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The purpose of this study was to evaluate the stress distributions of the fixed partial denture with five unit intermediate abutment. This fixed partial denture was attached to a three dimensional photoelastic epoxy resin model. Three dimensional photoelastic models were used, with the stress areas recorded photographically. A vertical load was applied to the second molar, which is the most posterior abutment of the fixed partial denture. Similarly, a vertical load was applied to the first molar because this tooth receives the heaviest masticatory load. These loads were added to two types of fixed partial denture. the rigid connector, and the nonrigid connector which was connected on the distal side of the intermediate abutment by a key and keyway device. After the stress patterns in surrounding tissues were observed, the following conclusions were as follows: 1. When the vertical load was applied to the first and second molars on the occlusal surfaces, the surrounding tissues of the roots of the canine, the second premolar, and the second molar were all compressive stresses. 2. When the vertical load was applied on the occlusal surface of the second molar, the tissue surrounding the roots of the canine, the second premolar, and the second molar all showed more stresses with the nonrigid connector than with the rigid connector. 3. When the vertical load was applied to the occlusal surface of the first molar, the stress concentration on the canine and the second molar was similar, whether the rigid or nonrigic connectors were used. However, on the second premolar, the stress concentration shown by the nonrigid connector was noticeably more than that shown by the rigid connector. 4. Whether the rigid or nonrigid connectors were used, when the load was placed on the first molar, the stress concentration on the canine and the second premolar was greater than that observed for the second molar. When the load was placed on the second molar, the load affected the second molar more than the canine and the second premolar.
The purpose of this study was to investigate about the relationship between the tapping sound and occlusal contacts in centric occlusion and apply its results to clinical parameter as a diagnostic aid. Forty-seven subjects, 20 to 25 years of age, without symptoms of stomatognathic dysfunction were selected from dental students in Chosun University for this study. The tapping sound in centric occlusion were recorded as bone conduction sounds using a gnathosonic instrument (Dental Sound Checker TME-202C,Yoshida Co.,Japan) and the average duration of the right and left sound was measured. With these records, the subjects were classified in three groups as Class I (with stable contacts), ClassⅡ (with mixed contacts) and Class Ⅲ (with unstable contacts). Occlusal stability was evaluated by the nature of centric occlusal contacts. The centric occlusal contacts were marked and surveyed on the upper and lower occlusal surfaces of the stone models which were mounted on Hanau model H articulator by the interocclusal records using rubber base impression material. Finally, the relationship between the occlusal pattern and nature of centric occlusal contacts was observed. The results of this study were as follows: 1. In the 47 subjects, 16 were Class Ⅰ,15 were Class Ⅱ and 16 were Class Ⅲ ,and their average durations were 8.50 msec., 9.77 msec. and 13.68 msec. respectively. 2. The average numbers of teeth with both mesiodistal and buccolingual coupled contact were 5.64 and those of occlusal contact points in C.O. were 57.81. The ratio of the surface contact over 1mm in diameter to the total contact point was 44.54% in Class I group. 3. The average numbers of teeth with coupled contact were 5.53 and those of contact points were 57.33. The ratio of the surface contact over 1mm in diameter to the total contact point was 52.67% in Class Ⅱ group. 4. The average numbers of teeth with coupled contact were 3.75 and those of contact point were 47.63. The ratio of the contact points over 1mm in diameter to the total contact points was 54.33% in Class Ⅲ group.
It has been known that noble metal alloys are one of the most important materials for dental use. In particular, silver base alloys containing copper are most widely used because of their age-hardenability. But their ageing process has not been fully understood. In the present work, the electrical resistivity and hardness change during ageing of dental silver alloys were measured and the ageing process was discussed. Principal results were as follows; (1) The standard compositions of the silver alloys were (50-55wt%) Ag+(28-20wt%) Pd+(10wt%)Cu+(5-12wt%)Au (2) The ageing treatment at 350 to 450℃ for 10 to 60 min should be the optimum condition for age-hardening treatment of these alloys. (3) The electrical resistivity showed a characteristic peak in the early stage of isochronal ageing. This peak will probably correspond to clustering of certain solute atom. (4) The isothermal ageing curves of A, B alloys were like each other in shape. The apparent activation energy for the precipitation process were calculated to be about 39 and 36Kcal/mol, respectively.
