A comparison of micro-CT and dental CT in assessing cortical bone morphology and trabecular bone microarchitecture

Characterization of mechanical stiffness using additive manufacturing and finite element analysis: potential tool for bone health assessment

BACKGROUND

Bone health and fracture risk are known to be correlated with stiffness. Both micro-finite element analysis (μFEA) and mechanical testing of additive manufactured phantoms are useful approaches for estimating mechanical properties of trabecular bone-like structures. However, it is unclear if measurements from the two approaches are consistent. The purpose of this work is to evaluate the agreement between stiffness measurements obtained from mechanical testing of additive manufactured trabecular bone phantoms and μFEA modeling. Agreement between the two methods would suggest 3D printing is a viable method for validation of μFEA modeling.

METHODS

A set of 20 lumbar vertebrae regions of interests were segmented and the corresponding trabecular bone phantoms were produced using selective laser sintering. The phantoms were mechanically tested in uniaxial compression to derive their stiffness values. The stiffness values were also derived from in silico simulation, where linear elastic μFEA was applied to simulate the same compression and boundary conditions. Bland-Altman analysis was used to evaluate agreement between the mechanical testing and μFEA simulation values. Additionally, we evaluated the fidelity of the 3D printed phantoms as well as the repeatability of the 3D printing and mechanical testing process.

RESULTS

We observed good agreement between the mechanically tested stiffness and μFEA stiffness, with R2 of 0.84 and normalized root mean square deviation of 8.1%. We demonstrate that the overall trabecular bone structures are printed in high fidelity (Dice score of 0.97 (95% CI, [0.96,0.98]) and that mechanical testing is repeatable (coefficient of variation less than 5% for stiffness values from testing of duplicated phantoms). However, we noticed some defects in the resin microstructure of the 3D printed phantoms, which may account for the discrepancy between the stiffness values from simulation and mechanical testing.

CONCLUSION

Overall, the level of agreement achieved between the mechanical stiffness and μFEA indicates that our μFEA methods may be acceptable for assessing bone mechanics of complex trabecular structures as part of an analysis of overall bone health.

Micro-CT analysis of the mandibular bone microarchitecture of rats after radiotherapy and low-power laser therapy

To investigate whether low-level laser therapy (LLLT), at different times of application (immediate and late) in the region of the parotid glands, has a distance effect on the microarchitecture of the trabecular bone in mandible of rats irradiated by volumetric modular arc therapy (VMAT). Thirty adult Wistar rats were randomly divided into placebo control groups (CG, n = 2), only radiotherapy (RG, n = 2), only LPLT (LG, n = 2), and two other groups using LLLT in the immediate time (24 h) (ILG, n = 12) and late (120 h) (LLG, n = 12) to radiotherapy by VMAT in a single dose of 12 Gy. LLLT with AsGaAl laser (660 nm, 100 mW), a spot size of 0.0028 cm², was applied in three points in the region of the right parotid gland, with energy of 2 J/cm², 20 s per point, for 10 consecutive days. After euthanasia, the right hemimandibles of each animal were dissected, prepared, and analyzed by computerized microtomography (micro-CT) and histomorphometry. The different groups were analyzed by the Tukey and Bonferroni multiple comparison tests. The micro-CT analysis found statistically significant differences between the groups, especially in the LLG, which had the highest average bone volume compared to the CG (p = 0.001) and ILG (p = 0.002) and a greater number of trabeculae than the CG (p = 0.000) and ILG (p = 0.031). The ILG also had a higher number of trabeculae than the CG (p = 0.005). Trabecula separation (Tb.Sp) was lower in the LLG (p = 0.000) and ILG (p = 0.002) when compared to the CG. In the histomorphometry, there was no statistical difference between the groups in relation to all the analyzed variables. Micro-CT analysis showed that the LLLT, even applied at a distance, both in the immediate and late VMAT times, has an effect on the mandibular bone microarchitecture by increasing the volume and number of trabeculae and decreasing the spaces between them.

Dual-energy X-ray Absorptiometry Does Not Represent Bone Structure in Patients with Osteoporosis: A Comparison of Lumbar Dual-Energy X-Ray Absorptiometry with Vertebral Biopsies

STUDY DESIGN

Prospective cross-sectional exploratory study.

OBJECTIVE

To evaluate the correlation between in vivo lumbar dual-energy x-ray absorptiometry (DXA) and parameters of bone architecture in micro-computed tomography (micro-CT) in patients with osteoporosis.

SUMMARY OF BACKGROUND DATA

DXA is the current diagnostic standard for evaluating osteoporosis. However, there are various concerns regarding its validity, especially in the spine. No study has so far investigated whether in vivo DXA correlates with the actual lumbar bone architecture.

METHODS

Lumbar DXA scans were compared with micro-CT analysis of vertebral biopsies in patients with osteoporotic vertebral fractures (fracture group) and those without (control group). Preoperatively, all patients underwent a DXA scan (L1-L4). Intraoperative biopsies from nonfractured vertebrae (preferably L3) were analyzed by micro-CT regarding bone quantity and quality. The groups were compared regarding differences in DXA and micro-CT results. In each group, a correlation analysis was performed between DXA and micro-CT.

