Cuspal deflection, strain and microleakage of endodontically treated premolar teeth restored with direct resin composites

ObjectivesTo measure cuspal deflection and tooth strain, plus marginal leakage and gap formation caused by polymerization shrinkage during direct resin composite restoration of root-filled premolars.MethodsThirty-two first and second maxillary premolars were divided into four groups (n = 8). Group 1 had standardised mesio-occlusal-distal (MOD) cavities and served as the control group. Group 2 had endodontic access and root canal treatment through the occlusal floor of the MOD cavity, leaving the axial dentine intact. Group 3 had endodontic access and root canal treatment with the mesial and distal axial dentine removed. Group 4 had endodontic access and root canal treatment with axial dentine removed and a glass ionomer base (GIC). All groups were restored incrementally using a low shrink resin composite. Cuspal deflection was measured using direct current differential transformers (DCDTs), and buccal and palatal strain was measured using strain gauges. Teeth were immersed in 2% methylene blue for 24 h, sectioned and scored for leakage and gap formation under light and scanning electron microscopy.ResultsTotal cuspal deflection was 4.9 ± 1.3 μm for the MOD cavity (group 1), 7.8 ± 3.3 μm for endodontic access with intact axial dentine (group 2), 12.2 ± 2.6 μm for endodontic access without axial dentine (group 3), and 11.1 ± 3.8 μm for endodontic access with a GIC base (group 4). Maximum buccal strain was 134 ± 56, 139 ± 61, 251 ± 125, and 183 ± 63 μstrain for groups 1–4 respectively, while the maximum palatal strain was 256 ± 215, 184 ± 149, 561 ± 123, 264 ± 87 μstrain respectively. All groups showed marginal leakage; however placement of GIC base significantly improved the seal (p = 0.007).ConclusionCusp deflection and strain increased significantly when axial dentine was removed as part of the endodontic access. Placement of a glass ionomer base significantly reduced tooth strain and marginal leakage. Therefore, a conservative endodontic access and placement of a glass ionomer base are recommended if endodontically treated teeth undergo direct restoration with resin composite.