• 한국안광학회지
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• 제12권4호
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• pp.29-35
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• 2007

본 연구는 착용하고 있는 콘택트렌즈의 종류에 따른 각막 중심 두께의 차이를 밝히고자 하였다. 20 30대 394명을 대상으로 초음파 각막 두께 측정계를 이용하여 각막 중심 두께를 측정하였다. 콘택트렌즈를 착용한 경험이 없는 Group 1의 각막 중심 두께는 성별 뿐만 아니라 좌우안 간에도 차이가 나타나지 않았으나, 굴절이상도가 높아질수록 얇아지는 경향을 보였다. 소프트콘택트렌즈만을 착용한 Group 2는 착용기간이 길어질수록 각막 중심 두께가 얇았으며, 10년 이상 착용안의 경우 4년 이하 착용안보다 각막 중심 두께가 유의하게 얇았다. 4년 이하의 기간 동안 RGP 렌즈만을 착용한 Group 3의 경우 소프트 콘택트렌즈만을 착용한 Group 2와 각막 중심 두께가 차이가 없었다. 또한, 소프트콘택트렌즈를 착용한 후 RGP 렌즈로 교체하여 사용하고 있는 Group 4와 Group 2의 각막 중심 두께를 비교하였을 때 통계적으로 유의한 차이가 없었다. 그러나, PMMA(polymethyl methacyrlate) 재질의 하드렌즈를 착용한 후 소프트 콘택트렌즈로 교체한 Group 5는 소프트 콘택트렌즈만을 착용한 Group 2에 비해 통계적으로 유의하게 각막 중심 두께가 얇았다.

• The Journal of Advanced Prosthodontics
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• 제15권5호
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• pp.227-237
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• 2023

PURPOSE. This study aimed to assess and compare the color stability, flexural strength (FS), and surface roughness of occlusal splints fabricated from heat-cured acrylic resin, milled polymethyl methacrylate (PMMA)-based resin, and 3D-printed (PMMA) based-resin. MATERIALS AND METHODS. Samples of each type of resin were obtained, and baseline measurements of color and surface roughness were recorded. The specimens were divided into three groups (n = 10) and subjected to distinct aging protocols: thermomechanical cycling (TMC), simulated brushing (SB), and control (without aging). Final assessments of color and surface roughness and three-point bending test (ODM100; Odeme) were conducted, and data were statistically analyzed (2-way ANOVA, Tukey, P <.05). RESULTS. Across all resin types, the most significant increase in surface roughness (Ra) was observed after TMC (P < .05), with the 3D-printed resin exhibiting the lowest Ra (P < .05). After brushing, milled resin displayed the highest Ra (P < .05) and greater color alteration (∆E₀₀) compared to 3D-printed resin. The most substantial ∆E₀₀ was recorded after brushing for all resins, except for heat-cured resin subjected to TMC. Regardless of aging, milled resin exhibited the highest FS (P < .05), except when compared to 3D-printed resin subjected to TMC. Heat-cured resin exposed to TMC demonstrated the lowest FS, different (P < .05) from the control. Under control conditions, milled resin exhibited the highest FS, different (P < .05) from the brushed group. 3D-printed resin subjected to TMC displayed the highest FS (P < .05). CONCLUSION. Among the tested resins, 3D-printed resin demonstrated superior longevity, characterized by minimal surface roughness and color alterations. Aging had a negligible impact on its mechanical properties.

• 한국진공학회지
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• 제18권5호
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• pp.372-376
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• 2009

현대 반도체 공정에서 일정한 패턴을 생성하기 위하여 리소그래피(Lithography) 공정을 이용하고 있으나 선폭의 감소로 인하여 기존 UV를 이용한 PR(Photoresist) 이외에 e-beam을 이용한 PMMA(Polymethyl methacrylate) 리소그래피에 대한 관심이 높아지고 있다. 또한 리소그래피에 의하여 생성된 패턴은 이후 세정 공정에서 잔류물을 제거하는 과정에서 패턴 붕괴를 일으키게 되는데 이러한 패턴 붕괴에 대한 방어력은 패턴 형성 물질의 탄성력(Elastic modulus)과 비례하는 것으로 알려져 있다. 이 논문에서 우리는 PMMA의 soft-baking 이후 Hardness(H)와 Elastic modulus(Er)의 변화를 압입력을 25 uN에서 8,500 uN으로 134.52 uN 간격으로 증가시키며 측정하였다. 또한 이 실험에서 Hardness(H)와 Elastic modulus(Er)는 Hysitron사의 Triboindenter를 이용하여 측정하였고 압입팁은 Berkovich 팁을 사용하였다.

