Organic Matrix Derived from Host-Microbe Interplay Contributes to Pathological Renal Biomineralization

Matrix stones are a rare form of kidney stones. They feature a high percentage of hydrogel-like organic matter, and their formation is closely associated with urinary tract infections. Herein, comprehensive materials and biochemical approaches were taken to map the organic-inorganic interface and gather insights into the host-microbe interplay in pathological renal biomineralization. Surgically extracted soft and slimy matrix stones were examined using micro-X-ray computed tomography and various microspectroscopy techniques. Higher-mineral-density laminae were positive for calcium-bound Alizarin red. Lower-mineral-density laminae revealed periodic acid-Schiff-positive organic filamentous networks of varied thickness. These organic filamentous networks, which featured a high polysaccharide content, were enriched with zinc, carbon, and sulfur elements. Neutrophil extracellular traps (NETs) along with immune response-related proteins, including calprotectin, myeloperoxidase, CD63, and CD86, also were identified in the filamentous networks. Expressions of NETs and upregulation of polysaccharide-rich mucin secretion are proposed as a part of the host immune defense to "trap" pathogens. These host-microbe derived organic matrices can facilitate heterogeneous nucleation and precipitation of inorganic particulates, resulting in macroscale aggregates known as "matrix stones". These insights into the plausible aggregation of constituents through host-microbe interplay underscore the unique "double-edged sword" effect of the host immune response to pathogens and the resulting renal biominerals.

Contact ratio and adaptations in the maxillary and mandibular dentoalveolar joints in rats and human clinical analogs

Spatial maps of function-based contact areas and resulting mechanical strains in bones of intact fibrous joints in preclinical small-scale animal models are limited. Functional imaging in situ on intact dentoalveolar fibrous joints (DAJs) in hemimandibles and hemimaxillae harvested from 10 male Sprague-Dawley rats (N = 5 at 12 weeks, N = 5 at 20 weeks) was performed in this study. Physical features including bone volume fraction (BVF), bone pore diameter and pore density, and cementum fraction (CF) of the molars in the maxillary and mandibular joints were evaluated. Biomechanical testing in situ provided estimates of joint stiffness, changes in periodontal ligament spaces (PDL-space) between the molar and bony socket, and thereby localization of contact area in the respective joints. Contact area localization revealed mechanically stressed interradicular and apical regions in the joints. These anatomy-specific contact stresses in maxillary and mandibular joints were correlated with the physical features and resulting strains in interradicular and bony socket compartments. The mandibular joint spaces, in general, were higher than maxillary, and this trend was consistent with age (younger loaded: Mn - 134 ± 55 μm, Mx - 110 ± 47 μm; older loaded: Mn - 122 ± 49 μm, Mx - 105 ± 48 μm). However, a significant decrease (P < 0.05) in mandibular and maxillary joint spaces with age (younger unloaded: Mn - 147 ± 51 μm; Mx - 125 ± 42 μm; older unloaded: Mn - 134 ± 46 μm; Mx - 116 ± 44 μm) was observed. The bone volume fraction (BVF) of mandibular interradicular bone (IR bone) increased significantly with age (P < 0.05) with the percent porosity of coronal mandibular bone lower than its maxillary counterpart. The contact ratio (contact area to total surface area) of maxillary teeth was significantly greater (P < 0.05) than mandibular teeth; both maxillary interradicular and apical contact ratios (IR bone: 41%, 56%; Apical bone: 4%, 12%) increased with age, and were higher than the mandibular (IR bone: 19%, 44%; Apical bone: 1%, 4%) counterpart. Resulting higher but uniform strains in maxillary bone contrasted with lower but higher variance in mandibular strains at a younger age. Anatomy-specific colocalization of physical properties and functional strains in bone provided insights into form-guided adaptive dominance of the maxilla compared to material property-guided adaptive dominance of the mandible. These age-related trends from the preclinical animal model paralleled with age- and tooth position-specific variabilities in mandibular craniofacial bones of adolescent and adult patients following orthodontic treatment.

Insights Into Pulp Biomineralization in Human Teeth

Introduction

Mineralized pulp (MP) compromises tooth function and its causation is unknown. The hypothesis of this study is that pulp mineralization is associated with pulpal tissue adaptation, increased mineral densities, and decreased permeabilities of tubular dentin and cementum. Methods will include correlative spatial mapping of physicochemical and biochemical characteristics of pulp, and contextualize these properties within the dentin-pulp complex (DPC) to reveal the inherent vunerabilities of pulp.

Methods

Specimens (N = 25) were scanned using micro X-ray computed tomography (micro-XCT) to visualize MP and measure mineral density (MD). Elemental spatial maps of MP were acquired using synchrotron X-ray fluorescence microprobe (μXRF) and energy dispersive X-ray spectroscopy (EDX). Extracted pulp tissues were sectioned for immunolabelling and the sections were imaged using a light microscope. Microscale morphologies and nanoscale ultrastructures of MP were imaged using scanning electron (SEM) and scanning transmission electron microscopy (STEM) techniques.

Results

Heterogeneous distribution of MD from 200 to 2,200 mg/cc, and an average MD of 892 (±407) mg/cc were observed. Highly mineralized pulp with increased number of occluded tubules, reduced pore diameter in cementum, and decreased connectivity in lateral channels were observed. H&amp;E, trichrome, and von Kossa staining showed lower cell and collagen densities, and mineralized regions in pulp. The biomolecules osteopontin (OPN), osteocalcin (OCN), osterix (OSX), and bone sialoprotein (BSP) were immunolocalized around PGP 9.5 positive neurovascular bundles in MP. SEM and STEM revealed a wide range of nano/micro particulates in dentin tubules and spherulitic mineral aggregates in the collagen with intrafibrillar mineral surrounding neurovascular bundles. EDX and μXRF showed elevated counts of Ca, P, Mg, and Zn inside pulp and at the dentin-pulp interface (DPI) in the DPC.

Conclusion

Colocalization of physical and chemical, and biomolecular compositions in MP suggest primary and secondary biomineralization pathways in pulp and dentin at a tissue level, and altered fluid dynamics at an organ level. Elevated counts of Zn at the mineralizing front in MP indicated its role in pulp biomineralization. These observations underpin the inherent mechano- and chemo-responsiveness of the neurovascular DPC and help elucidate the clinical subtleties related to pulpitis, dentin-bridge, and pulp stone formation.

Mineralized Peyronie's plaque has a phenotypic resemblance to bone

Mineralized Peyronie's plaque (MPP) impairs penile function. The association, colocalization, and dynamic interplay between organic and inorganic constituents can provide insights into biomineralization of Peyronie's plaque. Human MPPs (n = 11) were surgically excised, and the organic and inorganic constituents were spatially mapped using multiple high-resolution imaging techniques. Multiscale image analyses resulted in spatial colocalization of elements within a highly porous material with heterogenous composition, lamellae, and osteocytic lacuna-like features with a morphological resemblance to bone. The lower (520 ± 179 mg/cc) and higher (1024 ± 155 mg/cc) mineral density regions were associated with higher (11%) and lower (7%) porosities in MPP. Energy dispersive X-ray and micro-X-ray fluorescent spectroscopic maps in the higher mineral density regions of MPP revealed higher counts of calcium (Ca) and phosphorus (P), and a Ca/P ratio of 1.48 ± 0.06 similar to bone. More importantly, higher counts of zinc (Zn) were localized at the interface between softer (more organic to inorganic ratio) and harder (less organic to inorganic ratio) tissue regions of MPP and adjacent softer matrix, indicating the involvement of Zn-related proteins and/or pathways in the formation of MPP. In particular, dentin matrix protein-1 (DMP-1) was colocalized in a matrix rich in proteoglycans and collagen that contained osteocytic lacuna-like features. This combined materials science and biochemical with correlative microspectroscopic approach provided insights into the plausible cellular and biochemical pathways that incite mineralization of an existing fibrous Peyronie's plaque. STATEMENT OF SIGNIFICANCE: Aberrant human penile mineralization is known as mineralized Peyronie's plaque (MPP) and often results in a loss of form and function. This study focuses on investigating the spatial association of matrix proteins and elemental composition of MPP by colocalizing calcium, phosphorus, and trace metal zinc with dentin matrix protein 1 (DMP-1), acidic proteoglycans, and fibrillar collagen along with the cellular components using high resolution correlative microspectroscopy techniques. Spatial maps provided insights into cellular and biochemical pathways that incite mineralization of fibrous Peyronie's plaque in humans.

Functional Adaptation of LPS-affected Dentoalveolar Fibrous Joints in Rats

INTRODUCTION

The functional interplay between cementum of the root and alveolar bone of the socket is tuned by a uniquely positioned 70-80 µm wide fibrous and lubricious ligament in a dentoalveolar joint (DAJ). In this study, structural and biomechanical properties of the DAJ, periodontal ligament space (PDL-space also known as the joint space), alveolar bone of the socket, and cementum of the tooth root that govern the biomechanics of a lipopolysaccharide (LPS)-affected DAJ were mapped both in space and time.

METHODS

The hemi-maxillae from 20 rats (4 control at 6 weeks of age, 4 control and 4 LPS-affected at 12 weeks of age, 4 control and 4 LPS-affected at 16 weeks of age) were investigated using a hybrid technique; micro-X-ray computed tomography (5 µm resolution) in combination with biomechanical testing in situ. Temporal variations in bone and cementum volume fractions were evaluated. Trends in mineral apposition rates (MAR) in additional six Sprague Dawley rats (3 controls, 3 LPS-affected) were revealed by transforming spatial fluorochrome signals to functional growth rates (linearity factor - RW) of bone, dentin, and cementum using a fast Fourier transform on fluorochrome signals from 100-µm hemi-maxillae sections.

