Effect of Repressing Lithium Disilicate Glass Ceramics on The Shear Bond Strength of Resin Cements

Abstract

The aim of this study was to investigate the effect of repeated pressing of lithium disilicate ceramic on the shear bond strength (SBS) of three types of resin cement.

Methodology: A lithium disilicate ceramic (IPS e.max^® Press) was first heat-pressed to form rectangular disk specimens. Then, leftovers were used for the second and third presses. A total of 90 specimens were prepared and separated, according to the number of pressing cycles, into three groups: 1st, 2nd, and 3rd presses (n = 30). Each group was further subdivided into three groups (n = 10) according to the type of resin cement used, as follows: Multilink N (MN), Variolink Esthetic DC (VDC), and Variolink Esthetic LC (VLC). All the cement was bonded to the ceramic surface, which was etched with hydrofluoric acid and primed with Monobond Plus. All samples were light-cured and stored for 24 h. Shear bond strength was tested on a universal testing machine.

Results: A two-way ANOVA was used to evaluate the influence of repeated pressing cycles and cement type as well as their interaction. The results indicated that cement type has a significant impact (p < 0.001) but not the number of pressing cycles (p = 0.970) or their interaction (p = 0.836). The Bonferroni post-hoc test showed that the SBS of MN was significantly higher than that of VDC and VLC in the first press and second press cycles, respectively. The SBS of MN was significantly higher than that of VDC and VLC cements in the third pressing cycle. There was no significant difference in the SBS between VLC and VDC in all three pressing cycles.

Conclusion: The results of the current study did not report a detrimental effect of repeated pressing up to three cycles on the shear bond strength of the IPS e.max^® Press. Multilink resin cement showed the highest SBS to IPS e.max^® Press at the third pressing cycle. For all types of cement and heat pressing cycles, the majority of cement failures were adhesive. No cohesive failures occurred in any of the tested resin cements, regardless of the cement type or the number of heat pressing cycles tested.

Keywords: glass-ceramics; heat-pressing; lithium disilicate; repressing; resin cement; shear bond strength.

Figure 1

Bonding preparation and testing. (A) Shows the ceramic sample embedded in acrylic resin. (B,C) show the silicone mold before and after fixation with an elastic band. (D) Shows the sample during shear testing.

Figure 2

Percentage of each type of failure versus number of pressing cycles and type of cement. There is no significant difference in the type of failure between the number of pressing cycles or cement groups.

Figure 3

Stereomicroscopic images of the interface of selected failed samples (A,B) represent adhesive failure. The surface shows no remnant of the cement. (C,D) represent a mixed failure. A small remnant of cement is apparent at the site of loading (arrows).

Figure 4

SEM images of pressed IPS e.max^® Press samples. (A) first press, (B) second press, and (C) third press. All images were scanned at 5000×. The size of the crystals appears to be smaller and more compact in the first press cycle compared to the second and third press cycles.