Diabetes mellitus affects the biomechanical function of the callus and the expression of TGF-beta1 and BMP2 in an early stage of fracture healing

Transforming growth factor beta 1 (TGF-β1) and bone morphogenetic protein-2 (BMP-2) are important regulators of bone repair and regeneration. In this study, we examined whether TGF-β1 and BMP-2 expressions were delayed during bone healing in type 1 diabetes mellitus. Tibial fractures were created in 95 diabetic and 95 control adult male Wistar rats of 10 weeks of age. At 1, 2, 3, 4, and 5 weeks after fracture induction, five rats were sacrificed from each group. The expressions of TGF-β1 and BMP2 in the fractured tibias were measured by immunohistochemistry and quantitative reverse-transcription polymerase chain reaction, weekly for the first 5 weeks post-fracture. Mechanical parameters (bending rigidity, torsional rigidity, destruction torque) of the healing bones were also assessed at 3, 4, and 5 weeks post-fracture, after the rats were sacrificed. The bending rigidity, torsional rigidity and destruction torque of the two groups increased continuously during the healing process. The diabetes group had lower mean values for bending rigidity, torsional rigidity and destruction torque compared with the control group (P<0.05). TGF-β1 and BMP-2 expression were significantly lower (P<0.05) in the control group than in the diabetes group at postoperative weeks 1, 2, and 3. Peak levels of TGF-β1 and BMP-2 expression were delayed by 1 week in the diabetes group compared with the control group. Our results demonstrate that there was a delayed recovery in the biomechanical function of the fractured bones in diabetic rats. This delay may be associated with a delayed expression of the growth factors TGF-β1 and BMP-2.

The impact of topical prostaglandin analogs on the biomechanical properties of the cornea in patients with open angle glaucoma