RESULTS

The study included 66 patients (33 per group). Preoperative DXA results were worse in the fracture group than the control group (areal bone mineral density [aBMD] 0.95 vs. 1.31, T-score -1.97 vs. 0.92, each P < 0.001). Micro-CT analysis confirmed differences regarding quantitative parameters (bone/total volume: 0.09 vs. 0.12, P < 0.001) and qualitative parameters (connectivity index: 15.73 vs. 26.67, P < 0.001; structure model index: 2.66 vs. 2.27, P < 0.001; trabecular number: 2.11 vs. 2.28, P = 0.014) of bone architecture between both groups. The DXA results did not correlate with micro-CT parameters in the fracture group. In the control group, correlations were found for some parameters (bone/total volume vs. aBMD: r = 0.51, P = 0.005; trabecular number vs. aBMD: r = 0.56, P = 0.001).

CONCLUSION

These data constitute the first comparison of DXA measurements with microstructural analysis of vertebral biopsies in patients with osteoporosis. Our results indicate that lumbar DXA neither qualitatively nor quantitatively represents microstructural bone architecture and is therefore not a reliable tool for the evaluation of bone quality in the spine.Level of Evidence: 3.

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

The aim of this study was to measure the bone mineral density of specific regions of maxilla, mandible, and first cervical vertebra using the Hounsfield unit and trabecular microstructure pattern analysis and to compare the two methods. In this study, cone-beam computed tomography (CBCT) images were obtained from 58 patients. Trabecular thickness, trabecular number, trabecular separation, and bone volume fraction were measured in 484 regions for trabecular microstructure parameters and Hounsfield unit was measured for the grayscale value. There was no difference in bone mineral density between the right and left side in every site and between males and females. Trabecular thickness and trabecular number were high in the order of anterior base of the maxilla, mandibular body, first cervical vertebra, and mandibular condyle. Bone volume fraction and Hounsfield unit were high in the order of anterior base of the maxilla, mandibular body, mandibular condyle, and first cervical vertebra (p < 0.05). Trabecular thickness, trabecular number, and bone volume fraction was positively correlated to the Hounsfield unit, and trabecular separation was negatively correlated to the Hounsfield unit (p < 0.005). This study suggests that it is possible to compare the bone mineral density of trabecular bone in various sites using the Hounsfield unit and trabecular microstructure pattern analysis.

Examining trabecular morphology and chemical composition of peri-scaffold osseointegrated bone

Background

Porous titanium alloy scaffold fabricated by 3D printing technology could induce osseointegration well to repair bone defect during early postoperative period. However, trabecular histomorphological features and chemical compositions of ingrowth bone in the long term after surgery still lacked in-depth research.

Methods

Fourteen New Zealand rabbits were divided into two groups (7 rabbits in surgery group and 7 rabbits in control group). A 3D-printed porous titanium alloy scaffold was implanted into right femoral condyle of each rabbit in the surgery group. Preload was produced at the surface between bone tissue and scaffold through interference assembly during implantation process. Rabbits in the control group were feed free. All rabbits were sacrificed to extract femoral condyles at week 12 after surgery. All right femoral condyles were performed micro-CT scanning to test bone mineral density (BMD) and trabecular histomorphological parameters, including bone volume fraction (BV/TV), bone surface/volume ratio (BS/BV), bone surface density (BS/TV), structure model index (SMI), trabecular thickness (Tb.Th), trabecular number (Tb.N), trabecular separation (Tb.Sp), porosity (PO), connectivity density (Conn.Dn), and degree of anisotropy (DA). Scanning electron microscope was used to observe osteogenesis peri-scaffold. Fourier transform infrared spectroscopy (FTIR) scanning was performed to analyze chemical compositions of peri-scaffold trabeculae. All trabecular morphological parameters and BMDs were statistically analyzed between surgery group and control group.

Results

The pores of scaffold were filled with ingrowth bone tissues after 12 weeks osseointegration. However, the mean BMD peri-scaffold in surgery group was 800 ± 20 mg/cm³, which was 18.37% lower than that in the control group. There was a significant decrease in BV/TV, Tb.N, and BS/TV, and there was a significant increase in Tb.Sp and PO between the surgery group and control group (p < 0.05). There were no significant differences in Tb.Th, SMI, Conn.Dn, BS/BV, and DA. Although ingrowth of bone tissue was very effective, some fragmented connective tissues were still found instead of bone tissues on the partial beams of scaffolds through SEM images. It was found from FTIR that there was no significant hydroxyapatite peak signal in surgery group. Collagen in the control group mainly existed as cross-link structure, while non-cross-link structure in the surgery group.

Conclusions

Preload could promote the same good osseointegration ability as chemical surface modification method in the early term after surgery, and better osseointegration effect than chemical surface modification method in the mid-long term after surgery. However, histomorphological features of peri-scaffold trabeculae were still in deterioration and low collagen maturity caused by stress shielding. It was suggested from this study that extra physical training should be taken to stimulate the bone remodeling process for recovering to a healthy level.

Effects of fluorinated porcine hydroxyapatite on lateral ridge augmentation: an experimental study in the canine mandible

PURPOSE

The aim of this study was to evaluate the effects of porcine hydroxyapatite (PHA) and fluorinated porcine hydroxyapatite (FPHA) applied concomitantly with collagen membranes (CMs) on bone regeneration in mandibular lateral ridge defects.

MATERIALS AND METHODS

Mandibular third premolar to second molar were extracted bilaterally in six male beagle dogs. After 8 weeks of healing, six standardized box-shaped defects were bilaterally created at the buccal aspect of the mandibles and randomly allocated in a split-mouth design to the (i) PHA, (ii) FPHA or (iii) blank group and covered with CMs. After 12 weeks, biopsies of the defects were obtained for micro-computed tomography (micro-CT) evaluation and histological analysis.

