Effect of multi-system polishing on shear bond strength of nanohybrid composites to enamel: an in vitro study

Background The purpose of this study was to compare the influence of three enamel finishing and polishing systems (Sof-Lex discs, lithium disilicate Eve burs and lithium disilicate polishing burs) on the shear bond strength and distribution of failure modes of nanohybrid composite resin bonded to enamel. Materials and Methods A sample of 240 healthy human premolars were randomized into four treatment groups ( n = 60 per group): (1) untreated control, (2) Sof-Lex disc polishing, (3) lithium disilicate EVE burs (Li-EVE) burs, and (4) lithium disilicate polishing burs (Li-Polish) burs. Specimens were prepared with standardized protocols and restored with a nanohybrid composite and universal adhesive system. The enamel surfaces were etched with 35% phosphoric acid. Shear bond strength (SBS) was measured using a universal testing machine and fracture modes were assessed with a dissecting microscope. Descriptive statistics, one-way analysis of variance (ANOVA), Games–Howell post hoc test, and chi-square analysis of the mode of failure were conducted at α = 0.05. Results There were significant differences in SBS between the groups (F(3,236) = 10.54, p = 1.6 ± 10 −6 ). Both Sof-Lex (31.39 ± 7.81 MPa) and Li-Polish (30.94 ± 5.70 MPa) had significantly higher bond strength values than control (23.18 ± 14.04 MPa) and Li-EVE (26.00 ± 8.26 MPa) ( p ≤ 0.024). There was no significant difference between Sof-Lex and Li-Polish (p = 0.82). The failure modes were predominantly cohesive in all the groups and the distribution of failure modes was not significantly different ( χ 2 (3) = 6.31, p = 0.098, Cramér’s V = 0.162). Conclusion The enamel polishing system significantly influenced composite bond strength. Multi-step polishing systems, e.g. , Sof-Lex discs or Li-Polish burs, increased adhesive performance markedly over the control groups or one-step polished systems to untreated enamel. The failure mode was not significantly influenced by polishing systems. These findings demonstrated the importance of finishing systems for successful restorative performance.