Effect of novel restorative materials and retention slots on fracture resistance of endodontically-treated teeth

Objectives. The aim of this study was to evaluate the fracture resistance of endodontically-treated teeth restored with nano-hybrid composite resin, bulk-fill flowable and short fibre-reinforced-composite in the absence/presence of retention slots. Materials and methods. One hundred and ten extracted non-carious human mandibular molars received endodontic treatment followed by mesio-occlusodistal (MOD) cavities with 3 +/- 0.2 mm thicknesses of buccal and lingual walls. Teeth were divided into two main groups according to the retention slot preparation. The dove-tail retention slots were prepared on the middle of opposite buccal and lingual walls to create mechanical interlocking. Each group was further divided into four sub-groups according to restorative material types: control (no restoration), nano-hybrid composite resin (Filtek(TM) Z550), bulk-fill flowable (Filtek(TM) Bulk Fill) and short fibre-reinforced-composite (everX Posterior(TM)). Restored teeth were subjected to compressive load at a strain rate of 1 mm/min. The data were statistically analysed using two-way ANOVA and Tukey's test for multiple comparisons. Results. The fracture resistance was significantly affected by the presence of the retentive slots and restorative material (p < 0.05). Restored teeth with retentive slots significantly increased the fracture resistance compared with restored teeth without retentive slots (p < 0.05). Short fibre-reinforced-composite with retentive slot cavities had significantly higher fracture resistance values compared with the other test groups (p < 0.05). Conclusions. The preparation of retention slots may increase the fracture resistance of endodontically-treated teeth, especially, when restored with short fibre-reinforced composite. The use of short fibre-reinforced composite with retentive slots could be an alternative technique to prevent cuspal fracture on endodontically-treated teeth with MOD cavity.