The evaluation of vertical marginal disc-repancy induced by using as cast and as received base metal alloys with different mixing ratios for the construction of porcelain fused to metal copings

Abstract EN

In this study the effect of mixing as received and as cast metals by different ratios on the marginal fitness of metal cop-ings casted by two types of base–metal alloys (Wiron 99 and Heraenium–NA) whi-ch are used by dental technicians in Iraq was evaluated.

The general procedure consisted of first, fabrication of wax pattern on a standardized prepared brass die that represented an upper central incisor with a heavy chamfer cervical margin.

The wax patterns were standardized by the aid of a split mold constructed spec-ially for this purpose; the total number of wax patterns was 100.

Each fifty copings were casted with one of these two alloy types, and each type was divided into five sub–groups according to the amount of as received (new) and as cast (recasted) metals mixed.

Completed castings were finished and seated on the die.

The marginal fitness of each copying was determined by measur-ing the vertical discrepancies between the gingival margin of the copying and the margin of the preparation at four reference points on the labial, mesial, palatal, and distal aspects of the die with the aid of light traveling microscope.

The statistical analysis of the results re-lated to Wiron 99 alloy group showed that there were highly significant differences bet-ween its related five sub–groups indicating that the marginal fit changes increased with the increase of the recasted metal ratios of Wiron 99.

On the other hand, Heraenium–NA alloy did not show significant differen-ces among its sub–groups indicating that re-casting it, in different ratios reaching up to 100% as cast alloy, did not cause adverse changes on marginal fitness.

Based on this, conclusions drawn indi-cated that recasting of Heraenium–NA (Ni–Cr) can be utilized as a good substitute for the new alloy from an economical point of view.