Delayed Photoactivation of Dual-cure Composites: Effect on Cuspal Flexure, Depth-of-cure, and Mechanical Properties

Objectives:

This study tested whether delayed photoactivation could reduce shrinkage stresses in dual-cure composites and how it affected the depth-of-cure and mechanical properties.

Methods and Materials:

Two dual-cure composites (ACTIVA and Bulk EZ) were subjected to two polymerization protocols: photoactivation at 45 seconds (immediate) or 165 seconds (2 minutes delayed) after extrusion. Typodont premolars with standardized preparations were restored with the composites, and cuspal flexure caused by polymerization shrinkage was determined with three-dimensional scanning of the external tooth surfaces before restoration (baseline) and at 10 minutes and one hour after photoactivation. Bond integrity (intact interface) was verified with dye penetration. Depth-of-cure was determined by measuring Vickers hardness through the depth at 1-mm increments. Elastic modulus and maximum stress were determined by four-point bending tests (n=10). Results were analyzed with two- or three-way analysis of variance and pairwise comparisons (Bonferroni; α=0.05).

Results:

Delayed photoactivation significantly reduced cuspal flexure for both composites at 10 minutes and one hour (p≤0.003). Interface was >99% intact in every group. Depth-of-cure, elastic modulus, and flexural strength were not significantly different between the immediate and delayed photoactivation (p>0.05). The hardness of ACTIVA reduced significantly with depth (p<0.001), whereas the hardness of Bulk EZ was constant throughout the depth (p=0.942).

Conclusions:

Delayed photoactivation of dual-cure restorative composites can reduce shrinkage stresses without negatively affecting the degree-of-cure or mechanical properties (elastic modulus and flexural strength).

Darbepoetin alfa (Aranesp®) improves recognition memory in adult rats that have sustained bilateral ventral hippocampal lesions as neonates or young adults

Recognition memory was assessed in adult rats that received bilateral injections of saline (sham lesions) or ibotenic acid (lesioned) in the ventral hippocampus as neonates (postnatal day 7, PD7) or young adult (42 days of age, PD42) using the Novel Object Recognition Test (NORT). Normal or sham-lesioned rats were able to distinguish novel from familiar objects over a 0.5 and 2 h delay between the sample and choice phases. Adult rats (PD70) lesioned as neonates performed progressively worse than sham-lesioned animals at delays of 0.5 and 2 h. A single injection of darbepoetin alfa (500 or 5000 U/kg, i.p.), given 1 h before the sample phase restored performance 0.5 or 2 h later in the choice phase to same levels as sham-lesioned rats. Adults lesioned on PD42 displayed deficits in NORT performance with a 2 h delay between the choice and sample phases that were completely reversed by administration of darbepoetin alfa (5000 U/kg, i.p.) 1 h before the sample phase. These results suggest that darbepoetin alfa may have utility in treating memory deficits associated with brain dysfunction related to developmental disorders such as schizophrenia.

Effects of minocycline and tetracycline on retinal ganglion cell survival after axotomy

In the present study, we compared the in vivo neuroprotective efficacy of intraperitoneally administered tetracycline and minocycline to enhance the survival of retinal ganglion cells (RGCs) following unilateral axotomy of the adult rat optic nerve. We also examined the effects of the tetracycline drugs on the activation of retinal microglia. RGCs in retinal whole-mounts were visualized by retrograde labeling with fluorogold. The presence of activated microglia was confirmed immunohistochemically using OX-42 monoclonal antibodies. Optic nerve axotomy produced RGC death and increased activation of microglia. No significant RGC loss was seen prior to 5 days and approximately 50% and 80-90% cell loss occurred at 7 and 14 days, respectively. Examination of the effects of tetracycline and minocycline on RGC survival at 7 days post-axotomy, revealed increased numbers of RGCs in minocycline-treated animals (75% of non-axotomized control) compared with vehicle-only (52% of control) and tetracycline-treated (58% of control) animals. The densities of RGCs (RGCs/mm2+/-S.D.) for control, vehicle-, tetracycline- and minocycline-treated axotomized animals were 1996+/-81, 1029+/-186, 1158+/-190 and 1497+/-312, respectively. The neuroprotective effect of minocycline seen at 7 days was transient, since RGCs present in minocycline-treated animals at 14 days post-axotomy (281+/-43, 14% of control) were not significantly different to vehicle-treated animals (225+/-47, 11% of control). OX-42 staining of activated retinal microglia was reduced in tetracycline- and minocycline-treated axotomized animals compared with axotomized animals receiving vehicle-only. These results demonstrate that systemic administration of the second-generation tetracycline derivative, minocycline, delays the death of axotomized RGCs by a mechanism that may be associated with inhibition of microglia activation. The neuroprotective efficacy of minocycline following optic nerve axotomy was superior to that of tetracycline.

