Impacts of Contracted Endodontic Cavities on Instrumentation Efficacy and Biomechanical Responses in Maxillary Molars


      • This study evaluated CECs and TECs with respect to instrumentation efficacy, axial strain response at the mesiobuccal and palatal root surfaces, and load at failure under static compressive loading applied after cyclic loading.
      • Instrumentation efficacy was not significantly impacted by endodontic cavity design.
      • Axial root strain under cyclic loading varied without consistent patterns for CECs or TECs.
      • Load at failure for contracted endodontic cavities (CECs) did not differ significantly from traditional endodontic cavities (TECs) and was lower for both groups compared with intact molars controls.



      Recently, we reported that in mandibular molars contracted endodontic cavities (CECs) improved fracture strength compared with traditional endodontic cavities (TECs) but compromised instrumentation efficacy in distal canals. This study assessed the impacts of CECs on instrumentation efficacy and axial strain responses in maxillary molars.


      Eighteen extracted intact maxillary molars were imaged with micro–computed tomographic imaging (12-μm voxel), assigned to CEC or TEC groups (n = 9/group), and accessed accordingly. Canals were instrumented (V-Taper2H; SSWhite Dental, Lakewood, NJ) with 2.5% sodium hypochlorite irrigation, reimaged, and the proportion of the modified canal wall determined. Cavities were restored with bonded composite resin (TPH-Spectra-LV; Dentsply International, York, PA). Another 28 similar molars (n = 14/group) with linear strain gauges (Showa Measuring Instruments, Tokyo, Japan) attached to mesiobuccal and palatal roots were subjected to load cycles (50–150 N) in the Instron Universal Testing machine (Instron, Canton, MA), and the axial microstrain was recorded before access and after restoration. These 28 molars and additional 11 intact molars (control) were cyclically fatigued (1 million cycles, 5–50 N, 15 Hz) and subsequently loaded to failure. Data were analyzed by the Wilcoxon rank sum and Kruskal-Wallis tests (α = 0.05).


      The overall mean proportion of the modified canal wall did not differ significantly between CECs (49.7% ± 12.0%) and TECs (44.7% ± 9.0%). Relative changes in axial microstrain responses to load varied in both groups. The mean load at failure for CECs (1703 ± 558 N) did not differ significantly from TECs (1384 ± 377 N) and was significantly lower (P < .005) for both groups compared with intact molars (2457 ± 941 N).


      In maxillary molars tested in vitro, CECs did not impact instrumentation efficacy and biomechanical responses compared with TECs.

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