Some assumptions and simplifications have been made with regard to the material properties and model geometry. Bone tissue is assumed to have uniform isotropic elastic properties, although bone will exhibit a more complex situation in vivo. Implant bone interface conditions, as indi- cated, have a very strong influenceonthe bone loading patterns around the implant. The level and mode ofstress and strain distribution are highly affected by the interface conditions 10 . Even though the amount ofstress is not a actual number, the general tendency ofstressdistribution can be analyzed in this model.
Dept of Periodontology, *Dept of Prosthodontics, College of Dentistry Dental Science Research Institute Chonnam National University
Seven finite element models were constructed in mandible having single screw-type implant fixture connected to the premolar superstructure, in order to evaluate how the length, diameter and platform shape of a screw-type fixture influencethestress in the supporting tissue around fixtures. Each finite element model was varied in terms of length, diameter, and platform shape ofthe fixture. In each model, 250N of vertical load was placed onthe central pit of an occlusal plane and 250N of oblique load placed onthe buccal cusp. The stressdistribution in the supporting tissue and the other components was analysed using 2-dimensional finite element analysis and the maximum von Mises stress in each reference area was compared. Under lateral loading, thestress was larger at the abutment/fixture interface, and in the crestal bone, compared to thestress pattern under vertical loading. The amount ofstress at the superstructure was similar regardless ofthe length, diameter and platform shape of a fixture. Around the longer fixture, thestress was decreased at the bone crest and subjacent cancellous bone and increased in the cancellous bone area apical to the fixture. Around the wider fixture, thestress was decreased at the abutment/fixture interface, and the bone crest and increased in the cancellous bone area apical to the fixture. Around the fixture having wider platform, less stress was produced at the abutment/fixture interface and the upper part ofthe cortical bone, compared to the fixture having standard platform. In conclusion, thestressdistributionofthe supporting tissue was affected by length, diameter, and platform shape of a fixture, and the fixture which was larger in diameter and length could reduce thestress in the supporting tissues at the bone-fixture interface and bone crest area.
Mechanical simulation of restorations can be a powerful tool for researchers attempting to develop study designs.
Interestingly, it is possible to simulate a lot of test combina- tion without limit, since FEA allows the alteration of many variables, such as material and geometric configurations, by virtue of CAD and mechanical modeling software. For this reason, FEA is widely used in investigating the mechanical behavior of biomedical complex structures and the critical aspects related to stressdistribution in that structures under various loads or geometric conditions. In the last three decades 2D FEA was often used in thestressdistribution analysis because of its advantage of reducing working time, meshing and computing time. However, oral tissue is unlikely to the commercial products of relatively uniform and orderly configuration. A more detailed 3D FEA has come into wide use because of considerable advantage in the analyses ofthe complex and irregular morphology.
Different types of functional and parafunctional activities that occur in the mouth, such as chew- ing and bruxing, significantly influencethe rup- ture ofthe tooth structure. When a tooth is loaded in the long axis, the forces are dissipated with minimal stress in the dentin or enamel. If the direction ofthe force is moved laterally, how- ever, teeth are flexed toward both sides. The stress pattern in the same area is changed con- tinuously from compressive to tensile, especially underneath the enamel, since dentin appears to be substantially stronger than enamel when under lateral forces. Thus, the cyclic occurrence of compression and tension may reach the fatigue
As the results of this study, compressive stress- es were created under load A and tensile stresses under load B in the point of principal stresses.
The peak stresses of both principal stresses were decreased after restoration, but high stress con- centration still remained around mesial point angle. This compressive stresses over the failure range under load A could be decreased under the limit after restoration, but tensile stresses over the limit range under load B were still remained on various areas. These mean that the tensile stresses may be the major factor to jeopardize the restoration durability and to promote the lesion progression. Therefore some clinicians 28,32,33) recom- mended that occlusal adjustment be considered as a treatment option, in addition to restoration, for abfraction lesions. Occlusal adjustments may reduce stress concentration at the cervical lesion, but they may jeopardize equilibrium ofthe occlu- sion if careful consideration for the entire occlu- sion is omitted. And they are also difficult to do with confirm on which side of occlusion concerning tensile or compressive is modified. Therefore the restoration of NCCL is first concern and then the selection of restorative material may have influ- ence onthe prognosis ofthe lesion and restora- tion.
ofthe methods used to maximize the retention rates of class V restorations is the placement of low elastic modulus materials. Heymann and col- leagues 32) reported that the retention rates for restorations of a material with lower elastic mod- ulus were significantly higher than those of a material with higher elastic modulus. The ratio- nale behind this is that high modulus materials are unable to flex when the tooth structure is deformed under load and therefore they are dis- placed from the cavity. In contrast, low modulus materials can flex with the tooth and therefore can remain in situ. Thus, these resins will absorb much ofthe masticatory stresses rather than transferring it to the dentin-restoration inter- face 11) . A low elastic modulus also contributes to stress relief from polymerization shrinkage of composites, preserving the marginal integrity of restorations 33) . This property allows for good wet- ting along the cavity walls, which improves the adaptation ofthe restorative material.
