)). Group 4: direct relining auto-polymerizing acrylic resin (Tokuso Rebase(R)). Fresh specimens, 24 hrs. and 72 hrs. soaked specimens in distilled water were made. Responses with metabolic assay and mutagenesis assay to eluates from resin specimens were measured. Cultures with medium alone provided controls. Cytotoxicity was assessed with agar overlay test. The results were as follows: 1. Group 4 showed higher cytotoxicity than Group 1, Group 2 and Group 3 in fresh, 24-and 72-hour immersion cases (p<.05). Group 3 showed higher cytotoxicity than Group 2 in fresh cases and showed higher cytotoxicity than Group 1 and Group 2 in 24-and 72-hour immersion cases (p<.05). Group 1 and Group 2 showed no significant difference. 2. All acrylic denture base resins showed significant increase of cell activity as immersion time increased (p<.05). 3. Auto-polymerizing acrylic denture base resins showed higher cytotoxicity than heat-polymerizing acrylic denture base resins (p<.05). 4. All acrylic denture base resins showed lower mutagenicity than controls (p<.05).

Developement of the reinforced acrylic-based hybrid denture composite resin with vinyloligosilsesquioxane(POSS) / 대한치과보철학회지

The mainly used polymeric material for the denture is PMMA because of its cost and easiness to handle. So it was widely used material among dentists for past decades. But the acrylic-based denture materials have several common weak points such as shrinkage after curing and lack of strength. In order to solve these problems, we adapted one of hybrid system using acrylic polymer and vinyloligosilsesquioxane(POSS). POSS, which is a well known expandable monomer during polymerization process, may eventually suppress volumetric shrinkage. And the hybrid system makes it possible for the polymer to be stable in various severe conditions. Eight different kinds of samples were designed and synthesized. Each samples were characterized with dynamic mechanical analyser(DMA) to confirm their thermodynamic properties, fractured to analyze the cross-sectional morphology of the samples. And elongation, flexural and impact tests were also executed to evaluate the mechanical properties of the samples. From the results, hybrid composites had well defined crosslinked network structure compared to the widely used denture materials, and the mechanical strength improved without changing any surface condition as increment with POSS ratio in hybrid system. Fractured morphology showed homogeneous surfaces in spite of mutli component system, therefore we can conclude that the adoption of the POSS brought the reinforcement of the denture resin.

A STUDY OF CORE TYPE AND LUTING CEMENTS ON COMPLETE CAST CROWN RETENTION / 대한치과보철학회지

The purpose of this study was to compare the retention of complete cast crown over amalgam cores, composite resin cores, and cast gold cores when cemented with three different luting agents. Eighteen core specimens each of amalgam(Bestaloy, Dong Myung, Seoul, Korea), composite resin (Z100, 3M Dental product, st. Paul, Minn) and type N gold alloy (Ba 4, Heesung Engelhard Corp., Korea) were made in a customized milling stainless steel die. A wax pattern with a loop attached to occlusal surface was made for each core and a type 11 gold alloy casting was fabricated. The castings which had clinically acceptable marginal fit were used as test samples. The following luting cements were used to cement cast crowns on each core material : (1) zinc phosphate cement (Confi dental Products Co., USA) (2) glass-ionomer cement (Fuji Plus, GC Industrial Corp., Tokyo, Japan) (3) resin cement (Panavia 21, Kuraray Co., USA). All cements were mixed according to manufacturers instructions. A static load of 5kg was then applied for 10 minutes on the crowns. All specimens were stored in saline solution for 24 hours at 371C and thermocycled for 500 cycles. After storage and cycling, the tensile bond strengths were measured by using a universal testing machine (Instron Corp., Canton, Mass.) at a crosshead speed of 0.5mm/min. The results were as follows : 1. The retentive strength of resin cement was the highest of all three types of cement for resin core (p0.05). 3. The retentive strength of resin cement was higher than that of zinc phosphate for cast core, but there was no difference between the retentive strength of glass ionomer cement and those of rein and zinc phosphate cement. 4. The retentive strength of the zinc phosphate cement for amalgam core was the highest of all type of cores.

