The aim of the study is to evaluate the effect of preoperative administration of acetaminophen- codeine -caffeine combination on the success of the inferior alveolar nerve block versus bacetaminophen alone or placebo in patients with symptomatic irreversible pulpitis.

After ensuring eligibility, patients will be given premedication 1hr before treatment,which will be done in single visit.

After 1 hour, Pretreatment pain "pain after administration of analgesic or placebo" will be recorded using 0-10 numerical rating scale (NRS) .

Local anesthesia will, then, be done through inferior alveolar nerve block using 1.8 ml Mepivacaine.

The teeth will be isolated using rubber dam and access cavity will be prepared using #2 high-speed round bur.

The patients will be asked to rate their pain on the NRS. The degree of pain during access preparation and/or instrumentation will be recorded.

Success will be defined as no pain or mild pain during endodontic access preparation and/or instrumentation. Any pain more than no pain or mild pain will considered a failure.

The patients will be instructed to return after 2 days to complete the treatment procedures.

Inclusion Criteria:

1. Patients aging between 18-50 years old.
2. Patients with mandibular molar with symptomatic irreversible pulpitis.
3. Systemically- healthy patients.
4. Patients who agree to attend for recall appointments and provide a written consent.

Exclusion Criteria:

1. Pregnant or lactating female patients.
2. Patients had allergies to any of test medications.
3. Patients had taken analgesics medication within the last 6 hours.
4. Moderate or severe marginal periodontitis i.e. pocket probe>3mm.
5. Non-restorable teeth, teeth with necrotic pulp, pulp polyp, tooth tender to percussion, root resorption or root canal calcification, periapical disease