Influence of cortical canal architecture on lacunocanalicular pore pressure and fluid flow

A narrative review of the effects of vitamin D3 on orthodontic tooth movement: Focus on molecular and cellular mechanisms

Orthodontic tooth movement (OTM) is a critical process in dental alignment, driven by the application of calibrated orthodontic forces. This study delves into the intricate molecular and cellular mechanisms by which vitamin D3 influences OTM. Vitamin D3 is identified as a critical regulator in bone metabolism, enhancing osteoblast activity and bone formation while also modulating osteoclast quantity and RANKL expression, essential for the remodeling of the alveolar bone. The precise mechanisms through which vitamin D3 facilitates these processes are explored, highlighting its potential in accelerating bone remodeling and, consequently, tooth alignment. This comprehensive review underscores vitamin D3's anabolic impact on bone metabolism and its pivotal role in the synthesis and mineralization processes governed by osteoblasts. The findings illuminate vitamin D3's promise in augmenting orthodontic therapy, suggesting its utility in improving treatment efficiency and reducing duration. However, the need for further research into the optimal application of vitamin D3 in orthodontics is emphasized, particularly concerning dosage, timing, and delivery methods.

Mechanobiology of orthodontic tooth movement: An update

The purpose of this review is to provide an update on the changes at the cellular and tissue level occurring during orthodontic force application. For the understanding of this process, knowledge of the mechanobiology of the periodontal ligament and the alveolar bone are essential. The periodontal ligament and alveolar bone make up a functional unit that undergoes robust changes during orthodontic tooth movement. Complex molecular signaling is responsible for converting mechanical stresses into biochemical events with a net result of bone apposition and/or bone resorption. Despite an improved understanding of mechanical and biochemical signaling mechanisms, it is largely unknown how mechanical stresses regulate the differentiation of stem/progenitor cells into osteoblast and osteoclast lineages. To advance orthodontics, it is crucial to gain a better understanding of osteoblast differentiation from mesenchymal stem/progenitor cells and osteoclastogenesis from the hematopoietic/monocyte lineage.

Functional Biomaterials for Local Control of Orthodontic Tooth Movement

Orthodontic tooth movement (OTM) occurs with the application of a controlled mechanical force and results in coordinated tissue resorption and formation in the surrounding bone and periodontal ligament. The turnover processes of the periodontal and bone tissue are associated with specific signaling factors, such as Receptor Activator of Nuclear factor Kappa-β Ligand (RANKL), osteoprotegerin, runt-related transcription factor 2 (RUNX2), etc., which can be regulated by different biomaterials, promoting or inhibiting bone remodeling during OTM. Different bone substitutes or bone regeneration materials have also been applied to repair alveolar bone defects followed by orthodontic treatment. Those bioengineered bone graft materials also change the local environment that may or may not affect OTM. This article aims to review functional biomaterials that were applied locally to accelerate OTM for a shorter duration of orthodontic treatment or impede OTM for retention purposes, as well as various alveolar bone graft materials which may affect OTM. This review article summarizes various types of biomaterials that can be locally applied to affect the process of OTM, along with their potential mechanisms of action and side effects. The functionalization of biomaterials can improve the solubility or intake of biomolecules, leading to better outcomes in terms of increasing or decreasing the speed of OTM. The ideal timing for initiating OTM is generally considered to be 8 weeks post-grafting. However, more evidence is needed from human studies to fully understand the effects of these biomaterials, including any potential adverse effects.

Computation of physiological loading induced interstitial fluid motion in muscle standardized femur: Healthy vs. osteoporotic bone

BACKGROUND AND OBJECTIVES

Physiological loading-induced mechanical environments regulate bone modeling and remodeling. Thus, loading-induced normal strain is typically considered a stimulus to osteogenesis. However, several studies noticed new bone formation near the sites of minimal normal strain, e.g., the neutral axis of bending in long bones, which raises a question on how bone mass is maintained near these sites. Secondary mechanical components such as shear strain and interstitial fluid flow also stimulate bone cells and regulate bone mass. However, the osteogenic potential of these components is not well established. Accordingly, the present study estimates the distribution of physiological muscle loading-induced mechanical environments such as normal strain, shear strain, pore pressure, and interstitial fluid flow in long bones.