ACCURACY OF IMPROVED STONE CASTS FROM ELASTOMERIC IMPRESSION MATERIALS / 대한치과보철학회지

The purpose of this study was to compare the accuracy of currently used elastomeric impression materials for complete arch impression taking. Five elastomers (Impregum, Permlastic, Express, Extrude, Examix) and one Irreversible hydrocolloid (Aroma-fine) were tested. For each material, 5 impressions were made of stainless steel model to which five tapered posts were attached. Custom trays were used for polyether and polysulfide impression materials, and putty/wash two step technique was used for addition polyvinylsiloxane impression materials. Improved stone models were poured to all impressions. Accuracy of the materials was assessed by measuring ten distances on stone dies poured from impressions of the master model. All measurements for master and improved stone models were with three dimensional measuring machine. The results were as follows 1. The dimensional accuracy of polyether, extrude, and examix were significantly superior to polysulfide, exress, and alginate in reproducing full arch mode (p0.05). 3. there were no statistical differences in dimensional accuracy between polysulfide, express, and alginate (p>0.05). 4. There were no statistical differences between addition polyvinyl siloxane materials (p>0.05). 5. There were no statistical differences between anterior-posterior and lateral dimensional changes of all impression materials (p>0.05).

A STUDY ON FRACTURE STRENGTH OF COLLARLESS METAL CERAMIC CROWN WITH DIFFERENT METAL COPING DESIGN / 대한치과보철학회지

The metal ceramic crown is currently the most popular complete veneer restoration in dentistry, but in many cases, the metal cervical collar at the facial margin is unesthetic and unacceptable. Facial porcelain margin has been used in place of it. But this dose not solve the problems, such as dark gingival discoloration and cervical opaque reflection of porcelain veneer. Recently, metal copings which were designed to terminate its labio-cervical end on the axial walls coronal to the shoulder have been clinically used to solve the esthetic problem of metal ceramic crown. But in this design, porcelain veneer of labio-cervical area which is not supported by metal may not be able to resist the stress during cementation and mastication. The purpose of this study was to evaluate fracture strength and fractured appearance of crowns according to different coping designs. A resin maxillary left central incisor analogue was prepared for a metal ceramic crown, and metal dies were made with duplication mold. Metal copings were made and assigned to one of four groups based on facial framework designs: group 1, coping with 0.5mm metal collar; group 2, metal extended to the shoulder; group 3, metal extended to 1 mm coronal to the shoulder; group 4, metal extended to 2mm coronal to the shoulder. Copings and crowns were adjusted to be same size and thickness, and cemented to metal dies with zinc phosphate cement by finger pressure. Fracture strength was measured with Instron Universal Testing Machine. Metaldies were anchored in Three-way-vice at 3mm below finish line and at 130degree inclined to the lone axis of the crown. Load was directed lingually at 2mm below midincisal edge. Load value at initial crack and at catastrophic fracture was recorded. The results obtained were as follows: 1. Fracture strength values at initial crack were higher in groups 1, 2 than in groups 3, 4 but this difference was not statistically significant(P<0.05). 2. Conventional metal collared crown had greater catastrophic fracture strength than any other collarless crowns. 3. The greater the labial metal coping reduction, the lower the catastrophic fracture strength of crowns but when more than 1mm of labial metal reduction was done, the difference in strengths was not statistically significant(p<0.05). 4. The strongest collarless coping design was group 2.

DIMENSIONAL ACCURACY OF EPOXY RESINS AND THEIR COMPATIBILITY WITH IMPRESSION MATERIALS / 대한치과보철학회지

The indirect technique for making cast restoration requires that dies be as accurate and durable as possible. Currently, stone is the most commonly used material for die. However, it has some problems such as the weakness in its strength and low abrasion resistance. Recently, epoxy resin die systems have become available. The purpose of this study was to examine two commercially available resin die systems and evaluate some characteristics for their clinical performance. This study evaluated the dimensional accuracy of epoxy resins and their wettability with impression materials. In this study, the first experiment was about dimensional accuracy of different die materials. The master model was made of stainless steel. 10 models were made of two epoxy resins (Die-epoxy, Tri-epoxy) and a die stone (Fujirock) each. Occlusal diameter (Dimension I), occluso-gingival height (Dimension II), and interabutment distance (Dimension III) wee measured in each model. Next, the contact angles of die materials with impression materials were observed. The blocks were made of polyether, hydrophilic additional silicone, polysulfide impression materials. By dropping the same amount (0.05ml) of Tri-epoxy, Die-epoxy, and die stone on the blocks, 10 samples of each die material were made. After setting of materials, the contact angles were measured. The results of this study were as follows. 1. The expansion of stone die and the shrinkage of resin dies in occlusal diameter were observed, and stone and Tri-epoxy were expanded and Die-epoxy was shrinked in occluso-gin-gival height. There was little change among materials in interabutment distance (p>0.05). 2. In comparison with the mater model, Tri-epoxy had the least variation in measurement of the three die systems examined. Did-epoxy was next, and die stone showed the greatest variation. 3. The compatibility of die stone for polyether, hydrophilic additional silicone, polysulfide decreased in order, wherease epoxy materials had the decreased compatibility for polyether and polysulfide, hydrophilic additional silicone in order. It was not statistically different between polyether and polysulifide (p>0.05). 4. The contact angles of Tri-epoxy, Die-epoxy, die stone were getting bigger in order.

