Sometimes, there is no way to salvage the remaining teeth in an arch.  In this case, all of the upper teeth were removed and replaced with a complete denture.  At least there were enough sound teeth on the lower arch to be able to construct a removable partial denture.  This allows for more stability and helps prevent dislodgement while chewing food and talking.  A complete lower denture can be extremely difficult to wear and it is best to avoid wherever possible.