RESUMO
Objective To investigate the influence of different kinds of post?core materials on fracture resistant ability of different walls during weakened root restoration. Methods Forty?eight human single root mandibular first premolars were randomly assigned to two groups(groupⅠwas repaired with quartz?fiber post?core and mental crown ,and groupⅡwas repaired with Co?Cr cast metal post?core and mental crown). Each main group was then divided into four subgroups of 6 specimens. All samples were tested on the universal test machine. We observed the fracture load and the fracture mode of the specimens. Results Cr?Co ally post?core group exhibited significantly higher resistance to fracture than quartz fiber post?core in the same number weakened root walls(P<0.05). With the increase in the quantity of weakened root walls ,the fracture resistance was significant decreased in the same post?core material(P<0.05). The possibility of repairable fractures in groupⅠwas significantly higher than that in groupⅡ(P<0.05). Conclusion Cr?Co alloy post?core can bear a higher bite ,but quartz fiber post?core has the most favorable fracture modes.
RESUMO
STATEMENT OF PROBLEM: Many kinds of post and core systems are in the market, but there are no clear selection criteria for them. PURPOSE: The purpose of this study was to compare the flexural strength and modulus of elasticity of core materials, and measure the bending strength of post systems made of a variety of materials. MATERIAL AND METHODS: The flexural strength and elastic modulus of thirteen kinds core buildup materials were measured on beams of specimens of 2.0 x 2.0 x 24 +/- 0.1mm. Ten specimens per group were fabricated and loaded on an Instron testing machine at a crosshead speed of 0.25mm/min. A test span of 20 mm was used. The failure loads were recorded and flexural strength calculated with the measured dimensions. The elastic modulus was calculated from the slopes of the linear portions of the stress-strain graphs. Also nine kinds commercially available prefabricated posts made of various materials with similar nominal diameters, approximately 1.25mm, were loaded in a three-point bend test until plastic deformation or failure occurred. Ten posts per group were tested and the obtained data were anaylzed with analysis of variance and compared with the Tukey multiple comparison tests. RESULTS: Clearfil Photo Core and Luxacore had flexural strengths approaching amalgam, but its modulus of elasticity was only about 15% of that of amalgam. The strengths of the glass ionomer and resin modified glass ionomer were very low. The heat pressed glass ceramic core had a high elastic modulus but a relatively low flexural strength approximating that of the lower strength composite resin core materials. The stainless steel, zirconia and carbon fiber post exhibited high bending strengths. The glass fiber posts displayed strengths that were approximately half of the higher strength posts. CONCLUSION: When moderate amounts of coronal tooth structure are to be replaced by a post and core on an anterior tooth, a prefabricated post and high strength, high elastic modulus core may be suitable.