Measuring Depth of Cure in Dental Composites According to ISO 4049
Depth of cure of composites – acetone/ethanol shaking test:
This method is based on the ISO 4049 standard. An important difference is that the uncured material is dissolved in acetone or ethanol instead of being removed with a spatula. The acetone shaking test was used and explained in a paper by Kleverlaan and De Gee (Eur J Oral Sci 2004;112:84–88). Equally effective is ethanol according to Miletic et al. (Serb Dent J 2012;59(4):190-197).
The image is a step by step explanation. A material complies with the ISO requirements if the remaining thickness of the specimen divided by 2 exceeds 1.0 mm for opaque shades and 1.5 mm for all other shades. Since manufacturers’ recommended layer thickness is often 2.0 mm this reference may be used as well.
The acetone/ethanol shaking test is a simple yet reliable method of testing the efficiency of light-curing units and curing conditions used in clinical practice (e.g. time, distance). It may also be used to compare various composite materials/shades.
How to measure the depth of cure of composites according to ISO 4049?
The ISO4049 standard explains in detail how the depth of cure is measured and what is minimum depth that composites must have in order to comply with this standard. This simple procedure does not require sophisticated equipment and may be done in every dental office. It allows testing and comparison of materials and light curing units. Even if there is a radiometer to check the light intensity, it is recommended to measure the actual thickness of the composite cured by a a particular light curing unit.
Here is what we need:
light curing unit
cylindrical moulds (6 mm thick and 4-5 mm in diameter), originally it should be stainless steel, but plastic straws cut into moulds of this size may be used as well
plastic filling instrument
spatula or scalpel
And here is the step-by-step procedure:
1. Place the mould on the glass slab and fill it with composite.
2. Place the Mylar strip on top of the composite.
3. Light-cure the composite according the manufacturer’s instructions (i.e. 40 s using a conventional or 20 s using a high-power halogen or LED light).
4. Discard the Mylar strip and remove the cured material from the mould.
5. Peel off the uncured material from the bottom side of the sample using the spatula or scalpel.
6. Measure the remaining thickness of the sample and divide this number by two. The ISO 4049 standard requires that the result should be at least 1.5 mm for non-opaque shades and 0.5 mm for opaque shades.
Author: Vesna Miletic BDS, MSc, PhD in DENTAL MATERIAL Magazine