Resistance to bond degradation between dual-cure resin cements and pre-treated sintered CAD-CAM dental ceramics

Abstract

Objective: To evaluate the bond stability of resin cements when luted to glass-reinforced alumina and zirconia CAD/CAM dental ceramics.

Study design: Eighteen glass-infiltrated alumina and eighteen densely sintered zirconia blocks were randomly conditioned as follows: Group 1: No treatment; Group 2: Sandblasting (125 µm Al₂O₃-particles); and Group 3: Silica-coating (50 µm silica-modified Al₂O₃-particles). Composite samples were randomly bonded to the pretreated ceramic surfaces using different resin cements: Subgroup 1: Clearfil Esthetic Cement (CEC); Subgroup 2: RelyX Unicem (RXU); and Subgroup 3: Calibra (CAL). After 24 h, bonded specimens were cut into 1 ± 0.1 mm² sticks. One-half of the beams were tested for microtensile bond strength (MTBS). The remaining one-half was immersed in 10 % NaOCl aqueous solution (NaOClaq) for 5 h before testing. The fracture pattern and morphology of the debonded surfaces were assessed with a field emission gun scanning electron microscope (FEG-SEM). A multiple ANOVA was conducted to analyze the contributions of ceramic composition, surface treatment, resin cement type, and chemical challenging to MTBS. The Tukey test was run for multiple comparisons (p < 0.05).

Results: After 24 h, CEC luted to pre-treated zirconia achieved the highest MTBS. Using RXU, alumina and zirconia registered comparable MTBS. CAL failed prematurely, except when luted to sandblasted zirconia. After NaOClaq storage, CEC significantly lowered MTBS when luted to zirconia or alumina. RXU decreased MTBS only when bonded to silica-coated alumina. CAL recorded 100 % of pre-testing failures. Micromorphological alterations were evident after NaOClaq immersion.

Conclusions: Resin-ceramic interfacial longevity depended on cement selection rather than on surface pre-treatments. The MDP-containing and the self-adhesive resin cements were both suitable for luting CAD/CAM ceramics. Despite both cements being prone to degradation, RXU luted to zirconia or untreated or sandblasted alumina showed the most stable interfaces. CAL experimented spontaneous debonding in all tested groups.

Figure 1

FEG-SEM micrographs of pre-treated ceramics. A) Sandblasted alumina surfaces exhibited edge-shaped micro-roughness (850×; bar 10 µm).

Figure 2

A slight undulation in the zirconia surface texture was observed after silica-coating (850×; bar 10 µm).

Figure 3

FEG-SEM figures of Clearfil bonded to a sandblasted alumina surface at 24 h. A) Cohesive failure: the entire porcelain surface was covered by a resin cement film (95×; bar 100 µm).

Figure 4

Sparse, scattered cement porosities were detectable at higher magnification (850×; bar 10 µm).

Figure 5

FEG-SEM images of fractured beams after NaOClaq storage. A) Mixed failure of a sandblasted alumina stick bonded with Clearfil, showing cement layers with protruding filler particles (95×; bar 100 µm).

Figure 6

Micro-irregularities and dissolved cement residuals were noticed at higher magnification (850×; bar 10 µm).

Figure 7

Mixed failure of an untreated zirconia surface luted with RelyX Unicem (95×; bar 100 µm). Cement dissolution areas with round-shaped margins remained at the top side of the beam (cohesive phase).