RESULTS

An overall change in LPS-affected DAJ biomechanics (a 2.5-4.5X increase in tooth displacement and 2X tooth rotation at 6 weeks, no increase in displacement and a 7X increase in rotation at 12 weeks; 27% increase in bone effective strain at 6 weeks and 11% at 12 weeks relative to control) was associated with structural changes in the coronal regions of the DAJ (15% increase in PDL-space from 0 to 6 weeks but only 5% from 6 to 12 weeks compared to control). A significant increase (p < 0.05) in PDL-space between ligated and age-matched control was observed. The bone fraction of ligated at 12 weeks was significantly lower than its age-matched control, and no significant differences (p > 0.05) between groups were observed at 6 weeks. Cementum in the apical regions grew faster but nonlinearly (11% and 20% increase in cementum fraction (CF) at 6 and 12 weeks) compared to control. Alveolar bone revealed site-specific nonlinear growth with an overall increase in MAR (108.5 µm/week to 126.7 µm/week after LPS treatment) compared to dentin (28.3 µm/week in control vs. 26.1 µm/week in LPS-affected) and cementum (126.5 µm/week in control vs. 119.9 µm/week in LPS-affected). A significant increase in CF (p < 0.05) in ligated specimens was observed at 6 weeks of age.

CONCLUSIONS

Anatomy-specific responses of cementum and bone to the mechano-chemo stimuli, and their collective temporal contribution to observed changes in PDL-space were perpetuated by altered tooth movement. Data highlight the "resilience" of DAJ function through the predominance of nonlinear growth response of cementum, changes in PDL-space, and bone architecture. Despite the significant differences in bone and cementum architectures, data provided insights into the reactionary effects of cementum as a built-in compensatory mechanism to reestablish functional competence of the DAJ. The spatial shifts in architectures of alveolar bone and cementum, and consequently ligament space, highlight adaptations farther away from the site of insult, which also is another novel insight from this study. These adaptations when correlated within the context of joint function (biomechanics) illustrate that they are indeed necessary to sustain DAJ function albeit being pathological.

Food hardness can regulate orthodontic tooth movement in mice

BACKGROUND AND OBJECTIVES

Orthodontic treatment is often accompanied with prescription of softer foods to patients. The question to ask is, is this prescribed load regimen congruent with Wolff's law, and does it provide an adequate mechanical stimulus to maintain the functional health of periodontal complex? This question was answered by studying the effects of mice chewing on soft food (SF) and hard food (HF) while undergoing experimental tooth movement (ETM).

METHODS

Three-week-old C57BL/6 mice (n = 18) were fed either hard pellet (HF; n = 9) or soft-chow food (SF; n = 9). ETM was performed on mice at 8 weeks of age, and mice were euthanized at 1 min, 2 weeks, and 4 weeks (8, 10, and 12 weeks old, respectively). A logistic regression model was applied to the experimental data to extrapolate the prolonged effects of ETM on the physical features of the dentoalveolar joint (DAJ).

RESULTS

By 12 weeks, mice that chewed on SF expressed wider periodontal ligament space than those that chewed on HF. Mice that chewed on SF demonstrated increased alveolar socket roughness with larger alveoli and decreased bone volume fraction but with significantly lower bone mineral density and reduced overall tooth movement.

CONCLUSIONS

These altered physical features when contextualized within the DAJ illustrated that (a) the regions farther away from the "site of insult" also undergo significant adaptation, and (b) these adaptations vary between mesial and distal sides of the periodontal complex and topographically differentiate in the direction of the ETM. These insights underpin the main conclusion, in that there is a need to "regulate chewing loads" as a therapeutic dose following ETM to encourage regeneration of periodontal complex as an effective clinical outcome. The discussed multiscale image analyses also can be used on patient cone beam computed tomography data to identify the effectiveness of orthodontic treatment within the realm of masticatory function.

Biomineralization of Dental Tissues Treated with Silver Diamine Fluoride

Silver diamine fluoride (SDF) is a dental biomaterial used to arrest dental caries. To better understand SDF's mechanism of action, we examined the localization of silver within the tissues of SDF-treated teeth. Carious primary teeth fixed within 2 min of SDF application (SDF-minutes, n = 3), at 3 wk after SDF application in vivo (SDF-weeks, n = 4), and at 2 y after multiple SDF applications in vivo (SDF-multiple, n = 1) were investigated in this study. Carious primary teeth without SDF application (no-SDF, n = 3) served as controls. Mineral density and structural analyses were performed via micro-X-ray computed tomography and scanning electron microscopy. Elemental analyses were performed through X-ray fluorescence microprobe and energy-dispersive X-ray spectroscopic techniques. SDF-treated teeth revealed higher X-ray-attenuated surface and subsurface regions within carious lesions, and similar regions were not present in no-SDF teeth. Regions of higher mineral density correlated with regions of silver abundance in SDF-treated teeth. The SDF penetration depth was approximated to 0.5 ± 0.02 mm and 0.6 ± 0.05 mm (mean ± SD) for SDF-minutes and SDF-weeks specimens, respectively. A higher percentage of dentin tubular occlusion by silver or calcium phosphate particles was observed in primary teeth treated with SDF-weeks as compared with SDF-minutes. Elemental analysis also revealed zinc abundance in carious lesions and around the pulp chamber. SDF-weeks teeth had significantly increased tertiary dentin than SDF-minutes and no-SDF teeth. These results suggest that SDF treatment on primary teeth affected by caries promotes pathologic biomineralization by altering their physicochemical properties, occluding dentin tubules, and increasing tertiary dentin volume. These seemingly serendipitous effects collectively contribute to the cariostatic activity of SDF.

Structural and chemical heterogeneities of primary hyperoxaluria kidney stones from pediatric patients

OBJECTIVE

Calcium oxalate stones are the most common type among stone-forming patients and in some cases result from predisposed genetic conditions. In this work, we examined the differences in structure and chemical composition between oxalate stones from patients from three groups: 1) pediatric patients that were genetically predisposed (primary hyperoxaluria) to form stones (PPH); 2) control pediatric patients that did not have such genetic predisposition (PN-PH); 3) adult patients that formed oxalate stones without the genetic predisposition (A-CaOx). A variety of instrumental analyses were conducted to identify physicochemical properties of stones characteristic of predisposed pediatric (PPH), pediatric hyperoxaluria (PN-PH), and adult (A-CaOx) patient populations.

METHODS

Genetic variants of 16 stone-forming patients were determined using whole-exome gene sequencing. Components of stones from PPH (n = 6), PN-PH (n = 5), and A-CaOx (n = 5) groups were identified using Fourier transform infrared (FTIR) spectroscopy. Stone morphology and density were evaluated using high resolution X-ray computed tomography (micro-XCT). Stone microstructure and elemental composition were mapped with scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy, respectively.

RESULTS

Calcium oxalate bipyramidal crystals were found on stones from all groups. Stones from PPH patients with PH types I and II were composed of calcium oxalate monohydrate (COM) with relatively uniform mineral density (1224 ± 277 mg/cc) and distinct smooth surfaces. By contrast, micro-spherical calcium phosphate particles were found only on PN-PH stones, which also showed a broader range of mineral densities (1266 ± 342 mg/cc). Stones from the PN-PH group also contained phosphorus (P), which was absent in NP-PH stones. A-CaOx stones were of significantly lower mineral density (645 ± 237 mg/cc) than pediatric stones and were more heterogeneous in their elemental composition.

CONCLUSION

Unique structural and compositional characteristics were identified in stones from pediatric patients with primary hyperoxaluria. These include the absence of phosphorus, a narrower mineral density distribution, and a uniform elemental composition compared to stones from pediatric patients without the genetic predisposition. Thus, characterization of stones at the macro- and micro-scales in combination with genetic testing of patients can provide insights and accurate diagnosis to develop a treatment plan for effective patient care.

Structure and elemental composition of Ceftriaxone induced pediatric nephrolithiasis

Ceftriaxone is a widely used antibiotic because to its broad-spectrum gram-negative coverage, safety, and biological half life (5-9 h) permit dose once-daily administration. It is specifically used in pediatric patients in developing countries. Ceftriaxone forms insoluble sludge/stone when combined with calcium in the urinary system. In this study, Ceftriaxone induced sludge/stones from pediatric patients were collected to identify its microstructure and composition to gather insights into the mechanism of Ceftriaxone induced sludge/stone formation. The results illustrated that Ceftriaxone induced stones formed rapidly following antibiotic administration. Ceftriaxone calcium salt crystals could easily be broken with minimal intervention. However, Ceftriaxone combined with calcium phosphate formed an insoluble stone aggregate.

Functional adaptation of interradicular alveolar bone to reduced chewing loads on dentoalveolar joints in rats

OBJECTIVES

The effects of reduced chewing loads on load bearing integrity of interradicular bone (IB) within dentoalveolar joints (DAJ) in rats were investigated.

METHODS

Four-week-old Sprague Dawley rats (N = 60) were divided into two groups; rats were either fed normal food, which is hard-pellet food (HF) (N = 30), or soft-powdered chow (SF) (N = 30). Biomechanical testing of intact DAJs and mapping of the resulting mechanical strains within IBs from 8- through 24-week-old rats fed HF or SF were performed. Tension- and compression-based mechanical strain profiles were mapped by correlating digital volumes of IBs at no load with the same IBs under load. Heterogeneity within IB was identified by mapping cement lines and TRAP-positive multinucleated cells using histology, and mechanical properties using nanoindentation technique.

RESULTS

Significantly decreased interradicular functional space, IB volume fraction, and elastic modulus of IB in the SF group compared with the HF group were observed, and these trends varied with an increase in age. The elastic modulus values illustrated significant heterogeneity within IB from HF or SF groups. Both compression- and tension-based strains were localized at the coronal portion of the IB and the variation in strain profiles complemented the observed material heterogeneity using histology and nanoindentation.

SIGNIFICANCE

Interradicular space and IB material-related mechanoadaptations in a DAJ are optimized to meet soft food related chewing demands. Results provided insights into age-specific regulation of chewing loads as a plausible "therapeutic dose" to reverse adaptations within the periodontal complex as an attempt to regain functional competence of a dynamic DAJ.

Ectopic biomineralization in kidney stone formers compared to non-stone formers

Background

Kidney stone formers (SFs) are at increased risk of stroke, myocardial infarction, and atherosclerosis of the carotid and coronary arteries. These cardiovascular and urologic pathologies can result from ectopic biomineral deposition. The objectives of this study are: (I) to evaluate risk factors for ectopic biomineralization, and (II) to characterize the overall burden of ectopic minerals in known SFs compared to non-stone formers (NSFs) matched for these risk factors.

