The secondary flare results in a marginal metal of:
After the base (where indicated) is completed, the slender, flame shaped, fine-grit diamond instrument is used to bevel the occlusal and gingival margins and to apply the secondary flare on the distolingual and distofacial walls. This should result in 30o to 40o marginal metal on the inlay. This cavosurface design helps seal and protect the margins and results in a strong enamel margin with an angle of 140o to 150o. A cavosurface enamel angle of more than 150o is incorrect because it results in a less defined enamel margin (finish line), and the marginal cast-metal alloy is too thin and weak if its angle is less than 30o. Conversely, if the enamel margin is 140o or less, the metal is too bulky and difficult to burnish when its angle is greater than 40o.
Sturdevant operative dentistry 7th Edition, Page No:e104
140o – 150o
30o – 40o
180o
150o – 180o