Skeletal and Dentoalveolar Components of Maxillary Expansion: A Systematic Review of Post-Treatment Stability

Background: Maxillary transverse deficiency is a common skeletal discrepancy in orthodontic patients that often requires expansion therapy for correction. Failure to address this condition during growth may compromise the orthopedic prognosis, frequently necessitating surgically assisted rapid palatal expansion (SARPE) or other orthognathic surgical procedures after skeletal maturity. Methods: The studies in this systematic review were selected according to predefined inclusion criteria. Randomized controlled trials, controlled clinical studies, and cohort studies published within the last 10 years with a follow-up ≥ 6 months were included. The databases PubMed, Scopus, and Embase were searched. Orthodontic outcomes included midpalatal suture opening, skeletal transverse changes, intermolar width variations, dental tipping, and long-term stability. Thirteen studies met the eligibility criteria. Risk of bias was assessed using the RoB 2 and the Newcastle–Ottawa Scale. Results: All orthodontic devices produced significant transverse expansion in the short term. Bone-borne and hybrid systems showed a greater initial skeletal component, with greater expansion at the maxillary and nasal basal levels and limited relapse over time. Tooth-borne expansion was associated with greater dental tipping and reduction in buccal bone thickness, with partial recovery during retention. Over time, loss of expansion mainly affected the dentoalveolar component, whereas the skeletal component remained more stable. Long-term data (≥3–5 years) remain limited but suggest that relapse is predominantly related to dental uprighting rather than a true loss of skeletal base width. Conclusions: Long-term transverse stability improves when expansion is predominantly skeletal. Bone-supported and hybrid appliances may produce a greater initial skeletal contribution and reduce dental tipping in some clinical settings; however, current evidence does not demonstrate superior long-term stability compared with tooth-borne expansion. Additional prospective orthodontic studies with extended follow-up, particularly without prolonged retention, are required.