  Complementing previous theoretical and experimental work, we explore new
types of short-range modifications to Newtonian gravity arising from
spacetime-symmetry breaking. The first non-perturbative, i.e., to all orders in
coefficients for Lorentz-symmetry breaking, are constructed in the Newtonian
limit. We make use of the generic symmetry-breaking terms modifying the gravity
sector and examine the isotropic coefficient limit. The results show new kinds
of force law corrections, going beyond the standard Yukawa parameterization.
Further, there are ranges of the values of the coefficients that could make the
resulting forces large compared to the Newtonian prediction at short distances.
Experimental signals are discussed for typical test mass arrangements.
