In large Class 3 preparations or in situations when additional retention is desired, retentive features such as grooves and coves may be inserted. For example, where there is little or no enamel for reliable bonding, a gingival groove is placed. For added retention, an incisal cove complements the gingival groove. Note the retentive direction is gingival or incisal to prevent proximal displacement.
A clear mylar strip is placed between the involved tooth and its neighbor so that the incial and gingival margins of the preparation are covered by the mylar strip. A wedge is inserted between the strip and the uninvolved tooth to seal the gingival margin and separate the teeth to compensate for the thickness of the mylar strip so that the proximal contact is re-created.
