Intermittent Force Research Articles

Strain-Dependent Control of Transforming Growth Factor-?? Function in Osteoblasts in an In Vitro Model: Biochemical Events Associated with Distraction Osteogenesis

Distraction osteogenesis is an important clinical method for increasing bone mass, but its effects on bone-forming cells are not well understood. In this study, the authors asked how the mechanical forces that occur during this procedure alter specific osteoblast activities such as matrix synthesis, the rate of cell replication, and enzyme activities. The authors further asked whether these changes relate to differences in the biochemical response of osteoblasts to transforming growth factor-beta (TGF-beta), a potent regulator of bone formation. Osteoblasts were plated on flexible, collagen-coated membranes. One group was unstrained, a second group experienced a single maximum strain load once every 6 hours to simulate intermittent force associated with a distraction protocol of four screw turns per day, and a third group was strained continuously for 24 hours. In the third group, some cell cultures were allowed to recover from strain before analysis. Subsequently, each group was treated with vehicle or TGF-beta at 12 pM (0.3 ng/ml) or 120 pM (3 ng/ml). Data were collected from a minimum of 15 replicate cell culture wells obtained from at least three separate primary culture preparations. Results were assessed with statistical software. Differences were considered significant with values of p < 0.05. Both strain protocols increased basal osteoblast DNA synthesis but suppressed the relative stimulatory effect of TGF-beta on this event. However, neither intermittent nor continuous strain significantly altered collagen or noncollagen protein synthesis or the relative effect of TGF-beta on these processes in osteoblasts. Basal alkaline phosphatase activity, an intermediate marker of osteoblast differentiation and an early marker of matrix mineralization, decreased significantly in response to continuous strain or to TGF-beta treatment, and even more so in response to both conditions. In addition, TGF-beta binding to the type III TGF-beta receptor was increased in proportion to strain intensity. This study shows that cyclic strain can alter osteoblast activity in multiple ways and predicts that TGF-beta has different effects during the distraction process on osteoblasts and therefore on their ability to effect bone formation. They further indicate that mechanical load permits early aspects of osteoblast activation but delays in part later biochemical parameters associated with mineralization to allow new bone growth before consolidation.

Dynamical properties of the Q-controlled atomic force microscope

In intermittent contact mode atomic force microscopy (AFM), the quality factor (Q) of the oscillating probe is believed to account for the imaging speed and sensitivity. Q control is a method to artificially modify the quality factor of the probe. Here, we present a comprehensive study of the dynamics of the Q-controlled AFM. By comparing the analytical solutions of the force equations, we prove that the Q-controlled and non-Q-controlled systems are equivalent in the absence of surface forces. We also determine the conditions for the numerical simulation. In order to study the mechanism of contrast enhancement, we simulate the normal AFM operation including the surface forces. We found that there is a maximal probe sensitivity which cannot be exceeded even with Q control. Consistently, Q control enhances sensitivity only when imaging soft samples. Finally, we show that the phase signal of the Q-controlled system is more sensitive to the changes of the sample properties than in case of non-Q-controlled AFMs.

Intermittent 8-hour activation in orthodontic molar movement

The duration of force application is an important factor, together with the magnitude of force, in stimulating osteoclast recruitment in the periodontal ligament. The purpose of this study was to examine the effect of duration of intermittent versus continuous force application on the amount of molar movement in rats. Seventy-six molars of 38 rats were randomly assigned to continuous, intermittent, and sham-operation groups. A calibrated nickel-titanium coil spring exerting 40 g of initial force was suspended between the maxillary first molars and the incisors for 13 days. In the intermittent group, the coil spring was suspended for 8 hours per day. Tooth movement was measured on radiographs. There was no significant difference in the initial tooth displacement between the continuous-force and intermittent-force groups. Tooth movement at day 7 was significantly ( P < .05) less in the intermittent group than in the continuous group. Actual mesial tooth movement and total tooth movement in the intermittent group were 65.9% and 73.7%, respectively, of those in the continuous group. Our results suggest that the amount of tooth movement in response to intermittent force is less than that in response to continuous force, but that the amount of tooth movement achieved by intermittent force exceeds the expected value predicted by the duration (33.3%) of force application.

