Position of crown margin in relation to the tooth preparation line

It is of paramount importance to have the crown margin precisely adjusted to the preparation lines of the teeth in order to reduce the bacterial plaque which is known to cause inflammations of the periodontal tissues.

The aim of the present study was to determine the position of the crown margin in relation to the preparation line in axial and transversal directions for various types of crowns.

The study included 89 extracted teeth with the attached restorative construction (crown or crown bridge) divided into groups by types of tooth and construction. Each tooth was cleaved into two halves along its axial plane obtaining thus two crown surfaces (a total of 178). Each half of the cleft tooth was embedded in fast-polymerising resin, then sections were made which were studied using a standard ocular measure scale at a magnification of 20x. The position of the crown margin in relation to the preparation border in axial direction was defined as either a precise fit, or longer, or shorter, and in transversal direction--as a precise fit, reverse shoulder or wider. The results were analysed statistically by analysis of variance and alternative analysis.

Longer crown margins were seen more frequently in the axial direction (57 to 72% of all cases) but were prevalent in the cast veneer crowns. Wider crowns were found to be more frequent transversally (86 to 97% of all cases), but were prevalent in swaged crowns. Precise fit of the crown margin with the preparation line is very rare.

The crowns that are most often fabricated in our country are wider crowns followed by crowns with longer crown margin. The discrepancies in axial and transversal directions are a significant plaque retention factor of iatrogenic nature that is conducive to the development of periodontal diseases.