Methods

Presence and quantity of biominerals at eight anatomic locations (abdominal aorta, common iliac arteries, pelvic veins, prostate or uterus, mesentery, pancreas, and spleen) were determined in a case control study by retrospective analysis of clinical non-contrast computed tomography scans obtained from 190 SFs and 190 gender- and age-matched NSFs (renal transplant donors). Predictors of biomineralization were determined using negative binomial regression. A subgroup of 140 SFs and 140 NSFs were matched for risk factors for systemic biomineralization, and mineralization was compared between these matched SFs and NSFs using ordinal logistic regression.

Results

Hypertension, hyperlipidemia, diabetes mellitus, and smoking were more common amongst SFs. Risk factors for increased systemic biomineralization included history of nephrolithiasis, male gender, older age, and history of hyperlipidemia. When controlling for these comorbidities, SFs had significantly increased biomineralization systemically and at the abdominal aorta, iliac arteries, prostate, mesentery, pancreas, and spleen compared to NSFs.

Conclusions

The current study provides evidence that SFs are at increased risk of biomineralization systemically, independent of common risk factors of atherosclerosis.

High-Throughput Screening: today's biochemical and cell-based approaches

High-throughput screening (HTS) provides starting chemical matter in the adventure of developing a new drug. In this review, we survey several HTS methods used today for hit identification, organized in two main flavors: biochemical and cell-based assays. Biochemical assays discussed include fluorescence polarization and anisotropy, FRET, TR-FRET, and fluorescence lifetime analysis. Binding-based methods are also surveyed, including NMR, SPR, mass spectrometry, and DSF. On the other hand, cell-based assays discussed include viability, reporter gene, second messenger, and high-throughput microscopy assays. We devote some emphasis to high-content screening, which is becoming very popular. An advisable stage after hit discovery using phenotypic screens is target deconvolution, and we provide an overview of current chemical proteomics, in silico, and chemical genetics tools. Emphasis is made on recent CRISPR/dCas-based screens. Lastly, we illustrate some of the considerations that inform the choice of HTS methods and point to some areas with potential interest for future research.

Mechanoadaptive strain and functional osseointegration of dental implants in rats

Spatiotemporal implant-bone biomechanics and mechanoadaptive strains in peri-implant tissue are poorly understood. Physical and chemical characteristics of an implant-bone complex (IBC) were correlated in three-dimensional space (along the length and around a dental implant) to gather insights into time related integration of the implant with the cortical portion of a jaw bone in a rat. Rats (N = 9) were divided into three experimental groups with three rats per time point; 3-, 11-, and 24-day. All rats were fed crumbled hard pellets mixed with water (soft-food diet) for the first 3 days followed by a hard-food diet with intact hard-food pellets (groups of 11- and 24-day only). Biomechanics of the IBCs harvested from rats at each time point was evaluated by performing mechanical testing in situ in tandem with X-ray imaging. The effect of physical association (contact area) of a loaded implant with adapting peri-implant tissue, and resulting strain within was mapped by using digital volume correlation (DVC) technique. The IBC stiffness at respective time points was correlated with mechanical strain in peri-implant tissue. Results illustrated that IBC stiffness at 11-day was lower than that observed at 3-day. However, at 24-day, IBC stiffness recovered to that which was observed at 3-day. Correlative microscopy and spectroscopy illustrated that the lower IBC stiffness was constituted by softer and less mineralized peri-implant tissue that contained varying expressions of osteoconductive elements. Lower IBC stiffness observed at 11-day was constituted by less mineralized peri-implant tissue with osteoconductive elements that included phosphorus (P) which was co-localized with higher expression of zinc (Zn), and lower expression of calcium (Ca). Higher IBC stiffness at 24-day was constituted by mineralized peri-implant tissue with higher expressions of osteoconductive elements including Ca and P, and lower expressions of Zn. These spatiotemporal correlative maps of peri-implant tissue architecture, heterogeneous distribution of mineral density, and elemental colocalization underscore mechanoadaptive physicochemical properties of peri-implant tissue that facilitate functional osseointegration of an implant. These results provided insights into 1) plausible "prescription" of mechanical loads as an osteoinductive "therapeutic dose" to encourage osteoconductive elements in the peri-implant tissue that would facilitate functional osseointegration of the implant; 2) a "critical temporal window" between 3 and 11 days, and perhaps it is this acute phase during which key candidate regenerative molecules can be harnessed to accelerate osseointegration of an implant under load.

Data on biomechanics and elemental maps of dental implant-bone complexes in rats

Implant-bone biomechanics and mechanoadaptation of peri‑implant tissue in space (around and along the length of an implant) and time (3-, 11-, and 24-day following implantation) are important for functional osseointegration of dental implants. Spatiotemporal shifts in biomechanics of implant-bone complex in rat maxillae were correlated with maximum (tensile) and minimum (compressive) principal strain profiles in peri‑implant tissue using a hybrid model; biomechanics in situ paired with digital volume correlation. Spatiotemporal changes in elemental counts and their association with mineral density of the peri‑implant tissue were mapped using electron dispersive X-ray and X-ray fluorescence microprobe techniques. Data provided within are related to biomechanical testing of an implant-bone complex in situ. Data also highlight the power of correlating elemental colocalization with tension and compression regions of the peri‑implant tissues to explain spatiotemporal mechanoadaptation of implant-bone complexes. Further interpretation of data is provided in "Mechanoadaptive Strain and Functional Osseointegration of Dental Implants in Rats [1]."

Design of drug-like hepsin inhibitors against prostate cancer and kidney stones

Hepsin, a transmembrane serine protease abundant in renal endothelial cells, is a promising therapeutic target against several cancers, particularly prostate cancer. It is involved in the release and polymerization of uromodulin in the urine, which plays a role in kidney stone formation. In this work, we design new potential hepsin inhibitors for high activity, improved specificity towards hepsin, and promising ADMET properties. The ligands were developed in silico through a novel hierarchical pipeline. This pipeline explicitly accounts for off-target binding to the related serine proteases matriptase and HGFA (human hepatocyte growth factor activator). We completed the pipeline incorporating ADMET properties of the candidate inhibitors into custom multi-objective optimization functions. The ligands designed show excellent prospects for targeting hepsin via the blood stream and the urine and thus enable key experimental studies. The computational pipeline proposed is remarkably cost-efficient and can be easily adapted for designing inhibitors against new drug targets.

Biomechanical pathways of dentoalveolar fibrous joints in health and disease

Spatial and temporal adaptations within periodontal tissues and their interfaces result from functional loads. Functional loads can be physiologic and/or pathologic in nature. The prolonged effect of these loads can alter the overall biomechanics of a dentoalveolar fibrous joint (dentoalveolar joint) by changing the form of the tooth root and its socket. This "sculpting" of the tooth root and alveolar bony socket is a consequence of several mechano-biological changes that occur within the periodontal complex of a load-bearing dentoalveolar joint. These include changes in biochemical expressions, structure, elemental composition, and mechanical properties of alveolar bone, the underlying tissues of the roots of teeth, and their interfaces. These physicochemical changes in tissues continue to prompt mechano-responsive biochemical activities at the attachment sites of periodontal ligament (soft) with bone (hard), and ligament with cementum (hard), which are the entheses of a load-bearing dentoalveolar joint. Forces at soft-hard tissue attachment sites between disparate materials with different stiffness values theoretically generate strain singularities or discontinuities. These discontinuities under prolonged functional loading increase the probability for failure to occur specifically at the enthesial zones. However, in a normal dentoalveolar joint, gradual stiffness gradients exist from ligament to bone, and from ligament to cementum. The gradual transitions in stiffness from softer ligament (lower stiffness) to harder bone or cementum (higher stiffness) or vice versa optimize tissue and interfacial strains. Optimization of tissue and ligament-enthesial physical and chemical properties facilitates transmission of cyclic forces of varying magnitudes and frequencies that collectively maintain the overall biomechanics of a dentoalveolar joint. The objectives of this review are 3-fold: (i) to illustrate physicochemical adaptations at the periodontal ligament entheses of a human periodontal complex affected by subgingival calculus; (ii) to demonstrate how to "program" the hallmarks of periodontitis in small-scale vertebrates in vivo to generate spatiotemporal maps of physicochemical adaptations in a diseased dentoalveolar joint; and (iii) to correlate dentoalveolar joint biomechanics in healthy and diseased states to spatiotemporal maps of physicochemical adaptations within respective periodontal tissues. This interdisciplinary approach demonstrates that physicochemical adaptations within periodontal tissues using the mechanics of materials (tissue mechanics), materials science (tissue composition), and mechano-biology (matrix molecules) can help explain the mechano-adaptation of dentoalveolar joints in normal and diseased functional states. Multiscale biomechanics and mechano-biology approaches can provide insights into the functional competence of a diseased relative to a normal dentoalveolar joint. Insights gathered from interdisciplinary and multiscale biomechanics approaches include the following: (i) physiologic loads related to chewing maintain a balance between mineral-forming and-resorbing biochemical cellular events, resulting in gradual stiffness gradients at the periodontal ligament entheses, and, in turn, sustain the overall biomechanics of a normal "healthy" dentoalveolar joint; (ii) pathologic loads resulting from tissue degradation and physical changes to the periodontal complex promote an abrupt stiffness gradient at the periodontal ligament entheses. The shift from gradual to an abrupt stiffness gradient could prompt a shift in the biochemical cascades, exacerbate mechano-responsive biochemical expressions at periodontal ligament entheses farther away from the site of insult, and culminate in joint degradation; (iii) sustained pathologic function on periodontally diseased joints exacerbates degradation of periodontal ligament entheses providing insights into "rescue therapy", such as the use of an adequate "mechanocal dose" to regain joint function; and (iv) spatiotemporal maps of changes in biochemical expressions, and physicochemical properties of strain-dominated affected sites, including the periodontal ligament entheses, can guide anatomy-specific therapeutics for tissue regeneration and/or disease control with the purpose of regaining dentoalveolar joint function. Modulation of occlusal loads could minimize disease progression and potentially assist in regaining functional attachment of ligament to bone and/or ligament to cementum of the dentoalveolar joint. Elucidating mechanisms that drive the breakdown of the functionally active periodontal complex burdened with microbes will provide the required critical insights into regenerative medicine and/or biomimetic approaches that would facilitate rescue/regain of dentoalveolar joint function.

