SEARCH · Search PubMed

Results for “Compressive Strength”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,567 records · Page 87Linked to original sources

PubMed2002

Fractured teeth bonded with dentin adhesives with and without unfilled resin.

Fractured incisors were restored by reattaching the fragment to the remaining tooth structure. For this purpose, seven dentin adhesive systems were used with and without an unfilled resin (Heliobond) and the strength of the restored teeth was tested at a cross-head speed of either 1 or 500 mm/min. The hypothesis was that the strength of the reattachment would be higher when an unfilled resin was used. The dentin adhesive systems were Prime & Bond NT (PB), Excite (EX), One-Step (OS), PQ1 (PQ), SingleBond (SB), Optibond Solo Plus (OS), and an experimental adhesive (GL). Statistical analysis revealed that with all adhesives except EX, a significantly greater mean fracture strength was achieved when the adhesives were used with the resin (Heliobond). Furthermore, with all adhesives except PB, there was a significantly lower mean fracture strength when tested at 500 mm/min than at 1 mm/min. All the tested adhesives except EX should be used with an unfilled resin when restoring fractured teeth by reattachment.

Acrylates↗

PubMed2003

Fracture strength of cusp replacing resin composite restorations.

PURPOSE: To assess the influence of an additional shoulder preparation on the fracture strength of a cusp-replacing direct resin composite restoration in a premolar that previously had an amalgam MOD restoration followed by fracture of a cusp. MATERIALS AND METHODS: Two preparation designs were tested. In extracted sound premolars an MOD amalgam cavity was simulated followed by fracture of a cusp (Group A). Group B was the same as Group A but a shoulder was added along the cervical outline of the preparation. As a control group, cusp fracture was simulated but no MOD amalgam cavities were prepared. For each group, 14 preparations were made using a copy milling technique. All 42 preparations were restored using a direct resin composite restoration technique. Restorations were loaded until fracture. RESULTS: The fracture strength of the preparation with shoulder was not significantly different from the preparation without the shoulder. The fracture strength of the preparations in the reference group, which had no resistance form, was significantly less than in Groups A and B (ANOVA, P<0.05).

Analysis of Variance↗

PubMed2006

Mechanical behavior of quartz fiber reinforced epoxy resins for teeth restoration.

In this work composite materials, based on quartz fibers and epoxy resins, were employed with the aim to restore damaged teeth. The composite materials were chosen because they show biomechanical features very similar to that of the dentine, the main constituent of the tooth. Extracted teeth were rebuilt with two different restorative procedures: in the first, the composite material was pre-formed in a conical trunk shape abutment (PA) and then bonded to a fiber quartz post with a dental bonder. In the second rebuilt system the abutment was prepared by cross linking the resin on the fiber quartz post with a halogen lamp (CRA). The restored teeth were then mechanically tested and observed with a Scanning Electron Microscope (SEM) with the aim to study the interaction between the reconstructive materials. Wetting and roughness measurements were also carried out in order to study the interface adhesion between the post and the abutments. Characterization analysis evidenced that the CRA restorative procedure improves the adhesion between the substitutive materials and shows higher fracture strength than the PA ones. Anyway both the rebuilt systems are able to support the masticator load. An explanation of the interfacial post-abutment interaction phenomenon is discussed.

Adhesiveness↗

PubMed2002

Laboratory strength of glass ionomer cement, compomers, and resin composites.

