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At least 955 records · Page 53Linked to original sources
PubMed2004

Three-dimensional changes in the condyle during development of an asymmetrical mandible in a rat: a microcomputed tomography study.

A rapidly growing postnatal animal model was used to study changes in the calcified tissue of the mandibular condyle during altered muscle function. A maxillary occlusal splint was designed to shift the mandible laterally (left) during closure. Groups of 5 Wistar rats were killed at 5, 9, 15, 21, 30, and 40 weeks (n = 30), with an equal number of controls. The experimental animals developed shorter, asymmetrical mandibles compared with the control animals. The left condyle became larger and thicker than the right condyle. Microcomputed tomography assessment of the left and right condylar trabecular bone indicated that both had less bone volume than the control condyle. The right masseter muscle significantly lost fiber size and type IIA oxidative fibers, suggesting that the right masseter muscle was used with less tension development. In contrast, the left masseter maintained its fiber size and was similar to the control masseter fiber diameters. Comparison in the sequence of changes indicated that the morphologic changes occurred first in the ramus (age, 5 weeks), before the corpus (age, 15 weeks), and before changes in masseter fiber size and composition (age, 9 weeks). This study showed that both the mandible and the condyle modified their shape and size, as well as the trabecular bone of the condyle, during shifting of the mandible to one side as it closed.

Animals↗
PubMed2006

Physical properties of root cementum: part 8. Volumetric analysis of root resorption craters after application of controlled intrusive light and heavy orthodontic forces: a microcomputed tomography scan study.

INTRODUCTION: Intrusion is a critical type of orthodontic tooth movement in relation to external root resorption. Our aims in this prospective randomized clinical trial were to quantify, 3 dimensionally, the amount of root resorption when controlled light and heavy intrusive forces were applied to human premolars and to establish the sites where root resorption is more prevalent. METHODS: Fifty-four maxillary first premolars, orthodontically indicated for extraction from 27 patients (left and right maxillary first premolars from each), were intruded for 28 days with buccal and palatal beta-titanium-molybdenum alloy 0.017 x 0.025-in cantilever springs. The patients were randomly divided into 3 groups, and various levels of force were used: group 1, heavy force (225 g) on 1 side and control force (0 g) on the contralateral side; group 2, light force (25 g) on 1 side and control force (0 g) on the contralateral side; group 3, light force (25 g) on 1 side and heavy force (225 g) on the contralateral side. After the experimental period, the teeth were extracted under a strict protocol to prevent root surface damage and analyzed by using a microcomputed tomography scan x-ray system (SkyScan-1072, Skyscan, Aartselaar, Belgium) and specially designed software for direct volumetric measurements. RESULTS: The volume of the root resorption craters after intrusion was found to be directly proportional to the magnitude of the intrusive force applied. The results showed that the control group had fewer and smaller root resorption craters, the light force group had more and larger root resorption craters than the control group, and the heavy force group had the most and the largest root resorption craters of all groups. A trend of linear increase in the volume of the root resorption craters was observed from control to light to heavy groups, and these differences were statistically significant. The mean volumes of the resorption craters in the light and heavy force groups were 2 and 4 times greater than in the control groups, respectively. The mesial and distal surfaces had the greatest resorption volume, with no statistically significant difference between the 2 surfaces.

Adolescent↗
PubMed2006

Quantitative morphometric evaluation of critical size experimental bone defects by microcomputed tomography.

Our aim was to show that microcomputed tomography is a useful tool for acquiring high-resolution three-dimensional tomographic images to assess bone healing, the interface with materials, and the biocompatibility of bone substitutes. Acquired images can be used for non-invasive quantitative morphometric analysis of regenerating bone, leaving the option for conventional histology to be an adjunct used at defined intervals. The temporal characterisation of the mineralisation of bone potentially has a critical role in the understanding of the dynamics of mineralisation of healing bone. This has applications both for degradable and bioactive materials and for pharmaceutical products that act on bone. Formal validation of this promising new technique will be a critical part of continuing studies.

