Severe maxillary protrusion often requires Le Fort I osteotomy, either as a monobloc or two‑piece segmental approach. Comparative evidence on their long‑term skeletal stability remains limited. This study aimed to quantitatively compare the long-term skeletal stability of monoblock versus two-piece segmental Le Fort I osteotomy in patients with severe maxillary protrusion. A longitudinal comparative study was conducted on 70 patients (35 monoblock; 35 2-piece segmental). All subjects underwent virtual surgical planning (VSP) for maxillary setback and impaction. Skeletal stability was evaluated using lateral cephalograms at five standardized intervals over 24 months. Measurements focused on the horizontal and vertical positions of the A-point and maxillary central incisor. The results showed that the monoblock group followed a traditional recovery path, exhibiting a minor anterior relapse (+0.84 ± 0.38 mm at 2 years), with the jaw moving slightly forward toward its original position. The 2-piece segmental group demonstrated a pattern referred to here as "posterior drift", continuing to move backwards by an average of -0.52 ± 0.29 mm at the 2-year mark. Statistical testing showed a very large Time × Group interaction effect (ηp2
= 0.81, p < 0.001), suggesting that surgical technique may be associated with differences in stability rather than random variation alone. The study indicates that two‑piece Le Fort I segments are particularly prone to further posterior displacement after surgery, possibly due to compressive forces from the surrounding soft‑tissue environment. These findings might inform clinicians to consider this tendency during treatment planning to minimize relapse risk.
