A nondensity property of preperiodic points on Chebyshev dynamical systems

Let k be a number field with algebraic closure , and let S be a finite set of primes of k, containing all the infinite ones. Consider a Chebyshev dynamical system on P2. Fix the effective divisor D of P2 that is equal to a line nondegenerate on 2[−2,2]. Then we will prove that the set of preperiodic points on which are S-integral relative to D is not Zariski dense in P2.