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PubMed1993

Pressure sintering of apatite-collagen composite.

Preparation of a composite consisting of apatite and collagen was attempted. Starting from an aqueous solution of collagen, phosphoric acid, and calcium hydroxide suspension, an apatite (90wt%)-collagen (10wt%) composite of 1.75 g/ml in apparent density, with 2 GPa in Young's modulus, and 6.5 MPa in compression strength was synthesized at 40 degrees C, 200 MPa, successfully. It was found that the presence of liquid water in the system was essential for the sintering of the composite under high pressures. Without liquid water, the specimen that was pressure treated and brought in atmospheric pressure, broke into small pieces due to residual strain. The prepared composite could be cut by a razor blade, and was stable against immersion in water. The mean size of the apatite crystals in the composite was 10 nm in width and 40 nm in length.

Apatites↗
PubMedDate not supplied

Physical properties of fixed prosthodontic, resin composite luting agents.

This study determined and compared physical properties of six fixed prosthodontic resin composite luting agents and one control. Inorganic filler content, compressive strength, diametral tensile strength, film thickness, and Knoop hardness were determined. The amounts of filler and the physical properties varied widely among materials. One material, which contained a minimal amount of filler, underwent so much plastic deformation that its strengths could not be measured. All other materials demonstrated high strengths. The materials with the least filler demonstrated the least resistance to indentation. The material with the lowest film thickness had not set at the time of measurement, 10 minutes after mixing. Most materials had unacceptable film thicknesses. Only one material demonstrated acceptable physical properties throughout the study.

Analysis of Variance↗
PubMed1993

Biomechanical comparison of bone graft used in anterior spinal reconstruction. Freeze-dried demineralized femoral segments versus fresh fibular segments and tricortical iliac blocks in autopsy specimens.

This study compares the compression strength of frozen corticocancellous iliac blocks and short fibular segments with freeze-dried, partially ("surface") demineralized microperforated (FDPDM) short femoral segments. Three blocks from each iliac crest and segments from the fibular and femoral diaphyses were retrieved. The femoral segments were microperforated, demineralized for 24 hours, and freeze-dried. All were then loaded to failure in a stress testing machine. The FDPDM showed a significantly higher failure load and stiffness than the fibular segments and the iliac crest segments. The femoral and fibular segments were similar in strength but significantly higher than iliac crest grafts. Compared with commonly used frozen grafts, freeze-dried partially demineralized femoral segments may be used safely as axial load-bearing struts in anterior spine reconstruction.

Adult↗
PubMedDate not supplied

Mechanical properties and clinical performance of a gallium restorative material.

In a combination clinical/laboratory evaluation, a gallium restorative alloy (Galloy) was assessed for six mechanical properties: compressive strength, diametral tensile strength, creep, hardness, wear, and dimensional change. Laboratory tests indicated that the gallium alloy was similar to either Tytin or Dispersalloy in most respects, with the exception of lower wear and higher 7-day diametral tensile strength. In the clinical trial, all Galloy restorations were lined with a resin to prevent moisture contacting the material during the first hours after placement. All gallium restorations--class 1's only--were intact, and no teeth were fractured at the end of 1 year. There was little difference found at the 1-year evaluation compared to the 6-month results. The surface of the gallium alloy was generally rough, and many restorations exhibited some tarnish on the surface. It should be pointed out that this product has not been FDA approved at the present time and is not on the market.

Dental Alloys↗
PubMed1996

Comparison of calcium phosphate cement mixture and pure calcium hydroxide as direct pulp-capping agents.

Calcium phosphate cement (CPC) and pure calcium hydroxide were used as direct pulp-capping agents on the deliberately exposed pulp tissue of 60 teeth in five monkeys. Their effects on the pulp tissue of individual teeth were observed and histologically compared after 12, 20 and 24 weeks. The results showed that both materials produced similar responses with regard to their biocompatibility and induction of hard tissue barrier formation. Vasodilatation, chronic inflammation and calcification nidi scattered within the pulp tissue of the 12-week group were observed. Twenty weeks after application of capping materials, a crude reparative dentinal bridge with inclusion of soft tissue or bulky capping agents appeared. A more mature, hard tissue barrier with a better degree of mineralization and formation of dentinal tubules was demonstrated in the 24-week group. The above findings associated with the abilities of self-setting and fair compressive strength suggest that CPC appears superior to pure calcium hydroxide and may have potential for clinical application, although many issues remain to be further investigated.