RESULTS

Both FPHA and PHA promoted new bone formation and showed a better ridge width maintenance capacity than the blank control treatment. The micro-CT evaluation showed that the bone volume fraction (BV/TV) in the FPHA group was significantly higher than that in the PHA group. The trabecular number (Tb.N) in the FPHA group was significantly higher than that in the blank group. Histomorphometric analysis revealed a significantly larger area and higher ratio of newly formed bone in the FPHA group than those in the PHA group. The ratio of non-mineralized tissue in the FPHA group was significantly lower than that in the PHA group. No significant difference in the amount of residual materials was found between the FPHA and PHA groups.

CONCLUSIONS

FPHA achieved better ridge width maintenance and bone regeneration outcomes than PHA as a bone substitute in lateral ridge augmentation.

Ovariectomized rat model of osteoporosis: a practical guide

Osteoporosis affects about 200 million people worldwide and is a silent disease until a fracture occurs. Management of osteoporosis is still a challenge that warrants further studies for establishing new prevention strategies and more effective treatment modalities. For this purpose, animal models of osteoporosis are appropriate tools, of which the ovariectomized rat model is the most commonly used. The aim of this study is to provide a 4-step guideline for inducing a rat model of osteoporosis by ovariectomy (OVX): (1) selection of the rat strain, (2) choosing the appropriate age of rats at the time of OVX, (3) selection of an appropriate surgical method and verification of OVX, and (4) evaluation of OVX-induced osteoporosis. This review of literature shows that (i) Sprague-Dawley and Wistar rats are the most common strains used, both responding similarly to OVX; (ii) six months of age appears to be the best time for inducing OVX; (iii) dorsolateral skin incision is an appropriate choice for initiating OVX; and (iv) the success of OVX can be verified 1-3 weeks after surgery, following cessation of the regular estrus cycles, decreased estradiol, progesterone, and uterine weight as well as increased LH and FSH levels. Current data shows that the responses of trabecular bones of proximal tibia, lumbar vertebrae and femur to OVX are similar to those in humans; however, for short-term studies, proximal tibia is recommended. Osteoporosis in rats is verified by lower bone mineral density and lower trabecular number and thickness as well as higher trabecular separation, changes that are observed at 14, 30, and 60 days post-OVX in proximal tibia, lumbar vertebrae and femur, respectively.

Quantifying Subresolution 3D Morphology of Bone with Clinical Computed Tomography

The aim of this study was to quantify sub-resolution trabecular bone morphometrics, which are also related to osteoarthritis (OA), from clinical resolution cone beam computed tomography (CBCT). Samples (n = 53) were harvested from human tibiae (N = 4) and femora (N = 7). Grey-level co-occurrence matrix (GLCM) texture and histogram-based parameters were calculated from CBCT imaged trabecular bone data, and compared with the morphometric parameters quantified from micro-computed tomography. As a reference for OA severity, histological sections were subjected to OARSI histopathological grading. GLCM and histogram parameters were correlated to bone morphometrics and OARSI individually. Furthermore, a statistical model of combined GLCM/histogram parameters was generated to estimate the bone morphometrics. Several individual histogram and GLCM parameters had strong associations with various bone morphometrics (|r| > 0.7). The most prominent correlation was observed between the histogram mean and bone volume fraction (r = 0.907). The statistical model combining GLCM and histogram-parameters resulted in even better association with bone volume fraction determined from CBCT data (adjusted R² change = 0.047). Histopathology showed mainly moderate associations with bone morphometrics (|r| > 0.4). In conclusion, we demonstrated that GLCM- and histogram-based parameters from CBCT imaged trabecular bone (ex vivo) are associated with sub-resolution morphometrics. Our results suggest that sub-resolution morphometrics can be estimated from clinical CBCT images, associations becoming even stronger when combining histogram and GLCM-based parameters.

3-Dimensional characterization of cortical bone microdamage following placement of orthodontic microimplants using Optical Coherence Tomography

Microimplants are being used extensively in clinical practice to achieve absolute anchorage. Success of microimplant mainly depend on its primary stability onto the cortical bone surface and the associated Microdamage of the cortical bone during insertion procedure leads to many a microimplants to fail and dislodge from the cortical bone leading to its failure. Even though, previous studies showed occurrence of microdamage in the cortical bone, they were mainly 2-dimension studies or studies that were invasive to the host. In the present study, we used a non-invasive, non-ionizing imaging technique- Optical Coherence Tomography (OCT), to image and analyze the presence of microdamage along the cortical bone surrounding the microimplant. We inserted 80 microimplants in two different methods (drill and drill free method) and in two different angulations onto the cortical bone surface. Images were obtained in both 2D and 3D imaging modes. In the images, microdamage in form of microcracks on the cortical bone surface around the bone-microimplant interface and micro-elevations of the cortical bone in angulated microimplant insertions and the presence of bone debris due to screwing motion of the microimplant on insertion can be appreciated visually and quantitatively through the depth intensity profile analysis of the images.

Improving the prediction of the trabecular bone microarchitectural parameters using dental cone-beam computed tomography

Background

In this study, we explored how various preprocessing approaches can be employed to enhance the capability of dental CBCT to accurately estimate trabecular bone microarchitectural parameters.

