ABSTRACT
STATEMENT OF PROBLEM: The adjustable dental impression trays were made for being adjusted their width automatically along the width of dental arch. PURPOSE: The purpose of this study was to investigate the best retentive form of adjustable dental impression tray, and so to make it a more satisfactory product. MATERIALS AND METHODS: The eight pairs of adjustable trays were made of ABS(acrylonitrile butadiene styrene) with different distribution of holes and with or without the rim on the border area of them. The experiment was done with the horse-shoe shaped metal plate to pull out the set impression body from the tray, and the tray jig which was made for holding the tray on a lower part of Universal Testing achine(UTM, Zwick Z020, Zwick Co., Germany). After the impression in the tray was allowed to set four minutes, a tensile force was applied at right angles to the tray which had been previously seated on the jig. The force was applied to measure a maximum retentive force by use of a UTM at a constant strain rate of 100mm per minute. A 2-factor analysis of variance (p.05) 4. The rimless trays were more retentive generally, than the rimmed trays except 2 case: upper tray group-all area / 2 mm. intervals and lower tray group-margin only / 2 mm. intervals.(p<.05) 5. Most of the adjustable trays were showed higher retentive force than perforated metal tray except the lower group that perforated on the all area at intervals of 2 mm.
Subject(s)
Dental ArchABSTRACT
STATEMENT OF PROBLEM: Clinically, maxillary first premolar has a high risk of fracture. This is thought to be caused by the susceptible figure which the maxillary first premolar has. In other words, sharp cusp angles of the premolar is thought to influence this situation. PURPOSE: This study was to know stress distribution of all-ceramic crown according to the cusp angle. MATERIAL AND METHOD: It was manufactured a three dimensional finite element model simplified maxillary first premolar, and then analyzed stress distribution when cusp angle was each 80 degrees, 90 degrees, 100 degrees, 110 degrees and 120 degrees. RESULTS AND CONCLUSION: 1. The von Misses stress showed that stress decreases as cusp angle increases in the central groove of the occlusal surface. 2. It showed that maximum principal stress was centered at the region of the central groove of the occlusal surface and a region which the force was inflicted. And also it appeared high on the lingual and buccal side of finish line. 3. The X axis of normal stress was focused in the central groove of the occlusal surface. The Y axis normal stress appeared high in the central groove of the occlusal surface, buccal and lingual side. 4. The Stress near the finish line showed a low value compared with stress in the region of the central groove of the occlusal surface. 5. It shows that the most dangerous angle for tooth fracture was on 80 degrees of the cusp angle and low on 120 degrees of its.