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At least 199 records · Page 11Linked to original sources
PubMed1998

Long-term surface micro-hardness of resin-modified glass ionomers.

OBJECTIVES: The presence of a resin component in resin-modified glass-ionomer cements (RMGICs) results in considerable water sorption which may affect the surface hardness of the materials. This study investigated the effect of long-term storage in aqueous solutions on the surface hardness of RMGICs. METHODS: The surface micro-hardness of four RMGICs stored in either distilled water or artificial saliva was measured using the Wallace microindentation tester at regular time intervals up to 360 days. RESULTS: There was a substantial increase in hardness during the first day of storage when RMGICs were kept in distilled water. All RMGICs except one liner/base material reached their maximum hardness within 7 days and maintained their hardness for up to 1 year. RMGICs stored in artificial saliva were relatively softer and showed a decrease in surface hardness with time. CONCLUSIONS: The post-hardening reaction overcame the plasticising effect of water when RMGICs were stored in distilled water. However, progressive and high water uptake of specimens stored in artificial saliva resulted in a decrease in their surface hardness.

Analysis of Variance↗
PubMed1999

Evaluation of colour and hardness changes of soft lining materials in food colorant solutions.

The aim of this study was to measure the colour stability and viscoelastic properties of three commercially available soft lining materials in vitro, by exposing them to 3% erythrosine, tartrazine and sunset yellow solutions. The colour changes were determined using a computer controlled spectrophotometer. The colour change of three soft lining materials--Molloplast B, Flexor and Coe Super Soft--were determined after 1, 3 and 6 months storage in three different food colorant solutions. The colour changes of Molloplast B was not noticeable. Only the initial colour value of Flexor was significantly different from the other time interval colour measurements. On the other hand, the colour difference of Coe Super Soft was found to be significantly different at all comparative time interval measurements (P<0.05). According to Shore A hardness values, Molloplast B had an initial hardness of 44 in all three solutions, and there was a slight increase after 6 months. Flexor had an initial hardness of 39, at the end of 6 months the hardness changed a little. Coe Super Soft was fairly hard after processing and Shore A hardness was initially 89 which increased to 95 later on. According to these results, only the hardness values of Coe Super Soft showed a statistically significant difference when compared using Wilcoxon signed rank test at the P<0.05 level. As a conclusion, silicon type soft lining material seems to be more resistant to colour change and hardness than the acrylic type soft liners.

Acrylic Resins↗
PubMed1990

[Development of a system for static measurement of skin-muscle hardness and a fundamental study on its applications].

There have been many attempts to quantitatively measure the hardness of skin-muscle, but no objective method for doing so has been established, because there is no universal standard for the hardness of organisms. The author considered elasticity and viscosity as the most important mechanical properties of the hardness of skin-muscle and applied the Maxwell model, in which a spring and a dash-pot are arranged in a series, to the static mechanical behavior of skin-muscle. A relatively large globular pressing body with a radius of 5 mm was set as a transducer in the measuring system, so that the conformity of the practically measured values to those calculated theoretically by the model was increased. Strain of skin-muscle is expressed as a function of the load, which includes indices of elasticity (1/M) (M(N/mm2) = E/(1-lambda 2) (E: Young's modulus, lambda:Poisson's ratio)) and viscosity (1/eta) (eta:modulus of viscosity) in a particular region. Because hardness is defined as the degree of resistance against transformation by loading, decreases in the indices of both elasticity and viscosity mean increases of hardness. With 150 male and female office workers chosen as the subjects, the model was examined and the indices were calculated. The results were as follows. 1) Very good conformity of practically measured values to those calculated theoretically by the Maxwell model was recognized within the range of load velocity from 0.3 G to 3.0 G (N/sec). 2) In both males and females the regions with values nearest to those of a Newtonian fluid were, in descending order, the distal phalanxes of digiti 2-4, the palm, the distal phalanx of the first digitus and the arm. In reverse order these regions approached complete elasticity. 3) In males it was suggested that the element of viscosity in the region of the biceps brachii muscle and the hardness in the regions of the brachioradialis, the flexor carpi radialis and palmalis longus muscles and the distal phalanxes of the 4th and the 5th digiti were increased with age. In females, a decrease in hardness in the region of the biceps brachii muscle with age was observed. 4) The indices of not only elasticity, but also of viscosity in females were higher than those in males. The results showed that for both elasticity and viscosity, the hardness of skin-muscles in males were higher than that in females. Furthermore, the index of plasticity was determined by examining the mark remaining after unloading, and good correlation of the index to age was observed.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed2006

In-vitro investigation on suitability of light-cured resins for interocclusal splints : part II: surface hardness.

