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The purpose of this study was to evaluate the gutta-percha–occupied area (GPOA) and the relationship between GPOA and tug-back sensations in canals instrumented with reciprocating files.Twenty curved canals were instrumented using Reciproc R25 (VDW, Munich, Germany) (group R) and WaveOne Primary (Dentsply Maillefer, Ballaigues, Switzerland) (group W), respectively (n = 10 each). The presence or absence of a tug-back sensation was decided for both of #25/.08 and #30/.06 cones in every canal. The percentage of GPOA at 1-, 2-, and 3-mm levels from the working length was calculated using micro–computed tomographic imaging. The correlation between the sum of the GPOA and the presence of a tug-back sensation was also investigated. The data were analyzed statistically at P = .05.A tug-back sensation was present in 45% and 100% canals for #25/.08 and #30/.06 cones, respectively, with a significant difference (P < .05). At the 2- and 3-mm levels, #30/.06 cones produced significantly higher GPOA in groups R and W (P < .05). The sum of the GPOA score was significantly higher in the samples with a strong tug-back sensation (P < .05); however, there was no significant difference between the 2 cone types for this correlation (P > .05).Under the conditions of this study, the tug-back sensation can be a definitive determinant for indicating higher cone fitness in the curved canal regardless of the cone type.The tug-back sensation can be a definitive determinant for indicating higher cone fitness.There was no gutta-percha–occupied area (GPOA) difference between #25/.08 cones and #30/.06 cones at the 1-mm level.#30/.06 gutta-percha cones showed significantly higher GPOA scores than #25/.08 cones at the 2- and 3-mm levels.The sum of GPOA scores showed a strong correlation with the tug-back sensation.