Shigemi Ishikawa

The Colorimetric Study of the Musking Porcelain. The Evaluation of the Opacity Using a Hiding Power Index.

Translucency is a very important factor for obtaining an esthetic porcelain laminate veneer crown. This translucency is greatly affected by the opacity of the masking porcelain layer, but there is no objective criterion to evaluate the opacity. In general, opacity is well evaluated by hiding power. Therefore, hiding power of masking porcelain was calculated in this study using the ASTM (American Society for Testing and Materials) method.The reflectance value of each masking porcelain sample containing 5, 10, 15, 20, 25, or 30% opacity of pink, white, yellow, and blue were measured with white and black backing, and hiding power was calculated using its scattering coefficients. Hiding power increased in proportion to the opacity and ranged from 100 to 1, 400 for any shade. Color difference dE between white and black backing increased rapidly under the 25% opacity.It was concluded that (1) the opacity could be analyzed as hiding power and (2) hiding power under 20% opacity is very effective on visibility.

Color Modification of Porcelain Laminate Veneer Crowns by CCM. Part 1. Color Reproducibility using the Musking Porcelain with Opaque as a Coloring Element.

Porcelain laminate veneer crown is an excellent system to improve the color of a discolored tooth in the anterior region having occlusal contact. Since masking porcelain of porcelain laminate veneer crown has opacity for hiding the discolored tooth, it was difficult to give a high translucency to the laminate crowns by conventional methods.The purpose of this study was to produce the natural color and excellent appearance of laminate crowns with adequate translucency using the Computer Color Matching (CCM) System to compensate opacity of masking porcelain.Construction of CCM sample, discolored layer, and procedure of CCM formulation are the same as part 1.In this study, 1 kind of opaque porcelain was used as the hiding element, and 3 kinds of dentin were used as the coloring element. According to the CCM formulation, masking porcelain was baked and the CCM samples were made.In comparison of the target color and CCM sample, both reflectance curves were very similar and color difference dE was under 3.0. Furtheremore, CCM samples showed the color to be indistinguishable from the target color by the naked eye.

Clinical investigations on the use of the third molar as an abutment tooth for removable partial denture

Success in treating consecutive missing second premolar, first molar, and second molar, may depend upon how the third molar is used as an abutment. Our department tested the third molar as an abutment for such removable partial denture appliances as attachments and telescopic crowns.This report deals with the effects of these appliances on third molars having short vertical coronal lengths. Retention strengths of the following were measured and compared;1) Angles of the contacting wall surfaces of two primary crowns both set at 2 degrees, with different mesial and distal wall lengths labelled S and M.2) I-C attachment, 202 EL, Ipsoclip 783 C, and a telescopic crown where a horizontal pin was placed in the axial surface.3) Battesti 1183, Conod 1071, and Ceka 723.Results of the telescopic crowns in condition 1 showed the retention strength to be S=500g and M=860g, and that of the I-C attachment, Ipsoclip, and horizontal pin was720 g, 800g, and 740 g respectively. A retention modifier instrument was used to control the retention strength of the Battesti, Conod, Ceka, and horizontal pin telescopic crowns to its recommended strength of between 500-1, 000g.