Abstract
The aim of the present study was to investigate the shear bond strength of five different repair methods and adhesive systems for zirconia (Zr) cores layered with feldspathic porcelain. Seventy-five Zr specimens (10 × 10 × 4 mm3) were prepared, sintered, layered with 2 × 10 × 10 mm3 of feldspathic porcelain, and fired. The ceramic was fractured, and the load recorded using a shear-bond test. Specimens were thermocycled and randomly divided into 5 groups (n = 15/group) based on the repair methods. Composite repair blocks with similar dimensions to the layered ceramic (2 × 10 × 10 mm3) were built according to each repair method. Shear bond strength testing of the specimens with composite built up was carried out using a universal testing machine (Instron®5960, Massachusetts, USA). The shear bond strengths of the adhesive interface between repaired composite and the Zr were recorded for all the test groups. The fractured specimens’ surfaces were examined under a scanning electron microscope (Jeol, Musashino, Akishima, Tokyo, Japan) for evaluation of the type of failure and surface characteristics. Shear bond strength of the veneered ceramic bonded to the Zr for all the test groups was non-significant (ANOVA, p = 0.062). Shear bond strength after the repair revealed significant differences (ANOVA, p = 0.002). Group-C (13.79 ± 1.32) and Group-D (9.77 ± 4.77) showed the highest and lowest shear bond strength values, respectively. Paired Sample T-tests showed significantly lower values (p = 0.000) for the repaired (composite) Zr compared to the layered (ceramic) Zr. Multiple comparisons revealed differences (significant) between the shear bond strength of Group-D with Groups A (p = 0.010) and C (p = 0.003, Post Hoc Tukey test). The repair methods tested showed variations in their respective shear bond strengths. Complete ceramic/zirconia repair systems showed better bonding between the repaired composite and Zr core. The mean shear bond strength for the repaired fractured layered Zr showed acceptable outcomes in terms of clinical perspective, but was, however, unpredictable.
Highlights
A variety of materials are available for the indirect restoration of endodontically treated or badly damaged teeth e.g., all-metal, metal ceramic, all-ceramic, zirconia (Zr) veneered with ceramic, and monolithic Zr [1,2,3]
The studies reporting the bond strength of intraoral repair methods for adhering composite resin to zirconia are scarce [28]. The aim of this in vitro study was to compare the shear bond strength of five repair methods for Zr cores layered with feldspathic porcelain
Comparison of the shear bond strength before (Zr core layered with ceramic) and after with the tested repair methods, for the layered Zr with Paired Sample T-test, showed that the post-repair shear bond strength for all repair systems (p = 0.000) was significantly lower compared to the shear bond strength values between the layered ceramic and the Zr core (Table 3)
Summary
A variety of materials are available for the indirect restoration of endodontically treated or badly damaged teeth e.g., all-metal, metal ceramic, all-ceramic, zirconia (Zr) veneered with ceramic, and monolithic Zr [1,2,3]. To overcome the inherent deficiencies of color mismatch of metal crowns and brittleness of all-ceramic crowns, Zr crowns were introduced for the indirect restoration of teeth with compromised coronal tooth structure [4]. Despite the recent introduction of more translucent monolithic systems, Zr is still more opaque than traditional all-ceramics. The esthetics of the Zr core is further enhanced by the application of porcelain over the Zr to overcome the inherent deficiency of lack of translucency in Zr [6]. The bonding between the Zr core and the veneering ceramic layer makes these veneered Zr restorations weaker due to failure of adhesion between the two chemically different materials [7]
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