オールセラミック連続冠の適合性に関する研究

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Recently new types of all-ceramic restoration systems have been developed and clinically applied. Since the core or porcelain material has been much improved in strength, it may be possible to apply the systems not only to single crown but also to short span bridge. When clinically applied to the connected crowns, however, they have often presented a problem of poor fit although satisfactory fitness has been demonstrated for single crown by several reports. In the present study, therefore, the factors affecting the fit were examined at the stages after the green core casting and some experimental approaches were evaluated for fabricating better fitting all-ceramic connected crowns using Alceram^<TM> system. The results obtained were as follows : 1. All-ceramic connected crowns fabricated according to the manufacturer's standard firing schedule (control specimen) showed poor fit having large marginal gap on the working die although each component crown itself separately exhibited good fit to its die. 2. It was found that the connected crowns were distorted as a whole into mesio-distally warped shape and that most of the distortion might have been caused during firing for core sintering due to the release of inner stresses of the green core. No significant changes were observed at the stage of the porcelain firing. 3. The use of a sprue modified into webbed-shape slightly restrained the distortion of the connected crowns while no significant reduction in the average marginal gap was recognized. 4. A modified design having vertically enlarged connection between the crowns showed marked decrease in warped-shape distortion and marginal gap. 5. When the core firing was prolonged for 30 minutes at the maximum temperature of the standard schedule, the resultant core showed better fit with marginal gap as small as half the control specimen. 6. By introducing a preheating treatment of the green core at 200℃ as it was seated on the working die prior to the standard firing, the marginal gap reduced to half the control. 7. When the core was fired as the sprue was left uncut, the good fit of the green core on the working die was almost maintained even after firing and sprue cutting. It might be due to the stress relief annealing reaction by this treatment. It was suggested from the foregoing results that it would be the best way for improving the fit of the all-ceramic connected crowns to cut sprue after core firing although it might have a risk of fracturing the brittle core.
九州歯科学会の論文
1994-02-25

オールセラミック連続冠の適合性に関する研究

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