Mincer's Overtaking Point and the Life Cycle Earnings Distribution

In 1958 Jacob Mincer pioneered an important approach to understand earnings distribution. In the years since Mincer's seminal work, he as well as his students and colleagues extended the original human capital model, reaching important conclusions about a whole array of observations pertaining to human well-being. This line of research explained why education enhances earnings; why earnings rise at a diminishing rate throughout one's life; why earnings growth is smaller for those anticipating intermittent labor force participation; why men earn more than women; why Whites earn more than Blacks; why occupational distributions differ by gender; why geographic and job mobility predominate among the young; why unemployment is lower among the skilled; and why numerous other labor market phenomena occur. This paper surveys the answers to these and other questions based on research emanating from Mincer's original discovery. In addition, this paper provides new empirical evidence regarding Mincer's concept of the “overtaking age”–a topic not currently well-explored in the literature. In this latter vein, the paper shows that Mincer's original finding of a U-shaped (log) variance of earnings over the life cycle is upheld in recent data, both for the United States as well as at least seven other countries.

Dynamic functional force measurements on an anterior bite plane during the night.

Anterior bite planes are used in removable and fixed appliance treatment. In removable appliance treatment the question arising is whether the delivered forces can achieve active intrusion in terms of their amplitude and duration. In fixed appliance treatment, the force effect on the incisors and associated pathologic side effects, in particular under the application of intrusion mechanics, have to be considered. The aim of the present study was to investigate the effects of an anterior bite plane during the night. For this purpose ten subjects underwent nocturnal sleep investigations by means of a telemetric system. A silicon force sensor was integrated into an anterior bite plane for continuous measurement of bite forces and of the frequency of occlusal contact with the plate. The occlusal forces exerted on the anterior bite planes ranged between 3 and 80 N. The average forces were 5.5-24 N. The number of occlusal contacts varied between 39 and 558, with forces of between 7 and 9 N being registered in most cases. Major interindividual differences were detected in the magnitude of the force as well as in bite frequency. The intraindividual pattern of arising occlusal forces showed an intermittent force effect. No significant differences were found with regard to gender or growth pattern. In subjects with removable appliances, no active intrusion of teeth is possible during the night owing to the small number of occlusal contacts. Due to the partially very high forces in fixed appliance therapy, the integration of an anterior bite plane has to be assessed as critical in patients with unfavorable root geometry or bruxism.

Observation of stretched single DNA molecules by Kelvin probe force microscopy

Lambda bacteriophage deoxyribonucleic acid (DNA) molecules stained with YOYO-1 were deposited and stretched on chemically modified Si(1 0 0) wafer and cover glass substrates. The Si(1 0 0) wafer with a natural oxide layer and the cover glass surface were first chemically modified by vapor phase chemisorption with mixed two organosilanes. DNA molecules were then aligned on the substrate surfaces by chemical and physical adsorption from an aqueous solution during molecular combing. The aligned DNA molecules were observed by Kelvin probe force microscopy and intermittent contact-mode atomic force microscopy (AFM) as well as fluorescence microscopy. Interaction between the stretched DNA molecules and the chemically modified Si(1 0 0) substrate surface was examined using these AFMs.

Symmetrically arranged quartz tuning fork with soft cantilever for intermittent contact mode atomic force microscopy

A self-sensing and -actuating probe for dynamic mode atomic force microscopy (AFM) based on a commercial quartz tuning fork and a microfabricated cantilever is presented. The U-shaped cantilever, exhibiting a sharp tip, is combined with the tuning fork in a symmetrical arrangement, such that each of the two legs of the cantilever is fixed to one of the prongs of the tuning fork. The tuning fork is used as an oscillatory force sensor. Its frequency and amplitude govern that of the tip vibration, while the cantilever determines the spring constant of the whole probe. The frequency of the tip vibration for AFM operations can be much higher than the resonance frequency of the cantilever. A probe comprising a silicon nitride cantilever (0.1 N/m) is used to image monoatomic terraces of graphite in the intermittent contact mode. A much softer cantilever (0.01 N/m) is used to analyze the topography of a microelectronic chip in the same mode. Moreover, a bacterial surface layer hexagonally packed intermediate layer of Deinococcus radiodurans is imaged in a buffer solution. The tip vibration was again generated by the tuning fork while the sample interaction was measured using the standard optical detection scheme in this experiment. These probes are suited for batch fabrication and assembly and, therefore, enlarge the applications for the tuning fork based AFM.

