Mixed-phase clouds in polar regions play a crucial role in surface ice melting. To accurately predict their radiative impact in climate models, an accurate representation of their microphysical structure is required. However, cloud ice content is generally underpredicted in models when primary ice nucleation is constrained with measurements. Moreover, flight measurements often indicate that the observed Ice Crystal Number Concentrations are order(s) of magnitude larger than the available Ice Nucleation Particles. Ice multiplication has been suggested as a possible cause for this discrepancy, yet the underlying mechanisms and their relative importance remain unknown. In this study we investigate the impact of two ice multiplication mechanisms, rime-splintering and mechanical break-up upon ice-ice collisions, on polar mixed-phase clouds using modeling tools. The sensitivity of these processes to uncertainties in primary ice formation is further examined