Bone Tissue Strains Research Articles

Biomechanical effects of different materials for an occlusal device on implant-supported rehabilitation in a tooth clenching situation: A 3D finite element analysis.

The purpose of this 3D finite element analysis was to evaluate the biomechanical effects of different materials used to fabricate occlusal devices to achieve stress distribution in simulated abutment screws, dental implants, and peri-implant bone tissue in individuals who clench their teeth. Eight 3D models simulated a posterior maxillary bone block with three external hexagon implants (Ø4.0×7.0mm) supporting a 3-unit screw-retained metal-ceramic prosthesis with different crown connection (splinting), and the use of an occlusal device (OD). The OD was modeled to be 2-mm thick. ANSYS 19.2 software was used to generate the finite-element models in the pre-and post-processing phases. Simulated abutment screws and dental implants were evaluated by von Mises stress maps, and simulated bone was evaluated by maximum principal stress and microstrain maps by using a finite element software program. The highest stress values in the dental implants and screws were observed in single crowns without OD (M1). Furthermore, the highest stress values and bone tissue strain were found in single crowns without OD (M1). The simulated material for the OD did not cause many discrepancies in terms of the stress magnitude in the simulated dental implant and abutment screw for both single and splinted crowns; however, more rigid materials exhibited lower stress values. The use of OD was effective in reducing stress in the simulated implants and abutment screws and stress and strain in the simulated bone tissue. The material used to simulate the OD influenced the biomechanical behavior of implant-supported fixed prostheses, whereas splints with rigid materials such as PEEK and PMMA exhibited better biomechanical behavior.

Accelerometer-measured physical activity is associated with knee breadth in middle-aged Finns – a population-based study

BackgroundArticular surface size is traditionally considered to be a relatively stable trait throughout adulthood. Increased joint size reduces bone and cartilage tissue strains. Although physical activity (PA) has a clear association with diaphyseal morphology, the association between PA and articular surface size is yet to be confirmed. This cross-sectional study aimed to clarify the role of moderate-to-vigorous PA (MVPA) in knee morphology in terms of tibiofemoral joint size.MethodsA sample of 1508 individuals from the population-based Northern Finland Birth Cohort 1966 was used. At the age of 46, wrist-worn accelerometers were used to monitor MVPA (≥3.5 METs) during a period of two weeks, and knee radiographs were used to obtain three knee breadth measurements (femoral biepicondylar breadth, mediolateral breadth of femoral condyles, mediolateral breadth of the tibial plateau). The association between MVPA and knee breadth was analyzed using general linear models with adjustments for body mass index, smoking, education years, and accelerometer weartime.ResultsOf the sample, 54.8% were women. Most individuals were non-smokers (54.6%) and had 9—12 years of education (69.6%). Mean body mass index was 26.2 (standard deviation 4.3) kg/m2. MVPA was uniformly associated with all three knee breadth measurements among both women and men. For each 60 minutes/day of MVPA, the knee breadth dimensions were 1.8—2.0% (or 1.26—1.42 mm) larger among women (p < 0.001) and 1.4—1.6% (or 1.21—1.28 mm) larger among men (p < 0.001).ConclusionsHigher MVPA is associated with larger tibiofemoral joint size. Our findings indicate that MVPA could potentially increase knee dimensions through similar biomechanical mechanisms it affects diaphyseal morphology, thus offering a potential target in reducing tissue strains and preventing knee problems. Further studies are needed to confirm and investigate the association between articulation area and musculoskeletal health.