OBJECTIVE: The aim of the present study was to determine the surface hardness of light- and auto-cured resins for the fabrication of occlusal splints employing Vickers hardness measurements. MATERIALS AND METHOD: In this study we used three auto-polymerized resins (Palapress, Orthocryl, Steady-Resin M) and four light-polymerized resins (Acrylight, Primosplint, Triad Tran- Sheet Colorless and Triad TranSheet Pink). The Vickers hardness measurement was carried out by means of a universal Durimet indenter applying a test load of 50 g for 30 seconds. The light-cured resins were polymerized in a Tagris Power light oven for 10 and 15 minutes each. Three separate test series were carried out (the hardness of plates under optimal conditions and of occlusal splints was measured, and the curing of light-polymerizing materials in layers of varying depth was evaluated). Data underwent statistical analysis via ANOVA and the Scheffé test. RESULTS: The microhardness determined in each case amounted to values between 10.4 HV 0.5 and 39.3 HV 0.5. The Vickers hardness determined for the plates that had been produced under optimal conditions demonstrated that their surface was significantly (p < 0.05) harder than that of cylinders and splints. The hardness values of the light-cured material Triad TranSheet Pink (39.3 HV 0.5) were significantly higher (p < 0.05) than those of all other resins. In all auto-polymerized resins, the surface hardness of the samples we examined (in the form of plates and splints) was significantly lower (p < 0.05) than that of the light-cured materials Triad TranSheet Pink and Colorless. CONCLUSION: The results we have obtained so far concerning surface hardness indicate that, in the fabrication of occlusal splints, light-cured resins may represent an alternative to auto-polymerizing materials.

Absorption↗
PubMed1994

A comparison of the hardness of different types of titanium and conventional metal ceramics.

This study compared the surface hardness of machine milled titanium and cast titanium, and the surface hardness profile of a gold-palladium alloy, a nickel chromium alloy, milled and cast titanium. For each group, 15 discoid specimens, 10 mm in diameter and 5 mm thick, were fabricated by either casting or milling. Five specimens of each group underwent one of three treatments: (1) no heat treatment, (2) a standard heat treatment, or (3) an extended heat treatment. Knoop hardness values were determined. Results indicated that the Knoop hardness of cast titanium was less than that of the cast titanium standard treatment group, which was less than the Knoop hardness of the cast titanium extended treatment group. Knoop hardness of milled titanium was less than that of the milled titanium standard treatment and milled titanium extended treatment groups. For the surface hardness profile, cast titanium showed a decreasing surface hardness as the distance from the surface of the specimen increased. No such trend was identified for the other groups tested.

Chromium Alloys↗
PubMed2006

Age-related changes in hardness and modulus of elasticity of dentine.

OBJECTIVES: Little knowledge has been clarified about the relationship between the morphological and physical changes of dentine during aging. The purpose of this study was to clarify the modulus of elasticity and hardness related to the morphological changes of dentine by aging using a transmitted light microscope (TLM) and a nano-hardness tester (NHT). METHODS: Aged human molars and young third molars were used. The dentine morphology was observed under a TLM. The hardness and Young's modulus of elasticity related to the morphologic study were evaluated with an NHT. RESULTS: The thickness of mantle dentine and globular dentine of aged teeth were less than that of young teeth. Transparent dentine was observed only underneath the attrition of young teeth. Reactionary tertiary dentine formed and a "dark zone" was found at the junction between physiologic secondary and reactionary dentine only in aged teeth. At the mantle dentine, hardness and modulus of elasticity of aged dentine were higher than those of young dentine. The reactionary dentine in aged teeth and newly developed secondary dentine in young teeth demonstrated lower modulus of elasticity and hardness than those of other circumpulpal dentine. Relatively low modulus of elasticity and hardness were observed at the zone between secondary and reactionary dentine. CONCLUSIONS: Changes in dentine due to aging resulted in transformation of morphological features causing changes to their hardness and modulus of elasticity at the explicit areas such as the increase of hardness and modulus of elasticity at mantle dentin and the reduction of these properties at the "dark zone" that found in aged teeth.

