SonicFill3™ Bulk-Fill Versus Incremental Layering: Void Formation and Knoop Microhardness

Objectives: Compare presence of internal voids and surface microhardness in resin composites using sonic insertion or incremental layering techniques; analyzed using optical microscopy and Knoop microhardness.
Methods: Two resin composite systems, SonicFill™3 Nanohybrid Bulk-fill Composite (Kerr Corporation) and Mosaic™ Universal Conventional Composite (Ultradent Products Inc), were evaluated. Four groups (n=5) were evaluated according to insertion method (sonic or incremental layering) and shade (Vita A2, A3). Cylindrical brass molds, 5.5mm diameter by 4.0mm depth, were fabricated. For sonic insertion, bulk-fill composites (BA2, BA3) were inserted in a single increment (4mm). Sonic insertion was performed, using the SonicFill proprietary Handpiece (Kerr Corporation) at maximum dispensing rate, by keeping the tip within material while dispensing. For conventional composites (CA2, CA3), incremental layers (2mm) were utilized. Composites were light cured at their respective increments for 20s using a multi-peak light-emitting diode light-curing unit (VALO) in standard output mode (wavelength: 385-515nm; intensity: 1000mW/cm²) at a distance of 1mm through a glass microscope slide. Samples were stored (24hrs) in dH2O and light shelter, evaluated for Knoop microhardness (KHN) using Shimadzu Micro Hardness Tester (HMV-G Series) at 100g/15s stress; measured surface center plus two areas ~100um from center. Samples were then sectioned longitudinally and evaluated for internal voids (0.05-0.7mm) using Nikon Measuring Microscope (MM-11). Data were analyzed using ANOVA and Tukey-Kramer Multiple-Comparison (alpha = 0.05).
Results: Significant differences were observed in microhardness among groups based on type and shade of composite, and void formation based on type of composite. Conventional composites had significantly higher KHN (Table I). Sonic insertion had significantly fewer voids than incremental layering (Table II).
Conclusions: Results suggest sonic insertion might reduce void formation during composite delivery, while incremental layering might increase surface microhardness. Further studies are indicated to ensure differences observed in this study can influence the clinical relevance of resin composite delivery systems.