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PubMed2004

Effect of the particle size on the micro and nanostructural features of a calcium phosphate cement: a kinetic analysis.

The aim of this work is to investigate the possibility of controlling the final micro and nanostructural features of a calcium phosphate cement by modifying the particle size of the starting powder, and to study the effect of this parameter on the kinetics of the setting reaction. The development of calcium phosphate materials with tailored structures at the micro and nanoscale levels could allow the modulation of some specific responses in biologic phenomena such as protein adsorption and cell adhesion, which strongly depend on the nano-sized roughness of the interface. It is shown that the higher specific surface, produced by the reduction of the particle size of the powder, strongly accelerates the hydrolysis of the alpha-TCP into calcium-deficient hydroxyapatite. The higher degree of supersaturation attained in the solution favours the nucleation of smaller crystals. Thus, by increasing the specific surface of the starting powder in a factor of 5, the size of the precipitated crystals is strongly reduced, and the specific surface of the set cement increases by a factor of 2. The reduction of the particle size produces a substantial decrease of the setting time and accelerates the hardening of the cement without significantly affecting the final strength attained. The mechanical strength achieved by the cement cannot be univocally related to the degree of reaction, without considering the microstructural features.

Adhesiveness↗
PubMed1995

Effects of two resin adhesives on mechanical properties of set amalgam.

Two hundred amalgam (Dispersalloy) cylinders, 3 mm high x 4 mm wide, were tested to determine the compressive and diametral tensile strength of amalgam treated with 1 and 3 mixed drops of Amalgambond resin and 1:1 and 3:3 drops of resin powder paste of Panavia Ex resin. Twenty samples of each group, including a control group, were tested with a 1 cm diameter testing rod in an Instron universal testing machine at 0.5 mm/minute speed. All samples tested for compressive strength were not statistically different from one another (ANOVA). ANOVA and Tukey HSD test indicated no significant difference in diametral tension between the Amalgam and Amalgambond 1X materials, but significant differences were demonstrated with the Amalgambond 3X and Panavia 1X and 3X materials.

Adhesives↗
PubMed1997

Bond strengths of composite resin and compomers in primary and permanent teeth.

Previous clinical and in vitro studies have shown a higher failure rate of composite resins and conventional glass ionomer cements in primary teeth when compared to permanent teeth. A new generation of light-cured glass ionomer cements (compomers) were suggested to be used as restorative materials for the primary teeth. This study was conducted into two parts. The objective of the first part was to compare shear bond strength of compomers (Compoglass and Dyract) and composite resin (Herculite/Optibond) in both primary and permanent teeth. Buccal and lingual surfaces of extracted sound human primary and permanent molars were ground flat on 600-grit SiC paper and divided into 6 groups of 10 surfaces each. The materials were handled according to the instructions of the manufacturer and placed on to the tooth surfaces via clear plastic tubes of 3 mm in diameter. After light curing for 40 seconds, all samples were thermocycled in water bath of 5 degrees F and 55 degrees F for 500 cycles. The samples were embedded in acrylic resin and sheared with an Instron running at a crosshead speed of 0.5 mm/min. Results (mean shear bond strength) were recorded in MPa. Factorial ANOVA revealed that shear bond strength of Herculite/Optibond in the primary teeth (6.07 +/- 2.63) was significantly lower than that of the permanent teeth (17.61 +/- 4.34) (p < 0.0001), but there was no statistically significant difference of bond strength of Compoglass and Dyract between the primary and the permanent teeth. The results from the first part revealed that no materials tested in the primary teeth could provide a shear bond strength of at least 17.6 MPa as recommended. Thus, the objective of the second part of this study was to evaluate shear bond strength of composite resin (Herculite) using three different dentinal bonding agents (Optibond, One-Step and Amalgambond) in the primary teeth. Methods employed in this part were similar to that of the first part. Results showed that Amalgambond provided significantly higher mean shear bond strength (17.96 +/- 5.77) than One-step (11.79 +/- 4.73) and Optibond (6.07 +/-/- 2.63) as tested by Kruskal-Wallis ANOVA and Mann-Whitney U test (p < 0.0001).

