Preservation of Periodontium: -

 The disaster of crown / FPD — Overhanging /Overcontoured crown
o food lodgement
o could affect perio eventually
 Biological width — junctional epithelium + connective tissue = 2 mm
 If at aaalll we are going subgingivally – it is only for aesthetic reasons, otherwise never preferred.
 Preserve about 3 mm for assurance of preservation of periodontium.