Justification: Le glaucome entraîne une perte progressive de la vision causée par la détérioration du nerf optique. Le glaucome est répandu dans le monde et cause la cécité dans environ sept millions de personnes. Le glaucome touche plus de 400 000 Canadiens et sa prévalence augmente avec le vieillissement de la population.1,2 Il s'agit d'une maladie chronique surnoise dont les symptômes se manifestent uniquement lors des stades avancés et qui peuvent mener à la cécité. Présentement, le seul moyen possible d’arrêter la progression du glaucome au stade initial est de diminuer la pression intra-oculaire (PIO). Les analogues de prostaglandines (APG) topiques sont fréquemment utilisées comme traitement de première ligne. Cependant, la recherche démontre que cette classe de médicaments peut changer certaines propriétés de la cornée, et possiblement influencer la mesure de la PIO.3 Objectif: À déterminer si l'utilisation d'APG affecte les propriétés biomécaniques de la cornée. La conclusion sera basée sur l'analyse intégrée des résultats obtenus de l'analyseur Reichert oculaire Réponse (ORA), la tonométrie par applanation de Goldmann (TAG) et la pachymétrie ultrasonographique. Le deuxième objectif potentiel de cette étude est de déterminer la corrélation, le cas échéant, entre les propriétés biomécaniques de la cornée, l'épaisseur de la cornée centrale (ECC) et la PIO chez les patients subissant un traitement d’APG topique. L'hypothèse principale de cette étude est que l’APG influence les propriétés de la cornée telles que l'épaisseur centrale, l'élasticité et la résistance. Patients et méthodes : Soixante-dix yeux de 35 patients, âgés de 50-85 ans, atteints de glaucome à angle ouvert (GAO) et traités avec APG topique ont été examinés. Seulement les sujets avec une réfraction manifeste entre -6,00 D et +4,25 D ont été inclus. Les critères d'exclusion sont: patients avec n'importe quelle autre maladie de la cornée de l’œil, telles que la dystrophie endothéliale de Fuch’s et kératocône, ou tout antécédent de traumatisme ou d'une chirurgie de la cornée, ainsi que le port de lentilles de contact. Nous avons demandé aux patients atteints du glaucome qui ont des paramètres stables et qui utilisent l’APG dans les deux yeux de cesser l’APG dans l'œil moins affecté par la PIO, et de continuer l’utilisation d’APG dans l'œil contralatéral. Le meilleur œil est défini comme celui avec moins de dommage sur le champ visuel (CV) (déviation moyenne (DM), le moins négatif) ou une PIO maximale historique plus basse si la DM est égale ou encore celui avec plus de dommage sur la tomographie par cohérence optique (TCO, Cirrus, CA) ou la tomographie confocale par balayage laser (HRT, Heidelberg, Allemagne). Toutes les mesures ont été prises avant la cessation d’APG et répétées 6 semaines après l’arrêt. Les patients ont ensuite recommencé l’utilisation d’APG et toutes les mesures ont été répétées encore une fois après une période supplémentaire de 6 semaines. Après commencer ou de changer le traitement du glaucome, le patient doit être vu environ 4-6 semaines plus tard pour évaluer l'efficacité de la goutte.4 Pour cette raison, on été décidé d'utiliser 6 semaines d'intervalle. Toutes les mesures ont été effectuées à l’institut du glaucome de Montréal par le même technicien, avec le même équipement et à la même heure de la journée. L'œil contralatéral a servi comme œil contrôle pour les analyses statistiques. La tonométrie par applanation de Goldmann a été utilisée pour mesurer la PIO, la pachymétrie ultrasonographique pour mesurer l'ECC, et l’ORA pour mesurer les propriétés biomécaniques de la cornée, incluant l'hystérèse cornéenne (HC). L’hypothèse de l'absence d'effet de l'arrêt de l’APG sur les propriétés biomécaniques a été examiné par un modèle linéaire à effets mixtes en utilisant le logiciel statistique R. Les effets aléatoires ont été définies à deux niveaux: le patient (niveau 1) et l'œil de chaque patient (niveau 2). Les effets aléatoires ont été ajoutés au modèle pour tenir compte de la variance intra-individuelle. L’âge a également été inclus dans le modèle comme variable. Les contrastes entre les yeux et les temps ont été estimés en utilisant les valeurs p ajustées pour contrôler les taux d'erreur internes de la famille en utilisant multcomp paquet dans R. Résultats: Une augmentation statistiquement significative due l 'HC a été trouvée entre les visites 1 (sur APG) et 2 (aucun APG) dans les yeux de l'étude, avec une moyenne (±erreur standard) des valeurs de 8,98 ± 0,29 mmHg et 10,35 ± 0,29 mmHg, respectivement, correspondant à une augmentation moyenne de 1,37 ± 0,18 mmHg (p <0,001). Une réduction significative de 1,25 ± 0,18 mmHg (p <0,001) a été observée entre les visites 2 et 3, avec une valeur moyenne HC finale de 9,09 ± 0,29 mmHg. En outre, une différence statistiquement significative entre l’oeil d’étude et le contrôle n'a été observée que lors de la visite 2 (1,01 ± 0,23 mmHg, p <0,001) et non lors des visites 1 et 3. Une augmentation statistiquement significative du facteur de résistance conréen (FRC) a été trouvée entre les visites 1 et 2 dans les yeux de l'étude, avec des valeurs moyennes de 10,23 ± 0,34 mmHg et 11,71 ± 0,34 mmHg, respectivement. Le FRC a ensuite été réduit de 1,90 ± 0,21 mmHg (p <0,001) entre les visites 2 et 3, avec une valeur moyenne FRC finale de 9,81 ± 0,34 mmHg. Une différence statistiquement significative entre l’oeil d’étude et le contrôle n'a été observée que lors de la visite 2 (1,46 ± 0,23 mmHg, p <0,001). Une augmentation statistiquement significative de l'ECC a été trouvée entre les visites 1 et 2 dans les yeux de l'étude, avec des valeurs moyennes de 541,83 ± 7,27 µm et 551,91 ± 7,27 µm, respectivement, ce qui correspond à une augmentation moyenne de 10,09 ± 0,94 µm (p <0,001). L'ECC a ensuite diminué de 9,40 ± 0,94 µm (p <0,001) entre les visites 2 et 3, avec une valeur moyenne finale de 542,51 ± 7,27 µm. Une différence entre l’étude et le contrôle des yeux n'a été enregistré que lors de la visite 2 (11,26 ± 1,79 µm, p <0,001). De même, on a observé une augmentation significative de la PIO entre les visites 1 et 2 dans les yeux de l'étude, avec des valeurs moyennes de 15,37 ± 0,54 mmHg et 18,37 ± 0,54 mmHg, respectivement, ce qui correspond à une augmentation moyenne de 3,0 ± 0,49 mmHg (p <0,001). Une réduction significative de 2,83 ± 0,49 mmHg (p <0,001) a été observée entre les visites 2 et 3, avec une valeur moyenne de la PIO finale de 15,54 ± 0,54 mmHg. L’oeil de contrôle et d’étude ne différaient que lors de la visite 2 (1,91 ± 0,49 mmHg, p <0,001), ce qui confirme l'efficacité du traitement de l’APG. Lors de la visite 1, le biais de la PIO (PIOcc - PIO Goldmann) était similaire dans les deux groupes avec des valeurs moyennes de 4,1 ± 0,54 mmHg dans les yeux de contrôles et de 4,8 ± 0,54 mmHg dans les yeux d’études. Lors de la visite 2, après un lavage de 6 semaines d’APG, le biais de la PIO dans l'œil testé a été réduit à 1,6 ± 0,54 mmHg (p <0,001), ce qui signifie que la sous-estimation de la PIO par TAG était significativement moins dans la visite 2 que de la visite 1. La différence en biais PIO moyenne entre l'étude et le contrôle des yeux lors de la visite 2, en revanche, n'a pas atteint la signification statistique (p = 0,124). On a observé une augmentation peu significative de 1,53 ± 0,60 mmHg (p = 0,055) entre les visites 2 et 3 dans les yeux de l'étude, avec une valeur de polarisation finale de la PIO moyenne de 3,10 ± 0,54 mmHg dans les yeux d'études et de 2,8 ± 0,54 mmHg dans les yeux de contrôles. Nous avons ensuite cherché à déterminer si une faible HC a été associée à un stade de glaucome plus avancé chez nos patients atteints du glaucome à angle ouvert traités avec l’APG. Lorsque l'on considère tous les yeux sur l’APG au moment de la première visite, aucune association n'a été trouvée entre les dommages sur le CV et l'HC. Cependant, si l'on considère seulement les yeux avec un glaucome plus avancé, une corrélation positive significative a été observée entre la DM et l'HC (B = 0,65, p = 0,003). Une HC inférieure a été associé à une valeur de DM de champ visuelle plus négative et donc plus de dommages liés au glaucome. Conclusions : Les prostaglandines topiques affectent les propriétés biomécaniques de la cornée. Ils réduisent l'hystérèse cornéenne, le facteur de résistance cornéen et l'épaisseur centrale de la cornée. On doit tenir compte de ces changements lors de l'évaluation des effets d’APG sur la PIO. Plus de recherche devrait être menées pour confirmer nos résultats. De plus, d’autres études pourraient être réalisées en utilisant des médicaments qui diminuent la PIO sans influencer les propriétés biomécaniques de la cornée ou à l'aide de tonomètre dynamique de Pascal ou similaire qui ne dépend pas des propriétés biomécaniques de la cornée. En ce qui concerne l'interaction entre les dommages de glaucome et l'hystérésis de la cornée, nous pouvons conclure qu' une HC inférieure a été associé à une valeur de DM de CV plus négative. Mots Clés glaucome - analogues de prostaglandines - hystérèse cornéenne – l’épaisseur de la cornée centrale - la pression intraoculaire - propriétés biomécaniques de la cornée.

