Comparative Assessment of Fracture Resistance of Core Foundation Materials Employed in the Nayyar Technique: An in Vitro Study

Background: Endodontically treated teeth with extensive coronal destruction require core build-up for retention of definitive restoration. Nayyar core technique utilizes pulp chamber and coronal 2-4 mm of root canals for retention, avoiding additional post space preparation. The fracture resistance of such cores depends on mechanical properties of core material. ParaCore (fiber-reinforced dual-cure composite), everX Posterior (short fiber-reinforced composite) and Filtek One Bulk Fill are contemporary core materials with different compositions, but their performance in Nayyar technique has not been compared. Aim: To evaluate and compare coronal fracture resistance of endodontically treated mandibular premolars restored with ParaCore, everX Posterior and Filtek One Bulk Fill Posterior using Nayyar core technique. Materials and Methods: Thirty recently extracted human mandibular premolars with single root and single canal were selected. Access cavity was prepared, working length determined 0.5 mm short of apex, biomechanical preparation done with ProTaper Next up to X3, irrigation with 5.25% NaOCl and saline, obturation with gutta-percha and sealer by lateral condensation. Gutta-percha was removed to depth of 4 mm from orifice using Gates-Glidden drill maintaining 4 mm apical seal. Teeth were decoronated 2 mm above CEJ. Samples were randomly divided into 3 groups (n=10). Group 1: ParaCore (Coltene) - fiber-reinforced dual-cure composite core, Group 2: everX Posterior (GC) - short fiber-reinforced composite, Group 3: Filtek One Bulk Fill Posterior (3M). Standardized Nayyar cores were built using matrix. For PDL simulation, roots were coated with 0.2-0.3 mm wax and re-embedded with light-body PVS in acrylic blocks. Specimens were stored at 37°C for 24 hrs and subjected to axial compressive load in Universal Testing Machine (ACME UNITEST 10) with 4 mm spherical indenter at crosshead speed 0.5 mm/min till fracture. Load at fracture recorded in kN. Data analyzed with One-way ANOVA and Tukey's post-hoc test (p<0.05) using SPSS v24 Results: Mean fracture resistance was highest for Group 1 ParaCore (1.048 ± 0.084 kN), followed by Group 2 everX Posterior (0.715 ± 0.044 kN) and least for Group 3 Filtek One Bulk Fill (0.288 ± 0.031 kN). One-way ANOVA showed highly significant difference among groups (F=427.783, p<0.001). Pairwise comparison with Tukey's test showed Group 1 significantly higher than Group 2 and Group 3 (p<0.001), and Group 2 significantly higher than Group 3 (p<0.001). Conclusion: Within limitations of this in-vitro study, ParaCorefiber-reinforced dual-cure composite exhibited highest fracture resistance when used as Nayyar core, followed by everX Posterior short fiber-reinforced composite. Filtek One Bulk Fill showed least fracture resistance. ParaCore can be considered suitable core build-up material for Nayyar technique in endodontically treated premolars.