  In this work we derive global estimates for viscosity solutions to fully
nonlinear elliptic equations under relaxed structural assumptions on the
governing operator which are weaker than convexity and oblique boundary
conditions and under suitable assumptions on the dat. Our approach makes use of
geometric tangential methods, which consists of importing "fine regularity
estimates" from a limiting profile, i.e., the Recession operator, associated
with the original second order one via compactness and stability procedures. As
a result, we devote a special attention to the borderline scenario. In such a
setting, we prove that solutions enjoy BMO type estimates for their second
derivatives. In the end, as another application of our findings, we obtain
Hessian estimates to obstacle type problems under oblique boundary conditions
and no convexity assumptions, which may have their own mathematical interest. A
density result in a suitable class of viscosity solutions will be also
addressed.
