My new dentist

A plunger cusp is the name given to a destructive situation where the working cusp on one tooth (usually upper back tooth inner cusp) forces food between two opposing teeth.
This can occur when the tooth with the plunger cusp is slightly rotated due to wear or fracture of the tooth structure or filling in the opposing tooth. This allows space for the tooth to shift into the space and can lead to difficulty in restoring the worn or broken tooth as this cusp overloads the repair.
the solution would be to correct the shape of the plunger cusp (although a more complicated option is to move the tooth back with a brace) before repairing the fracture as this gives a much better chance of long term success