Tunnel tooth preparation: Conservative tooth preparation which occlusal and proximal lesions are joined by means of tunnel under the involved marginal ridge. In this way marginal ridge remain intact. These cavities usually restored by glass ionomer cement. In assessing this technique the adequacy of preparation access may be a controversial.
Extended margins: Cervical areas are caries prone because these areas difficult to clean i.e. old Class II restoration. When the margin ends on cementum, it may necessitate the alteration in cavity design. Lack of access in these places precludes the use of hand cutting instruments rather than the burs. A sharp chisel or hatchet is the most effective way to establish and execute a good gingival floor and margin.
36