Defects play a critical role in the dynamic fragmentation process of structural ceramics. Cracks initiate at seemingly random locations, propagate and coalesce to form fragments. The process is accompanied by stress release waves, whose influence is difficult to account for without numerical analysis. In this paper, we use a finite-element program with a cohesive fracture capability, to relate a defect distribution contained in a material with the resulting number of fragments. We show how the distribution tail, e.g. the number of large defects, and the rate at which cracks can be initiated at these sites have a critical influence on the generation of stress release waves and thus on the fragmentation process. Our numerical calculations yield a new factor, which we label communication factor, that we use to normalize the average fragment size and to define a new scaling function of material properties, defect statistics and loading rate.