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

Objectives: To 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. Methods: Thirty-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. Results: Total cuspal deflection was 4.9 +/- 1.3 mu m for the MOD cavity (group 1), 7.8 +/- 3.3 mu m for endodontic access with intact axial dentine (group 2), 12.2 +/- 2.6 mu m for endodontic access without axial dentine (group 3), and 11.1 +/- 3.8 mu m for endodontic access with a GIC base (group 4). Maximum buccal strain was 134 +/- 56, 139 +/- 61, 251 +/- 125, and 183 +/- 63 mu strain for groups 1-4 respectively, while the maximum palatal strain was 256 +/- 215, 184 +/- 149, 561 +/- 123, 264 +/- 87 mu strain respectively. All groups showed marginal leakage; however placement of GIC base significantly improved the seal (p = 0.007). Conclusion: Cusp 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. (C) 2009 Elsevier Ltd. All rights reserved.