Metal fillings cause artifacts with low energy X rays (i.e. a CT scan with kV energy). In the MV range this is not a problem.
I too have several metal fillings and the focus of the irradiation was the anterior mobile tongue, i.e. the portion between your teeth. No teeth were removed prior to IMRT, with enough irradiation positions they could get around the metal. However, if there are extensive metal parts obstructing the radiation path then this may be a problem.
I am a bit perplexed about shielding dental work form x rays. This is not going to work x rays are not deterred by wax.
What you can do is use wax or cotton to move lips a bit out of the radiation field.... but only if the RO is on board with this.

M