1. Mouthwash containing an aqueous solution: a. an effective amount of a basic amino acid in free or salt form b. an effective amount of a preservative selected from methylisothiazolinone (MIT), benzyl alcohol, phenoxyethanol, and combinations thereof. 2. A mouthwash according to claim 1, wherein the basic amino acid is arginine or a salt thereof. A mouthwash according to claim 1, wherein the basic amino acid is contained in an amount corresponding to from 0.01 to 2% by weight of the total composition, where the weight of the basic amino acid is designed for the free base form. Mouthwash according to claim 1, wherein the preservatives are contained separately or in combination in amounts as follows: a. MIT: 0.0005-0.03 wt.%, B. benzyl alcohol: 0.05-0.25 wt.%, c. phenoxyethanol: 0.1-0.7 wt.%. 5. A mouthwash according to claim 1, further comprising pyrophosphate. 6. A mouthwash according to claim 1, further comprising a synthetic anionic polymer polycarboxylate. 7. A mouthwash according to claim 1, further comprising a source of fluoride ions. A mouthwash according to claim 1, wherein the mouthwash does not contain ethanol. A mouthwash according to claim 1, further comprising one or more humectants, flavors and surfactants. 10. Mouthwash according to claim 1, wherein the preservative is contained in an effective amount to provide microbiological control. A method of improving oral health, including the use of an effective amount of mouthwash according to claims. 1-10 in the oral cavity of a subject in need thereof: a. reduce or suppress the image1. Жидкость для полоскания рта, содержащая водный раствор:a. эффективного количества основной аминокислоты в свободной форме или в форме соли；b. эффективного количества консерванта, выбранного из метилизотиазолинона (MIT), бензилового спирта, феноксиэтанола и их сочетаний.2. Жидкость для полоскания рта по п. 1, где основная аминокислота представляет собой аргинин или его соль.3. Жидкость для полоскания рта по п. 1, где основна
