The margin of the prepared tooth represents the line at which natural tooth structure and the laboratory-fabricated restoration will meet. Different marginal designs are required depending on the type of restoration being fabricated (full coverage crown, veneer, inlay, etc.)
NOTE: Subgingival (below the gum line) margins on the facial surface are often more esthetic, while supragingival (above the gum line) margins on the lingual surface are generally considered easier to keep clean.
(ref. 7)

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