合着による鋳造冠の浮き上がりとリリーフ効果

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Elevation of the cast crown was measured in cementation to resin model and a method was investigated to improve the seating of cemented crown by practically effective grooves prepared on the axial wall of the resin abutment. Besides, the influence of many other factors was investigated, such as type of the preparation, taper of the abutment wall, load of the cementation and frictional resistance of the cement slurry. Three types of resin model were prepared (shoulder, chamfer, and knife edge). The shoulder type had the three different taper angle (3, 5, 10°) and each of the other two types had one sole taper angle (5°). On the abutment axial wall of the resin models a pair of equal length of grooves was prepared on its opposite side lines from the occlusal portion towards the finishing line. The end of these grooves reached 5 different heights (3, 2, 1, 0.5, and 0 mm) from the finishing line. Unident (a water-settable carboxylate cement) was used as the cementation medium because of its excellent workability. Elevation was reasonably decreased when the cast crown was cemented to the resin models having the taper angle of 3 or 5° and a pair of grooves on their opposite side lines from the occlusal portion down to 0.5mm height from the finishing line. However, in case of the taper angle of 10°, elevation was not reduced so far as the furnished grooves did not reach the finishing line, i.e. even the grooves down to 0.5mm height had no elevation reducing effects. During the cementation of cast crown to resin model having taper angle of 3 or 5°, frictional resistance of cement increased abruptly as the crown margin gained 0.5∿1.0mm access from the finishing line. In case of taper angle 10°, such an abrupt increase in frictional resistance first occured by the 0∿0.5mm access. The elevation of cemented crown was the least (29.8μm) when a pair of grooves was prepared from the occlusal portion down to 0.5mm height from the finishing line of chamfer type resin model having the taper angle of 5°. In case of cementing of cast crown to resin model having the taper angle of 5°, the cementing load had no appreciable effect on the amount of elevation among 6, 10 and 15kg. From the findings mentioned above, it was concluded that the best method for the seating of cemented crown was to prepare the abutment in the shape of chamfer type with taper angle of 5°, as well as a pair of equal length of grooves on its opposite side lines from the occlusal portion down to 0.5mm height from the finishing line. The same will be said in the case of the cementation with the other two dental cements, Carbolit 100 and Elite Cement 100, at least when the abutment taper angle is prepared as 5°, because the behavior of frictional resistance is quite analogous in these two cements to that in the tested cement (Unident).
九州歯科学会の論文

合着による鋳造冠の浮き上がりとリリーフ効果

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