Biological impact of optical radiation
from curing lights
Ellen Bruzell
Nordic Institute of Dental Materials
Symposium on Light Sources in Dentistry
Halifax - May 28-30 - 2014
Optical sources in dentistry
Radiation
Wavelengths (nm)
UVC
100-280
UVB
280-315
UVA
315-400
Visible light
400-780
IR-A
780-1400
IR-B
1400-3000
IR-C
3000 nm-1 mm
(not exhaustive)
Application in
Light source
dentistry
Sterilization
Low pressure Hg
chamber
lamp
(Not to my
knowledge)
Light curing,
Plasma arc, halogen,
tooth bleaching
LED
• light curing
• tooth bleaching
• operating light
Plasma arc, halogen,
• diagnostics
LED, laser
• i-o illumination
• microscope/loupe
Various hard/soft
LED, laser
tissue interventions,
(diode, Nd:YAG,
diagnostics
Er:YAG, Er,Cr:YSGG
CO2)
Curing light irradiance over time
2500
Halogen
LED
Irradiance [mW/cm2]
2000
1500
1000
500
0
2002
11
2005
5
2004
11
2005
3
2006
5
2007
10
2008
4
2009
4
2010
4
2011
4
Note: LED variations: 95-4600 mW/cm2 (x 50)
Ref: www.niom.no/content/tested-depth-cure-and-curing-lamps
Year
n
UVB
280
UVA
320
visible light
400
infra red
700
(nm)
Visible light/UVA (children)
UVA
UVB
retina
lens
cornea
Ref.: Adapted from Norwegian Radiation Protection Authority Bulletin 19, 1999
UV- and light-induced eye damage
UVB
UVA
Visible light
320
400
500
Mechanism
Mostly thermal
Mostly photochemical
Part of eye
Cornea
Lens
Retina
Eye effects
Snow blindness
Cataract
Cataract
Retinal damage
Ref.: Sliney DH, Radiation Protection Dosimetry, 1997;72:197-206
nm
Light-induced retinal damage
• Acute
– From sun or strong radiation
sources (e.g. laser)
Normal
• Chronic
– Age-related macular
degeneration (AMD)?
(loss of visual acuity)
AMD (uneven pigmentation)
• Light contributes to ageing of
the retina
• AMD develops over 30-40
years
www.phys.ufl.edu/
www.northeastcare.org.uk
Chronic blue light retinal damage:
risk increases with age
1.
pigments
ROS +photoproducts
Increased tendency of pigments to react with light
2.
pigments
pigments
The number of light absorbing pigments increases
3.
ROS + photoproducts
Formation of ROS increases
4.
ROS + photoproducts
Antioxidant pool depletes
Retinal cell function
inhibited or stopped
Mostly toxic (less
allergic) reactions ,
systemic effects
Photoactivation of drugs
Drugs that can bind to eye tissue
•
•
•
•
•
•
Chloroquine (antimalarial)
Allopurinol (against gout and hyperuricemia)
Psoralens (antipsoriasis)
Chlorpromazine/other phenothiazides (antipsychotics)
Griseofulvin (antifungal)
Tetracyclines? (antibiotics)
45
1
40
0,9
0,8
35
0,7
30
0,6
25
0,5
20
0,4
15
0,3
10
0,2
5
0,1
0
0
350
370
390
410
430
450
470
490
510
530
550
Wavelength [nm]
Bluephase20i
LED
VCL
Complete
Halogen
Blue-light hazard function Bλ
Relative units
Spectral irradiance [mW/cm2/nm]
Lamp emission versus retinal hazard
Maximum permissible exposure time (tmax)
for eyes
• LED lamps: 2007-20111
• Mean irradiance: 2009 mW/cm2 (± 5%) (range: 635-4600)
• Exposure limit value according to international guidelines on radiation2:
100 J/cm2× sr
(per day, acute and chronic eye exposure, artificial sources, workers and the public, exposure times < 2.7 h)
Direct blue light
Mean tmax = 1.9 min
(range: 0.5-3.9 min)
Reflected blue light3:
Mean tmax = 23.7 min
(range: 5.1-89.9 min)
Ref: 1) www.niom.no/content/tested-depth-cure-and-curing-lamps
2) ICNIRP, Health Physics 2013; 105 (1): 74-96.
3) Bruzell E et al. Photochem and Photobiol Sci 2009; 8: 377–385.
Light protection filters
• Worst-case exposure: orthodontics (?):
2.5 hr/day (per operator)
Photo: nrpa.no
• Six of 13 filters on today’s (2013) market were
inferior
• Challenge: Filters are not made to protect against
emission from one particular lamp
• Lack of standards for filter protection used with light
curing (high irradiance sources)
Heating of skin
Relationship between exposure time and limit value irradiance
(heating of skin)
Irradiance (mW/cm*2)
2500
2000
1500
1000
500
0
1
2
5
7
Exposure time (sec)
Radiant exposure (H) (dose)
within 10 s of exposure:
1
H = 2 × 𝑡4
[ J/cm2]
Ref.: ICNIRP, Health Physics 2013; 105 (1): 74-96.
10
Regulations, directives, standards
• EU directive 2006/25/EC Artificial Optical Radiation
• ICNIRP (International Commission on Non-Ionizing
Radiation Protection): Guidelines on limits of exposure to incoherent
visible and infrared radiation, Health Physics 2013; 105 (1): 74-96.
• CIE S009/IEC 62741 Photobiological safety of lamps and lamp systems
• CEN 1455-2: Measurement and assessment of personal exposure to
incoherent optical radiation. Part 2: Visible and infrared radiation emitted by
artificial sources in the workplace.