Polymicrobial periodontal disease triggers a wide radius of effect and unique virome

Periodontal disease is a microbially-mediated inflammatory disease of tooth-supporting tissues that leads to bone and tissue loss around teeth. Although bacterially-mediated mechanisms of alveolar bone destruction have been widely studied, the effects of a polymicrobial infection on the periodontal ligament and microbiome/virome have not been well explored. Therefore, the current investigation introduced a new mouse model of periodontal disease to examine the effects of a polymicrobial infection on periodontal ligament (PDL) properties, changes in bone loss, the host immune response, and the microbiome/virome using shotgun sequencing. Periodontal pathogens, namely Porphyromonas gingivalis, Treponema denticola, Tannerella forsythia, and Fusobacterium nucleatum were used as the polymicrobial oral inoculum in BALB/cByJ mice. The polymicrobial infection triggered significant alveolar bone loss, a heightened antibody response, an elevated cytokine immune response, a significant shift in viral diversity and virome composition, and a widening of the PDL space; the latter two findings have not been previously reported in periodontal disease models. Changes in the PDL space were present at sites far away from the site of insult, indicating that the polymicrobial radius of effect extends beyond the bone loss areas and site of initial infection and wider than previously appreciated. Associations were found between bone loss, specific viral and bacterial species, immune genes, and PDL space changes. These findings may have significant implications for the pathogenesis of periodontal disease and biomechanical properties of the periodontium. This new polymicrobial mouse model of periodontal disease in a common mouse strain is useful for evaluating the features of periodontal disease.

Fatty acid-binding protein 4 downregulation drives calcification in the development of kidney stone disease

Nephrolithiasis is a significant source of morbidity, and its incidence has increased significantly over the last decades. This rise has been attributed to concurrent increasing rates of obesity, associated with a 3-time risk of developing NL. To date, the mechanism by which obesity is linked to stone formation has not been elucidated. We aimed to utilize a transcriptomics approach to discover the missing link between these two epidemic diseases. We investigated gene expression profiling of nephrolithiasis patients by two RNA-sequencing approaches: comparison between renal papilla tissue with and without the presence of calcified Randall's plaques (RP), and comparison between the papilla, medulla, and cortex regions from within a single recurrent stone forming kidney. Results were overlaid between differently expressed genes found in the patient cohort and in the severely lithogenic kidney to identify common genes. Overlay of these two RNA-sequencing datasets demonstrated there is impairment of lipid metabolism in renal papilla tissue containing RP linked to downregulation of fatty acid binding protein (FABP) 4. Immunohistochemistry of human kidney specimens and microarray analysis of renal tissue from a nephrolithiasis mouse model confirmed that FABP4 downregulation is associated with renal stone formation. In a FABP4 knockout mouse model, FABP4 deficiency resulted in development of both renal and urinary crystals. Our study revealed that FABP4 plays an important, previously unrecognized role in kidney stone formation, providing a feasible mechanism to explain the link between nephrolithiasis and metabolic syndrome.

Physicochemical and biochemical spatiotemporal maps of a mouse penis

Spatiotemporal mechanobiology resulting in penile pathologies continues to be investigated using small scale animals models such as mice. However, species-dependent functional biomechanics of a mouse penis, is not known. In this study, spatial mapping of a mechanosensitive transcription factor, scleraxis (Scx), at ages 4, 5, 6 weeks, and 1 year were generated to identify mechanoactive regions within penile tissues. Reconstructed volumes of baculum collected using micro X-ray computed tomography illustrated significantly increased baculum length with decreased porosity, and increased mineral density (p < 0.05) with age. The bony-baculum was held centrally in the Scx positive corpus cavernosum glandis (CCG), indicating mechanoactivity within the struts in a 6 week old mouse. The struts also were stained positive for fibrillar proteins including collagen and elastin, and globular proteins including protein gene product 9.5, and α-smooth muscle actin. The corpus cavernosum penis (CCP) contained significantly (p < 0.05) more collagen than CCG within the same penis, and both regions contained blood vessels with equivalent innervation at any given age. Comparison of volumes of flaccid and erect penile forms revealed functional characteristics of the CCP. Results of this study provided insights into biomechanical function of the CCG; in that, it is a high-pressure chamber that stiffens the penis and is similar to the human corpus cavernosum.

Novel insights into renal mineralization and stone formation through advanced imaging modalities

Purpose/Aim: The most common kidney stone composed of calcium oxalate forms on interstitial calcium phosphate mineral known as a Randall's plaque (RP). Due to limited information about events leading to the initial deposition of nanometer size interstitial calcium phosphate pre-clusters, there continues to be a debate on the initial site of calcium phosphate deposition and factors leading to stone formation.

MATERIALS AND METHODS

High-resolution X-ray micro-computed tomography (CT), and light and electron microscopy techniques were used to characterize human renal pyramids and five representative kidney stones with identifiable stems. Mineral densities of mineralized aggregates within these specimens were correlated with micro- and ultra-structures as seen using light and electron microscopy techniques.

RESULTS

The earliest detectable biominerals in the human renal papilla were proximal intratubular plate-like calcium phosphate deposits. Unoccluded tubules in stems connected to calcium phosphate stones were observed by electron microscope and X-ray micro-CT. These tubules were similar in diameter (30-100 μm) and shape to those observed in the distal regions of the renal papilla.

CONCLUSIONS

Observations were patterned through a novel and unified theory of stepwise-architecture guided biomineralization (a combination of smaller structures leading to a larger but similar structural framework). A plausible stepwise progression in renal biomineralization is proposed; proximal intratubular calcium phosphate deposits can lead to interstitial yet calcium phosphate rich RP and mature into a stem on which a calcium oxalate stone grows within the collecting system of a kidney.

Microanatomical changes and biomolecular expression at the PDL-entheses during experimental tooth movement

The novel aspect of this study was to contextualize the co-localization of biomolecular expression in widened and narrowed periodontal ligament (PDL)-space within a mechanically activated periodontal complex. The PDL is unique as it is the only ligament with both innervation and vascularization. Maxillary molars in 6-week-old male C57BL/6 mice (N = 5) were experimentally translated for 2 weeks using an elastic spacer. Contralateral teeth were used as controls. Mechanical testing of the periodontal complex of a mouse in situ and imaging using X-ray micro-computed tomography (micro-XCT) illustrated deformations within blood vessels (BV) of the PDL. PDL-bone and PDL-cementum entheses at the widened and narrowed PDL-spaces following experimental tooth movement (ETM) illustrated osterix (OSX), bone sialoprotein (BSP), cluster of differentiation 146 (CD146), and protein gene product 9.5 (PGP9.5), indicating active remodeling at these sites. PGP9.5 positive nerve bundles (NBs) were co-localized with multinucleated cells (MCs), Howship's resorption lacunae, and CD146 positive BVs. Association between nerves and MC was complemented by visualizing the proximity of osmium tetroxide stained NBs with the ultrastructure of MCs by performing scanning transmission electron microscopy. Spatial association of NB with BV, and NB with MC, provided insights into the plausible co-activation of NBs to initiate osteoclastic activity. Resorption of mineral occurred as an attempt to restore PDL-space of the load-bearing complex, specifically at the PDL-entheses. Mapping of anatomy-specific structural elements and their association with regenerative molecules by correlating light and electron micrographs provided insights into the use of these extracellular matrix molecules as plausible targets for pharmacological interventions related to tooth movement. Within the realm of tissue regeneration, modulation of load can reverse naturally occurring mineral formation to experimentally induced resorption, and naturally occurring mineral resorption to experimentally induced formation at the enthesial sites to permit tooth translation.

A continuum of mineralization from human renal pyramid to stones on stems

The development of new modalities for kidney stone prevention rests upon understanding the progression of mineralization within the renal pyramid. The progression from small foci of mineralized volumes within the renal pyramid to larger interstitial plaques that ultimately lead into clinically detectable calcium-based stones on calcium phosphate stems will be presented through correlative microscopy approach. High resolution X-ray computed tomography (micro-XCT), electron microscopy, and energy dispersive X-ray (EDX) compositional analyses of interstitial plaques, stems, and attached stones were performed. Increase in mineral density progressed with mineralization severity, with the highest mineral densities detected within mature Randall's plaque and stems to which kidney stones were attached. EDX analyses revealed variable elemental composition within interstitial plaque, stems, and stones. Micro-XCT reconstructions of stones with stems enabled visualization of unoccluded tubules within stems, with average tubule diameters corresponding to thin limbs of Henle, blood vessels, and collecting ducts. Correlative microscopy confirmed that the progression of mineralization leading to calcium-based nephrolithiasis occurs through a continuum involving four anatomically and structurally distinct biomineralization regions: 1) proximal intratubular mineralization within the renal pyramid; 2) interstitial Randall's plaque near the tip of the papilla; 3) emerging plaque (stems); and, 4) the body of heterogeneous stones.

STATEMENT OF SIGNIFICANCE

Nephrolithiasis is a common condition affecting nearly 1 in 11 Americans. The most common type of stone, calcium oxalate is known to form on a calcium phosphate deposit on the renal papilla known as Randall's plaque. Novel imaging techniques have identified distinct regions of biomineralization not just at the tip, but throughout the renal papilla. The classic understanding of Randall's plaque formation is reformulated using correlative imaging techniques. This study establishes a stepwise progression of anatomically-specific biomineralization events including, 1) proximal intratubular mineralization within the renal pyramid; 2) interstitial Randall's plaque near the tip of the papilla; 3) emerging plaque (stems); and, 4) the body of heterogeneous stones, and provides insights into the need for plausible site-specific therapeutic intervention.