치과용 고정체 소재는 주로 티타늄(titanium, Ti)이 임상적으로 가장 많이 사용되고 있다. 하지만 환자의 치은 점막이 얇거나 퇴축될 경우 티타늄 고정체의 고유의 색상으로 인해 심미성이 결여되는 문제가 발 Purpose: The purpose of this study was to evaluate the stability of abutment screws used with the zirconia fixture-based implant system and compare them with those used with the existing titanium fixture system via the finite element method.
Jemt 등 14-17 의 보고에 따르면, 보철물 장착 후 처음 일 년 동안 실패 및 후유증은 연결나사의 풀림(13.6%)이 가장 많았고, 심미 적인 불만(11.4%), 불편함(9.1%)의 순으로 조사되었다. 나사 풀림 은 두 단계의 과정을 통해 발생하는 데, 첫 단계는 저작력과 같 은 외력이 작용하면 나사선이 미끄러지면서 나사에 부여되고 있던 전하중이 감소하게 되고, 두 번째 단계에서 전하중이 지 속적으로 감소하면 나사선이 회전하여 의도된 나사 연결 기능 이 상실되어 풀림이 발생하게 된다. 18 한편 나사 풀림 자체가 큰 문제가 되는 것은 아니지만, 반복해서 발생하는 나사 풀림은 환자와 술자에게 귀찮은 일이며, 나사 파절이나 임플란트 파 Fig. 6. The stress contour ofthe bone under hexagonalheight. A: hexagonalheight
For posterior teeth with a mesio-occlusal-distal (MOD) cavity, the most suitable treatment consists of a direct restoration using composite resin due to its high bond strength to the dental substrate [3,13-15]. In cases where dental pulp has been compromised and endodontic treatment has been performed, the best protocol prior to performing the restoration, which may increase the resistance ofthe dental structure, is still not well-defined [16,17]. It has been generally reported in the literature that glass ionomer cement should be used to support the composite resin restoration [18,19]. Other authors have reported the use of fiberglass posts and filling the pulp chamber with resin cement . Finally, some manufacturers offer pre-framed metal posts with this indication. Therefore, this study evaluated whether there were any advantages in using a prefabricated post in terms of load-bearing capacity, cusp deflection, and stressdistributionof endodontically-treated human upper premolars with MOD restoration. The first null hypothesis was that different techniques would not influencethe cusp deflection and load-bearing capacity of human upper premolars with MOD
Although the passive fit of an implant prosthesis is regarded as one ofthe important factors which affect the longevity of an implant treatment, 41 the correlation between the mechanical fit ofthe framework and the bio- logical influenceonthe surrounding tissue still lacks scien- tific evidences. 9,42,43 However, the relationship between strain caused by the misfit and the biologic response ofthe surrounding tissue could only be discussed, after the in vivo assessment ofthe strain developmentis established. 44 Further clinical studies and cadaver researches is needed to evaluate the strain development in the actual clinical set- tings.
MATERIALS AND METHODS
In this study, the modeling was based onthe missing seg- ment ofthe right posterior mandible. A mandible block model was fabricated to have a regular shape with theheightof 23 mm, mesiodistal width of 20 mm, the maxi- mum buccolingual width of 15 mm and the uniform thick- ness ofthe cortical bone by scanning bones in the area of right molar teeth using a CT and extending this shape in the direction ofthe cross-section. The mandible model consisted ofthe cortical bone and the cancellous bone, modeled in a simple shape to set a uniform thickness ofthe cortical bone at 2 mm. Crown was modeled to have a dimension oftheheightof 10.5 mm, the mesiodistal width of 10 mm, and the buccolingual width of 13 mm, which was extended in the lingual direction by 4 mm to ensure the application of offset loads of 2, 3, 4, 5, 6, and 7 mm onthe lingual side. The top occlusal plane was modeled to a shape of a simple cusp. The implant was modeled by measuring the US II system (Osstem Implant, Pusan, Korea) that is an external type implant with the dimension ofthe 5.0 mm diameter and the 11 mm length. All models used in this study were generated using SolidWorks (DS SolidWorks Corp., Waltham, MA, USA), a commercial 3-dimensional CAD. The modeling was performed such that there was no choice but to add lingual offset to the mandibular implant crown where the resorption ofthe maxillary buccal and mandibular lingual alveolar bone was severe. Firstly, Model v0 was assigned to the case that the vertical load of 300 N was applied onthe center ofthe implant, followed by Models v2 to v7 corresponding to the vertical loads offset to the lingual side at 2, 3, 4, 5, 6, and 7 mm, respectively.
