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PubMed1988

[Peri-implantation enzymes and mineralization in bone tissue after implantation of bioactive vitroceramic material--a method for biomaterial testing for hard tissue substitutes. 2. Results of studies of vitroceramics and their modification by the admixture of metal oxides].

The activities of the alkaline and the acid bone phosphatases as well as the concentrations of calcium and phosphorus were measured in the periimplantal tissue of the rat femur bone after implantation of the vitroceramic Ap 40, the metal oxide stabilized vitroceramics Ap 40 A and Ap 40 Z, as well titanium after 2, 10, and 15 weeks. The incorporation of the vitroceramic Ap 40 turns out like a primary bone fracture healing. The implants Ap 40 A and Ap 40 Z are a compromise with a higher stability and the osteogenesis induced effect is preserved, but is belated in contrast to Ap 40.

Acid Phosphatase↗
PubMed1977

A study on the evaluation of local shati starch as a substitute of polysaccharides used in the preparation of capsules and tablets of antibiotics.

Local shati starch was extracted, purified and used as an excipient for the preparation of capsules and tablets of oxytetracycline and chloramphenicol. The weight variation test, disintegration time and hardness test of these dosage forms were done and compared with the conventional maize starch containing tables and capsules of the antibiotics. The results in respect of their potency test were found to conform to official pharmacopoeias (B.P. and U.S.P). Stability study for over one year of both varieties of tablets and capsules revealed that they retained their potencies equally well.

Anti-Bacterial Agents↗
PubMed2001

Material removal during the sliding of hydroxyapatite against UHMWPE.

Hydroxyapatite has been rubbed against ultra-high-molecular-weight-polyethylene (UHMWPE) under calcium-containg aqueous solutions. Further, hardness tests were carried out in air and in calcium-containing solutions whose pH ranged from pH 5 to pH 9. Hardness was found to vary with pH with a peak at around pH 7, i.e. - a chemomechanical effect was observed. Wear tests consisted in sliding hydroxyapatite samples against a UHMWPE disk for eight hours when lubricated by the same solutions as those used for the hardness tests. Volume loss, pH and calcium concentration were measured for up to 8 hours of sliding. Linking wear tests results with hardness results and supersaturation levels, it was concluded that two wear mechanisms occurred. A chemical mechanism depending on supersaturation occurred at the early stages of sliding. The wear rate was essentially independent of hardness during this stage. After a few hours, depending on the supersaturation of the lubricant, the chemical mechanism turned into a chemomechanical mechanism dependant on hardness.

Biocompatible Materials↗
PubMed2006

Halogen and LED light curing of composite: temperature increase and Knoop hardness.

This study assessed the Knoop hardness and temperature increase provided by three light curing units when using (1) the manufacturers' recommended times of photo-activation and (2) standardizing total energy density. One halogen--XL2500 (3M/ESPE)--and two light-emitting diode (LED) curing units--Freelight (3M/ESPE) and Ultrablue IS (DMC)--were used. A type-K thermocouple registered the temperature change produced by the composite photo-activation in a mold. Twenty-four hours after the photo-activation procedures, the composite specimens were submitted to a hardness test. Both temperature increase and hardness data were submitted to ANOVA and Tukey's test (5% significance). Using the first set of photo-activation conditions, the halogen unit produced a statistically higher temperature increase than did both LED units, and the Freelight LED resulted in a lower hardness than did the other curing units. When applying the second set of photo-activation conditions, the two LED units produced statistically greater temperature increase than did the halogen unit, whereas there were no statistical differences in hardness among the curing units.

Composite Resins↗
PubMed1999

Reinforcement mechanism of dentin mechanical properties by intracanal medicaments.

The reinforcement mechanism of dentin mechanical properties by intracanal medicaments was investigated. The dumbbell-shaped specimens were prepared from a collagen sheet, demineralized dentin and organic dissolved dentin. After immersing the specimens in intracanal medicaments (eugenol and formocresol), the tensile test was carried out in 37 degrees C water and the Vickers hardness test was performed. The tensile strengths increased after eugenol and formocresol immersion, especially collagen and organic dissolved dentin after formocresol immersion and demineralized dentin after eugenol immersion. Thus, formocresol immersion might have reinforced the dentin tensile strength by protein coagulation, while eugenol immersion might have reinforced the dentin tensile strength by not only protein coagulation but also chelation with hydroxyapatite. However, the hardness values did not significantly change after intracanal medicament immersion.

