Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61C—DENTISTRY; APPARATUS OR METHODS FOR ORAL OR DENTAL HYGIENE
  • A61C13/00—Dental prostheses; Making same
  • A61C13/0003—Making bridge-work, inlays, implants or the like
  • A61C13/0004—Computer-assisted sizing or machining of dental prostheses
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61C—DENTISTRY; APPARATUS OR METHODS FOR ORAL OR DENTAL HYGIENE
  • A61C13/00—Dental prostheses; Making same
  • A61C13/0003—Making bridge-work, inlays, implants or the like
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61C—DENTISTRY; APPARATUS OR METHODS FOR ORAL OR DENTAL HYGIENE
  • A61C19/00—Dental auxiliary appliances
  • A61C19/04—Measuring instruments specially adapted for dentistry

Definitions

• the invention relates to a device of the type specified in the preamble of claim 1.
• the invention is based on the object of facilitating operation in the case of a device of the type mentioned at the outset, the visual control or evaluation of a monitor image of the measured jaw area possibly having to be simplified.
• the invention is based on the knowledge that a scanning scan of the jaw region of interest by means of a laser beam allows a precise assignment of the control signal of the scanner and the distance measurement value determined by focus error detection. It is particularly advantageous that this enables simple storage and largely electronic evaluation of the value pairs of control signal / distance measurement value.
• the control signals form the address values for storing the assigned measured values, which are fed to an evaluation unit for determining the surface coordinates of the dental replacement part to be produced and adapted to the format of the input data of a numerically controlled machine tool via a converter.
• the focus error detection is based on the astigmatic effect of a cylindrical lens arranged in the beam path of the reflected laser light.
• the cylindrical lens designs an image that is distorted in a certain way on a matrix-shaped diode target.
• the intensity distribution of the photodiodes which can be evaluated via a differential amplifier circuit, is a direct measure of the distance of the imaging objective from the object point
• a 90 ′′ prism is provided in the beam path of the reflected laser light. Only a parallel beam is deflected by 90 ° over the entire beam cross-section. Divergent or convergent beams are caused by Reflection fanned out according to the critical angle of the prism, so that downstream photodiodes arranged symmetrically to the optical axis are illuminated differently. The difference in intensity, again determined via a differential amplifier circuit, is a measure of the distance to be determined.
• a focus error detection there is a reference edge in the beam path of the reflected light between a converging lens and a matrix-shaped diode target.
• a change in the distance between the object and the converging lens causes a shift in the focal point on the image side, as a result of which the light field diaphragm effect of the reference edge becomes stronger or weaker.
• the intensity distribution between the diodes changes accordingly and a downstream differential amplifier circuit enables an assignment to the distance change causing it.
• the methods for focus error detection described above can also be used to control a focus servo control loop, which causes the imaging lens to be tracked.
• the lens movement corresponds exactly to the height differences of the tooth or jaw area to be measured. This movement can easily be measured by means of a conventional inductive probe.
• Such a somewhat more complex measuring method has the advantage that the laser beam is sharply imaged on the object at all object distances. As a result, the measuring points can be very close to one another, as a result of which the measuring accuracy increases and even the smallest differences in distance can be determined.
• a laser beam preferably generated by means of a laser diode, is guided according to the invention by a scanning device which has a controlled beam deflection unit, via the object points to be scanned, the control signals simultaneously forming address values for storing the assigned measured values.
• the control means force a certain movement of the deflection elements and thus a scanning of the surface according to the principle of a scanner. Since the control signals are uniquely assigned plane coordinates (x; y) of the projection of the measurement beam onto the tooth or jaw area to be measured, each pair of control signal / measurement values [(x; y) / (z)] corresponds exactly to one point in space.
• the pairs of values are advantageously stored in a RAM read-only memory, the drive signals forming the address values. This is the prerequisite for convenient further processing of the data.
• the controlled deflection element is preferably a deflection mirror or a prism, which is guided in a meandering manner over the surface to be scanned, in particular by means of a slide guide according to the plotter principle.
• FIG. 1 shows a top view of a scanning device in a schematic representation, Figures 2 to c a measuring beam path according to the "astigmatism principle" and
• Figure 3 is an assembly overview for processing measured values for the automatic production of a dental prosthesis.
• the scanning device shown in FIG. 1 essentially consists of two parallel guides in the form of rails 1 and 2, which are rigidly connected to one another by struts 3 and 4 in the form of spacers, a carriage which can move on the rails 1 and 2 and forms a traverse 5 and a slider 6 which is displaceable on this crossbeam and which can be displaced on the carriage 5 perpendicular to the course of the rails 1 and 2. Due to its own displaceability on the carriage 5 and the displaceability of the carriage 5, the traverse 6 can reach any point on a plane spanned between the rails 1 and 2.
