A methodologic study of the effect of dental materials on growth and adhesion of animal cells in vitro

abstract – An in vitro method was used to investigate the ability of animal cells to (a) grow in the proximity of various dental materials, (b) adhere to and grow on the surface of the same materials during long-term contact. Disks (30 × 1 mm), made from the different materials, were placed in the center of plastic Petri dishes and incubated with human epithelial cells (NCTC 2544) and mouse fibroblasts (L 929). The growth around and on the surface of the disks was followed by measuring the amount of deoxyribonucleic acid (DNA) and/or cell number. The cultures were stained with crystal violet to visualize the distribution of the cells. In the presence of gold alloy, growth was similar to that obtained in control cultures, whereas the other materials tested showed various degrees of a toxic effect. With the two heat-cured acrylics tested, a transient toxic effect was observed on the surface of the disks. In the presence of silicate cement, various degrees of growth inhibition were observed, both on the surface of and around the disks. A toxic effect of silver amalgam was evident on the surface of and in the close proximity of the disks, whereas Addent 12® and copper amalgam appeared to have a general toxic effect. The present method might thus be of value in the evaluation of the tissue compatibility of biomaterials.     

Silicate cement in a cell culture system

abstract — Human epithelial cells (NCTG 2544) were grown as monolayer cultures in the presence of silicate cement disks (Bio-trey 9®). A cytotoxic effect was found on the surface of the disks after 24 h, whereas a corresponding effect was obvious around the disks after incubation for 3 d. In the silicate cement cultures more glucose was utilized and more lactate formed per cell than in control cultures. In the presence of silicate cement, pH of the culture medium decreased during incubation, reaching 6.3–6.4 after 6 d. Phosphate, silicon, zinc, and fluoride were released into the medium from the silicate cement disks. The medium concentration of sodium, however, remained constant, and aluminum was not detected. The concentrations of calcium and magnesium decreased, and experiments with ⁴⁵Ca showed that calcium was bound to the silicate cement disks.     

Effect of chlorhexidine on animal cells in vitro

abstract – When cultures of human epithelial cells were treated for 5 min at 37°C with chlorhexidine in Eagle's medium without serum added, concentrations from 0.05 mM were found to be toxic as measured by growth inhibition and differential staining. About 20 times higher concentrations were needed to obtain a toxic effect, however, when the cells were treated with chlorhexidine dissolved in calf serum. Human whole saliva collected from a single subject had no such protective effect. The intracellular activities of 5'-nucleotidase, alkaline phosphatase, and NADPH₂+ NADH₂-diaphorases decreased upon treatment of the cells with concentrations of chlorhexidine at 0.2 and 2 mM, whereas 0.02 mM had no measurable effect on these enzymes. Treatment with chlorhexidine at 10⁻⁴mM had no effect on the hypotonic hemolysis of human erythrocytes, 0.001–0.1 mM stabilized the cells, but increasing the concentration to 1 mM gave 100% hemolysis. A concentration-dependent inhibition of the Na⁺–K⁺–ATPase activity was found when erythrocyte membranes were incubated with chlorhexidine in the range of 0.002–0.2 mM.     

Inhibitory effect of NH4Cl on secretion of collagen in human gingival fibroblasts

Abstract – The general protein synthesis in human gingival fibroblasts as measured by ¹⁴C-proline incorporation was only moderately inhibited by 10 mM NH₄Cl during incubation for 36 h. The proportion secreted as noncollagen protein and recovered from the cellular fraction as collagen was not significantly affected, whereas a pronounced inhibitory effect on the secretion of collagen was evident after 24 h. This effect was dose dependent, with a significant inhibition of collagen secretion even at 2 mM ammonia. The applied concentrations of NH₄Cl had no significant effect on the hydroxylation of prolyl residues in collagen. Ammonia had no inhibitory effect on the secretion of fibronectin, another major secretory protein from fibroblasts. When comparing different lysosomotropic agents; NH₄Cl, chloroquine and methylamine, the most prominent effect was consistently found to be an inhibition of the secretion of collagen.     

Retention of Cu and Zn in the oral cavity following rinsing with aqueous solutions of copper and zinc salts

Abstract – Retention of Cu and Zn in the mouth after rinses with known volumes of aqueous solutions of the metal salts was measured by atomic absorption. The mean amounts retained in 10 subjects were 0.02 mg Cu and 0.22 mg Zn. These values represent approximately 31 % of the Cu and 15% of the Zn originally in the rinse. The intraindividual variation (s.d.), estimated by three mouthrinses at weekly intervals in three subjects averaged 2.1% for Cu and 2.3% for Zn. Following a rinse the salivary concentration of Cu and Zn decreased rapidly during the first 4 h, approaching premise levels.     

pH and the effect of fluoride and zinc on protein and collagen biosynthesis in rabbit dental pulp in vitro

abstract – The effect of pH in the range 5.6–8.2 on the incorporation of ¹⁴C-proline into the rabbit dental pulp incubated in vitro has been studied. The amount of label in the cold TCA-pool, total protein, and hydroxyproline (i.e. collagen) of the pulp tissue increased linearly with pH in all three fractions. A similar increase was found in the amount of labeled total protein and collagen recovered from the incubation medium. The results indicated that the uptake of ¹⁴C-proline into the TCA-soluble pool was the pH-sensitive step, whereas the incorporation into protein, formation of hydroxyproline, and the release of labeled macromolecules into the medium were not affected to any measurable degree by the ambient pH. In this system, zinc (60 μM) had less effect on the incorporation of ¹⁴C-proline into the different fractions of the pulp tissue at pH 6.6 as compared with pH 7.4, whereas with fluoride (1.3 mM) an increased inhibition of the uptake of ¹⁴C-proline into the TCA-soluble pool and the incorporation into total protein was found upon lowering the pH to 6.8. The inhibitory effect of zinc and fluoride on the release of labeled total protein and collagen into the incubation medium was not affected when the pH was lowered.