Aim: The aim of our study was to find out what the change in the slope of the prosthetic plane will be after five years of wearing a complete prosthesis. Materials and Methods: A total of 20 subjects participated in the study. Two lateral cephalograms were performed for each of the subjects, the first when the prosthesis was placed, and the second after five years of prosthesis wearing. Imaging was performed on an X-ray machine (Siemens Roentgen Kugel 2E), with all X-ray films being from the same manufacturer (AGFA-ORTHO CP- G PLUS) and obtained in a similar manner, in the same box using a developer produced by the same manufacturer (AGFA G 138 i). Cephalometric data were collected by manually tracing a teleroentgenogram on tracing paper with a 3H pencil. All detailed measurements were made using a precision sliding caliper (MEBA, Zagreb, Croatia). The statistical calculation was made using the SPSS 12.0 program (Statistical Package for Social Science, Chicago, Illinois, USA). Results: The results point to the fact that there were statistically significant changes in the angles of the prosthetic plane in relation to the mandibular (Me-Go), palatal (ANS-PNS), and Frankfurt horizontal plane (Po-Or) during the five-year-long prosthesis wearing. Conclusion: A statistically significant change in the angle of the prosthetic plane occurred in all participants during the five-year-long wearing of a complete prosthesis. New complete prostheses were required due to impaired functionality given the changes in the slope of the prosthetic surface.