Animals↗
PubMed2004

Risedronate preserves bone architecture in postmenopausal women with osteoporosis as measured by three-dimensional microcomputed tomography.

The deterioration of trabecular microarchitecture induced by elevated bone turnover is increasingly recognized as a factor in the pathogenesis of osteoporotic fractures. We investigated the effect of the reduction of turnover with risedronate on trabecular architecture in postmenopausal women with osteoporosis. Iliac crest bone biopsy specimens taken before and after 3 years of treatment from patients receiving risedronate 5 mg daily (n = 21) or placebo (n = 17) were analyzed using 3-D microcomputed tomography. We found a significant correlation between baseline bone turnover and bone loss in the placebo group, providing evidence that higher turnover induced higher bone loss leading to a greater degree of architectural degradation. When patients were classified into two groups based on baseline bone turnover (MS/BS less than or greater than the median value for the entire cohort), significant decreases in trabecular bone volume (BV/TV, P = 0.009) and trabecular thickness (Tb.Th*, P = 0.008) and an increase in marrow star volume (Ma.St.V, P = 0.008), a measure of trabecular porosity, were observed in the higher turnover (MS/BS> median) placebo-treated patients. The trabecular structure shifted from plates to rods as shown by an increase in structure model index (SMI, P = 0.028) and bone surface to bone volume ratio (BS/BV, P = 0.006). The changes from baseline in the lower turnover (MS/BS<median) placebo patients were variable and not statistically significant. In the risedronate group, the bone volume and the architectural parameters did not change significantly from baseline values in either the higher or the lower turnover groups. Comparing the pair-wise changes from baseline in the higher turnover group, the placebo group experienced decreases in BV/TV (P = 0.071) and Tb.Th* (P = 0.012), and increase in Ma.St.V (P = 0.043), compared to the risedronate-treated women. Also, in comparison to the risedronate group, the trabecular structures in the placebo group were more rod-like, indicated by higher SMI (P = 0.009) and BS/BV (P = 0.02). The results demonstrated that trabecular architecture deteriorated significantly in the placebo-treated women who had higher bone turnover at baseline, and this deterioration was prevented by 3 years of risedronate treatment, presumably because of the reduction in bone turnover. The preservation of architecture may be a contributory mechanism by which risedronate reduces the risk of vertebral fractures in osteoporotic women.

Aged↗
PubMed2004

Analysis of three-dimensional microarchitecture and degree of mineralization in bone metastases from prostate cancer using synchrotron microcomputed tomography.

Bone architecture and mineralization are generally considered to be important components of bone quality, and determine bone strength in conjunction with bone mineral density. Although the features of bone quality have recently been studied under conditions in which bone density decreases, such as osteoporosis, little is known in osteosclerotic diseases. In this study, we compared the trabecular bone microarchitecture and degree of mineralization between osteoblastic bone metastasis and degenerative osteosclerosis using synchrotron radiation microcomputed tomography (SR-microCT). Small cubes of lumbar vertebrae were excised postmortem from the sites of osteoblastic metastasis, degenerative osteosclerosis, and comparative sites of normal subjects without skeletal lesions. The samples were imaged at high spatial resolution (voxel size = 6 microm) using the SR-microCT system developed at the synchrotron facility (SPring-8), Hyogo, Japan. The three-dimensional (3D) image data were then analyzed for the morphological parameters and the degree of mineralization of bone (DMB). Trabecular bone in metastatic lesions showed a highly connected and isotropic network pattern compared with the normal samples. Although the trabecular surface was markedly irregular in osteoblastic metastases, no significant difference was found in the mean trabecular thickness (Tb.Th) between osteoblastic metastases and normal tissue. The DMB of trabeculae in metastatic lesions had a broader range and lower mean than that of the normal tissue. In contrast, trabecular bone in degenerative osteosclerotic lesions showed a similar degree of anisotropy (DA) and connectivity to the normal tissue, whereas the trabecular thickness was greater in the degenerative osteosclerotic lesions. No significant difference in DBM between degenerative osteosclerosis and normal tissue was detected. These results characterize the difference in bone quality between osteoblastic bone metastasis and degenerative osteosclerosis. Further study on the relationship between bone quality and bone strength in these osteosclerotic lesions would improve our understanding of the pathogenesis of bone fragility.

