Experimentally, there is no consensus to find out which of the alpha and beta crystal phases of polyvinylidene fluoride (PVDF) exhibits the highest melting temperature. To unveil this ambiguity, we use an established procedure based on achieving the Gibbs-Thomson equation from molecular dynamics simulation on pure crystals and crystals containing 10% of regioisomerism defects. The rightness of the protocol is confirmed by the agreement with experimental data. We thus show that in pure crystals, it is the a form that exhibits the highest melting temperature. However, insertion of regioisomerism defects inside crystals influences more the value of the melting point of the a form than for the b crystal. The pure and altered b phase then show the highest melting temperature. This conclusion explains the experimental difficulty on finding which of the a and b crystal forms displays the highest melting temperature, since PVDF samples always contain regioisomerism defects. (C) 2017 Elsevier Ltd. All rights reserved.