A Force on the Crown and Tug of War in the Periodontal Complex

The load-bearing dentoalveolar fibrous joint is composed of biomechanically active periodontal ligament (PDL), bone, cementum, and the synergistic entheses of PDL-bone and PDL-cementum. Physiologic and pathologic loads on the dentoalveolar fibrous joint prompt natural shifts in strain gradients within mineralized and fibrous tissues and trigger a cascade of biochemical events within the widened and narrowed sites of the periodontal complex. This review highlights data from in situ biomechanical simulations that provide tooth movements relative to the alveolar socket. The methods and subsequent results provide a reasonable approximation of strain-regulated biochemical events resulting in mesial mineral formation and distal resorption events within microanatomical regions at the ligament-tethered/enthesial ends. These biochemical events, including expressions of biglycan, decorin, chondroitin sulfated neuroglial 2, osteopontin, and bone sialoprotein and localization of various hypertrophic progenitors, are observed at the alkaline phosphatase-positive widened site, resulting in mineral formation and osteoid/cementoid layers. On the narrowed side, tartrate-resistant acid phosphatase regions can lead to a sequence of clastic activities resulting in resorption pits in bone and cementum. These strain-regulated biochemical and subsequently biomineralization events in the load-bearing periodontal complex are critical for maintenance of the periodontal space and overall macroscale joint biomechanics.

Periodontal ligament entheses and their adaptive role in the context of dentoalveolar joint function

OBJECTIVE

The dynamic bone-periodontal ligament (PDL)-tooth fibrous joint consists of two adaptive functionally graded interfaces (FGI), the PDL-bone and PDL-cementum that respond to mechanical strain transmitted during mastication. In general, from a materials and mechanics perspective, FGI prevent catastrophic failure during prolonged cyclic loading. This review is a discourse of results gathered from literature to illustrate the dynamic adaptive nature of the fibrous joint in response to physiologic and pathologic simulated functions, and experimental tooth movement.

METHODS

Historically, studies have investigated soft to hard tissue transitions through analytical techniques that provided insights into structural, biochemical, and mechanical characterization methods. Experimental approaches included two dimensional to three dimensional advanced in situ imaging and analytical techniques. These techniques allowed mapping and correlation of deformations to physicochemical and mechanobiological changes within volumes of the complex subjected to concentric and eccentric loading regimes respectively.

RESULTS

Tooth movement is facilitated by mechanobiological activity at the interfaces of the fibrous joint and generates elastic discontinuities at these interfaces in response to eccentric loading. Both concentric and eccentric loads mediated cellular responses to strains, and prompted self-regulating mineral forming and resorbing zones that in turn altered the functional space of the joint.

SIGNIFICANCE

A multiscale biomechanics and mechanobiology approach is important for correlating joint function to tissue-level strain-adaptive properties with overall effects on joint form as related to physiologic and pathologic functions. Elucidating the shift in localization of biomolecules specifically at interfaces during development, function, and therapeutic loading of the joint is critical for developing "functional regeneration and adaptation" strategies with an emphasis on restoring physiologic joint function.

Systematic effects from an ambient-temperature, continuously rotating half-wave plate

We present an evaluation of systematic effects associated with a continuously rotating, ambient-temperature half-wave plate (HWP) based on two seasons of data from the Atacama B-Mode Search (ABS) experiment located in the Atacama Desert of Chile. The ABS experiment is a microwave telescope sensitive at 145 GHz. Here we present our in-field evaluation of celestial (Cosmic Microwave Background (CMB) plus galactic foreground) temperature-to-polarization leakage. We decompose the leakage into scalar, dipole, and quadrupole leakage terms. We report a scalar leakage of ∼0.01%, consistent with model expectations and an order of magnitude smaller than other CMB experiments have been reported. No significant dipole or quadrupole terms are detected; we constrain each to be <0.07% (95% confidence), limited by statistical uncertainty in our measurement. Dipole and quadrupole leakage at this level lead to systematic error on r ≲ 0.01 before any mitigation due to scan cross-linking or boresight rotation. The measured scalar leakage and the theoretical level of dipole and quadrupole leakage produce systematic error of r < 0.001 for the ABS survey and focal-plane layout before any data correction such as so-called deprojection. This demonstrates that ABS achieves significant beam systematic error mitigation from its HWP and shows the promise of continuously rotating HWPs for future experiments.

Strain mapping and correlative microscopy of the alveolar bone in a bone-periodontal ligament-tooth fibrous joint

This study details a method to calculate strains within interradicular alveolar bone using digital volume correlation on X-ray tomograms of intact bone-periodontal ligament-tooth fibrous joints. The effects of loading schemes (concentric and eccentric) and optical magnification on the resulting strain in alveolar bone will be investigated with an intent to correlate deformation gradients with data sets from other complementary techniques. Strain maps will be correlated with structural and site-specific mechanical properties obtained on the same specimen using atomic force microscopy and atomic force microscopy-based nanoindentation technique. Specimens include polydimethylsiloxane as a standard material and intact hemi-mandibles harvested from rats. X-ray tomograms were taken at no-load and loaded conditions using an in situ load cell coupled to a micro X-ray computed tomography unit. Digital volume correlation was used to calculate deformations within alveolar bone. Comparison of strain maps was made as a result of different loading schemes (concentric vs eccentric) and at different magnifications (4× vs 10×). Virtual sections and strain maps from digital volume correlation solutions were aligned with structure and reduced elastic modulus to correlate datasets of the same region within a specimen. Strain distribution between concentrically and eccentrically loaded complexes was different but illustrated a similar range. Strain maps of homogeneous materials (polydimethylsiloxane) resulting from digital volume correlation at different magnifications were similar. However, strain maps of heterogeneous materials at lower and higher magnification differed. The digital volume correlation technique illustrated a dependence on optical magnification specifically for heterogeneous materials such as bone. The results at a higher optical magnification highlight the potential for extracting deformation at higher resolutions. Correlation of data spaces from different complementary techniques is plausible and could provide insights into biological and physicochemical processes that lead to functional adaptation of tissues and joints.

The origins of urinary stone disease: upstream mineral formations initiate downstream Randall's plaque

OBJECTIVES

To describe a new hypothesis for the initial events leading to urinary stones. A biomechanical perspective on Randall's plaque formation through form and function relationships is applied to functional units within the kidney, we have termed the 'medullo-papillary complex' - a dynamic relationship between intratubular and interstitial mineral aggregates.

METHODS

A complete MEDLINE search was performed to examine the existing literature on the anatomical and physiological relationships in the renal medulla and papilla. Sectioned human renal medulla with papilla from radical nephrectomy specimens were imaged using a high resolution micro X-ray computed tomography. The location, distribution, and density of mineral aggregates within the medullo-papillary complex were identified.

RESULTS

Mineral aggregates were seen proximally in all specimens within the outer medulla of the medullary complex and were intratubular. Distal interstitial mineralisation at the papillary tip corresponding to Randall's plaque was not seen until a threshold of proximal mineralisation was observed. Mineral density measurements suggest varied chemical compositions between the proximal intratubular (330 mg/cm³ ) and distal interstitial (270 mg/cm³ ) deposits. A review of the literature revealed distinct anatomical compartments and gradients across the medullo-papillary complex that supports the empirical observations that proximal mineralisation triggers distal Randall's plaque formation.

CONCLUSION

The early stone event is initiated by intratubular mineralisation of the renal medullary tissue leading to the interstitial mineralisation that is observed as Randall's plaque. We base this novel hypothesis on a multiscale biomechanics perspective involving form and function relationships, and empirical observations. Additional studies are needed to validate this hypothesis.

A Critical Role of TRPM7 As an Ion Channel Protein in Mediating the Mineralization of the Craniofacial Hard Tissues

Magnesium ion (Mg(2+)) is the fourth most common cation in the human body, and has a crucial role in many physiological functions. Mg(2+) homeostasis is an important contributor to bone development, however, its roles in the development of dental mineralized tissues have not yet been well known. We identified that transient receptor potential cation channel, subfamily M, member 7 (TRPM7), was significantly upregulated in the mature ameloblasts as compared to other ameloblasts through our whole transcript microarray analyses of the ameloblasts. TRPM7, an ion channel for divalent metal cations with an intrinsic serine/threonine protein kinase activity, has been characterized as a key regulator of whole body Mg(2+) homeostasis. Semi-quantitative PCR and immunostaining for TRMP7 confirmed its upregulation during the maturation stage of enamel formation, at which ameloblasts direct rapid mineralization of the enamel matrix. The significantly hypomineralized craniofacial structures, including incisors, molars, and cranial bones were demonstrated by microCT analysis, von Kossa and trichrome staining in Trpm7 (Δkinase∕+) mice. A previously generated heterozygous mouse model with the deletion of the TRPM7 kinase domain. Interestingly, the skeletal phenotype of Trpm7 (Δkinase∕+) mice resembled those found in the tissue-nonspecific alkaline phosphatase (Alpl) KO mice, thus we further examined whether ALPL protein content and alkaline phosphatase (ALPase) activity in ameloblasts, odontoblasts and osteoblasts were affected in those mice. While ALPL protein in Trpm7 (Δkinase∕+) mice remained at the similar level as that in wt mice, ALPase activities in the Trpm7 (Δkinase∕+) mice were almost nonexistent. Supplemented magnesium successfully rescued the activities of ALPase in ameloblasts, odontoblasts and osteoblasts of Trpm7 (Δkinase∕+) mice. These results suggested that TRPM7 is essential for mineralization of enamel as well as dentin and bone by providing sufficient Mg(2+) for the ALPL activity, underlining the key importance of ALPL for biomineralization.