Animals↗
PubMed1997

Development and clinical evaluation of Chitra visible light cure composite.

Two paste, self cured BIS-GMA based resin was developed and physicochemical and biological characterization carried out. Its suitability and safety for clinical use were evaluated. Clinical trials for direct bonding of Orthodontic brackets conducted at the College of Dental Surgery, Manipal showed a success rate of 83% against 85% with "Right On" adhesive used as control. Further research to improve shelf life of the material led to the development of light cure-BIS-GMA based resin. It was evaluated for physicochemical characteristics which included setting time, compressive strength, diametral tensile strength, microhardness, water sorption and exothermic reaction. Biological characterization studies on material toxicity and biocompatibility on animal models established the safety and suitability of this composite for clinical use in dentistry. Clinical evaluation for direct bonding of Orthodontic brackets in comparison to Ultralight (T.P Orthodontics, USA) showed its handling characteristics to be superior to control. Flash removal was easier around bracket bases bonded with Chitra light cure. However, bond strength of light cure composite was 66% as compared to 79% with Ultralight. Subsequent improvement of the material increased the bond strength significantly. Failure rate with the new material was 11% against 13% with control in the ongoing clinical trials.

Adolescent↗
PubMed1994

Water sorption by maxillary acrylic resin denture base and consequent changes in vertical dimension.

Many kinds of materials have been tried in the Laboratory and to some extent clinically prior to introduction of acrylic resin. With the introduction of acrylic resin as denture base material, continuous attempts have been made to evaluate its physical properties. To observe the changes in vertical measurements of acrylic resin dentures due to water sorption and to assess variations of vertical movements of individual teeth within dentures due to water sorption; present study was carried out on 25 maxillary acrylic dentures. From results, the maximum water sorption appears to take place within 24 hours and after 28 day of water sorption; there is no change in vertical dimension if the denture is placed for further more time. With the introduction of acrylic resin as denture base material continued attempts have been made to evaluate physical properties so as to determine its suitability as an ideal nonmetalic denture base materials. Several investigations have been carried out on physical properties of this material such as compressive strength, tensile strength, solubility and colour stability. These have proved their superiority over other nonmetalic denture base materials used so far. Also several studies have been carried out to assess dimensional changes that occur in acrylic resin during processing, but very few studies have been carried out about the water sorption changes in the acrylic resin and still few about the vertical dimensional changes in acrylic resin due to water sorption. While fabricating the denture base from the acrylic resin, it comes in contact with water during polishing as well as cleaning, consequently during the use of denture it is constantly wetted by oral fluids. It is the hypothesis that water sorption by denture base acrylic may effect the retention and stability of the denture. It has been shown that water molecules act according to the laws of diffusion. The diffusion presumably occurs between the macromolecules which are forced slightly apart. This separation renders the molecules mobile and the inherent stresses created during heat curing of the acrylic resin can be relieved with consequent intermolecular relaxation and possible changes in the shape of the denture. Exposure time also plays a significant role in water sorption. The present investigation was therefore, carried out by keeping the following objectives: (1) The primary objective was to observe the changes in vertical measurements of acrylic resin dentures due to water sorption. (2) To assess the variations of vertical movement of individual teeth within the dentures due to water sorption.

Absorption↗
PubMed1989

[The effect of the group and individual characteristics of the vertebrae on their strength in experimental compression fractures].

The authors give an account of their investigation into the strength characteristics of the vertebrae preparations depending on a number of geometric characteristics of the vertebral bodies, the biological state of the bone tissue (osteoporosis, degenerative and dystrophic changes) and their group belonging. A number of factors has been revealed in some parameters of which it is possible to determine the dynamics of the state of the support function of the injured segment in the modelling of compressive fractures of the vertebral bodies. The results obtained by the authors allow to specify the literature data concerning the strength properties of the compressed vertebral body.

