• 대한치과교정학회지
• /
• 제52권3호
• /
• pp.201-209
• /
• 2022

Objective: To compare the removal torque of microimplants upon post-use removal and post-retention removal and to assess the influencing factors. Methods: The sample group included 241 patients (age, 30.25 ± 12.2 years) with 568 microimplants. They were divided into the post-use (microimplants removed immediately after use or treatment) and post-retention (microimplants removed during the retention period) removal groups. The removal torque in both groups was assessed according to sex, age, placement site and method, and microimplant size. Pearson correlation and multiple linear regression analyses were performed for evaluating variables influencing the removal torque. Results: The mean period of total in-bone stay of microimplants in the post-retention removal group (1,237 days) was approximately two times longer than that in the post-use removal group (656.28 days). The removal torques in the post-retention removal group (range, 4-5 N cm) were also higher than those in the post-use removal group. The mandible and pre-drilling groups demonstrated higher placement and removal torques than did the maxilla and no-drilling groups, respectively. In the no-drilling post-use removal group, the placement torque and microimplant length positively correlated with the removal torque. In the post-retention removal group, unloading in-bone stay period and microimplant diameter positively correlated with the removal torque in the no-drilling and pre-drilling methods, respectively. Conclusions: The removal torques differed according to the orthodontic loading and removal time of microimplants. With prolonged retention of microimplants inserted using the no-drilling method, the removal torque was clinically acceptable and positively correlated with the unloading in-bone stay period.

• Restorative Dentistry and Endodontics
• /
• 제46권4호
• /
• pp.50.1-50.8
• /
• 2021

Although several techniques have been proposed to remove fiber-reinforced composite (FRC) post, no safe and efficient technique has been established. Recently, a guided endodontics technique has been introduced in cases of pulp canal obliteration. This study describes 2 cases of FRC post removal from maxillary anterior teeth using this guided endodontics technique with a dental operating microscope. Optically scanned data set from plaster cast model was superimposed with the data set of cone-beam computed tomography. By implant planning software, the path of a guide drill was selected. Based on them, a customized stent was fabricated and utilized to remove the FRC post. Employing guided endodontics, the FRC post was removed quickly and safely with minimizing the loss of the remaining tooth structure. The guided endodontics was a useful option for FRC post removal.

• Restorative Dentistry and Endodontics
• /
• 제30권3호
• /
• pp.215-220
• /
• 2005

포스트가 축조된 치아를 재근관 치료하는 경우 성공적인 비외과적 재근관치료를 시행하기 위해서는 포스트 제거가 선행되어야 한다. 기존의 포스트를 제거하는 방법으로는 초음파기구, Ruddle post removal system, Eaggler post remover, Masserann kit을 이용하는 방법 등 여러 가지가 소개 되고 있으나 기존의 방법들은 각 기구에 맞게 코어를 삭제해야 하는 시간과 많은 노력이 요구되며 포스트 제거시 치아나 포스트의 파절이 유발되기도 한다 그러나 최근에는 기존의 방법과는 다른 ATD automatic bridge remover를 이용해 포스트를 제거하는 새로운 방법이 소개되고 있으며 코어에 구멍을 형성하는 시간만 소요되어 비교적 빨리 제거 할 수 있다는 장점을 가지고 있다. 따라서 본 증례에서는 ATD automatic bridge remover를 이용해 주조포스트를 제거하고 성공적으로 재근관치료를 시행한 증례에 대해서 보고하고자 한다.

• 한국정밀공학회지
• /
• 제17권5호
• /
• pp.116-123
• /
• 2000

This paper presents an NC code post-processor that adjusts feedrates to keep the variation of metal removal rate along the tool paths minimum. Metal removal rate is estimated by virtually machining the part, whose surface model is built from a series of NC codes defined in operation plan, with cutting-tool-assembly models, whose geometry are defined in a machining database. The NC code post-processor modifies the feedrates by the adjustment rules, which are based on the machining knowledge for effective machining. This paper illustrates a procedure fur grouping machining conditions and we also show how to determine an adjustment rule for a machining-condition group. An example part was machined and it shows that the variation of cutting force was dramatically reduced after applying the NC code post-processor. The NC code post-processor is expected to increase productivity while maintaining the quality of the machined part.

• 한국환경보건학회지
• /
• 제27권4호
• /
• pp.93-98
• /
• 2001

Wastewaters produced in textile industrial processes contain dyes which are not easily amenable to biological treatment. The object of this study is to determine the post-treatment system of biological process for the textile wastewater by comparing three different types of chemical process, which were 1) post-treatment by ozone or UV, 2) post-treatment by coagulation,3) post-treatment by ozone or UV followed by coagulation. In an application ozone or UV as a post-treatment, color was generally decreased with time, however, SCOD removal effect was not that good. When coagulation was used as point-treatment process, the effluent quality was satisfying. Therefore, the application of coagulation process as a post-treatment of biological process would be more desirable than that as a ozone or UV.

