37, congenital lack of enamel. Reasons for Zirconia on top and Acrylic on bottom?

I am a 37 year old woman who is having to have this procedure this young due to a congenital lack of enamel that has caused my teeth to completely crumble. I also have a really significant issue with bruxism as well. So the periodontist I’m seeing recommended we do zirconia on the top and acrylic on the bottom. He explained his reasoning for this, but so much info was being thrown at me that I didn’t retain all of it. Price isn’t a prohibitive factor in this decision, so can anyone explain why he would choose acrylic on the bottom instead of doing all zirconia? From what I understand, acrylic isn’t nearly as durable and has to be replaced much sooner than zirconia and given my young age, I don’t understand why he wouldn’t go with the option that would last for as long as possible. Thanks for any insight!