Sung Ho Park

Hardness of celluloid strip-finished or polished composite surfaces with time ☆ ☆☆

STATEMENT OF PROBLEM An in-vitro study revealed that a celluloid strip-finished composite surface discolored more than the polished composite surface. Thus, the celluloid strip-finished composite surface may not cure enough compared with the polished composite surface. PURPOSE This study tested the hypothesis that the celluloid strip-finished composite surface did not cure enough compared with the polished composite surface. METHODS AND MATERIAL The composite was placed in a 1.5-mm thick aluminum mold and the upper surface was covered with a celluloid strip. Composite was light cured for 60 seconds, then a layer of approximately 200 microm thick was ground away from the lower surface and polished. The hardness of the upper composite surface that was polymerized under a celluloid strip and the polished lower surface were measured with Vickers hardness measuring instrument 15 minutes, 6 hours, and 6 days after light curing. The hardnesses of polished and celluloid strip-finished surfaces were compared using a paired t test. One-way ANOVA and Tukey was used for tests for the significant differences in hardnesses between 15 minutes, 6 hours, and 6 days after light curing for a given surface. RESULTS Microhardness of the celluloid strip-finished composite surface was 380.6 N/mm(2) at 15 minutes, 442.5 N/mm(2) at 6 hours, and 519.2 N/mm(2) at 6 days after light curing. Microhardnesses of the polished composite surface was 476.6 N/mm(2) at 15 minutes, 511.7 N/mm(2) at 6 hours, and 535.0 N/mm(2) at 6 days after light curing. The hardness of the celluloid strip-opposed composite surface was significantly lower than that of the polished surface 15 minutes and 6 hours after light curing (P <. 001). There was no difference in hardness between the celluloid strip-opposed surface and the polished surface on the sixth day. CONCLUSION The hardness of the celluloid strip-opposed composite surface was lower than that of the polished surface at 15 minutes and at 6 hours after light curing. However, there was no difference in microhardness in 6 days.

Consistency in the amount of linear polymerization shrinkage in syringe-type composites

OBJECTIVES The purpose of this study was to investigate whether the composite resin in a syringe showed a consistent shrinkage through its content. Additionally, the amount of linear shrinkage was compared between materials. METHODS Five brands of syringe-type and one brand of carpule-type composite resins were used in this study. To each brand, two to three syringes were assigned. In the carpule-type composite, 15 carpules were used. The linear polymerization shrinkage was measured using a custom-made linometer. In this linometer, the amount of displacement of an aluminum disk, which was caused by the linear shrinkage of composite resin, was recorded by a computer every second for 90 s. RESULTS The syringe-type composites showed similar consistencies in the amount of linear shrinkage except one. The linear shrinkage of the carpule-type Tetric Ceram showed more consistency compared with syringe-type composites. The amount of linear polymerization shrinkage varied between materials. SIGNIFICANCE This investigation demonstrates that the use of carpule-type composites is recommended instead of syringe-types, because of the consistency in its linear shrinkage. The custom-made linometer provides an effective way to study polymerization shrinkage.

The influence of elastic modulus of base material on the marginal adaptation of direct composite restoration.

This study compared the marginal adaptation of direct composites under base materials with different elastic moduli. MOD cavities were prepared in 30 teeth. The cervical margin was placed 1 mm above the cementoenamel junction (CEJ) in one side and 1 mm below the CEJ in dentin in the other. The teeth were randomly divided into the following six groups (five teeth each) according to the base materials used: No base (Group 1), experimental flowable composite (Group 2), Helioflow (Ivoclar Vivadent) (Group 3), Tetric Flow (Group 4), Heliomolar HB (Ivoclar Vivadent) (Group 5) and Fuji II LC (Group 6). In Group 1, after etching the cavity enamel with 35% phosphoric acid, the cavities were primed and bonded with AdheSE, then filled with Tetric Ceram according to the manufacturers instructions. In the other groups, after placing the base materials (1 mm thick) into the cavity, the cavity was filled with Tetric Ceram using the same methods as in Group 1. After storing the specimens in distilled water for seven days, they were finished and polished. Using stereomicroscopy at 150x magnification, marginal adaptation of the specimens was determined and the percentage of the imperfect margin (IM%) in the pre-loaded specimens was calculated. A mechanical load was applied using a custom-made Chewing simulator. All specimens were submitted to 600,000 load cycles at 49N with a frequency of 2Hz. The IM% in the post-load specimens was calculated. Repeated measured one-way ANOVA with Tukey was applied to compare the IM% in the six groups at the 95% confidence level. The results of statistical analysis indicated that the IM% was Group 3, 4, 6 < or = 2 < or = 5 < or = 1.