METHODS

A poroelastic finite element muscle standardized femur (MuscleSF) model is developed to compute the distribution of the mechanical environment as a function of bone porosities associated with osteoporotic and disuse bone loss.

RESULTS

The results indicate the presence of higher shear strain and interstitial fluid motion near the minimal strain sites, i.e., the neutral axis of bending of femoral cross-sections. This suggests that secondary stimuli may maintain the bone mass at these locations. Pore pressure and interstitial fluid motion reduce with the increased porosity associated with bone disorders, possibly resulting in diminished skeletal mechano-sensitivity to exogenous loading.

CONCLUSIONS

These outcomes present a better understanding of mechanical environment-mediated regulation of site-specific bone mass, which can be beneficial in developing prophylactic exercise to prevent bone loss in osteoporosis and muscle disuse.

Computational modeling for osteogenic potential assessment of physical exercises based on loading-induced mechanobiological environments in cortical bone remodeling

Osteoporosis and disuse can cause bone loss which reduces the weight-bearing strength of long bones. Physical exercise or mechanical loading prevents bone loss as it promotes bone modeling through osteogenesis, i.e., new bone formation. Several studies have observed distinct bone remodeling responses to physical exercises; nevertheless, the underlying mechanism behind such responses is not well established. Loading-induced pore-pressure and fluid motion act as mechanobiological stimuli to bone cells namely osteocytes which further initiate osteoactivities. The shape of loading waveforms also affects the poromechanical environment of bone. Accordingly, the present study hypothesizes that loading waveforms associated with physiological exercises may expose the bone to different mechanobiological stimuli resulting in distinct bone remodeling. A poromechanical finite element model is developed to compute pore-pressure and interstitial fluid velocity in femoral cortical bone tissue (healthy and osteoporotic) subjected to loading waveforms of three physiological exercises namely walking, running, and jumping. The model also computes the mechanobiological stimulus as a function of fluid velocity. The outcomes indicate that pore-pressure and fluid velocity decrease significantly in osteoporotic bone tissue in comparison with healthy tissue. Jumping and running both improve pore-pressure and fluid velocity in healthy and osteoporotic tissues, whereas running significantly enhances mechanobiological stimulus in both the tissues which indicates a possible explanation for distinct bone remodeling to different physical exercises. The present work also suggests that running may be recommended as a potential biomechanical therapeutic to prevent bone loss. Overall, the present work contributes to the area of orthopedic research to develop effective designs of prophylactic exercises to improve bone health.

Bone permeability and mechanotransduction: Some current insights into the function of the lacunar-canalicular network

Lacunar-canalicular (LC) permeability involves the passage of fluids, nutrients, oxygen, ions, and signalling molecules through bone tissue, facilitating the maintenance of bone vitality and function and responses to various physiological conditions and diseases. LC permeability and fluid flow-shear stress/drag force play important roles in mechanotransduction in bone tissue by inducing mechanical stimuli in osteocytes, modulating cellular functions, and determining bone adaptation. Alterations in LC structure may therefore influence the fluid flow pattern through the LC network, thereby affecting the ability of osteocytes to sense and translate mechanical signals and possibly contributing to bone remodelling. Several bone-health conditions are associated with changes in LC structure and function and may affect mechanotransduction and responses, although the mechanisms underlying these associations are still not fully understood. In this review, recent studies of LC networks, their formation and transfer mechanical stimuli, and changes in structure, functional permeability, and mechanotransduction that result from age, pathology, and mechanical loading are discussed. Additionally, applications of vibration and low-intensity pulsed ultrasound in bone healthcare and regeneration fields are also presented.

