[Mechanical evaluation of crown restoration by means of laser holographic interferometry, with a primary regard to establish a system for an experimental method].

This study was conducted to perform mechanical evaluations of crown restorations by Laser Holographic Interferometry (LHI). However, in an application of LHI, the Fujinon Holox FHLX-II system (He-Ne Gas Laser GLG-5700, NEC Co.) to this experiment, it was mandatory to do some modifications for loading and measuring evaluations, thereby a whole sequence of this system could be successfully carried out. The experiments were conducted in the following manner: Ten pieces of full cast crowns were constructed by a conventional procedure with 12% Au-Ag-Pd alloy and each test-piece was cemented alternately by zinc phosphate cement on a master die (stainless steel) with a chamfer margin. Successive vertical loadings (0kg-30kg) were applied for each test-piece and holograms were taken for crown restorations under loadings of both 15Kg & 30Kg with an accuracy of 0.3 micron. Three-dimensional measurements of nine points on surface of a testpiece were obtained through interference fringes, which were converted into mathematical values and statistical comparisons were performed for mean values under loadings of both 15 Kg & 30 Kg. The following results were obtained from this experiment. 1. It was successfully performed that an application of Laser Holographic Interferometry (a real time) became an efficient method with some modifications for mechanical evaluations of crown restorations. 2. Besides modification for rigid fixation of a test-piece, it made possible to conduct the loading experiment under Kg unit, which was impossible in previous studies. 3. Three-dimensional measurements were also made possible by an application of mathematical calculations, thereby a total system of experimental procedures was established. 4. Reference points were marked on surface of a test-piece, and this made possible to compare with the displacement values of other test-pieces. 5. Displacements of experimental crowns with both 15 Kg & 30 Kg under areas of loadings showed remarkably and they were gradually spread out toward the outer directions of restorations with slight displacements. From this experiment, it was proved that a cemented crown showed a certain deformational behavior under loadings. Therefore, this system contributes to become an efficient method evaluating mechanical features of crown restorations for further studies.