Center of Resistance for Maxillary Expansion in Unilateral Cleft Lip and Palate Compared to Normal Skull: A 3-Dimensional Finite Element Analysis

Objective To identify and compare the location of the center of resistance (CRes) for maxillary expansion in a normal skull model and a unilateral complete cleft lip and palate (UCLP) model using 3-dimensional finite element analysis. Study Design A 3-dimensional craniofacial model was constructed from computed tomography images of a 10-year-old patient. Two models were generated: one representing a normal mid-palatal suture and another representing a UCLP defect. A transverse force of 5 N was applied bilaterally at multiple anteroposterior positions and vertical levels. The displacement of 8 bony landmarks within the nasomaxillary complex, along with color-coded displacement maps, was recorded and compared across all loading conditions. Results In the normal skull model, symmetrical lateral displacement of the nasomaxillary complex was observed when force was applied 20 mm anterior to the posterior nasal spine and 12 mm above the palatal plane. In the UCLP model, symmetrical movement occurred at the same anteroposterior position but at a higher vertical level, 20 mm above the palatal plane. Force application below, anterior, or posterior to these points resulted in asymmetric and tipping movements of the maxillary segments. Conclusion The CRes location for maxillary expansion varies with maxillary morphology. In the normal model, the optimal force application point is near the second primary molar, approximately 12 mm above the palatal plane. In the UCLP model, this point shifts superiorly to 20 mm. These findings reflect altered biomechanical behavior in cleft conditions and emphasize the importance of individualized force application in maxillary expansion.