• Restorative Dentistry and Endodontics
• /
• 제22권1호
• /
• pp.181-192
• /
• 1997

The difficulty of endodontic retreatment depends on various factors and it is affected by retention of post. In this experiment, root canal therapy was done in extracted human teeth and cut into 10mm length from the root apex, and then cemented by zinc phosphate cement, Vitremer$^{(R)}$(glass ionomer) luting cement and Panavia 21$^{(R)}$(resin cement). Post preparation was done by #4 Parapost drill at 6mm length and cement was inserted by lentulo spiral. After 24 hours, tensile bond strength, post removal time was measured after the ultrasonic application and the separation site was measured. The following results were obtained. 1. In measuring tensile bond strength, there is no statistical difference between zinc phosphate cement and Panavia 21$^{(R)}$, but Vitremer$^{(R)}$ showed lower value compared with those two cements. (p<0.001) 2. When the post removal time was measured after ultrasonic application, significant different value in order of Panavia 21$^{(R)}$, zinc phosphate cement and Vitremer$^{(R)}$ was shown. (p<0.001) 3. As a result of examining the separating site of each cement, all 16 of zinc phosphate cement group showed the fracture site between cement and post, Vitremer$^{(R)}$ was 13/16, and Panavia 2$^{(R)}$ was 8/16. In case of tooth restoration using Parapost, the use of Panavia 21 showed good retention property than Vitremer$^{(R)}$, but when retreatment is needed the difficulty of post removal will be increased.

• 한국재료학회지
• /
• 제16권2호
• /
• pp.75-79
• /
• 2006

The effect of ozone and/or ultrasound treatments on the efficiency of slurry removal in post sliced cleaning (PSC) of silicon ingot was studied. Efficiency of slurry removal was evaluated as functions of time, temperature and surfactant with DOE (Design of Experiment) method. Residual slurries were observed on the wafer surface in case of cleaning by ozone or ultrasound separately. However, a clean wafer surface was appeared when cleaned with ozone and ultrasound simultaneously. It has found that cleaning time was the main effect among temperature, time and surfactant. Elevated temperature, addition of surfactant and high ozone concentration helped to accelerate efficient removal of slurry. The improvement of removal efficiency seems to be related to the formation of more active OH radicals. The highly cleaned surface was achieved at 10 wt% ozone, 1 min and 10 vol% surfactant with ultrasound. Application of ozone and ultrasound might be a useful method for PSC process in wafer cleaning.

• 한국환경보건학회지
• /
• 제26권4호
• /
• pp.45-48
• /
• 2000

Reverse osmosis filtration(RO) system and ultrafiltration(UF) system are principally use for domestic home drinking water treatment systems. The object of this study is to make a comparison between two systems in terms of theirs abilities to remove RNA coilphage QB as an indicator of pathogenic enteroviruses. The virus removal ratio of RO system was 99.999%, which was higher than EPA virus treatment guideline(99.99%). In the course of filtration, removal ratios of sediment filter, pre-carbon filter, reverse osmosis membrane and post-carbon filter were 75.000%, 93.208%, 99.997% and 99.999%, repectively. In case of UF system, virus removal ratio was 99.708%. Removal ratios of sediment filter, pre-carbon filter, post-carbon filter and ultrafiltration membration membrane were 71.038%, 91.530%, 98.283% and 99.708%, respecively, in UF steps. Therefore, RO system is more effective than UF system in virus removal.

• Journal of Biosystems Engineering
• /
• 제39권4호
• /
• pp.336-344
• /
• 2014

Purpose: In this study, the effect of milling on paddy rice stored at low temperature, the changes in grain temperature of bulk storage bags exposed at room temperature, the post-milling water content of paddy rice, the whiteness of rice, and the rate of pest incidence were investigated and data were analyzed. Methods: Changes in temperature inside the bulk storage bags kept at low temperature and grain temperature after exposure to room temperature were measured. Experiments were conducted for identifying the reasons of post-milling quality changes in paddy rice stored at low temperature. Results: It was determined that a short-term increase of water content in paddy rice was directly related to surface condensation, and that rice should be milled at least 72 h after removal from low-temperature storage, in order to completely eliminate surface condensation of paddy rice kept in bulk storage bags. It was observed that post-milling quality of rice changed, but water content was maintained at high levels for more than 18 d in rice that was milled when condensation occurred, regardless of paper or vinyl packaging. Rice whiteness rapidly decreased in rice that was milled when condensation occurred, regardless of packaging, while rice that was milled 72 h or more after removal from low temperature storage did not show any significant changes in whiteness. No pest incidence was observed up to 12 d after removal from low temperature storage, regardless of packaging. Starting at 18 d, after removal from low temperature storage, rice that was milled when condensation occurred, was affected by pests, while 24 d after removal from low temperature storage, all portions of rice were affected by pests. Conclusions: Our results suggest that changes in post-milling quality of rice could be significantly reduced by exposing paddy rice to room temperature for at least 72 h before milling, in order to allow the increase of grain temperature and prevent surface condensation.

• Restorative Dentistry and Endodontics
• /
• 제39권4호
• /
• pp.265-269
• /
• 2014

Objectives: To evaluate the effect of different ultrasonic tip designs on intraradicular post removal. Materials and Methods: The crowns of forty human canine teeth were removed, and after biomechanical preparation and filling, the roots were embedded in acrylic resin blocks. The post spaces were made, and root canal molding was performed with self-cured acrylic resin. After casting (Cu-Al), the posts were cemented with zinc phosphate cement. The specimens were randomly separated into 4 groups (n = 10), as follows: G1 - no ultrasonic vibration (control); G2 - ultrasonic vibration using an elongated cylindrical-shaped and active rounded tip; G3 - ultrasonic vibration with a flattened convex and linear active tip; G4 - ultrasonic vibration with active semicircular tapered tip. Ultrasonic vibration was applied for 15 seconds on each post surface and tensile test was performed in a Universal Testing Machine (Instron 4444 - 1 mm/min). Results: G4 presented the highest mean values, however, with no statistically significant difference in comparison to G3 (p > 0.05). G2 presented the lowest mean values with statistically significant difference to G3 and G4 (p < 0.05). Conclusions: Ultrasonic vibration with elongated cylindrical-shaped and active rounded tip was most effective in reducing force required for intraradicular post removal.