Adolescent↗
PubMed1998

A pilot study comparing the efficacy of hard and soft stabilizing appliances in treating patients with temporomandibular disorders.

STATEMENT OF PROBLEM: Soft and hard stabilizing appliances have been used to treat temporomandibular disorders. No data exist to suggest whether a hard or soft appliance is beneficial. PURPOSE: This study compared soft and hard acrylic resin stabilizing appliances in the reduction of masticatory muscle pain in patients with temporomandibular disorders. MATERIALS AND METHODS: Twenty-three patients with at least one clinical sign from the list of diagnostic subgroups of temporomandibular disorders were alternately assigned a hard or soft appliance for temporomandibular disorder treatment. No other temporomandibular disorder treatment (self-care, physical therapy, biofeedback, or muscle or joint injections) was rendered. Each patient was seen by two dentists at each visit. One dentist initially fabricated the appliance and adjusted the appliance on each visit and an examining dentist examined the patient each visit and recorded signs of temporomandibular disorders. The appliance material (soft or hard) was not disclosed to the examining dentist, only to the dentist who fabricated and adjusted the appliance. Patients were examined and appliances were adjusted every 2 to 3 weeks for a minimum of 10 weeks. Masticatory muscles were palpated and charted on each visit. Data were analyzed and subjected to nonparametric Mann-Whitney test. RESULTS: Eighteen of the initial 23 patients, 7 in the hard appliance group and 11 in the soft appliance group finished the study over 10- to 15-week period. Soft and hard appliances performed the same in reduction of masticatory muscle pain. CONCLUSION: This study suggests, based on the limited number of participants, that soft and hard stabilizing appliances may be equally useful in reducing masticatory muscle pain in short-term appliance therapy.

Acrylic Resins↗
PubMed2002

The hardness of food plays an important role in food selection behavior in rats.

To examine the importance of the hardness of foods, we conducted behavioral and electromyographical experiments in Wistar male rats using three kinds of pellets, a hard commercially made pellet (MF), a hard privately produced pellet (H) and a soft privately produced pellet (S). MF and H had the same hardness but contained different ingredients, and S and H had the same ingredients but different degrees of hardness (S<H). In the behavioral experiment, when the rats fed with MF during the 3 weeks following weaning were presented with two types of pellets, S and H, they preferred S to H. On the other hand, the rats fed with powdered MF during the 3 weeks following weaning could not discriminate between S and H on the 1st day of the 6th week. When we compared the EMG activities of the masseter muscle during feeding of S or H pellets, we found that the rats raised on powdered food could not control their muscular power according to the hardness of foods on the first test day; however, rats recovered from this disability after one-day feeding of H and S pellets. After ingestion of either S or H was paired with an intraperitoneal (ip) injection of 0.15 M LiCl (2% of body weight), the animals of both groups avoided the pellets paired with LiCl. However, when the presented pellets were crushed, rats did not discriminate between crushed S and crushed H. These results suggest that the hardness of food plays an important role in the selection and ingestion of food and that the hardness of food could be a conditioned stimulus for conditioned food aversion.

Animals↗
PubMed1993

The relationship between clinical classification of cataract and lens hardness.

'Hardness' of the cataractous lens is one of the major factors influencing the suitability of a patient for phacoemulsification. Surgeons should be able to estimate hardness when choosing patients for this method of cataract extraction. The aims of the study were to investigate the relationship between the clinical appearance of cataracts and their hardness. Ninety-one lenses were studied from patients undergoing endocapsular cataract extraction. Lenses were assessed using a classification based on the Lens Opacities Classification System II and hardness was assessed using an automated lens guillotine. The degree of nuclear sclerosis and the age of the patient were found to influence lens hardness. Regression analysis showed that 56% of the variation in hardness could be explained in terms of age and the degree of nuclear sclerosis. The presence of posterior subcapsular and cortical cataract did not influence hardness. These findings confirm our clinical suspicions and enable surgeons to make a more objective analysis of hardness prior to phacoemulsification.

