WO1996005782A1

WO1996005782A1 - A device for the manufacture of dental fillings and the like

Info

Publication number: WO1996005782A1
Application number: PCT/SE1995/000943
Authority: WO
Inventors: Andreas Dahr
Original assignee: Andreas Dahr
Priority date: 1994-08-19
Filing date: 1995-08-18
Publication date: 1996-02-29
Also published as: AU3358295A; WO1996005781A1; EP0794741A1

Abstract

A device (1) for the manufacture of replicas from patterns, i.e. insert bodies, such as dental fillings, dental crowns, human joints and the like, by a method of copy milling or profile grinding a blank (2) with the aid of a pattern (3). Two spindles (4, 5), one pattern-supporting spindle (4) and one blank-supporting spindle (5), driven in synchrony and positioned in mutually aligned relationship, are each provided at their ends with an attachment means (6, 7). A sensing unit (8) provided with a sensing tool (9), and a machining unit (10), provided with a machining tool (11), both are mounted in a holder arm (12) which is movable relatively to the pattern spindle (4) and the blank spindle (5). The holder arm (12) is rotatably mounted in a link (15) which in turn is rotatably mounted in end walls (17, 18) mounted in a carriage (20). The pivot shafts like the carriage movement are parallel with the axis of alignment of the pattern spindles (4, 5). The device makes possible manual as well as automatic machining and upon automatic machining it may shift automatically from coarse shaping to precision-shaping.

Description

A DEVICE FOR THE MANUFACTURE OF DENTAL FILLINGS AND

THE LIKE

Technical Field

The subject invention concerns a device for the manufacture of replicas, i.e. insert bodies, such as dental fillings, dental crowns, human joints and the like, by a method of copy milling or profile grinding a blank with the aid of a pattern in the form e.g. a cast of the dental cavitity to be filled.

Background of the Invention

Nowadays, dental repairs are often carried out by filling a cavity by some ceramic material shaped to fit the cavity. A cast of the cavity is made initially and this cast is sent to a dental laboratory for pro¬ duction of a fitting filling of a ceramic material. The patient has to wait for about a week, which of course is a considerable disadvantage. For this reason several apparatuses have been developed by means of which the dentist himself is able to produce the filling from a hard material. In several of these apparatuses a copy or profile milling method is used, resulting in an over-sized body. The body is shrunk in a sintering process. However, this method often leads to consider¬ able problems as regards the fit because of the uneven shrinking. In another type of equipment a method involving filming the tooth is used, and a computer calculates the desired shape. This equipment is used for dental crowns. However, it is difficult to obtain a sufficiently precise picture of a tooth cavity by means of filming to allow an exact insert body to be produced. NO-90 261 1 discloses an apparatus intended for purely manual use. Like other apparatuses for pure copy machining purposes, the operative part of this apparatus is the tip of the machining tool. In order to shape ceramic, diamand tools are required. Such tools are designed as a cylindrical rod having diamonds at its tip and along its envelope surface. In order to shape concave surfaces corresponding e.g. to the masticating surface of a tooth, the tool must be of small diameter size and the shaping is effected by means of the tool tip. This results in wear of such considerable magnitude that several tools are required for the manufacture of one single filling. In the case of the manual machine this problem is solved by exchanging the shaping tool once or several times during the operation and tools of different diameter size may be used. Obviously, it is a considerable draw-back not to be able to run the apparatus automatically and to have to resort to tool exhanges during the work, which often takes about half an hour.

Purpose of the Invention

The purpose of the invention is to considerably reduce the above-mentioned problem by creating a device of simple structure which is well suited for automatic or manual operation.

Summary of the Invention

The above purpose is achieved by means of a device in accordance with the invention having the characteristics appearing from the appended claims. The device in accordance with the invention thus is essentially characterized in that two spindles, one pattern-supporting spindle and one blank-supporting spindle are driven in synchrony and positioned in mutually aligned relationship, each provided at their ends with an attachment means, one for attachment of the pattern and one for attachment of the blank, and in that a sensing unit provided with a sensing tool and a machining unit provided with a machining tool both are mounted in a holder arm which is movable relatively to the pattern spindle and the blank spindle. Owing to this construction it becomes possible to create a particularly simple device which is suitable for manual as well as automatic operations and combinations thereof. Because of the structure, with the pattern and the blank positioned in alignment, a compact low-height device is created wherein the spindle and hinge mountings also largely are in alignment. The result is low machining costs combined with high precision, since bearing positions can be machined in one operation, for instance by means of arboring, if needed followed by reaming. Extremely good parallelity and position-orientation are ensured also, which is important for the achievement of a good fit of the blank. In addition, it is easy to design the device for manual as well as for automatic operation. In accordance with a further development of the device it is designed to automatically shift from precision shaping to coarse shaping and vice versa. The major part of the shaping therefore takes place as coarse shaping by means of the envelope surface of the tool whereas the finishing precision-shaping is effected by means of the tool tip. Also very thin tools thus become durable enough for shaping several fillings. A finishing manual shaping and checking of the tooth filling can also be made. In all, this leads to a highly rational use of the apparatus, combined with high quality of the finished tooth filling or the like.

