Class III Composite Preparation / page 2

RESISTANCE  FORM The clinician preserves tooth structure by angulating the bur in the most conservative approach to remove all caries and defects. The outline is gently rounded in all internal and external corners.  Whether approached from the facial or lingual, the preparation has supported enamel rods at all cavosurface margins

The use of gingival margin trimmers (GMT) is useful to plane the walls to remove unsupported enamel at the cavosurface margins. Here in this lingual approach Class 3, a mesial GMT is used to plane the facial wall.