Biomechanical and histologic evaluation of non-washed resorbable blasting media and alumina-blasted/acid-etched surfaces

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Influence of Implant Connection Type on the Biomechanical Environment of Immediately Placed Implants - CT-Based Nonlinear, Three-Dimensional Finite Element Analysis

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Physiological and Stroke Parameters to Assess Aerobic Capacity in Swimming

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Determination of broiler femur parameters at different growth phases

The objective of this experiment was to analyse macroscopically the femur and determine the biochemical values at 8, 22 and 42 days of age, producing basic results that can help to understand the pathogeny of the locomotor problems and the broiler physiologic growth. A total of 60 Cobb male broilers were distributed in three age groups (8, 22 and 42 days of age) of 20 birds. All macroscopic measurements, except the cranial compact layer increased (p<0.05) over the course of the ages. The cranial compact layer presented the biggest measure at 22 days of age. The ash percentage increased (p<0.05) until 22 days of age, but at 42 days of age this values decreased. Calcium and phosphorus percentage in ash increased (p<0.05) until 22 days of age and evidenced constancy from 22 to 42 days of age. The biomechanical adaptation capacity of femur was evidenced by the increase of the macroscopic measures over the course of the ages and the different behavior of cranial compact layer at 22 days of age suggested an adaptation attempt of the immature bone to muscle mass increase. The ash and mineral percentage confirmed that the relative growth occurs with more intensity until 21 days of age. The calcium and phosphorus percentage evidenced the physiologic balance acting on the deposition of these minerals in femur. © Asian Network for Scientific Information, 2011.

