Introduction: Failure to obtain adequate anesthesia in teeth with inflamed pulp has always been a major clinical problem for the dentists generally, specially endodontists. Capsaicin and zostrix depletes substance P, blocks axonal transport and apparently inactivates small A-delta and C-type  fibers. Morphine which is an efficient analgesic drug, blocks nerve conduction and shows  its anesthetic and analgesic property via  voltage dependent sodium channels⁽¹⁾. The purpose of this clinical   study was comparison of the  effect of local application of capsaicin, zostrix and Morphine on complete anesthesia of teeth with inflamed pulp and poor response to traditianl local anesthetics.
Materials & Methods: In this study sixty patients with pain during access preparation despite successful local anesthesia were selected. All patients had received one to three injections of lidocaine 2% with 1.80000 epinephrine. Capsaicin,  zostrix or morphine was applied in the cavity on the dentin or exposed pulp for 5-10 minutes and severity of pain due to access preparation or intrapulpal injection was recorded. The data were gathered and statistically analyzed by wilcoxon and kruskal-wallis tests.
Results: The best results were obtained following application of zostrix over the exposed pulp. In 88.2% of these patients application of zostrix made the painfree or tolerable interapulpal injection possible(P<0.05).
Conclusion: with regard to the results obtained, the use of dehydrating and decalcifying materials such as alcohol and phosphoric acid prior to topical application of drugs on complete pulp  anesthesia,  is recommended