Role of nitric oxide in orthodontic tooth movement (Review)

Nitric oxide (NO) is an ubiquitous signaling molecule that mediates numerous cellular processes associated with cardiovascular, nervous and immune systems. NO also plays an essential role in bone homeostasis regulation. The present review article summarized the effects of NO on bone metabolism during orthodontic tooth movement in order to provide insight into the regulatory role of NO in orthodontic tooth movement. Orthodontic tooth movement is a process in which the periodontal tissue and alveolar bone are reconstructed due to the effect of orthodontic forces. Accumulating evidence has indicated that NO and its downstream signaling molecule, cyclic guanosine monophosphate (cGMP), mediate the mechanical signals during orthodontic-related bone remodeling, and exert complex effects on osteogenesis and osteoclastogenesis. NO has a regulatory effect on the cellular activities and functional states of osteoclasts, osteocytes and periodontal ligament fibroblasts involved in orthodontic tooth movement. Variations of NO synthase (NOS) expression levels and NO production in periodontal tissues or gingival crevicular fluid (GCF) have been found on the tension and compression sides during tooth movement in both orthodontic animal models and patients. Furthermore, NO precursor and NOS inhibitor administration increased and reduced the tooth movement in animal models, respectively. Further research is required in order to further elucidate the underlying mechanisms and the clinical application prospect of NO in orthodontic tooth movement.

Interstitial fluid velocity is decreased around cortical bone vascular pores and depends on osteocyte position in a rat model of disuse osteoporosis

Muscle paralysis induced with botulinum toxin (Botox) injection increases vascular porosity and reduces osteocyte lacunar density in the tibial cortical bone of skeletally mature rats. These morphological changes potentially affect interstitial fluid flow in the lacunar-canalicular porosity, which is thought to play a role in osteocyte mechanotransduction. The aim of this study was to investigate the effects of disuse-induced morphological changes on interstitial fluid velocity around osteocytes in the bone cortex. Micro-CT images from a previous study that quantified the effects of Botox-induced muscle paralysis on bone microarchitecture in skeletally mature rats were used to create high-resolution, animal-specific finite element models that included the vascular pores and osteocyte lacunae within the tibial metaphysis of Botox-injected (BTX, n = 8) and saline-injected control (CTRL, n = 8) groups. To quantify fluid flow, lacunar and canalicular porosities were modeled as fluid-saturated poroelastic materials, and boundary conditions were applied to simulate physiological loading. This modeling approach allowed a detailed quantification of the fluid flow velocities around osteocytes in a relatively large volume of bone tissue. The analysis demonstrated that interstitial fluid velocity at the vascular pore surfaces was significantly lower in BTX compared to CTRL because of the decreased vascular canal separation. No significant differences in average fluid velocity were observed at the osteocyte lacunae and no correlation was found between the fluid velocity and the lacunar density, which was significantly lower in BTX. Instead, the lacunar fluid velocity was dependent on the osteocyte's specific position in the bone cortex and its proximity to a vascular pore.

A 3D, Dynamically Loaded Hydrogel Model of the Osteochondral Unit to Study Osteocyte Mechanobiology

Osteocytes are mechanosensitive cells that orchestrate signaling in bone and cartilage across the osteochondral unit. The mechanisms by which osteocytes regulate osteochondral homeostasis and degeneration in response to mechanical cues remain unclear. This study introduces a novel 3D hydrogel bilayer composite designed to support osteocyte differentiation and bone matrix deposition in a bone-like layer and to recapitulate key aspects of the osteochondral unit's complex loading environment. The bilayer hydrogel is fabricated with a soft cartilage-like layer overlaying a stiff bone-like layer. The bone-like layer contains a stiff 3D-printed hydrogel structure infilled with a soft, degradable, cellular hydrogel. The IDG-SW3 cells embedded within the soft hydrogel mature into osteocytes and produce a mineralized collagen matrix. Under dynamic compressive strains, near-physiological levels of strain are achieved in the bone layer (≤ 0.08%), while the cartilage layer bears the majority of the strains (>99%). Under loading, the model induces an osteocyte response, measured by prostaglandin E2, that is frequency, but not strain, dependent: a finding attributed to altered fluid flow within the composite. Overall, this new hydrogel platform provides a novel approach to study osteocyte mechanobiology in vitro in an osteochondral tissue-mimetic environment.