Alterations in osteocyte lacunar morphology affect local bone tissue strains

Osteocytes are capable of remodeling their perilacunar bone matrix, which causes considerable variations in the shape and size of their lacunae. If these variations in lacunar morphology cause changes in the mechanical environment of the osteocytes, in particular local strains, they would subsequently affect bone mechanotransduction, since osteocytes are likely able to directly sense these strains. The purpose of this study is to quantify the effect of alterations in osteocyte lacunar morphology on peri-lacunar bone tissue strains. To this end, we related the actual lacunar shape in fibulae of six young-adult (5-month) and six old (23-month) mice, quantified by high-resolution micro-computed tomography, to microscopic strains, analyzed by micro-finite element modeling. We showed that peak effective strain increased by 12.6% in osteocyte cell bodies (OCYs), 9.6% in pericellular matrix (PCM), and 5.3% in extra cellular matrix (ECM) as the lacunae volume increased from 100-200 μm3 to 500–600 μm3. Lacunae with a larger deviation (>8°) in orientation from the longitudinal axis of the bone are exposed to 8% higher strains in OCYs, 6.5% in PCM, 4.2% in ECM than lacunae with a deviation in orientation below 8°. Moreover, increased lacuna sphericity from 0 to 0.5 to 0.7–1 led to 25%, 23%, and 13% decrease in maximum effective strains in OCYs, PCM, and ECM, respectively. We further showed that due to the presence of smaller and more round lacunae in old mice, local bone tissue strains are on average 5% lower in the vicinity of lacunae and their osteocytes of old mice compared to young. Understanding how changes in lacunar morphology affect the micromechanical environment of osteocytes presents a first step in unraveling their potential role in impaired bone mechanoresponsiveness with e.g. aging.

17. Understanding proximal junctional kyphosis: New way of evaluating adjacent segment strain and vulnerability to failure after long segment instrumentation

<h3>BACKGROUND CONTEXT</h3> Proximal junctional kyphosis (PJK) is a common and devastating complication of long segment fusions. Presumably, PJK occurs due to excessive or altered strain distribution at the proximal level above a fusion construct; however, this has not been previously studied or proven experimentally. <h3>PURPOSE</h3> Evaluate the patterns of proximal junction discoligamentous and bone strain distribution following long-segment pedicle screw fixation in a cadaveric model. <h3>STUDY DESIGN/SETTING</h3> Human cadaveric biomechanical testing. <h3>PATIENT SAMPLE</h3> Seven human cadaver specimens (T2-T12). <h3>OUTCOME MEASURES</h3> Range of motion (ROM), posterior rod strain (RS), as well as intervertebral disc (IVD), endplate and bone surface strains at the proximal junction. <h3>METHODS</h3> Nondestructive flexibility tests (4.0 Nm) were performed on 7 specimens (T2-T12) to compare range of motion (ROM), posterior rod strain (RS), as well as intervertebral disc (IVD), endplate and bone surface strains at the proximal junction during flexion, extension, axial rotation (AR) following pedicle screw fixation (PSR) from T4 to T12. Specimens were coated with a high contrast speckle pattern for optical tracking of movements using digital image correlation (DIC) with conversion to principle strain measured at the proximal junction disc and vertebral body bone surfaces. Data were analyzed using a two-way ANOVA followed by post hoc comparisons. <h3>RESULTS</h3> PSR resulted in significantly greater mobility at the proximal free level (T3-4) in flexion compared to intact (p=0.005), but not extension (p=0.3). PSR resulted in significantly lower ROM in flexion and extension across the instrumented T5-T12 levels (p<0.001) compared to intact. In flexion, PSR resulted in decreased strain at the posterior T3 inferior endplate compared to intact (p=0.038). In extension, PSR resulted in decreased strain at the anterior aspect of the disc (p=0.014), but increased strain at the posterior aspect of the disc (p=0.026) compared to intact. In AR, PSR resulted in elevated strain at the T3 inferior endplate (p=0.02), and reduced strain at the T4 superior endplate (p=0.028). Average T4 surface bone strain was lower with PSR compared to intact in flexion (p=0.039) and extension (p=0.028), and lower in the inferior anterior vertebral body in left AR (p=0.045). <h3>CONCLUSIONS</h3> This represents the first cadaveric biomechanical study of bone and soft tissue strain following long segment spinal instrumentation. Our results suggest that instrumentation alters the normal anterior-posterior and cranial-caudal strain profile across the proximal disc and vertebral body—the most common failure points in PJK. This study provides a foundation for understanding the biomechanics underlying PJK and will allow for the development of more targeted prevention strategies. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.