齒科用 非貴金屬合金으로 널리 使用되고 있는 니켈-크롬系 合金인 Ticonium Premium 100 과 코발트-크롬系 合金인 Regalloy 를 對象으로 500, 600, 700, 800, 900 및 1,0000℃의 鑄型溫度로 變化시켜 遠心鑄造한 後, 硬度 및 引張强度를 測定하고 微細組織과 引張試片 破齒面을 觀察하여 아래의 結果를 얻었다. 니켈-크롬系 合金인 Ticonium Premium 100 은 鑄型溫度가 上昇할수록 結晶粒 이 粗大하게 變化함에 따라 硬度 및 引張强度도 多少의 減少를 나타내었다. 코발트-크롬계 合金인 Regalloy 는 鑄型溫度가 上昇할수록 結晶粒이 粗大하게 變化함에 따라 硬度 및 引張强度의 顯著한 減少를 나타내었다. 코발트-크롬계인 Regalloy 는 니켈-크롬系 合金인 Ticonium Premium 100 비해 硬度 및 引張强度가 높게 나타났다. 引張試片 破齒面은 두 合金 모두에서 鑄型溫度가 上昇할수록 微細氣孔이 破齒面의 中心部에 集中되는 傾向이 增加하였으며 延性破斷에서 脆性破斷으로 轉移되는 樣相을 觀察할 수 있었다. 良質의 鑄造組織을 얻고 鑄造本의 適合性을 向上시키기 위해서는 適切한 材料에 따른 適切한 鑄型溫度의 選擇이 要求된다. The purpose of this study was to investigate the effect of model temperature on the change in microstructure and physical properties of Ticonium Premium 100(Ni-Cr-alloy) and Regalloy(Go-Cr alloy). Tensile and hardness specimens were casted from the two types of alloys by centrifugal casting machine in mold temperatures of 500, 600, 700, 800, 900, and 1,000℃. After testing the hardness and the tensile strength of castings, the microstructure and the pattern of fracture were investigated and correlated with the above two mechanical properties. The results were as follows: As the grain size of Ticonium Premium 100 increased with the increase of mold temperature, the hardness and the tensile strength reduced slightly with the increase of grain size. As the grain size of Regalloy increased with the increase of mold temperature, the hardness and the tensile strength reduced remarkably with the increase of grain size. The values of the hardness and the tensile strength obtained from Ticonium Premium 100 were lower than those from Regalloy. As the mold temperature increased, the fractured surfaces of tensile specimens in the two types of alloys showed the tendency to form large voids in the center of specimens. Thus the ductile fracture was changed into the brittle fracture with the increase of mold temperature. There was the needs for the users to select the proper alloys and to control the mold temperature accurately in order to obtain the good and suitable castings.