Adult↗
PubMed2005

Loading induces site-specific increases in mineral content assessed by microcomputed tomography of the mouse tibia.

Adaptation to mechanical loading has been studied extensively in cortical, but not cancellous bone. However, corticocancellous sites are more relevant to osteoporosis and related fracture risk of the hip and spine. We tested the hypotheses that adaptation in a long bone would be greater at cancellous than cortical sites and would depend on the term of daily in vivo cyclic axial loading. We applied compressive loads to the adolescent, 10-week old, male C57BL/6 mouse tibia to examine the skeletal response immediately prior to attainment of peak bone mass. Adaptation was quantified at the completion of either 2-week (n = 8) or 6-week (n = 12) loading terms by directly comparing volumetric bone mineral content between loaded and contralateral limbs by microcomputed tomography. The increase in mineral content was site specific with a greater response found in the corticocancellous proximal metaphysis (14%) than the cortical mid-shaft (2%) after 6 weeks of loading. Furthermore, bone volume fraction and average trabecular thickness of cancellous bone in the proximal tibia increased after 6 weeks by 15% and 12% respectively. Diaphyseal response was only evident proximal to the mid-shaft as indicated by an 8% increase in maximum principal moment of inertia. Both loading terms produced similar results for mineral content, volume fraction, and moments of inertia. Our finding that non-invasive loading increases the bone volume and fraction at a corticocancellous site by as much as 15% motivates exploring the use of mechanical loading to attain greater peak bone mass and inhibit osteoporosis.

Animals↗
PubMed1978

An inexpensive microcomputer-based stopped-flow data acquisition system.

A low-cost (less than $2,500) microcomputer-controlled data acquisition system for use with a stopped-flow instrument is described. Data acquisition, reduction, signal averaging, kinetic modeling, and plotting are performed under software control. Applications to biological and inorganic systems are presented.

Computers↗
PubMed1995

Microcomputed tomography: an advanced system for detailed endodontic research.

This study evaluated the value of microcomputed tomography (MCT) for use in endodontic research. Four periodontally involved highly calcified maxillary first molars were extracted and then scanned for evaluation by a MCT system. The teeth were then instrumented, and 2 of the 4 obturated before rescanning for comparison evaluation. Several capabilities of the MCT to advance endodontic research significantly were observed: the ability of the MCT to present accurately the external and internal morphologies of the tooth without tooth destruction; the possibility of showing changes over time in surface areas and volumes of tissues; the ability to assess area and volume changes after instrumentation or obturation; and the capability of evaluating canal transportation following instrumentation or instrumentation and obturation. The tremendous potential of this scientific tool was discussed.

Dental Pulp Calcification↗
PubMed2002

The influence of microcomputed tomography threshold variations on the assessment of structural and mechanical trabecular bone properties.

In this study, we investigate how morphological parameters and mechanical properties derived from microcomputed tomography (microCT) are affected by small errors in threshold value when variable bone structures and different bone volume fractions are involved. For this purpose, biopsies of vertebrae of 6-, 23-, and 230-week-old female pigs were scanned using microCT. For each specimen, five threshold values were determined within the range of thresholds that an observer could select realistically, in steps of 0.5%. The scans were converted to microfinite-element (microFE) models, used to determine the elastic moduli. A variation of 0.5% in threshold resulted in a 5% difference in bone volume fraction and 9% difference in maximal stiffness for bone cubes with a volume fraction of <0.15. When the volume fraction was >0.2, these differences were only 2% and 3%, respectively. For all bone cubes, the differences for trabecular thickness and bone surface density were <3%. The effects on morphological anisotropy and trabecular number were negligible for threshold variations of 0.5%. These findings suggest that threshold selection is important for the accurate determination of volume fraction and mechanical properties, especially for low bone volume fractions; the architectural directionality is less sensitive to changes in threshold.