Adhesiveness↗
PubMed2002

Compressional characteristics of native and pregelatinized forms of sorghum, plantain, and corn starches and the mechanical properties of their tablets.

A study was made of the compressional characteristics of native and pregelatinized forms of sorghum, plantain, and corn starches and the mechanical properties of their tablets. Compressional characteristics were analyzed using density measurements and the Heckel and Kawakita plots. Pregelatinized starches exhibited more densification than native starches during die filling and at low pressures. The ranking for the mean yield pressure (Py) values for the starches was plantain < corn < sorghum, with the pregelatinized starches having lower values than the native starches. The ranking for the values of another pressure term, Pk--an inverse measure of plasticity, was corn < plantain < sorghum, but with the native starches having the lower values. For the tablets, the ranking for values of tensile strength (T) was corn > plantain > sorghum, while the ranking for the brittle fracture index (BFI) was plantain > corn > sorghum. Tablets made from pregelatinized starches had lower T and BFI values than those made from native starches. The results suggest that pregelatinization of the starches facilitated faster onset of plastic deformation but reduced the amount of plastic deformation which occurred during the compression process.

Compressive Strength↗
PubMed2001

The development of a test specification to determine the rollover protection of passengers in light commercial vehicles fitted with canopies.

In this paper, a basic test specification is proposed to assess the structural integrity of a canopy that covers the load-area of a light commercial vehicle (LCV) used to carry passengers in the rear. The proposed test specification is a first step towards improving the safety of these passengers during rollover accidents. Different test methods were evaluated for applicability, ease of use and financial implications. The mass and geometric characteristics of three different one-ton LCVs were experimentally obtained and used to determine the minimum lateral velocity that will result in a rollover should a tripping mechanism be encountered. These velocities, in conjunction with other published data, were used to determine the energy required for a pendulum qualification test. It was decided that 7.7 kJ of energy delivered by a pendulum travelling between 4 and 7 m/s just prior to impact would be the most representative load case. A finite element analysis (FEA) of the proposed impact test on a specimen canopy was completed. Thereafter, the actual pendulum impact test was conducted to demonstrate the applicability of the proposed test procedure as well as the correlation with the FEA. It was shown that both FEA and actual testing are viable qualification procedures and that they can in fact be used to reliably assess the strength of the canopy. Finally, the outline of a test specification was developed and proposed, which can be used by national regulatory institutions to assess the structural integrity of commercially manufactured canopies.

Accidents, Traffic↗
PubMed2007

The effect of chronic nicotine administration on bone mineral content and bone strength in normal and castrated male rats.

Tobacco, containing nicotine as the principal pharmacologically active chemical, has been identified as being a risk factor for the development of osteoporosis. Thirty-two male Wistar rats of two months of age were castrated or sham operated to evaluate the effects of long-term administration (four months) of nicotine in drinking water (9.0 mg/kg/day). The presence of cotinine in urine confirmed successful delivery of nicotine. The bones were tested mechanically by a three point bending test in a Mini Bionix (MTA) testing system. The bones from castrated rats were characterized by a reduction in bone density as well as ash, calcium and phosphate content. Castration significantly altered mechanical properties of bone (9%) and femoral cortical thickness. When intact rats were treated with a high dose of nicotine, nicotine had negative effect on tibial bone density as well as ash, calcium, phosphate content and significantly altered the mechanical properties of bone (12%) and femoral cortical thickness compared to intact animals. Nicotine itself does not exert any anti-androgenic effect and does not produce changes in the weight of seminal vesicles. Nicotine-induced bone loss is associated with high bone turnover in the male rats as expressed by increased TrACP and B-ALP. When castrated rats were treated with the high dose of nicotine the changes in bone density resulting from castration were not further potentiated. These results document the efficacy of nicotine at high doses to cause bone loss and loss of bone mechanical strength in intact rats. The results of the present study may be interpreted as supporting the hypothesis of nicotine as a risk factor for osteoporosis.

