Jin Hee Kwak

Wide-field Raman imaging for bone detection in tissue.

Inappropriate bone growth in soft tissue can occur after trauma to a limb and can cause a disruption to the healing process. This is known as Heterotopic Ossification (HO) in which regions in the tissue start to mineralize and form microscopic bone-like structures. These structures continue to calcify and develop into large, non-functional bony masses that cause pain, limit limb movement, and expose the tissue to reoccurring infections; in the case of open wounds this can lead to amputation as a result of a failed wound. Both Magnetic Resonance Imaging (MRI) and X-ray imaging have poor sensitivity and specificity for the detection of HO, thus delaying therapy and leading to poor patient outcomes. We present a low-power, fast (1 frame per second) optical Raman imaging system with a large field of view (1 cm(2)) that can differentiate bone tissue from soft tissue without spectroscopy, this in contrast to conventional Raman microscopy systems. This capability may allow for the development of instrumentation which permits bedside diagnosis of HO.

Novel role for cyclophilin A in regulation of chondrogenic commitment and endochondral ossification.

ABSTRACT Recent studies showed that cyclophilin A (CypA) promotes NF-κB/p65 nuclear translocation, resulting in enhanced NF-κB activity and altered expression of its target genes, such as the Sox9 transcriptional factor, which plays a critical role in chondrogenic differentiation and endochondral ossification. In this report, we unveil the role of CypA in signal-induced chondrogenic differentiation and endochondral ossification. Expression levels of the chondrogenic differentiation markers and transcriptional regulators Sox9 and Runx2 were all significantly lower in CypA knockdown chondrogenic cells than in wild-type cells, indicating that CypA plays a functional role in chondrogenic differentiation. In vitro differentiation studies using micromass cultures of mouse limb bud cells further supported the conclusion that CypA is needed for chondrogenic differentiation. Newborn CypA-deficient pups double stained with alcian blue and alizarin red exhibited generalized, pronounced skeletal defects, while high-resolution micro-computed tomography (microCT) analyses of the femurs and lumbar vertebrae revealed delayed or incomplete endochondral ossification. Comparative histology and immunohistochemistry (IHC) analyses further verified the effects of CypA deficiency on chondrogenic differentiation. Our results provide evidence for the important contribution of CypA as a pertinent component acting through NF-κB–Sox9 in regulation of chondrogenesis signaling. These findings are important to better understand signal-induced chondrogenesis of chondrogenic progenitors in physiological and pathophysiological contexts.

Effects of variable attachment shapes and aligner material on aligner retention

OBJECTIVE To evaluate the retention of four types of aligners on a dental arch with various attachments. MATERIALS AND METHODS For this study, three casts were manufactured, two of which contained attachments (ellipsoid and beveled), and one without any attachments to serve as a control. Four types of aligners were thermoformed: Clear-Aligner (CA)-soft, CA-medium, and CA-hard, with various thicknesses, and Essix ACE. Measurements of vertical displacement force during aligner removal were performed with the Gabo Qualimeter Eplexor. Means and standard deviations were next compared between different aligner thicknesses and attachment shapes. RESULTS CA-soft, CA-medium, and CA-hard did not present a significant increase in retention, except when used in the presence of attachments. Additionally, CA-medium and CA-hard required significantly more force for removal. Essix ACE demonstrated a significant decrease in retention when used with ellipsoid attachments. The force value for Essix ACE removal from the cast with beveled attachments was comparable to that of CA-medium. Forces for aligner removal from the model without attachments showed a linear trend. Essix ACE did not show a continuous increase in retention for each model. Overall, ellipsoid attachments did not present a significant change in retention. In contrast, beveled attachments improved retention. CONCLUSIONS Ellipsoid attachments had no significant influence on the force required for aligner removal and hence on aligner retention. Essix ACE showed significantly less retention than CA-hard on the models with attachments. Furthermore, beveled attachments were observed to increase retention significantly, compared with ellipsoid attachments and when using no attachments.