Bone's Response to Mechanical Loading in Aging and Osteoporosis: Molecular Mechanisms

Mechanotransduction is pivotal in the maintenance of homeostasis in different tissues and involves multiple cell signaling pathways. In bone, mechanical stimuli regulate the balance between bone formation and resorption; osteocytes play a central role in this regulation. Dysfunctions in mechanotransduction signaling or in osteocytes response lead to an imbalance in bone homeostasis. This alteration is very relevant in some conditions such as osteoporosis and aging. Both are characterized by increased bone weakness due to different causes, for example, the increase of osteocyte apoptosis that cause an alteration of fluid space, or the alteration of molecular pathways. There are intertwined yet very different mechanisms involved among the cell-intrinsic effects of aging on bone, the cell-intrinsic and tissue-level effects of estrogen/androgen withdrawal on bone, and the effects of reduced mechanical loading on bone, which are all involved to some degree in how aged bone fails to respond properly to stress/strain compared to younger bone. This review aims at clarifying how the cellular and molecular pathways regulated and induced in bone by mechanical stimulation are altered with aging and in osteoporosis, to highlight new possible targets for antiresorptive or anabolic bone therapeutic approaches.

Liver Bioreactor Design Issues of Fluid Flow and Zonation, Fibrosis, and Mechanics: A Computational Perspective

Tissue engineering, with the goal of repairing or replacing damaged tissue and organs, has continued to make dramatic science-based advances since its origins in the late 1980’s and early 1990’s. Such advances are always multi-disciplinary in nature, from basic biology and chemistry through physics and mathematics to various engineering and computer fields. This review will focus its attention on two topics critical for tissue engineering liver development: (a) fluid flow, zonation, and drug screening, and (b) biomechanics, tissue stiffness, and fibrosis, all within the context of 3D structures. First, a general overview of various bioreactor designs developed to investigate fluid transport and tissue biomechanics is given. This includes a mention of computational fluid dynamic methods used to optimize and validate these designs. Thereafter, the perspective provided by computer simulations of flow, reactive transport, and biomechanics responses at the scale of the liver lobule and liver tissue is outlined, in addition to how bioreactor-measured properties can be utilized in these models. Here, the fundamental issues of tortuosity and upscaling are highlighted, as well as the role of disease and fibrosis in these issues. Some idealized simulations of the effects of fibrosis on lobule drug transport and mechanics responses are provided to further illustrate these concepts. This review concludes with an outline of some practical applications of tissue engineering advances and how efficient computational upscaling techniques, such as dual continuum modeling, might be used to quantify the transition of bioreactor results to the full liver scale.

The effects of dynamic compressive loading on human mesenchymal stem cell osteogenesis in the stiff layer of a bilayer hydrogel

Bilayer hydrogels with a soft cartilage-like layer and a stiff bone-like layer embedded with human mesenchymal stem cells (hMSCs) are promising for osteochondral tissue engineering. The goals of this work were to evaluate the effects of dynamic compressive loading (2.5% applied strain, 1 Hz) on osteogenesis in the stiff layer and spatially map local mechanical responses (strain, stress, hydrostatic pressure, and fluid velocity). A bilayer hydrogel was fabricated from soft (24 kPa) and stiff (124 kPa) poly (ethylene glycol) hydrogels. With hMSCs embedded in the stiff layer, osteogenesis was delayed under loading evident by lower OSX and OPN expressions, alkaline phosphatase activity, and collagen content. At Day 28, mineral deposits were present throughout the stiff layer without loading but localized centrally and near the interface under loading. Local strains mapped by particle tracking showed substantial equivalent strain (~1.5%) transferring to the stiff layer. When hMSCs were cultured in stiff single-layer hydrogels subjected to similar strains, mineralization was inhibited. Finite element analysis revealed that hydrostatic pressures ≥~600 Pa correlated to regions lacking mineralization in both hydrogels. Fluid velocities were low (~1-10 nm/s) in the hydrogels with no apparent correlation to mineralization. Mineralization was recovered by inhibiting ERK1/2, indicating cell-mediated inhibition. These findings suggest that high strains (~1.5%) combined with higher hydrostatic pressures negatively impact osteogenesis, but in a manner that depends on the magnitude of each mechanical response. This work highlights the importance of local mechanical responses in mediating osteogenesis of hMSCs in bilayer hydrogels being studied for osteochondral tissue engineering.

