Margins of complete crowns—Literature review

Abstract

The margin is one of the components of the cast restoration most susceptible to failure, both biologically and mechanically. Most of the investigative proof shows that supragingival margins are kinder to the gingiva than are subgingival margins. However, practicality dictates that supragingival margins are not always usable. There is some indication that quality of the margin may be of as much importance to gingival health as location. Research on the configuration of margins seems to agree with the majority of authors writing technical articles. Most agree that feather edge or knife edge margins are not always the most acceptable. Apparently bulky margins with subtle internal line angles are best. Bevels are recommended where esthetics allows due to their slip-joint effect affording closer adaptation. Most cemented castings do not fit nearly as well as theoretical tests of cement film thicknesses would lead us to believe. Venting or providing space for cement through electromilling, aqua regia etching, or die spacing markedly improves the seating and, therefore, the marginal fit of castings. This seems to be a more useful approach to close fitting margins than burnishing and finishing margins, particularly for subgingival margins. Most of the commonly used fixed partial denture alloys, both precious and non-precious, are too hard to be burnished effectively. As long as fixed prosthodontics must rely on the cemented casting, the search for more knowledge about an innocuous, esthetic, indestructible margin must continue.