Adult↗
PubMed1997

Effects of food texture and sample thickness on mandibular movement and hardness assessment during biting in man.

This study was designed to investigate the relationship among jaw movements, physical characteristics of food, and sensory perception of hardness in man. Vertical movements of the mandible were recorded with an infrared tracking device in humans during biting on two test foods, carrot and cheese. Samples of standard length (2 cm) and width (2 cm) were prepared in three different thicknesses (0.5, 1.0, and 1.5 cm). Nine subjects were asked to perform two types of bite with their incisor teeth. In the first, they cut through the food, then stopped and spat out the pieces (bite alone); in the second, biting was followed by mastication and swallowing (bite+chew). The 12 conditions (thickness x3, food x2, and bite x2) were presented in a random order within each block, and blocks were repeated five times (60 trials per subject). Subjects also estimated the hardness of the samples twice for each condition on visual analogue scales (VAS) 100 mm long. The duration, vertical amplitude, and maximum vertical velocity of the mandible during biting were calculated by computer for the three phases of the movements (opening, and fast and slow closing). Multilevel statistical models were used for data analysis. The estimated hardness scores associated with the first bite of thin carrot (59.0 VAS units) was significantly greater than for cheese (16.8 VAS units). The type of bite had no significant effect on these scores, but the estimate of hardness was significantly greater for the thickest sample (+13.3 VAS units). Food type had its strongest effect on the slow-closing phase. In particular, the peak velocity that followed the fracturing of the food sample was much greater for carrot than for cheese (thin, 34.1 mm.s-1 vs. 26.6 mm.s-1), and the difference between foods increased with thickness. The amplitude of opening was significantly greater for the thickest sample than for the other two. There were no significant relationships between VAS scores and the movement parameters. These results suggest that, when humans bite food: (1) changing the thickness of food has a greater effect on movement parameters than changing from soft to hard food, (2) the parameters of biting change little if biting is followed by mastication, (3) hardness perception is dependent on the thickness of food, (4) hardness perception is not different when food is removed from the mouth than when it is chewed and swallowed, and (5) there is no relationship between any of the parameters of movement that change with food type and the perceived hardness of food.

Adult↗
PubMed1993

Gingival recession in relation to history of hard toothbrush use.

Gingival recession studies in the U.S. have related primarily to sex and age with little consideration of toothbrush hardness. This preliminary study examined the relation between a history of hard toothbrush use and gingival recession. A total of 182 subjects, male and female, between 18 and 65 years of age, with a minimum of 18 natural teeth, no advanced periodontitis or history of periodontal surgery were examined. Gingival recession was scored as present whenever the free gingival margin was apical to the cemento-enamel junction and root surface was exposed. History of hard toothbrush use was ascertained. Eighty-two subjects had a history of hard toothbrush use, 77 did not, and 23 did not know. The percentage of subjects with recession increased with age from 43% to 81%, with a figure of 63% for all age groups combined. Males tended to show slightly greater levels of recession than females. Regression analysis showed that females had about 4 percentage points less receded surfaces than males. Recession was also found to be more pronounced for subjects with a history of hard toothbrush use, with a mean of 9.4% receded surfaces versus 4.7% for those who had never used a hard brush. For users of hard toothbrushes, the percent of surfaces with recession showed a significant and dramatic increase with increasing brushing frequency; this effect did not exist for those without a history of hard brush use. The relation with age was highly significant, with regression analysis showing that the percent of surfaces with recession tends to increase about 3.5 percentage points per decade.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMedDate not supplied

Reliability and validity of an instrument to measure tissue hardness in breasts.

The author investigated the effectiveness of the Roberts Durometer, an instrument developed to measure human tissue hardness for a study on breast engorgement. The instrument is a small portable pressure gauge comprising a probe attached to a spring and contained in a tubular housing, connected to a dial gauge. The instrument was first trialed using foam rubber of differing hardness and football bladders of differing hardness. It was then used to measure the hardness of a non-pregnant, non-lactating human breast, followed by trials on postpartum women comparing breast tissue hardness on the day of birth with that of subsequent days. The instrument detected significant differences in hardness of foams, football bladders and human breast tissue. It was therefore considered suitable for measuring, in both research and clinical applications, hardness of breast tissue, which is a major physical feature of breast engorgement. Other clinical applications could include the hardness of abdominal and other skin tissues in conditions such as ascites, peritonitis and cellulitis.

