Numerical Three-dimensional Finite Element Modeling of Cavity Shape and Optimal Material Selection by Analysis of Stress Distribution on Class V Cavities of Mandibular Premolars

Computational models and their applications in biomechanical analysis of mandibular reconstruction surgery

Advanced head and neck cancers involving the mandible often require surgical removal of the diseased parts and replacement with donor bone or prosthesis to recreate the form and function of the premorbid mandible. The degree to which this reconstruction successfully replicates key geometric features of the original bone critically affects the cosmetic and functional outcomes of speaking, chewing, and breathing. With advancements in computational power, biomechanical modeling has emerged as a prevalent tool for predicting the functional outcomes of the masticatory system and evaluating the effectiveness of reconstruction procedures in patients undergoing mandibular reconstruction surgery. These models offer cost-effective and patient-specific treatment tailored to the needs of individuals. To underscore the significance of biomechanical modeling, we conducted a review of 66 studies that utilized computational models in the biomechanical analysis of mandibular reconstruction surgery. The majority of these studies employed finite element method (FEM) in their approach; therefore, a detailed investigation of FEM has also been provided. Additionally, we categorized these studies based on the main components analyzed, including bone flaps, plates/screws, and prostheses, as well as their design and material composition.

Mechanical and Thermal Stress Analysis of Cervical Resin Composite Restorations Containing Different Ratios of Zinc Oxide Nanoparticles: A 3D Finite Element Study

Due to an increase in prevalence of cervical lesions, it is important to use appropriate restorative materials to reduce the incidence of secondary lesions. Owing to having antibacterial properties, cervical composite restorations containing different ratios of Zinc Oxide nanoparticles (ZnO NPs) have been analyzed using the Finite Element method to determine the optimal incorporation ratio from mechanical and thermal perspectives. A numerical simulation is conducted for a mandibular first premolar with a cervical lesion (1.5 × 2 × 3 mm³) restored with composites containing 0 to 5% wt. ZnO NPs. Subsequently, the samples are exposed to different thermo-mechanical boundary conditions, and stress distributions at different margins are examined. The accumulated stress in the restoration part increases for the 1% wt. sample, whereas the higher percentage of ZnO NPs leads to the reduction of stress values. In terms of different loading conditions, the least and most stress values in the restoration part are observed in central loading and lingually oblique force, respectively. The change in the surface temperature is inversely correlated with the ratio of ZnO NPs. In conclusion, the composite containing 5% wt. ZnO NPs showed the most proper thermo-mechanical behavior among all samples.

Mechanical Behavior of Alkasite Posterior Restorations in Comparison to Polymeric Materials: A 3D-FEA Study

The present investigation evaluated the effect of the combination of different dental filling materials in Class I cavities under occlusal loading using three-dimensional finite elements analysis (FEA). Six computer-generated and restored models of a lower molar were created in the CAD software and compared according to the biomechanical response during chewing load condition. Two adhesively bonded bulk restorative materials [bulk-fill resin composite (BF) or Alkasite (Alk)] were evaluated with or without the presence of a base material below (flowable resin composite or glass ionomer cement). A food bolus was placed on the occlusal surface mimicking the compressive occlusal load (600 N) during the static linear analysis. The maximum principal stress (tensile) was calculated as stress criteria in enamel, dentin and restoration. All models showed high stresses along the enamel/restoration margin with a similar stress trend for models restored with the same upper-layer material. Stress values up to 12.04 MPa (Alk) or up to 11.12 MPa (BF) were recorded at the enamel margins. The use of flexible polymeric or ionic base material in combination with bulk-fill resin composite or Alk did not reduce the stress magnitude in dentine and enamel. Class I cavities adhesively restored with bulk-fill resin composite showed lighter stress concentration as well as Alk. Therefore, adhesively bonded Alk restoration showed a promising mechanical behavior when used with different base materials or as a bulk restoration for posterior Class I cavity.

[Mandibular defect reconstruction using digital design-assisted free fibula flap and threedimensional finite element analysis of stress distribution]

OBJECTIVE

To evaluate of the clinical value of preoperative digital design-assisted free fibular flap for reconstruction of different types of mandibular tissue defects using three-dimensional finite element analysis.

METHODS

This retrospective analysis was conducted in 48 patients undergoing reconstruction of mandibular defects following tumor resection using free fibular flaps. In 24 of the cases, digital design of free fibular flap was performed before the operation (experimental group), and the other 24 patients with digital design of the flap served as the control group. At 1 year after the surgery, the patients underwent mandibular CT examination and a 3-dimensional finite element model of the mandible was constructed using Mimics, Geomagic, Solidworks and Ansys. The stress distribution on the reconstructed mandibles with the H, L, or LCL types of defects, classified according to the HCL classification method, was determined under specific constraints and load conditions and compared between the experimental and control groups.

RESULTS

The operations were completed successfully in all the patients, and none of them had tumor recurrence at 1 year after the operation. On the reconstructed mandibles using free fibular flaps, the stress was concentrated mainly on the neck of the bilateral condyle, the anterior and posterior edges of the ascending mandibular ramus, and the connection between the posterior end of the fibula and the mandible. A large size of mandibular defects caused greater stress at the contralateral condyle. For L-shaped defects, the maximum stress at the healthy and ipsilateral condyle necks and transplanted fibula were significantly lower, while the stress level at the healthy side mandibular angle was significantly greater in the experimental group than in the control group (P < 0.05). For LCL type defects, the maximum stress at the contralateral condyle neck was smaller but the stress in the condyle area on the affected side, the bilateral mandibular angle area and the fibula area were all significantly greater in the experimental group than in the control group (P < 0.05).

CONCLUSION

Digital design of the free fibular flap improves the accuracy of reconstruction of mandibular defects and helps to achieve uniform stress distribution on the reconstructed mandible.