Cervical sealing for internal whitening. Sealing prior to internal tooth whitening, a mandatory measure to prevent inflammatory cervical resorption, a possible sequel according to the literature.

In: Costa et al. Comparison of two types of cervical cap during internal tooth whitening. Rev APCD 2010.

INTRODUCTION
Whitening devitalized teeth has become a common procedure in dental practice, especially
in darkened anterior teeth. Among the main causes of color change in devitalized teeth are the presence of necrotic pulp, intrapulpal hemorrhage, intracanal medication, trauma and root canal filling material.

Whitening devitalized teeth was proposed in 1924 through the use of a saturated solution of sodium perborate and
hydrogen peroxide2 , and this product is still used today. This technique provides aesthetically satisfactory results, but it is not uncommon to come across an unwanted side effect - external cervical resorption - which can jeopardize or even make it impossible for the tooth to remain in the oral cavity.

The etiology in these cases has been given by an inflammatory reaction generated in the periodontal ligament, resulting in osteoclastic action potentiated by defects in the cementum, however the cause of this inflammatory response is not well elucidated, it is believed that there is an intimate link with the caustic action of hydrogen peroxide leading to denaturation of dentin and consequently the immune response.

Studies evaluating different bleaching agents have shown that they all have cytotoxic and genotoxic effects
when applied to fibroblast cultures5, where hydrogen peroxide even when mixed with sodium perborate resulted in major cytotoxic effects when exposed to periodontal ligament cells.

In addition, the use of such substances can increase dentin permeability, facilitating its substantial passage to the periodontal region, a fact observed in the evaluation of the diffusibility of the bleaching agent from the pulp chamber to the external
region of the tooth, which is potentiated and proportional to the concentration of hydrogen peroxide.

Therefore, a cervical barrier during internal tooth whitening has been proposed to minimize this adverse effect. The
first material to be used for this purpose was polycarboxylate cement in 1983. Since then, various materials have been analyzed in the search for the one that provides the best seal, but the infiltration rate is still high. Glass Ionomer Cement has been widely used in the dental clinic as lining, cementing and restorative materials. In addition to releasing fluoride, it has the ability to chemically adhere to dental tissue, and its coefficient of thermal expansion is similar to that of the tooth structure. However, studies have shown that conventional glass ionomer has low peripheral sealing capacity, and when it is modified by adding resin monomers, it becomes more effective in restorations, resulting in lower microleakage. resin cements are composite materials, made up of a resin matrix, used to cement indirect composite resin restorations. In comparisons
with glass ionomer, dual resin cement has shown superior results in relation to microleakage
of cemented parts.