上顎前歯部ポーセレンジャケットクラウンの咬合応力分布
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概要
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Recently in the field of crown prosthodontics for anterior teeth, porcelain fused to metal crown has been dominantly employed, while the use of porcelain jacket crown diminished. The most definite cause of such an inclination is the fact that the latter is more liable to get serious fracture than the former. The fracture often results from improper formation of the abutment tooth, in addition to the brittleness of porcelain itself, erroneous indications and/or technical errors. It will be expected to occus less frequently by the reasonable preparation of the abutment tooth as such that no undesirable stresses can be distributed in the porcelain jacket crown. It may, therefore, still be worthwhile to appreciate the adequate application of porcelain jacket crown, considering its superiority over the porcelain fused to metal crown in some aspects such as aesthetic, fitting, histological affinity, cost, etc. For this purpose, the stress distribution produced on the porcelain jacket crown was estimated in the present study with respect to the shape of the abutment tooth, by means of three-dimensional stress freeziag photoelasticity tests as well as strain gage measurements. The results obtained were as follows : 1. When the compressive load was applied to the normal coverage portion at an angle of 45°to the tooth axis, tensile stress was produced on the edge side of the labial surface of the crown and compressive stress on the cervix side, irrespective of the shoulder of acute-angled, right-angled, obtuse-angled or chamfered. On the lingual surface, tensile stress appeared up to the lingual tubercle except for the loaded portion. 2. It may be feasible to moderate the stress concentration by forming the lingual contour so as to make the crown contact uniformly as wide as possible with the opposite tooth. 3. Direction of the maximum shear stress obtained at the labial cervix was found to correspond with the reported crescent-shaped fracture plane. 4. When the retention of the crown was not sufficient, the elevation of the lingual cervix was likely to occur on applying the load, and hence the apparent stress became smaller at the portion for any type of the shoulder. When the lingual cervix of the crown was firmly fixed to the abutment, on the contrary, significantly larger tensile stress was observed at the area than at the other portions. 5. In the case of the short abutment, the fracture of the crown would be liable to occur resulting from the increased bending moment toward the labial side at the edge of the crown. 6. From the analyses in detail of the stress distribution on the vicinity of labial cervix, it may be supposed that the fracture of the porcelain jacket crown will occur more frequently in those having the chamfered or obtuse-angled shoulder than the right-angled or acute-angled.
- 九州歯科学会の論文
- 1982-06-25
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