Analysis of Variance↗
PubMed2006

Influence of corn hybrid traits on digestibility and the efficiency of gain in feedlot cattle.

Two experiments were conducted to determine the influence of chemical and physical corn kernel traits on digestibility and feedlot cattle performance. Seven commercially available corn hybrids representing a range in kernel traits were evaluated for a variety of chemical and physical traits that included test weight, 1,000-grain weight, kernel size, starch, CP, amylose, Stenvert Hardness tests (kernel hardness traits), tangential abrasive dehulling device loss, 12-h in vitro starch disappearance, and rate and extent of in situ DM disappearance. Differences among hybrids existed for all physical kernel traits measured. In Exp. 1, 224 steers in 28 pens were fed the same hybrids for 167 d in a completely randomized design. All diets were formulated to have 12.5% CP and contained 66% dry-rolled corn (DM basis). There were no differences (P >0.20) among corn hybrids for DMI, ADG, or carcass characteristics. However, efficiency of gain (G:F) was influenced by hybrid (P < 0.01) with a difference of 9.5% from the least to the most efficient. In Exp. 2, 7 ruminally cannulated heifers were used in a 7 x 7 Latin square design to determine the effects of these hybrids on nutrient digestibility, VFA concentrations, and ruminal pH. Total-tract OM and starch digestibilities were not different (P >0.15) among hybrids and averaged 77.9 and 95.1%, respectively. Differences (P < 0.05) among hybrids existed for ruminal propionate concentration and the acetate to propionate ratio. Kernel hardness traits correlated (P < 0.05) with G:F were 1,000-grain weight (r = -0.81), Stenvert time to grind (r = -0.83), and the proportion of Stenvert soft to coarse particle height (r = 0.83). Propionate concentration was not correlated (r = 0.45) with G:F but was correlated (P = 0.02) to the Stenvert time to grind (r = -0.83). Cattle fed dry-rolled corn hybrids with greater proportions of soft endosperm had greater concentrations of propionate and gained more efficiently than cattle fed hybrids with a harder endosperm. Selecting for these softer kernel traits may improve the efficiency of gain in feedlot cattle.

Animal Feed↗
PubMed1996

Quantitative analysis of a presence/absence microbiological assay: the hard surface carrier test of disinfectant efficacy.

The Hard Surface Carrier Test (HSCT) is a presence/absence assay for determining the extent to which chemical disinfectants kill bacteria. The disinfectants are marketed for cleaning surfaces in hospitals, restaurants, the home, etc. In the HSCT, a presence response (or equivalently, a positive carrier) is recorded if one or more bacteria survive among M bacteria attached to a glass carrier and exposed to the chemical disinfectant; otherwise, the response is absence. The presence or absence response is observed for each of many (usually 60) glass carriers and the disinfectant is considered effective if few (e.g., < or = 5%) of the carriers are positive. It would be more satisfactory to microbiologists if effectiveness were based on the fraction of bacteria that survive exposure; denote the expected survival fraction by phi. An equivalent parameter commonly used in antimicrobial research is the log-reduction, denoted by psi, where psi = -log10(phi). Although the number M of bacteria on each exposed carrier is not known, this paper shows it is possible to estimate psi. The suggested estimator is based on the assumption that M follows a gamma distribution. The gamma parameters are estimated using counts of bacteria on the HSCT nonexposed (control) carriers. This paper provides a formula for the standard error of the estimate, a computer simulation technique for calculating the lower confidence limit, and a computer simulation study of these statistical methods.

Bacteria↗
PubMed1986

Effects of polymerization techniques on uniformity of cure of large-diameter, photo-initiated composite resin restorations.

The polymerization effectiveness of various methods of exposing large-diameter, light-activated composite resin samples is reported. Results of Knoop hardness testing showed that highest mean hardness was achieved by using a wide tip (13 mm) with either the spot cure or overlap method for 60 seconds. More uniform hardness resulted from the wide-tip with scanning methods and 60-second cure than resulted from the narrow-tip (8 mm) with the spot or overlap method and 20-second cure.

