MECHANICAL AND CHEMICAL INTERACTIONS BETWEEN DENTAL SURFACES AND BLEACHING AGENTS

In the age of social media and sharing, the smile takes on an increasingly important role in mine society; basically a “bright and white” smile is required. For this reason, the demand for teeth whitening treatment is increasingly popular. Teeth bleaching is an aesthetic treatment, which therefore requires positive and evident results. Whitening is generally obtained by applying commercial gels, by professional doctor or autonomously, created to decolor teeth both based upon hydrogen peroxide or carbamide peroxide (urea peroxide), in different compositions, formulations and different percentages of peroxide. [1] The effectiveness of the bleaching treatment depends mainly on the nature and severity of the discolouration on the tooth surface, which can be extrinsic (i.e. external to the tooth surface), intrinsic (generated from the internal matrix of the tooth and visible from the outside) or internalised (penetrated internally by extrinsic discolorations), but also on the correct choice of the bleaching product and the bleaching method. [2] Aesthetics have played a significant role throughout human society and civilization. Nowadays, maintaining a good appearance is crucial, and teeth whiteness, specifically, may impact the quality of life before and after the bleaching treatment. Despite intrinsic stains being a consequence of pathologic processes, widespread habits such as drinking wine, coffee, tea, smoking, eating coloured food, and abusing antibiotics can also cause stains.[3] Tannins, furfurals, carotenes, artificial colours, and tetracyclines may affect the structure of dentin or enamel, inducing tooth discoloration. However, tooth whitening can cause dental sensitivity and gingival irritation due to incorrect treatment, which can have a negative impact on people's lives. [3-4] Bleaching agents may also have antibacterial effects, leading to oral microbiome dysbiosis. Therefore, the positive influence of white teeth on the quality of life and the negative influence of tooth sensitivity are related. Tooth bleaching can be performed by patients themselves or by professionals in dental practices using products based on calcium peroxide or hydrogen peroxide. However, the tooth is a highly complex organic-inorganic biocomposite, and aggressive hydrogen peroxide bleaching may damage the organic matrix in the tooth. Additionally, tooth surface structure changes and damages, as well as microscopic pores and defects on its surface, can lead to reversible pulpitis and correlated diseases. [1;3;5]. The effect of bleaching on enamel has been evaluated primarily in three aspects: mineral loss, surface morphological changes, and alteration of surface microhardness; most enamel effect studies were conducted using in vitro systems. Overall data indicate that there is a loss of minerals during the bleaching treatment; however, this does not appear to constitute a significant risk because of the effective remineralisation mechanisms readily available in the oral cavity. Most scanning electron microscopy (SEM) and surface microhardness studies showed little or no changes of bleached enamel surface. On the other hand, several investigators reported alteration of enamel surfaces associated with bleaching. However, in most cases the observed alterations of enamel surface morphology varied among different products and were associated with products using acidic pre-rinse or gels of low pH.