I have been told that I have a cavity. My DDS said that he requires me to pay for a 'desensitizer' during the procedure. I am blessed with no having sensitvie teeth and believe this is just a way to make money off me. Is this critical? I did not have this in the past with other fillings and don't believe this is needed now.

What do you recommend?

What kind of desensitizer is he talking about? I'd call and ask what the product is he is using for desensitizing. Where is he placing the desensitizer, along the gumline or under the filling?
You could also go for a second opinion in another office.

Some times this is done when the decay is very close to the nerve. I agree with the first person, get a 2nd opinion.