Low-cycle full-field residual strains in cortical bone and their influence on tissue fracture evaluated via in situ stepwise and continuous X-ray computed tomography

As a composite material, the mechanical properties of bone are highly dependent on its hierarchical organisation, thus, macroscopic mechanical properties are dictated by local phenomena, such as microdamage resulting from repetitive cyclic loading of daily activities. Such microdamage is associated with plastic deformation and appears as a gradual accumulation of residual strains. The aim of this study is to investigate local residual strains in cortical bone tissue following compressive cyclic loading, using in situ X-ray computed tomography (XCT) and digital volume correlation (DVC) to provide a deeper insight on the three-dimensional (3D) relationship between residual strain accumulation, cortical bone microstructure and failure patterns. Through a progressive in situ XCT loading–unloading scheme, localisation of local residual strains was observed in highly compressed regions. In addition, a multi-scale in situ XCT cyclic test highlighted the differences on residual strain distribution at the microscale and tissue level, where high strains were observed in regions with the thinnest vascular canals and predicted the failure location following overloading. Finally, through a continuous in situ XCT compression test of cycled specimens, the full-field strain evolution and failure pattern indicated the reduced ability of bone to plastically deform after damage accumulation due to high number of cyclic loads. Altogether, the novel experimental methods employed in this study, combining high-resolution in situ XCT mechanics and DVC, showed a great potential to investigate 3D full-field residual strain development under repetitive loading and its complex interaction with bone microstructure, microdamage and fracture.

Differing trabecular bone architecture in dinosaurs and mammals contribute to stiffness and limits on bone strain.

The largest dinosaurs were enormous animals whose body mass placed massive gravitational loads on their skeleton. Previous studies investigated dinosaurian bone strength and biomechanics, but the relationships between dinosaurian trabecular bone architecture and mechanical behavior has not been studied. In this study, trabecular bone samples from the distal femur and proximal tibia of dinosaurs ranging in body mass from 23-8,000 kg were investigated. The trabecular architecture was quantified from micro-computed tomography scans and allometric scaling relationships were used to determine how the trabecular bone architectural indices changed with body mass. Trabecular bone mechanical behavior was investigated by finite element modeling. It was found that dinosaurian trabecular bone volume fraction is positively correlated with body mass similar to what is observed for extant mammalian species, while trabecular spacing, number, and connectivity density in dinosaurs is negatively correlated with body mass, exhibiting opposite behavior from extant mammals. Furthermore, it was found that trabecular bone apparent modulus is positively correlated with body mass in dinosaurian species, while no correlation was observed for mammalian species. Additionally, trabecular bone tensile and compressive principal strains were not correlated with body mass in mammalian or dinosaurian species. Trabecular bone apparent modulus was positively correlated with trabecular spacing in mammals and positively correlated with connectivity density in dinosaurs, but these differential architectural effects on trabecular bone apparent modulus limit average trabecular bone tissue strains to below 3,000 microstrain for estimated high levels of physiological loading in both mammals and dinosaurs.

Assessment of stress/strain in dental implants and abutments of alternative materials compared to conventional titanium alloy—3D non-linear finite element analysis

The aim of this study was to assess the stress/strain in dental implant/abutments with alternative materials, in implants with different microgeometry, through finite element analysis (FEA). Three-dimensional models were created to simulate the clinical situation of replacement of a maxillary central incisor with implants, in a type III bone, with a provisional single crown, loaded with 100 N in a perpendicular direction. The FEA parameters studied were: implant materials—titanium, porous titanium, titanium-zirconia, zirconia, reinforced fiberglass composite (RFC), and polyetheretherketone (PEEK); and abutment materials—titanium, zirconia, RFC, and PEEK; implant macrogeometry—tapered of trapezoidal threads (TTT) and cylindrical of triangular threads (CTT) (ø4.3 mm × 11 mm). Microstrain, von Mises, shear, and maximum and minimum principal stresses in the structures and in peri-implant bone were compared. There was increased stress and strain in peri-implant bone tissue caused by implants of materials with lower elastic modulus (mainly for PEEK and RFC). They also presented higher concentration of stresses in the implant itself (especially RFC). Zirconia implants led to lower stress and strains in peri-implant bone tissue. Less rigid abutments (RFC and PEEK) associated with titanium implants led to higher stress in the implant and in peri-implant bone tissue. The TTT macrogeometry showed a higher stress concentration in the implant and peri-implant bone tissue. The stress/strain in peri-implant bone tissue and implant structures were affected by the material used, where reduced values were caused by stiffer materials. Lower stress/strain values were obtained with cylindrical implants of triangular treads.