Mincer's Overtaking Point and the Lifecycle Earnings Distribution

In 1958 Jacob Mincer pioneered an important approach to understand earnings distribution. In the years since Mincer’s seminal work, he as well as his students and colleagues extended the original human capital model, reaching important conclusions about a whole array of observations pertaining to human wellbeing. This line of research explained why education enhances earnings; why earnings rise at a diminishing rate throughout one’s life; why earnings growth is smaller for those anticipating intermittent labor force participation; why men earn more than women; why whites earn more than blacks; why occupational distributions differ by gender; why geographic and job mobility predominate among the young; why unemployment is lower among the skilled; and why numerous other labor market phenomena occur. This paper surveys the answers to these and other questions based on research emanating from Mincer’s original discovery. In addition, this paper provides new empirical evidence regarding Mincer’s concept of the “overtaking age” – a topic not currently well explored in the literature. In this latter vein, the paper shows that Mincer’s original finding of a U-shaped (log) variance of earnings over the life cycle is upheld in recent data, both for the U.S. as well as at least seven other countries.

牽引療法により顔面骨の整復と同時に外傷性盲が回復した重症頭蓋顔面骨折の１例

We treated a patient who had serious visual disturbance (blindness) caused by severe cranial and facial fractures. The patient had right-sided blindness and no response to light before surgery.Eight days after injury, the patient underwent surgery. Continuous or intermittent traction force was applied by means of an elastic band and wire.Immediately after surgery, visual acuity was restored. At about 2 months, visual acuity was 1.0.The traction force method we used is effective for reducing some cranial and facial depressed fractures. In our patient, the optic nerve was decompressed effectively.

頬骨骨折手術における１工夫

Molar bone fractures are often associated with mid-face fractures. Many patients present with this condition. We treated a molar complex fracture by continuous or intermittent reduction force applied with a head frame. Reduction force was produced by traction with an elastic band and compression with a screw bar. Traction and compression force were applied concurrently to three dimensionally reduce the fracture. Force was adjusted with the elastic band and screw bar. This technique could three dimensionally manipulate large fragments and restore the continuity of each buttress. It is considered one of the ideal methods to treat fractures that are difficult to reduce with rigid or semi-rigid internal fixation plates.

Vibration-induced muscle fatigue, a possible contribution to musculoskeletal injury.

Localized muscle fatigue resulting from 30-min sustained and intermittent grip exertions of 5% maximal voluntary contraction (MVC) with and without hand-vibration exposure (10 Hz, 7 mm displacement amplitude) was investigated. Muscle fatigue was quantified by the magnitude of the twitch force elicited in the right flexor digitorum superficialis muscle of the long finger using the low-frequency fatigue (LFF) method. The influence of vibration in the sustained grip exertion condition exacerbates fatigue as seen with the reduction in twitch force 30-60 min post-work task. Intermittent low grip force exertion conditions with and without vibration exposure show negligible fatigue, suggesting the benefit of rest in the work cycle. Perception of muscle fatigue was dissociated from the objective measure of twitch force, suggesting that LFF was not perceived. The presence of LFF and the lack of perception of LFF may increase the risk for the development of musculoskeletal disorders. The findings of this study may apply to the design of the work cycles and tasks that require the use of vibratory tools.

Material anisotropy revealed by phase contrast in intermittent contact atomic force microscopy.

Phase contrast in intermittent-contact atomic force microscopy (AFM) reveals in-plane structural and mechanical properties of polymer monolayers. This is surprising, because measurements of nanoscale in-plane properties typically require contact mode microscopies. Our measurements are possible because the tip oscillates not just perpendicular but also parallel to the sample surface along the long axis of the cantilever. This lateral tip displacement is virtually universal in AFM, implying that any oscillating-tip AFM technique is sensitive to in-plane material properties.

Intermittent force in orthodontic tooth movement.