Biomechanical Phenomena↗
PubMed1989

Mechanical properties of BIS-GMA resin short glass fiber composites.

The use of short glass fibers as a filler for dental restorations or cement resins have not been examined extensively. The mechanical properties and untreated glass fibers (5 microns dia x 25 microns) in Bis-phenol A glycidyl methacrylate (BIS-GMA) diluted with triethylene-glycol dimethacrylate (TEGDMA) resin were investigated for possible use as a restorative dental composite or bone cement. Compression, uniaxial tension and fracture toughness tests were conducted for each filler composite mixtures of 40, 50, 60 and 70%. Set time and maximum temperature of polymerization were determined. The results show that the elastic modulus, tensile strength and compressive strength are dependent on the percent of filler content. Elastic modulus and compressive yield (0.2%) strength of silane treated glass fibers filled composite increased from 2.26 to 4.59 GPa and 43.3 to 66.6 MPa, respectively, wtih increasing the filler content while the tensile strength decreased from 26.7 to 18.6 MPa. The elastic modulus of the untreated composite was less than that of the silane treated fiber composite. The tensile strength and compressive strengths were 20 to 50% lower than those of silane treated composites. The fracture toughness of the silane treated glass fiber additions were not significantly different from the untreated additions. The highest fracture toughness was obtained at 50% filler content with 1.65 MPa m.5. Set time increased from 3.5 to 7.7 minutes with increased filler content and peak temperature dropped from 68.3 to 34 degrees C. The results of this study indicate that the addition of silane coated glass fiber to BIS-GMA resin increased the elastic modulus, tensile and compressive strengths compared with non-treated fibers. The addition of either treated or non-treated fibers increased the set time of the material and decreased the maximum temperature.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1992

Compressive and diametral tensile strength of titanium-reinforced composites.

This article determines the compressive and diametral tensile strength of two titanium-reinforced composites (Bis-GMA-based), Ti-Core and Flexi-Flow cem with titanium and compares their strengths to dentin and commercially available core materials and cements. In addition scanning electron microscope (SEM) photographs were taken of Ti-Core and Flexi-Flow cem with titanium. Compressive and tensile loading was performed on a modified universal testing apparatus. Ti-Core and Flexi-Flow cem with titanium were measured to have compressive strengths of 41,132 and 41,876 psi and tensile strengths of 5219 and 4930 psi, respectively. Statistically (ANOVA, one-way analysis of variance), these titanium-reinforced composites are stronger in compressive and tensile strength than Ketac-Silver, Fleck's zinc cement, Durelon, Ketac-Cem, and GC Miracle Mix. Both titanium-reinforced composite materials approach the compressive and diametral tensile strengths of dentin (43,100 and 6000 psi). SEMs revealed that the titanium was uniformly and homogeneously interspersed within the resin matrix of the material.

Analysis of Variance↗
PubMed2006

The polymethyl methacrylate cervical cage for treatment of cervical disk disease Part III. Biomechanical properties.

BACKGROUND: In a previous article, we used the PMMA cervical cage in the treatment of single-level cervical disk disease and the preliminary clinical results were satisfactory. However, the mechanical properties of the PMMA cage were not clear. Therefore, we designed a comparative in vitro biomechanical study to determine the mechanical properties of the PMMA cage. METHODS: The PMMA cervical cage and the Solis PEEK cervical cage were compressed in a materials testing machine to determine the mechanical properties. RESULTS: The compressive yield strength of the PMMA cage (7030 +/- 637 N) was less than that of the Solis polymer cervical cage (8100 +/- 572 N). The ultimate compressive strength of the PMMA cage (8160 +/- 724 N) was less than that of the Solis cage (9100 +/- 634 N). The stiffness of the PMMA cervical cage (8106 +/- 817 N/mm) was greater than that of the Solis cage (6486 +/- 530 N/mm). The elastic modulus of the PMMA cage (623 +/- 57 MPa) was greater than that of the Solis cage (510 +/- 42 MPa). The elongation of PMMA cage (43.5 +/- 5.7%) was larger than that of the Solis cage (36.1 +/- 4.3%). CONCLUSIONS: Although the compressive yield strength and ultimate compressive strength of the PMMA cervical cage were less than those of the Solis polymer cage, the mechanical properties are better than those of the cervical vertebral body. The PMMA cage is strong and safe for use as a spacer for cervical interbody fusion. Compared with other cage materials, the PMMA cage has many advantages and no obvious failings at present. However, the PMMA cervical cage warrants further long-term clinical study.

