• 한국재료학회지
• /
• 제25권5호
• /
• pp.226-232
• /
• 2015

본 연구에서는 손상된 알루미늄 금형의 복원을 위해 고온플라즈마 용사법을 이용하여 금형의 표면에 $Al/Al_2O_3$ 혼합분말을 용사한 후 코팅층과 모재의 증착강도에 대한 평가를 수행하였다. 증착강도의 평가는 분사노즐의 이동속도, 순수한 알루미늄 bond coat 층의 유무에 따라 평가되었으며, bond coat 층을 생성시키지 않았을 때, 코팅층의 두께는 열팽창에 의한 잔류인장응력의 감소를 위해 두껍지 않아야 하지만 일정두께 이상이 되어야 최대의 증착강도를 얻을 수 있음이 나타났다. 또한 순수한 알루미늄 bond coat 층은 내부 결함이 없는 응고된 금속이기 때문에 두께에 따른 증착강도의 영향을 그대로 받아 두께가 두꺼울수록 bond coat 층을 생성시키지 않은 시험편보다 증착강도가 매우 낮게 측정되었다. 반면, 가장 얇게 bond coating 된 시험편 Bc3(3회의 bond coating층과 분사건의 이동속도가 20 cm/sec인 시험편) 는 bond coating을 하지 않은 시험편 중 가장 높은 증착강도를 가지는 시험편 Wbc20(bond coating층이 없고 분사건의 이동속도가 20 cm/sec인 시험편)보다 약 2배 이상증착강도가 향상되었다. 따라서 금형의 복원시에 중간층의 형성이 반드시 필요하며, 이는 코팅층의 잔류 인장응력을 보완시키며 고인성의 순수한 알루미늄과 같은 코팅층과 유사한 층을 코팅하는 것이 필요한 것으로 사료된다.

• 대한치과보철학회지
• /
• 제40권6호
• /
• pp.545-559
• /
• 2002

There has been increasing use of IPS Empress $2^{(R)}$ owing to easy fabrication method, high esthetics similar to natural teeth, good marginal accuracy, and sufficient fracture strength. However, in clinical application, although a luting agent and the tooth cementation bonding procedure influence the marginal accuracy and fracture strength restoration, there has been a controversy in the selection of proper luting agent. This study was to measure the marginal fidelites and fracture strength of IPS Empress crowns according to three cement types, Protec $cem^{(R)}$, Variolink $II^{(R)}$ and Panavia $21^{(R)}$. After construction of 12 experimental dies for each group, IPS Empress $2^{(R)}$ crowns were fabricated and luted the metal master die prepartion of the maxillary right premolar. Marginal gaps before cementation and after cementation were measured. Buccal incline on the functional cusp of specimens were loaded until the catastrophic failure and fracture strength was measured. The results of this study were as follows: 1. The range of gap was $34.04{\pm}4.84{\mu}m$ before cementation and $37.88{\pm}5.00{\mu}m$ after cementation, which showed significant difference by paired t-test (p<0.05). The difference in the results from marginal accuracy according to measuring point proved to be not statistically significant by two-way ANOVA test (p>0.05). 2. The difference in the results from marginal accuracy according to three cement types Proved that The Variolink $II^{(R)}$ cement group had the least gap, $35.43{\pm}5.03{\mu}m$, and showed superior marginal accuracy while there existed statistic significance in Protec $cem^{(R)}$ cement group, $39.06{\pm}4.41{\mu}m$ or Panavia $21^{(R)}$ cement group, $39.16{\pm}4.39{\mu}m$ by two-way ANOVA test & multiple range test (p<0.05). 3. The difference in the results from fractures strength testing according to three cement type groups proved to be statistically significant (p<0.05). The Variolink $II^{(R)}$ cement group shows highest fracture strength of $1257.33{\pm}226.77N$, Panavia $21^{(R)}$ cement group has $1098.08{\pm}138.45N$, and Protec $cem^{(R)}$ cement group represents the lowest fracture strength of $926.75{\pm}115.75N$. 4. Three different cement groups of different components showed acceptable marginal fidelity and fracture strength. It is concluded that IPS Empress $2^{(R)}$ crowns luted using Variolink $II^{(R)}$ cement group had stronger fracture strength and smaller marginal gap than the other cement groups. Although Variolink $II^{(R)}$ resin cement seemed acceptable to clinical applications in IPS Empress $2^{(R)}$ system, the IPS Empress $2^{(R)}$ system still requires long-term research due to the lack of data in clinical applications.

