Improvement in coping strength of all-ceramic crowns by a new method

Abstract

We previously developed a porcelain firing method by which all ceramic crown copings can easily be produced in a short time without using special apparatuses or duplicated models, and reported its possible clinical application. However, improvements are necessary because its strength was lower than that of conventional copings. We increased the strength of the coping, increased the diameter of the mixing alumina powder grains from 4 μm to 8.5 μm, and after investigating the plasticity and manipulability of the copings on plaster models, we evaluated the ratio of alumina powders and the strength of the coping. We found that the 3-point bending strength of the coping markedly increased to 183-211.3 MPa, and the highest strength was achieved when the mixing ratio of rough to fine grains was 40:50 (wt%). A 4-step build up was most suitable for producing a coping of 0.5 mm in thickness. By making a rounded shoulder type margin design for the abutment teeth, removal of the coping became possible if the axial surface taper angle was greater than 6 degrees. These results showed that it is possible to produce copings with excellent plasticity and manipulability, as well as increased strength, suggesting the clinical feasibility of this process.