Adaptive changes in micromechanical environments of cancellous and cortical bone in response to in vivo loading and disuse

The skeleton accommodates changes in mechanical environments by increasing bone mass under increased loads and decreasing bone mass under disuse. However, little is known about the adaptive changes in micromechanical behavior of cancellous and cortical tissues resulting from loading or disuse. To address this issue, in vivo tibial loading and hindlimb unloading experiments were conducted on 16-week-old female C57BL/6J mice. Changes in bone mass and tissue-level strains in the metaphyseal cancellous and midshaft cortical bone of the tibiae, resulting from loading or unloading, were determined using microCT and finite element (FE) analysis, respectively. We found that loading- and unloading-induced changes in bone mass were more pronounced in the cancellous than cortical bone. Simulated FE-loading showed that a greater proportion of elements experienced relatively lower longitudinal strains following load-induced bone adaptation, while the opposite was true in the disuse model. While the magnitudes of maximum or minimum principal strains in the metaphyseal cancellous and midshaft cortical bone were not affected by loading, strains oriented with the long axis were reduced in the load-adapted tibia suggesting that loading-induced micromechanical benefits were aligned primarily in the loading direction. Regression analyses demonstrated that bone mass was a good predictor of bone tissue strains for the cortical bone but not for the cancellous bone, which has complex microarchitecture and spatially-variant strain environments. In summary, loading-induced micromechanical benefits for cancellous and cortical tissues are received primarily in the direction of force application and cancellous bone mass may not be related to the micromechanics of cancellous bone.

Finite element model of load adaptive remodelling induced by orthodontic forces

Many hypotheses have been formulated to explain orthodontic tooth movement. However, none of them can satisfactorily explain how small static orthodontic forces can induce bone remodelling. Our hypothesis assumes that small orthodontic forces do not lead to bone remodelling response directly, but rather indirectly by offsetting the tooth, leading to changes in bone loading during chewing that far exceed the changes caused by the orthodontic force alone. We developed a finite element model of a tooth with the periodontal ligament and the surrounding bone, and calculated the changes in strain energy density caused by the chewing force alone, the orthodontic force alone, and the combined action of the chewing and orthodontic forces. The results (average strain energy density 0.0005–0.01 kPa) demonstrate that the orthodontic loading alone does not produce strain energy density values in a range that is expected to induce remodelling (0.016–1.6 kPa). However, when the chewing and orthodontic forces are applied together, the highest values for the average strain energy density (0.02–0.99 kPa) as well as large changes in the bone tissue strain energy density (31.19–166.65%) are obtained. We conclude that the proposed hypothesis can indeed explain the observed bone remodelling that agrees with Wolff's law.

A new open-source tool for measuring 3D osteocyte lacunar geometries from confocal laser scanning microscopy reveals age-related changes to lacunar size and shape in cortical mouse bone.

Osteocytes can participate in systemic mineral homeostasis through perilacunar maintenance and remodeling, where changes to osteocyte lacunar morphology may affect bone structural integrity, tissue strains, and osteocyte mechanosensitivity. Though aging is associated with both decreased bone quality and altered mineral metabolism, it is not known if osteocyte lacunae undergo age-related changes in geometry. In order to survey lacunar changes with age, we developed an open-source program whereby 3D osteocyte lacunae are automatically segmented and then subsequently reconstructed from confocal laser scanning microscopy (CLSM) depth stacks for quantitative analysis of geometry and orientation. This approach takes advantage of the availability and speed of CLSM while avoiding time-consuming and bias-prone manual segmentation. Unlike conventional approaches used to quantify osteocyte lacunar morphology, CLSM enables facile analysis in three-dimensions with clear identification of osteocyte lacunae. We report that 3D osteocyte lacunae measured by CLSM become smaller, more spherical, more oblate, more spatially disorganized, and more sparsely populated with increased age in C57Bl/6 mouse cortical bone in groups spanning 6-24 months old. Critically, these age-related changes are in large part not observed in 2D analyses from the same samples. These results (1) demonstrate proof-of-concept of an efficient method to quantitatively assess osteocyte lacunae in 3D for application to a wide range of studies and (2) motivate further inquiry into how changes to osteocyte lacunar geometries and perilacunar material contribute to diminished bone quality in aging.