Breast↗
PubMed1992

[Comparison of methods for determining corn hardness (Zea mays L.)].

One of the most important intrinsic properties of corn kernels is hardness. Nowadays controversy exists as to which method is more accurate to measure this property. In the present study, therefore, several methods for measuring hardness in corn kernels are compared, for the purpose of finding the most appropriate one. A corn population ranking from hard to soft was tested. The methods tested were: endosperm texture (ET), pearling index (PI) floating index (FI), density (D), near infrared reflectance (NIR), test weight (Ph) and time required to grind the corn with the Brabender automatic micro-hardness (TDB) method. The floating index (FI) method was found to be the most suitable one for determining hardness of corn kernels. This method permitted determination of the differences existing in corn with hard, intermediate, and soft-textured endosperms, with low variation coefficients. The TDB and NIR methods were not appropriate to determine the hardness of corn kernels, showing high variability in the results. With the Ph and D methods it was difficult to distinguish between corn with hard, intermediate and soft texture endosperm.

Evaluation Studies as Topic↗
PubMed1997

Surface hardness and wear of glass ionomers and compomers.

PURPOSE: To determine the surface hardness and in vitro wear of glass ionomer cements (GIC) and compomers in comparison with a resin composite and to test for a possible correlation between the determined hardness and wear values. MATERIALS AND METHODS: Samples were made of conventional GIC (Ketac-Fil, Fuji II, Fuji IX, Ketac-Prototype = Ketac-Molar), resin-modified GIC (Photac-Fil, Fuji II LC, Vitremer), compomers (Dyract, Compoglass) and resin composite (Z100) for the hardness test (n = 10) and for the wear test (n = 3). The materials were handled according to the manufacturers' instructions. The samples were stored in deionized water for 48 hours at 37 degrees C prior to the determination of Rockwell hardness and three-body in vitro wear. RESULTS: Hardness could not be measured on Ketac-Fil and Fuji II as the samples fractured before a reading was obtainable. Statistically significant differences were found in hardness and wear between brands and between the four types of material. Surface hardness: resin-modified GIC < conventional GIC = compomers < resin composite. In vitro wear: resin-modified GIC > compomers > conventional GIC > resin composite. A negative correlation between hardness and wear was recorded.

Analysis of Variance↗
PubMed1993

The health status and health care utilization of deaf and hard-of-hearing persons.

OBJECTIVE: To evaluate whether health habits, self-reported health status, and communication with physicians play a role in the known altered health care utilization patterns of deaf and hard-of-hearing persons. DESIGN: A cross-sectional survey. Respondents were given the choice of completing either a self-administered written survey or an American Sign Language interview-administered survey. POPULATION: Eighty-seven deaf and hard-of-hearing members of various organizations serving this population in southeastern Michigan and 88 hearing patients from a family practice clinic in the same area. RESULTS: Deaf and hard-of-hearing persons visit physicians more frequently (P = .01), have a lower incidence of ever smoking tobacco (P < .0006) and of alcohol use (P = .04), have more difficulties communicating with physicians (P < .001), have trouble understanding physicians (P < .001), and feel less comfortable with physicians (P < .001). Lower current tobacco use among deaf and hard-of-hearing persons was only seen in persons who were not educated beyond high school. Increased frequency of physician visits for deaf and hard-of-hearing persons was especially noticeable in the group of persons 60 years of age and older. Our finding that use of interpreters is associated with increased utilization and decreased understanding suggests deaf and hard-of-hearing patients presenting with interpreters warrant more focused attention from physicians. Reasons for seeing physicians did not explain the difference in frequency of physician visits between the two groups. CONCLUSIONS: Deaf and hard-of-hearing persons report a lower subjective health status and higher physician utilization, as well as substantial communication difficulties with physicians. They also report better health-related behaviors, namely less use of tobacco and alcohol. The use of interpreters did not decrease physician utilization or improve the understanding of physicians by these persons. Overall, our results underscore the fact that deaf and hard-of-hearing persons constitute a minority population that experiences considerable difficulties in the patient-physician relationship.