Key Words : Boundary shape (테두리 모양), Weld specimen (용접시편), Finite element method (유한 요소법)
In finite element analysis of mechanical behavior of weld, typical process is first to obtain a finite element model containing residual stress by conducting welding analysis and then to examine the computational specimen for various external loading. The numerical specimen with residual stress has irregular boundary lines since one usually begins the welding analysis from a body having regular straight boundary lines and large thermal contraction takes place during cooling of weld metal. We notice that these numerical weld specimens are different from the real weld specimens as the real specimens are usually cut from a bigger weld part and consequently have straight boundaries neglecting elastic relaxation associated with the cutting. In this paper, an iterative finite element method is described to obtain a weld specimen which is bounded by straight lines. The stress distributions of two types of weld specimen, one with regular and the other with irregular boundaries, are compared to check the effect ofthe boundary shape. Results show that thestressdistribution can be different when large plastic deformation is induced by the application of external loading. In case of elastic small deformation, the difference turns out almost negligible.
time points. Because participants were patients newly diagnosed with advanced gastric cancer and supposed to receive chemotherapy for the first time, the point for initial assessment would be related to the time of acute high stress with patients’ emotional disturbance from cancer diagnosis and anticipatory fear of chemotherapy. On the other hand, the point for follow-up assessment would be related to period of long-lasting stress during 6 weeks of palliative chemotherapy. For the sample as a whole, paired-sample t-test over time showed that anxiety level at follow-up point was not significantly different from initial state, whereas depression level at follow-up point was significantly higher than initial state (8.5 ± 5.1 vs. 7.7 ± 4.1, p=0.038). For the FKBP5 genotypes, as shown in Figure 2, there were no significant differences of initial anxiety and depression levels among the three groups on each SNP, whereas distress level at 6 week follow-up tends to be different depending on FKBP5 genotypes. These findings indicate that the genetic variants of FKBP5 may play an important role in individual vulnerability to prolonged stress response rather than acute stress response. Not surprisingly, this can be explained by alteration ofthe GR sensitivity after prolonged stress exposure, because FKBP5 expression is associated with receptor sensitivity.
Table 3.1-3.3에서 ˆ σ 1 과 ˆ σ 2 의 MSE가 차이나는 것보다는 그 정도가 매우 미약하다. 한편 중도절단모형 이 모수 σ를 포함하지 않는다고 가정한 ˆ σ 0 의 경우 Table 3.1-3.3의 경우와 똑같은 경향을 보이고 있으 며 MSE가 상대적으로 크게 나타났다.
Table 3.4 Comparison of estimates when the true model is F T = (F Y 0 ) β2 and the true value is σ = 0.5 n γ β 1 β 2 σ ˆ 0 ˆ σ 1 σ ˆ 2 MSE(ˆ σ 0 ) MSE(ˆ σ 1 ) MSE(ˆ σ 2 )
Dept. of Nursing, Pukyong National University ***
요 약 본 연구에서는 지각된 스트레스 , 스트레스 대처 , 완벽주의 , 자아존중감이 대학생의 정신건강에 미치는 영향
에 대해 살펴봄으로써 이들의 정신건강 증진을 위한 방법을 모색하고자 하였다 . K 도의 3 개 대학에 재학 중인 209 명 의 남녀 대학생을 대상으로 설문조사를 실시한 후 SPSS 18.0 을 이용하여 빈도 , 피어슨 상관관계 , 회귀분석을 실시하 였다 . 대학생의 정신건강은 지각된 스트레스 , 과업중심 및 정서중심 스트레스 대처 , 사회적으로 부과된 완벽주의 , 자 아존중감과 유의한 상관관계가 있었다 . 본 연구결과를 토대로 한 대학생의 정신건강 증진을 위해 대학생의 사회성을 강화하고 , 신체활동증진 및 자아존중감 증진을 위한 다학제적 교육프로그램 개발이 필요하다고 판단된다 .