Further characteristics and advantages will appear from the following detailed description of one embodiment with reference to the drawings.

Description of the Drawings

Fig. 1 is a perspective view of an apparatus for the manufacture of tooth fillings etc in accordance with the invention. Rotational arrows indicate associated directions of drive with respect to the driven shafts.

Fig. 2 is an elevational side view of some of the main parts of the device during position-shaping.

Fig. 3 shows a blocking element allowing limited movement of the link of Fig. 2.

Fig. 4 illustrates the change of position of the main parts resulting in an automatic shift from precision-shaping as in Fig. 2 to coarse shaping with the aid of the tool envelope surface in accordance with Fig. 4. Fig. 5 illustrates the manner in which the blocking element has allowed restricted rotation to make possible the shift to the coarse shaping position.

Description of Preferred Embodiments In Fig. 1 numeral reference 1 designates a device in accordance with the invention. A frame part 28 supports the other components. The frame portion has two recesses 23 and 30. A number of spindles 4, 5 and 14 are positioned close to the bottom face of the recesses 29 and 30. A pattern-holding spindle 4 is provided with a pattern attachment means 6 designed to secure a pattern, for instance a cast of a tooth cavity. As a rule, this is a plastics cast and it is secured to the pattern attachment means 6, the latter being formed with a conical tip, a corresponding conical depression having been drilled in the pattern 3. The pattern then is glued to the pattern attachment. In addition, the pattern is supported by a dowel pin 13. In the conven¬ tional way, the latter projects into the pattern by means of its sharp end. The dowel pin 13 is axially displaceable in the dowel spindle 14. A spring, not shown, is held between the dowel spindle and the dowel pin, whereby the dowel pin is urged against the pattern. The design including a rotating dowel pin is unique and lessens the risk of the pattern becoming loose. A blank- supporting spindle 5 is provided at its end with an attachment means 7 for securing a blank 2. Normally, the blank attachment means is in the form of an insert spindle in¬ cluding an attachment disc for holding the blank, the latter usually being a hard ceramic blank, such as for example a ceramic block, which is glued to the attachment disc. The blank spindle 5, the pattern spindle 4, and the dowel spindle 14 are positioned in mutual alignment relationship. They are driven in synchrony. Preferably, this is achieved by means of an input drive shaft 31 which drives each spindle by means of a cogged belt. A drive motor, not shown, thus is connected to the drive shaft 31. The bottom of the depression 29 is formed with a sieve 32, considering the shaping chips that form during the shaping operation.

A sensing unit 8 provided with a sensing tool 9 and a machining unit 10 provided with a machining tool 11 are both mounted in a holder arm 12 which is movable relatively to the pattern spindle 4 and blank spindle 5. It is essential that the sensing tool 9 and the machin¬ ing tool 11 move in perfect mutual synchrony and this is achieved in the most simple way by mounting them in the common holder arm 12. But obviously other solutions are possible, provided that they ensure synchronous movement of tools 9 and 11. Tools 9 and 11 preferably have an exactly identical external configuration and their tips assume an identical position. The holder arm 12 is rotatably mounted in a link 15 by means of first pivot shaft 16 and in turn the link is mounted in end walls 17, 18 by means of a second pivot shaft 19. The end walls are mounted in a carriage 20 which is arranged to perform to and fro movements in a direction parallel to the alignment axis of pattern spindle 4 and the blank spindle 5. Also the first and the second pivot shafts 16 and 19, respectively, extend in parallel with said alignment axis of spindles 4 and 5. A motor-driven power means 22 is arranged between the link 15 and the holder arm 12. In this case a drive motor 22 including a gear box and with an output shaft 33 serves as the power means. A belt 34 is secured to the holder arm 12 at one of its ends whereas the opposite end thereof is attached to the output shaft 33. When the drive motor 22 runs in one direction the belt is tightened whereas it is slackened when the motor operates in the opposite direction. The drive motor 22 imparts a lowering movement to the sensing and machining units 8, 10. A lifting spring 35 is compressed so as to turn the holder arm relatively to the link, thus creating a lifting movement of the sensing and machining units 8 and 10. This will become clearer in the ensuing description with reference to Figs. 2-4. By means of a rear shaft 36 the handle 21 is attached to the holder arm 12. The handle is used when the appara- tus is operated manually. A front shaft 37 is used to position a torsion spring the opposite end which acts on a pivot pin 38 positioned along the second rotational shaft 19.

