Implants involve a titanium screw placed in your jaw bone with an attached tooth-like crown. An implant is usually for a single tooth due its cost.
When a tooth cannot be saved and an implant is not possible, then an alternative plan is for a bridge that spans the space by attaching to the adjacent teeth.
Plates involve replacing a tooth or teeth with an appliance that can be removed for cleaning and at night. This is an alternative plan when the other treatments are not possible.