pH and the cytotoxicity of fluoride in an animal cell culture system

abstract — To investigate the mechanism for the toxicity of silicate cement as observed in a cell culture system, the effects of pH and fluoride were tested on human epithelial cells (NCTC 2544). At pH 7.3, fluoride concentrations from 15 to 25 μg/ml (0.79 to 1.3 mM) had a growth inhibitory effect. When pH of the incubation medium was lowered in the range 7.0 to 6.4, an enhanced cytotoxic effect of fluoride was found, and even at 5 to 10 μg/ml growth inhibition occurred. Concomitant with the enhanced cytotoxicity of fluoride at low pH, there was an increased utilization of glucose and formation of lactate. Upon lowering the pH of the incubation medium from 7.4 to 6.7 a twofold increase in the intra-cellular concentration of fluoride was found.     

Infant Stimulation: Modification of an Intervention Based on Physiologic and Behavioral Cues

Research involving developmental intervention with premature infants in the hospital has traditionally taken two paths: application of a sensory stimulation protocol and individualized assessment and treatment. This article describes a new method that combines some of the philosophical strengths of these two approaches. A decision tree is presented to standardize the modifications of a developmental intervention based on physiologic and behavioral cues.     

Environmental Influences on the Developing Premature Infant: Theoretical Issues and Applications to Practice

The neonatal intensive-care unit (NICU) environment may interfere with the maturation and organization of premature infants' central nervous systems and may fail to meet these infants' developmental needs. In particular, immature distance receptors (i.e., hearing and vision) may receive overwhelming stimulation, whereas more mature tactile and vestibular pathways receive little stimulation. Furthermore, research on fetal learning suggests that the NICU environment should sensitively address requirements for learning by providing contingent experience. Nurses are ideally suited to reorganize the NICU and intervene to optimize infants' growth and development.     

Factors affecting retention of Cu in the human oral cavity after mouth rinses

Abstract — Retention of Cu in the mouth after rinses with aqueous solutions of CuSC₄ was measured by atomic absorption spectrophotometry. The retained amount of Cu exhibited a linear relationship against the concentration of the rinsing solution in the range tested. Approximately one third of the Cu retained after a 60 s rinse was retained within the first 15 s, and about 75% within 30 s. Retention of Cu was only little affected by the pH of the rinsing solution in the range from 2.0 to 5.7, being reduced by about 50% at pH 9.0. However, variations in cupric ion activity rather than pH per se could explain these effects. A mutual reduction in retention of either metals was seen when Cu and Zn were applied simultaneously.     

Fluoride retention in clean and plaque-covered demineralized enamel in vivo after application of monofluorophosphate

The retention of fluoride in clean and plaquc-covcred demineralized enamel in vivo was measured 1 wk after a single application of a MFP solution with low or high content of free fluoride. Demineralization of the enamel was induced in vivo during a 4-wk period prior to application of fluoride by applying orthodontic bands on a pair of premolars scheduled for extraction of orthodontic reasons. The band from one tooth of each pair was then removed and the tooth cleaned (clean enamel lesion). The band on the contralateral tooth (plaque-covered enamel lesion) was left in place. The MFP solutions were applied and the teeth extracted after one more week. The chemical form of fluorine in the lesions was analyzed by conventional acid etching of the enamel combined with KOH dissolution and by a nondestructive surface analysis using ESCA to detect intact monofluorophosphate ions. The ESCA measurements showed that MFP was only present in the clean enamel lesions, indicating complete hydrolysis by dental plaque. Alkali soluble fluoride could be extracted from both plaque-covered and clean enamel lesions. Conflicting results regarding the amount of fluoride uptake in the lesions were obtained with the acid etching and the ESCA technique. It was thus not clearly established whether plaque enhanced fluoride uptake in carious lesions after MFP application.     

pH and the effect of NH4Cl on human gingival fibroblasts

pH variations in the range from 6.9 to 7.9 modified the growth rate of human gingival fibroblasts in culture, a pH optimum being found at 7.6-7.8. A pH dependent growth inhibition by ammonia was evident, being particularly prominent in the presence of 2 mM NH₄Cl. At this concentration an effect ranging from a complete cessation of growth at pH 8.0 to an indication of a slight stimulatory effect at pH 7.2 was found. Concomitant with this amplification of the growth inhibitory effect, a state of unbalanced growth in the sense of an increased cellular protein content was induced by ammonia upon increasing the pH of the medium. The incorporation of 14C-proline into the total protein fraction decreased rapidly, particularly in the control cultures, with pH; an inhibition by ammonia being found at pH 7.9 and 7.5 with no effect at pH 7.1. Except for part of the inhibition by ammonia, changes in specific activity of 14C-proline in the cellular amino acid pool could account for these pH effects. Ammonia reduced the proportion of radiolabeled protein recovered as collagen both from the cells and medium at the lower pHs, whereas the only significant effect on noncollagen protein was an increased fraction being secreted at pH 7.1 in the presence of 10 mM NH₄Cl.