Effect of Drugs on Orthodontic Tooth Movement in Human Beings: A Systematic Review of Randomized Clinical Trials

Background:

Orthodontic tooth movement represents a series of events at both cellular and molecular levels which in turn stimulates inflammatory pathway to induce tooth movement. Some drugs taken by patients have a negative effect which can block this pathway, on the other hand, others may influence these events and reduce treatment time.

Search Methods:

A search strategy was implemented using both manual hand search and electronic databases, including Cochrane database of clinical trials, PubMed, ScienceDirect and Scopus. The risk of biased eligible studies to be included in the final analysis was assessed independently by two authors using Cochrane risk of bias tool.

Results:

A total of 491 articles were identified in both manual and electronic searches as well as by checking the reference lists of articles to be included in the study. After reviewing the titles, abstracts and full-text articles, only 8 RCTs met the inclusion criteria, and thus, were included in the final analysis. Six out of the 8 RCTs were assessed as of low quality. No statistical methods were employed to combine the studies due to the heterogeneities of the studies and the low level of evidence.

Conclusion:

Acetylsalicylic acid and ibuprofen reduced orthodontic tooth movement whereas paracetamol, Rofecoxib and tenoxicam had no impact on orthodontic tooth movement. Due to the low quality of the studies included, therefore to base our practice on scientific evidence, better-controlled RCTs are needed to investigate the impact of common medications on orthodontic tooth movement.

Orthodontic tooth movement: The biology and clinical implications

Orthodontic tooth movement relies on coordinated tissue resorption and formation in the surrounding bone and periodontal ligament. Tooth loading causes local hypoxia and fluid flow, initiating an aseptic inflammatory cascade culminating in osteoclast resorption in areas of compression and osteoblast deposition in areas of tension. Compression and tension are associated with particular signaling factors, establishing local gradients to regulate remodeling of the bone and periodontal ligament for tooth displacement. Key regulators of inflammation and tissue turnover include secreted factors like RANK ligand and osteoprotegerin, transcription factors such as RUNX2 and hypoxia-inducible factor, cytokines, prostaglandins, tissue necrosis factors, and proteases, among others. Inflammation occurred during tooth movement needs to be well controlled, as dysregulated inflammation leads to tissue destruction manifested in orthodontic-induced root resorption and periodontal disease. Understanding the biology has profound clinical implications especially in the area of accelerating orthodontic tooth movement. Surgical, pharmacological, and physical interventions are being tested to move teeth faster to reduce treatment times and time-dependent adverse outcomes. Future developments in acceleratory technology and custom appliances will allow orthodontic tooth movement to occur more efficiently and safely.

Microstructural changes associated with osteoporosis negatively affect loading-induced fluid flow around osteocytes in cortical bone

Loading-induced interstitial fluid flow in the microporosities of bone is critical for osteocyte mechanotransduction and for the maintenance of tissue health, enhancing convective transport in the lacunar-canalicular system. In recent studies, our group has reported alterations of bone's vascular porosity and lacunar-canalicular system microarchitecture in a rat model of postmenopausal osteoporosis. In this work, poroelastic finite element analysis was used to investigate whether these microstructural changes can affect interstitial fluid flow around osteocytes. Animal-specific finite element models were developed combining micro-CT reconstructions of bone microstructure and measures of the poroelastic material properties. These models were used to quantify and compare loading-induced fluid flow in the lacunar-canalicular system of ovariectomized and sham-operated rats. A parametric analysis was also used to quantify the influence of the lacunar-canalicular permeability and vascular porosity on the fluid velocity magnitude. Results show that mechanically-induced interstitial fluid velocity can be significantly reduced in the lacunar-canalicular system of ovariectomized rats. Interestingly, the vascular porosity is shown to have a major influence on interstitial fluid flow, while the lacunar-canalicular permeability influence is limited when larger than 10^-20m². Altogether our results suggest that microstructural changes associated with the osteoporotic condition can negatively affect interstitial fluid flow around osteocytes in the lacunar-canalicular system of cortical bone. This fluid flow reduction could impair mechanosensation of the osteocytic network, possibly playing a role in the initiation and progression of age-related bone loss and postmenopausal osteoporosis.

