Influence on retentive force of negative pressure generated between an electroformed telescope outer crown and improved zirconia inner crown

Abstract

This study was performed to clarify the effect on retentive force of negative pressure generated between the improved inner zirconia crown and outer electroformed crown during vertical dislodgement. Inner crowns with 2° taper and a combination taper (0° taper for the cervical 1.5 mm and 2° taper above that) were made of zirconia, and five outer crowns were made by electroforming on the inner crowns. We measured the retentive force and the negative pressure generated between the inner and outer crowns with 20%, 40% and 60% glycerin solution substituted for saliva. There was no difference in peak retentive force between the 2° taper crowns and the combination taper crowns. The retentive force generating distance with the combination taper was significantly greater than with the 2° taper, and increased with the glycerin concentration of the solution in the combination taper type. The negative pressure generated between the double crowns using a zirconia inner crown with a combination taper increased with the glycerin concentration of the solution. The above findings suggest that the negative pressure generated between zirconia inner crowns and electroformed outer crowns increases the retentive force generating distance as the saliva viscosity increases.