Spinal Cord Boundary Conditions Affect Brain Tissue Strains in Impact Simulations

Brain and spinal cord injuries have devastating consequences on quality of life but are challenging to assess experimentally due to the traumatic nature of such injuries. Finite element human body models (HBM) have been developed to investigate injury but are limited by a lack of biofidelic spinal cord implementation. In many HBM, brain models terminate with a fixed boundary condition at the brain stem. The goals of this study were to implement a comprehensive representation of the spinal cord into a contemporary head and neck HBM, and quantify the effect of the spinal cord on brain deformation during simulated impacts. Spinal cord tissue geometries were developed, based on 3D medical imaging and literature data, meshed, and implemented into the GHBMC 50th percentile male model. The model was evaluated in frontal, lateral, rear, and oblique impact conditions, and the resulting maximum principal strains in the brain tissue were compared, with and without the spinal cord. A new cumulative strain curve metric was proposed to quantify brain strain distribution. Presence of the spinal cord increased brain tissue strains in all simulated cases, owing to a more compliant boundary condition, highlighting the importance of the spinal cord to assess brain response during impact.

Left ventricular longitudinal strain is a major determinant of CT-derived three-dimensional maximum principal strain: comparison with two-dimensional speckle tracking echocardiography

Computed tomography (CT)-derived three-dimensional maximum principal strain (MP-strain) can provide incremental value to coronary CT angiography for cardiac dysfunction assessment with high diagnostic performance in patients with myocardial infarction. Global longitudinal strain (GLS) measured using two-dimensional speckle tracking echocardiography (2D-STE) is more sensitive than left ventricular ejection fraction (LVEF) for detecting early myocardial dysfunction. We aimed to compare CT-derived MP-strain with each of 2D-STE-derived strains (i.e., longitudinal, circumferential, and radial strains), and identify the major determinants of CT-derived MP-strain among 2D-STE-derived strains. We studied 51 patients who underwent cardiac CT and echocardiography. CT images were reconstructed at every 5% (0-95%) of the RR interval. A dedicated workstation was used to analyze CT-derived MP-strain on the 16-segment model. We calculated CT-derived global MP-strain with all the 16 segments on a per patient basis. Pearson's test was used to assess correlations between CT-derived MP-strain and STE-strain at global and segmental levels. The intra-class correlation coefficient for interobserver agreement for CT-derived global MP-strain was 0.98 (95% confidence interval 0.96-0.99). The low-CT-derived global MP-strain group (≤ 0.43) had more patients with LV dysfunction than the high-CT-derived global MP-strain group (> 0.43). CT-derived global MP-strain was associated with STE-GLS (r = 0.738, P < 0.001), global circumferential strain (r = 0.646, P < 0.001), and global radial strain (r = 0.432, P = 0.001). In multivariate analysis, STE-GLS had the strongest association to CT-derived global MP-strain among three directional STE-strains and LVEF by echocardiography (standardized coefficient =  - 0.527, P < 0.001). STE-GLS is a major determinant of CT-derived global MP-strain. CT-derived MP-strain may enhance the value of coronary CT angiography by adding functional information to CT-derived LVEF.

Reduction in maxillary complete denture deformation using framework material made by computer-aided design and manufacturing systems

The aim of this study was to investigate the effects of framework materials manufactured by dental CAD/CAM systems on complete denture deformation. Four materials were used for the maxillary complete denture framework: fiber-reinforced composite (FRC), nano-zirconia (N-Zr), cobalt-chromium-molybdenum alloy (CCM), and polyether-ether-ketone (PEEK). The framework materials were prepared using CAD/CAM systems. Six dentures of each material were fabricated, using polymethyl-methacrylate (PMMA) as a control. The thickness of the palatal area was 1.0 mm for PMMA and PEEK and 0.5 mm for FRC, N-Zr, and CCM. The denture deformation during occlusal load was monitored using four rosette strain gauges placed on the midline of the denture. The maximum principal strain (MPS) of each gauge, except that at the labial frenum, increased proportionally with increasing applied load. The directions of MPS were predominantly perpendicular to the midline of the denture. When a 200-N load was applied, the MPS at the incisive papilla in N-Zr and CCM was half that of PMMA; there was no significant difference among MPSs of PEEK, PMMA and FRC. The MPS at the end point of the denture in FRC, N-Zr, and CCM was significantly smaller than that of PMMA. The MPSs of the complete denture decreased when the CAD/CAM fabricated framework was used. The effects of the CAD/CAM fabricated framework on complete denture deformation varied due to the material used; however, a CAD/CAM fabricated framework material is considered to be effective for reducing complete denture deformation.

Maximum principal strain as a criterion for prediction of orthodontic mini-implants failure in subject-specific finite element models

OBJECTIVE

To investigate the most reliable stress or strain parameters in subject-specific finite element (FE) models to predict success or failure of orthodontic mini-implants (OMIs).

MATERIALS AND METHODS

Subject-specific FE analysis was applied to 28 OMIs used for anchorage. Each model was developed using two computed tomography data sets, the first taken before OMI placement and the second taken immediately after placement. Of the 28 OMIs, 6 failed during the first 5 months, and 22 were successful. The bone compartment was divided into four zones in the FE models, and peak stress and strain parameters were calculated for each. Logistic regression of the failure (vs success) of OMIs on the stress and strain parameters in the models was conducted to verify the ability of these parameters to predict OMI failure.

RESULTS

Failure was significantly dependent on principal strain parameters rather than stress parameters. Peak maximum principal strain in the bone 0.5 to 1 mm from the OMI surface was the best predictor of failure (R(2) = 0.8151).

CONCLUSIONS

We propose the use of the maximum principal strain as a criterion for predicting OMI failure in FE models.