Multiscale biomechanical responses of adapted bone-periodontal ligament-tooth fibrous joints

Reduced functional loads cause adaptations in organs. In this study, temporal adaptations of bone-ligament-tooth fibrous joints to reduced functional loads were mapped using a holistic approach. Systematic studies were performed to evaluate organ-level and tissue-level adaptations in specimens harvested periodically from rats (N=60) given powder food for 6 months over 8,12,16,20, and 24 weeks. Bone-periodontal ligament (PDL)-tooth fibrous joint adaptation was evaluated by comparing changes in joint stiffness with changes in functional space between the tooth and alveolar bony socket. Adaptations in tissues included mapping changes in the PDL and bone architecture as observed from collagen birefringence, bone hardness and volume fraction in rats fed soft foods (soft diet, SD) compared to those fed hard pellets as a routine diet (hard diet, HD). In situ biomechanical testing on harvested fibrous joints revealed increased stiffness in SD groups (SD:239-605 N/mm) (p<0.05) at 8 and 12 weeks. Increased joint stiffness in early development phase was due to decreased functional space (at 8 weeks change in functional space was -33 μm, at 12 weeks change in functional space was -30 μm) and shifts in tissue quality as highlighted by birefringence, architecture and hardness. These physical changes were not observed in joints that were well into function, that is, in rodents older than 12 weeks of age. Significant adaptations in older groups were highlighted by shifts in bone growth (bone volume fraction 24 weeks: Δ-0.06) and bone hardness (8 weeks: Δ-0.04 GPa, 16 weeks: Δ-0.07 GPa, 24 weeks: Δ-0.06 GPa). The response rate (N/s) of joints to mechanical loads decreased in SD groups. Results from the study showed that joint adaptation depended on age. The initial form-related adaptation (observed change in functional space) can challenge strain-adaptive nature of tissues to meet functional demands with increasing age into adulthood. The coupled effect between functional space in the bone-PDL-tooth complex and strain-adaptive nature of tissues is necessary to accommodate functional demands, and is temporally sensitive despite joint malfunction. From an applied science perspective, we propose that adaptations are registered as functional history in tissues and joints.

Distinct decalcification process of dentin by different cariogenic organic acids: Kinetics, ultrastructure and mechanical properties

OBJECTIVES

We studied artificial dentin lesions in human teeth generated by lactate and acetate buffers (pH 5.0), the two most abundant acids in caries. The objective of this study was to determine differences in mechanical properties, mineral density profiles and ultrastructural variations of two different artificial lesions with the same approximate depth.

METHODS

0.05M (pH 5.0) acetate or lactate buffer was used to create 1) 180μm-deep lesions in non-carious human dentin blocks (acetate 130h; lactate 14days); (2) demineralized, ∼180μm-thick non-carious dentin discs (3 weeks). We performed nanoindentation to determine mechanical properties across the hydrated lesions, and micro X-ray computed tomography (MicroXCT) to determine mineral profiles. Ultrastructure in lesions was analyzed by TEM/selected area electron diffraction (SAED). Demineralized dentin discs were analyzed by small angle X-ray scattering (SAXS).

RESULTS

Diffusion-dominated demineralization was shown based on the linearity between lesion depths versus the square root of exposure time in either solution, with faster kinetics in acetate buffer. Nanoindentation revealed lactate induced a significantly sharper transition in reduced elastic modulus across the lesions. MicroXCT showed lactate demineralized lesions had swelling and more disorganized matrix structure, whereas acetate lesions had abrupt X-ray absorption near the margin. At the ultrastructural level, TEM showed lactate was more effective in removing minerals from the collagenous matrix, which was confirmed by SAXS analysis.

CONCLUSIONS

These findings indicated the different acids yielded lesions with different characteristics that could influence lesion formation resulting in their distinct predominance in different caries activities, and these differences may impact strategies for dentin caries remineralization.

Differentiating zones at periodontal ligament-bone and periodontal ligament-cementum entheses

BACKGROUND AND OBJECTIVE

The structural and functional integrity of bone-periodontal ligament (PDL)-cementum complex stems from the load-bearing attachment sites (entheses) between soft (PDL) and hard (bone, cementum) tissues. These attachment sites are responsible for the maintenance of a bone-PDL-cementum complex biomechanical function. The objective was to investigate changes in spatiotemporal expression of key biomolecules in developing and functionally active entheses.

MATERIAL AND METHODS

Multilabeling technique was performed on hemimandibles of 3 wk and 3 mo-old scleraxis-GFP transgenic mice for CD146, CD31, NG2, osterix and bone sialoprotein. Regions of dominant stretch within the PDL were evaluated by identifying directionality of collagen fibrils, PDL fibroblasts and PDL cell cytoskeleton.

RESULTS

CD146+ cells adjacent to CD31+ vasculature were identified at PDL-bone enthesis. NG2+ cells were located at coronal bone-PDL and apical cementum-PDL entheses in the 3-wk-old group, but at 3 mo, NG2 was positive at the entheses of the apical region and alveolar crest. NG2 and osterix were colocalized at the osteoid and cementoid regions of the PDL-bone and PDL-cementum entheses. Bone sialoprotein was prominent at the apical region of 3-wk-old mice. The directionality of collagen fibers, fibroblasts and their cytoskeleton overlapped, except in the apical region of 3 wk.

CONCLUSION

Colocalization of biomolecules at zones of the PDL adjacent to attachment sites may be essential for the formation of precementum and osteoid interfaces at a load-bearing bone-PDL-tooth fibrous joint. Biophysical cues resulting from development and function can regulate recruitment and differentiation of stem cells potentially from a vascular origin toward osteo- and cemento-blastic lineages at the PDL-bone and PDL-cementum entheses. Investigating the coupled effect of biophysical and biochemical stimuli leading to cell differentiation at the functional attachment sites is critical for developing regeneration strategies to enable functional reconstruction of the periodontal complex.

Mineral density volume gradients in normal and diseased human tissues

Clinical computed tomography provides a single mineral density (MD) value for heterogeneous calcified tissues containing early and late stage pathologic formations. The novel aspect of this study is that, it extends current quantitative methods of mapping mineral density gradients to three dimensions, discretizes early and late mineralized stages, identifies elemental distribution in discretized volumes, and correlates measured MD with respective calcium (Ca) to phosphorus (P) and Ca to zinc (Zn) elemental ratios. To accomplish this, MD variations identified using polychromatic radiation from a high resolution micro-computed tomography (micro-CT) benchtop unit were correlated with elemental mapping obtained from a microprobe X-ray fluorescence (XRF) using synchrotron monochromatic radiation. Digital segmentation of tomograms from normal and diseased tissues (N=5 per group; 40-60 year old males) contained significant mineral density variations (enamel: 2820-3095mg/cc, bone: 570-1415mg/cc, cementum: 1240-1340mg/cc, dentin: 1480-1590mg/cc, cementum affected by periodontitis: 1100-1220mg/cc, hypomineralized carious dentin: 345-1450mg/cc, hypermineralized carious dentin: 1815-2740mg/cc, and dental calculus: 1290-1770mg/cc). A plausible linear correlation between segmented MD volumes and elemental ratios within these volumes was established, and Ca/P ratios for dentin (1.49), hypomineralized dentin (0.32-0.46), cementum (1.51), and bone (1.68) were observed. Furthermore, varying Ca/Zn ratios were distinguished in adapted compared to normal tissues, such as in bone (855-2765) and in cementum (595-990), highlighting Zn as an influential element in prompting observed adaptive properties. Hence, results provide insights on mineral density gradients with elemental concentrations and elemental footprints that in turn could aid in elucidating mechanistic processes for pathologic formations.

The narwhal (Monodon monoceros) cementum-dentin junction: a functionally graded biointerphase

In nature, an interface between dissimilar tissues is often bridged by a graded zone, and provides functional properties at a whole organ level. A perfect example is a "biological interphase" between stratified cementum and dentin of a narwhal tooth. This study highlights the graded structural, mechanical, and chemical natural characteristics of a biological interphase known as the cementum-dentin junction layer and their effect in resisting mechanical loads. From a structural perspective, light and electron microscopy techniques illustrated the layer as a wide 1000-2000 μm graded zone consisting of higher density continuous collagen fiber bundles from the surface of cementum to dentin, that parallels hygroscopic 50-100 μm wide collagenous region in human teeth. The role of collagen fibers was evident under compression testing during which the layer deformed more compared to cementum and dentin. This behavior is reflected through site-specific nanoindentation indicating a lower elastic modulus of 2.2 ± 0.5 GPa for collagen fiber bundle compared to 3 ± 0.4 GPa for mineralized regions in the layer. Similarly, microindentation technique illustrated lower hardness values of 0.36 ± 0.05 GPa, 0.33 ± 0.03 GPa, and 0.3 ± 0.07 GPa for cementum, dentin, and cementum-dentin layer, respectively. Biochemical analyses including Raman spectroscopy and synchrotron-source microprobe X-ray fluorescence demonstrated a graded composition across the interface, including a decrease in mineral-to-matrix and phosphate-to-carbonate ratios, as well as the presence of tidemark-like bands with Zn. Understanding the structure-function relationships of wider tissue interfaces can provide insights into natural tissue and organ function.

Essential role of osterix for tooth root but not crown dentin formation

Tooth is made of crown and root. It is widely believed that dentin formation in crown and root uses the same regulatory mechanism. However, identification of nuclear factor 1 C (NFIC)'s unique function in determining root but not crown dentin formation challenges the old thinking. In searching for the target molecules downstream of NFIC, we unexpectedly found a sharp reduction of osterix (OSX), the key transcription factor in skeleton formation, in the Nfic knockout (Nfic-KO) tooth root. We then demonstrated a dose-dependent increase of Osx in the odontoblast cell line due to a transient transfection of Nfic expression plasmid. Studies of global and conditional Osx-KO mice revealed no apparent changes in the crown dentin tubules and dentin matrix. However, the OSX conditional KO (cKO) mice (crossed to the 2.3-kb collagen type 1 [Col1]-Cre) displayed an increase in cell proliferation but great decreases in expressions of root dentin matrix proteins (dentin matrix protein 1 [DMP1] and dentin sialophosphoprotein [DSPP]), leading to an inhibition in odontoblast differentiation, and short, thin root dentin with few dentin tubules. Compared to the Nfic-KO tooth, which contains essentially no dentin tubules and remains in a "root-less" status at adult stages, the Osx-cKO root phenotype had partially improved at the late stage, indicating that other factors can compensate for OSX function. Thus, we conclude that OSX, one of the key downstream molecules of NFIC, plays a critical role in root, but not crown, formation.

