Defects can be converted into retentive features if not very extensive. The walls of the remaining defects can be shaped to remove undercuts and provide vertical walls One or a combination of the following can be utilized to get added retention and resistance forms: 1. Grooves: Are placed usually vertical axial walls at 1mm depth and width. They can be also be placed internally at line angles of oversize boxes to enhance their resistance form 2. Slots: are basically grooves whose length is in a horizontal plane. They are 0.5mm in depth and about 1-4um in length and are placed 0.5mm axial to DEJ 3. Coves and locks: Are smaller slots and grooves respectively. They are never used alone but always with pins / slots 4. Convert classical grooves to box forms: When the destruction occurs beyond the outline of a standard groove form, the situation calls for a conversion to a box form. Ideally > 180o of sound tooth should be presented between the 2 retentive features to prevent tooth fracture. Thoughtful location will help over- come such problems 5. Sloping surface orientation: On brood sloping surfaces left after cusp fracture, it is better to form multiple small steps instead of one long and broad single step which would weaken the tooth and jeopardize pulpal health. 6. Pinholes and pins: Are probably the only retention features that do not require existing vertical supragingival tooth structures for their placement. They can be used in 2 ways. 
Pinholes parallel to path of insertion where the pins are an integral part of the cast restoration. These pins aid in enhancing retention of over tapered preparations