Indirect cytotoxicity of dental materials: a study with Transwell inserts and the neutral red uptake assay

A modification of the Transwell insert methodology was evaluated by using the neutral red uptake (NRU) assay in a cytotoxicity test. The Transwell insert methodology was developed to assess the biocompatibility of solid materials used in dentistry and, when initially designed, used the release of radiochromium ((51)Cr) in the cytotoxicity assay. Another aim of this study was to evaluate different exposure regimes with which to assess cytotoxicity. The exposure regimes included: a 1-hour exposure in buffer followed by a 24-hour incubation in growth medium; a 2-hour exposure in buffer followed by a 24-hour incubation in growth medium; a 24-hour exposure in serum-limited medium; and a 24-hour exposure in a serum-sufficient medium. The bioindicator target was the Smulow-Glickman (S-G) human gingival cell line and the biomaterials were dental restoratives. The Transwell insert methodology with the NRU cytotoxicity assay as the cytotoxicity endpoint was effective in differentiating the potencies of the dental restoratives; a 2-hour exposure in buffer and a 24-hour exposure in serum-limited medium were the exposure regimes that most clearly differentiated the test agents according to their potencies. The sequence of cytotoxicity of the dental restoratives to the S-G cells was Vitremer > Ketac-Molar Aplicap > Flow-It.

The versatility of calcium sulfate: resolving periodontal challenges

The multifaceted properties of calcium sulfate demonstrate its usefulness in periodontal practice. Calcium sulfate can function as a resorbable space filler, a resorbable barrier (compatible with guided tissue regeneration principles) and as a vehicle for controlled-release chemotherapy. Various periodontal challenges are demonstrated through case reports using calcium sulfate.

Triclosan: cytotoxicity, mode of action, and induction of apoptosis in human gingival cells in vitro

The in vitro cytotoxicology of triclosan, the active ingredient in some mouthrinses and dentifrices used in the prevention and treatment of gingivitis and plaque, was studied using the Smulow-Glickman (S-G) human gingival epithelial cell line. The 24 h midpoint cytotoxicity value was 0.05-0.06 mM triclosan as assessed with the neutral red (NR) assay. Triclosan is used in dentifrices in combination with either zinc citrate or sodium fluoride (NaF). The sequence of potencies of these test agents, as assessed with the NR assay, was triclosan>zinc citrate>>NaF; combinations of triclosan + zinc citrate and triclosan + NaF were additive in their toxicities. Damage to the integrity of the plasma membrane, as assessed by the leakage of lactic acid dehydrogenase during a 3-h exposure, was initially evident with 0.1 mM triclosan. When exposed to triclosan for 3 d, a lag in the growth kinetics of the S-G cells was first observed at 0.01 mM triclosan. A reduction in attachment of S-G cells to dentin chips, previously exposed to triclosan for 1 h, was noted at 0.25 mM triclosan and greater. Triclosan-induced cell death was apparently by apoptosis, as noted by fluorescence microscopy and DNA agarose gel electrophoresis of extracted oligonucleosomal fragments.

An in vitro study on the cytotoxicity of chlorhexidine digluconate to human gingival cells

Chlorhexidine digluconate is the active ingredient in mouthrinses used to prevent dental plaque and gingivitis. The in vitro cytotoxicity of chlorhexidine was evaluated with the Smulow-Glickman (S-G) gingival epithelial cell line. The potency of chlorhexidine was dependent on the length of exposure and composition of the exposure medium. The midpoint cytotoxicity values for 1-, 24-, and 72-h exposures were 0.106, 0.011, and 0.0045 mmol/L, respectively. S-G cells exposed for 2 h to chlorhexidine and then maintained for 48 h in chlorhexidine-free medium were unable to recover from the initial insult. The adverse effects of chlorhexidine on the plasma membrane were suggested by the leakage of lactic acid dehydrogenase from chlorhexidine-treated S-G cells and by the increased permeability of chlorhexidine-treated liposomes to Ca2+. The toxicity of a 24-h exposure to chlorhexidine to the S-G cells was progressively lessened as the content of fetal bovine serum (FBS) in the exposure medium was increased from 2% to 8%. The potency of a 1-h exposure to chlorhexidine was reduced in medium amended with albumin, lecithin, and heat-killed Escherichia coli. These reductions in toxicity were presumably due to the binding of the cationic chlorhexidine to the negatively charged chemical moieties of the components of FBS and of albumin and lecithin and of sites on the surfaces of bacteria. Combinations of chlorhexidine and carbamide peroxide were additive in their cytotoxicities.

Oxidative stress aspects of the cytotoxicity of carbamide peroxide: in vitro studies

Carbamide peroxide is the active ingredient in many at-home patient-applied tooth whiteners. The cytotoxicity of carbamide peroxide, as related to oxidative stress, was evaluated in vitro with several human cell lines, including Smulow-Glickman (S-G) gingival epithelial cells. The potency of carbamide peroxide was related to its hydrogen peroxide component rather than to carbamide, was eliminated in the presence of exogenous catalase, and was enhanced in the presence of aminotriazole, an inhibitor of cellular catalase. The intracellular level of glutathione, a scavanger of toxic oxygen metabolites, was decreased in cells exposed to carbamide peroxide; at higher concentrations of carbamide peroxide, leakage of lactic acid dehydrogenase was also evident. Cells pretreated with the glutathione-depleting agents, buthionine sulfoximine, chlorodinitrobenzene, and bis(chloroethyl) nitrosourea, were hypersensitive to subsequent challenge with carbamide peroxide. Conversely, pretreatment with the iron chelator, deferoxamine, protected the cells against subsequent exposure to carbamide peroxide.