  We study the local H\"older regularity of strong solutions $u$ of
second-order uniformly elliptic equations having a gradient term with
superquadratic growth $\gamma > 2$, and right-hand side in a Lebesgue space
$L^q$. When $q > N\frac{\gamma-1}{\gamma}$ ($N$ is the dimension of the
Euclidean space), we obtain the optimal H\"older continuity exponent $\alpha_q
> \frac{\gamma-2}{\gamma-1}$. This allows us to prove some new results of
maximal regularity type, which consist in estimating the Hessian matrix of $u$
in $L^q$. Our methods are based on blow-up techniques and a Liouville theorem.