The Effects of Systemic Therapy of PEGylated NELL-1 on Fracture Healing in Mice

Fractures are common, with an incidence of 13.7 per 1000 adults annually. Systemic agents have been widely used for enhancing bone regeneration; however, the efficacy of these therapeutics for the management and prevention of fracture remains unclear. NEL-like protein 1 (NELL-1) is a potent pro-osteogenic cytokine that has been modified with polyethylene glycol (PEG)ylation [PEGylated NELL-1 (NELL-PEG)] to enhance its pharmacokinetics for systemic therapy. Our aim was to investigate the effects of systemic administration of NELL-PEG on fracture healing in mice and on overall bone properties in uninjured bones. Ten-week-old CD-1 mice were subjected to an open osteotomy of bilateral radii and treated with weekly injections of NELL-PEG or PEG phosphate-buffered saline as control. Systemic injection of NELL-PEG resulted in improved bone mineral density of the fracture site and accelerated callus union. After 4 weeks of treatment, mice treated with NELL-PEG exhibited substantially enhanced callus volume, callus mineralization, and biomechanical properties. NELL-PEG injection significantly augmented bone regeneration, as confirmed by high expression of bone turnover rate, bone formation rate, and mineral apposition rate. Consistently, the immunohistochemistry results also confirmed a high bone remodeling activity in the NELL-PEG-treated group. Our findings suggest that weekly injection of NELL-PEG may have the clinical potential to accelerate fracture union and enhance overall bone properties, which may help prevent subsequent fractures.

Cyclophilin A (CypA) Plays Dual Roles in Regulation of Bone Anabolism and Resorption

CypA (Cyclophilin A) is a peptidyl-prolyl isomerase previously shown to be required for chondrogenic differentiation and endochondral ossification. However, the effects of CypA on osteoclast activity and bone maintenance are entirely unknown. Here, we show that Ppia−/− mice demonstrate low bone mineral density, reduced osteoblast numbers, and increased osteoclast numbers. When isolated from the calvaria, Ppia−/− osteoblasts demonstrate decreased osteogenic differentiation, whereas Ppia−/− osteoclasts derived from the long bones showed increased osteoclastic activity. Overexpression and gene silencing of CypA verified osteogenic and anti-osteoclastic effects. In osteoblasts, CypA is necessary for BMP-2 (Bone Morphogenetic Protein-2)-induced Smad phosphorylation. In osteoclasts, loss of CypA activates BtK (Bruton’s tyrosine kinase) and subsequently integrates with TRAF6 (TNF receptor-associated factor 6) and/or c-fos signaling to induce NFATc1 (nuclear factors of activated T cells, cytoplasmic 1). Collectively, CypA dually exerts pro-osteogenic and anti-osteoclastic effects. Thus, modulation of CypA may be useful in future efforts targeting osteoporosis.

Inactivation of Nell-1 in chondrocytes significantly impedes appendicular skeletogenesis