Alkaline Phosphatase↗
PubMed2004

Fatigue crack propagation resistance of highly crosslinked polyethylene.

A higher degree of cross-linking has been shown to improve wear properties of ultra-high molecular weight polyethylene in laboratory studies. However, cross-linking can also affect the mechanical properties of ultra-high molecular weight polyethylene. Fatigue crack propagation resistance was determined for electron beam cross-linked ultra-high molecular weight polyethylene and compared with gamma irradiation cross-linked and noncross-linked polyethylene fatigue specimens. Crosslinking was done with different dosages of irradiation followed by melting. For one irradiation dose (50 kGy) extrusion and molding processes were compared. A fracture mechanics approach was used to determine how the degree of cross-linking affects resistance to crack propagation in ultra-high molecular weight polyethylene. Fatigue crack propagation resistance was reduced in proportion to the irradiation dose. The type of irradiation (gamma or electron beam) or manufacturing method (extrusion or molding) did not affect fatigue crack propagation resistance. The reduced fatigue strength of highly cross-linked ultra-high molecular weight polyethylene could lead to mechanical failure in conditions that are associated with cyclic local tensile stresses.

Case-Control Studies↗
PubMed1996

Effects of viscosity and surface moisture on bond strengths of resin-modified glass ionomers.

PURPOSE: To evaluate the effects of surface moisture and material viscosity on the shear bond strength of resin-modified glass ionomers to dentin. MATERIALS AND METHODS: Sixty human teeth were mounted in phenolic rings and ground to obtain flat facial and lingual dentin surfaces. The specimens were assigned to six treatment groups. Three groups were first conditioned with 10% polyacrylic acid. On one surface of each specimen, dentin was left visibly moist prior to application of the restorative material. On the opposite surface the dentin was dried, but not desiccated, after conditioning. For these three groups, Fuji II LC resin-modified glass ionomer was mixed at powder/liquid (P/L) ratios of 1.4, 3.0 and 3.6 and applied to the conditioned dentin in 2.5 mm diameter molds. The other three groups were treated with Vitremer primer. One surface of each specimen was "dry" and one surface was "moist" before primer application. Vitremer restorative material was mixed at P/L ratios of 2.2, 2.5 and 2.8 and applied to the primed surfaces. Shear bond strengths were measured using a universal testing machine. Data were subjected to three-way ANOVA and Tukey's multiple comparisons test. RESULTS: Mean shear bond strengths of the two materials ranged from 6.9 to 10.4 MPa and varied little regardless of the viscosity of the materials or the degree of surface moistness. The differences among viscosities and surface moistness were not statistically significant. IN this in vitro study, the shear bond strengths of two resin-modified glass ionomers were unaffected by the viscosity of the materials and the surface moisture of the dentin substrate.

Analysis of Variance↗
PubMed1995

The anabolic effects of parathyroid hormone on cortical bone mass, dimensions and strength--assessed in a sexually mature, ovariectomized rat model.

The aim of the study was to determine the effect of parathyroid hormone (PTH), the antiresorptive agents estrogen and bisphosphonate (risedronate), and also the combination of PTH with these antiresorptive drugs on femoral cortical bone mass, dimensions and strength in a sexually mature, ovariectomized rat model. A total of 138, 3-month-old Sprague-Dawley rats were randomized into seven groups: 1--sham operated (control); 2--ovariectomized (OVX); 3--OVX plus estrogen; 4--OVX plus bisphosphonate (risedronate [NE]; 5--OVX plus hPTH (1-34); 6--OVX plus hPTH (1-34) and estrogen; 7--OVX plus hPTH (1-34) and risedronate. Treatment regimens were initiated 4 weeks after OVX and were continued for 5 and 15 weeks for each treatment group. Changes in bone mass (ash content), cross-sectional area, cortical thickness and dimensions and bone strength were assessed in middiaphyseal, femoral specimens. The results revealed that ovariectomy had no effect on cortical bone mass and biomechanical competence. OVX rats treated with estrogen and also OVX rats treated with risedronate showed no significant difference from either OVX or control groups. After only 5 weeks of treatment, hPTH monotherapy increased ash content, cross-sectional area, cortical thickness and compressive bone strength (load) significantly. After 15 weeks of treatment, OVX rats treated with PTH monotherapy or PTH in combination with risedronate showed identical load-values. These values were significantly higher than those seen in both control and OVX rats. However, PTH in combination with estrogen failed to augment cortical bone strength over control or OVX levels after therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed2007

Contact damage in an yttria stabilized zirconia: implications.

