The aim of the current study is to compare a newly introduced material which is a combination of triple mix antibiotics paste and anti-hyperlipidemia drug simvastatin, the new material is named 3MIX-TATIN & will be compared to triple antibiotic paste for management of necrotic primary molars by using lesion sterilization and tissue repair LSTR technique.

3Mix-tatin will prepared by mixing three commercially available antibiotics with simvastatin. After removing the coating materials, 3 types of antibiotics are pulverized by porcelain mortars and pestles to achieve fine powders. A total of 100 mg ciprofloxacin, 100 mg metronidazole, and 100 mg cefixime will be mixed in a ratio of 1: 1: 1. Two milligrams of simvastatin will be added to the drugs blend to form 3-Mix-tatin. Preparation of 3Mixtatin will be trained and supervised by an expert pharmacist. 3Mixtatin will be stored in a tightly capped porcelain container, adding a small amount of silica gel in a bag inside the container to maintain low humidity. This powder will be mixed with normal saline to form a creamy paste of 3Mixtatin at the time of application.

Local anesthesia using mepivicaine hydrochloride 3% (septodont, saint-maurdesFosses, France) will be administered.

Rubber dam isolation.

Access cavity will be prepared with a fissure bur in a high-speed handpiece, necrotic pulp tissue will be removed using a sterile sharp spoon excavator.

The canal orifices will be enlarged with a round bur (one mm diameter and two mm depth) to create medication receptacles.

Cotton pellet moistened with 2.5% sodium hypochlorite (NaOCl) will be placed in the pulp chamber for 1 minute.

Bleeding, if present, will be controlled by applying sterile cotton pellet moistened with 10% sodium hypochlorite against the pulp stumps and will be maintained for 1 min.

The 3-Mix-Tatin will be mixed with saline to obtain a creamy mix and placed over the canal orifices and the pulpal floor.

The access opening will be sealed with a glass ionomer cement , and the tooth will be restored with a stainless steel crown.

Inclusion Criteria:

• Children age range from 5-8 years.
• Children free from any systemic diseases or medical problems.
• Primary molar with necrotic pulp, with pain, gingival abscess, fistula openings, or clinical mobility not exceeding grade two.
• Radiographic evidence of non-perforating internal resorption, external resorption not exceeding 1\3 of the root, furcation or periapical radiolucency.

Exclusion criteria:

• Non-restorable molars or beyond repair, for example: decay reaches to bifurcation, a hard gingival margin cannot be established or infection cannot be eradicated by other mean (Balaji, 2007).
• Patient with known allergy to any type of antibiotics or anti-hyperlipidemia drugs.
• Patient with facial cellulitis or lymphadenopathy
• Lack of patient/parent compliance and cooperation.
• Refusal of participation or failure to obtain an informed consent.