If a line of stain appears along the gingival margin after polishing, what is likely the cause?

A line of stain appearing along the gingival margin after polishing typically indicates that there may have been an issue with the adaptation of the polishing cup to the tooth. When the polishing cup does not conform well to the contour of the tooth, it may not effectively remove all plaque and stain from the gingival area. This can lead to a residual line of stain being visible after the polishing process is complete.

Effective polishing requires that the instrument or material being used makes adequate contact with the surface of the tooth to ensure thorough cleaning. If the polishing cup is inadequately adapted, it not only fails to polish effectively but can also compromise the overall aesthetics of the tooth surface. Furthermore, improper cleaning before polishing could contribute to additional staining, but it is the adaptation to the tooth that primarily impacts the results seen along the gingival margin.