DIMENSIONAL ACCURACY OF DENTURE BASE USING LASER SCANNER OF REVERSE ENGINEERING TECHNIC / 대한치과보철학회지

The purpose of this study was to evaluate and compare the fit of denture bases processed by injection pressing technic using laser scanner of reverse engineering technic. The auther duplicated 20 maxillary edentulous models and 20 mandibular edentulous models, which were scanned on HYSCAN 45C 3D SCANNER(Hymarc Co., Canada). The scanned data was stored in the personal computer using SURFACER (Imageware Co., U.S.A.) software program. After 40 dentures were cured by PERform Inkovac system. SR-Ivocap system, Palajet system, and Sulfon system, they were stored in water at room temperature for 24 hours. The dentures were scanned on HYSCAN 45C 3D SCANNER(Hymarc Co. Canada). The scanned data were stored in the personal computer using SURFACER (Imageware Co., U.S.A) software program. By overlapping two images using the same program, the fit between two surfaces was scaled by positive and negative errors. The obtained results were as follows : 1. In the upper denture, most of the positive errors occurred on the lingual side of anterior alveolar ridge and the negative errors were on the flange of denture bases. 2. In the lower denture, most of the positive errors occurred on the inner side of lingual flange and the negative errors were on the border of anterior labial flange areas. 3. There were no statistical differences among the positive errors of the four types of inject-ion denture curing methods and also no statistical differences between negative errors except only in negative maximum errors. 4. In PRERform system and SR-Ivocap system, they have the tendency of inaccurate fit lower denture bases comparing to that of upper denture bases. 5. The negative error scales were greater than the positive error scales in all types of inject-ion denture curing methods.

A STUDY OF ION BEAM ASSISTED DEPOSITION(IBAD) OF TiN ON Ni-Cr Be ALLOY FOR SURFACE CHARACTERISTIC / 대한치과보철학회지

Dental restorative materials must have the physical properties to withstand wear and corrosion. Base metal alloys possess better mechanical properties and lower price than the gold alloys. For these reason such alloys have largely replaced the precious metal alloys. One aspect to consider is the release of metal substances to oral environment. The release of elements from dental alloys is a continuing concern because the elements may have the potentially harmful biological effects on local tissue. The purpose of this study was to minimize metal release on the nonprecious metal surfaces by ion bea assisted deposition(IBAD) of titanium nitride (TiN). Ni-Cr-Be alloys with and without TiN coatings were secured in an wear test machine opposing ruby ball to determine their relative resistance to wear with 100m, 200m, 300m and 400m sliding distance. And the corrosion behavior of the Ni-Cr-Be alloys with and without TiN coating and 3 dental noble alloys have been studied. Potentiodynamic curves were used to analyse the corrosion characteristics of the alloys. The measurement of the released Ni and Ci ions was conducted by analysis of the electrolyte solution with atomic absorption spectroscopy. The results were as follows : 1. The critical sliding distance that wore down TiN coating of 2.5micrometer thickness in this study condition was 300m. 2. Ion beam assisted deposition of TiN showed a good surface modification with respect to the properties of wear and corrosion resistance. 3. X-ray diffraction showed that the strongest peak of TiN(111) in the coatings. 4. The release of Ni and Cr ions from alloys measured by means of atomic absorption spectroscopy was reduced by ion beam assisted deposition of TiN.