This paper presents the results of a combined experimental and computational study of contact damage in a 3 mole% yttria partially stabilized zirconia (3-YSZ) that is relevant to hip implants and dental restorations. Contact-induced loading in real applications is idealized using Hertzian contact model to explain plasticity phenomena and failure mechanisms observed under monotonic and cyclic loading. Under monotonic loading, the elastic moduli increase with increasing loading levels. Under cyclic loading, the ceramic specimens fail with progressive cone cracking. X-ray analyses reveal that stress-induced phase transformation (from tetragonal to monoclinic phases) occurs under cyclic contact loading above the critical load levels (approximately 8.5 kN). Furthermore, when the cyclic loading level (5.0 kN) is less than a critical load levels (7.5 kN) that is required to induce surface cone cracks, significant plastic damage is observed in the subsurface zone underneath the contact area. These suggest that the cyclic contact loading induce both plastic damage and tetragonalto-monoclinic phase transformation in the 3-YSZ, leading to significant degradation in long-term strength. The implications of the results are discussed for the design of zirconia femoral heads in total hip replacements and zirconia crowns in dental restoration.

Biocompatible Materials↗
PubMed2005

Uncatalyzed synthesis, thermal and mechanical properties of polyurethanes based on poly(epsilon-caprolactone) and 1,4-butane diisocyanate with uniform hard segment.

Polyurethanes based on poly(epsilon-caprolactone) (PCL) (750-2800 g/mol) and 1,4-butane diisocyanate (BDI) with different soft segment lengths and constant uniform hard segment length were synthesized in absence of catalysts for the production of a degradable meniscus scaffold. First the polyesterdiols were endcapped with BDI yielding a macrodiisocyanate with a minimal amount of side reactions and a functionality of 2.0. Subsequently, the macrodiisocyanates were extended with 1,4-butanediol in order to obtain the corresponding polyurethane. The polyurethanes had molecular weights between 78 and 160 kg/mol. Above molar masses of 1900 g/mol of the polyesterdiol crystalline PCL was found while the hard segment showed an increase in melting point from 78 to 122 degrees C with increasing hard segment content. It was estimated that the percentage crystallinity of the hard segment varied between 92 and 26%. The Young's modulus varied between 30 and 264 MPa, the strain at break varied between 870 and 1200% and tear strengths varied between 97 and 237 kJ/m2.

Absorbable Implants↗
PubMed1985

Time-dependent deformation of composite resins--compositional considerations.

The compressive yield strength and creep of 21 dental composite resins were evaluated and correlated with filler volume percent and extent of cure in the resin. In general, yield and creep of composites were more dependent upon filler volume fraction than on extent of cure. However, the types of monomers and fillers used in the composite formulation appeared to play a major role in determining the compressive characteristics of the materials.

Carbon↗
PubMed2003

The effect of tension on esophagogastric anastomotic wound healing in rats.

