An apparatus for photopolymerizing synthetic materials, specifically dental materials containing camphor quinone or phosphine oxide as a photo-initiator, includes a light source constituted by a semiconductor base solid-state radiation emitter 12 which emits in the blue spectral range. Since the radiation emitter emits in a small useful spectral range only, any heat radiation is avoided. The overall device is formed as a small, light-weight and handy device with a built-in battery 15. The solid-state radiation emitter 12, which is preferably operated in the light emitting diode (LED) mode, may be arranged directly on the tip 20 of the apparatus which can be directed toward the treatment site.

BACKGROUND OF THE INVENTION 
In the dental technology, a plurality of synthetic materials, so-called 
composites, are known which polymerize due to a metacrylate based curing 
mechanism when irradiated with light. As the essential photo-initiator 
these materials contain camphor quinone or phosphine oxide which absorbs a 
broad band within the blue spectral range, with an absorption maximum at 
about 472 nm and 430 nm, respectively. 
Depending on the color of the material, the polymerization reaction 
requires light having an intensity of at least 1 to 5 mW/cm.sup.2 within a 
very thin layer. In the practice of polymerizing tooth stoppings or dental 
replacement parts, a light intensity of at least 250 mW/cm.sup.2 is 
required within an appropriate period of time to achieve polymerization of 
sufficient degree and depth. Commercially available dental polymerization 
apparatus emit light at an intensity of about 400 to 500 mW/cm.sup.2, 
sometimes up to 700 mW/cm.sup.2. 
Desk apparatus are known in which the light is generated and focused within 
the apparatus and transmitted to the treatment site within the patient's 
mouth by means of a flexible optical waveguide having a length of 
typically 1.5 to 2 m. In addition to a substantial loss of light that 
occurs at its input and output faces, such an optical waveguide usually 
has a diameter of about 10 to 15 mm and is therefore relatively stiff and 
unwieldy. 
In other prior-art apparatus, such as known from, e.g., German 
Offenlegungsschrift No. 3,840,984, the light is generated and focused 
within a gun-shaped hand piece and transmitted to the treatment site by 
means of a rigid light conducting rod made of fibers or quartz. A chief 
disadvantage of these apparatus results from a considerable heating of the 
hand piece and, as that is held close to the treatment site, of the 
irradiated location itself. Moreover, the power supply cable required in 
this type of apparatus for feeding current to the hand piece is considered 
troublesome. 
German Offenlegungsschrift No. 4,211,230 discloses a battery-powered 
apparatus which is independent of the mains or a power supply unit but 
requires comparatively large and heavy batteries to provide the necessary 
high electric output, and is thus difficult to handle. 
The known photopolymerization apparatus often employ tungsten-halogen lamps 
which emit light in a comparatively wide spectral range, thus output the 
largest portion of their energy as heat and light in the red and green 
wavelength ranges. Only about 2 percent of the power input is emitted in a 
spectral range of about 400 to 515 nm, which is the range useful for the 
above-mentioned composite materials using camphor quinone or phosphine 
oxide as a photo-initiator. 
Conventionally employed light sources have the further difficulty that 
their light output decays throughout their life in a manner that is not 
readily detected by the user, so that the quality of the polymerization 
deteriorates with time. 
Another disadvantage resides in the fact that optical components such as 
lenses and reflectors are required in order suitably to image the helix of 
the lamp to the entry end of the waveguide and illuminate the full area of 
the entry end without losing light energy. Also, filters are needed to 
absorb the heat radiation and to reduce the halogen light of the desired 
spectral range. These optical components may also reduce the light output 
due to ageing and defects, thereby rendering a safe polymerization 
impossible. 
It is a further disadvantage of known apparatus, specifically hand-held 
apparatus, that air circulation required for the removal of heat also 
causes a spreading of bacteria. Due to their open design, as is necessary 
for ventilation, and due to their size, these apparatus are difficult to 
sterilize and disinfect. 
SUMMARY OF THE INVENTION 
It is a general object of the invention to avoid at least some of the 
disadvantages encountered with comparable prior-art apparatus. As a more 
specific object of the invention, an apparatus for the photopolymerizing 
synthetic materials, specifically dental materials using camphor quinone 
or phosphine oxide as a photo-initiator, is to be provided which generates 
light in the useful blue spectral range with maximum efficiency. 
This object is met by an apparatus for photopolymerizing synthetic 
materials, specifically dental materials containing photo-initiators, 
including a light source for emitting light in the blue spectral range, 
wherein the light source is a solid-state radiation emitter on the basis 
of a semiconductor composed of elements of the main groups III and V of 
the Periodic Table. 
The use of this type of solid-state radiation emitter in a polymerization 
apparatus, specifically in a dental polymerization apparatus, results in 
the following advantages: 
(1) Since the light emission is limited to a defined wavelength range, in 
this case the blue range, no additional heat is generated. Accordingly, 
the apparatus requires no ventilator and may thus be designed as a closed, 
encapsulated device that can be sterilized as a whole. 
(2) The fact that any heat generation is avoided, is advantageous also for 
the polymerization process itself because shrinkage of the synthetic 
material caused by heating and cooling and the danger of boundary gaps 
resulting therefrom are avoided. 