Methods

In total, 30 bovine vertebrae cancellous bone specimens were used for in study. Voxel resolution 18-μm micro-computed tomography (micro-CT) and 100-μm dental CBCT were used to scan each specimen. Micro-CT images were used to calculate trabecular bone microarchitectural parameters; the results were set as the gold standard. Subsequently, before the dental CBCT images were converted into binary images to calculate trabecular bone microarchitectural parameters, three preprocessing approaches were used to process the dental CBCT images. For Group 1, no preprocessing approach was applied. For Group 2, images were sharpened and despeckable noises were removed. For Group 3, the function of local thresholding was added to Group 2 to form Group 3. For Group 4, the air pixels was removed from Group 3 to form Group 4. Subsequently, all images were imported into a software package to estimate trabecular bone microarchitectural parameters (bone volume fraction (BV/TV), trabecular thickness (TbTh), trabecular number (TbN), and trabecular separation (TbSp)). Finally, a paired t-test and a Pearson correlation test were performed to compare the capability of micro-CT with the capability of dental CBCT for estimating trabecular bone microarchitectural parameters.

Results

Regardless of whether dental CBCT images underwent image preprocessing (Groups 1 to 4), the four trabecular bone microarchitectural parameters measured using dental CBCT images were significantly different from those measured using micro-CT images. However, after three image preprocessing approaches were applied to the dental CBCT images (Group 4), the BV/TV obtained using dental CBCT was highly positively correlated with that obtained using micro-CT (r = 0.87, p < 0.001); the correlation coefficient was greater than that of Group 1 (r = −0.15, p = 0.412), Group 2 (r = 0.16, p = 0.386), and Group 3 (r = 0.47, p = 0.006). After dental CBCT images underwent image preprocessing, the efficacy of using dental CBCT for estimating TbN and TbSp was enhanced.

Conclusions

Image preprocessing approaches can be used to enhance the efficacy of using dental CBCT for predicting trabecular bone microarchitectural parameters.

Osteoconductive 3D porous composite scaffold from regenerated cellulose and cuttlebone-derived hydroxyapatite

Recently, usage of marine-derived materials in biomedical field has come into prominence due to their promising characteristics such as biocompatibility, low immunogenicity and wide accessibility. Among these marine sources, cuttlebone has been used as a valuable component with its trace elemental composition in traditional medicine. Recent studies have focused on the use of cuttlebone as a bioactive agent for tissue engineering applications. In this study, hydroxyapatite particles were obtained by hydrothermal synthesis of cuttlebone and incorporated to cellulose scaffolds to fabricate an osteoconductive composite scaffold for bone regeneration. Elemental analysis of raw cuttlebone material from different coastal zones and cuttlebone-derived HAp showed that various macro-, micro- and trace elements - Ca, P, Na, Mg, Cu, Sr, Cl, K, S, Br, Fe and Zn were found in a very similar amount. Moreover, biologically unfavorable heavy metals, such as Ag, Cd, Pb or V, were not detected in any cuttlebone specimen. Carbonated hydroxyapatite particle was further synthesized from cuttlebone microparticles via hydrothermal treatment and used as a mineral filler for the preparation of cellulose-based composite scaffolds. Interconnected highly porous structure of the scaffolds was confirmed by micro-computed tomography. The mean pore size of the scaffolds was 510 µm with a porosity of 85%. The scaffolds were mechanically characterized with a compression test and cuttlebone-derived HAp incorporation enhanced the mechanical properties of cellulose scaffolds. In vitro cell culture studies indicated that MG-63 cells proliferated well on scaffolds. In addition, cuttlebone-derived hydroxyapatite significantly induced the ALP activity and osteocalcin secretion. Besides, HAp incorporation increased the surface mineralization which is the major step for bone tissue regeneration.

Assessment of cortical bone microdamage following insertion of microimplants using optical coherence tomography: a preliminary study

OBJECTIVES

The study was done to evaluate the efficacy of optical coherence tomography (OCT), to detect and analyze the microdamage occurring around the microimplant immediately following its placement, and to compare the findings with micro-computed tomography (μCT) images of the samples to validate the result of the present study.

METHODS

Microimplants were inserted into bovine bone samples. Images of the samples were obtained using OCT and μCT. Visual comparisons of the images were made to evaluate whether anatomical details and microdamage induced by microimplant insertion were accurately revealed by OCT.

RESULTS

The surface of the cortical bone with its anatomical variations is visualized on the OCT images. Microdamage occurring on the surface of the cortical bone around the microimplant can be appreciated in OCT images. The resulting OCT images were compared with the μCT images. A high correlation regarding the visualization of individual microcracks was observed. The depth penetration of OCT is limited when compared to μCT.

CONCLUSIONS

OCT in the present study was able to generate high-resolution images of the microdamage occurring around the microimplant. Image quality at the surface of the cortical bone is above par when compared with μCT imaging, because of the inherent high contrast and high-resolution quality of OCT systems. Improvements in the imaging depth and development of intraoral sensors are vital for developing a real-time imaging system and integrating the system into orthodontic practice.

Alternative cone-beam computed tomography method for the analysis of bone density around impacted maxillary canines

INTRODUCTION

Genetic and environmental etiologic factors have been described for maxillary canine impaction, except for the trabecular bone characteristics in the impacted area. The aim of this study was to evaluate the surface area and fractal dimension of the alveolar bone on cone-beam computed tomography (CBCT) images of patients with maxillary impacted canines.

METHODS

The sample comprised preorthodontic treatment CBCT images of 49 participants with maxillary impacted canines (31 unilateral and 18 bilateral). CBCT images were acquired in portrait mode (17 × 23 cm high field of view) at 120 kV, 5 mA, 8.9-seconds exposure time, and 0.3-mm voxel size. Coronal slices (0.3 mm) were obtained from the right and left alveolar processes between the first and second maxillary premolars. We collected 64 × 64-pixel regions of interest between the premolars to assess maxillary bone area and fractal dimension using ImageJ software (National Institutes of Health, Bethesda, Md). Comparisons were made using paired t tests and linear regression. Repeated measurements were obtained randomly from about 20% of the sample.