• 대한치과기공학회지
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• 제37권4호
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• pp.191-197
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• 2015

Purpose: The purpose of this study was to compare the accuracy of the scan data acquired by the extra-oral and intra-oral scanner. Methods: The maxillary right first molar was made of polymethyl methacrylate(PMMA) specimen. This PMMA specimen was scanned with a engineering scanner and intra-oral scanner. Meanwhile, extra-oral scanner scanned stone die duplicated from PMMA master die. Trueness and precision of scan datas was measured by 3-dimensinal inspection. Independent t-test was conduct to analysis the significant difference(a=0.05). Results: In the trueness analysis, mean of discrepancies were 13.82um for intra oral scanner and 16.84 um for extra-oral scanner. In the precision analysis, mean of discrepancies were 11.72 for inta-oral scanner and 9.2 for extra-oral scanner. Both trueness and precision showed a statistically significant difference (Table 1, p<0.05). Conclusion: Intra-oral scanner can show higher trueness than extra-oral scanner, it has lower precision.

• Imaging Science in Dentistry
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• 제47권2호
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• pp.75-86
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• 2017

Purpose: The purpose of this study was to apply a newly developed free software program, at low cost and with minimal time, to evaluate the quality of dental and maxillofacial cone-beam computed tomography (CBCT) images. Materials and Methods: A polymethyl methacrylate (PMMA) phantom, CQP-IFBA, was scanned in 3 CBCT units with 7 protocols. A macro program was developed, using the free software ImageJ, to automatically evaluate the image quality parameters. The image quality evaluation was based on 8 parameters: uniformity, the signal-to-noise ratio (SNR), noise, the contrast-to-noise ratio (CNR), spatial resolution, the artifact index, geometric accuracy, and low-contrast resolution. Results: The image uniformity and noise depended on the protocol that was applied. Regarding the CNR, high-density structures were more sensitive to the effect of scanning parameters. There were no significant differences between SNR and CNR in centered and peripheral objects. The geometric accuracy assessment showed that all the distance measurements were lower than the real values. Low-contrast resolution was influenced by the scanning parameters, and the 1-mm rod present in the phantom was not depicted in any of the 3 CBCT units. Smaller voxel sizes presented higher spatial resolution. There were no significant differences among the protocols regarding artifact presence. Conclusion: This software package provided a fast, low-cost, and feasible method for the evaluation of image quality parameters in CBCT.

• Journal of Korean Neurosurgical Society
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• 제61권2호
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• pp.258-266
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• 2018

Objective : The diagnosis of insufficiency fractures of the sacrum in an elder population increases annually. Fractures show very different morphology. We aimed to classify sacral insufficiency fractures according to the position of cortical break and possible need for intervention. Methods : Between January 1, 2008 and December 31, 2014, all patients with a proven fracture of the sacrum following a low-energy or an even unnoticed trauma were prospectively registered : 117 females and 13 males. All patients had a computer tomography of the pelvic ring, two patients had a magnetic resonance imaging additionally : localization and involvement of the fracture lines into the sacroiliac joint, neural foramina or the spinal canal were identified. Results : Patients were aged between 46 and 98 years (mean, 79.8 years). Seventy-seven patients had an unilateral fracture of the sacral ala, 41 bilateral ala fractures and 12 patients showed a fracture of the sacral corpus : a total of 171 fractures were analyzed. The first group A included fractures of the sacral ala which were assessed to have no or less mechanical importance (n=53) : fractures with no cortical disruption ("bone bruise") (A1; n=2), cortical deformation of the anterior cortical bone (A2; n=4), and fracture of the anterolateral rim of ala (A3; n=47). Complete fractures of the sacral ala (B; n=106) : parallel to the sacroiliac joint (B1; n=63), into the sacroiliac joint (B2; n=19), and involvement of the sacral foramina respectively the spinal canal (B3; n=24). Central fractures involving the sacral corpus (C; n=12) : fracture limited to the corpus or finishing into one ala (C1; n=3), unidirectional including the neural foramina or the spinal canal or both (C2; n=2), and horizontal fractures of the corpus with bilateral sagittal completion (C3; n=8). Sixty-eight fractures proceeded into the sacroiliac joint, 34 fractures showed an injury of foramina or canal. Conclusion : The new classification allowes the differentiation of fractures of less mechanical importance and a risk assessment for possible polymethyl methacrylate leaks during sacroplasty in the direction of the neurological structures. In addition, identification of instable fractures in need for laminectomy and surgical stabilization is possible.

