HomeDentistry The peripheries of the custom tray should be under extended to all border and clearance from the frenum areas.. 2mm The peripheries of the custom tray should be under extended to all border and clearance from the frenum areas:2mm.***4mm.6mm.8mm. Facebook Twitter Share:The peripheries of the custom tray should be under extended to all border and clearance from the frenum areas.. 2mm Facebook Twitter WhatsApp Pinterest LinkedIn Reddit Tumblr Telegram Email