NELL‐1, an osteoinductive protein, has been shown to regulate skeletal ossification. Interestingly, an interstitial 11p14.1‐p15.3 deletion involving the Nell‐1 gene was recently reported in a patient with short stature and delayed fontanelle closure. Here we sought to define the role of Nell‐1 in endochondral ossification by investigating Nell‐1‐specific inactivation in Col2α1‐expressing cell lineages. Nell‐1flox/flox; Col2α1‐Cre+ (Nell‐1Col2α1KO) mice were generated for comprehensive analysis. Nell‐1Col2α1KO mice were born alive but displayed subtle femoral length shortening. At 1 and 3 months postpartum, Nell‐1 inactivation resulted in dwarfism and premature osteoporotic phenotypes. Specifically, Nell‐1Col2α1KO femurs and tibias exhibited significantly reduced length, bone mineral density (BMD), bone volume per tissue volume (BV/TV), trabecular number/thickness, cortical volume/thickness/density, and increased trabecular separation. The decreased bone formation rate revealed by dynamic histomorphometry was associated with altered numbers and/or function of osteoblasts and osteoclasts. Furthermore, longitudinal observations by in vivo micro‐CT showed delayed and reduced mineralization at secondary ossification centers in mutants. Histologically, reduced staining intensities of Safranin O, Col‐2, Col‐10, and fewer BrdU‐positive chondrocytes were observed in thinner Nell‐1Col2α1KO epiphyseal plates along with altered distribution and weaker expression level of Ihh, Patched‐1, PTHrP, and PTHrP receptor. Primary Nell‐1Col2α1KO chondrocytes also exhibited decreased proliferation and differentiation, and its downregulated expression of the Ihh‐PTHrP signaling molecules can be partially rescued by exogenous Nell‐1 protein. Moreover, intranuclear Gli‐1 protein and gene expression of the Gli‐1 downstream target genes, Hip‐1 and N‐Myc, were also significantly decreased with Nell‐1 inactivation. Notably, the rescue effects were diminished/reduced with application of Ihh signaling inhibitors, cyclopamine or GANT61. Taken together, these findings suggest that Nell‐1 is a pivotal modulator of epiphyseal homeostasis and endochondral ossification. The cumulative chondrocyte‐specific Nell‐1 inactivation significantly impedes appendicular skeletogenesis resulting in dwarfism and premature osteoporosis through inhibiting Ihh signaling and predominantly altering the Ihh‐PTHrP feedback loop.

An overview of the american board of orthodontics certification process

The American Board of Orthodontics (ABO) was founded nearly ninety years ago as the first American specialty board in the field of dentistry. The ABO, in affiliation with the American Association of Orthodontists, is, in fact, the only orthodontic specialty board that is recognized by the American Dental Association. In order to become board-certified by the ABO, an orthodontist must successfully pass a written examination as well as a clinical examination. Important to the clinical exam is the ability to measure case complexity and case outcome. To this end, the ABO has established a comprehensive Discrepancy Index (DI) system which systematically analyzes and scores every element of the selected case and its difficulty, thereby measuring case complexity. Similarly, the ABO has established a comprehensive Cast-Radiograph (CR) evaluation which systematically analyzes every element of the selected case and its finished occlusion, thereby measuring case outcome. This review article presents an overview of the ABO certification process and reviews a classic high-angle Class II growing patient case that successfully passed the ABO exam. This article further presents a walkthrough of how to complete the DI and CR evaluation using the high-angle Class II growing patient case as an example. By establishing the DI form and CR evaluation and by making this information available to the public, the ABO strives to be both objective and transparent in allowing orthodontists to self-assess their finished cases.

Cyst-Like Osteolytic Formations in Recombinant Human Bone Morphogenetic Protein-2 (rhBMP-2) Augmented Sheep Spinal Fusion

Multiple case reports using recombinant human bone morphogenetic protein-2 (rhBMP-2) have reported complications. However, the local adverse effects of rhBMP-2 application are not well documented. In this report we show that, in addition to promoting lumbar spinal fusion through potent osteogenic effects, rhBMP-2 augmentation promotes local cyst-like osteolytic formations in sheep trabecular bones that have undergone anterior lumbar interbody fusion. Three months after operation, conventional computed tomography showed that the trabecular bones of the rhBMP-2 application groups could fuse, whereas no fusion was observed in the control group. Micro-computed tomography analysis revealed that the core implant areas bone volume fraction and bone mineral density increased proportionately with rhBMP-2 dose. Multiple cyst-like bone voids were observed in peri-implant areas when using rhBMP-2 applications, and these sites showed significant bone mineral density decreases in relation to the unaffected regions. Biomechanically, these areas decreased in strength by 32% in comparison with noncystic areas. Histologically, rhBMP-2-affected void sites had an increased amount of fatty marrow, thinner trabecular bones, and significantly more adiponectin- and cathepsin K-positive cells. Despite promoting successful fusion, rhBMP-2 use in clinical applications may result in local adverse structural alterations and compromised biomechanical changes to the bone.