Dentistry – Apparatus – Having means to emit radiation or facilitate viewing of the...
Patent
1998-06-11
2000-07-11
Wilson, John J.
Dentistry
Apparatus
Having means to emit radiation or facilitate viewing of the...
606 2, 606 12, A61C 100
Patent
active
060863668
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a device for removing material from a workpiece, particularly removing a hard dental substance such as tooth enamel or dentine from a tooth, or for removing material from ceramic workpieces, by means of a laser.
Devices of this type are known from, for example, DE 41 28 617, GB 01 25 944, U.S. Pat No. 5,020,995, DE 4 038 809, DE 34 15 293 and DE-GM 92 01 056.3, and employ pulsed laser radiation with pulse lengths of either less than 100 ns or greater than 100 .mu.s to remove hard dental substances. The focus size of the laser beam, in other words the expansion of the laser beam on the irradiated workpiece surface, is relatively large, namely between 0.2 and 1.5 mm. It is also known from the cited publications to counteract contamination of the end optics by blasting it free with a water/air spray. It is also known from DE 39 11 871 to use a water/air spray to cool the laser process, which results in a distinct qualitative improvement in the ablation result.
DE 42 11 233 describes a device of this type for removing a hard dental substance, which has an Er:YAG laser that is integrated into a treatment chair and a handle part for positioning the laser beam, with the laser and the handle part being connected by a mirror articulated arm.
In the context of such devices for removing material, it is also known to guide the laser beam line by line over the ablation area (scanning) for attaining uniform material removal.
A disadvantage of the known devices for machining hard dental substances is re-crystallized deposits on the surface of the cavity formed by the radiation. Another problem associated with removing material from teeth is that, as the removal area deepens, the removal rate increases dramatically in the transition from the tooth enamel to the dentine, which may surprise the patient and, in the known devices, can lead to an accidental pulpotomy. A further disadvantage of the known devices is that the relatively high pulse energies give rise to shock waves that may damage the tooth pulp.
SUMMARY OF THE INVENTION
It is therefore the object of the invention to provide a device and a method of the type mentioned at the outset, with which the material removal can be controlled laterally and axially.
The invention includes the technical teaching of using a laser distance-measuring device to continuously measure the distance from the material surface in the ablation region during the material removal in order to determine the depth of the material removal, and, if necessary, to halt or reduce the intensity of the irradiation.
The invention is based on the surprising realization that, with the energy density being maintained, a reduction in the spot diameter--that is, the diameter of the laser beam in the ablation region--and a simultaneous increase in the pulse-repetition rate and a reduction in the pulse energy do not lead to a reduction in the removed quantity in comparison to conventional ablation with high pulse energies. This is surprising because an increase in disturbing edge effects would be anticipated with a reduction in the spot diameter due to the unfavorable ratio of the ablation surface (.about.r.sup.2) to the circumference (.about.r). The reduction in the spot diameter makes it possible to determine the completed material removal with high local resolution, and--in refining variations of the invention--to control the material removal with high local resolution.
It is therefore also possible to efficiently machine ceramic, biological hard dental substances and plastics with pulse energies of less than 50 mJ and spot diameters of less than 350 .mu.m, taking into consideration the absorption behavior of hard dental substances with wavelengths in a range of 1.9 . . . 2.1 .mu.m and 2.5 . . . 3.3 .mu.m or 9.2 . . . 11 .mu.m, but preferably 2.78 .mu.m and 2.94 .mu.m or 9.6 .mu.m and 10.6 .mu.m, and the use of spray-cooling with a fluid/air mixture. The fluid should have a high absorption for laser energy. The low pulse energies can be compensated
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Benthin Hartmut
Ertl Thomas
Mueller Gerhard
Clinicon Corporation
Kinberg Robert
Voorhees Catherine M.
Wilson John J.
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