Comparative in vivo study of commercially pure Ti implants with surfaces modified by laser with and without silicate deposition: Biomechanical and scanning electron microscopy analysis

The purpose of this study was to evaluate commercially pure titanium implant surfaces modified by laser beam (LS) and LS associated with sodium silicate (SS) deposition, and compare them with machined surface (MS) and dual acid-etching surfaces (AS) modified. Topographic characterization was performed by scanning electron microscopy-X-ray energy dispersive spectroscopy (SEM-EDX), and by mean roughness measurement before surgery. Thirty rabbits received 60 implants in their right and left tibias. One implant of each surface in each tibia. The implants were removed by reverse torque for vivo biomechanical analysis at 30, 60, and 90 days postoperative. In addition, the surface of the implants removed at 30 days postoperative was analyzed by SEM-EDX. The topographic characterization showed differences between the analyzed surfaces, and the mean roughness values of LS and SS were statistically higher than AS and MS. At 30 days, values removal torque LS and SS groups showed a statistically significant difference (p < 0.05) when compared with MS and AS. At 60 days, groups LS and SS showed statistically significant difference (p < 0.05) when compared with MS. At 90 days, only group SS presented statistically higher (p < 0.05) in comparison with MS. The authors can conclude that physical chemistry properties and topographical of LS and SS implants increases bone-implant interaction and provides higher degree of osseointegration when compared with MS and AS. © 2012 Wiley Periodicals, Inc.

Lower limb strength is associated with gait biomechanical abnormalities in older female fallers and non-fallers

BACKGROUND: Age-related loss in lower limb strength is related with impaired mobility. However, the association between decreased lower limb strength and gait biomechanical abnormalities is unclear. %In line with this, With respect to these statements, our study aimed to compare the maximum isokinetic voluntary strength (MIVS) of hip, knee and ankle of older women with and without history of falls. Also, we correlate the strength of each group with gait biomechanics. METHODS: The MIVS were assessed during concentric/concentric movements performed for hip, knee and ankle joints. Gait biomechanics (kinematic and electromyography) were assessed during 1-minute recorded during the volunteers walking on the treadmill at self-selected speed. Electromyographic signal was analyzed by the linear envelop after heel strike and before toe-off. The kinematic data were analyzed using the variables: step time, length and step width and ankle angle at heel strike, and hip angle at toe-off. RESULTS: In faller group, we found that a decreased hip abduction and adduction MIVS is associated with a higher tibialis anterior activation at initial stance (p =0.04 and r =-0.53 and p=0.04 and r=-0.52). CONCLUSION: Therefore, an impaired strength of hip could causes compensation in ankle stabilizer muscles activation at initial stance in older female fallers. © 2013 - IOS Press and the authors. All rights reserved.

Morphologic and biomechanical changes of thoracic and abdominal aorta in a rat model of cigarette smoke exposure

Background: Smoking is the most relevant environmental factor that affects the development of aortic aneurysm. Smokers have elevated levels of elastase activity in the arterial wall, which leads to weakening of the aorta. The aim of this study was to verify whether cigarette smoke exposure itself is capable of altering the aortic wall. Methods: Forty-eight Wistar rats were divided into 2-, 4-, and 6-month experimental periods and into 2 groups: smokers (submitted to smoke exposure at a rate of 40 cigarettes/day) and nonsmokers. At the end of the experimental periods, the aortas were removed and cross-sectioned to obtain histologic specimens for light microscopic and morphometric analyses. The remaining longitudinal segments were stretched to rupture and mechanical parameters were determined. Results: A degenerative process (i.e., a reduction in elastic fibers, the loss of lamellar arrangement, and a reduction of smooth muscle cells) was observed, and this effect was proportional in intensity to the period of tobacco exposure. We observed a progressive reduction in the yield point of the thoracic aorta over time (P < 0.05). There was a decrease in stiffness (P < 0.05) and in failure load (P < 0.05) at 6 months in the abdominal aorta of rats in the smoking group. Conclusions: Chronic exposure to tobacco smoke can affect the mechanical properties of the aorta and can also provoke substantial structural changes of the arterial wall. © 2013 Elsevier Inc. All rights reserved.