PURPOSE: The study evaluates the compressive, flexural, and diametral tensile strengths of 8 core build-up materials from different material classes (highly viscous glass ionomer cement, autocured resin composite, and compomers). MATERIALS AND METHODS: All materials were manipulated according to the manufacturers' recommendations for use as core materials. At a temperature of 23.0 +/- 1.0 degrees C the properties of compressive, diametral tensile and flexural strength were determined using a universal testing machine at 15 minutes, 1 hour, and 24 hours after material preparation. Using one-way analysis of variance (ANOVA), multiple mean value comparisons were performed to determine significant differences (p< or =.05) between the core restoration materials. RESULTS: The values for compressive strength varied from 40.3 +/- 5.2 MPa (compomer) to 237.4 +/- 37.3 MPa (autocured resin composite) for the 3 measurement times. At 15 minutes, 1 hour, and 24 hours after first mixing, the ANOVA showed significant differences (p < or =.05) between the resin composite Core Paste and all of the other materials. Diametral tensile strengths ranged from 5.5 +/- 1.1 MPa for glass ionomer cement to 39.1 +/- 2.9 MPa for composite core material. Three-point flexural strength showed values ranging from 12.1 +/- 2.5 MPa for glass ionomer cement to 92.1 +/- 9.7 MPa for compomer between the 3 measurement times. CONCLUSIONS: Setting time influences the mechanical properties of the materials tested in this study. Autopolymerizing resin composite Core Paste demonstrated greater compressive and flexural strengths at the 3 measurement times than the other materials tested. Reinforced composites, in comparison to the autocured resin composites, yielded no improvement in tensile strength. Flexural and tensile strengths of the glass ionomer cement were lower than those of autocured resin composites and compomers.

Analysis of Variance↗

PubMedDate not supplied

Biomechanical study of pedicle screw fixation in severely osteoporotic bone.

BACKGROUND CONTEXT: Obtaining adequate purchase with standard pedicle screw techniques remains a challenge in poor quality bone. The development of alternate insertion techniques and screw designs was prompted by recognition of potential fixation complications. An expandable pedicle screw design has been shown to significantly improve fixation compared to a conventional screw in poor quality bone. PURPOSE: The purpose of this study was to determine if polymethylmethacrylate (PMMA) bone cement augmentation of an expandable pedicle screw can further improve fixation strength compared to the expandable screw alone in severely osteoporotic bone. A technique for cement insertion into the pedicle by means of the cannulated central portion of the expandable screw is also described. STUDY DESIGN: The axial pullout strength, stiffness and energy absorbed of cemented and noncemented expandable pedicle screws was determined in cadaveric vertebrae. METHODS: Twenty-one fresh unembalmed vertebrae from the thoracolumbar spine were used. Radiographs and bone mineral density measurements (BMD) were used to characterize bone quality. Paired cemented and noncemented pedicle screw axial pullout strength was determined through mechanical testing. Mechanical pullout strength, stiffness and energy to failure was correlated with BMD. RESULTS: Overall, there was a 250% increase in mean pullout strength with the cemented expandable screw compared with a noncemented expandable screw including a greater than twofold increase in pullout strength in the most severely osteoporotic bone. The mean stiffness and energy absorbed to failure was also significantly increased. A cemented conventional screw achieved a pullout strength similar to the noncemented expandable screw. CONCLUSIONS: PMMA cement augmentation of the expandable pedicle screw may be a viable clinical option for achieving fixation in severely osteoporotic bone.

Aged↗

PubMed2006

Effect of hydroxypropyl cellulose (HPC) on dissolution rate of hydrochlorothiazide tablets.

Hydrochlorothiazide (HCTZ) 60 mg strength tablets containing commonly used excipients and hydroxypropyl cellulose, marketed as either Klucel-EF (HPC, NF from Hercules, USA) or HPC-L (HPC, NF from Nippon Soda, Japan), as a binder were manufactured using identical aqueous wet granulation process. The tablets containing Klucel-EF as a binder exhibited higher dissolution rates than those manufactured using HPC-L. The granulations containing Klucel-EF or HPC-L showed no significant differences in compressibility and compactibility based on analysis performed using the Instron-Stress-Strain Analyzer. Both HPC grades met NF specifications and there were no differences for the NF test results in the certificates of analysis by their respective vendors. Further evaluation of both HPC grades indicated that the cloud point values for Klucel-EF and HPC-L in water were 39(+/- 1) and 48 degrees C, respectively. The differences in cloud points of Klucel-EF and HPC-L were correlated to the differences in the percent hydroxypropoxy content and the degree of molecular substitution, which were higher for Klucel-EF than for HPC-L. These structural features make Klucel-EF less hydrophilic. Since the cloud point of Klucel-EF was similar to the dissolution medium temperature of 37(+/- 2) degrees C, it may present a less viscous layer surrounding the HCTZ granules enabling faster dissolution of the drug.

