OBJECTIVE Dental traumatic injuries are common in children during the mixed dentition stage. These injuries usually require splinting for stabilization, which is complicated by the various stages of the permanent tooth development and primary tooth exfoliation. The aim of this study was to evaluate the effect on mobility of splint materials and extensions for an avulsed central incisor, stabilized with and without the adjacent incisor under intrusive and extrusive loading with different periodontal ligament (PDL) conditions. METHODS Seventeen 3D model variations were created from a CBCT scan of a 7-year-old patient without erupted permanent upper lateral incisors. A 1000 N palatal load on the right central incisor simulated the avulsion injury and created an increased alveolus and bone deformation, resulting in an increased PDL thickness of 0.45 mm. Wire-resin composite splints with 0.9 mm cross-section (WCS) or 1.0 mm diameter nylon-resin composite splints (NCS) were created. The models simulated conditions with and without the adjacent upper central incisor. Two PDL conditions were investigated, simulating detached PDL or PDL with polyether impression material-like properties. Mobility was calculated under simulated biting loads in horizontal and vertical (intrusive and extrusive) directions. RESULTS The NCS allowed greater tooth mobility of the avulsed incisor than the WCS, irrespective of splint extension, PDL condition, or load application. During horizontal loading, polyether-like properties for the PDL allowed around 0.2 mm mobility of the avulsed tooth with the WCS, similar to the intact tooth, whereas a simulated detached PDL allowed 25% more mobility with a WCS than with a NCS. CONCLUSIONS Based on the FEA analysis, a 1.0 mm NCS may be suitable for splinting avulsion injuries during the mixed dentition stage compared to the considerably more rigid WCS. The NCS models provided flexibility for PDL healing while maintaining stability, even when missing adjacent teeth increased span widths. Extensions beyond directly adjacent teeth did not alter the mobility with the NCS but should still be considered an extra protection in case of bond failure or exfoliation.