Adult↗
PubMed1996

Association of elevated serum lipid levels with retinal hard exudate in diabetic retinopathy. Early Treatment Diabetic Retinopathy Study (ETDRS) Report 22.

OBJECTIVE: To evaluate the relationship between serum lipid levels, retinal hard exudate, and visual acuity in patients with diabetic retinopathy. DESIGN: Observational data from the Early Treatment Diabetic Retinopathy Study. PARTICIPANTS: Of the 3711 patients enrolled in the Early Treatment Diabetic Retinopathy Study, the first 2709 enrolled had serum lipid levels measured. MAIN OUTCOME MEASURES: Baseline fasting serum lipid levels, best-corrected visual acuity, and assessment of retinal thickening and hard exudate from stereoscopic macular photographs. RESULTS: Patients with elevated total serum cholesterol levels or serum low-density lipoprotein cholesterol levels at baseline were twice as likely to have retinal hard exudates as patients with normal levels. These patients were also at higher risk of developing hard exudate during the course of the study. The risk of losing visual acuity was associated with the extent of hard exudate even after adjusting for the extent of macular edema. CONCLUSIONS: These data demonstrate that elevated serum lipid levels are associated with an increased risk of retinal hard exudate in persons with diabetic retinopathy. Although retinal hard exudate usually accompanies diabetic macular edema, increasing amounts of exudate appear to be independently associated with an increased risk of visual impairment. Lowering elevated serum lipid levels has been shown to decrease the risk of cardiovascular morbidity. The observational data from the Early Treatment Diabetic Retinopathy Study suggest that lipid lowering may also decrease the risk of hard exudate formation and associated vision loss in patients with diabetic retinopathy. Preservation of vision may be an additional motivating factor for lowering serum lipid levels in persons with diabetic retinopathy and elevated serum lipid levels.

Adult↗
PubMed2002

Expression of wild-type pinB sequence in transgenic wheat complements a hard phenotype.

Wheat grain hardness is a major factor in the wheat end-product quality. Grain hardness in wheat affects such parameters as milling yield, starch damage and baking properties. A single locus determines whether wheat is hard or soft textured. This locus, termed Hardness ( Ha), resides on the short arm of chromosome 5D. Sequence alterations in the tryptophan-rich proteins puroindoline a and b (PINA and PINB) are inseparably linked to hard textured grain, but their role in endosperm texture has been controversial. Here, we show that the pinB-D1b alteration, common in hard textured wheats, can be complemented by the expression of wild-type pinB-D1a in transformed plants. Transgenic wheat seeds expressing wild-type pinB were soft in phenotype, having greatly increased friabilin levels, and greatly decreased kernel hardness and damaged starch. These results indicate that the pinB-D1b alteration is most likely the causative Ha mutation in the majority of hard wheats.

Journal Article↗
PubMed2006

Grain characterization and milling behaviour of near-isogenic lines differing by hardness.

Wheat grain hardness is a major factor affecting the milling behaviour and end-product quality although its exact structural and biochemical basis is still not understood. This study describes the development of new near-isogenic lines selected on hardness. Hard and soft sister lines were characterised by near infrared reflectance (NIR) and particle size index (PSI) hardness index, grain protein content, thousand kernel weight and vitreousness. The milling behaviour of these wheat lines was evaluated on an instrumented micromill which also measures the grinding energy and flour particle size distribution was investigated by laser diffraction. Endosperm mechanical properties were measured using compression tests. Results pointed out the respective effect of hardness and vitreousness on those characteristics. Hardness was shown to influence both the mode of fracture and the mechanical properties of the whole grain and endosperm. Thus, this parameter also acts on milling behaviour. On the other hand, vitreousness was found to mainly play a role on the energy required to break the grain. This study allows us to distinguish between consequences of hardness and vitreousness. Hardness is suggested to influence the adhesion forces between starch granules and protein matrix whereas vitreousness would rather be related to the endosperm microstructure.

Alleles↗