## 4 Discussion
In 2017, a comprehensive review [9] surfaced, presenting findings from a range of randomized clinical trials investigating the impact of utilizing 10% carbamide peroxide gel for at-home teeth bleaching. The focus was on assessing potential shifts in enamel microhardness, a factor influencing oral health resilience against the pressures of chewing. The comprehensive analysis indicated negligible alterations in enamel microhardness when employing the 10% carbamide peroxide bleaching gel over 7-, 14-, and 21-day spans. Additionally, [PERSON] et al. [36] described that bleaching with 38% HP for 45 min causes irreversible pulp damage in lower incisors but not in premolars. Correlation among increased tooth sensitivity, alteration in the surface topography of enamel, and the time and the number of treatments suggest that with a 10% higher HP concentration, it is necessary to avoid prolonged and long-term bleaching use [37]. Of note, shortening the contact time of 35% HP to nearly 5 min reduces trans-enamel and trans-dentinal cytotoxicity to pulp cells [38]. Lastly, [PERSON] et al. [39] demonstrated that the number of bleaching sessions affects pulp tissue damage in rat teeth. Essentially, after 5 sessions with 35% HP, necrotic areas in the pulp tissue (the second third of the radicular pulp) and intense inflammation at the apical third were induced in the animals treated [39]. All our analysed products exhibit more than 10% HP. However, among the four bleaching agents tested in this study, BlancOne ULTRA\({}^{+}\) is the only one that requires a maximum of three cycles of 8 min to release free radicals and singlet oxygen and perform the best bleaching result. Actually, there are certain weaknesses in our work. Indeed, despite the suitability of the bovine dental sample that was recently extensively reported [40], some differences could be experienced in vital human teeth and particularly concerning the long effects and a faster return of the teeth towards a darker shade. However, the work shows strengths. The choice of samples coming from animals of the same breeding and same age which were reared similarly and biologically and without antibiotics has allowed us, as demonstrated by the statistical analysis, to have a uniform brightness before the treatments, to better compare results after them. Indeed, a statical power higher than 99% on the primary variable results supports it. Additionally, the design of a bioreactor, which, as previously shown, mimics the oral cavity [17], and the use of a spectrophotometer to measure the bleaching effect, support the reliability of our data. As can be seen in Table 2, only the ULTRA\({}^{+}\) product has a pH slightly below the neutral threshold. This could lead one to think that being a more acidic agent than the others, it could cause superficial damage to the enamel surfaces. However, these are not the answers obtained from the tests performed. Products with a neutral pH or above the neutrality threshold are balanced with buffer substances capable of raising the pH and keeping it stable over the working time [25]. However, as described by [PERSON] et al. [26], the additives used to buffer the bleaching agents are able to dramatically increase the dehydration of dental tissues such as enamel and dentin, especially in bleaching treatments that involve very long tooth-gel contact times. Also to be considered is the description made by [PERSON] et al. [41], who highlight that bleaching gel products with a high concentration of hydrogen peroxide undergo a change in state before releasing the reactive oxygen species, passing from a gelled state to a liquid one. This liquid phase can determine the ease of penetration within the hard tissues of the tooth, thus increasing the risk of sensitivity perceived by patients.