The diatoric designs of posterior porcelain teeth without airvent holes were decided on the basis of the results of part 1. They were composed of three sizes of diameter, height, angle of inclination of the axis of crown and two sizes of the depth undercut wells.
The molars amounted to 43 sets, the premolars 45 sets. Specimens were made in a similar manner of a previous paper. This experiments consisted of
(1) tensile test, Experiment (I)
(2) repetitive impact test and measurement of mobility of teeth planting in resin-blocks, Experiment (II)
(3) after mechanical and thermal stimuli were applied to the specimens selected from the experiment (I) and the experiment (II), tensile test, Experiment (III)
(4) The two foregoing tests of porcelain teeth with the airvent holes, Experiment (IV)
The results of this study were as follow;
Experiment (I): Molar-Among 43 sets, there were 12 sets whose values of the strength was higher than that of control, 0.55±1.54kg. A maximal strength was obtained with No.24, 19.51±2.31kg, a minimum was No.2, 6.75±1.74kg. Premolar-the values of 20 sets out of 45 sets were higher than the control, 8.38±1.17kg. The maximum was No.43 of 6.48±1.81kg, and the minimum No.8, 3.55±1.09kg.
Experiment (II): In the impacti strength, the values of the molars were higher than the premolars, but in the mobility the elative composition was entirely reversed. The specimens of the higher impact strength was not necessarily those of the low obility. Though the specimens with the porcelain having the small diameters surely took high values of the strength, for em to have the appropriate height or angle, their strength was also high.
In the molars there were 17 sets that were superior to their control, 123.93×10
2.
In the premolars 20 sets were higher than their control, 74.09×10
2Experiment (III): The specimens which took the higher values than the controls of both the impact and the tensile strength as No.17, 22, 24, and 28 of the molars, similarly of the premolars were No.14, 20, 21, 30 and 32. It could not be found that eir strength became low even after providing the mechanical and thermal stimuli, which suggested that the change of the etention of teeth had little to do with time.
Experiment (IV): In tensile test, their values were not change as usual, but in the repetitive impact test they became low. onsequently setting the air-vent holes in the porcelain teeth only brought about the fragibility of them.
Judging from these results, the diatoric form in the posterior porcelain teeth with the sufficient retention and toughness was, the molar their diameter, 3.0mm; their height, 2.3mm; their angle of inclination, 20°and their depth of the undercut wells 4mm.
In the premolar, their diameter, 3.2mm or 2.3mm; their height, 1.8mm their angle, 20°or 40°; and their undercut wells 0.4mm, oreover these teeth should have no air-vent holes.
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