Ultimate tensile strength of dentin: Evidence for a damage mechanics approach to dentin failure

Dentin structure and properties are known to vary with orientation and location. The present study explored the variation in the ultimate tensile strength (UTS) of dentin with location in the tooth. Hourglass specimens were prepared from dentin located in the center, under cusps, and in the cervical regions of human molar teeth. These were tested in tension at various distances from the pulp. Median tensile strengths ranged from 44.4 MPa in the inner dentin near the pulp, to 97.8 MPa near the dentino-enamel junction (DEJ). This increase in the median UTS with distance from the pulp to the DEJ was statistically significant (P <.001). Of particular importance was the observation that the UTS measurements followed a Weibull probability distribution, with a Weibull modulus of about 4.5. The Weibull behavior of the UTS data strongly suggests that the large variances in fracture strength data result from a distribution of preexisting defects in the dentin. These findings justify a damage-mechanics approach to studies of dentin failure.     

Vitamin A deficiency and the acute phase response among HIV-1-infected and -uninfected women in Kenya

Among HIV-1-infected individuals, vitamin A deficiency has been associated with faster disease progression and greater infectivity in observational studies, but randomized clinical trials have shown no effect of vitamin A supplementation. We conducted a cross-sectional study of 400 HIV-1-infected and 200 HIV-1-uninfected women in Mombasa, Kenya to examine the relations between vitamin A deficiency (serum retinol <30 microg/dL) and HIV-1 status, HIV-1 disease stage, and the acute phase response (serum C-reactive protein >or=10 mg/L and/or alpha1-acid glycoprotein >or=1.2 g/L). Among the HIV-1-infected women, the effect of vitamin A supplementation was examined in a randomized trial. Vitamin A deficiency was independently associated with HIV-1 infection (OR = 2.7, 95% CI: 1.9-4.0) and the acute phase response (OR = 2.8, 95% CI: 1.9-4.1). Among HIV-1-infected women, vitamin A deficiency and the acute phase response were associated with each other and were both independently associated with higher HIV-1 plasma viral load and lower CD4 count. HIV-1-infected women having an acute phase response had no increase in serum vitamin A levels after supplementation. Serum levels increased significantly among women without an acute phase response, although not to normal levels among women who were deficient at baseline. Among HIV-1-infected individuals, it is likely that low serum vitamin A concentrations reflect more active infection and the acute phase response. These results provide possible explanations for the disparity between observational studies and randomized trials of vitamin A for HIV-1 infection.     

Method for primary culture of purified leydig cells isolated from adult rat testes

Summary Preparations of 75–80% pure Leydig cells are prepared by Percoll gradient centrifugation of crude testicular interstitial cell suspensions. Using the methods described herein, the purified Leydig cells retain their functional characteristics for at least 72 hours in primary culture.     

Transformation ofGaeumannomyces graminis to benomyl resistance

Summary Gaeumannomyces graminis var.graminis andtritici were transformed to benomyl resistance using pBT3, a plasmid encoding fungicide-resistant -tubulin. Either circular or linear plasmid DNA producedG. graminis var.graminis transformants in which plasmid DNA was integrated into the fungal genome. There was no evidence for autonomous plasmid replication in any of the transformants examined. 4/11 linear DNA transformants had a single plasmid copy, whereas 8/9 circular DNA transformants had multiple copies of the plasmid. Integration of transforming DNA occurred by nonhomologous recombination in all (20/20) of these transformants.     

Atypical glandular cells--an update

The diagnostic category of atypical glandular cells (AGC) in the Bethesda system for the reporting of cervicovaginal cytology has undergone significant modification since its inception in 1988. More than a decade later, this category remains a diagnostic challenge to both clinicians and cytopathologists because of the lack of uniform cytologic criteria, the lack of interobserver agreement in the diagnosis, and the lack of standardized patient management guidelines. This article reviews the current classification of AGC in the Bethesda system, the cytomorphologic features and differential diagnosis, the clinical significance of a diagnosis of AGC, and the clinical management of patients with AGC. This article provides a comprehensive clinicopathologic review of the category of AGC.     

