Comparison of Trabecular Bone Mineral Density Measurement Using Hounsfield Unit and Trabecular Microstructure in Orthodontic Patients Using Cone-Beam Computed Tomography

From SPECT/CT towards absolute quantification? - the case of unilateral condylar hyperplasia of the mandible

BACKGROUND

Unilateral condylar hyperplasia (UCH) of the mandible is a rare condition characterized by asymmetric growth of the mandibular condyles. Bone scintigraphy with SPECT(/CT) is commonly used to diagnose UCH and guide treatment. Still, varying results have been reported using the traditional threshold of 55%:45% in relative tracer uptake. While absolute quantification of uptake on SPECT/CT could improve results, optimal correction and reconstruction settings are currently unknown.

METHODS

Three anthropomorphic phantoms representing UCH were developed from patient CT volumes and produced using 3D printing technology. Fillable spherical inserts of different sizes (Ø: 8-15 mm) were placed in the condylar positions representing symmetrical and asymmetrical distributions. Recovery coefficients were determined for SPECT/CT using various reconstruction corrections, including attenuation and scatter correction (ACSC), resolution modeling (RM), and partial volume correction (PVC) using phantom measurements. Uptake ratios between condyles and condyle to clivus were evaluated. Finally, the impact of these correction techniques on absolute activity and diagnostic accuracy was assessed in a retrospective patient cohort for the diagnostic threshold of 55%:45%.

RESULTS

The activity was only partially recovered in all spherical inserts (range: 22.5-64.9%). However, RM improved relative recovery by 20.2-62.3% compared to ACSC. In the symmetric phantoms, the 95% confidence interval (CI) of condyle ratios included the diagnostic threshold (57.6%:42.4%) for UCH when using ACSC potentially leading to false positives, but not for ACSCRM datasets. Partial volume corrections coefficients from the NEMA IQ phantom was positionally dependent, with improvements seen performing PVC using coefficients derived from anthropomorphic phantoms. Retrospective application in a patient cohort showed only a weak linear correlation (R²: 0.25-0.67) and large limits of agreement (9.6-12.5%) between different reconstructions. Up to 44% of patients were reclassified using the 55%:45% threshold. Using clinical outcome data, ACSCRM had highest sensitivity (91%; 95% CI 59-100%) and specificity (66%; 95% CI 47-81%), significantly improving specificity (P = 0.038).

CONCLUSIONS

Anthropomorphic phantoms were shown to be essential in determining optimal settings for acquisition, reconstruction, and analysis. SPECT/CT reconstructions with attenuation and scatter correction and resolution modeling are recommended and could improve specificity when using the 55%:45% threshold to assess condylar growth.

Comparison of stress distribution in fully porous and dense-core porous scaffolds in dental implantation

The aim of this study is to compare the stress distribution in porous scaffolds with different structures with similar geometric parameters to study a new approach in dental implantation. Three-dimensional finite element models of the fully porous and dense-core porous scaffolds with defined porosity parameters including space diameter and thickness with two porosity patterns were embedded in the jaw bone model with cortical and cancellous bone. The cylindrical shape was considered as the main shape of the scaffolds. To evaluate the mechanical performance, the Von Mises stress was compared in the models under static and dynamic masticatory loading. Incidentally, to validate the modeling results, experimental strain gauge tests were performed on four specimens fabricated from Ti6Al4V. Finally, the stress distribution in the models was compared with the results of previous studies on commercial implants. The results of the finite element analysis show that there are considerable differences in the magnitude of the equivalent stress in the models in static and dynamic phases. Also, changes in the defined geometric parameters have significant effects on the stress distribution in terms of Von Mises stress in the overall models. The experimental results indicated good agreement with those of the modeling. It can be concluded that some porous structures with optimal geometries can be proposed as a new structure for dental implants. However, considering the physiology of bone when confronted with porous structures, further studies such as in vivo experiments are needed in this field.