Cellulose↗

PubMed2004

A new selective estrogen receptor modulator HMR-3339 fully corrects bone alterations induced by ovariectomy in adult rats.

The selective estrogen receptor modulator (SERM) raloxifene has been shown to reduce the risk of vertebral fracture, but without significant effect on nonvertebral fractures. However, there is a need for SERMs capable of improving mechanical competence and reducing the risk of fractures at multiple skeletal sites, with minimal side effects. We investigated the effects of a new steroidal SERM, HMR-3339, compared to raloxifene, on bone strength and its determinants (BMD, microarchitecture, dimensions) at various skeletal sites (lumbar spine, tibia, and femur) of adult ovariectomized rats in both prevention and intervention protocols. In a prevention study, HMR-3339 and raloxifene treatments fully prevented alterations of bone strength. In an intervention protocol, where treatment was started 8 weeks after ovariectomy, HMR-3339 fully restored mechanical properties by influencing both areal BMD and outer diameter. This effect was observed at skeletal sites formed of cancellous and cortical bone or of cortical bone only. In contrast, raloxifene positively influenced structures containing mainly cancellous bone. In HMR-3339-treated rats, IGF-I plasma levels were higher than in ovariectomized controls; this was not observed with raloxifene. In conclusion, these results indicate that HMR-3339 increased not only bone mineral mass, but also restored bone mechanical strength at multiple sites in adult osteoporotic rats. In contrast to raloxifene, HMR-3339 also influenced skeletal sites predominantly formed of cortical bone.

Animals↗

PubMed1997

Why do shear bond tests pull out dentin?

It is widely accepted that a dentin shear bond test which pulls out dentin must mean that the adhesive strength is superior to the cohesive strength of the dentin. Using numerical modeling techniques, Van Noort et al. (1988, 1989) and DeHoff et al. (1995) alerted the scientific community that there were massive stress concentrations in the familiar dentin bond test. It is not inconceivable that these localized high tensile stresses could initiate cracks which diverge monolithically into dentin, leaving the interface unchallenged. To test this hypothesis, we developed a failure accumulation simulation program which determined localized failure interactively "on the fly" with a finite element solver, and also included brittle behavior, adhesive and cohesive failure, stochastic response, and dynamic remeshing. All of the familiar dentin bond variables were included in the simulation. A parallel experimental dentin bond test validation was run, and the fractography was examined in the scanning electron microscope for mode of failure. The simulation confirmed the tensile monolithic fracture hypothesis. It is also confirmed that dentin pull-out was partly due to the biomechanics of the test and did not necessarily mean superior adhesive strength or even that the cohesive strength of the dentin was reduced. There is clear need for a new technology for the evaluation of biological interfaces, and the present work has shown the vital role of numerical modeling in the interpretation of such experimental procedures.

Adhesiveness↗

PubMed2005

Fabrication using a rapid prototyping system and in vitro characterization of PEG-PCL-PLA scaffolds for tissue engineering.

In the field of tissue engineering new polymers are needed to fabricate scaffolds with specific properties depending on the targeted tissue. This work aimed at designing and developing a 3D scaffold with variable mechanical strength, fully interconnected porous network, controllable hydrophilicity and degradability. For this, a desktop-robot-based melt-extrusion rapid prototyping technique was applied to a novel tri-block co-polymer, namely poly(ethylene glycol)-block-poly(epsilon-caprolactone)-block-poly(DL-lactide), PEG-PCL-P(DL)LA. This co-polymer was melted by electrical heating and directly extruded out using computer-controlled rapid prototyping by means of compressed purified air to build porous scaffolds. Various lay-down patterns (0/30/60/90/120/150 degrees, 0/45/90/135 degrees, 0/60/120 degrees and 0/90 degrees) were produced by using appropriate positioning of the robotic control system. Scanning electron microscopy and micro-computed tomography were used to show that 3D scaffold architectures were honeycomb-like with completely interconnected and controlled channel characteristics. Compression tests were performed and the data obtained agreed well with the typical behavior of a porous material undergoing deformation. Preliminary cell response to the as-fabricated scaffolds has been studied with primary human fibroblasts. The results demonstrated the suitability of the process and the cell biocompatibility of the polymer, two important properties among the many required for effective clinical use and efficient tissue-engineering scaffolding.