RESULTS

In subjects with unilateral impactions, the maxillary bone area (P = 0.0227) was higher in the impacted side, with a mean difference of 245.5 pixels (SD, 569.2), but the fractal dimension (P = 0.9822) was not, -0.0003 pixels (SD, 0.082). Comparisons of unilateral and bilateral subjects using a general linear mixed model test confirmed the increased bone area in the impacted side (P = 0.1062). The repeated measurements showed similar results.

CONCLUSIONS

The maxillary alveolar bone area is increased in the impacted side compared with the nonimpacted side.

Opioids delay healing of spinal fusion: a rabbit posterolateral lumbar fusion model

BACKGROUND CONTEXT

Opioid use is prevalent in the management of pre- and postoperative pain in patients undergoing spinal fusion. There is evidence that opioids downregulate osteoblasts in vitro, and a previous study found that morphine delays the maturation and remodeling of callus in a rat femur fracture model. However, the effect of opioids on healing of spinal fusion has not been investigated before. Isolating the effect of opioid exposure in humans would be limited by the numerous confounding factors that affect fusion healing. Therefore, we have used a well-established rabbit model to study the process of spinal fusion healing that closely mimics humans.

PURPOSE

The objective of this work was to study the effect of systemic opioids on the process of healing of spinal fusion in a rabbit posterolateral spinal fusion model.

STUDY DESIGN/SETTING

This is a preclinical animal study.

MATERIALS AND METHODS

Twenty-four adult New Zealand white rabbits were studied in two groups after approval from the Institutional Animal Care and Use Committee (IACUC). The opioid group (n=12) received 4 weeks' preoperative and 6 weeks' postoperative transdermal fentanyl. Serum fentanyl levels were measured just before surgery and 4 weeks postoperatively to ensure adequate levels. The control group (n=12) received only perioperative pain control as necessary. All animals underwent a bilateral L5-L6 posterolateral spinal fusion using iliac crest autograft. Animals were euthanized at the 6-week postoperative time point, and assessment of fusion was done by manual palpation, plain radiographs, microcomputed tomography (microCT), and histology.

RESULTS

Twelve animals in the control group and 11 animals in the opioid group were available for analysis at the end of 6 weeks. The fusion scores on manual palpation, radiographs, and microCT were not statistically different. Three-dimensional microCT morphometry found that the fusion mass in the opioid group had a lower bone volume (p=.09), a lower trabecular number (p=.02), and a higher trabecular separation (p=.02) compared with the control group. Histologic analysis found areas of incorporation of autograft and unincorporated graft fragments in both groups. In the control group, there was remodeling of de novo woven bone to lamellar organization with incorporation of osteocytes, formation of mature marrow, and relative paucity of hypertrophied osteoblasts lining new bone. Sections from the opioid group showed formation of de novo woven bone, and hypertrophied osteoblasts were seen lining the new bone. There were no sections showing lamellar organization and development of mature marrow elements in the opioid group. Less dense trabeculae on microCT correlated with histologic findings of relatively immature fusion mass in the opioid group.

CONCLUSIONS

Systemic opioids led to an inferior quality fusion mass with delay in maturation and remodeling at 6 weeks in this rabbit spinal fusion model. These preliminary results lay the foundation for further research to investigate underlying cellular mechanisms, the temporal fusion process, and the dose-duration relationship of opioids responsible for our findings.

Effect of Multilaminate Small Intestinal Submucosa as a Barrier Membrane on Bone Formation in a Rabbit Mandible Defect Model

A barrier membrane (BM) is essential for guided bone regeneration (GBR) procedures. Absorbable BMs based on collagen have been widely applied clinically due to their excellent biocompatibility. The extracellular matrix (ECM) provides certain advantages that can compensate for the rapid degradation and insufficient mechanical strength of pure collagen membrane due to the porous scaffold structure. Recently, small intestinal submucosa (SIS), one of the most widely used ECM materials, has drawn much attention in bone tissue engineering. In this study, we adopted multilaminate SIS (mSIS) as a BM and evaluated its in vivo and in vitro properties. mSIS exhibited a multilaminate structure with a smooth upper surface and a significantly coarser bottom layer according to microscopic observation. Tensile strength was 13.10 ± 2.56 MPa. In in vivo experiments, we selected a rabbit mandibular defect model and subcutaneous implantation to compare osteogenesis and biodegradation properties with one of the most commonly used commercial collagen membranes. mSIS was retained for up to 3 months and demonstrated longer biodegradation time than commercial collagen membrane. Quantification of bone regeneration revealed significant differences in each group. Micro-computed tomography (micro-CT) revealed that the quantity and maturity of bones in the mSIS group were significantly higher than those in the blank control group (P < 0.05) and were similar to those in a commercial collagen membrane group (P > 0.05) at 4 and 12 weeks after surgery. Hematoxylin and eosin staining revealed large amounts of mature lamellar bone at 12 weeks in mSIS and commercial collagen membrane groups. Therefore, we conclude that mSIS has potential as a future biocompatible BM in GBR procedures.

Atlases with Arcuate Foramen Present Cortical Bone Thickening That May Contribute to Lower Fracture Risk

BACKGROUND

To date, no information about the cortical bone microstructural properties in atlas vertebrae with arcuate foramen has been reported. As a result, we aimed to test in an experimental model if there is a cortical bone thickening in an atlas vertebra which has an arcuate foramen that may play a protective role against bone fracture.