Animals↗
PubMed1998

Analysis of trabecular microarchitecture of human iliac bone using microcomputed tomography in patients with hip arthrosis with or without vertebral fracture.

Iliac bone samples were obtained from 50 women with osteoarthrosis of the hip (50-80 years of age) during hip surgery for total hip joint replacement. After determining the resolution and threshold for the binary image, the two-dimensional (2D) and three-dimensional (3D) data of the trabecular structure were obtained in these iliac bone samples using microcomputed tomography (micro-CT). Conventional histomorphometry was then performed. Both 2D and 3D parameters of the trabecular structure were significantly correlated with the parameters of conventional histomorphometry (r = 0.63-0.86 in 2D analysis, and r = 0.60-0.77 in 3D analysis). The patients were classified into the non-spinal-fracture group (n = 36) and the spinal fracture group (n = 14). There was no significant difference in patient age between the two groups. The parameter values of bone mass, such as 2D fractional trabecular bone area and 3D fractional bone volume, and the values of trabecular number (Tb.N) in terms of both 2D and 3D analyses were significantly smaller, and those of trabecular separation (Tb.Sp) were significantly higher in the spinal fracture group than in the non-spinal-fracture group. Trabecular thickness (Tb.Th) values did not significantly differ between the two groups. There was no significant difference between 2D and 3D parameters in discriminating the spinal fracture group from the non-spinal-fracture group. However, 3D analysis demonstrated that the value of the bone surface to bone volume (BS/BV) ratio could discriminate between these two groups. These data demonstrated that micro-CT can evaluate the 3D structure of the human iliac bone, and that decreases in the parameters of the 3D-structure-related bone surface density as well as decreases in trabecular bone volume are related to osteoporotic fracture.

Aged↗
PubMed1999

Calibration of trabecular bone structure measurements of in vivo three-dimensional peripheral quantitative computed tomography with 28-microm-resolution microcomputed tomography.

It has recently been shown that high-resolution computed tomography and magnetic resonance imaging have the potential to assess information about the microarchitecture of bone in a noninvasive way. However, due to the limited spatial resolution of the in vivo measurements, the individual trabeculae are not depicted with their true thickness. Nevertheless, the spacing of the structural elements allows the assessment of trabecular number. In a previous publication, the ridge number density (RND) was introduced as a measure for this structural index. It can be extracted from high-resolution three-dimensional (3D) images of patients and shows a reproducibility of 1.6%. In this work the Ridge extraction procedure is compared to and calibrated with microcomputed tomography (microCT) measurements. Three-dimensional measurements of 15 bone biopsies are made with a 28-microm-resolution microCT scanner as well as with a 165-microm-resolution peripheral quantitative computed tomography (pQCT) scanner. For the latter, the same settings are used as for patient examinations. The 15 pairs of measurements are analyzed and the resulting structural indices are compared. The results show that structural indices such as trabecular number, mean thickness, and mean separation can be determined from the 3D pQCT data with an r2 of between 0.81 and 0.96 if the microCT data are taken as the gold standard. The calibration equation found for the bone volume fraction has an intercept of 0.04 and a slope of 0.86 (r2 = 0.98), and trabecular number as the main additional structural index shows a nonsignificant intercept and a calibration slope of 0.91 with the microCT. The calibration procedure can be used directly for patient examinations. Applied to time-series measurements it may be of value for monitoring and quantifying microarchitectural changes due to therapy or aging.

Adult↗
PubMedDate not supplied

Evaluation of the in vitro degradation of macroporous hydrogels using gravimetry, confined compression testing, and microcomputed tomography.