In a view seen straight from the side, i.e. from the side of the handle 21, Fig. 2 illustrates the main components of the device. The link 15 is, as already mentioned, rotatably mounted in the end walls for pivotal movement about the pivot shaft 19. The holder arm 12 in turn is rotatably mounted in the link 15 for pivotal movement about the first pivot shaft 16. The machining unit 10 including its machin¬ ing tool 1 1 are mounted in the left-hand part of the pivotable arm 12. At its tip and in the area adjacent said tip the sensing tool 9 is con¬ figured and positioned in exactly the same way as the machining tool 1 1 and the sensing unit 8 therefore will not be shown. The machining unit 1 1 may be in a form of an air-operated industrial turbine supporting the diamand-coated tool 11. The nature of the very machining could be described most closely as resembling a grinding operation. In automatic operation of the apparatus, the link 15 is locked completely or partly with respect to the end walls. In accordance with an earlier development of the device one blocking arrangement is used for precise shaping operations, corresponding to Fig. 2, and another blocking arrangement for coarse shaping operations, corresponding to Fig. 4. In coarse shaping operations the grinding takes place by means of the tool envelope surface, allowing a larger-area machining to be effected with reduced tool wearing. According to a further development of the invention, transition from precise-shaping opera- tions to coarse shaping operations and vice versa, is effected auto¬ matically. This is achieved by blocking the link 15 in such a manner that it is restrictedly movable about its pivot shaft 19, for instance having an approximately 5% movability. This could be effected for instance by making the piston rod 39 of a pneumatic cylinder 40, positioned in the link, project into an oblique aperture formed in one end wall. However, it could also be achieved by making use of a movable locking member 23 which is allowed only a restricted move¬ ment in the direction of rotation of the link for the blocking function. The locking member 23 preferably is mounted on the pin 19 and has a restricted rotatability, with fixed or adjustable stops relatively to the end walls. Upon extension of the piston rod 39 it hits the aperture 41 and this action is facilitated by means of a conical entrance part 42 formed on the inner face of element 23. Once this locking between the link and part 23 is obtained, the automatic machining operation may be initiated. This is effected by the belt 34 being wound by the lower¬ ing motor 22 about the motor output shaft 33. The opposite end of the belt is attached to the rear end of the holder arm 22, i.e. the end opposite to the machining and sensing units vis-a-vis its mounting means 16. Thus, the machining unit 10 including its tool 1 1 are turned downwards, towards and against the rotating blank.

In the beginning, the blank is a great deal larger than the pattern and machining in accordance with Fig. 2 commences. But the lowering motor 22 continues to urge the tool 11 downwards, which encounters an increasing resistance from the blank 2. This forces the link 15 to turn within its limited movability range. As a result, the machining tool 1 1 slides across the blank 2, by means of its tip such that its envelope surface instead comes into contact with the blank and, as mentioned previously, the envelope surface has a greater grinding capability and is more wear-resistant than the tip. The coarse shapening of the blank 2 thus is effected, and this continuous until the shaping of the blank has proceeded sufficiently for the blank to have achieved the same size as the pattern 3. The pattern 3 is provided with an electrically conductive cover and when the sensing tool 9 comes into contact with this cover it issues a signal for reversal of the movement of the lowering motor 22. This may be effected for instance by pole reversal. In consequence thereof, the lifting spring 35 will raise the holder arm 12, and thus also the machining unit 10 including the tool 1 1 thereof. The sensing tool therefore will lose con¬ tact with the electrically conductive pattern and a new reversal of the motor will take place, the latter returning to the original lowering direction, and the process restarts. The position corresponding to that of Fig. 2 thus is obtained. If the shape is very close to the finished shape there might not be a transition to the coarse machining posi¬ tion illustrated in Fig. 4 but precision shaping is effected by lowering and raising the tool. In Figs. 2 and 4 the lifting spring 35 is illustrated in principle. Fig. 1 shows the design thereof in reality but obviously it could be varied considerably. It is a considerable advantage that the machine may also be run manually. Manual operation is of particular interest for finishing off the very operation. Thus, the operator may move the sensing tool 9 along the surface for checking purposes. The checking is facilitated by the lighting-up of a light-emitting diode when the tool assumes its contact position. Normally, the stroke of the carriage 20 is adjusted to prevent machining to be performed all the way out to the end of the attachment of the blank 2. Should this happen, the blank 2 would be cut off too early. Instead, it is preferable that the cutting loose is effected as a final adjustment operation, which is performed manually on the last portion closest to the attachment to the blank attachment means 7. In manual operation, the operator thus controls the holder arm 12 by means of the handle 21. The latter is mounted e.g. in the attachment means 43. During manual operation the carriage 20 is freely movable laterally just as the link 15 is freely pivotable.

