The convergence of buccal and lingual walls will prevent the restoration to be dislodged in an occlusal direction (retention form).

The nice thing about 330 bur and 245 bur is that these burs have an inverted pear shape shape that forms the convergence of these walls. So by just maintaining the angulation of your bur when you move along the tooth, you will achieve convergence of the buccal and lingual walls.

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