This study investigated the in vitro degradation characteristics of macroporous hydrogels based on poly(propylene fumarate-co-ethylene glycol) (P(PF-co-EG)). Four formulations were fabricated to test the effect of porosity and cross-linking density on the degradation of the resulting macroporous hydrogels. Macroporosity was introduced by the addition of sodium bicarbonate and ascorbic acid, the precursors of the carbon dioxide porogen, in the initiation system for the hydrogel cross-linking. Macroporous hydrogels with porosities of 0.80 +/- 0.03 and 0.89 +/- 0.03 were synthesized by the addition of sodium bicarbonate of concentrations 40 and 80 mg/mL and ascorbic acid of concentrations 0.05 and 0.1 mol/L, respectively. Poly(ethylene glycol) diacrylate (PEG-DA) was utilized as a cross-linker. The molecular weight between cross-links had a significant effect on weight loss after 12 weeks, where samples with M(C) of 1,880 +/- 320 synthesized with a P(PF-co-EG):PEG-DA ratio of 3:1 had a significantly greater mass loss due to degradation than those with M(C) of 1,000 +/- 100 synthesized with a P(PF-co-EG):PEG-DA ratio of 1:1. In contrast, porosity played a minimal role in determining the weight loss. Mechanical testing of the hydrogels under confined compression showed a decrease in compressive modulus over the degradation time for all formulations. In addition, an increase in hydrogel equilibrium water content and pore wall thickness was observed with degradation time, whereas the hydrogel porosity and surface area density remained invariant. The results from microcomputed tomography corroborated with the rest of the measurements and indicated a bulk degradation mechanism of the macroporous hydrogels.

Compressive Strength↗
PubMed1990

CHEMLEARN: microcomputer-based training for CHEMLINE, an alternative to formal classroom training.

CHEMLINE (CHEMical Dictionary OnLINE), the National Library of Medicine's online chemical dictionary file, is primarily used by librarians and information scientists to enhance the retrieval of bibliographic information associated with chemical substances. This paper will discuss CHEMLEARN, a microcomputer-based training program designed to provide inexpensive, easily accessible self-instruction as an alternative to formal classroom training in the use of CHEMLINE. CHEMLEARN allows novice users to learn at their own pace and with considerable program feedback. In addition, it provides the skilled searcher with a way to reinforce or recall previously learned search techniques without incurring online charges. CHEMLEARN may be used in place of formal training or as a precursor to or a refresher following formal training.

Chemical Phenomena↗
PubMed2000

A comparison of two nickel-titanium instrumentation techniques in teeth using microcomputed tomography.

AIM: The aim of the study was to compare the shaping of root canals by two nickel-titanium instrumentation techniques using microcomputed tomography (MCT). METHODOLOGY: Ten mandibular first molar teeth (30 canals) that had intact crowns and fully formed roots were scanned using MCT. Fifteen canals were instrumented using NiTiFlex hand files (Maillefer) using balanced force. The remainder were instrumented using prototype ProFile 0.04 Taper instruments (Dentsply) in a crown-down manner to an apical size ISO 25. The teeth were scanned again following instrumentation. The two instrumentation techniques were compared in a total of 27 canals. The area of dentine removed at predetermined levels (2.0, 3.0, 4.5, 6.0, 7.5 mm) from the apex was measured. Transportation and centring were recorded. Images constructed at these levels were compared with video images of equivalent physical sections created after the second scan. The volume of dentine removed in the apical 7.5 mm of the root canals of each tooth was calculated and the different techniques compared. Rendered three-dimensional images were used to assess the preparations qualitatively. The time taken for preparation was recorded. RESULTS: There was no significant difference between hand instrumentation with NitiFlex files and machine instrumentation with prototype ProFile 0.04 Taper instruments for any of the variables tested. CONCLUSIONS: Both techniques produced well centred and tapered preparations.

Dental High-Speed Technique↗
PubMed2005

Microcomputed tomography colonography for polyp detection in an in vivo mouse tumor model.