• 대한치과보철학회지
• /
• 제39권3호
• /
• pp.260-272
• /
• 2001

All-ceramic restorations have had a more limited life expectancy than metal ceramic restorations because of their low strength. Their relatively lower strength and resistance to fracture have restricted the use of all-ceramic crowns to anterior applications where occlusal loads are lower. But there has been increasing interest in all-ceramic restorations because patients are primarily concerned with improved esthetics. Many efforts have been made to in prove the mechanical properties of dental ceramics. This study was designed to elucidate the influence of the luting agent on the strength of the Empress 2 crown (staining technique) cemented on human teeth. Seventy extracted human permanent molar teeth were chosen. Teeth were prepared for Empress 2 crowns with milling machine on a surveyor. A dental bur was placed in the mandrel that was positioned so that the long axis of the bur was perpendicular to the surveyor base. Dimensions of the Empress 2 crown preparation were $6^{\circ}$ taper on each side, $1.5{\pm}0.1mm$ shoulder margin, and 4mm crown height. The luting cements used in this study were as follow: 1. Uncemented 2. Zinc phosphate cements (Confi-Dental) 3. Conventional glass ionomer cement : Fuji 1 (GC) 4. Resin-modified glass ionomer cements : Fuji plus (GC) 5. Adhesive cements : Panavia F (Kuralay), Variolink II (Vivadent), Choice (Bisco). Fracture test using Instron. The crowns were loaded in compressive force to evaluate the effect of these cements on the breaking strength of these all-ceramic crowns. A steel ball with a diameter of 4mm was placed on the occlusal surface and load was applied to the steel ball by a cylindrical bolt with a crosshead speed of 0.5mm per minute until fracture occurred. The fractured surface was examined using Scanning Electron Microscopic Image (SEM) to discover the correlation between fracture strength and bonding capacity. Within the limitation of this in vitro study design, the results were as follows : 1. fomentations significantly increased the fracture resistance of Empress ceramic crowns compared to control. Uncemented (206.9 N): ZPC (812.9 N): Fuji 1 (879.5 N): Fuji Plus (937.7 N): Choice (1105.4 N): Variolink II (1221.1 N): Panavia F (1445.2 N). 2. Resin luting agent, treated by a silane bond enhancing agents, yielded a significant increase in fracture resistance. In some of the Panavia F group, a fracture extended into dentin. 3. According to SEM images of fractured Empress crowns, the stronger the bond at both interfaces(crown and die), the more fracture strength was acquired.

• Design & Manufacturing
• /
• 제17권1호
• /
• pp.20-26
• /
• 2023

Lab-on-a-disc is a circular disc shape of cartridge that can be used for blood-based liquid biopsy to diagnose an early stage of cancer. Currently, liquid biopsies are regarded as a time-consuming process, and require sophisticated skills to precisely separate cell-free DNA (cfDNA) and circulating tumor cells (CTCs) floating in the bloodstream for accurate diagnosis. However, by applying the lab-on-a-disc to liquid biopsy, the entire process can be operated automatically. To do so, the lab-on-a-disc should be designed to prevent blood leakage during the centrifugation, transport, and dilution of blood inside the lab-on-a-disc in the process of liquid biopsy. In this study, the main components of lab-on-a-disc for liquid biopsy are fabricated by injection molding for mass production, and ultrasonic welding is employed to ensure the bonding strength between the components. To guarantee accurate ultrasonic welding, the flatness of the components is optimized numerically by using the response surface methodology with four main injection molding processing parameters, including the mold & resin temperatures, the injection speed, and the packing pressure. The 27 times finite element analyses using Moldflow® reveal that the injection time and the packing pressure are the critical factors affecting the flatness of the components with an optimal set of values for all four processing parameters. To further improve the flatness of the lab-on-a-disc components for stable mass production, a quarter-disc shape of lab-on-a-disc with a radius of 75 mm is used instead of a full circular shape of the disc, and this significantly decreases the standard deviation of flatness to 30% due to the reduced overall length of the injection molded components by one-half. Moreover, it is also beneficial to use a quarter disc shape to manage the deviation of flatness under 3 sigma limits.