Effect of photo-thermal acceleration on in-office bleaching

Feng Qi,Chamari Lasindra Wijethunge,Junji Tagami,Masayuki Otsuki,Takashi Hatayama,Noriko Hiraishi

doi:10.1007/s10266-021-00612-5

Abstract

The purpose is to evaluate the effect of photo-thermal acceleration on in-office bleaching efficiency using a bleaching agent without photocatalysts in vitro. Artificially discolored bovine lower incisors were prepared, and the mixed in-office bleaching material contained hydrogen peroxide 23% was applied by following treatment for 10 min: high-(HI group) and low-intensity LED lights (LI group), oven at 38 °C (OV group), and room temperature at 23 °C (RT group). Color was measured before and after bleaching and color difference (∆E*) was calculated. The data were statistically analyzed using a two-way ANOVA and Tukey’s post hoc test. The temperature change (∆T) of applied bleaching agent in HI and LI groups was measured using a thermography and was analyzed using a T test. The bleaching procedures were repeated 6 times. Irradiation in the HI group resulted in the highest ΔE, followed by the LI group whose ΔE was significantly lower. Both irradiated modes exhibited higher ΔE compared to non-irradiated OV and RT groups which were not significantly different from each other. The average temperature rise of bleaching agents in HI and LI groups after 10 min irradiation was 15.00 °C and 11.80 °C, respectively. The effect of photo-thermal acceleration was proved for an in-office bleaching agent without photocatalysts in vitro.

Highlights

Tooth bleaching is one of the most popular and conservative dental procedures to lighten discolored teeth, which can be accomplished in-office, at-home, or dentist-supervised nightguard bleaching and bleaching with over-the-counter (OTC) products[1, 2]
When the light is irradiated onto a bleaching product, respective photons are absorbed by bleaching agents, and its energy is converted into heat, which is the important factor for a temperature rise [18, 25, 26]
More hydroxyl radicals that react with the organic molecules are produced from hydrogen peroxide when the temperature rises

Summary

Introduction

Tooth bleaching is one of the most popular and conservative dental procedures to lighten discolored teeth, which can be accomplished in-office, at-home, or dentist-supervised nightguard bleaching and bleaching with over-the-counter (OTC) products[1, 2]. The bleaching mechanism is described as the process that hydrogen peroxide decomposes to produce free radicals which react with chromogens composed of pigmented dual-bond compounds and/or metallic compounds [7,8,9]. This kind of chromogen accumulates in the tooth (intrinsic) or on the tooth (extrinsic) [9]. Many influence factors such as the temperature, light, or energy sources, photocatalyst, pH, the concentration of hydrogen peroxide, and the number of bleaching times affect the bleaching effect [11, 12]. The theoretical advantages of the light sources are to increase the chemical reaction rate of the bleaching process by producing heat [13] or to enhance the bleaching efficacy of bleaching materials by light activation of photocatalysts [14, 15] and

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