Removal of SOST or blocking its product sclerostin rescues defects in the periodontitis mouse model

Understanding periodontal ligament (PDL) biology and developing an effective treatment for bone and PDL damage due to periodontitis have been long-standing aims in dental medicine. Here, we first demonstrated by cell lineage tracing and mineral double-labeling approaches that murine PDL progenitor cells display a 2- and 3-fold higher mineral deposition rate than the periosteum and endosteum at the age of 4 weeks, respectively. We next proved that the pathologic changes in osteocytes (Ocys; changes from a spindle shape to round shape with a >50% reduction in the dendrite number/length, and an increase in SOST) are the key pathologic factors responsible for bone and PDL damage in periostin-null mice (a periodontitis animal model) using a newly developed 3-dimensional FITC-Imaris technique. Importantly, we proved that deleting the Sost gene (a potent inhibitor of WNT signaling) or blocking sclerostin function by using the mAb in this periodontitis model significantly restores bone and PDL defects (n = 4-5; P < 0.05). Together, identification of the key contribution of the PDL in normal alveolar bone formation, the pathologic changes of the Ocys in periodontitis bone loss, and the novel link between sclerostin and Wnt signaling in the PDL will aid future drug development in the treatment of patients with periodontitis.

Adaptive properties of human cementum and cementum dentin junction with age

OBJECTIVES

The objective of this study was to evaluate age related changes in physical (structure/mechanical properties) and chemical (elemental/inorganic mineral content) properties of cementum layers interfacing dentin.

METHODS

Human mandibular molars (N=43) were collected and sorted by age (younger=19-39, middle=40-60, older=61-81 years). The structures of primary and secondary cementum (PC, SC) types were evaluated using light and atomic force microscopy (AFM) techniques. Chemical composition of cementum layers were characterized through gravimetric analysis by estimating ash weight and concentrations of Ca, Mn, and Zn trace elements in the analytes through inductively coupled plasma mass spectroscopy. The hardness of PC and SC was determined using microindentation and site-specific reduced elastic modulus properties were determined using nanoindentation techniques.

RESULTS

PC contained fibrous 1-3 µm wide hygroscopic radial PDL-inserts. SC illustrated PC-like structure adjacent to a multilayered architecture composing of regions that contained mineral dominant lamellae. The width of the cementum dentin junction (CDJ) decreased as measured from the cementum enamel junction (CEJ) to the tooth apex (49-21 µm), and significantly decreased with age (44-23 µm; p<0.05). The inorganic ratio defined as the ratio of post-burn to pre-burn weight increased with age within primary cementum (PC) and secondary cementum (SC). Cementum showed an increase in hardness with age (PC (0.40-0.46 GPa), SC (0.37-0.43 GPa)), while dentin showed a decreasing trend (coronal dentin (0.70-0.72 GPa); apical dentin (0.63-0.73 GPa)).

SIGNIFICANCE

The observed physicochemical changes are indicative of increased mineralization of cementum and CDJ over time. Changes in tissue properties of teeth can alter overall tooth biomechanics and in turn the entire bone-tooth complex including the periodontal ligament. This study provides baseline information about the changes in physicochemical properties of cementum with age, which can be identified as adaptive in nature.

In situ compressive loading and correlative noninvasive imaging of the bone-periodontal ligament-tooth fibrous joint

This study demonstrates a novel biomechanics testing protocol. The advantage of this protocol includes the use of an in situ loading device coupled to a high resolution X-ray microscope, thus enabling visualization of internal structural elements under simulated physiological loads and wet conditions. Experimental specimens will include intact bone-periodontal ligament (PDL)-tooth fibrous joints. Results will illustrate three important features of the protocol as they can be applied to organ level biomechanics: 1) reactionary force vs. displacement: tooth displacement within the alveolar socket and its reactionary response to loading, 2) three-dimensional (3D) spatial configuration and morphometrics: geometric relationship of the tooth with the alveolar socket, and 3) changes in readouts 1 and 2 due to a change in loading axis, i.e. from concentric to eccentric loads. Efficacy of the proposed protocol will be evaluated by coupling mechanical testing readouts to 3D morphometrics and overall biomechanics of the joint. In addition, this technique will emphasize on the need to equilibrate experimental conditions, specifically reactionary loads prior to acquiring tomograms of fibrous joints. It should be noted that the proposed protocol is limited to testing specimens under ex vivo conditions, and that use of contrast agents to visualize soft tissue mechanical response could lead to erroneous conclusions about tissue and organ-level biomechanics.

The plastic nature of the human bone-periodontal ligament-tooth fibrous joint

This study investigates bony protrusions within a narrowed periodontal ligament space (PDL-space) of a human bone-PDL-tooth fibrous joint by mapping structural, biochemical, and mechanical heterogeneity. Higher resolution structural characterization was achieved via complementary atomic force microscopy (AFM), nano-transmission X-ray microscopy (nano-TXM), and microtomography (MicroXCT™). Structural heterogeneity was correlated to biochemical and elemental composition, illustrated via histochemistry and microprobe X-ray fluorescence analysis (μ-XRF), and mechanical heterogeneity evaluated by AFM-based nanoindentation. Results demonstrated that the narrowed PDL-space was due to invasion of bundle bone (BB) into PDL-space. Protruded BB had a wider range with higher elastic modulus values (2-8GPa) compared to lamellar bone (0.8-6GPa), and increased quantities of Ca, P and Zn as revealed by μ-XRF. Interestingly, the hygroscopic 10-30μm interface between protruded BB and lamellar bone exhibited higher X-ray attenuation similar to cement lines and lamellae within bone. Localization of the small leucine rich proteoglycan biglycan (BGN) responsible for mineralization was observed at the PDL-bone interface and around the osteocyte lacunae. Based on these results, it can be argued that the LB-BB interface was the original site of PDL attachment, and that the genesis of protruded BB identified as protrusions occurred as a result of shift in strain. We emphasize the importance of bony protrusions within the context of organ function and that additional study is warranted.

Matrix metalloproteinase-13 is required for osteocytic perilacunar remodeling and maintains bone fracture resistance

Like bone mass, bone quality is specified in development, actively maintained postnatally, and disrupted by disease. The roles of osteoblasts, osteoclasts, and osteocytes in the regulation of bone mass are increasingly well defined. However, the cellular and molecular mechanisms by which bone quality is regulated remain unclear. Proteins that remodel bone extracellular matrix, such as the collagen-degrading matrix metalloproteinase (MMP)-13, are likely candidates to regulate bone quality. Using MMP-13-deficient mice, we examined the role of MMP-13 in the remodeling and maintenance of bone matrix and subsequent fracture resistance. Throughout the diaphysis of MMP-13-deficient tibiae, we observed elevated nonenzymatic cross-linking and concentric regions of hypermineralization, collagen disorganization, and canalicular malformation. These defects localize to the same mid-cortical bone regions where osteocyte lacunae and canaliculi exhibit MMP-13 and tartrate-resistant acid phosphatase (TRAP) expression, as well as the osteocyte marker sclerostin. Despite otherwise normal measures of osteoclast and osteoblast function, dynamic histomorphometry revealed that remodeling of osteocyte lacunae is impaired in MMP-13(-/-) bone. Analysis of MMP-13(-/-) mice and their wild-type littermates in normal and lactating conditions showed that MMP-13 is not only required for lactation-induced osteocyte perilacunar remodeling, but also for the maintenance of bone quality. The loss of MMP-13, and the resulting defects in perilacunar remodeling and matrix organization, compromise MMP-13(-/-) bone fracture toughness and postyield behavior. Taken together, these findings demonstrate that osteocyte perilacunar remodeling of mid-cortical bone matrix requires MMP-13 and is essential for the maintenance of bone quality.

Functional remineralization of dentin lesions using polymer-induced liquid-precursor process

It was hypothesized that applying the polymer-induced liquid-precursor (PILP) system to artificial lesions would result in time-dependent functional remineralization of carious dentin lesions that restores the mechanical properties of demineralized dentin matrix. 140 µm deep artificial caries lesions were remineralized via the PILP process for 7–28 days at 37°C to determine temporal remineralization characteristics. Poly-L-aspartic acid (27 KDa) was used as the polymeric process-directing agent and was added to the remineralization solution at a calcium-to-phosphate ratio of 2.14 (mol/mol). Nanomechanical properties of hydrated artificial lesions had a low reduced elastic modulus (E_R = 0.2 GPa) region extending about 70 μm into the lesion, with a sloped region to about 140 μm where values reached normal dentin (18–20 GPa). After 7 days specimens recovered mechanical properties in the sloped region by 51% compared to the artificial lesion. Between 7–14 days, recovery of the outer portion of the lesion continued to a level of about 10 GPa with 74% improvement. 28 days of PILP mineralization resulted in 91% improvement of E_R compared to the artificial lesion. These differences were statistically significant as determined from change-point diagrams. Mineral profiles determined by micro x-ray computed tomography were shallower than those determined by nanoindentation, and showed similar changes over time, but full mineral recovery occurred after 14 days in both the outer and sloped portions of the lesion. Scanning electron microscopy and energy dispersive x-ray analysis showed similar morphologies that were distinct from normal dentin with a clear line of demarcation between the outer and sloped portions of the lesion. Transmission electron microscopy and selected area electron diffraction showed that the starting lesions contained some residual mineral in the outer portions, which exhibited poor crystallinity. During remineralization, intrafibrillar mineral increased and crystallinity improved with intrafibrillar mineral exhibiting the orientation found in normal dentin or bone.

