This review examines the adverse outcomes linked to two adult rapid maxillary expansion procedures—Surgically Assisted Rapid Palatal Expansion (SARPE) and Miniscrew-Assisted Rapid Palatal Expansion (MARPE)—to support decision-making for the most efficient and cost-effective treatment strategy. The protocol adhered to the PRISMA-ScR framework for scoping reviews. Study eligibility was aligned with the research goals, and a PICO question guided article selection. Data were collected from MEDLINE (via PubMed), Scopus, Cochrane Library, Web of Science, and Embase, along with hand-searching. From 746 retrieved records, 26 fulfilled all inclusion criteria. Among them, 11 were retrospective studies, 12 prospective studies, and 3 randomized clinical trials. SARPE was the subject of 21 papers, MARPE of 4, and 1 addressed both. Reported side effects were grouped into five categories: treatment failure, asymmetric opening, dentoalveolar changes, surgical risks, and appliance-related issues. Both techniques carry inherent risks. The most frequent were surgical and dentoalveolar complications. Dental tipping and related dentoalveolar alterations were primarily observed in MARPE, whereas SARPE was more commonly associated with surgical problems. Age and device planning strongly influence outcomes; hence, case selection and careful preparation are essential to reduce complications in adult expansion.
