Aim: To evaluate the influence of contracted endodontic cavity (CEC) design on debridement efficacy of laser-activated (LA), ultrasonic-activated (UA), and sonic-activated (SA) irrigant systems in the distal canals of human permanent mandibular molars using scanning electron microscopy (SEM) analysis. Materials and methods: Sixty (N = 60) freshly extracted human intact permanent mandibular first molars were randomly assigned to one of two groups: traditional endodontic cavity (TEC) and CEC (n = 30 per group). A preoperative cone-beam computed tomography (CBCT) scan was taken. After access cavity preparation, the canals were instrumented with an Mtwo rotary system up to size #30, 0.06 taper. During instrumentation, each canal was irrigated with 3 mL of 5.25% NaOCl followed by 3 mL of 17% ethylenediaminetetraacetic acid (EDTA) for 1 minute. Following cleaning and shaping, samples were randomized for final irrigation into three treatment subgroups: laser, ultrasonic, and sonic (n = 10 per subgroup). Final irrigant activation was done with 5 mL of 5.25% NaOCl, 5 mL of 17% EDTA, and lastly, 5 mL of 5.25% NaOCl using either LA, UA, or SA. All specimens were decoronated, and the distal roots were separated from the mesial using a diamond disk. The distal roots were then split longitudinally and viewed under an SEM for debris removal. Statistical analysis was done using an unpaired t-test. Results: Overall, debris scores were similar between TEC and CEC at all levels of the root canals. In the intergroup analysis, LA irrigants showed maximum debris removal at all levels of the root canals compared to UA and SA irrigants in both TEC and CEC. Conclusion: The debridement efficacy of CEC in the distal root of the mandibular molar was comparable to TEC irrespective of the activation system. However, LA irrigants were more efficient in removing debris in both TEC and CEC at the coronal third, middle third, and apical third of the root canal. Clinical significance: CEC design preserves more pericervical dentin compared to traditional access cavities, thereby increasing fracture resistance. However, the reduced cavity size may pose a challenge in cleaning and shaping of the canal system, which could compromise debridement efficacy. Hence, irrigation activation plays a pivotal role. The findings of this study influence clinical guidelines, helping practitioners decide when and how to use CEC designs and which irrigant activation system to employ for achieving optimal results.