A STUDY ON THE STRESS DISTRIBUTION OF ABUTMENT TEETH AND RESIDUAL RIDGE AREA BETWEEN TELESCOPIC AND CLASP TYPE RPD BY FEM METHOD / 대한치과보철학회지

The purpose of this study was to compare and evaluate the stress distribution and displacement developed in the abutment teeth and residual ridge area by madibular unilateral distal extension removable partial denture with 2 different retainer designs. The retainers on right and left canine and right 2nd molar were Akers clasp in one model and telescopic crown in the other model. The stress distribution of abutment teeth and residual ridge area on two model were compared and analyzed with 3-dimensional finite element method. 150N and 400N forces were applied vertically, 30 degree and horizontally on the central fossa area of left 1st molar of the removable partial denture, and then stress distribution patterns were analyzed and compared. The results were as follows 1. As the magnitude and angulation of applied force were increased, the magnitude of stress on the right and central residual ridge area and the right canine of the telescopic type increased and comparing to those of the Akers clasp type. 2. As the magnitude and angulation of applied force were increased, the mesial direction of displacement on the right residual ridge area and the right tooth of the telescopic type increased and the distal direction of displacement on left residual ridge area and the left canine increased comparing to those of Akers clasp type. 3. As the vertical force was applied, the distal direction of the displacement of the right tooth were greater and that of the left canine was smaller and the upward displacement of the right canine was greater in telescopic partial denture than those of Akers clasp type. 4. As the 30 degree force was applied, the mesial direction of the displacement of the right tooth were greater and the distal direction of the displacement of the left canine was smaller and the upward displacement of the right canine was greater in telescopic partial denture than those of Akers clasp type. In the horizontal force the results were same in right area tooth but the distal direction of displacement was greater in left canine. 5. In both removable partial dentures, as the magnitude and degree of force were increased, the stress and displacement were increased. The compressive force was dominative than the tensile force. 6. In both removable partial dentures, the magnitude of stress was greater on mucosal tissue area than that of the alveolar bone area on distal extension residual ridge area but the result was reversed on anterior residual ridge area. The displacement was always greater on mucosal tissue area than that of alveolar bone area.

MECHANICAL PROPERTIES OF TITANIUM CONNECTORS TREATED BY VARIOUS WELDING TECHNIQUES / 대한치과보철학회지

The use of pure titanium and titanium alloys have been increased recently in fixed, removable prosthodontics and implant fields as a framework. But when they were used for superstructures of implant of metal framework of removable prosthesis, welding is necessary to reconnect the fracture site to control the casting distortions. To overcome the difficulties in soldering the titanium due to high oxidation property, much effort have been devoted. In this study, some of mechanical properties were compared between pure titanium and Ti-6Al-4V alloy by usingl aser welding, electron beam welding technique and tungsten arc welding. Mechanical properties such as tensile strength, yield strength, elongation and microhardness were measured. And, in order to compare the effect of welding site and surrounding metal tissue according to the welding condition, SEM photographs were taken an element distribution was observed by Wave Dispersion Spectroscopy. Through analyses of the data, following results were obtained; 1. In items such as tensile strength, yield strength and elongation according to the welding techniques of pure titanium, only tungsten arc welded group showed significant lower value than other groups(P<0.05). 2. In items such as tensile strength and yield strength according to the welding techniques of Ti-6Al-4V alloy, control group and tungsten arc welded group showed significant difference among all the groups(P<0.05). 3. Ti-6Al-4V alloy exhibited significantly greater elongation than control group when the laser welding method and electron beam welding method were used, and elongation showed increasing tendency. 4. Pure titanium specimens exhibited increasing tendency of microhardness regardless of the welding technique applied, and especially tungsten arc welded group demonstrated a great increase of microhardness than parent metal. 5. There was no hardness change in laser welded group and electron bean welded group of Ti-6Al-4V ally, but in tungsten arc welded group, hardness changed greatly from parent metal to weld seam. 6. Through the metallographic examination and scanning electron microscopy, laser welding caused central fusion and recristallizations were formed and tungsten arc welding caused localized fusion to 0.3-0.7mm from the surface.

THE EFFECTS OF METAL SURFACE TREATMENTS ON THE BONE STRENGTH OF POLYMETHYL METHACRYLATE BONDED REMOVABLE PROSTHESE / 대한치과보철학회지