Claims

1. A device for the manufacture of replicas from patterns, i.e. insert bodies, such as dental fillings, dental crowns, human joints and the like, by a method of copy milling or profile grinding a blank (2) with the aid of a pattern (3) in the form e.g. a cast of the dental cavity to be filled, c h a r a c t e r i s e d in that two spindles (4, 5), one pattern- supporting spindle (4) and one blank- supporting spindle (5), are driven in synchrony and positioned in mutually aligned relationship, each provided at their ends with an attachment means (6, 7), one (6) for attachment of the pattern (3) and one (7) for attachment of the blank (2), and in that a sensing unit (8) provided with a sensing tool (9), and a machining unit (10), provided with a machining tool (1 1), both are mounted in a holder arm (12) which is movable relatively to the pattern spindle (4) and the blank spindle (5).

2. A device as claimed in claim 1, c h a r a c t e r i s e d in that in addition to the pattern attachment (6) the device comprises a pattern supporting dowel pin (13) which is enclosed in a dowel spindle (14) and is axially displaceable therein, said dowel spindle being aligned with the pattern spindle (4) and with the blank spindle (5) and driven in synchrony with said spindles.

3. A device as claimed in claim 1 or 2, c h a r a c t e r i z e d in that the holder arm (12) is rotatably mounted in the link (15) by means of a first pivot pin (16) and in that the link in turn is mounted in end walls (17, 18) by means of a second pivot pin (19), in that said end walls in turn are mounted in a carriage (20) which is arranged for movement to and fro in a direction in parallel with the axis of align¬ ment of the pattern spindle (4) and blank spindle (5) and in that also the first and the second pivot pins (16 and 19), respectively, are parallel with said axis of alignment of said spindles (4 and 5).

4. A device as claimed in any one of the preceding claims, c h a r a c t e r i z e d in that the device is arranged to be run both manually and automatically, whereby upon manually use the carriage (20) is freely movable laterally, the link (15) is freely pivotable and an operating handle (21), which is attached to the holder arm (12), is used for the actuation, whereas upon automatic operation the link (15) is locked in its movement completely or partly, i.e. it is afforded only a limited freedom of movement relatively to the end walls (17, 18), and in that a motor operated power means (22) which acts between the link (15) and the holder arm (12) pivots their holder arm (12) relatively to the link (15) such that the holder arm is lowered or raised while at the same time the carriage is driven in its to and fro movement by another drive motor.

5. A device as claimed in claim 4, c h a r a c t e r i z e d in that upon automatical operation the link is locked to a movable locking member (23) which has limited movability with respect to the end wall in the rotational direction of the link (15), such that the link obtains a limited possibility of rotation, for instance over approximately 5°, and thus the tip of the machining tool (1 l)can, when encountering a certain resistance, travel further outwards away from the carriage (20), allowing subsequent machining operations to be effected by means of the envelope surface of the tool, i.e. an automatic transition from precision-shaping to coarse shaping.

6. A device as claimed in claim 4 or 5, c h a r a c t e r i z e d in that the power means (22) is a drive motor (24) about the shaft (25) of which a belt (26), which is attached to the holder arm at the side opposite from that of the first pivot shaft (16) with relation to the machining unit (10), its wound when the drive motor (24) is run in one direction, as a result which the holder arm (12) is lowered, where¬ as when the drive motor (24) is run in the opposite direction the belt (26) is unwound and a lifting spring (27) raises the holder arm (12).

7. A device as alcimed in any one of the preceding claims, characterized in that the pattern (13) is coated by an electric¬ ally conductive surface coating, e.g. a graphite coating, and in that when contact is established between said coating and the sensing tool (9) a signal is emitted to the power mean (22) for raising the holder (12), for instance by pole reversal of the associated drive motor, and when the contact between the tool (9) and the coating ceases, a signal is emitted for return to the lowering movement operation of the holder arm, and so on.