Vital bleaching: The effects of heat and hydrogen peroxide on pulpal enzymes

Abstract

Pulpal reactions to bleaching of vital teeth with H2O2 and heat have ranged from reversible inflammation to frank necrosis. Little is known of the effects of such treatments on actual molecular activities in pulpal tissues. This study examines the effects of H2O2 and heat, separately and together, on seven enzymes found in bovine dental pulp. A phosphate buffer extract of calf dental pulps was made immediately after slaughter and maintained at 4°C until used. Enzyme activities examined were alkaline phosphatase, aldolase, glucose 6-phosphate dehydrogenase (G6-PDH), serum glutamic-oxaloacetic transaminase (SGOT), isocitrate dehydrogenase, malate dehydrogenase, and phosphohexose isomerase. Enzyme activities were measured as a percentage of untreated control activities. The heat treatment was as follows: 50°C for 1 to 30 min then recooled to 4°C for assay. H2O2 treatment: H2O2 was added to pulp extract for a final H2O2 concentration of 1.25 to 15%. In combined treatments, the final H2O2 concentration was 2.5, 7.5, and 15% and the heat at 50°C for 7.5, 15, and 30 min, respectively. The sensitivity of the enzymes to H2O2 (in descending order) was G6-PDH, isocitrate dehydrogenase, malate dehydrogenase, alkaline phosphatase, SGOT, aldolase, and phosphohexose isomerase. In the sensitivity to heat test, after 30 min, G6-PDH retained 5% of the original activity, SGOT retained 60%, and all others retained 80% or more. Combined heat and H2O2 treatment, even under the mildest conditions (2.5% H2O2, 7.5 min of heating), totally inhibited G6-PDH and isocitrate dehydrogenase; SGOT was least affected (50% activity). Pulpal enzymes are significantly inhibited by H2O2, in vitro, especially when heated. Pulpal reactions to bleaching of vital teeth with H2O2 and heat have ranged from reversible inflammation to frank necrosis. Little is known of the effects of such treatments on actual molecular activities in pulpal tissues. This study examines the effects of H2O2 and heat, separately and together, on seven enzymes found in bovine dental pulp. A phosphate buffer extract of calf dental pulps was made immediately after slaughter and maintained at 4°C until used. Enzyme activities examined were alkaline phosphatase, aldolase, glucose 6-phosphate dehydrogenase (G6-PDH), serum glutamic-oxaloacetic transaminase (SGOT), isocitrate dehydrogenase, malate dehydrogenase, and phosphohexose isomerase. Enzyme activities were measured as a percentage of untreated control activities. The heat treatment was as follows: 50°C for 1 to 30 min then recooled to 4°C for assay. H2O2 treatment: H2O2 was added to pulp extract for a final H2O2 concentration of 1.25 to 15%. In combined treatments, the final H2O2 concentration was 2.5, 7.5, and 15% and the heat at 50°C for 7.5, 15, and 30 min, respectively. The sensitivity of the enzymes to H2O2 (in descending order) was G6-PDH, isocitrate dehydrogenase, malate dehydrogenase, alkaline phosphatase, SGOT, aldolase, and phosphohexose isomerase. In the sensitivity to heat test, after 30 min, G6-PDH retained 5% of the original activity, SGOT retained 60%, and all others retained 80% or more. Combined heat and H2O2 treatment, even under the mildest conditions (2.5% H2O2, 7.5 min of heating), totally inhibited G6-PDH and isocitrate dehydrogenase; SGOT was least affected (50% activity). Pulpal enzymes are significantly inhibited by H2O2, in vitro, especially when heated.