• 한국초전도ㆍ저온공학회논문지
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• 제19권1호
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• pp.47-50
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• 2017

Carbon is proven to be very effective in pinning the magnetic vortices and improving the superconducting performance of $MgB_2$ at high fields. In this work, we have used polymethyl methacrylate (PMMA) polymer as a safe and cost effective carbon source. The effects of molecular weight of PMMA on crystal structure, microstructure as well as on superconducting properties of $MgB_2$ were studied. X-ray diffraction analysis revealed that there is a noticeable shift in (100) and (110) Bragg reflections towards higher angles, while no shift was observed in (002) reflections for $MgB_2$ doped with different molecular weights of PMMA. This indicates that carbon could be substituted in the boron honeycomb layers without affecting the interlayer interactions. As compared to undoped $MgB_2$, substantial enhancement in $J_c(H)$ properties was obtained for PMMA-doped $MgB_2$ samples both at 5 K and 20 K. The enhancement could be attributed to the effective carbon substitution for boron and the refinement of crystallite size by PMMA doping.

• 대한치과기공학회지
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• 제41권4호
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• pp.263-269
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• 2019

Purpose: The purpose of this study was to evaluate the internal fitness of prostheses fabricated with non-contact extra-oral scanner and those fabricated with intra-oral video scanner, with a comparative accuracy analyses of their precision and trueness. Methods: A polymethyl methacrylate (PMMA) model was fabricated by replicating a master model. The prostheses in the first group were fabricated based on the PMMA model with an intra-oral video scanner (IVS group). Following the fabrication of work models with Type IV Stone that were based on the PMMA model, the prostheses in the second group were fabricated with a non-contact extra-oral scanner (ENB group). The precision and trueness of the prostheses were calculated from comparisons of the three-dimensional images of the internal surfaces of the prostheses and those of the master model. Kruskal-Wallis tests were used to determine the statistical significance, with the level of type 1 error set at 0.05. Results: Trueness (P < 0.009) and precision (P < 0.001) did not differ significantly between the ENB and IVS groups. The IVS group exhibited lower trueness values and larger precision values than the ENB group. Conclusion: Although no significant differences were found in the internal fitness of the prostheses that were fabricated by the two different scanners, the intraoral video scanner-fabricated prostheses had better trueness, whereas the non-contact extra-oral scanner-fabricated prostheses had better precision.

• 한국진공학회지
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• 제16권3호
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• pp.221-226
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• 2007

광 발광성 (photoluminescence, PL)과 광 반사성(reflectivity)의 두 가지 광학적 성질을 동시에 가지고 있는 새로운 다층 DBR(distributed Bragg reflector) 다공성 실리콘 composite 필름을 개발하였다. 발광 효율이 높은 실리콘 고분자 폴리실올을 PMMA(polymethylmethacrylate)에 첨가하여 다층 DBR 다공성 실리콘 표면에 코팅을 한 composite 필름을 제조하였다. 이 composite 필름은 510 nm에서의 발광스펙트럼과 565 nm에서의 반사스펙트럼을 동시에 나타낸다. 이러한 composite 필름은 광학적 정보가 저장되어있고 물리적인 힘을 가하여도 그 광학적 정보를 잃지 않는 장점을 갖는다. 또한 다층 DBR 다공성 실리콘 필름은 쉽게 부서지는 단점 때문에 다루기가 어려운 반면 composite 필름은 고분자로 고형화 되어있으므로 기계적인 안정도를 증가시킬 수 있었다.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• 제26권6호
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• pp.672-676
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• 2000

One of the current treatment methods for chronic osteomyelitis is removal of the infected and necrotic tissue to reduce the bacterial concentration as much as possible. This is performed concomitantly with antibiotic therapy. Chronic osteomyelitis(C.O.) implies chronic ischemia of the diseased bone. Thus, the treatment for C.O. requires high systemic level of antibiotics. In some cases, however, inherent undesirable adverse effects(for example, nephrotoxicity, ototoxicity, and others) may render this course of treatment difficult. Knowing that residual monomers are released from hardened bone cement, installation of antibiotic-impregnated PMMA(polymethyl-methacrylate) beads in situ have been one of treatment methods of C.O. When introduced into the wound, they established an exceedingly high level of local antibiotics for prolonged period without high systemic level of antibiotics. We experienced favorable results with vancomycin-impregnated PMMA beads for the treatment of C.O. of the mandible. So, we report it with literature reviews.