The findings of a recent study published in the scientific studies showed void formation varied depending on cavity area, layer thickness, and vibration application.

This study evaluated the effect of vibration on the adaptation of bulk-fill composite resin. A scanning laser doppler vibrometer measured the frequency and amplitude of a vibratory device (COMO; B&L Biotech) used for resin placement and visualized its effect on the resin according to depth. A bulk-fill composite resin (Filtek Bulk Fill; 3M ESPE) was placed in simulated cavities (4 mm diameter, 4 mm depth) by different layering methods (incremental filling with two 2-mm-thick layers vs. bulk filling with a single 4-mm-thick layer).


Composite resins are the most widely used direct restorative dental materials because of their aesthetics and ability to adhere to teeth with proper bonding materials. However, composite resins inevitably shrink by 2–4% during polymerization, which can cause stress-induced debonding at the tooth-restoration interface when shrinkage stress exceeds bond strength. Incremental filling, in which each layer of a 2-mm-thick composite is light-cured, is recommended to minimize potentially detrimental polymerization shrinkage stress
The groups were further divided based on the application of vibration during restoration (no vibration vs. vibration). In addition to the surface void area at the cavity floor, the overall void volume and the void volumes of the bottom, middle, and top thirds were obtained for micro-computed tomography analysis. The frequency and amplitude of the COMO were approximately 149 Hz and between 26 and 51 µm, respectively. When vibration was not applied, the incremental filling had a lower void volume in the bottom third of the cavity than did bulk filling (p < 0.05). Vibration applied with a 4-mm-thick bulk fill had no significant effect on the adaptation of composite resin (p > 0.05). In contrast, vibration reduced the amount of void formation in the bottom third of the cavity during incremental filling (p < 0.05).
Application of vibration to resin with a 2-mm incremental-layering technique formed a smaller void at the interface between the cavity and resin and within the bulk-fill composite resin.
Reference:
Kim, YS., Baek, SH. & Kim, R.J.Y. Effect of vibration during bulk and incremental filling on an adaptation of a bulk-fill composite resin. Sci Rep 12, 21652 (2022).
https://doi.org/10.1038/s41598-022-26197-9