Homecrown For onlay preparation, reduction of functioning cusp should be.. 1.5 mm. f cusp publisher :NIL NAM -June 23, 2017 For onlay preparation, reduction of functioning cusp should be: a. 1.5 mm. f cusp*** b. 2 mm. c. 1 mm.non f cusp. Labels crown Facebook Twitter Share:For onlay preparation, reduction of functioning cusp should be.. 1.5 mm. f cusp Facebook Twitter WhatsApp Pinterest LinkedIn Reddit Tumblr Telegram Email