カラーレスセラモメタルクラウンへの試作光重合型モノマーの応用 : マージン修正用ポーセレンの築盛

Abstract

Collarless ceramo-metal crowns have been widely used because of their superior esthetics at the shoulder as well as the protection of the gingival margin from direct exposure to metal. There are, however, some difficulties in fabricating the crown with satisfactory marginal fit and/or correcting the contour of the loosely fitting porcelain shoulder. In order to overcome such problems in this study, the light-curing process was attempted for forming the porcelain with the experimental monomers. The monomers were composed of 1, 3-butanediol dimethacrylate monomer (BDMA) as a base monomer, glycidil methacrylate monomer (GMA) as a diluent, dl-camphor quinone as a photosensitizer, and N, N-dimethyl-p-toluidine as a reducing agent. Four monomers with different BDMA to GMA ratios were prepared : 1 : 0 0 (referred to as M_<1-0>), 1 : 1 (M_<1-1>), 1 : 1.5 (M_<1-1.5>), and 1 : 2 (M_<1-2>). Their performances were discussed by comparing with the porcelain formed with distilled water followed by firing at 900℃ as a control. The porcelain formed by the light-curing process showed 10 to 15% larger volumetric shrinkage in firing than the control because the porcelain powders could be less incorporated in the mixture with the viscous monomers. The shrinkage not only compensated for the lowered density of the porcelain but also markedly reduced the size of porosities except for the monomer M_<1-0> that produced significantly larger size and number of porosities in the fired porcelain. It was reflected in the compressive strength not smaller than that of the control. When the porcelains formed with the monomers were fired at a temperature lower than 850℃, the shade turned blackish due to the incomplete combustion of the polymers. However, distinguishable color differences could no more be found after firing at 900℃ among the control and the porcelains formed with M_<1-0>, M_<1-1> and M_<1-1.5>. The monomers were applied to form the shoulder porcelain at the margin of the collarless ceramo-metal crown on the plaster die to correct its margin contour. When distilled water was routinely used, a considerable amount of porcelain powders remained on the die shoulder in lifting the crown. With the use of M_<1-0> and M_<1-1>, however, almost all the powders could be withdrawn as a bulk from the die together with the crown, although no improvements were found on the separation from the die with M_<1-1.5> and M_<1-2>. As a result, the margins showed excellent fit to the die shoulder after firing when M_<1-0> and M_<1-1> were used for formation, while larger marginal gaps were observed in the cases of the control and the other two monomers. From the foregoing findings, it was suggested that the light-curing forming of the shoulder porcelain with the experimental monomer M_<1-1> would be an extremely useful technique for improving the workability and marginal fit without adversely affecting the physical and mechanical properties.