CA2281194C

CA2281194C - Illumination system for polymerization

Info

Publication number: CA2281194C
Application number: CA002281194A
Authority: CA
Inventors: Guenther Nath
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-08-21
Filing date: 1999-08-19
Publication date: 2009-12-08
Anticipated expiration: 2019-08-19
Also published as: GB9919759D0; DE19846580A1; GB2340926B; CA2281194A1; GB2340926A

Abstract

An illumination system for the polymerization of epoxies in dental and industrial applications in the range from 280 to 500 nm is described. It comprises a mercury vapor discharge lamp with an operating pressure of up to 200 bar, a selectively reflecting elliptoid, with a high reflection in the 280 to 500 nm range, and a light guide, preferably a liquid core light guide, located at the focal point of the reflected radiation.

Description

ILLUMINATION SYSTEM FOR POLYMERIZATION.
BACKGROUND.
1. Field of the Invention The invention relates to an i]].umination system for polymerization in dentistry and for industrial applications in the spectral range of 280 to 500 nm (UVB, UVA
and blue).

2. Description of the Prior Art The use of a light guide, especially a liquid core light guide , emitting light at short-wavelengths in the polymerization of epoxies is common practice. The main components of an illumLination system are a light source and a light guide to transmit the light energy to the target, for example for the curing of epoxies in a dental filling or as an industrial assembly. High pressure mercury vapor lamps have been used but up to now their gap distance between the electrodes was too wide resulting in too low a light coupli.ng efficiency for speedy curing.
Another disadvantage was a warmup time of several minutes. Mercury super-pressure lamps with a narrower electrode gap and a higher operational vapor pressure of approx. 80 bar have never been. a success in dentistry, mainly because of the long warm-up time, the short life and the unfavorable spectral distribution with only a small quasi-continuo-us content of background radiation. This is particularly noticeable in the blue range :preferred today. Later illumination devices with liquid lightguides such as Translux devices available from Heraeus Kulzer were provided with tungsten halogen lamps of 150 W and elliptoidic reflectors.
But also these devices have disadvantages. Their emission spectrum is inadequate for curing in the UV spectral range. With an output of only 300 mW
in the blue spectral range of approx. 400 to 500 nm the curing time is long, in dentistry it takes more than one minute to cure a filling. More recent dental curing lamps include a xenon super-pressure lamp (Cermax lamp) with an integrated elliptoidic reflector which can be connected to a lightguide. Such lamps have an electrical input power of 300 W and a lightguide output of approx.
2.5 W in the range of 400 to 500 nm, where extra UV light can be added. Using these lamps composite fillings for dental work are cured within 1 to 2 seconds and they are also used for bleaching teeth for a nice looking smile. Lamps of this type are expensive and two th:irds of the emitted radiation is within the near infrared spectral range thus requiring efficient radiation filtration to prevent damage to the connecte(i liquid lightguide. In case of filter failure the lamp is a potential risk to the~ equipment and to patients. Modern industrial polymerization processes, like those for the curing of adhesives, make use of flexible lightguides and mercury super-pressure lamps, e.g. those of the type HBO 100 and HBO 200 available from Osram. Active radiation for polymerization is predoYninantly in the UVA spectral range, more recently also in the blue range. With an electrode gap of only 0.2 mm for a HBO 100 such lamps possess a high luminosity of 170,000 cd/cm2, which is particularly advantageous for radiation input into thin lightguides having a diameter of 2-5 mm. A
focussing assembly coinprising lamp and reflector, especially an elliptoidic reflector, like HBO R 103 W/45 (by OSRAM) offers efficiency, economy and small size. However, in contrast to a tungsten halogen and a xenon lamp the HBO
lamps take a few minuites to obtain full operational pressure which delays their usability. This long warm-up time is a disadvantage in dentistry. Furthermore, the lightguide output power is halved after approx. 100 hours of operation, especially in the UVA range.

SUNIlViARY OF THE INVENTION.

The objective of the invention is the combination of the following characteristics:
a) An ultra high-pressure mercury vapor discharge lamp of the VIP type (100 to 300 W) available fromt Osrani or of the equivalent UHP type available from Philips and with an operational pressure of more than 100 and up to 200 bar;

b) a selectively reflecting elliptoidic reflector manufactured using reflecting dielectric thin film coating, said reflector having a high reflectivity in the spectral range of below 500 nm and a low reflectivity in the spectral range of above 500 nm, c) a liquid lightguide with a maximum transmission in the spectral range of UVB, UVA and blue up to approx. 500 nm.
An advantage of the invention is an efficient high light energy transfer in the range from 280 to 500 nin for efficient curing of epoxy in its most sensitive photochemical absorption range.
Another advantage of the invention is a short curing time of epoxies, e.g.
dental fillings, in the range of 1 to 5 seconds.
Another advantage of the invention is a short warmup time in the range below one minute.
Another advantage of' the invention is a long life time of the light source in the range of 1,000 hours.
Another advantage of the invention is the narrow gap between electrodes in the mercury vapor lamp for easy coupling radiation into the light guide.
Another advantage of the invention is the efficient high emission of about 3 -W of the lamp in the spectral range below 500 nm for an input energy of only W, i.e. a high degree of energy conversion can be achieved in the range of several percents.

