Objective: The aim of this study was to compare the microshear bond strength (µSBS) of lithium disilicate microdiscs with cement film thicknesses of 20 µm, 40 µm, and 100 µm at the coronal, middle, and cervical areas of the buccal surface of maxillary premolars.
Methods: Eighty-one lithium disilicate microdiscs (IPS e.max CAD, Ivoclar Vivadent) were divided into three groups (n=9) according to different cement film thicknesses. Group A=20 µm, Group B=40 µm, Group C=100 µm. Each group was subdivided into coronal (c), middle (m), and cervical (v) areas. The buccal surfaces were prepared with a 0.5 mm depth in enamel. The cemented specimens were thermocycled for 2,500 cycles between 5 and 55°C. A universal testing machine was used for the µSBS test until failure. Failure modes were assessed using a stereomicroscope.
Results: One-way ANOVA statistical test (p < 0.0001) and Tukey's post hoc test showed a statistical difference in the mean µSBS of groups A, B, and C. Pairwise comparisons (p≤0.05) showed no significant difference between groups Ac and Am, nor Bc and Bm. Significant differences were observable in all other subgroups. Failure modes showed no significant differences in their overall distribution, however, cohesive failures were predominant in groups Ac and Bm, while adhesive failures were mostly seen in Cv.
Conclusion: A thicker cement film thickness in the cervical area of the tooth greatly decreases µSBS of lithium disilicate, while microdiscs cemented coronally with a thinner film showed better adhesion.