## 4 Discussion  
The present study adopted an integrative methodology, combining three-dimensional modeling with finite element analysis (FEA) to investigate the biomechanical behavior of mandibular second premolars restored with amalgam and a composite under varying masticatory forces. The results provide valuable insights into the complex interactions between the mandibular structure, the dynamics of the muscular forces, and the integrity of the restored tooth. In the mathematical model presented, the muscular force was applied at a specific angle relative to the horizontal plane, and its transfer to the premolar was conceptualized as a lever system, with the temporomandibular joint functioning as the fulcrum--a model similar to that described by [PERSON] and collaborators as early as the 1970s [1]. The vectorization of the masticatory force enabled the differentiation between its vertical component--responsible for the axial loading of the tooth--and its horizontal component, which contributes to the lateral displacement of the dental surface. This distinction is essential for rigorous biomechanical analysis, as each component induces distinct stress responses within the dental and restorative structures. Correlations with clinical studies and FEA simulations, such as those conducted by [PERSON] et al. [3], confirm that vertical forces, while essential for efficient mastication, generate significant stress at the base of restorations and at the restorative interface, whereas horizontal forces substantially contribute to the occurrence of marginal fractures and delamination, particularly in patients with bruxism [6]. Figure 12: Global stress distribution in the amalgam filling, 200 N.  
The comparison of the mechanical behavior of the amalgam and composite under these loads revealed significant differences. The amalgam, characterized by rigidity and an elastic modulus closely matching that of dentin, demonstrated a more homogeneous stress distribution, with reduced concentration in high-risk areas. This behavior supports the hypothesis of the functional integration of amalgam into the dental structure, forming a biomechanically cohesive unit capable of withstanding high loads without excessive deformation--a fact also confirmed by [PERSON] et al., who highlighted its remarkable clinical durability in posterior restorations [16]. In contrast, the composite--despite its aesthetic advantages and clinical manageability--exhibited a more complex internal stress distribution, with a pronounced tendency for stress accumulation at deeper levels, particularly in the case of extensive restorations. This finding aligns with the results reported by [PERSON] [15], who demonstrated an increased susceptibility of composites to microcracks and progressive deterioration under the conditions of repetitive loading. The mandible, as a mobile and adaptable structure, directly influences stress distribution within restorations, especially under conditions of bruxism or parafunctional activity. In such cases, sudden increases in masticatory force magnitude, combined with atypical angles of application, can exacerbate stress in the basal region of the dental crown--a zone also identified as vulnerable in a study by [PERSON] et al. [26]. The FEA simulations in the present study indicated that the maximum stresses recorded for the composite (3047 MPa) significantly exceeded the material's strength limits, suggesting increased structural vulnerability in patients subjected to extreme occlusal loads. This study also emphasizes that the interface between the dental tissue and the restorative material represents the area most prone to deterioration, regardless of the type of material used. The difference between the elastic moduli of the dentin and the restorative material governs the transfer of stress, and a significant mismatch may lead to the accumulation of residual stresses.