Adult↗

PubMed2005

The processing, mechanical properties and bioactivity of zinc based glass ionomer cements.

The suitability of Glass Ionomer Cements (GICs) for use in orthopaedics is retarded by the presence in the glass phase of aluminium, a neurotoxin. Unfortunately, the aluminium ion plays an integral role in the setting process of a GIC and its absence is likely to hinder cement formation. However, zinc oxide, a bacteriocide, can act both as a network modifying oxide and an intermediate oxide in a similar fashion to alumina and so ternary systems based on zinc silicates often have extensive regions of glass formation. The purpose of this research was to produce novel GICs based on calcium zinc silicate glasses and to evaluate their rheological, mechanical and biocompatible properties with the ultimate objective of developing a new range of cements for skeletal applications. The work reported shows that GICs based on two different glasses, A and B (0.05CaO.0.53ZnO.0.42SiO2 and 0.14CaO.0.29ZnO.0.57SiO2, respectively), exhibited handling properties and flexural strengths comparable to conventional GICs. Upon immersion in simulated body fluid of a GIC based on glass B, an amorphous calcium phosphate layer nucleated on the surface of the cement indicating that these cements are bioactive in nature.

Aluminum↗

PubMed2002

Investigations into the stabilisation of drugs by sugar glasses: I. Tablets prepared from stabilised alkaline phosphatase.

The aim of this study was to investigate the formulation of sugar glass stabilised alkaline phosphatase from bovine intestine (BIAP) into tablets. Two major subjects of tablet formulation were investigated. First, the compaction behaviour of the inulin sugar glass was investigated. Secondly, the effect of the compaction process on the physical stability of sugar glass stabilised BIAP was investigated, comparing inulin and trehalose glass. The tabletting properties of freeze-dried inulin without BIAP were studied first. Freeze-dried inulin conditioned at either 20 degrees C/0% relative humidity (RH) or 20 degrees C/45% RH was compacted at various pressures. As expected, the yield pressure of the material conditioned at 0% RH was higher (68 MPa) than after conditioning at 45% RH (39 MPa). Tablets made of the material stored at 0% RH showed severe capping tendency, especially at high compaction pressures. In contrast, material conditioned at 45% RH gave tablets without any capping tendency and a friability of less than 1%. Sugar glasses of BIAP and either inulin or trehalose were prepared by freeze-drying (BIAP/sugar 1/19 (w/w)). The material was subsequently compacted. Tablets and powders were stored at 60 degrees C/0% RH. The activity of the incorporated BIAP was measured at various time intervals. It was found that inulin was by far superior to trehalose as stabiliser of BIAP in tablets. The poor stabilising capacities of trehalose after compaction are explained by crystallisation of trehalose induced by the compaction process and moisture in the material. The results clearly show that inulin is an excellent stabiliser for BIAP. The tabletting properties are adequate, showing sufficient tablet strengths and low friability. Furthermore, the good (physical) stability of inulin glass with respect to exposure to high relative humidities makes it practical to work with.

Alkaline Phosphatase↗

PubMed2003

Structure and function of the temporomandibular joint disc: implications for tissue engineering.

