Effect of Alkalic Hydraulic Calcium-silicate Cement on the Covering Material

Objectives: Hydraulic calcium-silicate cement (hCSC) is a clinically proven pulp-capping agent. Which material is best applied to cover hCSC is not yet fully clear. In this study, the flexural strength of four restorative materials exposed to high alkali from hCSC was measured and their interface with hCSC upon 1-year water storage characterized by SEM.
Methods: The three-point bending strength (n=10) of the conventional glass-ionomer cement (GIC) Fuji lX GP Extra (GC), the resin-modified GIC Fuji ll LC (GC), the BisGMA-based composite Clearfil Majesty ES-2 (Kuraray Noritake) and the UDMA-based composite Unifil Flow (GC) were measured (ANOVA and Tukey's post-hoc test (α=0.05)) after 24-h, 3-m and 1-y storage in either distilled water (control) or alkali solution (pH=10.8). For SEM interfacial characterization, the hCSC Proroot MTA (Dentsply Sirona) was mixed and allowed to harden for 24 h in 100% humidity. The four restorative materials were applied on the set hCSC, with the application of the two composites preceded by an air-dried and light-cured layer of Scotchbond Universal (3M Oral Care). Upon 1-y water storage, interfacial cross-sections were embedded and polished using an argon-ion-beam cross-section polisher for SEM.
Results: The flexural strength upon alkali storage remained stable for Fuji lX GP Extra and Clearfil Majesty ES-2, but significantly decreased for Fuji ll LC and Unifil flow, the latter’s solution having become cloudy. SEM interfacial characterization revealed structural matrix damage of the conventional and resin-modified GICs close to the hCSC. Also the adhesive layers underneath the composites were structurally damaged, even close to the composite in case of Unifil flow.
Conclusions: Despite not having reduced the flexural strength of all restorative materials, they all appeared sensitive to high alkali, with the resin-modified GIC and UDMA-based composite having structurally been damaged most severely.