Objectives: The aim of the study was the long-term assessment of the condition of periodontal tissues after corticotomy-assisted orthodontic expansion in patients with transverse maxillary deficiency. Materials and Methods: The study included a group of 18 adults (9 women, 9 men) aged between 24 and 40 years who were at least 5 years post treatment. The following parameters were assessed: the full mouth plaque index (FMPI), full mouth bleeding on probing (FMBOP), probing depth (PD), clinical attachment level (CAL), gingival recession height (GR), recession width (RW), papilla height (PH), papilla width (PW), bone sounding (BS), phenotype, and KT. Results: During examination performed at least 5 years after the completion of orthodontic treatment, the values of PD and CAL were found to be considerably decreased compared to the examination one year post treatment (PD: −0.23; 95% Cl: −0.29, −0.16) (CAL: −0.04; 95% Cl: −0.17, 0.10). The other parameters—FMPI, FMBOP, GR, RW, PH, PW, BS, phenotype, and KT—did not change significantly. Conclusions: Corticotomy-assisted orthodontic arch expansion does not have a negative effect on the periodontium in long-term observations. Clinical Relevance: Orthodontic arch expansion can lead to bone dehiscence and gingival recession. Long-term observations revealed that corticotomy-assisted orthodontic expansion of the upper arch is not followed by negative changes in periodontal status.