AIM: The effect of tension on the occurrence of esophagogastric anastomotic leaks has been controversial for along time. We used a rat model and investigated the effect of tension on the esophagogastric anastomotic wound healing. METHODS: Eighty Sprague-Dawley rats were divided into 8 groups and each group has 10 rats. A side-to-side single layer esophagogastric anastomosis was constructed using interrupted sutures through laparotomy. Anastomoses were excised on day 0, 3, 5, 7, 14, mounted in an Instronmini-44 Tension meter and distracted at 10 mm/min to measure breaking strength. On the other hand, the increased anastomotic tensions were obtained by increasing the distance between esophageal incision and gastrotomy, and anastomotic leak rates in different anastomotic tension groups were investigated. RESULTS: A total of 11 rats were excluded from the studies because of pulmonary complication. Breaking strength on day 0, 3, 5, 7, 14 were 3.35+/-0.89, 1.18+/-0.31, 1.92+/-0.46,3.47+/-0.83, 5.06+/-1.22 (Newton), respectively. The breaking strength is significantly different between day 0 and day 3, day 5 and day 7, day 7 and day 14 (p<0.05). There is no difference between day 3 and day 5, day 0 and day 7(p>0.05). Breaking strength is lowest on day 3 and close to culmination on day 14. Esophagogastric anastomotic leaks increased along with anastomotic tension increasing. CONCLUSION: Anastomotic tension could be a key factor resulting in esophagogastric anastomotic leaks.

Anastomosis, Surgical↗
PubMed2004

Open wedge high tibial osteotomy: biomechanical investigation of the modified Arthrex Osteotomy Plate (Puddu Plate) and the TomoFix Plate.

OBJECTIVE: To determine the biomechanical properties of different fixation methods for high tibial medial opening wedge osteotomy in order to determine appropriate surgical and rehabilitation guidelines. DESIGN: A biomechanical testing examined the construct stiffness and the fixation strength of two different plates. BACKGROUND: Although medial opening wedge techniques for high tibial osteotomies have become popular in recent years, biomechanical data of frequently used implants is lacking. METHODS: A 15-mm medial opening gap was stabilized in each of eight medium composite tibial bones either with the modified Arthrex Osteotomy Plate (Puddu Plate) or the TomoFix Plate. RESULTS: Both constructs failed under compression and torsion at the lateral cortex and occurred at higher maximal forces by using the TomoFix Plate. After fracture of the lateral cortex the axial stiffness was reduced by 47% and the torsional rigidity by 54% for the TomoFix. For the Puddu Plate these reductions were 66% and 78%, respectively. The differences between the two groups were significant in all conducted tests (P < 0.05). CONCLUSIONS: This study indicates that an unharmed lateral hinge largely dictates the stability after high tibial osteotomy. If the lateral cortex is injured, the TomoFix plate provides superior stability in both compression and torsion compared to the Puddu Plate. In the latter case additional fixation might be considered. RELEVANCE: These biomechanical tests helped to identify clinical situations in which the mechanical attributes of the plates would prove advantageous.

Biomimetic Materials↗
PubMedDate not supplied

Mechanical characterization of commercially made carbon-fiber-reinforced polymethylmethacrylate.

Acrylic bone cement is significantly weaker and of lower modulus of elasticity than compact bone. It is also weaker in tension than in compression. This limits its use in orthopedics to areas where tensile stresses were minimum. Many authors have shown that addition of small percentages of fiber reinforcement by hand mixing improved the mechanical properties significantly but with variable results. In this investigation we have examined the mechanical properties of machine-mixed, commercially available carbon-fiber-reinforced bone cement. Appropriate samples of normal low-viscosity cement and carbon-fiber-reinforced cement were prepared and tested mechanically. Carbon fiber increased the tensile strength and modulus by 30% and 35.8% respectively. The compression strength and modulus, however, increased by only 10.7%. Similarly, bending and shear strengths improved by 29.5% and 18.5%, respectively. Diametral compression strength, which is an indirect measure of tensile strength, however, showed only 6.2% improvement. The maximum temperature rise during polymerization was also reduced significantly by the fiber reinforcement.

Bone Cements↗
PubMed2001

Quantitative assessment of forearm muscle size, forelimb grip strength, forearm bone mineral density, and forearm bone size in determining humerus breaking strength in 10 inbred strains of mice.

