Impact of access cavity design on the filling ability of two obturation protocols evaluated by micro-computed tomography

This study investigated the effects of traditional access cavity (TAC) and contracted access cavity (CAC) designs on the filling ability of two obturation protocols, single cone obturation (SC) and continuous wave compaction (CWCT), using micro-computed tomography (micro-CT). Twenty standardized 3D-printed mandibular first molar replicas were allocated according to access cavity design ( n = 10). All canals were prepared with the EdgeFile X7 rotary system to size 30/0.04 and scanned using micro-CT. The specimens were then allocated to four groups according to access design and obturation protocol: TAC/CWCT, TAC/SC, CAC/CWCT, and CAC/SC ( n = 5). Filling quality was assessed by percentage of voids (POV), isthmus filling, and residual filling-material volume in the pulp chamber. Gaussian generalized estimating equation analysis of POV demonstrated a significant access cavity design × obturation protocol interaction (Wald χ² = 6.37, P = 0.012), with an estimated interaction contrast of 1.903% points (95% CI, 0.426–3.381). The highest descriptive apical POV values were observed in the CAC/CWCT group, reaching 8.810 ± 1.082% in the mesiobuccal canal and 12.069 ± 0.768% in the mesiolingual canal. Residual filling-material volume also showed a significant access design × obturation protocol interaction ( P < 0.001), with CAC/CWCT showing the greatest residual volume (0.409 ± 0.064 mm³). Isthmus filling was absent in all CAC/CWCT specimens; however, differences between TAC and CAC were not statistically significant within either CWCT ( P = 0.167) or SC ( P = 1.000). Overall, filling outcomes depended on the combination of access cavity design and obturation protocol, with the CAC/CWCT combination showing the least favorable pattern. Because different sealers were used with CWCT and SC, these findings reflect the complete obturation protocols rather than the obturation techniques alone.