A single orthodontic activation lasting one hour can initiate tooth movement. The purpose of this study is to examine tooth movement, osteoclasts, and root resorption in rats following several one-hour activations. Rats (n = 144) were randomly assigned to intermittent (multiple activations of 1 hr/day), continuous, and sham appliances. Twelve rats were killed at 3, 5, 7, and 14 days. Tooth movement, osteoclasts, osteoclast %, and root resorption % were quantified. Continuous force moved molars mesially at days 3 and 14 (p < 0.05), but intermittent and sham did not. Intermittent and continuous force increased osteoclast numbers at days 3, 5, and 7 (p < 0.05). Continuous force increased osteoclast surface on days 3 and 14 (p < 0.05). Continuous force increased root resorption at days 5, 7, and 14 (p < 0.05). These results demonstrate that orthodontic force for one hour in 24 stimulates osteoclasts at compression sites but does not stimulate tooth movement or root resorption.

Tip-sample interaction in tapping-mode scanning force microscopy

Tip-sample interaction in intermittent contact scanning force microscopy, also called tapping mode, is experimentally studied to determine under which conditions tip-sample contact is established. Force vs distance curves are made while the cantilever is oscillating at its resonance frequency. Cantilevers with different force constants driven at different oscillation amplitudes have been used. In addition, samples with different hardness, such as silicon oxide, glass, and highly orientated pyrolytic graphite were taken as sample surface. From the analysis of the data we conclude that by choosing appropriate operating conditions, tip-sample contact can be avoided. This operating regime is of general interest in scanning force microscopy, since it allows imaging of even the softest samples.

Do Casual Workers Find Permanent Full‐Time Employment? Evidence from the Australian Youth Survey

The growth of casual employment in Australia is sometimes viewed with concern. Such ‘non‐standard’ forms of employment are often associated with intermittent labour force attachment, underemployment and low income. In this paper, we use data from the Australian Youth Survey to analyze the transition from casual work to full‐time permanent jobs. In the short term, gender, employer‐provided training and the receipt of government benefits are among the more important factors affecting the transition. However, these factors are less important in the long term. Overall, the results suggest that casual employment may be more of a ‘stepping stone’ than a ‘dead‐end’.

Tunneling spectroscopic study of hydrogenase Langmuir–Blodgett film

Hydrogenase Langmuir–Blodgett films from Thiocapsa roseopersicina were prepared on gold-coated mica substrates using 20 mer of poly- l-lysine, which stabilizes the enzyme and improves the protein transfer. Scanning tunneling microscopy and intermittent contact mode atomic force microscopy were used to observe the films and to determine that the single hydrogenase–hexagonal complex was laid horizontally to the gold surface. Tunneling spectroscopy of the hydrogenase complex demonstrated the diodelike current-voltage characteristics. The rectification of the tunneling current might be ascribed to the alignment of cofactors, a nickel atom and iron sulfur clusters of the hydrogenase.

Mechanical stimulation of tissue repair in the hydraulic bone chamber.

A hydraulically activated bone chamber model was utilized to investigate cellular and microstructural mechanisms of mechanical adaptation during bone repair. Woven trabecular bone and fibrotic granulation tissue filled the initially empty chambers by 8 weeks postimplantation into canine tibial and femoral metaphyses. Without mechanical stimulation, active bone remodeling to lamellar trabecular bone and reconstitution of marrow elements were observed between 8 and 24 weeks. In subsequent loading studies, the hydraulic mechanism was activated on one randomly chosen side of 10 dogs following 8 weeks of undisturbed bone repair. The loading treatment applied an intermittent compressive force (18 N, 1.0 Hz, 1800 cycles/day) for durations of a few days up to 12 weeks. Stereological analysis of three-dimensional microcomputed tomography images revealed an increase in trabecular plate thickness and connectivity associated with the loaded repair tissue microstructure relative to unloaded contralateral controls. These microstructural alterations corresponded to an over 600% increase in the apparent modulus of the loaded bone tissue. A significant increase in the percentage of trabecular surfaces lined by osteoblasts immunopositive for type I procollagen after a few days of loading provided further evidence for mechanical stimulation of bone matrix synthesis. The local principal tissue strains associated with these adaptive changes were estimated to range from approximately -2000 to +3000 mustrain using digital image-based finite element methods. This study demonstrates the sensitivity of bone tissue and cells to a controlled in vivo mechanical stimulus and identifies microstructural mechanisms of mechanical adaptation during bone repair. The hydraulic bone chamber is introduced as an efficient experimental model to study the effects of mechanical and biological factors on bone repair and regeneration.