Precision of Digital Volume Correlation Approaches for Strain Analysis in Bone Imaged with Micro-Computed Tomography at Different Dimensional Levels

Accurate measurement of local strain in heterogeneous and anisotropic bone tissue is fundamental to understand the pathophysiology of musculoskeletal diseases, to evaluate the effect of interventions from preclinical studies, and to optimize the design and delivery of biomaterials. Digital volume correlation (DVC) can be used to measure the three-dimensional displacement and strain fields from micro-Computed Tomography (µCT) images of loaded specimens. However, this approach is affected by the quality of the input images, by the morphology and density of the tissue under investigation, by the correlation scheme, and by the operational parameters used in the computation. Therefore, for each application the precision of the method should be evaluated. In this paper we present the results collected from datasets analyzed in previous studies as well as new data from a recent experimental campaign for characterizing the relationship between the precision of two different DVC approaches and the spatial resolution of the outputs. Different bone structures scanned with laboratory source µCT or Synchrotron light µCT (SRµCT) were processed in zero-strain tests to evaluate the precision of the DVC methods as a function of the subvolume size that ranged from 8 to 2500 micrometers. The results confirmed that for every microstructure the precision of DVC improves for larger subvolume size, following power laws. However, for the first time large differences in the precision of both local and global DVC approaches have been highlighted when SRµCT or in vivo µCT images were used instead of conventional ex vivo µCT. These findings suggest that in situ mechanical testing protocols applied in SRµCT facilities should be optimized in order to allow DVC analyses of localized strain measurements. Moreover, for in vivo µCT applications DVC analyses should be performed only with relatively course spatial resolution for achieving a reasonable precision of the method. In conclusion, we have extensively shown that the precision of both tested DVC approaches is affected by different bone structures, different input image resolution and different subvolume sizes. Before each specific application DVC users should always apply a similar approach to find the best compromise between precision and spatial resolution of the measurements.

Study of Bone Tissue Stress and Strain State Aimed at Development of Intelligent Biomaterials for Osteoimplantation

This article studies the stress and strain state of simulated microvolumes of compact bone tissue under uniaxial compression, having different orientation of collagen-mineral fibers, different porosity and mineral content. The purpose of the study is to work out recommendations on development of artificial mechanically compatible biomaterials for osteoimplants. It has been found out that it is necessary to take into account the effective mechanical parameters defining the distribution of the bone tissue stress and strain when making individual implants.

Four-point bending protocols to study the effects of dynamic strain in osteoblastic cells in vitro.

Strain engendered within bone tissue by mechanical loading of the skeleton is a major influence on the processes of bone modeling and remodeling and so a critical determinant of bone mass and architecture. The cells best placed to respond to strain in bone tissue are the resident osteocytes and osteoblasts. To address the mechanisms of strain-related responses in osteoblast-like cells, our group uses both in vivo and in vitro approaches, including a system of four-point bending of the substrate on which cells are cultured. A range of cell lines can be studied using this system but we routinely compare their responses to those in primary cultures of osteoblast-like cells derived from explants of mouse long bones. These cells show a range of well-characterized responses to physiological levels of strain, including increased proliferation, which in vivo is a feature of the osteogenic response.

Ex vivo determination of bone tissue strains for an in vivo mouse tibial loading model

Previous studies introduced the digital image correlation (DIC) as a viable technique for measuring bone strain during loading. In this study, we investigated the sensitivity of a DIC system in determining surface strains in a mouse tibia while loaded in compression through the knee joint. Specifically, we examined the effect of speckle distribution, facet size and overlap, initial vertical alignment of the bone into the loading cups, rotation with respect to cameras, and ex vivo loading configurations on the strain contour maps measured with a DIC system.We loaded tibiae of C57BL/6 mice (12 and 18 weeks old male) up to 12N at 8N/min. Images of speckles on the bone surface were recorded at 1N intervals and DIC was used to compute strains. Results showed that speckles must have the correct size and density with respect to the facet size of choice for the strain distribution to be computed and reproducible. Initial alignment of the bone within the loading cups does not influence the strain distribution measured during peak loading, but bones must be placed in front of the camera with the same orientation in order for strains to be comparable. Finally, the ex vivo loading configurations with the tibia attached to the entire mouse, or to the femur and foot, or only to the foot, showed different strain contour maps.This work provides a better understanding of parameters affecting full field strain measurements from DIC in ex vivo murine tibial loading tests.