(3) While the light output of solid-state radiation emittters varies over 
time, this effect may be compensated by simply adjusting the diode current 
so as to correct the light output. Since laser diodes emit two opposite 
beams of light, it is generally possible to use one of these beams as the 
useful beam for the polymerization and the other as a reference beam for 
controlling the intensity of the useful beam. 
(4) Due to the fact that the solid-state radiation emitter emits light in a 
small useful spectral range only, it requires little power to achieve 
radiation of sufficient intensity. Therefore, the apparatus may be readily 
powered by a built-in-battery, thereby avoiding optical waveguides or 
power supply cables as required in known devices. 
(5) The small size of the solid-state radiation emitter in connection with 
the absence of any heat generation results in an apparatus which may be of 
a small, light-weight and handy design. 
(6) Since the generation of light is virtually free of inertia, pulsed 
operation is possible to achieve very high intensities for short periods. 
This results in an increased transparently of the material to be 
polymerized, because all absorption levels of the material can be occupied 
due to the high quantity of photons. 
(7) Other than with conventional lasers, the divergent elliptical radiation 
characteristic of laser diodes makes the use of optical components for 
optimum irradiation of the wave guide unnecessary. 
In a preferred embodiment, the semiconductor is based on gallium nitride 
containing suitable ternary additives. 
When the solid-state radiation emitter is operated in the LED mode, there 
is the advantage of a two-dimensional radiation in a bandwidth that is not 
excessively small. Both features are specifically advantageous for dental 
applications because a larger radiating surface is closer to the usual 
dimensions of tooth surfaces to be irradiated and because the larger 
spectral width corresponds more closely to the absorption band width of 
the molecules which initiate the polymerization. All this contributes to 
an efficient polymerization. 
Alternatively, a particularly intensive beam of light is achieved when the 
solid-state radiation emitter is operated in the laser mode. 
Due to its small size, the solid-state radiation emitter may be disposed 
directly on the tip of a polymerization apparatus which may be directed 
toward the treatment site. This results in the advantage of specifically 
low radiation loss. 
Alternatively, the solid-state radiation emitter may be disposed at the 
light entry and of an optical waveguide which may be directed toward the 
treatment site. In this embodiment, in which the radiation emitter is 
disposed inside the apparatus, the absence of any heat generation again 
allows the apparatus to be made extremely small and handy. 
In another embodiment, the apparatus may include a rechargeable or 
non-rechargeable battery for powering the solid-state radiation emitter. 
The solid-state radiation emitter is preferably a laser diode which emits a 
forward beam used for the polymerization proper and a backward beam used 
as a reference beam for controlling the intensity of the polymerization 
beam. 
In accordance with a further embodiment of the invention, the solid-state 
radiation emitter is pulsed, which permits a substantially higher 
intensity and, thereby, a deeper penetration of the light beam into the 
material to be polymerized. 
The diode and the optical waveguide may be arranged in such a fixed mutual 
orientation that the use of a waveguide entry aperture which is 
geometrically adapted to the cross-section of the laser beam, preferably 
an elliptical aperture, allows the useful beam to be completely imaged 
onto the entry end of the waveguide.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
The apparatus of FIG. 1 consists of a hand piece 10 with a light conducting 
rod 11 having its entry end inserted into the front end of the hand piece. 
The light spill end of the light conducting rod 11 is curved for easier 
handling. 
The light entry end of the rod 11 receives the useful beam emitted by a 
solid-state radiation emitter 12, which is a light emitting diode composed 
of elements of the main groups III and V of the Periodic Table, preferably 
gallium nitride, emitting in the blue spectral range. The diode is 
preferably operated in a pulse mode. For adaptation to the elliptical 
cross-section of the useful beam 13, the entry end of the light conducting 
rod 11 also has an elliptical cross-section. 
The hand piece 10 further comprises a printed circuit board 14 with an 
integrated circuit for controlling the solid-state radiation emitter 12 
and a battery 15 for power supply. 
Disposed on the circuit board 14 and connected to the integrated circuit is 
a sensor 16 which receives the beam 17 emitted from the reverse side of 
the light emitting diode 12 as a reference beam for controlling the light 
output of the diode 12 and thus the energy of the useful beam 13. 
At the end remote from the light conducting rod 11, the hand piece 10 is 
provided with a time control 18 in the form of a rotary knob. Two light 
emitting diodes 19 of low radiation output are arranged on a side of the 
hand piece 10 for optically displaying the operating condition. 
The light conducting rod 11 may be rotatable with respect to the hand piece 
10 so that the light spill end can be rotated to assume the most 
convenient position with respect to the location to be irradiated without 
requiring a change in the position of the hand piece 10 and thus of the 
time control 18 and the display diodes 19. 
The apparatus of FIG. 2 differs from that of FIG. 1 in that the solid-state 
radiation emitter 12 is disposed directly on the tip portion 20 of the 
hand piece 10. The tip portion 20, which contains the radiation emitter 
12, is curved similar to the light spill end of the light conducting rod 
11 of FIG. 1, and is rotatable with respect to the hand piece 10 so that 
the most convenient position relative to the treatment site may be 
achieved without changing the position of the hand piece 10 itself.