Dentistry – Apparatus – Having means to emit radiation or facilitate viewing of the...
Patent
1998-10-05
2000-05-23
Lucchesi, Nicholas D.
Dentistry
Apparatus
Having means to emit radiation or facilitate viewing of the...
433226, A61C 100, A61C 300, A61C 504
Patent
active
060659653
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a device and a process for curing a photocurable filler, e.g. a plastics or composite material.
As a replacement for amalgam, such plastic fillers are introduced into the tooth cavity in a more or less viscous state and will cure there subsequently. The polymerization may be initiated with light, if a corresponding photo-initiator has been added to the filler. The fillers are cured by photopolymerization. The polymerization of dental plastics materials for tooth cavities is effected using blue light, e.g. with a wavelength from 420 to 470 nm, that is, within the range of the maximum absorption of an initiator used in the plastic filler, such as camphor-chinon. The shrinking entailed by the polymerization causes the forming of edge gaps at the edge of the tooth cavity and tensions within the filler by the build-up of internal tensions. These tensions will result in a loss of the tight sealing of the tooth cavity, especially under load. Via the edge gaps, bacteria may enter deep into the tooth cavity where they again foster cariogenicity.
It is another problem of photopolymerization that the filler always polymerizes in the direction of the curing light source. The first areas to polymerize are the ones closest to the light source. Therefore, plastic fillers typically polymerize last at the borders of the tooth cavity. This causes substantial tension forces at the interface between the hard tooth substance and the plastics material. The tension becomes more complex as the the walls of a tooth cavity increase.
It has been attempted to ameliorate the problem occurring during photopolymerization by arranging the light source laterally so that the polymerizing light radiates through the tooth, thereby to effect a polymerization starting from the edge of the tooth cavity.
Conventional photopolymerization light sources with wavelengths between 400 and 500 nm and a power density of <200 mW/cm.sup.2, however, are very much attenuated when radiating through dentine and the outer enamel layer of the tooth. Thus, this method can be used only for very thin dentine/enamel walls. With larger wall thicknesses, the plastic filler cannot be cured.
It has been suggested to use an argon laser with a wavelength of 488 mn as the light source for the polymerization of the plastic material. Such a laser has a wavelength within the maximum absorption range of the photo-initiator so that this type of laser is no different from conventional polymerization light sources, except for the radiation intensity. The laser light is largely absorbed in the plastic filler, which is why it has a small penetration depth and the disadvantage of edge gap formation.
It is an object of the present invention to provide a device for and a process of curing a photocurable plastic filler with which the build-up of tension during polymerization shrinking can be substantially reduced.
The object is solved with the features of claims 1 and 8, respectively.
The invention advantageously provides for successively introducing small amounts of plastic filler into the tooth cavity and for curing these, respectively. Preferably, these amounts of plastic filler that spread to form thin layers, are injected into the tooth cavity through a separate applicator or the laser light applicator, whereupon they are immediately polymerized by the application of laser light.
Laser light irradiation causes an improved cross-linking of the plastic filler material due to the higher power density of the laser light as compared with conventional polymerization light sources, and thereby causes improved material properties. Until now, this improved cross-linking could only be achieved experimentally during extra-oral additional polymerization and was thus not suited for practical use. An improved cross-linking causes a reduction of the free or releasable monomers of the plastic filler. This goes together with a reduction in the toxicity of the plastic filler.
A laser light source is used having a laser light beam of a wavelength that is only weakly abso
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