A comparative finite element analysis of maxillary expansion with and without midpalatal suture viscoelasticity using a representative skeletal geometry

Objective analysis of facial bone fracture CT images using curvature measurement in a surface mesh model

The human facial skeleton consists of multiple segments and causes difficulty during analytic processes. We developed image analysis software to quantify the amount of injury and validate the smooth curvature of the surface after facial bone reduction surgery. Three-dimensional computed tomography images of facial bone were obtained from 40 patients who had undergone open reduction surgery to treat unilateral zygomaticomaxillary fractures. Analytic software was developed based on the discrete curvature of a triangular mesh model. The discrete curvature values were compared before and after surgery using two regions of interest. For the inferior orbital rim, the weighted average of curvature changed from 0.543 ± 0.034 to 0.458 ± 0.042. For the anterior maxilla, the weighted average of curvature changed from 0.596 ± 0.02 to 0.481 ± 0.031, showing a significant decrement (P < 0.05). The curvature was further compared with the unaffected side using the Bray-Curtis similarity index (BCSI). The BCSI of the inferior orbital rim changed from 0.802 ± 0.041 to 0.904 ± 0.015, and that for the anterior maxilla changed from 0.797 ± 0.029 to 0.84 ± 0.025, demonstrating increased similarity (P < 0.05). In computational biology, adequate analytic software is crucial. The newly developed software demonstrated significant differentiation between pre- and postoperative curvature values. Modification of formulas and software will lead to further advancements.

Cranial suture morphometry and mechanical response to loading: 2D vs. 3D assumptions and characterization

Cranial sutures are complex soft tissue structures whose mechanics are often studied due to their link with bone growth in the skull. Researchers will often use a cross-sectional two-dimensional slice to define suture geometry when studying morphometry and/or mechanical response to loading. However, using a single cross section neglects the full suture complexity and may introduce significant errors when defining their form. This study aims to determine trends in suture path variability through skull thickness in a swine model and the implications of using a 'representative' cross section on mechanical modeling. To explore these questions, a mixture of quantitative analysis of computed tomography images and finite element models was used. The linear interdigitation and width of coronal and sagittal sutures were analyzed on offset transverse planes through the skull thickness. It was found that sagittal suture width and interdigitation were largely consistent through the skull thickness, whereas the coronal suture showed significant variation in both. The finite element study found that average values of displacement and strain were similar between the two-dimensionally variable and three-dimensionally variable models. Larger ranges and more complex distributions of strain were found in the three-dimensionally variable model. Outcomes of this study indicate that the appropriateness of using a representative cross section to describe suture morphometry and predict mechanical response should depend on specific research questions and goals. Two-dimensional approximations can be sufficient for less-interdigitated sutures and when bulk site mechanics are of interest, while taking the true three-dimensional geometry into account is necessary when considering spatial variability and local mechanical response.

Finite element simulations of the effects of an extraoral device, RAMPA, on anterosuperior protraction of the maxilla and comparison with gHu-1 intraoral device

OBJECTIVES

To investigate the effects of an extraoral device, right-angle maxillary protraction appliance (RAMPA), combined with a semi-rapid maxillary expansion intraoral device (gHu-1) on the anterosuperior protraction of maxillary bone.

MATERIALS AND METHODS

The finite element (FE) model included craniofacial bones and all sutures. The linear assumption was assumed for the FE simulations and the material properties of bones and sutures. The gHu-1 was simulated under screw activations equal to Δx = 0.25 and 0.5 mm in the lateral direction with and without RAMPA under a set of external forces {F1 = 2.94, F2 = 1.47, F3 = 4.44} N.

RESULTS

Displacement contours, nodal displacements of 12 landmarks, and von Mises stresses were compared. Combining RAMPA and gHu-1 (with Δx = 0.25 mm) resulted in changes in the displacement of the front part of the maxilla near the mid-palatal suture from (0.02, -0.1, -0.02) mm to (0.02, 0.3, 0.8) mm. For gHu-1 with Δx = 0.5 mm, the displacement of the same part changed from (0.04, -0.04, -0.2) mm to (0.04, 0.3, 0) mm. Similar trends were found in other locations.

CONCLUSIONS

The findings are in agreement with the previous cephalometric clinical data of an 8-year-old patient and prove the positive effects of RAMPA on the anterosuperior protraction of the maxilla when it is combined with the intraoral device gHu-1. In addition, RAMPA does not interfere with the lateral expansion generated by the intraoral device.