개교증, 절연부 파절, 변색등 심미적 요인으로 라미네이트를 설측연장시 연장길이에 따른 파절강도를 알아보기위해 발거된 60개의 상악 전치의 순면에 3개의 seating form을 형성하고sheet wax를 사용하여 가로 5mm $^*$세로 5mm $^*$두께 0.9mm의 block을 형성하고, 각 군에 따라 I군 : 0.5mm, II군 : 1mm, III군 : 2mm, IV군 : 0mm로 설측 연장 길이를 달리하여 block을 형성 이를 인상채득하여 내화모형을 제작하였다. 여기에 라미네이트용 도재를 2회에 걸쳐 축성 통법대로 소성 제작하였다. block에 맞추어 contouring하고, 내화매몰재를 제거 sandblast처리를 시행하였다. 그후 레진시멘트로 합착하였다. 절치간 각도를 127도로 특별히 제작된 holding device를 이용하여 인스트론 만능시험기에 시편을 거상하고, 분당 0.5mm cross head speed로 파절강도를 측정하여 다음과 같은 결과를 얻었다. 1. 각 군의 평균파절강도는 대조군인 설면으로 연장치 않은 IV군에서 86.95Mpa, 0.5mm 연장한 I군에서 44.98Mpa, 1.0mm연장한 II군에서 27.47Mpa, 2.0mm연장한 III군에서 19.61Mpa의 순으로 나타났다. 2. 모든 실험군 사이에는 통계적으로 유의성 있는 차이를 나타냈고(p<0.01), 이러한 실험 결과로 미루어 보아 라미네이트 디자인시, 설면으로 연장치 않거나, 절연부의 피개가 불가피한 경우에는 설면으로 0.5mm 연장하는 것이 파절 강도면에서 유리하다고 사료된다. The purpose of this study was to evaluate the fracture strength of porcelain laminate veneer with various lingual extention length when incisal restoring. Sixty recently extracted, intact maxillary incisors were used and stored in a physiologic saline solution from the time of extraction. Seating form was preparation at the labial surface of each tooth with a water-cooled round diamond bur. Standard block was formed with 32 gauge and 24 gauge wax at tooth labial and lingual surface. Lingual extention length differed according to each group. (group I : 0.5mm, group II : 1 mm, group III : 2mm, group IV : 0mm) All tooth specimens were impressioned with examix(GC Inc., Japan). Refractory cast were maked with refractory die material(Ceramco Inc., U.S.A.) Laminate porcelain (Ceramco II Veneer porcelain, Ceramco Inc., U.S.A.) was condensed in refractory die cast and baked according to the manufacturer's recommendations. Each surface was contoured with low speed diamond bur according to guide block. All porcelain specimens were sandblasted and ultrasonically cleaned in distlled water for 3 minutes. Then, all porcelain specimen were etched with 8% hydrofluoric acid for 5 minutes. Sixty specimens were bonded with composite resin cement(Choice Porcelain Veneer System, Bisco Inc., U.S.A.) according to manufacture's directions. The fracture loads of the specimen were measured by Instron universal testing machine. The mean values of fracture loads for the groups were statistically compared by Duncan's multiful range test. The result were as follows : Mean fracture strengths of each group were 86.95Mpa in no lingual extention group, 44.98Mpa in 0.5mm lingual extention group, 27.47Mpa in 1mm lingual extention group, 19.61Mpa in 2mm lingual extention group. There was a statistically significant difference between all group(p<0.01).
The purpose of this study was to investigate the displacement of and the stress distribution on the prosthesis, abutment, and its supporting tissues under functional load, and the effect of alteration in root length of 2nd abutment. The 3-dimensional finite element method was used and the finite element models were prepared in which the abutments of left mandibular 5 unit axed partial denture were canine, the 1st pre-molar and the 2nd molar, and the root lengths of canines were as follows. Model I : Root length of canine was 2mm longer than the 1st premolar Model II : Root length of canine was 2mm shorter than the 1st premolar Static compressive force of 300N was applied to connector between 2nd premolar & 1st molar, and then von Mises stress, displacement and reaction force were obtained. The results were as follows : 1. In fixed partial denture, prosthesis under load on pontic was rotated around mesio-distal long axis of it from longual side to buccal, and simultaneously bended in buccal and gingival direction with mesial end deformed in gingival direction and distolingual end in occlusal. 2. Clinical crowns of abutments were bended in the same directions with those in which prosthesis deforms. Due to that, roots of anterior abutments were twisted in counterclockwise with concentration of shear stress on distal or distobuccal sides of their cervices, and that of posterior was in clockwise with concentration of shear stress on mesiobuccal side of it in the same level with anterior abutments. 3. In case that root length of the 2nd abutment was longer than that of the 1st abutment, its displacement and reaction force which means the force tooth exerts on the surrounding periodontal tissues were smaller but shear stress on itself was larger than in the case root length of 2nd abutment was shorter.