In-vitro Compressive Strength and Edge Stability of Glass Ionomer Cements (GICs)

Objectives: Investigating null hypothesis: there’s no difference in compressive strength (CS) / edge stability (ES) of 6 GICs and 1 resin-modified glass-ionomer (RMGIC - + control), tested using in-vitro modelling.
Methods: 448 normal / 192 “repaired” cylindrical specimens (6 × 4 mm) were produced from 6 GICs and 1 RMGIC (n = 8/group). Post-water bath immersion at 37^oC for 1h, specimens were stored in tap water at 37^oC for 1d, 1week, 1month & 3months. “Repaired” samples consisted of a cone-shaped GIC base, aged for 1-month before being placed in standardised cylindrical moulds and filled with the same GIC (different shade). These were stored as above pre-testing. CS tests were performed over the whole sample surface (12.56 mm², CS) or directed to the sample edge (1.4 mm², ES) by a universal testing machine (Instron 5569A, UK). Data were statistical analysed by ANOVA with Tukey’s test (p < 0.05).
Results: Normal specimens: Ketac Universal (KU) showed a significantly higher CS vs. all groups across all time periods (p < 0.001). CS of ChemFil Rock (CFR), Fuji IX (FIX), IonoStar Plus (ISP) and Riva Self Cure (RSC) plateaued after 1 week and then decreased from 1 month. ES of KU was weaker than Equia Forte (EQF), FIX and RSC on 1d, but increased after 1 week. “Repaired” specimens showed a similar CS to those of normal specimens (p > 0.05). Repaired KU (KU-R) had a significantly better CS compared to that in Repaired EQF (EQF-R) and repaired Fuji II LC (FII-R) after 1d. Nevertheless, no statistical difference was found in ES of these three groups (p > 0.05).
Conclusions: KU matured rapidly with greatest CS and ES in both normal and “repaired” models after short-term ageing. Results suggests that KU, EQF and FII could be used to repair partly failing GICs in vivo.