This study was initiated to evaluate the efficacy of negative contrast-enhanced microcomputed tomography (microCT) colonography for the noninvasive detection of colonic tumors in living mice. After colonic preparation, 20 anesthetized congenic mice were scanned with high-resolution microCT. Images were displayed by using commercial visualization software and interpreted by two gastrointestinal radiologists, who were unaware of tumor prevalence and findings at gross pathology. Two-dimensional multiplanar images were assessed by using a five-point scale to distinguish colonic tumors (polyps) from fecal pellets (5 = definitely a tumor, 4 = probably a tumor, 3 = indeterminate, 2 = probably not a tumor, 1 = definitely not a tumor). Gross pathologic evaluation of excised mouse colons served as the reference standard. Data analysis included dichotomizing results, with 1-2 indicating no tumor and 3-5 indicating tumor and also receiver operator characteristic curve analysis with area under the curve for threshold-independent assessment. A total of 41 colonic polyps in 18 of the 20 mice were identified at gross examination on necropsy, of which 30 measured 2-5 mm and 11 measured <2 mm in size. The pooled per-polyp sensitivity for lesions >2 mm was 93.3% (56/60). The pooled per-mouse sensitivity for polyps >2 mm was 97.1% (33/34). Pooled specificity for distinguishing fecal pellets from tumor was 98.5% (65/66). The combined area under the curve from receiver operator characteristic curve analysis was 0.810 +/- 0.038 (95% confidence interval, 0.730-0.890). These findings indicate that accurate noninvasive longitudinal monitoring of colon tumor progression or response to various therapies is now technically feasible in live mice by using this microCT colonography method.

Animals↗
PubMed1990

Can microcomputers help the problem drinker?

The evidence in favour of brief interventions and self-help materials for problem drinkers raises the possibility that microcomputer programmes can provide an effective and inexpensive treatment option in the addictions field. This paper reports on a controlled drinking computer programme currently in operation with drink driving offenders.

Journal Article↗
PubMed1981

Microcomputer assisted hematology quality control using a modified average of normals program.

A microcomputer based program package has been developed which utilizes a modified "average of normals" method to analyze data and monitor random and systematic error in the clinical hematology laboratory. The daily workload of normal patient values for leukocyte count, erythrocyte count, hemoglobin, mean corpuscular volume, prothrombin time, and activated partial thromboplastin time is entered through the keyboard and sorted by sex. The daily mean, standard deviation, standard error index, and F-ratio are then calculated for each test. Significant deviations from target values are automatically flagged. The system combines ease of data input with automatic statistical calculation, graphic display, and printout of the calculated data. The system has the capability of data analysis by shift, and incorporates cumulative sum, Trigg's tracking algorithm, and analysis of variance calculations. This statistical analysis had proven to be a sensitive indicator of random and systematic error in our laboratory and has allowed us to decrease the assay frequency of expensive commercial control material.

Computers↗
PubMed1994

DNA modeller: an interactive program for modelling stacks of DNA base pairs on a microcomputer.

DNA Modeller is a microcomputer program for interactively manipulating up to 20 bp in a DNA double helical arrangement. It calculates the van der Waals and electrostatic energies of base-base interactions using the AMBER potential, minimizes the energy with respect to the pair (buckle, propeller, opening, shear, stretch, stagger) and step (tilt, roll, twist, shift, slide, rise) parameters, calculates lengths of the canonical hydrogen bonds between the complementary bases, and calculates interatomic distances between the successive base pairs. Input/output files are simple lists of the step and pair parameters or lists of the atom specifications (N1, C2, etc.) and their Cartesian coordinates (compatible with the Desktop Molecular Modeller*.mol files). The program is supplied with a readbrk utility which transforms PDB/NDB to the *.mol format readable by DNA Modeller. The DNA crystal structures deposited in the PDB or NDB databases can thus be analyzed, and their bases visualized and interactively manipulated. In addition, DNA Modeller can calculate the base pair and step geometrical parameters and interaction energies. A plotter utility creates wire mono or stereo pictures of the bases. This program is designed for IBM-compatible computers working under DOS or can run as a DOS application under MS Windows 3.x or Merge (SCO Unix DOS emulator).

Base Composition↗