Labiolingual Loading Biomechanics on Central Incisor Under Different Periodontal Conditions: A Finite Element Study

Objective: In this finite element study, the biomechanical effects of force application at different lingual versus labial sites on a maxillary central incisor with alveolar bone loss and proclination were compared. Methods: Finite element models were constructed to simulate 4 levels of alveolar bone loss: none, 1/3, 1/2, and 2/3 of the root length. Labiolingual inclination was defined by the U1-SN angle (97°-115°). A combined force of 1.5 N retraction and 0.5 N intrusion was applied at 4 sites: the labial crown centre (La), the lingual fossa midpoint (Li(M)), the lingual fossa-cingulum transition (Li(T)), and the cingulum prominence (Li(P)). Results: In models with 0–1/3 bone loss, labial forces produced predictable mesial crown displacement with increasing U1 SN angle, improving sagittal control. Lingual forces reduced distal displacement—most effectively at Li(M)—while Li(P) best controlled lingual inclination. Vertically, intrusion occurred under labial force with 1/3 loss, but extrusion under lingual force. Models with 1/2–2/3 bone loss showed complex horizontal movements, vertical extrusion, and reduced 3-dimensional control. Periodontal ligament (PDL) stress varied with force site, angle, and bone loss. Without loss, peak stress occurred near 100°; greater loss shifted this peak and increased stress. Sensitivity analysis showed that a 30% reduction in PDL modulus increased displacement by 43%, whereas a 30% increase reduced it by 23%. Conclusions: Alveolar bone loss is the dominant factor influencing tooth displacement patterns and results in greater than ±30% changes in the PDL modulus inclination. Increased bone loss exacerbates crown lingual tipping and extrusion. Labial force provides better control over lingual tipping than lingual force does. Among lingual sites, the cingulum minimizes these adverse movements. Sensitivity analysis confirmed that variations in the elastic modulus of the PDL led to changes in initial tooth displacement, whereas the tooth movement rate remained relatively stable.