There is little info on this subject on the web, we usually do these through a intra-oral incision (as for a Lefort 1 approach), subperiosteally, then fixing the implant with a miniscrew.
Several types do exist. Medpor seems the best option, but silicone is also possible.
Contoured Mandibular Angle Implants
The MEDPOR Contoured Mandibular Angle is anatomically shaped for augmentation of the mandibular ramus and body to the mental foramen. The anatomical shape of this implant is designed to minimize dead space under the implant as well as the need for reshaping at the time of surgery.