• Both the radiation source and the receiver of the measuring beam 8 with one on the rotor element 6 are in a common housing 9 via a beam guide channel 7, which is firmly connected to the rotor 6 and has approximately the length of a rail 1 or 2 Measuring unit 10 connected.
• the radiation source and receiver are consequently moved with the rotor.
• the measuring unit 10 forms a complete distance measuring device which determines the distance of an obstacle located below the measuring unit and outputs a signal which is representative of this distance related to a point of the runner.
• FIG. 1 shows two different positions of the measuring arrangement displaced with carriage 5 and rotor 6.
• the carriage 5 and the runner 6 can be driven, for example, by stepper motors 11 and 12, the drivers 13 and 14 of which in each case set a spindle-shaped worm 15 or 16 adapted to the rail length or the carriage length, the carriage 5 and the rotor 6 engage in the screws 15 and 16 by means of toothed racks and are thereby moved.
• the voltage profiles of the control voltages for the motors 11 and 12, which are assigned to the x / y values to be set for the position to be maintained in each case, are supplied by an external module 17 and in the form of coded control signals 17a ( x-position) and 17b (y-position) are coded so that they can advantageously simultaneously form the address values for later storage of the measured values (z-position) which are obtained at the output 17c.
• the design of the rotor 6 with the measuring system 10 and the crossbar of the carriage 5 corresponds to the guidance of a scanner in a conventional CD player, so that the corresponding miniaturized components available on the market can largely be used in the construction .
• FIG. 2 shows a measurement beam path for determining the distance using the astigmatism method.
• the one Laser diode 18 generated laser light is directed via a deflecting prism 19 and an objective 20 onto the tooth to be measured.
• a dividing cube 21 with a partially mirrored surface 22 for separating the reflected and illuminating light is also arranged in the beam path.
• a cylindrical - astigmatic - lens is located behind the division cube 21 in the beam path of the reflected laser light in front of a photodetector 23. At a certain distance between the objective and the tooth, the cylindrical lens focuses a circular shape (FIG. 2b) on the four diodes of the photodetector 23 arranged in matrix form.
• a focus error arises, which arises from the cylindrical lens as an elliptical light spot the photodiodes is imaged (Fig. 2a and 2c).
• the different illumination of the photodiodes is measured via a differential amplifier 25. This value is proportional to the distance to be determined.
• FIG. 3 shows a control circuit for the device of FIGS. 1 and 2 in a block diagram. Furthermore, assemblies for the fully automated manufacture of dentures are shown.
• the scanner of a scanning device 38 connected to a radiation source 37 is controlled by an external controller 39 in such a way that the measuring beam moves over the tooth area to be measured with a specific movement sequence to be led.
• Each control signal is assigned a unique point on the scanning plane, so that when a point to be measured is selected, the electric motors effect a corresponding setting of the scanner 10.
• the corresponding Corresponding control lines are again designated 17a and b.
• the outputs of the control circuit 39 are also connected via a recoding device 40 to the address input 41 of a RAM read-only memory 42.
• the x and y control signals are converted directly into address signals of a memory and can, for example, form two parts of a word within a longer address word.
• the measurement signals containing the distance information then arrive via a circuit for converting the measured values 43 directly into the assigned memory locations 44, each of which is addressed with the setting of the position of the measuring head 10. After the scanning process has been completed, all coordinate information describing the surface is contained in the memory.
• a computer 45 connected to the memory 42 processes the determined and stored coordinate values of the surfaces for a closed graphic structure description, such as is used, for example, as a program language for CAD / CAM systems, as a result of which the tooth area of interest is displayed as a graphic on a connected one Monitor 46 can be displayed.
• the computer 35 is connected to an evaluation unit 47 for determining the contours of the tooth replacement part to be produced, the data of an ideal tooth contained in the memory 42 being used to complete the outline of the replacement part.
• the monitor graphic can also be completed manually in order to determine the missing boundary surface of the Inley, Onley or the like.
• the connections between the memory 42 and the evaluation unit 47 as well as the monitor 46 and the evaluation unit 47 are shown in dashed lines because of the alternative or parallel use.
• the output data of the evaluation unit 47 characterize a measured negative impression of a tooth defect, which was completed manually or by comparison in such a way that the outlines of the tooth replacement part to be produced are given.
• These data are fed to a converter 48 for adaptation to the format of the input data of a numerically controlled machine tool 49 and are then used to control the machine tool 49, in particular a milling machine, which cuts the dental prosthetic item in a suitable form from a corresponding raw material. ling out.
• the embodiment of the invention is not limited to the preferred exemplary embodiment specified above. Rather, a number of variants are conceivable which make use of the solution shown, even in the case of fundamentally different types.

Applications Claiming Priority (2)

Publications (1)

Family

ID=6390247

Family Applications (1)

Country Status (2)

Cited By (10)

Citations (8)

• 1990
  • 1990-09-24 AU AU64356/90A patent/AU6435690A/en not_active Abandoned
  • 1990-09-24 WO PCT/DE1990/000728 patent/WO1991003988A1/de unknown

Patent Citations (8)

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