IN THE DRAWINGS.
FIG. 1 shows a schematic of the illuminator FIG. 2 shows a table cornparing transmitted light energies of diverse iIluminators at the light exit end of the light guide.

3 DESRIPTION OF THE PREFERRED EMBODIMENTS.

An iIlumination system 10 for the polymerization of epoxies, such as used in dental work and in industria:l assembly is described below. An ultra high-pressure mercury vapor (UHPMV) lamp is used as a light source. The high operational pressure of about 200 bar results in a considerable broadening of the mercury spectral lines compared to regular mercury lamps, and in a significantly increased quasi-continuous spectral background radiation in the range of 300 nm < a, < 650 nm. This radiation spectrum can be assigned a color temperature of approx. 8,500 K which corresponds to a the maximum range of emission of such a lamp in the blue and UVA, range. Further advantages of the ultra high-pressure lamp include the coniparatively short - for mercury lamps -warm-up time of approx. 20-40 s and the long life of more than 1,000 hours of operation.
For the purpose of the present invention the radiation content above k = 500 nm in a ultra high-pressure mercury vapour lamp is undesirable as this portion generates additional heat without having a photo-chemical effect. That is why a focussing, selectively reflecting elliptoidic reflector is provided transmitting the undesirable radiation content above 500 nm and reflecting the one below 500 nm.
An UHPMV lamp (VIP Lamp by OSRAM) 100 contains a mixture of mercury and a noble gas that in operation heats up to create an internal pressure of up to bar. Here it has been affixed in a horizontal position to an elliptoidic reflector 110 as being used by Osram in connection with the HBO 100 lamp, the so called HBO R 103 W/45, by means of' cement in such a way that the plasma center 120 of the VIP lamp is in the first focal point 122 of the elliptoidic reflector 110. The second focal point 123 of elliptoidic reflector 110 is on the light entrance face 132 of the liquid lightguide 130. Elliptoidic reflector 110 is implemented such that the light radiation reflected by the reflector is higher than 80% for wavelengths smaller than 500 nm and less than 20% for wavelengths above 600 nm.

4 Preferably for lamp 100 a VIP lamp is used with an electrical input power between 80 and 220 watt, an operational voltage of about 75 - 100 volts, an operational current of about 1 - 2 amps and a gap between the electrodes of about 0.8 - 2mm. More preferably the VIP lamp is operated with about 120 watts, 85 volts and 1.4 amps.
Elliptoidic reflector 110 has a diameter of about 67 mm and a total length of about 75 mm. The focal point produced by reflector 110 has a distance of about 45 mm as measured from the aperture area of the reflector. The full cone angle of the reflected radiation is about 44 . Elliptoidic reflector 110 is made out of glass and is coated on its inner surface with a dielectric thin film filter with a high reflectivity in the wavelength range between about 280 and 500 nm and a high transparency for radiation in the wavelength range above 500 nm.
A polymerization filter 124 can suitably be deposited directly onto the light entrance face 132 of the liquid lightguide by means of vacuum evaporation, said filter having a maximurn transmission range in the blue range (400 nm <k <500 nm or UV + blue range). A shutter 150 activated by means of a timer 160 controls the amount of radiation transmitted to a composite filling. The timer is activated by means of a manually operated switch mounted on the end of the lightguide adjacent to the patient or by means of a foot pedal. With an output power of approx. 1-3 W in the blue range 3 to 4 pulses each having a length of 1 to 2 s suffice to cure the composite filling completely. Due to their high light transmission and good flexibility dentists prefer to use _ liquid lightguides comprising tubes of THV (3M) filled with a mixture of glycol and water or triethylene glycol and water. For industrial applications the liquid lightguides are made out of Teflon FEP or Hyflon MFA tubes filled with a concentrated aqueous solution of NaH2PO4, CaClz or CaBr2 with refractive indices ranging from 1.38-1.46 for improved transmission and photochemical stability of these liquids in the UVB
and UVA spectral range. Tubes made out of THV (3M) and Teflon FEP or Hyflon MFA can be i.nternally coated with a thin layer of an amorphous fluoropolymer such as Teflon AF or Hyflon AD or Teflon SF in order to