Masticatory muscle pain before, during, and after treatment with orthopedic protraction headgear: a pilot study.

Protraction headgear has been used in conjunction with a palatal expansion appliance to correct Class III malocclusion with maxillary deficiency and/or mandibular prognathism. In general, 800 gm of orthopedic force is used to protract the maxilla, and 75% of this force is transmitted to the temporomandibular joint (TMJ) area via the mandible. The effect of this heavy intermittent force on the TMJ has not been reported in the literature. The objectives of this study were to determine the level of masticatory muscle pain and EMG activity in patients treated with maxillary protraction headgear. Ten patients with skeletal Class III malocclusion whose treatment plan called for maxillary protraction headgear treatment participated in this study. Nocturnal masticatory muscle activity was determined using a portable electromyographic (EMG) recording device. Subjects wore the EMG device 14 nights before treatment, 14 nights during treatment, and 14 nights 1 month after active treatment. Masticatory muscle pain level was determined by muscle palpation, scored on a scale of 0 to 3 each period, according to the method of Gross and Gale. The examiner followed a sequence outlined by Burch to examine the masticatory muscles. Results showed no significant differences for masticatory muscle activities before, during, and after treatment. Only a few patients experienced level 1 masticatory pain during treatment. None of the patients experienced masticatory muscle pain 1 month after treatment. These results demonstrate no significant increase in masticatory muscle activity or muscle pain associated with orthopedic treatment using maxillary protraction headgear.

Influences of handgrip on shoulder muscle activity.

Four shoulder muscles (the supraspinatus, the infraspinatus, the middle portion of the deltoid and the descending part of the trapezius muscle) were examined using electromyography (EMG) in abducted and flexed arm positions, in nine subjects who had no history of illness from arm or shoulder. The subjects were asked to supply an intermittent isometric handgrip force of 30% and 50% of maximal voluntary contraction, in a total of eight different arm positions. The EMG activity with and without hand activity was compared in all positions. There was a statistically significant increase in the EMG activity in the supraspinatus muscle in humeral flexion from and above 60 degrees. In the infraspinatus muscle the changes were less; a significant decrease was however noticed in abduction. In the deltoid muscle there was a significant decrease with hand activity in flexion from and above 90 degrees. There was no statistically significant alteration regarding the EMG activity of the trapezius muscle. The result of this study implies that high demands on handgrip force, particularly while using hand tools in elevated arm positions, adds further to the already high load on some shoulder muscles. This factor should be considered in the design of manual work and in the places of work.

Intermittent compression stimulates cartilage mineralization.

The effects of intermittent hydrostatic compressive force (ICF; 13 kPa applied at 0.3 Hz frequency), as a substitute for moderate loading in vivo, on ossifying bone organ cultures, were evaluated by means of (histo)-morphometry. In earlier studies, biochemical tests have shown an increased 45Ca intake and an increased alkaline phosphatase activity in bone organ cultures that received ICF, suggesting that ICF promoted matrix mineralization. The purpose of this study was to examine whether an effect of ICF on mineralization can be described by means of histomorphometrical analysis. Fetal mouse metatarsal bone rudiments were cultured for 5 days in serum-free medium, with (experimental) or without (control) ICF. Linear measurements taken during culture demonstrated that the dark zone in the center of the rudiment, representing mineralized hypertrophic cartilage, became significantly longer in the group that received ICF when compared with the control group. This finding was in conformation with the former studies. Histological sections of the rudiments, stained with Goldner's trichrome method were used to study changes at the cellular level and to describe the position and relative amount of mineralizing cartilage matrix (defined as Goldner-positive matrix [GPM]). Histomorphometry demonstrated that ICF treatment significantly increased the length of the hypertrophic cartilaginous zone and enhanced the amount of GPM between the mineralizing hypertrophic chondrocytes. However, the total length of the zone containing GPM was not increased, nor was the future bone collar, consisting of a thin osteoid seam, lengthened by ICF. These data indicate that the cellular processes involved in chrondrocyte hypertrophy were accelerated by ICF, as well as the extracellular processes leading to matrix mineralization. The study supports the earlier conclusion that embryonic bone rudiments are sensitive to mechanical stimulation and that moderate loading promotes their ossification in vitro.