The temporomandibular joint (TMJ) disc is a little understood structure that, unfortunately, exhibits a plethora of pathologic disorders. Tissue engineering approaches may be warranted to address TMJ disc pathophysiology, but first a clear understanding of structure-function relationships needs to be developed, especially as they relate to the regenerative potential of the tissue. In this review, we correlate the biochemical content of the TMJ disc to its mechanical behavior and discuss what this correlation infers for tissue engineering studies of the TMJ disc. The disc of the TMJ exhibits a somewhat biconcave shape, being thicker in the anterior and posterior bands and thinner in the intermediate zone. The disc, which is certainly an anisotropic and nonhomogeneous tissue, consists almost entirely of type I collagen with trace amounts of type II and other types. In general, collagen fibers in the intermediate zone appear to run primarily in an anteroposterior direction and in a ringlike fashion around the periphery. Collagen orientation is reflected in higher tensile stiffness and strength in the center anteroposteriorly than mediolaterally and in the anterior and posterior bands than the intermediate zone mediolaterally. Tensile tests have shown the disc is stiffer and stronger in the direction of the collagen fibers. Elastin fibers in general appear along the collagen fibers and most likely function in restoring and retaining disc form after loading. The 2 primary glycosaminoglycans of the disc by far are chondroitin sulfate and dermatan sulfate, although their distribution is not clear. Compression studies are conflicting, but evidence suggests the disc is compressively stiffest in the center. Only a few tissue engineering studies of the TMJ disc have been performed to date. Tissue engineering studies must take advantage of existing information for experimental design and construct validation, and more research is necessary to characterize the disc to create a clearer picture of our goals in tissue engineering the TMJ disc.

Compressive Strength↗

PubMed2003

In vitro comparison of orthodontic band cements.

The aim of the study was to compare the mean retentive strength of microetched orthodontic bands cemented to extracted human third molars with a modified composite, a resin-modified glass ionomer cement, and a conventional glass ionomer cement. The mode of band failure and amount of cement remaining on the tooth at deband were also assessed. Finally, survival time of bands with each cement was assessed with simulated mechanical stress in a ball mill. Ninety banded specimens were used to assess retentive strength, and another 30 banded specimens were used to assess survival time. The mean retentive strength of the modified composite (0.415 MPa) was significantly less than that of either the resin-modified (1.715 MPa) or the conventional glass ionomer cement (1.454 MPa; P <.001). Specimens failed predominantly at the cement-enamel interface. The amount of cement remaining on the tooth at deband differed significantly between bands cemented with the resin-modified cement and those cemented with the conventional glass ionomer cement (P <.05). Mean survival time of bands cemented with the resin-modified glass ionomer cement (14.3 hours) was significantly longer (P <.01) than for bands cemented with the conventional glass ionomer cement (9.9 hours) but did not differ significantly from that of bands cemented with the modified composite (11.1 hours; P >.05). Orthodontic bands cemented with the modified composite appear to have a significantly lower mean retentive strength than bands cemented with resin-modified or conventional glass ionomer cement, but mean survival time did not differ significantly for bands cemented with modified composite or resin-modified glass ionomer.

Acrylic Resins↗

PubMed2004

Anatomical and biomechanical investigations of the iliotibial tract.

