# Effect of a 4 mm vs. a 6 mm Diameter Mold on the Depth of Cure of 6 Bulk-Fill Resin-Based Composites

## TL;DR

This study compares how mold size affects the depth of cure for dental composites, finding that a 6 mm mold gives higher cure depths than a 4 mm mold.

## Contribution

The study reveals that the ISO 4049 standard's 4 mm mold underestimates the depth of cure compared to a 6 mm mold for bulk-fill composites.

## Key findings

- The 6 mm mold consistently produced greater depth of cure values than the 4 mm mold for all six tested composites.
- A broad-spectrum LED curing light did not improve cure depth compared to a single-peak light for the tested materials.
- A frosty, solvent-resistant region was observed in all specimens, indicating incomplete curing near the mold walls.

## Abstract

Dental researchers and manufacturers use the ISO 4049 standard to determine the depth of cure (DoC) of resin-based composites (RBCs). This standard uses a 4 mm diameter stainless-steel mold and subsequently divides the length of the remaining hard RBC by 2. However, the DoC values obtained using this mold have been challenged. Six bulk-fill RBCs (Tetric plus Fill, Tetric plus Flow, Tetric PowerFill, Tetric PowerFlow, Filtek One, and Aura Bulk Fill) were used to investigate the limitations of the 4 mm diameter mold used in the ISO 4049 standard when compared to a 6 mm diameter metal mold that represented the dimensions of a large cavity in a tooth. Two distinct light curing units were used. One light (Elipar S10) emitted a single peak wavelength of light, while the other (Bluephase G4) was a broad-spectrum, multiple-peak curing light. After 10 s of photocuring, the uncured RBC was immediately removed using acetone. The maximum length of the hard RBC remaining was measured and divided by two so that the effect of these two mold diameters on the DoC results could be compared. The DoC of all six RBCs tested was consistently greater in the 6 mm diameter mold (p < 0.0001). Sectioning revealed that the solvent-dissolved specimens had a clear internal boundary between the apparently well-cured RBC and a peripheral, solvent-resistant, “frosty” region. Using a 4 mm diameter stainless-steel mold resulted in a reduced depth of cure values compared to those obtained when the 6 mm diameter mold was used. The use of a broad-spectrum, multiple-peak LED curing light proved unnecessary for photocuring the six RBCs used in this study.