Irradiance, radiant exposure and the depth of cure are three different numbers. A curing light that is strong on paper can still leave the bottom of a restoration soft.
Three numbers, one restoration
Irradiance is what the light delivers per second and per square millimetre. Radiant exposure is irradiance multiplied by time: what the composite receives. The depth of cure is what the composite does with it, and it depends on the shade, the filler and the distance to the tip.
Most clinical failures attributed to the light are failures of distance and angle: a tip held five millimetres away delivers a fraction of what the box promises.1
What a typical increment needs
| Composite | Irradiance at the tip | Time | Radiant exposure |
|---|---|---|---|
| Universal, 2 mm, shade A2 | 1,000 mW/cm² | 20 s | 20 J/cm² |
| Universal, 2 mm, shade A4 | 1,000 mW/cm² | 40 s | 40 J/cm² |
| Bulk fill, 4 mm | 1,200 mW/cm² | 20 s | 24 J/cm² |
| Flowable, 1 mm | 1,000 mW/cm² | 10 s | 10 J/cm² |
Broad spectrum or single peak?
- Cures every photoinitiator on the market
- No surprises with a new material
- Slightly lower peak irradiance
- The default for a general practice
- Higher irradiance at one wavelength
- Camphorquinone materials only
- A risk with some bulk fills and bleach shades
- Fine where the materials are known
How to switch modes on the VALO X curing light.
Timing the cure from the moment the light is switched on, not from the moment the tip is in position. The first seconds of a twenty-second cure are often spent finding the tooth.2
What clinicians ask
Does a stronger light cure faster?
Up to a point. Above about 1,500 mW/cm² the gain in time is small, and the heat delivered to the pulp is not.
How often should the tip be checked?
Weekly, with a radiometer, and whenever the tip has been dropped or shows a residue of composite.
Is a plastic barrier a problem?
A thin barrier costs around ten percent of the irradiance; a thick or creased one can cost half. Add time accordingly.
References
- Price RB, Ferracane JL, Shortall AC. Light-curing units: a review of what we need to know. Journal of Dental Research. 2015;94(9):1179–1186.
- Rueggeberg FA, Giannini M, Arrais CAG, Price RBT. Light curing in dentistry and clinical implications: a literature review. Brazilian Oral Research. 2017;31(suppl 1):e61.