Biomechanical Phenomena↗
PubMed1995

Compressive and bone-bonding strength of hydroxyapatite thermal decomposition product implanted in the femur of rabbit as a bioactive ceramic bone cement.

Hydroxyapatite thermal decomposition product (HATDP) after mixing with water was injected into the femur of rabbits, and its biocompatibility, compressive strength and bone-bonding strength were investigated. The compressive strength of a block of HATDP was 56.0 MPa 4 weeks after injection, which was about 60% of that of poly(methyl methacrylate) (PMMA) cement. The bone-bonding strength was 8.2 MPa 4 weeks after injection, which was significantly higher than that of PMMA cement. HATDP seems to be useful as a cement material because of its good bone-bonding property and relatively high mechanical strength.

Absorption↗
PubMed1997

Prediction of human femoral bone strength using ultrasound velocity and BMD: an in vitro study.

The stiffness and strength of cancellous bone are important in the management of skeletal diseases such as osteoporosis. These properties are a function not only of bone density but also of bone architecture, some measure of which can be provided by quantitative ultrasound. The ability of quantitative ultrasound and bone mineral density (BMD) to predict stiffness and strength of human femoral heads removed from live subjects during hip replacement was assessed. Stiffness and strength were measured using a uniaxial compression test. Ultrasound velocity was measured using the pulse-submersion technique (McCue CUBAResearch) and BMD using DXA (Lunar DPX-L). Ultrasound velocity (quantitative ultrasound) and stiffness varied with the three orthogonal directions, the highest significance being between the proximo-distal (PD) and antero-posterior (AP) directions (p < 0.0001 for stiffness and p = 0.0003 for velocity). Ultrasound velocity was significantly correlated with compressive bone strength (r = 0.76, p < 0.0001) and stiffness (r = 0.79-0.83, p < 0.0001). BMD was also significantly correlated with compressive strength (r = 0.82, p < 0.0001) and stiffness (r = 0.66-0.81. p < 0.001). Using multiple regression analysis both BMD and velocity were significant predictors of strength (r = 0.88, p = 0.0004 and 0.0054 respectively) and stiffness (r = 0.92, p = 0.0001 and 0.0003 respectively). BMD and velocity were still independent significant predictors of both stiffness (r = 0.93, p < 0.0001 and 0.0001 respectively) and strength (r = 0.89, p < 0.0001 and 0.02) when they were combined as a product (BMDn*Vm). This suggests that BMD measured using DXA, if used in conjunction with ultrasound velocity, may be able to improve osteoporosis risk assessment. The information about femur anisotropy may also be important for hip prosthesis and in vivo modelling.

Absorptiometry, Photon↗
PubMedDate not supplied

Skin tensile strength modulation by compressive garments in burn patients. A pilot study.

Compression therapy is frequently used to prevent hypertrophy of post-burn scars. This pilot study was performed in 6 patients to assess non-invasive changes induced in the tensile strength of the skin before any clinical improvement can be perceived. Assessments were performed using a computerized suction device delivering three 5 s cycles of 500 mbar depression. Measurements were made at one-month intervals for three months after initiating the garment compression therapy. Comparisons were made between the intact skin, the ungrafted and grafted post-burn scars and the graft donor sites. Data show that garment compression therapy alters the tensile strength in the skin of all test sites. The most reliable variations consist of an increase in both the extensibility and elasticity of the tissues submitted to traction.

Bandages↗
PubMed2006

Synthesis and heavy metal immobilization behaviors of slag based geopolymer.