Divergent descriptions of the anatomic location and biomechanical function of the iliotibial tract (IT) can be found in the literature. This study attempted to obtain exact data regarding the anatomic course and material characteristics including the biomechanical properties of this structure. The following were its aims: (1) anatomical investigations of the IT; (2) mechanical properties of the IT; (3) femoral head centralizing force of the IT and subligamentous forces in the height of the greater trochanter in different joint positions by using a custom-made measuring prosthesis and a subligamentous positioned sensor; (4) construction of a finite element model of the proximal femur including the IT and measuring the femoral neck angle under variation. The hip joints and IT in a total of 18 unfixed corpses were evaluated. We studied the anatomic relationship to surrounding structures, as well as the material properties with the help of tensile strength testing utilizing an uniaxial apparatus. During the test, a load-displacement curve was registered, documenting the maximum load and deformation of the IT. To measure the subligamentous pressure at the height of the greater trochanter, a custom-made sensor with a power-recording instrument was constructed. Furthermore, an altered hip prosthesis with a pressure gauge at the height of the femoral neck was used to measure the forces which are directed at the acetabulum. The investigations were done in neutral-0 position and ab/adduction of the hip joint of the unfixed corpse. In addition, we varied the femoral neck angle between 115 degrees and 155 degrees in 5 degrees steps. To confirm the subligamentous forces, we did the same measurements intraoperatively at the height of the greater trochanter before and after hip joint replacement in 12 patients. We constructed a finite element model of the proximal femur and considering the IT. The acquisition of the data was done at physiological (128 degrees), varus (115 degrees), and valgus (155 degrees) femoral neck angles. The influencing forces of the IT at the height of the greater trochanter and the forces at the femoral head or the acetabulum could be measured. Our anatomical investigations revealed a splitting of the IT into a superficial and a deep portion, which covers the tensor fasciae latae. The tensor fasciae latae has an insertion on the IT. The IT continues down the femur, passing over the greater trochanter without developing an actual fixation to the bone. Part of the insertion of the gluteus maximus radiates into the IT. The IT passes over the vastus lateralis and inserts at the infracondylar tubercle of the tibia or Gerdy's tubercle, at the head of the fibula, as well as at the lateral intermuscular septum. Portions also insert on the transverse and longitudinal retinaculum of the patella. Concerning the material properties of the IT, we found a structural stiffness of 17 N/mm extension on average (D = 17 N/mm). The subligamentous measurements at the height of the greater trochanter in the unfixed corpse and intraoperatively during hip joint replacement showed an increase of the forces during adduction and a decrease during abduction of the hip joint. We found thereby a maximum increase up to 106 N with 40 degrees adduction. Concerning the femoral neck angle, we can state that valgus leads to lower subligamentous forces and varus to higher subligamentous forces. The forces directed at the acetabulum, which were measured by the prosthesis with a sensor along the femoral neck, showed a decrease with varus angles and an increase with valgus angles. The highest force of 624 N was measured with 40 degrees adduction and an angle of 155 degrees. The finite element model of the proximal femur showed a sole hip joint-centralizing force of the IT of 655 N with a femoral neck angle of 128 degrees after subtraction of the gluteal muscle force and the body weight. At 115 degrees, we found an increase up to 997 N and a decrease to 438 N at 155 degrees. Concerning the resulting forces in the acetabulum, we found opposite forces in comparison with the force of the IT at the height of the greater trochanter: at 115 degrees, a femoral head-centralizing force of 1601 N; at 128 degrees, 2360 N; and at 155 degrees, 2422 N. By our investigations, we can approximately prove the hip joint-centralizing force of the IT. By variation of the femoral neck angle and the position of the hip joint, we can predict the subligamentous force of the IT and the resulting force at the femoral head or at the acetabulum. The intraoperative measurement of the subligamentous forces of the IT is a good monitoring mechanism for the persistent hip-centralizing function of the IT in the course of hip joint replacement. The surgeon has the opportunity to check the stability of the hip joint after replacement. The finite element model gives the opportunity to check the divergent relative strength by variation of the femoral neck angle and the tension of the IT. In this way, the changes in the forces induced by a displacement osteotomy could be estimated preoperatively.

Aged↗

PubMed2005

Three-point bending and acoustic emission study of adult rat femora after immobilization and free remobilization.