METHODS

We analyzed by means of micro-computed tomography the cortical bone thickness, the cortical volume, and the medullary volume (SkyScan 1172 Bruker micro-CT NV, Kontich, Belgium) in cadaveric dry atlas vertebrae with arcuate foramen and without arcuate foramen. We also reviewed a case series of 31 posterior atlas arch fractures to correlate the possible presence in the same atlas of both fracture and arcuate foramen.

RESULTS

The micro-computed tomography study revealed significant differences in cortical bone thickness (P < 0.001), cortical volume (P < 0.004), and medullary volume (P = 0.013) values between the arcuate foramen vertebrae and the nonarcuate foramen vertebrae. The clinical series found no coexistence in the same vertebra of a posterior atlas arch fractures and the arcuate foramen.

CONCLUSIONS

An atlas with arcuate foramen presents cortical bone thickening. This advantage in bone microarchitecture seems to contribute to a lower fracture risk compared to subjects without arcuate foramen as no coexistence in the same vertebra of a posterior atlas arch fractures and arcuate foramen was found.

Quantification of Volumetric Bone Mineral Density of Proximal Femurs Using a Two-Compartment Model and Computed Tomography Images

Objectives

Dual-energy X-ray absorptiometry (DXA) is frequently used to measure the areal bone mineral density (aBMD) in clinical practice. However, DXA measurements are affected by the bone thickness and the body size and are unable to indicate nonosseous areas within the trabecular bone. This study aims to quantify the volumetric bone mineral density (vBMD) using computed tomography (CT) images and the two-compartment model (TCM) methods.

Methods

The TCM method was proposed and validated by dipotassium phosphate (K₂HPO₄) phantoms and a standard forearm phantom. 28 cases with DXA scans and pelvic CT scans acquired within six months were retrospectively collected. The vBMD calculated by TCM was compared with the aBMD obtained from DXA.

Results

For the K₂HPO₄ phantoms with vBMD ranging from 0.135 to 0.467 g/cm³, the average difference between the real and calculated vBMD was 0.009 g/cm³ and the maximum difference was 0.019 g/cm³. For the standard forearm phantom with vBMD of 0.194, 0.103, and 0.054 g/cm³, the average differences between the real and calculated vBMD were 0.017, 0.014, and 0.011 g/cm³. In the clinical CT image validation, a good linear relationship between vBMD and aBMD was observed with the Pearson correlation coefficient of 0.920 (p < 0.01).

Conclusions

The proposed TCM method in combination with the homemade cortical bone equivalent phantom provides accurate quantification and spatial distribution of bone mineral content.

Topographical Anatomy of the Distal Ulna Attachment of the Radioulnar Ligament

PURPOSE

The deep component of the distal radioulnar ligament provides translational stability and rotational guidance to the forearm. However, controversy exists regarding the importance of this structure as well as the nature of its attachment to the distal ulna. We aimed to evaluate the topographic anatomy of the distal ulna attachment of both the superficial and the deep components of the radioulnar ligament and to assess the relationship between its internal and its external morphometry.

METHODS

Thirteen human distal ulnae attached by ulnar part of the distal radioulnar ligament were scanned using micro-computed tomography and reconstructed in 3 dimensions. In addition, the distal radioulnar ligaments were examined under polarized light microscopy to determine the histological characteristics of collagen contained within the ligaments.

RESULTS

The deep limbs have broad marginal insertions at the fovea, whereas the superficial limbs have a circular and condensed insertion to the ulnar styloid. The center of the deep limb was separated from the base of the ulnar styloid by a mean of 2.0 ± 0.76 mm, and this distance was positively correlated with the width of the ulnar styloid. The mean distance between the center of the ulnar head and the center of the fovea was 2.4 ± 0.58 mm. The proportion of collagen type I was lower in the deep limb than in the superficial limb.

CONCLUSIONS

This new observation of the footprint of the radioulnar ligament in the distal ulna indicates that the deep limb may serve as an internal capsular ligament of the distal radioulnar joint, whereas the superficial limb as the external ligament.

CLINICAL RELEVANCE

Knowledge of the topographic anatomy of the radioulnar ligament's attachment to the distal ulna may provide a better understanding of distal radioulnar ligament-related pathologies.

Comparison of micro-CT and cone beam CT on the feasibility of assessing trabecular structures in mandibular condyle

OBJECTIVES

To evaluate the accuracy of CBCT in assessing trabecular structures.

METHODS

Two human mandibles were scanned by micro-CT (Skyscan 1173 high-energy spiral scan micro-CT; Skyscan NV, Kontich, Belgium) and CBCT (3D Accuitomo 170; Morita, Japan). The CBCT images were reconstructed with 0.5 and 1 mm thicknesses. The condylar images were selected for registration. A parallel algorithm for histogram computation was introduced to perform the registration. A mutual information (MI) value was used to evaluate the match between the images obtained from micro-CT and CBCT.

RESULTS

In comparison with the micro-CT image for the two samples, the CBCT image with 0.5 mm thickness has a MI value of 0.873 and 0.903 while that with 1.0 mm thickness has a MI value of 0.741 and 0.752. The CBCT images with 0.5 mm thickness were better matched with micro-CT images.

CONCLUSIONS

CBCT shows comparable accuracy with high-resolution micro-CT in assessing trabecular structures. CBCT can be a feasible tool to evaluate osseous changes of jaw bones.

Intermittent parathyroid hormone improve bone microarchitecture of the mandible and femoral head in ovariectomized rats

BACKGROUND

Intermittent parathyroid hormone (PTH) can be used to treat osteoporosis of the spine and hip. However, whether it can be used to treat osteoporosis of the mandible is unclear. The purpose of this study was to explore the influence of applying intermittent PTH to ovariectomized rats on the trabecular bone microarchitecture of the mandible and femoral head.