Bisphenol A-Glycidyl Methacrylate↗
PubMed2005

Structure and mechanical properties of Cresco-Ti laser-welded joints and stress analyses using finite element models of fixed distal extension and fixed partial prosthetic designs.

STATEMENT OF PROBLEM: The Cresco-Ti System uses a laser-welded process that provides an efficient technique to achieve passive fit frameworks. However, mechanical behavior of the laser-welded joint under biomechanical stress factors has not been demonstrated. PURPOSE: This study describes the effect of Cresco-Ti laser-welding conditions on the material properties of the welded specimen and analyzes stresses on the weld joint through 3-dimensional finite element models (3-D FEM) of implant-supported fixed dentures with cantilever extensions and fixed partial denture designs. MATERIAL AND METHODS: Twenty Grade III (ASTM B348) commercially pure titanium specimens were machine-milled to the dimensions described in the EN10002-1 tensile test standard and divided into test (n = 10) and control (n = 10) groups. The test specimens were sectioned and laser-welded. All specimens were subjected to tensile testing to determine yield strength (YS), ultimate tensile strength (UTS), and percent elongation (PE). The Knoop micro-indentation test was performed to determine the hardness of all specimens. On welded specimens, the hardness test was performed at the welded surface. Data were analyzed with the Mann-Whitney U test and Student's t test (alpha=.05). Fracture surfaces were examined by scanning electron microscopy to characterize the mode of fracture and identify defects due to welding. Three-dimensional FEMs were created that simulated a fixed denture with cantilever extensions supported by 5 implants (M1) and a fixed partial denture supported by 2 implants (M2), 1 of which was angled 30 degrees mesio-axially. An oblique load of 400 N with 15 degrees lingual-axial inclinations was applied to both models at various locations. RESULTS: Test specimens fractured between the weld and the parent material. No porosities were observed on the fractured surfaces. Mean values for YS, UTS, PE, and Knoop hardness were 428 +/- 88 MPa, 574 +/- 113 MPa, 11.2 +/- 0.4%, 270 +/- 17 KHN, respectively, for the control group and 642 +/- 2 MPa, 772 +/- 72 MPa, 4.8 +/- 0.7%, 353 +/- 23 KHN, respectively, for the test group. The differences between the groups were significant for all mechanical properties ( P <.05). For both models, the FEA revealed that maximum principal stresses were concentrated at the framework-weld junction but did not exceed the UTS of the weld joint. CONCLUSION: Within the constraints of the finite element models, mechanical failure of the welded joint between the support and the framework may not be expected under biomechanical conditions simulated in this study.

Computer Simulation↗
PubMed2005

[A methodological study on testing the elastic modulus of soft bio-anthropomorphic materials].

It is difficult to test the elastic modulus of the soft bio-anthropomorphic materials by using the general stretch-strain test method. With the equipment for a hardness testing system of bio-anthropomorphic materials and millesimal gauge, we introduce in this paper a compress-strain test method and carry out the related test-data curve-fitness. The test results indicate that this kind of method can be adopted in testing the elastic modulus of the soft bio-anthropomorphic materials and help to compare and distinguish the biomechanics equivalent between the tissues.

Biocompatible Materials↗
PubMed2004

Polymerization time for a microwave-cured acrylic resin with multiple flasks.

This study aimed at establishing the polymerization time of a microwave-cured acrylic resin (AcronTM MC), simultaneously processing 2, 4, and 6 flasks. Required time was measured according to the parameters: monomer release in water, Knoop hardness, and porosity. Samples were made with AcronTM MC in different shapes: rectangular (32 x 10 x 2.5 mm) for monomer release and porosity; and half-disc (30 mm in diameter x 4 mm in height) for Knoop hardness. There were four experimental groups (n = 24 per group): G1) one flask (control); G2) two flasks; G3) four flasks, and G4) six flasks. At first, polymerization protocol was similar for all groups (3 min/450 W). Time was then adjusted for G2, G3, and G4, based on monomer release evaluation in the control group, obtained by spectrophotometer Beckman DU-70, with emitting wave of 206 nm. Knoop hardness test was performed using a Shimadzu HMV 2000 hardness tester, and 10 indentations were performed on each specimen's surface. Porosity was assessed after specimens were immersed in black ink and the pores counted in a microscope. Results showed that the complete polymerization of the resin occurred in 4.5 min for two flasks (G2); 8.5 min for four flasks (G3); and 13 min for six flasks (G4), all with 450 W. Statistical analysis revealed that the number of flasks does not interfere with polymerization, Knoop hardness, and porosity of the resin. Results showed that polymerization of microwave-curing resin with more than one flask is a viable procedure, as long as polymerization time is adjusted.

