When we look at the proximal view of the preparation, the relationship between the buccal and lingual walls should converge towards one another. This principle is important because since amalgam doesn’t bond on the tooth, it needs to be locked in by the mechanical retention provided by the convergence of the walls.

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Errors

Most often overlooked principle, convergence could only be checked with the use of a mirror looking through from the proximal area. Confirm the convergence with the proper use of a mirror.

Improper utilization of the 330 bur. 330 bur is actually manufactured in a way that will help the operator to achieve the convergence of walls. When you look into it closely, the walls of the bur are not parallel but are angled towards each other. So all you have to do is have the bur in constant angulation bur angulation and let the bur do the convergence for you.

Bur angulation and height were not kept constant.

Troubleshooting

When the isthmus width is still narrow, you may resolve this problem by slightly touching the walls with a 330 bur just so that you can transform that wall into a convergent one. Remember to keep you bur angulation in place and do not lift your bur as you glide through the walls.

Prevention

Prevention is the key. The way to get convergence is not by creating it but by allowing the bur to make the convergence for you. As long as your bur angulation and height is constant as you extend your outline form, you will definitely achieve a convergent wall.