METHODS

Eighteen female rats were divided into three groups: the healthy group, ovariectomized (OVX) group, and OVX + PTH group. The OVX group and OVX + PTH group had an OVX at 8 weeks of age. The OVX + PTH group received intermittent PTH therapy for 12 weeks. The mandibles and femurs of all rats were removed at 20 weeks and were then scanned using microcomputed tomography (micro-CT).

RESULTS

From the micro-CT analysis, the trabecular bone microarchitecture of the mandible and femoral head are offered as follows: (1) The bone volume fraction and trabecular thickness in the OVX group were lower than those in the healthy group. (2) The bone volume fraction and trabecular thickness in the OVX + PTH group approximated those in the healthy group.

CONCLUSION

The conclusions of this study regarding the trabecular bone microarchitecture of the mandible and femoral head are offered as follows: (1) The BV/TV and TbTh in the OVX group were lower than those in the healthy group. (2) The BV/TV and TbTh in the OVX + PTH group approximated those in the healthy group, therefore, intermittent PTH displayed high efficacy for treating femoral or mandibular deterioration of bone microstructure resulting from loss of ovarian function. Osteoporosis of the femur or mandible in the rats was ameliorated by intermittent PTH therapy.

Enamel Thickness Determination by Optical Coherence Tomography: In vitro Validation

Optical coherence tomography (OCT) has been introduced in dentistry as a nondestructive diagnostic imaging tool that does not utilize ionizing radiation. This study investigated the agreement between polarization-sensitive OCT (PS-OCT), microcomputed tomography (μ-CT), and histology for enamel thickness measurements. Human enamel samples were prepared and evaluated with μ-CT and PS-OCT and then sectioned and observed via digital transversal light microscopy. For all methods, a standard transversal section (b-scan) in each sample was selected, and the enamel thickness was measured at three predetermined positions using ImageJ analysis software. The results revealed significant high agreement between all tested methods, indicating the potential of PS-OCT as a clinical tool to effectively measure enamel thickness.

Cortical Bone Morphological and Trabecular Bone Microarchitectural Changes in the Mandible and Femoral Neck of Ovariectomized Rats

Objective

This study used microcomputed tomography (micro-CT) to evaluate the effects of ovariectomy on the trabecular bone microarchitecture and cortical bone morphology in the femoral neck and mandible of female rats.

Materials and Methods

Twelve female Wister rats were divided into two groups: the control and ovariectomized groups. The rats in the ovariectomized group received ovariectomy at 8 weeks of age; all the rats were sacrificed at 20 weeks of age, and their mandibles and femurs were removed and scanned using micro-CT. Four microstructural trabecular bone parameters were measured for the region below the first mandibular molar and the femoral neck region: bone volume fraction (BV/TV), trabecular thickness (TbTh), trabecular separation (TbSp), and trabecular number (TbN). In addition, four cortical bone parameters were measured for the femoral neck region: total cross-sectional area (TtAr), cortical area (CtAr), cortical bone area fraction (CtAr/TtAr), and cortical thickness (CtTh). The CtTh at the masseteric ridge was used to assess the cortical bone morphology in the mandible. The trabecular bone microarchitecture and cortical bone morphology in the femoral necks and mandibles of the control group were compared with those of the ovariectomized group. Furthermore, Spearman’s correlation (r_s) was conducted to analyze the correlation between the osteoporosis conditions of the mandible and femoral neck.

Results

Regarding the trabecular bone microarchitectural parameters, the BV/TV of the trabecular bone microarchitecture in the femoral necks of the control group (61.199±11.288%, median ± interquartile range) was significantly greater than that of the ovariectomized group (40.329±5.153%). Similarly, the BV/TV of the trabecular bone microarchitecture in the mandibles of the control group (51.704±6.253%) was significantly greater than that of the ovariectomized group (38.486±9.111%). Furthermore, the TbSp of the femoral necks in the ovariectomized group (0.185±0.066 mm) was significantly greater than that in the control group (0.130±0.026mm). Similarly, the TbSp of the mandibles in the ovariectomized group (0.322±0.047mm) was significantly greater than that in the control group (0.285±0.041mm). However, the TbTh and TbN trends for the mandibles and femoral necks were inconsistent between the control and ovariectomized groups. Regarding the cortical bone morphology parameters, the TtAr of the femoral necks in the ovariectomized group was significantly smaller than that in the control group. There was no significant difference in the TtAr, CtAr, or CtTh of the femoral necks between the control and ovariectomized groups, and no significant difference in the CtTh of the mandibles between the control and ovariectomized groups. Moreover, the BV/TV and TbSp of the mandibles were highly correlated with those of the femurs (r_s = 0.874 and r_s = 0.755 for BV/TV and TbSp, respectively). Nevertheless, the TbTh, TbN, and CtTh of the mandibles were not correlated with those of the femoral necks.

Conclusion

After the rats were ovariectomized, osteoporosis of the trabecular bone microarchitecture occurred in their femurs and mandibles; however, ovariectomy did not influence the cortical bone morphology. In addition, the parametric values of the trabecular bone microarchitecture in the femoral necks were highly correlated with those of the trabecular bone microarchitecture in the mandibles.

Does Orthodontic Treatment Affect the Alveolar Bone Density?