Validation of bone mineral density measurement using quantitative CBCT image based on deep learning

The bone mineral density (BMD) measurement is a direct method of estimating human bone mass for diagnosing osteoporosis, and performed to objectively evaluate bone quality before implant surgery in dental clinics. The objective of this study was to validate the accuracy and reliability of BMD measurements made using quantitative cone-beam CT (CBCT) image based on deep learning by applying the method to clinical data from actual patients. Datasets containing 7500 pairs of CT and CBCT axial slice images from 30 patients were used to train a previously developed deep-learning model (QCBCT-NET). We selected 36 volumes of interest in the CBCT images for each patient in the bone regions of potential implants sites on the maxilla and mandible. We compared the BMDs shown in the quantitative CBCT (QCBCT) images with those in the conventional CBCT (CAL_CBCT) images at the various bone sites of interest across the entire field of view (FOV) using the performance metrics of the MAE, RMSE, MAPE (mean absolute percentage error), R² (coefficient of determination), and SEE (standard error of estimation). Compared with the ground truth (QCT) images, the accuracy of the BMD measurements from the QCBCT images showed an RMSE of 83.41 mg/cm³, MAE of 67.94 mg/cm³, and MAPE of 8.32% across all the bone sites of interest, whereas for the CAL_CBCT images, those values were 491.15 mg/cm³, 460.52 mg/cm³, and 54.29%, respectively. The linear regression between the QCBCT and QCT images showed a slope of 1.00 and a R² of 0.85, whereas for the CAL_CBCT images, those values were 0.32 and 0.24, respectively. The overall SEE between the QCBCT images and QCT images was 81.06 mg/cm³, whereas the SEE for the CAL_CBCT images was 109.32 mg/cm³. The QCBCT images thus showed better accuracy, linearity, and uniformity than the CAL_CBCT images across the entire FOV. The BMD measurements from the quantitative CBCT images showed high accuracy, linearity, and uniformity regardless of the relative geometric positions of the bone in the potential implant site. When applied to actual patient CBCT images, the CBCT-based quantitative BMD measurement based on deep learning demonstrated high accuracy and reliability across the entire FOV.

Does zinc oxide nanoparticles potentiate the regenerative effect of platelet-rich fibrin in healing of critical bone defect in rabbits?

Background

Many encouraging studies confirmed the ability of Zinc Oxide Nanoparticles (ZnONPs) in accelerating bone growth and mineralization. The use of Platelet Rich-Fibrin (PRF) as a sole filling material for large segmental bone defects remains questionable. The objectives are to investigate the regenerative efficacy of autologous Platelet Rich-Fibrin (PRF) and Zinc Oxide Nanoparticles (ZnONPs) in repairing large segmental bone ulnar defects in a randomized controlled study in rabbits using computed tomographic interpretations. A 12 mm critical size defect was surgically induced in the ulna of 30 rabbits (n = 10/ group). In the control group, the defect was left empty. In the PRF group, the defect is filled with PRF. In the PRF/ZnONPs group, the defect is filled with PRF that was inoculated with 0.1 ml of 0.2% ZnONPs. Radiologic healing capacity was evaluated at the first, second, and third postoperative months.

Results

Statistical analysis showed significant differences in the radiologic healing scores between the groups (P = 0.000–0.0001) at all-time points (P = 0.000–0.047) during the study.

Conclusion

Rabbits in the PRF/ZnONPs group showed the highest appreciable bone quality and quantity followed by the PRF group with high quantity but low bone quality meanwhile, rabbits in the control group showed minimal quantity but medium bone quality. Interestingly, the addition of ZnONPs to PRF can accelerate the healing of ulnar critical-size defects in rabbits.

A Damage Model to Trabecular Bone and Similar Materials: Residual Resource, Effective Elasticity Modulus, and Effective Stress under Uniaxial Compression

Experimental research of bone strength remains costly and limited for ethical and technical reasons. Therefore, to predict the mechanical state of bone tissue, as well as similar materials, it is desirable to use computer technology and mathematical modeling. Yet, bone tissue as a bio-mechanical object with a hierarchical structure is difficult to analyze for strength and rigidity; therefore, empirical models are often used, the disadvantage of which is their limited application scope. The use of new analytical solutions overcomes the limitations of empirical models and significantly improves the way engineering problems are solved. Aim of the paper: the development of analytical solutions for computer models of the mechanical state of bone and similar materials. Object of research: a model of trabecular bone tissue as a quasi-brittle material under uniaxial compression (or tension). The new ideas of the fracture mechanics, as well as the methods of mathematical modeling and the biomechanics of bone tissues were used in the work. Compression and tension are considered as asymmetric mechanical states of the material. Results: a new nonlinear function that simulates both tension and compression is justified, analytical solutions for determining the effective and apparent elastic modulus are developed, the residual resource function and the damage function are justified, and the dependences of the initial and effective stresses on strain are obtained. Using the energy criterion, it is proven that the effective stress continuously increases both before and after the extremum point on the load-displacement plot. It is noted that the destruction of bone material is more likely at the inflection point of the load-displacement curve. The model adequacy is explained by the use of the energy criterion of material degradation. The results are consistent with the experimental data available in the literature.