Biomechanical and histologic evaluation of non-washed resorbable blasting media and alumina-blasted/acid-etched surfaces

Objectives: To compare the biomechanical fixation and histomorphometric parameters between two implant surfaces: non-washed resorbable blasting media (NWRBM) and alumina-blasted/acid-etched (AB/AE), in a dog model. Material and methods: The surface topography was assessed by scanning electron microscopy, optical interferometry and chemistry by X-ray photoelectron spectroscopy (XPS). Six beagle dogs of similar to 1.5 years of age were utilized and each animal received one implant of each surface per limb (distal radii sites). After a healing period of 3 weeks, the animals were euthanized and half of the implants were biomechanically tested (removal torque) and the other half was referred to nondecalcified histology processing. Histomorphometric analysis considered bone-to-implant contact (BIC) and bone area fraction occupancy (BAFO). Following data normality check with the Kolmogorov-Smirnov test, statistical analysis was performed by paired t-tests at 95% level of significance. Results: Surface roughness parameters Sa (average surface roughness) and Sq (mean root square of the surface) were significantly lower for the NWRBM compared with AB/ AE. The XPS spectra revealed the presence of Ca and P in the NWRBM. While no significant differences were observed for both BIC and BAFO parameters (P>0.35 and P>0.11, respectively), a significantly higher level of torque was observed for the NWRBM group (P = 0.01). Bone morphology was similar between groups, which presented newly formed woven bone in proximity with the implant surfaces. Conclusion: A significant increase in early biomechanical fixation was observed for implants presenting the NWRBM surface.

Analysis of nonlinear dynamics of vocal folds using high-speed video observation and biomechanical modeling

Primary voice production occurs in the larynx through vibrational movements carried out by vocal folds. However, many problems can affect this complex system resulting in voice disorders. In this context, time-frequency-shape analysis based on embedding phase space plots and nonlinear dynamics methods have been used to evaluate the vocal fold dynamics during phonation. For this purpose, the present work used high-speed video to record the vocal fold movements of three subjects and extract the glottal area time series using an image segmentation algorithm. This signal is used for an optimization method which combines genetic algorithms and a quasi-Newton method to optimize the parameters of a biomechanical model of vocal folds based on lumped elements (masses, springs and dampers). After optimization, this model is capable of simulating the dynamics of recorded vocal folds and their glottal pulse. Bifurcation diagrams and phase space analysis were used to evaluate the behavior of this deterministic system in different circumstances. The results showed that this methodology can be used to extract some physiological parameters of vocal folds and reproduce some complex behaviors of these structures contributing to the scientific and clinical evaluation of voice production. (C) 2010 Elsevier Inc. All rights reserved.

Morphologic and biomechanical changes of thoracic and abdominal aorta in a rat model of cigarette smoke exposure

Background: Smoking is the most relevant environmental factor that affects the development of aortic aneurysm. Smokers have elevated levels of elastase activity in the arterial wall, which leads to weakening of the aorta. The aim of this study was to verify whether cigarette smoke exposure itself is capable of altering the aortic wall. Methods: Forty-eight Wistar rats were divided into 2-, 4-, and 6-month experimental periods and into 2 groups: smokers (submitted to smoke exposure at a rate of 40 cigarettes/day) and nonsmokers. At the end of the experimental periods, the aortas were removed and crosssectioned to obtain histologic specimens for light microscopic and morphometric analyses. The remaining longitudinal segments were stretched to rupture and mechanical parameters were determined. Results: A degenerative process (i.e., a reduction in elastic fibers, the loss of lamellar arrangement, and a reduction of smooth muscle cells) was observed, and this effect was proportional in intensity to the period of tobacco exposure. We observed a progressive reduction in the yield point of the thoracic aorta over time (P < 0.05). There was a decrease in stiffness (P < 0.05) and in failure load (P < 0.05) at 6 months in the abdominal aorta of rats in the smoking group. Conclusions: Chronic exposure to tobacco smoke can affect the mechanical properties of the aorta and can also provoke substantial structural changes of the arterial wall