Acrylic Resins↗
PubMed2004

The changes caused by modification of biomechanical properties of a bone.

The paper presents the distribution of the parameters of mechanical stiffness in a sample of animal bone. The parameters are measured at different distances from the cortical bone. As it is widely known, bone properties vary significantly depending on the length of the bone. Additionally, the properties of trabecular bone also depend on its distance from the cortical bone. The study presents the results for both samples of normal bone tissue and samples of bone tissue with chemically modified biomechanical properties. For each sample a matrix of measurement points was defined. For each measurement point, a micro hardness test was performed in order to define hardness of the micro volume and to measure the Young's modulus. This test was carried out using Micro-Combi-Tester equipment. Micro hardness was measured with Vickers diamond, and the analysis of deformation properties was realized by the Olivier and Pharr method. The application of Oliver and Pharr method enabled the calculation of Young's modulus directly from the unloading curve. Additionally, mineral density for all samples was measured using Dual Energy X-ray Absorptiometry method. This study allowed for comparison of bone mineral density parameter with Young's modulus. The aim of this comparison was to demonstrate changes caused by modification of biomechanical properties of bone.

Absorptiometry, Photon↗
PubMed2001

Reinforcement of acrylic denture base resin by incorporation of various fibers.

This study was designed to evaluate improvements in the mechanical properties of acrylic resin following reinforcement with three types of fiber. Polyester fiber (PE), Kevlar fiber (KF), and glass fiber (GF) were cut into 2, 4, and 6 mm lengths and incorporated at concentrations of 1, 2, and 3% (w/w). The mixtures of resin and fiber were cured at 70 degrees C in a water bath for 13 h, then at 90 degrees C for 1 h, in 70 x 25 x 15 mm stone molds, which were enclosed by dental flasks. The cured resin blocks were cut to an appropriate size and tested for impact strength and bending strength following the methods of ASTM Specification No. 256 and ISO Specification No. 1567, respectively. Specimens used in the impact strength test were reused for the Knoop hardness test. The results showed that the impact strength tended to be enhanced with fiber length and concentration, particularly PE at 3% and 6 mm length, which was significantly stronger than other formulations. Bending strength did not change significantly with the various formulations when compared to a control without fiber. The assessment of Knoop hardness revealed a complex pattern for the various formulations. The Knoop hardness of 3%, 6 mm PE-reinforced resin was comparable to that of the other formulations except for the control without fiber, but for clinical usage this did not adversely affect the merit of acrylic denture base resin. It is concluded that, for improved strength the optimum formulation to reinforce acrylic resin is by incorporation of 3%, 6 mm length PE fibers.

Acrylic Resins↗
PubMed1976

[Technological studies on high pressure polymerization of dental plastic materials].

The author in his present paper reports a program of comparative materials testing of which the purpose was to assess the value of positive pressure polymerization of thermosets. This particular program required polymerization temperature measurements. K-value determinations, and cone indentation hardness tests to be made on samples of plastic material polymerized under positive liquid or steam pressure and in cuvets, respectively, the conditions of polymerization being those which are used in actual practice. The results obtained indicated a favorable influence of positive liquid pressure polymerization on the final hardness of the plastic material.

Dental Materials↗
PubMed2001

Physical properties of root cementum: Part I. A new method for 3-dimensional evaluation.

Cementum is a nonuniform connective tissue that covers the roots of human teeth. Investigation of the physical properties of cementum may help in understanding or evaluating any possible connection to root resorption. A variety of engineering tests are available to investigate these properties. However, the thickness of the cementum layer varies, and this limits the applicability of these techniques in determining the physical properties of cementum. Hardness testing with Knoop and Vickers indentations overcame some of these limitations, but they prohibited the retrieval and retesting of the sample and therefore the testing was restricted to one area or section of the tooth. Another limiting factor with the existing techniques was the risk of artifacts related to the embedding material such as acrylic. A new method to investigate the physical properties of human premolar cementum was developed to obtain a 3-dimensional map of these properties with the Ultra Micro Indentation System (UMIS-2000; Commonwealth Scientific and Industrial Research Organization, Campbell, Australia). UMIS-2000 is a nano-indentation instrument for investigation of the properties of the near-surface region of materials. Premolars were harvested from orthodontic patients requiring extractions and then mounted on a newly designed surveyor that allowed sample retrieval and 3-dimensional rotation. This novel method enabled the quantitative testing of root surface cementum, on all 4 root surfaces, extending from the apex to the cementoenamel junction at 60 different sites.

