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Background: bleaching has been widely studied, mainly due to the possible undesirable effects that can be caused by this esthetic procedure. The cytotoxicity of the bleaching agents and its components to pulp cells has been demonstrated in several researches. The aim of this study was to evaluate the toxic effects of successive applications of 10% carbamide peroxide (CP) gel on odontoblast-like cells., Materials and Methods: Enamel-dentin discs obtained from bovine incisors were adapted to artificial pulp chambers (APCs). The groups were formed as follows: G1: Without treatment (control group); G2: 10% carbamide peroxide, CP (five applications/one per day); G3: 10% CP (one unique application); and G4: 35% hydrogen peroxide, HP (three applications of 15 min each). After treatment, cell metabolism (MTT), alkaline phosphatase (ALP) activity and plasma membrane damage (flow cytometry) were analyzed., Results: Reductions in cell metabolism and alkaline phosphatase activity along with severe damage of the cytoplasmic membrane were noted in G2. In G3, no damage was observed, compared to the control group. Intermediary values of toxicity were obtained after 35% HP application., Conclusion: It can be concluded that one application of 10% CP did not cause toxic effects in odontoblast-like cells, but the successive application of this product promoted severe cytotoxic effects. The daily application of the bleaching agents, such as used in the at-home bleaching technique, can increase the damages caused by this treatment to the dental pulp cells.

In the microsomal fraction isolated from rat incisor odontoblasts, the influence of several inhibitors on p-nitrophenyl phosphatase activity (p-NPPase) was demonstrated at pH 10.3 and compared with the influence at pH 8.8. The inhibiting effect of EDTA on the p-NPPase activity was reversed by equimolar concentrations of Zn2+. The inhibitory effect of three diphosphonates, ethane-1-hydroxydiphosphonate (EHDP), methanediphosphonate (MDP), and dichloromethanediphosphonate (Cl2MDP) was equal to that of a chelating agent. Tetramisole and levamisole exerted an inhibitory effect that was different from the complexing type. L-Cystein, but not L-ascorbic acid, inhibited p-NPPase activity with a maximum inhibitory effect at pH 10.5.

The ATP-splitting enzyme activity in odontoblasts isolated from rat incisors has been studied by means of a radiochemical and a colorimetric micromethod. The results with the two methods were virtually identical. The reaction was linear with time for at least 45 min. The pH optimum was found to be 9.8 independently of the ATP concentration. Maximal substrate saturation occurred at a total ATP concentration of 3 mM. Ca2+ and Mg2+ ions activated ATP degradation. F-ions did not affect the activity at low concentrations, whereas higher concentrations were inhibitory. Na+ and ions were slightly inhibitory. Urea inhibited the enzyme activity at concentrations above 1.5 M, while EDTA and EGTA were strong inhibitors at very low concentrations. When incubating in the presence of low concentrations of specific inhibitors for nonspecific alkaline phosphatase, levamisole and R8231, about 20% ATP degrading enzyme activity remained. In conclusion it is suggested that there are at least two ATP degrading phosphatases active at alkaline pH.

The inorganic pyrophosphatase (PPiase) activity was determined by a colorimetric method in the odontoblasts and the parts of the enamel organ related to enamel matrix formation and enamel maturation. The effects on PPi hydrolysis by EDTA, R 8231, urea and heat treatment were found to be almost identical to those reported for nonspecific alkaline phosphatase (APase) in the same tissues. The Mg2+ activation curve for PPiase was also similar. Like those of APase, these characteristics of PPiase activity were identical in the three locations studied. It is suggested that the close similarity in the properties of PPiase and APase is due to activity of the same enzyme, a concept which is in agreement with recent biochemical and histochemical studies of calcification.

Coronal odontoblast-predentin tissue was taken from intact teeth and from teeth with carious lesions of varying depths, and the samples (20, 200 x g, saline-soluble fractions) were studied for their ability to hydrolyze adenosine triphosphate (ATP) and phosphoserine. A significantly higher rate of ATP hydrolysis at pH 9.8 was detected in enamel caries and a significantly lower rate in advanced caries than in intact teeth. The rates of the hydrolysis of phosphoserine at pH 9.8 did not differ between the various tooth groups, and the only clear trend indicating elevated enzyme activity was seen in the group of initial dentin caries. The ATP and phosphoserine hydrolysis at pH 9.8 were considered to have been due to the nonspecific alkaline phosphatase (EC 3.1.3.1) activity. In the presence of both levamisole and ouabain, maximal enzyme-dependent ATP hydrolysis was observed at pH 7.9. The remaining ATP-cleaving activity was thought to have been due to the Ca2+Mg2+-dependent ATPase (EC 3.6.1.3). The Ca2+Mg2+-dependent ATPase activities at pH 7.9 remained at constant levels in both the intact and carious groups. The parameters studied in vitro were thought to reflect changes in the mineralization rate of reparative dentin as a response to caries in vivo.