Biological response at the cellular level within the periodontal ligament on application of orthodontic force - An update

Orthodontic force elicits a biological response in the tissues surrounding the teeth, resulting in remodeling of the periodontal ligament and the alveolar bone. The force-induced tissue strain result in reorganization of both cellular and extracellular matrix, besides producing changes in the local vascularity. This in turn leads to the synthesis and release of various neurotransmitters, arachidonic acid, growth factors, metabolites, cytokines, colony-stimulating factors, and enzymes like cathepsin K, matrix metalloproteinases, and aspartate aminotransferase. Despite the availability of many studies in the orthodontic and related scientific literature, a concise integration of all data is still lacking. Such a consolidation of the rapidly accumulating scientific information should help in understanding the biological processes that underlie the phenomenon of tooth movement in response to mechanical loading. Therefore, the aim of this review was to describe the biological processes taking place at the molecular level on application of orthodontic force and to provide an update of the current literature.

A physiologically-based flow network model for hepatic drug elimination I: regular lattice lobule model

We develop a physiologically-based lattice model for the transport and metabolism of drugs in the functional unit of the liver, called the lobule. In contrast to earlier studies, we have emphasized the dominant role of convection in well-vascularized tissue with a given structure. Estimates of convective, diffusive and reaction contributions are given. We have compared drug concentration levels observed exiting the lobule with their predicted detailed distribution inside the lobule, assuming that most often the former is accessible information while the latter is not.

A physiologically-based flow network model for hepatic drug elimination II: variable lattice lobule models

We extend a physiologically-based lattice model for the transport and metabolism of drugs in the liver lobule (liver functional unit) to consider structural and spatial variability. We compare predicted drug concentration levels observed exiting the lobule with their detailed distribution inside the lobule, and indicate the role that structural variation has on these results. Liver zonation and its role on drug metabolism represent another aspect of structural inhomogeneity that we consider here. Since various liver diseases can be thought to produce such structural variations, our analysis gives insight into the role of disease on liver function and performance. These conclusions are based on the dominant role of convection in well-vascularized tissue with a given structure.

Computation models simulating notochordal cell extinction during early ageing of an intervertebral disc

Lower back pain due to intervertebral disc (IVD) degeneration is a prevalent problem which drastically affects the quality of life of millions of sufferers. Healthy IVDs begin with high populations of notochordal cells in the nucleus pulposus, while by the second stage of degeneration, these cells will be replaced by chondrocyte-like cells. Because the IVD is avascular, these cells rely on passive diffusion of nutrients to survive. It is thought that this transition in cell phenotype causes the shift of the IVD's physical properties, which impede the flow of nutrients. Our computational model of the IVD illustrates its ability to simulate the evolving chemical and mechanical environments occurring during the early ageing process. We demonstrate that, due to the insufficient nutrient supply and accompanying changes in physical properties of the IVD, there was a resultant exponential decay in the number of notochordal cells over time.