Influence of osteon area fraction and degree of orientation of HAp crystals on mechanical properties in bovine femur

Cortical bone has a hierarchical structure, spanning from the macrostructure at several millimeters or whole bone level, the microstructure at several hundred micrometers level, to the nanostructure at hydroxyapatite (HAp) crystals and collagen fibrils levels. The aim of the study is to understand the relationship between the HAp crystal orientation and the elastic modulus and the relationship between the osteon area fraction and the deformation behavior of HAp crystals in cortical bone. In the experiments, five strip specimens (40×2×1mm3) aligned with the bone axis were taken from the cortical bone of a bovine femur. The degree of c-axis orientation of HAp crystals in the specimens was measured with the X-ray diffraction technique with the imaging plate. To measure the deformation behavior of HAp crystals in the specimens, tensile tests under X-ray irradiation were conducted. The specimens were cut at the X-ray measurement positions and osteon area fraction and porosity at the transverse cross-sections were observed. Further, the volume fraction of HAp of the specimens was measured. Results showed the degree of c-axis orientation of HAp crystals was positively correlated with the elastic modulus of the specimens (r=0.94). The volume fraction of HAp and the porosity showed no statistical correlation with the elastic modulus and the tensile strength. The HAp crystal strain εH increased linearly with the bone tissue strain ε. The average value of εH/ε was 0.69±0.13 and there was no correlation between the osteon area fraction and εH/ε (r=−0.27, p=0.33). The results suggest that the degree of c-axis orientation of HAp crystals affects the elastic modulus and the magnitude of HAp crystal strain does not depend on the osteon area fraction.

Cranial Bone and Suture Strains Incident to Spring-Assisted Cranioplasty

Spring-assisted cranioplasty transmits forces throughout the craniofacial complex that can be measured as strain. The strain magnitude in relation to normal background physiologic strains and the distribution of these strains are currently unknown. Twenty New Zealand White rabbits were randomized into two groups: the treatment group, which included posterofrontal suture removal and spring insertion (n = 10); and the control group, which consisted of posterofrontal suture removal (n = 10). Strain gauges were placed across the interfrontal suture, both coronal sutures, and the frontal bone. Continuous strain recordings were made for 15 minutes after spring insertion. Physiologic strains caused by dural pulsation and intracerebral swelling measured were higher within sutures (40 to 50 microepsilon) than in bone (10 to 20 microepsilon). Spring activation produced large increases in strain across all sutures and bone. Compared with controls, tensile strains were 20 times higher in the frontal bone (mean, 341 microepsilon; p = 0.000), 15 times higher in the interfrontal suture (539 microepsilon; p = 0.000), and 21 times higher in the coronal suture (700 microepsilon; p = 0.000). Compressive strain in the left coronal suture confirmed a shear force at these sutures (-503 microepsilon; p = 0.000). The variability of background physiologic strain was not dampened by spring loading. Spring-assisted cranioplasty produces supraphysiologic strain in adjacent cranial bone and suture tissue. Mechanotransduction converts these forces into the biological processes that modulate calvarial morphology. Contrary to expectations, bone lateral to the spring insertion is subjected to tensile strain on its ectocranial surface. A compressive strain on its endocranial surface is likely because of bone flexion. This has implications for subsequent calvarial morphology.

Human Ex Vivo Bone Tissue Strains Around Immediately-Loaded Implants Supporting Mandibular Fixed Prostheses

The purpose of this study was to qualify and quantify bone strains around immediately-loaded implants supporting mandibular fixed prostheses with regard to number of implant support. Linear strain gauges were bonded on the labial bone of 5 Straumann dental implants placed in the mandibular symphysis region of 2 completely edentulous mandibles of fresh human cadavers. Installation torque value of each implant was measured by a custom-made torque wrench and resonance frequency analyses were undertaken. A one-piece full-arch fixed prosthesis was fabricated for each cadaver and 2 miniature load cells were integrated in the cantilever region of the prostheses for controlled loading experiments. 5-, 4-, and 3-implant support designs were consecutively tested. Strain measurements were performed at a sample rate of 10 KHz and under a maximum load of 100 N, simultaneously monitored from a computer connected to data acquisition system. The installation torque values and implant stability quotient values of the implants ranged between 42.12 to 145.67 N cm and 61 to 80, respectively. Between-group comparisons revealed that the highest strain magnitudes were recorded for the 3-implant design followed by the 4- and 5-implant designs, although there was a tendency toward similar load partitioning between 4- and 5-implant designs (P < 0.05). Bone strains around 3-implant supported mandibular fixed prostheses is significantly higher than those around 4- and 5-implant designs, and this may lead to failure of supporting implants. Four- and 5-implant designs might have similar clinical outcome.

