Resin bonding of metal brackets to glazed zirconia with a porcelain primer

OBJECTIVE: The aims of this study were to compare the shear bond strength between orthodontic metal brackets and glazed zirconia using different types of primer before applying resin cement and to determine which primer was more effective. METHODS: Zirconia blocks were milled and embedded in acrylic resin and randomly assigned to one of four groups: nonglazed zirconia with sandblasting and zirconia primer (NZ); glazed zirconia with sandblasting, etching, and zirconia primer (GZ); glazed zirconia with sandblasting, etching, and porcelain primer (GP); and glazed zirconia with sandblasting, etching, zirconia primer, and porcelain primer (GZP). A stainless steel metal bracket was bonded to each target surface with resin cement, and all specimens underwent thermal cycling. The shear bond strength of the specimens was measured by a universal testing machine. A scanning electron microscope, three-dimensional optical surface-profiler, and stereoscopic microscope were used to image the zirconia surfaces. The data were analyzed with one-way analyses of variance and the Fisher exact test. RESULTS: Group GZ showed significantly lower shear bond strength than did the other groups. No statistically significant differences were found among groups NZ, GP, and GZP. All specimens in group GZ showed adhesive failure between the zirconia and resin cement. In groups NZ and GP, bonding failed at the interface between the resin cement and bracket base or showed complex adhesive and cohesive failure. CONCLUSIONS: Porcelain primer is the more appropriate choice for bonding a metal bracket to the surface of a full-contour glazed zirconia crown with resin cement.ope

지르코니아 표면에 교정용 메탈 브라켓 부착시 프라이머의 효과

Dept. of Dental Science/석사The use of zirconia in conservative aesthetic dentistry has become more common. With this trend, it’s been extensively investigated to get acceptable bond strength with zirconia surface. But these studies are all focusing on resin luting cement with “naked” zirconia. Therefore, the aims of this study were to compare shear bond strength of resin cement to zirconia surface with using different primers and determine the effective surface treatment method for metal bracket bonding, zirconia primer or conventional porcelain primer.Zirconia blocks(Zirkonzhan) were milled and embedded in cylinder-shaped acrylic resin required for using testing machine. Specimens were randomly assigned to four groups (n=10): NZ, Non-glazed surface / Sand blasting + Zirconia primer; GZ, Glazed surface / Sand blasting + Etching + Zirconia primer; GP, Glazed surface / Sand blasting + Etching + Porcelain primer and GZP, Glazed surface / Sand blasting + Etching + Zirconia primer + Porcelain primer. Mandibular incisor stainless steel metal bracket was bonded to target surface with resin cement and all specimens underwent thermal cycling for 2,000 cycles (5 ℃ to 55 ℃) with a dwelling time of 30 seconds.Shear bond strengths of specimens were measured using a universal testing machine at a cross-head speed of 1 mm/min. Scanning electron microscopy, 3D optical profiler and stereoscopic microscopy were used for imaging the zirconia surface before and after surface roughening and debonding. The data were analyzed by one-way ANOVA and Fisher’s exact test (p<.05).The group GZ, using zirconia primer on glazed surface showed significantly lower shear bond strength than other groups. As for group NZ, GP and GZP, there was no statistically significant difference among them. While specimens in group NZ and GP showed adhesive failure between the resin cement/bracket base or complex adhesive and cohesive failure, all specimens in group GZ failed at the zirconia/resin cement interface. Based on the results of this study, it does not seem proper to use a zirconia primer to bond metal bracket on the surface of full contour zirconia crown with resin cement. In such situations, the use of porcelain primer is more appropriate.ope

입출고점의 위치 및 경로를 동시에 결정하는 물류 네트워크 설계에 관한 연구

학위논문(석사) - 한국과학기술원 : 산업공학과, 2006.2, [ ii, 41 p. ]This thesis focuses on the problem of designing a material flow network for a given block layout. For an efficient design of a network, locations of input and output points, flow paths, and the smoothness of material flows are considered simultaneously. The problem is formulated as a mixed integer program by representing a block layout as a directed graph. For the problem with the objective of minimizing the sum of transportation cost, flow path construction cost and penalty cost for non-smooth material flows, we suggest two heuristic algorithms based on the LP-relaxation and the Lagrangian relaxation techniques. To evaluate performance of the suggested algorithms, a series of computational experiments is performed on well-known problem instances as well as randomly generated test problems. Results show that the suggested algorithms give good solutions in a reasonable amount of computation time.한국과학기술원 : 산업공학과