5 improve transmission and to increase the optical aperture of the liquid light guide. This coating has a refi-active index of below 1.33 to increase a light transmission by internal. reflections in a tube filled with a liquid with a refractive index of about 1.4. The advantages of liquid light guides are a high transmission rate between 280 - 500 nm anci economy as compared to fiber bundles of quartz glass or plastic. These alternatives can serve the purpose of the invention but have lower transmission. FIG. 2 shows that the video projector lamp VIP 120 W
with integrated reflector of the HBO R 103 W/45 type and connected liquid lightguide is especially suitable for polymerization in dentistry using blue light and for industrial applications in the UVA and blue range. The table compares lightguide emissions (iin W) of the VIP lamp with two other important polymerization lamps. FIG. 2 shows clearly that the lightguide output values of the illumination device according to the invention comprising a VIP 120 W lamp and an elliptoidic reflector of' the HBO R103W/45 type more than add up compared to the state of'the art illumination devices. This is particularly evident in the case of the 200 W HBO I)C lamp having definitely lower lightguide output values despite an electrical input power almost twice as high as the VIP lamp with 120 W. Also compared to the HBO 100 W lamp with elliptoidic reflector the VIP 120 W lamp with the same reflector has surprisingly high emission values.

Even if the lightguide output values measured with the VIP 120 W lamp are arithmetically corrected. for an electrical input power of 100 W - as done in table 1 - the lightguide emission values of the VIP reflector lamp are clearly superior in the spectral range important for polymerization. The emission and output values of lightguides with an active diameter of 5 mm and 8 mm are of particular importance in this connection as these are the ones most commonly used in practice.
Considering the surprisingly and significantly higher lightguide output values in the blue and UV range obtainable with a VIP 120 W lamp in combination with a selectively reflecting elliptoidic reflector as well as the faster warm-up time of approx. 20 - 40 s and the increased life of more than 1,000 hours of operation the

6 lamp has superior polyn:ierization properties as compared to lamp - lightguide systems based on the state of the art.

7

Claims

What is claimed is:

1. An illumination system for curing adhesives in dentistry and industrial applications, emphasizing wavelengths ranges from about 280 to 500 nm, comprising, in combination:
a) an ultra high-pressure Hg vapor discharge lamp, having a gas pressure of at least 100 bar, as a light source;
b) an elliptoidic reflector, said reflector having a high reflectivity in the spectral range of below 500 nm and a low reflectivity in the spectral range of above 500 nm; and c) a liquid light guide having an entry end and an exit end, wherein light from the light source is selectively reflected by the reflector and focussed into the entry end of the light guide to be transmitted to the exit end for use in the polymerization of epoxies.

2. The illumination system of claim 1, wherein a reflectivity of light energy reflected by the elliptoidic reflector is higher than 80% for wavelengths shorter than 500 nm and less than 20%
for wavelengths above 600 nm.

3. The illumination system of claim 2, wherein an electrode gap of the ultra high-pressure Hg vapor discharge lamp is between 0.8 and 2 mm.

4. The illumination system of claim 2, wherein the lamp contains mercury and a noble gas.

5. The illumination system of claim 3, wherein the lamp has a colour temperature of about 8500 Kelvin at an inside pressure of about 200 bar.

6. The illumination system of claim 1, wherein the liquid light guide is a liquid core light guide comprising a tubular hose made out at least partially of a first fluoropolymer, the inside of which is coated by a second plastic polymer having a refractive index below 1.33, the tubular hose filled with an aqueous salt solution as a light-transmitting liquid.

7. The illumination system of claim 1, wherein the liquid light guide is a liquid core light guide comprising a tubular hose made out at least partially of a first fluoropolymer, the tubular hose holding a mixture of glycol and water as a light-transmitting liquid.

8. The illumination system of claim 6, wherein the first fluoropolymer is Teflon® FEP.

9. The illumination system of claim 6, wherein the first fluoropolymer is Hyflon® MFA.

10. The illumination system of claim 7, wherein the first fluoropolymer is THV
(3M).

11. The illumination system of claim 6, wherein the second plastic polymer is a perfluorated amorphous fluoropolymer

12. The illumination system of claim 11, wherein the perfluorated amorphous fluoropolymer is Teflon® AF..

13. The illumination system of claim 11, wherein the perfluorated amorphous fluoropolymer is Hyflon®AD.

14. The illumination system of claim 11, wherein the perfluorated amorphous fluoropolymer is Teflon® SF.

15. The illumination system of claim 6, wherein the aqueous salt solution comprises CaCl2.

16. The illumination system of claim 6, wherein the aqueous salt solution comprises CaBr2.

17. The illumination system of claim 6, wherein the aqueous salt solution comprises NaH2PO4.

18. The illumination system of claim 7, wherein the light transmitting liquid comprises Triethylenglycol and water.

19. The illumination system of claim 7, wherein a light entry window of the liquid light guide at the entry end has a coating of a dielectric film transmitting in the range from 280 to 500 nm.

20. The illumination system of claim 1, wherein the liquid light guide comprises quartz fibers.

21. The illumination system of claim 1, wherein the liquid light guide comprises glass fibers.

22. The illumination system of claim 1, wherein the liquid light guide comprises plastic fibers.