The overvaluation of aesthetics for a better smile appearance in contemporary society has demanded the search for materials and techniques that contribute to satisfactory esthetic results. Due to this, tooth whitening is a conservative treatment in great demand and accepted by both patients and clinicians for providing a more harmonious smile appearance without significant changes in dental structure and at a low cost [1,2].

The principle of tooth whitening is based on dissociating free radicals from hydrogen peroxide (HP) derived whitening gels that permeate the tooth structure and oxidize the chromophore molecules of C = C double bonds that cause tooth pigmentation. The degradation of these bonds promotes chromophore saturation resulting in lower light absorption and consequently providing lighter aspects of whitened teeth [1,2].

However, the high diffusing power of HP and the non-selectivity of its free radicals only by the chromophores can generate concerns of biocompatibility and cytotoxicity [3], changes on the tooth surface [4,5], reactions in the pulp and cause bleaching sensitivity (BS) [6,7]. This possible sensitivity is the most common adverse effect of tooth whitening and is directly related to the concentration of bleaching gel and its exposure time to dental tissues [8], [9], [10]. Moreover, we can mention factors related to the pH and chemical composition of the whitening gel as influencers of adverse effects [11]. This type of sensitivity is usually reported by "electric shock" symptoms and was described in the literature as the "Zinger effect"[8,12].

High HP concentration whitening gels are still the most commonly used because they quickly change color in the first few sessions [10]. However, knowing that HP diffusion is proportional to the concentration of the bleaching gel, new low-concentration products have been tested. They show good esthetic results with less discomfort for the patient [13], [14], [15].

Besides this, a new trend of using low-concentration gels has been frequently seen an association with LEDs and lasers that which are considered advanced technology that promotes interaction with the gel in a photothermal or photochemical way to accelerate the production and vibration of free radicals to interact with the pigment chromophore molecules, thus improving the performance of the bleaching process [13], [14], [15].

However, the evaluation of photo accelerates light bleaching should be explored due to the exacerbated increase in the release of free radicals that rapidly modify the pH of the bleaching agent [4,11,16]. Another change we should study is the increase in the internal temperature of bleaching gels to understand the tolerable limit for not causing pulpal alteration, resulting in possible pulpitis [17,18].

The different concentrations of HP currently used in association with violet light can generate variations in pH [19,20] and temperature [21,22] throughout the treatment, which can cause side effects related to BS. Another essential detail to mention is that free radicals such as oxygen, hydroperoxyl, sodium hypochlorite, hydrogen peroxide, ozone, and hydroxyl, have different redox potentials (Eo, in Volts; + 1.229 V, + 1.510 V, +  1.630 V, +  1.780 V, +  2.075 V, and +  2.800 V, respectively), where the higher the redox potential, the more reactive is the radical [23]. These different electro-voltages promote electrical potential variation during the tooth whitening procedure, as observed by Pretel et al. [24]. It is hypothesized to trigger changes in the process of nerve depolarization and sensitivity in tooth whitening [24,25]. Therefore, procedures with higher electrical potential in volts will exhibit more effective esthetic results and higher incidences of BS.

Based on the correlation between pH and mV previously described by Pretel et al. [24], the aim was to evaluate the kinetics of pH, mV, and the temperature of different concentrations of hydrogen peroxide in many adding infrared laser and violet light LED intermittent protocol, without the presence of dental substrate, and in a standardized time. The null hypothesis is that the different HP concentrations and protocols with or without photo acceleration violet LED/infrared laser do not show differences in pH, mV, and temperature kinetics throughout the procedure.