Development of a mobile surveillance robot

An unmanned surveillance robot consists of a machine gun, a laser receiver, a thermal imager, a color CCD camera, and a laser illuminator. It has two axis control systems for elevation and azimuth. A human guard can be replaced with such a robot system to take care of dangerous surveillance tasks. However, the robot system is mounded at a fixed post to take care of surveillance tasks. In order to watch blind areas, it is necessary to modify such a surveillance robot to be installed on an UGV (Unmanned Ground Vehicle) system. Thus, it is required to have a stabilization system to compensate the disturbance from the UGV. In this paper, a simulation based design scheme has been adopted to develop a mobile surveillance robot. The 3D CAD geometry model has first been produced by using Pro-Engineer. The required pan and tilt motor capacities have been analyzed using ADAMS inverse dynamics analysis. A target tracking and stabilization control algorithm of the mobile surveillance robot has been developed in order to compensate the motion of the vehicle which experiences the rough terrain. A virtual motion simulator which reproduces UGV motion has also been developed for a virtual testing of the mobile surveillance robot. To test the performance of the stabilization control system of the robot, ADAMS/simulink co-simulations has been carried out.

Stabilization control for the mobile surveillance robot using motion simulator

A mobile surveillance robot consists of a machine gun, a laser receiver, a thermal imager, a color CCD camera, and a laser illuminator. It has two axis control systems for elevation and azimuth. The robot system is mounded on an UGV (unmanned ground vehicle) system. Thus, it is required to have a stabilization system to compensate the disturbance from the UGV. To develop such a robot, expensive field tests are necessary. To reduce the numbers of field tests, a motion simulator that can regenerate UGV motion is a very effective tool to test the mobile surveillance robot in the laboratory environment. Virtual test of the mobile surveillance robot has been carried out using 3D CAD modeling and ADAMS dynamics and control simulation. Based on the simulation result, actual motion simulator has been fabricated. Stabilization control has been verified by testing the robot with motion simulator.

Evaluation of Resin Composite Translucency by Two Different Methods

The purpose of this study was 1) to compare the translucency of seven different types of composite materials and three different shade categories (dentin, enamel, and translucent) by determining the translucency parameter (TP) and light transmittance (%T) and 2) to evaluate the correlation between the results of the two evaluation methods. Three shades (dentin A3, enamel A3, and clear translucent) of seven composite materials (Beautifil II [BF], Denfil [DF], Empress Direct [ED], Estelite Sigma Quick [ES], Gradia Direct [GD], Premise [PR], and Tetric N-Ceram [TC]) from different manufacturers were screened in this study. Ten disk-shaped specimens (10 mm in diameter and 1 mm in thickness) were prepared for each material. For the TP measurements, the colors of each specimen were recorded according to the CIELAB color scale against white and black backgrounds with a colorimeter and used to calculate the TP value. For the %T measurements, the mean direct transmittance through the specimen in the range between 380 and 780 nm was recorded using a spectrometer and computer software. Two-way analysis of variance (ANOVA) tests were performed to compare the TP and %T for the composite materials and shade categories. One-way ANOVA and Tukey tests were used for the seven composite materials per shade category and the three shade categories per composite material. The correlation between the two evaluation methods was determined using the Pearson correlation coefficient. All statistical procedures were performed within a 95% confidence level. TP differed significantly by composite material within each shade category (p<0.05) and by shade category within each composite material (p<0.05). %T differed significantly by composite material within each shade category (p<0.05) and by shade categories within each composite material (p<0.05), except for BF and ES. For the two evaluation methods, TP and %T, were positively correlated (r=0.626, p<0.05). These methods showed strong correlation for each composite material except ES (r=0.763-0.992, p<0.05) and moderate correlation for each shade category (r=0.403-0.528, p<0.05).

