Push-out strength of a core-built-up resin for fiber post cementation

Objectives: In this in-vitro-study, the push-out bond strength of a core-built-up resin used for fiber post (DentinPost, Komet/Brasseler) cementation was tested. Furthermore, the effect of different adhesives and different surface treatments of the post should be evaluated. Methods: 108 extracted, single-rooted human teeth were endodontically treated. Teeth were randomly divided into 9 groups (n=12). Fiber posts received three different surface treatments: None, etching with hydrofluoric acid for 20 seconds and silane, tribochemical treatment (Rocatec) and silane. For luting posts to root canal a dual-cured material (Rebilda DC, Voco) was used in combination with two adhesives (ExciteDSC, Vivadent or Solobond Plus light-cured, Voco) and no adhesive as control. Specimen were sectioned in equal thirds perpendicular to the post with 2 mm height each. Push-out test was performed to evaluate the regional bond strength between root canal and post. Qualitative analysis by stereomicroscope was performed to investigate failure mode. Data were analyzed using a mixed regression model and Mann-Whitney-Test to compare means (alpha=0.05). Results: The push-out test values varied significantly according to the root segments (p<0.01), surface treatment of the post (p<0.01) and adhesive system (p<0.01). Bond strength was significantly higher in the cervical third (11.08 MPa) than in apical third (9.31 MPa). Surface treatment with hydrofluoric acid/silane (9.85 MPa) and tribochemical treatment/silane (13.18 MPa) significantly increased bond strength compared with no surface treatment (7.65 MPa). The bond strength significantly decreased when Solobond Plus was used (7.40 MPa). Excite DSC (12.28 MPa) showed no significant effect on bond strength compared with control (11.00 MPa). Optical analysis of post surface showed mixed adhesive failure modes in most cases. Conclusion: Tribochemical treatment and etching post surface with hydrofluoric acid can be recommended when using a core-built-up resin for cementation.