Biomechanical modelling of human knee during living activities

The knee joint is a key structure of the human locomotor system. The knowledge of how each single anatomical structure of the knee contributes to determine the physiological function of the knee, is of fundamental importance for the development of new prostheses and novel clinical, surgical, and rehabilitative procedures. In this context, a modelling approach is necessary to estimate the biomechanic function of each anatomical structure during daily living activities. The main aim of this study was to obtain a subject-specific model of the knee joint of a selected healthy subject. In particular, 3D models of the cruciate ligaments and of the tibio-femoral articular contact were proposed and developed using accurate bony geometries and kinematics reliably recorded by means of nuclear magnetic resonance and 3D video-fluoroscopy from the selected subject. Regarding the model of the cruciate ligaments, each ligament was modelled with 25 linear-elastic elements paying particular attention to the anatomical twisting of the fibres. The devised model was as subject-specific as possible. The geometrical parameters were directly estimated from the experimental measurements, whereas the only mechanical parameter of the model, the elastic modulus, had to be considered from the literature because of the invasiveness of the needed measurements. Thus, the developed model was employed for simulations of stability tests and during living activities. Physiologically meaningful results were always obtained. Nevertheless, the lack of subject-specific mechanical characterization induced to design and partially develop a novel experimental method to characterize the mechanics of the human cruciate ligaments in living healthy subjects. Moreover, using the same subject-specific data, the tibio-femoral articular interaction was modelled investigating the location of the contact point during the execution of daily motor tasks and the contact area at the full extension with and without the whole body weight of the subject. Two different approaches were implemented and their efficiency was evaluated. Thus, pros and cons of each approach were discussed in order to suggest future improvements of this methodologies. The final results of this study will contribute to produce useful methodologies for the investigation of the in-vivo function and pathology of the knee joint during the execution of daily living activities. Thus, the developed methodologies will be useful tools for the development of new prostheses, tools and procedures both in research field and in diagnostic, surgical and rehabilitative fields.

Bioengineering of exercise: biomechanical and metabolic aspects

The field of research of this dissertation concerns the bioengineering of exercise, in particular the relationship between biomechanical and metabolic knowledge. This relationship can allow to evaluate exercise in many different circumstances: optimizing athlete performance, understanding and helping compensation in prosthetic patients and prescribing exercise with high caloric consumption and minimal joint loading to obese subjects. Furthermore, it can have technical application in fitness and rehabilitation machine design, predicting energy consumption and joint loads for the subjects who will use the machine. The aim of this dissertation was to further understand how mechanical work and metabolic energy cost are related during movement using interpretative models. Musculoskeletal models, when including muscle energy expenditure description, can be useful to address this issue, allowing to evaluate human movement in terms of both mechanical and metabolic energy expenditure. A whole body muscle-skeletal model that could describe both biomechanical and metabolic aspects during movement was identified in literature and then was applied and validated using an EMG-driven approach. The advantage of using EMG driven approach was to avoid the use of arbitrary defined optimization functions to solve the indeterminate problem of muscle activations. A sensitivity analysis was conducted in order to know how much changes in model parameters could affect model outputs: the results showed that changing parameters in between physiological ranges did not influence model outputs largely. In order to evaluate its predicting capacity, the musculoskeletal model was applied to experimental data: first the model was applied in a simple exercise (unilateral leg press exercise) and then in a more complete exercise (elliptical exercise). In these studies, energy consumption predicted by the model resulted to be close to energy consumption estimated by indirect calorimetry for different intensity levels at low frequencies of movement. The use of muscle skeletal models for predicting energy consumption resulted to be promising and the use of EMG driven approach permitted to avoid the introduction of optimization functions. Even though many aspects of this approach have still to be investigated and these results are preliminary, the conclusions of this dissertation suggest that musculoskeletal modelling can be a useful tool for addressing issues about efficiency of movement in healthy and pathologic subjects.

Quantifying the influence of bone density and thickness on resonance frequency analysis: an in vitro study of biomechanical test materials

PURPOSE: Resonance frequency analysis (RFA) offers the opportunity to monitor the osseointegration of an implant in a simple, noninvasive way. A better comprehension of the relationship between RFA and parameters related to bone quality would therefore help clinicians improve diagnoses. In this study, a bone analog made from polyurethane foam was used to isolate the influences of bone density and cortical thickness in RFA. MATERIALS AND METHODS: Straumann standard implants were inserted in polyurethane foam blocks, and primary implant stability was measured with RFA. The blocks were composed of two superimposed layers with different densities. The top layer was dense to mimic cortical bone, whereas the bottom layer had a lower density to represent trabecular bone. Different densities for both layers and different thicknesses for the simulated cortical layer were tested, resulting in eight different block combinations. RFA was compared with two other mechanical evaluations of primary stability: removal torque and axial loading response. RESULTS: The primary stability measured with RFA did not correlate with the two other methods, but there was a significant correlation between removal torque and the axial loading response (P < .005). Statistical analysis revealed that each method was sensitive to different aspects of bone quality. RFA was the only method able to detect changes in both bone density and cortical thickness. However, changes in trabecular bone density were easier to distinguish with removal torque and axial loading than with RFA. CONCLUSIONS: This study shows that RFA, removal torque, and axial loading are sensitive to different aspects of the bone-implant interface. This explains the absence of correlation among the methods and proves that no standard procedure exists for the evaluation of primary stability.