Few studies involving human participants have been conducted to investigate the effect of orthodontic treatment on alveolar bone density around the teeth. Our previous study revealed that patients who received 6 months of active orthodontic treatment exhibited an ∼24% decrease in alveolar bone density around the teeth. However, after an extensive retention period following orthodontic treatment, whether the bone density around the teeth can recover to its original state from before the treatment remains unclear, thus warranting further investigation.The purpose of this study was to assess the bone density changes around the teeth before, during, and after orthodontic treatment.Dental cone-beam computed tomography (CBCT) was used to measure the changes in bone density around 6 teeth in the anterior maxilla (maxilla central incisors, lateral incisors, and canines) of 8 patients before and after orthodontic treatment. Each patient underwent 3 dental CBCT scans: before treatment (T0); at the end of 7 months of active orthodontic treatment (T1); after several months (20-22 months) of retention (T2). The Friedman test was applied to evaluate the changes in the alveolar bone density around the teeth according to the 3 dental CBCT scans.From T0 to T1, a significant reduction in bone density was observed around the teeth (23.36 ± 10.33%); by contrast, a significant increase was observed from T1 to T2 (31.81 ± 23.80%). From the perspective of the overall orthodontic treatment, comparing the T0 and T2 scans revealed that the bone density around the teeth was relatively constant (a reduction of only 0.75 ± 19.85%). The results of the statistical test also confirmed that the difference in bone density between T0 and T2 was nonsignificant.During orthodontic tooth movement, the alveolar bone density around the teeth was reduced. However, after a period of bone recovery, the reduced bone density recovered to its previous state from before the orthodontic treatment. However, the bone density around ∼10% of the teeth in this region could not recover to 80% of its state from before the orthodontic treatment.

Test in canine extraction site preservations by using mineralized collagen plug with or without membrane

The aim of this study was to discuss the feasibility of porous mineralized collagen plug and bilayer mineralized collagen-guided bone regeneration membrane in site preservation in extraction sockets. The third mandibular premolars on both sides were extracted from four dogs, thus there were 16 alveolar sockets in all dogs and were randomly assigned into three groups. Group A had six alveolar sockets, and groups B and C had five alveolar sockets, respectively. Each alveolar socket of group A was immediately implanted with a porous mineralized collagen plug and covered with a bilayer mineralized collagen-guided bone regeneration membrane after tooth extraction. Alveolar sockets of group B were implanted with porous mineralized collagen plug only, and group C was set as blank control without any implantation. The healing effects of the extraction sockets were evaluated by gross observation, morphological measurements, and X-ray micro-computed tomography after twelve weeks. Twelve weeks after operation, both groups A and B had more amount of new bone formation compared with group C; in terms of the degree of alveolar bone height, group A was lower than groups B and C with significant differences; the bone mineral density in the region of interest and bone remodeling degree in group A were higher than those of groups B and C. As a result, porous mineralized collagen plug could induce the regeneration of new bone in extraction socket, and combined use of porous mineralized collagen plug and bilayer mineralized collagen guided bone regeneration membrane could further reduce the absorption of alveolar ridge and preserve the socket site.

New quantitative classification of the anatomical relationship between impacted third molars and the inferior alveolar nerve

BACKGROUND

Before extracting impacted lower third molars, dentists must first identify the spatial relationship between the inferior alveolar nerve (IAN) and an impacted lower third molar to prevent nerve injury from the extraction. Nevertheless, the current method for describing the spatial relationship between the IAN and an impacted lower third molar is deficient. Therefore, the objectives of this study were to: (1) evaluate the relative position between impacted lower third molars and the IAN; and (2) investigate the relative position between impacted lower third molars and the IAN by using a cylindrical coordinate system.

METHODS

From the radiology department's database, we selected computed tomography images of 137 lower third molars (from 75 patients) requiring removal and applied a Cartesian coordinate system by using Mimics, a medical imaging software application, to measure the distribution between impacted mandibular third molars and the IAN. In addition, the orientation of the lower third molar to the IAN was also measured, but by using a cylindrical coordinate system with the IAN as the origin.

RESULTS

According to the Cartesian coordinate system, most of the IAN runs through the inferior side of the third molar (78.6 %), followed by the lingual side (11.8 %), and the buccal side (8.9 %); only 0.7 % is positioned between the roots. Unlike the Cartesian coordinate system, the cylindrical coordinate system clearly identified the relative position, r and θ, between the IAN and lower third molar.

CONCLUSIONS

Using the cylindrical coordinate system to present the relationship between the IAN and lower third molar as (r, θ) might provide clinical practitioners with a more explicit and objective description of the relative position of both sites. However, comprehensive research and cautious application of this system remain necessary.

In vivo small animal micro-CT using nanoparticle contrast agents

Computed tomography (CT) is one of the most valuable modalities for in vivo imaging because it is fast, high-resolution, cost-effective, and non-invasive. Moreover, CT is heavily used not only in the clinic (for both diagnostics and treatment planning) but also in preclinical research as micro-CT. Although CT is inherently effective for lung and bone imaging, soft tissue imaging requires the use of contrast agents. For small animal micro-CT, nanoparticle contrast agents are used in order to avoid rapid renal clearance. A variety of nanoparticles have been used for micro-CT imaging, but the majority of research has focused on the use of iodine-containing nanoparticles and gold nanoparticles. Both nanoparticle types can act as highly effective blood pool contrast agents or can be targeted using a wide variety of targeting mechanisms. CT imaging can be further enhanced by adding spectral capabilities to separate multiple co-injected nanoparticles in vivo. Spectral CT, using both energy-integrating and energy-resolving detectors, has been used with multiple contrast agents to enable functional and molecular imaging. This review focuses on new developments for in vivo small animal micro-CT using novel nanoparticle probes applied in preclinical research.