This section will focus on the Axial wall of the proximal box and the axiopulpal line angle.

Axial Walls

The axial walls (buccolingual direction) follow the external outline of the tooth. This is to preserve tooth structure.

The axial walls (occlusogingival direction) is slightly divergent, this is for convenience form : for the ease of insertion of instruments in the proximal box and adequate visualization in this area. It is also because of the enamel is thicker on the occlusal than on the gingival area thus there will be more reduction from the occlusal than the gingival area of the proximal. This is to create a uniform amount of reduction. Then naturally when you imagine the tooth in sagittal view, the wall should be divergent.

However, overdoing the divergence just for the sake of doing a divergence is a bad habit because of the risk of making the entrance of the proximal box bigger instead. Some would say, “Oh, I think my divergence in this are is not so clear, I think I should do more!” Please do not do this. If you did a slight angle of your bur in this area then that’s it. So, keep in mind that by doing a slight a divergence in this area is because of the anatomy of the tooth and not just because of doing so.

Axiopulpal line angle

The axiopulpal line angle is beveled, this is to prevent excessive force to be applied from the tooth towards the restoration (prevent fracture). Use a hand instrument, marginal trimmers, to bevel the corner of the axiopulpal line angle.