In this paper, two aspects of studies are carried out: (1) synthesis of geopolymer by using slag and metakaolin; (2) immobilization behaviors of slag based geopolymer in a presence of Pb and Cu ions. As for the synthesis of slag based geopolymer, four different slag content (10%, 30%, 50%, 70%) and three types of curing regimes (standard curing, steam curing and autoclave curing) are investigated to obtain the optimum synthesis condition based on the compressive and flexural strength. The testing results showed that geopolymer mortar containing 50% slag that is synthesized at steam curing (80 degrees C for 8h), exhibits higher mechanical strengths. The compressive and flexural strengths of slag based geopolymer mortar are 75.2 MPa and 10.1 MPa, respectively. Additionally, Infrared (IR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques are used to characterize the microstructure of the slag based geopolymer paste. IR spectra show that the absorptive band at 1086 cm(-1) shifts to lower wave number around 1007 cm(-1), and some six-coordinated Als transforms into four-coordination during the synthesis of slag based geopolymer paste. The resulting slag based geopolymeric products are X-ray amorphous materials. SEM observation shows that it is possible to have geopolymeric gel and calcium silicate hydrate (C-S-H) gel forming simultaneously within slag based geopolymer paste. As for immobilization of heavy metals, the leaching tests are employed to investigate the immobilization behaviors of the slag based geopolymer mortar synthesized under the above optimum condition. The leaching tests show that slag based geopolymer mortar can effectively immobilize Cu and Pb heavy metal ions, and the immobilization efficiency reach 98.5% greater when heavy metals are incorporated in the slag geopolymeric matrix in the range of 0.1-0.3%. The Pb exhibits better immobilization efficiency than the Cu in the case of large dosages of heavy metals.

Aluminum Silicates↗
PubMed1981

[Mechanical properties of microfilled composite resins (author's transl)].

The various mechanical properties of seven microfilled composite resins were evaluated, comparing with two conventional composite resins. The following results were obtained. 1) Though microfilled composite resins were more excellent than conventional ones on surface roughness after polishing or brushing, but they were inferior to conventional ones on the resistance to brushing abrasion. 2) Tensile, compressive and bending strength were dependent on inorganic filler content and properties of matrix resin. Particularly, their mechanical properties in the wet condition were strongly influenced by whether matrix resin was hydrophilic or hydrophobic. Compared with conventional composite resins, microfilled ones contained 30 to 40 wt% of filler had lower values of tensile and bending strength, and near values of compressive strength. While, microfilled ones contained 50 to 60 wt% of filler had higher values of compressive strength, and near values of tensile and bending strength, compared to conventional ones. 3) Modulus of elasticity and hardness were mainly dependent on inorganic filler content. Moduli of elasticity of microfilled composite resins were about 25 to 33% of them of conventional ones, and hardnesses of microfilled ones were approximately 50% of them of conventional ones except some materials. Hardnesses of microfilled composite resins with 50 to 60 wt% of filler were similar to them of conventional ones.

Chemical Phenomena↗
PubMed1993

Compressive and diametral tensile strengths of current adhesive luting agents.

Strength parameters greatly influence the selection of luting agents. This study compared the compressive and diametral tensile strengths of six classes of new adhesive luting agents (ALAs) with zinc phosphate as the controls. The 11 materials tested were prepared according to the manufacturers' instructions for use as luting agents. Mean compressive and diametral strengths and standard errors were calculated for each luting agent (n = 10). Analysis of variance was computed (p < 0.0011) and multiple comparisons tests were performed. Compressive strengths varied from 41.5 MPa for a hydroxyapatite ALA to 178.5 MPa for a composite resin ALA. Diametral tensile strengths ranged from 8.1 MPa for a hydroxyapatite ALA to 45.1 MPa for a composite resin ALA. Conventional powder-liquid glass ionomer ALAs, an encapsulated glass ionomer ALA, a composite resin-glass ionomer hybrid ALA, and the composite resin ALAs demonstrated significantly greater compressive and diametral strengths than the zinc phosphate cements.

Analysis of Variance↗