Objectives: The aim of this in-vitro-study was to investigate the adaption behaviour and homogeneity of retrograde root canal filling materials as well as the impact of various cavity preparation forms. Methods: A total of 135 human single-rooted teeth were filled with gutta-percha after endodontic treatment. The specimens were randomly assigned to one of nine series (n=15). Specimens without retrograde root filling were used as the control group. The other specimens were divided into two subgroups according to the sonically supported retrograde preparation form (parallel or retentive preparation) which contain four material groups in each case (BiodentineTM, Pro RootTM MTA, Super-EBA^®, Ketac filTM Plus Aplicap). Afterwards three histological cuts were prepared at 1 mm, 2 mm, and 3 mm distance from the apex. The following criteria were examined using an optical microscope (5x zoom): imperfect margin, maximal marginal gap, and the number of air pockets in each section. Results: The statistical evaluation revealed significantly better results for retentive retrograde preparation regarding the proportion of imperfect margin and the amount of air pockets than parallel preparation (p≤ 0.05, Tukey's test). The pairwise comparison of maximal marginal gap showed no significant differences (p>0.05, Tukey's test). For the groups filled with Ketac filTM Plus Aplicap, a significantly higher proportion of maximal marginal gaps compared to all other materials (p≤ 0.05, Tukey's test) was evaluated. Furthermore, significant differences could be found considering imperfect margins compared to Pro Root MTA fillings, and air pockets compared to the fillings with Pro Root MTA, Biodentine and the control group (p≤ 0.05, Tukey's test). Conclusions: The preparation form and the selection of the retrograde root filling material during an apicoectomy can have a significant influence on the adaptation behaviour and homogeneity of the retrograde root filling and therefore might have an influence on the clinical outcome. Keywords: retrograde Cavities, root canal filling materials, cavity preparation