Bicuspid↗
PubMed2001

In vitro assessment of polymerization procedures in Class II restorations: sealing, FTIR, and microhardness evaluations.

PURPOSE: This study was undertaken to evaluate several polymerization and filling procedures (incremental, bulk, light-tip, soft-cured, plasma devices) in Class II restorations through (1) a sealing evaluation of restorations filled with Tetric Ceram (TC) and Bisfil 2B (B2B, self-cured composite used as a control), (2) a FTIR analysis measuring the variations of the degree of conversion in terms of area unit ratio of the relevant resin composites and (3) a microhardness test to corroborate the FTIR analysis. MATERIALS AND METHODS: The length of the tracer penetration was measured from the gingival margin up to the cavity wall with an episcope on sectioned teeth. A ceramic mould, simulating a Class II, was filled according to the different groups and the samples were analyzed with a Bruker IFS 55 spectrometer on ultrathin sections (3 mu). The results were analyzed in terms of area unit ratio and total exposed energy. Under the same conditions, a microhardness test was run with a Frank Weihem machine. RESULTS: The results of the sealing evaluation for light-tip, incremental and self-cured techniques did not differ. The plasma procedure failed in this evaluation as the bottom increment was not polymerized. The smallest area unit ratio (the best degree of conversion) was observed in 2 groups: one, the combination of the light-tip and soft process, and two, the self-cured resin composite (B2B). The distance at which the plasma procedure failed to cure the resin composite was between 3.5 and 4.5 mm. The microhardness test confirmed the FTIR analysis except for the group G2 (TC + light-tip). As also shown by FTIR analysis, no difference between the two relevant levels was observed with the hardness test. CONCLUSION: The dentin marginal sealing efficiency of Tetric Ceram restorations was increased with the light-tip technique, but was not better than the self-cured resin composite (B2B). For Tetric Ceram, the combination of the light-tip and soft process leads to a higher degree of conversion than the other groups. There is no linear relationship between the degree of conversion, the microhardness and the total exposed energy. The combination of the soft polymerization and the light-tip device might be an alternative restorative technique to the current incremental technique.

Acrylates↗
PubMedDate not supplied

Effects of a glass-ionomer cement on the remineralization of occlusal caries--an in situ study.

This work evaluated the remineralization of demineralized enamel of pits and fissures of human third molars sealed with a glass ionomer cement (Fuji IX, GC Corporation--Japan) or with a Bis-GMA sealant (Delton--Dentsply). Ten volunteers participated in this in situ study that consisted of two thirty-day periods using intra-oral devices, with a weeks interval in between. Four experimental treatment procedures and one control were randomly assigned to the volunteers specimens: Group I, no treatment, control; Group II, artificial caries process; Group III, same treatment as Group II, but sealed with Delton (Dentsply); Group IV, same treatment as Group II, but sealed with Fuji IX (GC Corporation--Japan); Group V, same treatment as Group II and no sealing. Groups I and II were not submitted to the oral environment and served as controls. After a period of 30 days in the oral environment, the specimens were removed from the devices, embedded in acrylic resin, ground flat and polished. Then, Knoop hardness tests were performed, with a 25 g static load applied for 15 seconds. The measurements were made from the base of the fissure up to an opening of 600 microm, pre-established between the inclines of the cusps. Three indentations were then made, located at 25, 75, and 125 microm in depth from the outer enamel margin and 100 microm apart from each other (Micromet 2003). The Brieger F and Bonferronis tests were applied to the measurements. It was concluded that sealing with the glass ionomer cement Fuji IX was capable of making the enamel of pits and fissures more resistant by increasing the value of Knoop hardness.

Bisphenol A-Glycidyl Methacrylate↗