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The effect of various veneering techniques on the marginal fit of zirconia copings
Mahroo Vojdani,Rashin Giti,Masumeh Taghva,Soheil Pardis,Kianoosh Torabi 대한치과보철학회 2015 The Journal of Advanced Prosthodontics Vol.7 No.3
PURPOSE This study aimed to evaluate the fit of zirconia ceramics before and after veneering, using 3 different veneering processes (layering, press-over, and CAD-on techniques). MATERIALS AND METHODS Thirty standardized zirconia CAD/CAM frameworks were constructed and divided into three groups of 10 each. The first group was veneered using the traditional layering technique. Press-over and CAD-on techniques were used to veneer second and third groups. The marginal gap of specimens was measured before and after veneering process at 18 sites on the master die using a digital microscope. Paired t-test was used to evaluate mean marginal gap changes. One-way ANOVA and post hoc tests were also employed for comparison among 3 groups (α=.05). RESULTS Marginal gap of 3 groups was increased after porcelain veneering. The mean marginal gap values after veneering in the layering group (63.06 µm) was higher than press-over (50.64 µm) and CAD-on (51.50 µm) veneered groups (P<.001). CONCLUSION Three veneering methods altered the marginal fit of zirconia copings. Conventional layering technique increased the marginal gap of zirconia framework more than pressing and CAD-on techniques. All ceramic crowns made through three different veneering methods revealed clinically acceptable marginal fit.
The effect of various veneering techniques on the marginal fit of zirconia copings
Torabi, Kianoosh,Vojdani, Mahroo,Giti, Rashin,Taghva, Masumeh,Pardis, Soheil The Korean Academy of Prosthodonitics 2015 The Journal of Advanced Prosthodontics Vol.7 No.3
PURPOSE. This study aimed to evaluate the fit of zirconia ceramics before and after veneering, using 3 different veneering processes (layering, press-over, and CAD-on techniques). MATERIALS AND METHODS. Thirty standardized zirconia CAD/CAM frameworks were constructed and divided into three groups of 10 each. The first group was veneered using the traditional layering technique. Press-over and CAD-on techniques were used to veneer second and third groups. The marginal gap of specimens was measured before and after veneering process at 18 sites on the master die using a digital microscope. Paired t-test was used to evaluate mean marginal gap changes. One-way ANOVA and post hoc tests were also employed for comparison among 3 groups (${\alpha}$=.05). RESULTS. Marginal gap of 3 groups was increased after porcelain veneering. The mean marginal gap values after veneering in the layering group ($63.06{\mu}m$) was higher than press-over ($50.64{\mu}m$) and CAD-on ($51.50{\mu}m$) veneered groups (P<.001). CONCLUSION. Three veneering methods altered the marginal fit of zirconia copings. Conventional layering technique increased the marginal gap of zirconia framework more than pressing and CADon techniques. All ceramic crowns made through three different veneering methods revealed clinically acceptable marginal fit.
임성준(Seongjune Lim),박민영(Minyoung Park),손대현(Daehyun Son),이대인(Dae In Lee),임현준(Hyunjune Yim) 대한기계학회 2021 大韓機械學會論文集A Vol.45 No.11
프레스 금형의 캠 모듈을 구성하는 부품들은 큰 성형력을 지탱해야 하므로 서로 간에 크고 많은 접촉면을 요구하며, 각 부품의 접촉면은 금형의 복잡한 구조로 인해 제한된 위치에 놓이게 된다. 많은 수의 접촉면은 과잉제약을 유발하고, 이는 프레스 작업의 재현성을 감소시켜 제품의 품질 일관성을 저하시킨다. 또, 접촉면들의 위치가 한쪽으로 치우치면 금형 성형면의 간격이 금형 부품의 편차에 민감해져서 요구되는 치수 조건을 만족하기 어려워진다. 본 논문에서는 부품의 수가 많은 더블 캠 모듈을 예시로 하여 기존 프레스 금형 설계의 문제점을 분석하고, 강건한 적정제약이 구현되는 설계 개선안을 개발하여 제시하였다. 공차해석을 통해 개발된 개선안이 성형면의 간격 요건 만족율을 현저히 향상시킴을 확인하였다. 본 연구에서 제안하는 강건 적정제약 설계는 모든 조립품의 설계에 적용되는 중요한 원리이므로 설계자들이 이를 적용하여 높은 품질을 경제적으로 확보할 수 있기를 기대한다. The parts that comprise a cam module of a press die require many large contact surfaces with each other because they need to deliver large forming loads for production, and each contact surface has limited area for location due to the complex structure of the press die. Many contact surfaces can lead to over-constrained design, thereby yielding low repeatability among successive operations. Also, contact surfaces distributed over only a small region of a part may increase the sensitivity to part variations, leading to a less-robust design. In this paper, as an example, the existing design of a double cam module with many parts was analyzed to find that it is a highly over-constrained design and suffers from the lack of robustness. An improved design was developed by eliminating all over-constraints and increasing the robustness, which exhibited, via tolerance simulations, substantial improvements of the critical sheet forming clearance. As the general principles of proper-constraint and robust design are applicable to any assembly, it is expected that designers of mechanical components will adopt them to improve product quality at lower cost.
Lead Frame용 캠 프레스의 이송장치 고속화 설계
이찬홍,임선종 한국공작기계학회 2007 한국공작기계학회 추계학술대회논문집 Vol.2007 No.-
The high speed feeding units, that are known generally weak points at the high speed semiconductor press are developed to increase feeding velocity up to 155%. The new designed feeding units has the performance, feeding velocity 170spm, positioning accuracy under 100㎛, decrease of link joint in feeding units, overload monitoring system with high sensitivity.
Seen-Young Kang,Ha-Na Lee,Ji-Hwan Kim,Woong-Chul Kim 대한치과보철학회 2018 The Journal of Advanced Prosthodontics Vol.10 No.5
PURPOSE. The purpose of this study was to evaluate the marginal discrepancy of heat-pressed ceramic veneers manufactured using a CAD/CAM system. MATERIALS AND METHODS. The ceramic veneers for the abutment of a maxillary left central incisor were designed using a CAD/CAM software program. Ten veneers using a microstereolithography apparatus (AM group), ten veneers using a five-axis milling machine (SM group), and ten veneers using a traditional free-hand wax technique (TW group) were prepared according to the respective manufacturing method. The ceramic veneers were also fabricated using a heat-press technique, and a silicone replica was used to measure their marginal discrepancy. The marginal discrepancies were measured using a digital microscope (×160 magnification). The data were analyzed using a nonparametric Kruskal-Wallis H test. Finally, post-hoc comparisons were conducted using Bonferroni-corrected Mann-Whitney U tests (α=.05). RESULTS. The mean켚D of the total marginal discrepancy was 99.68±28.01 μm for the AM group, 76.60±28.76 μm for the SM group, and 83.08±39.74 μm for the TW group. There were significant differences in the total marginal discrepancies of the ceramic veneers (P<.05). CONCLUSION. The SM group showed a better fit than the AM and TW groups. However, all values were within the clinical tolerance. Therefore, CAD/CAM manufacturing methods can replace the traditional free-hand wax technique.