Based on what I've read, I would second the vote for Valplast suggested by the first person to respond. Only possible down side would be that it is hard to polish and cannot be easily relined during adjustments.
Dr. Frank Jerome, a holistic dentist dedicated a whole section in his book to partials and which type to use. The chapter called "replacing missing teeth" in his book Tooth Truth says they should be made of Flexite, a flexible plastic but to avoid the pink color they can use to make it flesh-toned due to metals in that plastic. He says this is an alternative to cemented bridges to replace one or two back teeth.
He recommends "flippers" if you have one or two missing teeth in the upper front. Also says patient's attitude plays an important role in the success of wearing any partial denture.
He also suggests you ask your dentist to show the MSDS (material safety data sheet) for any pink coloured acrylic that is being used in any partials you are considering having placed in your mouth as many contain small but toxic metals.