Localization and modulation of calcitonin gene-related peptide-receptor component protein-immunoreactive cells in the rat central and peripheral nervous systems

Calcitonin gene-related peptide (CGRP) is widely distributed in the central and peripheral nervous system. Its highly diverse biological activities are mediated via the G protein-coupled receptor that uniquely requires two accessory proteins for optimal function. CGRP receptor component protein (RCP) is a coupling protein necessary for CGRP-receptor signaling. In this study, we established the anatomical distribution of RCP in the rat central and peripheral nervous system and its relationship to CGRP immunoreactivity. RCP-immunoreactive (IR) perikarya are widely and selectively distributed in the cerebral cortex, septal nuclei, hippocampus, various hypothalamic nuclei, amygdala, nucleus colliculus, periaqueductal gray, parabrachial nuclei, locus coeruleus, cochlear nuclei, dorsal raphe nuclei, the solitary tractus nucleus and gracile nucleus, cerebellar cortex, various brainstem motor nuclei, the spinal dorsal and ventral horns. A sub-population of neurons in the dorsal root ganglia (DRG) and trigeminal ganglia were strongly RCP-IR. Overall, the localization of RCP-IR closely matched with that of CGRP-IR. We also determined whether RCP in DRG and dorsal horn neurons can be modulated by CGRP receptor blockade and pain-related pathological stimuli. The intrathecal injection of the antagonist CGRP(8-37) markedly increased RCP expression in the lumbar DRG and spinal dorsal horn. Carrageenan-induced plantar inflammation produced a dramatic bilateral increase in RCP expression in the dorsal horn while a partial sciatic nerve ligation reduced RCP expression in the ipsilateral superficial dorsal horn. Our data suggest that the distribution of RCP immunoreactivity is closely matched with CGRP immunoreactivity in most of central and peripheral nervous systems. The co-localization of RCP and CGRP in motoneurons and primary sensory neurons suggests that CGRP has an autocrine or paracrine effect on these neurons. Moreover, our data also suggest that RCP expression in DRG and spinal cord can be modulated during CGRP receptor blockade, inflammation or neuropathic pain and this CGRP receptor-associated protein is dynamically regulated.

Pyrocatechol Violet Complexation at the Boehmite-Water Interface

Acid/base reactions and pyrocatechol violet complexation at the boehmite-solution interface have been investigated in 0.10 M K(Cl) solution at 298.2 K in the range 5.0</=-log h</=9.0. Equilibrium measurements were performed as potentiometric titrations complemented by spectrophotometric analysis of a ligand (batch adsorption experiments). The experimental data were evaluated on the basis of the extended constant capacitance model, allowing for inner-sphere and/or outer-sphere complexation. The acid/base properties are described by the equilibria: H(+)+ identical withAlOHleft harpoon ovet right harpoon identical withAlOH(2)(+); log beta(1,1,0(int))=7.46+/-0.04 and identical withAlOH left harpoon ovet right harpoon identical withAlO(-)+H(+); log beta(-1,1,0(int))=-9.87+/-0.12. The specific capacitance was determined as 1.00 F m(-2). The binding of pyrocatechol violet {PCV, 2-[(3,4-dihydroxyphenyl)(3-hydroxy-4-oxocyclohexa-2,5-diene-1-ylidene)methyl]benzenesulfonic acid}, H(4)L, was described by the formation of a single inner-sphere complex according to the reaction identical withAlOH+H(4)Lleft harpoon ovet right harpoon identical withAlL(3-)+3H(+)+H(2)O. Allowing for a charge distribution of this complex between the inner plane and beta-plane (-2, -1), a significant improvement of the fit was obtained. The adsorbed complex exhibited a dark blue color over the pH range 5-8.5, indicative of proton loss from the 1,2-dihydroxyl moiety. Furthermore, DRIFT spectra showed the bonding environment of PCV bound to the surface to exhibit similarities with corresponding catechol adsorption to different aluminium (hydr)oxides. These spectral features turned out to be very similar to soluble catechol complexes of Al(III). Thus, it is suggested that PCV forms a mononuclear chelating complex at the boehmite-water interface. The maximum surface coverage reached was ca. 33%, indicating that the high negative charge of the species may result in surface charge "saturation" rather than saturation of surface binding sites. Steric hindrances caused by the large size of PCV may also contribute to the low surface coverage. Copyright 2000 Academic Press.