Investigation of bone inelastic response in interaction phenomena with dental implants

Objectives The aim of the paper is to analyze the effects of misfits in multi-implant oral prostheses caused by defects in manufacturing of bar connecting implants. The consequent stress–strain state on peri-implant bone tissue must be carefully considered because of the significant effects induced. Materials and methods The case of a two-implant prosthesis connected by a titanium cast bar in the pre-molar mandible region is investigated. The complex geometry requires the use of refined finite element model. In consideration of the action induced on the bone tissue, a specific constitutive model that includes inelastic behavior is implemented. The linear misfits considered, estimated with reference to experimental works already present in the literature, induce relevant strains in the peri-implant bone tissue up to a post-elastic phase. Relaxation phenomena are also evaluated. The interaction between the bone and implant is modeled by using contact elements to represent possible detachments at the bone–implant interface. Results The response of the bone material is reported with regard to the stress/strain field induced, evaluating the inelastic behavior in terms of plastic and relaxation responses. The effects on the peri-implant bone tissue at the interface are evaluated. Significance The analysis confirms that the interaction phenomena between the multi-implant oral prostheses and bone induced by the misfit defects of normal intensity induce significant strain in the bone tissue and inelastic phenomena must be taken into account. Local permanent strains of bone tissue and relaxation phenomena represent short-term tissue response for a correct interpretation of the real biomechanical behavior of multiple implant frames.

Estimating nanoscale deformation in bone by X-ray diffraction imaging method

Knowledge of internal stress–strain in bone tissue is important for clinical diagnosis and remedies. The inorganic mineral phase of apatite crystals in bone composite, because of its crystalline nature, provides a reliable way of measurement through X-ray diffraction system. Use of two-dimensional detector, imaging plate (IP), is considered to expedite the process with much more information, hence, is widely applied in the study of organization, stress, strain, etc. for crystalline substance. The distortion of Debye rings in the image obtained by IP can be directly related to the deformation in lattice plane of the crystals. Since X-ray diffraction method involves measurement at nano-level, proper focus on the extraction of data and corresponding analysis is needed. In the current work, we considered weighted average value of intensity to locate radius vectors along azimuthal direction in the diffracted rings from the primary array of digital data in steps of pixels. The widely applied approaches for profile shift measurement—peak shift and full width at half maximum (FWHM) of a peak, and shift of center of gravity of profile—were compared with a new concept of segmental shift (SS) proposed previously by the authors. We observed reliable and effective outcomes with higher precision in the consideration of SS while using IP as a detector. Our approach in this work for intensity integration and radius vector positioning especially add precision in such applications.

Inhomogeneity of tissue-level strain distributions in individual trabeculae: Mathematical model studies of normal and osteoporosis cases

Little is known about the distributions of mechanical strains and stresses in individual trabeculae of cancellous bone, despite evidence that tissue-level strains affect the metabolism of bone. Recently, micro-finite element (micro-FE) studies have provided the first insights into the mechanical conditions in trabeculae, and suggested that osteoporotic cancellous bone experience higher and substantially less-uniform strains with respect to healthy cancellous bone. We may therefore ask whether the inhomogeneity of bone tissue strains is predominantly a consequence of micro-architectural differences between trabeculae, or is it mostly caused by the curvatures of each individual trabecula. Accordingly, the objectives of the present study were to determine the contribution of the shape of a trabecula to the intra-trabecula strain inhomogeneity, and to determine potential differences in intra-trabecula strain inhomogeneities between normal and thinner, osteoporotic-like trabeculae. We employed our previously reported generic single-trabecula model, which is a mathematical representation of the shape of a trabecula based on statistical analyses of mammalian trabecular dimensions. The single-trabecula model was loaded axially and in bending, and strain distributions were calculated for individual trabeculae as well as for “populations” of trabeculae, formed by assigning different trabecular thickness values in the trabecular model, in order to represent the distributions of trabecular shapes in normal and osteoporotic bones. We found that when subjected to equivalent loads, thinner, osteoporotic-like individual trabeculae and populations of thin trabeculae developed substantially greater strain inhomogeneities compared with normal trabeculae. We conclude that the intra-trabecula strain inhomogeneities are likely to be an important factor contributing to the overall increased strain inhomogeneity in osteoporotic cancellous bone, as previously observed in micro-FE studies.