Verification of Camera-Image-Based Target-Tracking Algorithm for Mobile Surveillance Robot Using Virtual Simulation

In this study, a 3-axis camera system design is proposed for application to an existing 2-axis surveillance robot. A camera-image-based target-tracking algorithm for this robot has also been proposed. The algorithm has been validated using a virtual simulation. In the algorithm, the heading direction vector of the camera system in the mobile surveillance robot is obtained by the position error between the center of the view finder and the center of the object in the camera image. By using the heading direction vector of the camera system, the desired pan and tilt angles for target-tracking and the desired roll angle for the stabilization of the camera image are obtained through inverse kinematics. The algorithm has been validated using a virtual simulation model based on MATLAB and ADAMS by checking the corresponding movement of the robot to the target motion and the virtual image error of the view finder.

Interrater and intrarater reliability of FDI criteria applied to photographs of posterior tooth-colored restorations

Statement of problem. Since 2007, the FDI World Dental Federation (FDI) criteria have been used for the clinical evaluation of dental restorations. However, the reliability of the FDI criteria has not been sufficiently addressed. Purpose. The purpose of this study was to assess and compare the interrater and intrarater reliability of the FDI criteria by evaluating posterior tooth‐colored restorations photographically. Material and methods. A total of 160 clinical photographs of posterior tooth‐colored restorations were evaluated independently by 5 raters with 9 of the FDI criteria suitable for photographic evaluation. The raters recorded the score of each restoration by using 5 grades, and the score was dichotomized into the clinical evaluation scores. After 1 month, 2 of the raters reevaluated the same set of 160 photographs in random order. To estimate the interrater reliability among the 5 raters, the proportion of agreement was calculated, and the Fleiss multirater kappa statistic was used. For the intrarater reliability, the proportion of agreement was calculated, and the Cohen standard kappa statistic was used for each of the 2 raters. Results. The interrater proportion of agreement was 0.41 to 0.57, and the kappa value was 0.09 to 0.39. Overall, the intrarater reliability was higher than the interrater reliability, and rater 1 demonstrated higher intrarater reliability than rater 2. The proportion of agreement and kappa values increased when the 5 scores were dichotomized. The reliability was relatively lower for the esthetic properties compared with the functional or biological properties. Conclusions. Within the limitations of this study, the FDI criteria presented slight to fair interrater reliability and fair to excellent intrarater reliability in the photographic evaluation of posterior tooth‐colored restorations. The reliability was improved by simplifying the evaluation scores.

Effects of Age, Sex, and Blood Pressure on the Blood Flow Velocity in Dental Pulp Measured by Doppler Ultrasound Technique

To examine the effects of age, sex, and BP on the PBFV in human maxillary anterior teeth.

Healing of Horizontal Intra-alveolar Root Fractures after Endodontic Treatment with Mineral Trioxide Aggregate

INTRODUCTION The purpose of this retrospective study was to evaluate the healing type and assess the outcome of horizontal intra-alveolar root fractures after endodontic treatment with mineral trioxide aggregate (MTA) as filling material. METHODS The clinical database of the Department of Conservative Dentistry at Yonsei University Dental Hospital, Seoul, Korea, was searched for patients with histories of intra-alveolar root fractures and endodontic treatments with MTA between October 2005 and September 2014. Radiographic healing at the fracture line was evaluated independently by 2 examiners and was classified into 4 types according to Andreasen and Hjørting-Hansen. RESULTS Of the 22 root-fractured teeth that received endodontic treatment with MTA, 19 cases participated in the follow-up after a period of at least 3 months. Seventeen of the 19 teeth (89.5%) exhibited healing of the root fractures. For each healing type, 7 teeth (36.8%) showed healing with calcified tissue, 8 teeth (42.1%) showed interposition of connective tissue, 2 teeth (10.5%) showed interposition of connective tissue and bone, and 2 teeth (10.5%) showed interposition of granulation tissue without healing. CONCLUSIONS Within the limitations of this study, intra-alveolar root fractures showed satisfactory healing outcomes after endodontic treatment with MTA. MTA could be considered to be suitable filling material for the endodontic treatment of horizontal intra-alveolar root fractures.