Housestaff experience, workload, and test ordering in a neonatal intensive care unit

BACKGROUND

Little is known of how the inexperience or the clinical workload of housestaff affects the decisions they make in the neonatal intensive care unit (NICU). The authors hypothesized that less experienced interns would order more tests per infant than more experienced residents, especially under conditions of heavy workload.

METHOD

The NICU at the University of Kentucky A. B. Chandler Medical Center has either an intern or a resident on call by himself or herself at night, a natural setting to compare test ordering by interns and residents. The authors counted the numbers of X rays, analyses of arterial blood gases (ABGs), and electrolyte determinations ordered by the house officers on call for 321 infants from July through November 1993. Data for nine interns and seven residents were compared using multivariate linear regression.

RESULTS

When workload became heavier (about five NICU patients), the interns increased their ordering of ABGs per infant to a significantly greater degree than did the residents (p = .01), with the difference being even greater on weekends when the housestaff were under less supervision (p = .004).

CONCLUSION

As workload becomes greater in the NICU, interns order more ABGs per infant than do more experienced residents, especially when the interns are less supervised.

Vegetarian diet as a risk factor for tuberculosis in immigrant south London Asians

BACKGROUND

In a previous retrospective study of tuberculosis in south London among Asian immigrants from the Indian subcontinent Hindu Asians were found to have a significantly increased risk for tuberculosis compared with Muslims. This finding has been further investigated by examining the role of socioeconomic and lifestyle variables, including diet, as risk factors for tuberculosis in Asian immigrants from the Indian subcontinent resident in south London.

METHODS

Using a case-control study technique Asian immigrants from the Indian subcontinent diagnosed with tuberculosis during the past 10 years and two Asian control groups (community and outpatient clinic controls) from the Indian subcontinent were investigated. Cases and community controls were approached by letter. A structured questionnaire concerning a range of demographic, migration, socioeconomic, dietary, and health topics was administered by a single trained interviewer to subjects (56 cases and 100 controls) who agreed to participate.

RESULTS

The results confirmed earlier findings that Hindu Asians had an increased risk of tuberculosis compared with Muslims. However, further analysis revealed that religion had no independent influence after adjustment for vegetarianism (common among Hindu Asians). Unadjusted odds ratios for tuberculosis among vegetarians were 2.7 (95% CI 1.1 to 6.4) using community controls, and 4.3 (95% CI 1.8 to 10.4) using clinic controls. There was a trend of increasing risk of tuberculosis with decreasing frequency of meat or fish consumption. Lactovegetarians had an 8.5 fold risk (95% CI 1.6 to 45.4) compared with daily meat/fish eaters. Adjustment for a range of other socioeconomic, migration, and lifestyle variables made little difference to the relative risks derived using either community or clinic controls.

CONCLUSIONS

These results indicate that a vegetarian diet is an independent risk factor for tuberculosis in immigrant Asians. The mechanism is unexplained. However, vitamin D deficiency, common among vegetarian Asians in south London, is known to affect immunological competence. Decreased immunocompetence associated with a vegetarian diet might result in increased mycobacterial reactivation among Asians from the Indian subcontinent.

Aluminum(III)-Isocitrate Solution Chemistry. A Potentiometric Study

The equilibrium reactions of isocitrate with protons and Al3+ have been studied by potentiometric titration in aqueous 0.10 M KCl at 25°C. The protonation constants, corrected for K+-isocitrate complexing , were logβ0,1,1 = 5.838, logβ0,2,1 = 10.126 and logβ0,3,1 = 13.219. The stabilities and stoichiometries of the complexes, AlpHqLr, were defined by the constants logβ1,1,1 = 9.55(05), logβ1,0,1 = 6.90(02), logβ1,-1,1 = 3.06(04) and logβ2,-3,2 = 4.08(04) or logβ3,-4,3 = 10.36(06). Compared with the Al3+-citrate system, complexes are of lower thermodynamic stability, but equilibrate more rapidly.

Screening for Down syndrome in the first trimester

Second-trimester maternal serum screening for Down syndrome is now well established, and permits detection of up to 70% of cases. The disadvantage of this sort of screening is that the timing of maternal blood sampling is relatively late (after 15 weeks). There is an accumulating body of evidence to suggest that in the first trimester concentrations of a number of pregnancy-associated proteins and hormones differ in chromosomally normal and abnormal pregnancies. A first-trimester maternal serum screening test for Down syndrome may therefore be possible. In addition, new methods of screening have recently been described based on ultrasound findings at 11 to 13 weeks of gestation. This review article presents a discussion of published data on the feasibility of first-trimester screening for Down syndrome.

Pulmonary oedema following immersion in sea-water

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