Bone strength is an important clinical endpoint of osteoporosis research. The evaluation of the relative importance of bone and muscle components to bone strength has widespread implications for the understanding and preventing of osteoporosis. The objectives of this study were to understand the interrelationship between the different components of the muscular skeletal system and to determine the effect of forearm muscle size, forelimb grip strength, forearm bone mineral density (BMD), and forearm bone size on the humerus breaking strength among 10 inbred strains of mice. The forearm muscle size was measured using a peripheral quantitative computed tomography (pQCT). The forearm BMD and forearm bone size were measured using a PIXIMUS Densitometer. The forelimb grip strength and humerus breaking strength were measured using an Instron Mechanical Tester. Significant correlations were found among the five regional phenotypes. All variables have a moderately high genetic component with heritability estimates of 0.83 for forelimb grip strength, 0.76 for forearm muscle size, 0.6 for forearm BMD, 0.63 for forearm bone size, and 0.68 for humerus breaking strength. Forward stepwise multiregression analysis showed that the forearm BMD, forelimb grip strength, and forearm bone size were three major determinants of bone strength and explained 61% of the variation in bone breaking strength. These data suggest that evaluation of these three parameters together, rather than BMD alone, is a more effective, noninvasive approach for predicting fracture risk.

Absorptiometry, Photon↗
PubMedDate not supplied

Dentin bond strength and marginal adaptation: direct composite resins vs ceramic inlays.

The aim of this in vitro study was to compare the dentin bond strength and marginal adaptation of directly and indirectly inserted restorations. A conically modified push-out test was designed to consider polymerization shrinkage and facilitate inlay placement. A total of 260 cavities were prepared into disks of freshly extracted human third molars and filled with direct composite resins or with adhesively luted ceramic inlays. Dentin adhesives of the third--(with self-etching primer: ART Bond, Syntac Classic), fourth--(with total etching: Scotchbond Multi-Purpose Plus), and fifth-generation (one-bottle adhesives: Syntac Single Component, Prime & Bond 2.1) were used in combination with one hybrid composite (Tetric) or luting composite (Variolink Low). Control groups did not use an adhesive. Polymerization of the bonding agent was carried out prior to insertion of the filling/inlay or afterwards simultaneously with the composite/luting composite. The thickness of the adhesive layer and luting composite was recorded, and after 7 days of storage and 24 hours of thermocycling (1150 cycles) replicas were made and extrusion testing performed. Fracture modes were determined and replicas were examined regarding marginal adaptation using SEM (X200 magnification). Precuring of the bonding resin increased dentin bond strength independent of the material combination or insertion mode (P < 0.05). In general, third- and fourth-generation dentin adhesives produced better results in bond strength and marginal adaptation than one-bottle systems (P < 0.05). In the third generation, ART Bond achieved significantly higher push-out values than Syntac (P < 0.05), but no better marginal adaptation. Cohesive fractures within the dentin were only observed in the inlay groups with precured resin. Precuring of the bonding resin is an important factor for both direct and indirect restorations. Nevertheless, precuring of the bonding resin prior to insertion of adhesive inlays cannot be recommended clinically, because the 120-micron luting spaces were too large. In simulated cavities, direct composite fillings with precuring achieved bond strengths similar to inlays without precuring. One-bottle adhesive systems performed poorly compared with multi-step adhesives of the third and fourth generation.

Analysis of Variance↗
PubMed2005

[Microstructure and mechanical property of a new IPS-Empress 2 dental glass-ceramic].

OBJECTIVE: To investigate the microstructure and mechanical properties of a new IPS-Empress 2 dental glass-ceramic. METHODS: AFM, SEM and XRD were used to analyze the microstructure and crystal phase of IPS-Empress 2 glass-ceramic. The flexural strength and fracture toughness were tested using 3-point bending method and indentation method respectively. RESULTS: IPS-Empress 2 glass-ceramic mainly consisted of lithium disilicate crystal, lithium phosphate and glass matrix, which formed a continuous interlocking structure. The crystal phases were not changed before and after hot-pressed treatment. AFM showed nucleating agent particles of different sizes distributed on the highly polished ceramic surface. The strength and fracture toughness were 300 MPa and 3.1 MPam(1/2). CONCLUSION: The high strength and fracture toughness of IPS-Empress 2 glass ceramic are attributed to the fine lithium disilicate crystalline, interlocking microstructure and crack deflection.

Aluminum Silicates↗