The effect of haemorrhage on haemoglobin concentration, blood volume and arterial pressure in kittens and cats

1. The arterial haemoglobin concentration in kittens less than 24 hr old was inversely related to body weight. There was about twice as much haemoglobin/unit body weight at birth as in adult cats. Haemoglobin concentrations were minimal at 3-6 weeks of age.2. In animals lightly anaesthetized with sodium pentobarbitone, arterial pressure rose from 52 mm Hg at birth in kittens to 133 mm Hg in adult cats. Blood volume decreased from 73 ml./kg at birth to 60 ml./kg in adults.3. When kittens less than a fortnight old were subjected to stepwise blood letting, arterial pressure fell proportionately with blood volume; in older kittens and in cats, arterial pressure was less well maintained at similar proportionate reductions of blood volume than in young kittens.4. The responses to haemorrhage of kittens and cats were compared with those of rabbits similarly treated and with those of adult cats anaesthetized with urethane and chloralose reported in the literature.     

Effects of stimulus emotionality and sentence generation on memory for words in adults with unilateral brain damage

Does sentence generation and/or stimulus emotionality enhance verbal memory in patients with neurological impairment? This question was addressed by testing 40 patients with unilateral stroke (20 with left-brain and 20 with right-brain damage) and 20 healthy control participants for recall and recognition of 48 target words. During encoding, emotional and nonemotional words were either presented in sentences (read condition) or used to form sentences (generate condition). Both word emotionality and generative processing improved memory performance in all groups. The authors suggest that a similar influence (i.e., cognitive activation) underlies both of these memory-enhancing effects, although the putative origins of the 2 effects are quite different. Neuropsychological underpinnings and clinical implications of these phenomena are discussed.     

Postnatal growth of lung parenchyma in the piglet: Morphometry correlated with mechanics

Background: A previous study of piglet lung growth (Mansell et. al. 1989. J. Appl. Physiol., 67:1422–1427) showed transient stiffness to changes in shape and volume immediately after birth. Later, elastic recoil was found to increase as the lung grew in weight and volume. The present study uses morphometry to test possible structural correlates of these two mechanical changes. Methods: Piglet lungs were fixed near full inflation via the airways during the immediate newborn period (6–12 hours, n=3), at 3–5 days (n=6), 25–30 days (n=5), and 80–85 days (n=3). Morphometry comprised arithmetic and harmonic mean thicknesses of alveolar septae and average mean surface curvature. Measurements of curvature and airspace volume were combined to differentiate alveolar expansion from septal proliferation as mechanisms for volumetric growth. Results: The unique mechanical behavior of the newborn lungs was associated with relatively thick alveolar septae. Marked thinning of the septae and resolution of the stiffness to shape and volume change had occurred by 3–5 days. An increase in elastic recoil during the first postnatal month was found to be associated with simple airspace expansion. The second and third months were characterized by septal proliferation and increase in arithmetic mean septal thickness but elastic recoil did not increase further. Harmonic mean septal thickness and airspace volume per gram of lung tissue did not change over the course of the study. Conclusions: 1) A relative stiffness to shape and volume change in freshly newborn piglet lung is associated with relatively thick alveolar septal walls; 2) postnatal development of piglet lung parenchyma involves septal lengthening and thinning followed by septal proliferation; 3) the initial phase of septal lengthening, rather than the later phase of septal proliferation, is associated with increase in parenchymal recoil. © 1995 Wiley-Liss, Inc.     

Evidence for linkage of nonsyndromic cleft lip with or without cleft palate to a region on chromosome 2

Results from a genome-wide screen of 10 multiplex families ascertained through probands with nonsyndromic cleft lip with or without cleft palate (CL/P) in Mexico, Argentina, and the United States yielded suggestive evidence of linkage to chromosomes 2, 6, 17 and 18. Fine mapping excluded all regions except chromosome 2. Subsequent analysis was performed on the original 10 families plus an additional 16 families using 31 markers on chromosome 2. This analysis showed intriguing evidence of linkage to 2q (Zlr=2.26, empirical P-value=0.028 in a chromosome-wide analysis). Transmission disequilibrium tests also revealed evidence of linkage and disequilibrium for two markers in this region (D2S168 and D2S1400 with P-values=0.022 and 0.006, respectively). A subset of these 26 families provided additional evidence for a susceptibility gene for CL/P on 2q, suggesting that further studies of genes in this region are warranted.