Introduction: the research was conducted to evaluate the influence of conservative (CEC) and ultraconservative (truss access, TUS) endodontic access cavity designs on canal cleanliness when compared with traditional one (TEC). Methods: Sixty (n=60) mandibular molars were divided into three groups according to the access cavity design (each n=20). Mesial root canals were instrumented then sectioned horizontally into three equal thirds (coronal, middle and apical thirds). All were grooved buccolingually then split vertically. Photos of all thirds were taken by a stereomicroscope. The amount of debris presented were calculated by the Image J software. Results: For all sections, the highest percentage of debris was found in TUS followed by the CEC design while the lowest value was found with the TEC. Statistically, a significant difference between the groups in the middle and apical sections was found. Conclusion: CEC and TUS are more conservative but compromise the cleanliness of root canal system.