Traditionally, many kinds of mechanical bonding techniques were used for bonding resins to the surface of the metal alloys. If there is a seperation between resin and metal junction by stress accumulation and temperature change of oral cavity, the cracks or crazing may occur, accompanied by failure of resin bonding to metal. This study was designed to compare the shear bond strength of the type IV gold alloy and Cr-Co alloy surfaces treted with various methods and thermocyling. Universal Instron (Model 1000) and scanning electron Microscope (JEOL, Japan) was used to record the shear bond strength of 5 groups. Forty specimens were made for each group ; group 1 was treated with sandblasting only, group 2 was coated with V-primer after sandblasting, group 3 was coated with Metal primer, group 4 wase coated with MR Bond and group 5 was coated with silane. After treated with various methods, thermocycling was done for half of the each group. The surfaces of failed pattern were observed with SEM. The results were as follows: 1. Shear bond strength of the group 1 was lower than that of another groups in type IV gold alloys and bond strength of the group 1, 2 were lower than that of group 3, 4, 5 in Cr-Co alloys. 2. Shear bond strength of the gold alloy with resin was higher than that of Cr-Co alloy when specimens were coated with V-primer. 3. Shear bond strength of the Co-Cr alloys with resin was higher than that of gold alloys when specimens were coated with Metal primer. 4. The bond strength of all specimens did not decreased significantly after thermocycling. 5. Adhesive failures were found in group 1 and Cr-Co alloy in group 2, but adhesive and cohesive failures ere found in another groups.

A STUDY ON THE EFFECTS TEXTURE OF FOOD ON CHEWING MOVEMENTS AND EMG OF MASTICATORY MUSCLE / 대한치과보철학회지

To elucidate the effects of food texture such as hardness, cohesiveness, adhesiveness on mastication procedure, the electromyographic activity (EMG) of the masticatory muscles and the chewing movements were analyzed in eighteen young subjects during ordinary chewing. Seven different foods were selected by sensory texture profiling and mechanical test with texturometer; egg white, sausage, pizza cheese, yang-geng, biscuit, peanut and almond. The indexes of jaw movements used were the chewing number, chewing time, maximum opening, average opening, closing velocity and opening velocity. The EMG indexes analyzed were maximum and average integrated amplitude of the anterior temporal and masseter muscles. The results obtained were as follows. 1. The chewing time and chewing number, mandibular displacement and mandibular movement velocity were not changed by the hardness, cohesiveness and adhesiveness of the food (p>0.05). 2. The harder food materials showed a higher amplitude of the anterior temporal muscle integrated EMGs than the softer ones (p<0.05). 3. The maximum and average integrated EMGs of the masseter muscle increased with the increase of hardness of the food (p<0.05). 4. The integrated EMGs of preferred side and non-preferred side masticatory muscles increased with the increase of hardness of the food (p<0.05). 5. The adhesiveness and cohesiveness of the food were not the determining factor to the integrated EMGs of masticatory muscles (p<0.05).

THREE DIMENSIONAL FINITE ELEMENT ANALYSIS OF THE EFFECTS OF ALVEOLAR BONE LOSS ON STRESS DISTRIBUTION IN POST-RECONSTRUCTED TEETH / 대한치과보철학회지

There're many cases that should be reconstructed with post and core when clinical crown is destructed. But this post and core restoration may cause damaging stress on the teeth. Previous finite element study was restricted to normal bone model relatively close to cementoenamel junction. Moreover, the test of a model with diminished bone support was rare. The purpose of this study is to test the effects of alveolar bone loss on the magnitude, stress distribution and displacement of post reconstructed teeth. In this study, it was assumed that the coronal portion of upper incisor was severely destructed. After conventional endodontic treatment, it was restored with post and core. The PFM restoration was made on it. This crown was cemented with ZPC. Alveolar bone was classified by 4 types of bone, such as normal, 2 mm, 4 mm, 6 mm bone, according to the bone loss. Meanwhile, the material of post are divided into 2 types of materials, such as gold, co-cr. Force was applied to two directions. One was fuctional maximum bite force (300 N) applied to the spot just lingual to the incisal edge with the angle of 45 degree to the long axis of the tooth, and the other one was horizontal force (300 N) applied to the labial surface. The results analyzed with three dimensional finite element method were as follows : 1. Stress was concentrated on the adjacent dentin of the post apex., one third portion of the post apex and the labial & lingual mid-portion of the root in all case. The stress of middle third of the root was apparently concentrated on the labial aspect. 2. The stress on adjacent dentin of the post apex and one third of the post apex increased as alveolar bone height moved apically. This increase was dramatic beyond 4 mm bone loss model. 3. The stress of the post apex was spreaded to the middle third of the post and greater than gold post in the case of metal post. 4. The displacement of the neck of post was the greatest in one of the post-cement interface and this increased as alveolar bone height moved apically. Besides the displacement of the metal post is slightly lower than one of the gold post.

The influence of impression materials on the accuracy of the stone casts poured from complete arch impression / 대한치과보철학회지

No abstract available.