The experiment concerned effects of immobilization and remobilization on mechanical properties of femoral shaft. Twenty-four weeks old male rats were used: two groups (I3 and I3R4) with the right hindlimb immobilized for 3 weeks by taping, and one control (C). In I3R4 immobilization was followed by 4 weeks of free remobilization. Mechanical properties in three-point bending, mass, geometry, and mineralization of bone tissue were measured post mortem in both femora in I3 and I3R4 and in right femora in control. Acoustic emission signals (AE) were recorded during the bending test. The right femora in I3, I3R4 and C did not differ significantly in size, mass and mineralization (ANOVA). The differences were significant considering mechanical parameters and AE signals. In I3 yield bending moment and stiffness were lower (p=0.013 and 0.025) and deflection was larger (p=0.030) than in C. In I3R4 maximum bending moment, yield moment, stiffness and work to failure were lower than in C (p=0.013, 0.009, 0.032, and 0.005). Paired t-test showed that remobilization resulted in worsening of properties of right femora. Side-to-side differences in I3R4 were more pronounced than in I3. Moreover, AE signals from the right femora were more numerous and burst type than from the left. The results demonstrate that strength of bone decreases during the first period of free remobilization. The decrease is accompanied by a significant decrease of bone toughness. The AE data support the hypothesis that immobilization-related degradation of bone mechanical properties is associated with increasing brittleness of cortical bone tissue.

Animals↗

PubMed2005

Risk factors for noncontact ankle sprains in high school athletes: the role of hip strength and balance ability.

BACKGROUND: Ankle sprains are among the most common sports injuries. HYPOTHESIS: Poor balance as measured on a balance board and weakness in hip abduction strength are associated with an increased risk of noncontact ankle sprains in high school athletes. STUDY DESIGN: Cohort study; Level of evidence, 2. METHODS: One hundred sixty-nine high school athletes (101 male athletes, 68 female athletes) from football, men's basketball, men's soccer, women's gymnastics, women's basketball, and women's soccer were observed for 2 years. Balance in single-limb stance on an instrumented tilt board and hip flexion, abduction, and adduction strength (handheld dynamometer) were assessed in the preseason. Body mass, height, generalized ligamentous laxity, previous ankle sprains, and ankle tape or brace use were also documented. RESULTS: There were 20 noncontact inversion ankle sprains. Balance ability (P = .72), hip abduction strength (P = .66), hip adduction strength (P = .41), and hip flexion strength (P = .87) were not significant risk factors for ankle sprains. The incidence of grade II and grade III sprains was higher in athletes with a history of a previous ankle sprain (1.12 vs 0.26 per 1000 exposures, P < .05). A higher body mass index in male athletes was associated with increased risk (P < .05). The combination of a previous injury and being overweight further increased risk (P < .01). CONCLUSION: Balance as measured on a balance board and hip strength were not significant indicators for noncontact ankle sprains. The apparent high injury risk associated with the combination of a history of a previous ankle sprain and being overweight in male athletes warrants further examination.

Adolescent↗

PubMed2001

[Micromechanical characteristics of restoration stomatological materials and human dental enamel and dentin].

Polished sections of human teeth and 11 Russian and foreign restoration materials (silver amalgam, cements, and polymer-based materials) were studied with an MTI-3M microhardness meter. Microhardness immediately under loaded diamond indentor of the device, elastic and plastic deformations were evaluated. Dental enamel is characterized by the greatest microhardness. Inorganic filler essentially (3-fold) increases the microhardness of polymer-based material. Microhardness of dental tissues and restoration materials notably decreased as the strength of indentor loading, i.e. the depth of its submerging in material, increased. Dental enamel is characterized by the most elastic deformation; dentin approximates the enamel by this parameter, as well as some restoration materials (prodigy, degufil-H, degufil-SC) when exposed to the saliva.

Compressive Strength↗

PubMed2003

A novel liner locking mechanism enhances retention stability.

Acetabular liner retention of a novel design of liner locking was evaluated in static and cyclic endurance modes. The locking mechanism combines geometric form and accurate machining to give high conformity to the acetabular shell and minimise relative motion against the metal shell, minimising debris generation and escape or ingress. Using amended test liners with integral coupling, mean static pullout strength was determined to be 399+/-53 N and lever-out strength 28.03+/-2.8 N m. Cyclic loading of 5 N m for up to 10 million cycles caused no significant reduction in strength, no detectable fretting wear, and the sealing mechanism prevented particle access between the cup interior and the "effective joint space". The stability measured ensures secure and reliable in vivo retention of the liner, comparable with extant component designs using other liner locking mechanisms.

Compressive Strength↗