Effect of Ultrasound on the Micromorphology of Glass Ionomer Restorations

Objectives: To evaluate the influence of ultrasound application (UA) on void frequency (VF) in resin-modified (RMGI) and conventional (GIC) glass ionomer cements using polarization-sensitive, spectral-domain optical coherence tomography (PS-OCT).
Methods: Standardized cavities measuring 6mm (diameter) X 2mm (depth) were prepared on the facial surfaces of 60 extracted bovine incisors. Specimens were assigned randomly to one of six groups (n=10): Ketac Nano (G1); Ketac Nano with UA (G2); Fuji II LC (G3); Fuji II LC with UA (G4); Fuji IX GP (G5); and Fuji IX GP with UA (G6). Materials were used following manufacturers’ recommendations. Ultrasound was applied for 15s at 28KHz (Cavitron Select SPS) with a dental scaler tip in contact with a Mylar strip that was covering the cements during the initial setting reaction. After the finishing procedure with Sof-Lex discs and 24h of storage in 100% humidity at room temperature, 160 cross-sectional images were obtained along each restoration in increments of 25μm using a PS-OCT system. The total dimensions sampled in volume were 4mm (length) × 4mm (width) × 1.36mm (depth). B-scan images were analyzed using Image J and the VF in each specimen was recorded. Data were statistically analyzed using Shapiro-Wilk and one-way ANOVA (SPSS v.23).
Results: Mean and standard deviation values for VF were: G1: 13±5.3; G2: 14.2±3.2; G3: 112.5±24.9; G4: 218.8±57.2; G5: 96.5±23.8; G6: 209.3±142.9. ANOVA showed that Fuji II LC and Fuji IX GP presented significantly higher VF (p<0.05) after UA. Ketac Nano showed significantly less VF than the other test materials (p<0.05) regardless UA.
Conclusions: UA may result in higher VF when used during the initial setting reaction of Fuji II LC and Fuji IX GP restorations.