Maintenance of primary dentition is imperative for the development of arch form, esthetics, function, mastication and normal eruption of permanent teeth. Premature loss, especially of the primary second molar, can cause various problems. This usually results in mesial eruption of the first permanent molars and causes subsequent problems such as ectopic eruption of the second premolar, space loss for the successor permanent teeth, alterations in speech and impairment of function. Therefore, decayed primary teeth should be treated whenever possibleThe major goal of modern dentistry is to maintain the integrity of the primary dentition until normal exfoliation Lesion Sterilization and Tissue Repair (LSTR)-3mix MP therapy has been proposed to fulfil the bacteria free zone in the root canal. LSTR-3mix therapy is a new biologic approach in the treatment of carious lesions with or without pulpal and periapical involvement using a mixture of three antibiotics.The LSTR technique involves the use of 3 broad-spectrum antibiotics-ciprofloxacin, Metronidazole, and minocycline (3Mix)-in a carrier of Macrogol and propylene glycol (MP). This mixture is also known as triple antibiotic paste.