Multiple effects of the cellular prion protein on tooth development

The role of the prion protein (PrP) in transmissible spongiform encephalopathies has been the focus of intense investigation. However, less is known about the physiological function of normal cellular PrP (PrP(C)). In adult human teeth, PrP(C) has been identified in odontoblasts, cementoblasts and epithelial remnants of Malassez. In this study, we have localized PrP(C) in developing human and mouse teeth, and investigated the function of PrP using a PrP-knockout (Prnp(0/0) ) mouse model. PrP(C) was detected in developing human and mouse ameloblasts and odontoblasts. In vitro, undifferentiated dental mesenchymal cells from embryonic day 18 (E18) Prnp(0/0) mouse molars proliferated much more rapidly compared to age-matched, wild-type (wt) mouse molar dental mesenchymal cells. Histochemistry and immunohistochemical analyses showed a subtle but measurable phenotype, with the absence of PrP resulting in earlier initiation of both dentin and enamel formation. Consistent with this finding, laser microdissected odontoblasts from newborn Prnp(0/0) mouse incisors had a reduced proliferation rate, as measured by the expression of proliferating cell nuclear antigen (PCNA), and increased type 1 collagen mRNA expression. Dentin microhardness of the fully erupted molars was reduced and incisal enamel mineralization was delayed in Prnp(0/0) compared to age-matched wt mouse teeth. Taken together, these results suggest that PrP(C) affects multiple processes involved in tooth formation, through regulating the differentiation of ameloblasts and odontoblasts.

Presacral teratocarcinoma presenting as anal fistula and rectal adenocarcinoma: a unique case presentation and literature review

Somatic malignancy arising from presacral or retroperitoneal primary teratoma is extremely rare. We report the case of a 37-year-old male patient with adenocarcinoma of respiratory type arising from primary presacral teratoma, but which first presented as anal fistula and rectal adenocarcinoma. The two tumors show the same morphology and immunophenotype (CK7–CK20+CDx2+). Malignant adenocarcinoma transformations from the normal respiratory epithelium are also found. To the best of our knowledge, this is the second case of respiratory type adenocarcinoma arising from primary presacral mature cystic teratoma.

Age-related adaptation of bone-PDL-tooth complex: Rattus-Norvegicus as a model system

Functional loads on an organ induce tissue adaptations by converting mechanical energy into chemical energy at a cell-level. The transducing capacity of cells alters physico-chemical properties of tissues, developing a positive feedback commonly recognized as the form-function relationship. In this study, organ and tissue adaptations were mapped in the bone-tooth complex by identifying and correlating biomolecular expressions to physico-chemical properties in rats from 1.5 to 15 months. However, future research using hard and soft chow over relevant age groups would decouple the function related effects from aging affects. Progressive curvature in the distal root with increased root resorption was observed using micro X-ray computed tomography. Resorption was correlated to the increased activity of multinucleated osteoclasts on the distal side of the molars until 6 months using tartrate resistant acid phosphatase (TRAP). Interestingly, mononucleated TRAP positive cells within PDL vasculature were observed in older rats. Higher levels of glycosaminoglycans were identified at PDL-bone and PDL-cementum entheses using alcian blue stain. Decreasing biochemical gradients from coronal to apical zones, specifically biomolecules that can induce osteogenic (biglycan) and fibrogenic (fibromodulin, decorin) phenotypes, and PDL-specific negative regulator of mineralization (asporin) were observed using immunohistochemistry. Heterogeneous distribution of Ca and P in alveolar bone, and relatively lower contents at the entheses, were observed using energy dispersive X-ray analysis. No correlation between age and microhardness of alveolar bone (0.7 ± 0.1 to 0.9 ± 0.2 GPa) and cementum (0.6 ± 0.1 to 0.8 ± 0.3 GPa) was observed using a microindenter. However, hardness of cementum and alveolar bone at any given age were significantly different (P<0.05). These observations should be taken into account as baseline parameters, during development (1.5 to 4 months), growth (4 to 10 months), followed by a senescent phase (10 to 15 months), from which deviations due to experimentally induced perturbations can be effectively investigated.

Reduced functional loads alter the physical characteristics of the bone-periodontal ligament-cementum complex

BACKGROUND AND OBJECTIVE

Adaptive properties of the bone-periodontal ligament-tooth complex have been identified by changing the magnitude of functional loads using small-scale animal models, such as rodents. Reported adaptive responses as a result of lower loads due to softer diet include decreased muscle development, change in structure-function relationship of the cranium, narrowed periodontal ligament space, and changes in the mineral level of the cortical bone and alveolar jaw bone and in the glycosaminoglycans of the alveolar bone. However, the adaptive role of the dynamic bone-periodontal ligament-cementum complex to prolonged reduced loads has not been fully explained to date, especially with regard to concurrent adaptations of bone, periodontal ligament and cementum. Therefore, in the present study, using a rat model, the temporal effect of reduced functional loads on physical characteristics, such as morphology and mechanical properties and the mineral profiles of the bone-periodontal ligament-cementum complex was investigated.

MATERIAL AND METHODS

Two groups of 6-wk-old male Sprague-Dawley rats were fed nutritionally identical food with a stiffness range of 127-158 N/mm for hard pellet or 0.3-0.5 N/mm for soft powder forms. Spatio-temporal adaptation of the bone-periodontal ligament-cementum complex was identified by mapping changes in the following: (i) periodontal ligament collagen orientation and birefringence using polarized light microscopy, bone and cementum adaptation using histochemistry, and bone and cementum morphology using micro-X-ray computed tomography; (ii) mineral profiles of the periodontal ligament-cementum and periodontal ligament-bone interfaces by X-ray attenuation; and (iii) microhardness of bone and cementum by microindentation of specimens at ages 6, 8, 12 and 15 wk.

RESULTS

Reduced functional loads over prolonged time resulted in the following adaptations: (i) altered periodontal ligament orientation and decreased periodontal ligament collagen birefringence, indicating decreased periodontal ligament turnover rate and decreased apical cementum resorption; (ii) a gradual increase in X-ray attenuation, owing to mineral differences, at the periodontal ligament-bone and periodontal ligament-cementum interfaces, without significant differences in the gradients for either group; (iii) significantly (p < 0.05) lower microhardness of alveolar bone (0.93 ± 0.16 GPa) and secondary cementum (0.803 ± 0.13 GPa) compared with the higher load group insert bone = (1.10 ± 0.17 and cementum = 0.940 ± 0.15 GPa, respectively) at 15 wk, indicating a temporal effect of loads on the local mineralization of bone and cementum.

CONCLUSION

Based on the results from this study, the effect of reduced functional loads for a prolonged time could differentially affect morphology, mechanical properties and mineral variations of the local load-bearing sites in the bone-periodontal ligament-cementum complex. These observed local changes in turn could help to explain the overall biomechanical function and adaptations of the tooth-bone joint. From a clinical translation perspective, our study provides an insight into modulation of load on the complex for improved tooth function during periodontal disease and/or orthodontic and prosthodontic treatments.

Discontinuities in the human bone-PDL-cementum complex

A naturally graded interface due to functional demands can deviate toward a discontinuous interface, eventually decreasing the functional efficiency of a dynamic joint. It is this characteristic feature in a human bone-tooth fibrous joint bone-PDL-tooth complex that will be discussed through histochemistry, and site-specific high resolution microscopy, micro tomography(Micro XCT™), X-ray fluorescence imaging and wet nanoindentation techniques. Results demonstrated two causes for the occurrence of 5-50 μm narrowed PDL-space: 1) microscopic scalloped regions at the PDL-insertion sites and macro-scale stratified layers of bone with rich basophilic lines, and 2) macroscopic bony protrusions. Narrowed PDL-complexes illustrated patchy appearance of asporin, and when imaged under wet conditions using an atomic force microscope (AFM), demonstrated structural reorganization of the PDL, collagen periodicity, organic-dominant areas at the PDL-cementum and PDL-bone entheses and within cementum and bone. Scanning electron microscopy (SEM) results confirmed AFM results. Despite the narrowed PDL, continuity between PDL and vasculature in endosteal spaces of bone was demonstrated using a Micro XCT™. The higher levels of Ca and P X-ray fluorescence using a microprobe were correlated with higher elastic modulus values of 0.1-1.4 and 0.1-1.2 GPa for PDL-bone and PDL-cementum using wet nanoindentation. The ranges in elastic modulus values for PDL-bone and PDL-cementum entheses in 150-380 μm wide PDL-complex were 0.1-1.0 and 0.1-0.6 GPa. Based on these results we propose that strain amplification at the entheses could be minimized with a gradual change in modulus profile, a characteristic of 150-380 μm wide functional PDL-space. However, a discontinuity in modulus profile, a characteristic of 5-50 μm wide narrowed PDL-space would cause compromised mechanotransduction. The constrictions or narrowed sites within the bone-tooth fibrous joint will become the new "load bearing sites" that eventually could cause direct local fusion of bone with cementum.

The biomechanical characteristics of the bone-periodontal ligament-cementum complex

The relative motion between the tooth and alveolar bone is facilitated by the soft-hard tissue interfaces which include periodontal ligament-bone (PDL-bone) and periodontal ligament-cementum (PDL-cementum). The soft-hard tissue interfaces are responsible for attachment and are critical to the overall biomechanical efficiency of the bone-tooth complex. In this study, the PDL-bone and PDL-cementum attachment sites in human molars were investigated to identify the structural orientation and integration of the PDL with bone and cementum. These attachment sites were characterized from a combined materials and mechanics perspective and were related to macro-scale function. High resolution complimentary imaging techniques including atomic force microscopy, scanning electron microscopy and micro-scale X-ray computed tomography (Micro XCT) illustrated two distinct orientations of PDL; circumferential-PDL (cir-PDL) and radial-PDL (rad-PDL). Within the PDL-space, the primary orientation of the ligament was radial (rad-PDL) as is well known. Interestingly, circumferential orientation of PDL continuous with rad-PDL was observed adjacent to alveolar bone and cementum. The integration of the cir-PDL was identified by 1-2 microm diameter PDL-inserts or Sharpey's fibers in alveolar bone and cementum. Chemically and biochemically the cir-PDL adjacent to bone and cementum was identified by relatively higher carbon and lower calcium including the localization of small leucine rich proteins responsible for maintaining soft-hard tissue cohesion, stiffness and hygroscopic nature of PDL-bone and PDL-cementum attachment sites. The combined structural and chemical properties provided graded stiffness characteristics of PDL-bone (E(r) range for PDL: 10-50 MPa; bone: 0.2-9.6 GPa) and PDL-cementum (E(r) range for cementum: 1.1-8.3 GPa), which was related to the macro-scale function of the bone-tooth complex.