The material used ninja jaw angle implant is irrelevant. What matters is whether the design of the implant can achieve the desired external facial effect. When dropping the jaw angles down 2 cms that will require custom made jaw angle implants.
The type of material can have some effect on the 'look' of the jawline. For example, implants like Gortex or Medpor allow a 'tighter' integration with the overlying soft tissue and create a bit of a sharper jawline. Silastic is fine but has a bit of a 'softer/rounder' look at the angle. If you want to increase the height at the angle, you require a firmer implant material that does not 'bend' inwards due to its flex. Gortex or medpor work in that regard. For females, Gortex is preferred in my opinion. The change in the 'slope' of the jawline requires a proper assessment of the shape of the face viewed frontally. Consult a cosmetic Maxillofacial surgeon for consultation