Assessment of Oxygen Expansion during Internal Bleaching with Enamel and Dentin: A Comparative In Vitro Study

Abstract

Internal bleaching is a conservative, non-invasive, and simple treatment that is frequently performed in daily clinical practice. The present in vitro study analyzes the oxygen expansion of different bleaching agents resulting from the oxidation reaction when interacting with enamel and dentin. Enamel and dentin were crushed separately until obtaining a fine powder with particles of an approximate size between 0.06 and 0.2 mm. Each enamel and dentin sample were mixed with 37% carbamide peroxide (CP 37%), 30% hydrogen peroxide (HP 30%), sodium perborate (SP) combined with HP 30% (HP 30% + SP) and SP with distilled water (SP). A total of 280 1 mm diameter glass tubes were used with 70 for each bleaching agent (30 for powdered enamel evaluation, 30 for powdered dentin evaluation, and 10 controls). The bleaching agents were placed in the prepared tubes immediately after mixing the components. As expansion occurred, the oil inside the tube was displaced, through which the resulting expansion was evaluated and measured for 10 days. A significant expansion was observed that varied in magnitude according to the bleaching agent and the tooth structure used. Student’s t test and Welch’s ANOVA were used to analyze the data obtained. The highest mean expansion of both enamel and dentin was observed with 30% HP (66.6 mm for enamel, 94.5 mm for dentin) followed by HP 30% + SP (48.6 mm for enamel, 52.7 mm for dentin), CP 37% (38.4 mm for enamel, 52.6 mm for dentin) and finally SP with water (12.7 mm for enamel, 4.4 mm for dentin). It was observed that the expansion in the SP group with enamel was significantly lower than in the rest of the groups, while that registered for HP 30% was significantly higher. (p < 0.001). The results with dentin were similar, with a significantly lower expansion for SP and higher for HP 30% (p < 0.001). The oxygen expansion observed as a result of the interaction between bleaching agents and dental tissues could contribute to improving our understanding of bleaching and its results. These results suggest that bleaching agents react with the organic component of the tooth structure.

Comparative Study of the Expansive Behaviour of Different Internal Bleaching Agents

“…A very different behaviour was therefore observed in the SP group. These results are very similar to those reported in an in vitro study carried out by Pallarés-Serrano et al [28], in which the authors separated the enamel from the dentine to observe the expansive behaviour of the bleaching agents upon both structures separately.…”

“…The reaction observed in this experimental model creates an increase in intracameral pressure and would be responsible for the displacement of the temporary restoration that has been observed in other studies over the years, which can leave a microscopic gap between the restoration and the tooth [21,23,28,29].…”

Study of the Intra-Coronal Pressure Generated by Internal Bleaching Agents and Its Influence on Temporary Restoration

“…However, in the SP group, the aforementioned strong expansion did not continue to grow after 10 days, but a discrete, constant and homogeneous expansion, and was significantly lower than the other two groups. These results coincide with the findings observed in an in vitro study, in which expansion in enamel and dentin separately was also measured [31].…”

Evaluation of the Effect of Intra-Coronal Bleaching after Using C-Phycocyanin as a Photosensitizing Agent- In vitro Study.

“…The significant increase in color lightness after 7 days could be due to the complete penetration and diffusion of hydrogen peroxide into the deep layers of enamel and dentin owing to its low viscosity and high flowability. The oxidation of the bleaching agent leads to an expansive reaction that could dislodge the temporary restoration and decrease the effectiveness of the bleaching action after 14 days (44) .…”