Book thickness of planar zero divisor graphs

Let R be a finite commutative ring with identity. We form the zero divisor graph of R by taking the nonzero zero divisors as the vertices and connecting two vertices, x and y, by an edge if and only if xy = 0. We establish that if the zero divisor graph of a finite commutative ring with identity is planar, then the graph has a planar supergraph with a Hamiltonian cycle. We also determine the book thickness of all planar zero divisor graphs.