Bimodal distribution of osteocyte lacunar size in the human femoral cortex as revealed by micro-CT

Tomographic reconstructions of sections of human femoral bone were created from x-ray data sets taken using synchrotron radiation of 26.4 keV and with isotropic voxels 1.47 μm on a side. We demonstrate that it is possible to segment the data to isolate both the osteocyte lacunae and the Haversian canals in the bone as well as identifying osteon boundaries. From this information a wealth of data relating to bone structure becomes available. The data were used to map the spatial positions of the osteocyte lacunae, relative to the Haversian canals and of the osteon boundaries. The dimensions and volume of the imaged osteocyte lacunae were measured for close to 10,000 lacunae. When averaged over the 11 osteons measured, osteocyte densities varied from 4×10(4)per mm(3) close to the Haversian canals to about 9×10(4)per mm(3) at 80% of osteon radius. The nearest-neighbour distances varied from 10 μm to 40 μm with a peak at 23 μm and an approximately normal distribution. The distribution of lacunar long-axis length was also approximately normal with a small positive skew and the peak value was 8 μm with a range from 3 μm to 20 μm. The most significant finding from this study was that the distribution of the measured volumes of osteocyte lacunae had two distinct peaks, one at 200 μm(3) and a second at 330 μm(3).

On a Path to Unfolding the Biological Mechanisms of Orthodontic Tooth Movement

Orthodontic forces deform the extracellular matrix and activate cells of the paradental tissues, facilitating tooth movement. Discoveries in mechanobiology have illuminated sequential cellular and molecular events, such as signal generation and transduction, cytoskeletal re-organization, gene expression, differentiation, proliferation, synthesis and secretion of specific products, and apoptosis. Orthodontists work in a unique biological environment, wherein applied forces engender remodeling of both mineralized and non-mineralized paradental tissues, including the associated blood vessels and neural elements. This review aims at identifying events that affect the sequence, timing, and significance of factors that determine the nature of the biological response of each paradental tissue to orthodontic force. The results of this literature review emphasize the fact that mechanoresponses and inflammation are both essential for achieving tooth movement clinically. If both are working in concert, orthodontists might be able to accelerate or decelerate tooth movement by adding adjuvant methods, whether physical, chemical, or surgical.

The relation of femoral osteon geometry to age, sex, height and weight

As computational modeling becomes an increasingly common tool for probing the regulation of bone remodeling, the need for experimental data to refine and validate such models also grows. For example, van Oers et al. (R.F. van Oers, R. Ruimerman, B. van Rietbergen, P.A. Hilbers, R. Huiskes, Relating osteon diameter to strain. Bone 2008;43: 476-482.) recently described a mechanism by which osteon size may be regulated (inversely) by strain. Empirical data supporting this relation, particularly in humans, are sparse. Therefore, we sought to determine if there is a link between body weight (the only measure related to loading available for a cadaveric population) and osteon geometry in human bone. We hypothesized that after controlling for age, sex and height, weight would be inversely related to femoral osteon size (area, On.Ar; diameter, On.Dm). Secondarily we sought to describe the relation between osteon circularity (On.Cr) and these parameters. Osteons (n=12,690) were mapped within microradiographs of femoral mid-diaphyseal specimens (n=88; 45 male, 43 female; 17-97 yrs). Univariate analysis of covariance was conducted (n=87; 1 outlier) with sex as a fixed factor and height, weight and log-transformed age as covariates. Weight was negatively related to On.Ar and On.Dm (p=0.006 and p=0.004, respectively). Age was significantly related to osteon and, it was also significantly related to circularity (all p<0.001). This relation was negative for On.Ar and On.Dm and positive for On.Cr (increasing circularity with age). On.Ar and On.Dm were found to be significantly different between the sexes (p=0.021 and p=0.019, respectively), with females having smaller osteons. No relation between sex and On.Cr was detected (p=0.449). Height was not significantly related to any of the geometric parameters. Partial eta-squared values revealed that age accounted for the largest proportion (On.Ar: 28%, On.Dm: 18%, On.Cr: 30%), weight accounted for the second largest (On.Ar: 9%, On.Dm: 10%) and sex accounted for the smallest proportion (On.Ar: 6%, On.Dm: 7%) of the variance in geometry. While previous studies have reported relations between osteon size and sex/age, we believe that our findings are the first to demonstrate a link with weight. We believe that this negative relation with weight is most probably mechanical in nature; however, alternative (endocrine) links between bone and adipose tissue cannot be ruled out by our design.