Apparatus for tooth treatment BACKGROUND AND PRIOR ART Dental repair and dental and/or oral surgery involves precision and non-ergonomic work that creates much physical stress for dentists. A dentist's major working area is within the patient's mouth, which frequently puts the dentist in awkward positions, and hinders clear visibility of the full working environment. In order to have a better view of the patient's inner mouth, the dentist must often lean above the patient, and use mirrors to view"blind spots"known in the art as dead surfaces. Methods that alleviate some of the physical stress of dentists'work are therefore appreciated.

A significant portion of a dentist's work relates to the removal of dental material, such as of caries-affected tooth bone tissue or the shaping of tooth stumps for the insertion of dentures and artificial teeth. It is-in particular in the former case-of concern to the dentist not to remove more healthy bone tissue than necessary, as the outer parts of the teeth, the enamel layer and the intermediate dentin layer are not regenerated once destroyed.

Repair of dental decay such as caries may be broadly divided into direct and indirect repair methods. In direct repair methods the caries is removed and the cavity thus created is further cleaned and prepared. Thereafter a filling material, most often dental mercury amalgam or a plastic composite material is inserted into the prepared cavity.

The filling, once hardened, is finished to smoothen out any rough edges and essentially create a surface similar in morphology to the original tooth.

Indirect repair methods on the other hand, involve the use of prepared fillings, e. g. from ceramic material (porcelain or glass) or gold, that are cast in a mold made after the cavity which has been prepared as described above. The filling, which typically takes a couple of days to manufacture, is fastened in place with dental adhesive cement.

Indirect methods have been used for a long time and they provide stronger and longer- lasting fillings than can be provided by direct methods. The indirect methods however, are significantly more expensive, both due to the cost of producing the fillings (i. e. equipment needed for such production) and more work needed by the dentist, and at least two visits are required by the patient.

Modified indirect methods have been developed based on pre-fabricated fillings such as described in e. g. US 5, 567, 156, US 5,697, 787, DE 19513568, DE 4123237, and DE 3620542. Such fillings however are typically conically shaped (such as e. g. in US 5,567, 156, or as manufactured under the trademark Cerna) or semi-spherically shaped (US 5,697, 787). These shapes are limited by methods to readily prepare cavities to match pre-fabricated fillings. The Cerana method provides a conical diamond bur to prepare the cavity and specially formed devices are described in DE 19513568 and DE 4123237, to prepare cavities to round shapes of particular diameters.

Such specially shaped tools limit the shapes of cavities that are made, and their use requires precision handling and a steady hand so as not to make the cavity too large.

Means for guiding the operation of a dental tool are proposed in US 5,545, 039 comprising a probe or stylus fastened to a segment of an apparatus, which segment holds a dental operating instrument such that when the instrument is operated within the mouth of a patient, three CCD cameras record the corresponding movement of the stylus.

The present invention provides an apparatus that significantly reduces both the time and the physical stress of the precision work typically required by the dentist to prepare cavities of a particular shape such as to match pre-fabricated fillings. The invention provides an apparatus that makes possible the control of the function and/or location of a dental operating tool to within a predetermined space.

The dentist is relieved from holding the full weight of a dental tool, but more importantly, the dentist can with the use of the apparatus create accurate pre-defined shapes (e. g. cavities and surfaces for crowns and bridges) without the precision and concentration required by conventional methods, which often causes the dentist muscular tension and other physical and mental stress.

BRIEF DESCRIPTION OF FIGURES

Figure 1: Overview of a preferred embodiment of the apparatus of the invention with a tool connected to a base mounted on a jaw of teeth of a patient.

Figure 2: Lower portion of figure shows a preferred embodiment of a base frame, upper portion shows a tool connected to a pantograph and guiding means, for connecting to the base frame.

Figure 3: Portion of apparatus (base frame and shoe-holding member), pantograph and guiding shoe not mounted.

Figure 4: Exploded view of a lockable joint member for engaging the pantograph and guiding shoe-holding member to the base frame.

Figure 5 a-c: Portion of the apparatus for illustrating adjustment of guiding means.

Figure 6 a, b: An embodiment of the apparatus showing a rack-and-pinion gear mechanism for gearing down the relative movement of the operating tool in relation to the guiding pin.

Figure 7: More detailed overview of apparatus with rack-and-pinion gear mechanism for movement in x-direction.

Figure 8 a-c: Different embodiment, having a clamp (110) hooked onto the shoe-holding member (44) in a fixed position.

Figure 9 a-c: An apparatus with alternative arrangement for joining the tool to the shoe- holding member and base frame.

Figure 10: An apparatus with a different height adjustment mechanism for the elongated body within the clamp.

Figures 11-12: Different frames according the invention.

Figures 13-14 : Exploded views of different joint members.

Figure 15 :"Belt-wheel"pantograph apparatus where the tool and guiding member are connected via three belt-connected wheels.

Figure 16: A similar"belt-wheel"pantograph arrangement as in Figure 15, but a different height adjustment mechanism.

DESCRIPTION OF INVENTION The apparatus according to the invention comprises a base, which base is mountable inside the mouth of a subject and in a fixed position with respect to a tooth to be repaired, and a tooth treatment tool, connected to said base wherein the connection between the base and the tooth treatment tool allows for a supported movement of the tool in relation to the tooth, and guiding means for controlling the movement and/or function of said tool to within a pre-determined space. The base may e. g. be a frame, a body, a plate or another construction which is produced in a suitable material and form for insertion and positioning in a fixed position in the mouth of a subject, and allowing a tooth treatment tool to be connected to said base such that the connection between the base and the tooth treatment tool allows for a supported movement of the tool in relation to the tooth. The invention thus relieves the physical stress of holding a dental tool during treatment with said tool.

Preferably, the guiding means for controlling the movement and/or function of said tool, allow manually steered supported movement of said tool within said pre-determined space.

In this context, a tooth treatment tool represents any tool used for dental and/or oral treatment, prophylaxis or diagnosis, including dental turbines, burs, sand blasters, laser beam cutters and water jets; imaging devices such as miniature video cameras or digital (CMOS or CCD) image sensors, also including scanning devices (image, contact and distance sensors) for obtaining 2-D or 3-D image data. In useful embodiments the tooth treatment tool is a turbine or other dental. tool that has a powered mechanical or physical action, i. e. where the action of the tool is not merely a result of the actual movement of the tool by a dentist. In the following description the term'turbine'is to be understood as

referring to both high-and low speed handpieces referred to in the art as handpieces, turbines or air-rotors.

The manually steered supported movement is preferably non-path limited, where the term'non-path limited'in this context refers to movement which is not limited to following any given pre-defined or direction-limited path, rather, the movement of the tool as described herein has at least two and preferably three degrees of freedom, within a pre- determined space as further described below, and can be moved substantially freely within said pre-determined space.

A preferred embodiment of the apparatus comprises a fork shaped frame, wherein a member is shaped such as to fit inside the mouth of a patient, substantially following the arch of the jaw, e. g. by forming a curved"U-shape". A fixed supporting member extends out from the mouth when the base is in place, onto which the tooth treatment tool connects by appropriate connective means. An example of such a base is illustrated in Figure 1 (bottom), showing a frame with flexible holders, which are affixed to the teeth by use of a quick-hardening molding paste such as e. g. Duralay or Impregum. It is estimated that three varying sizes of the frame will suit most patients, 2 years and older.

Depending on the particular embodiment of the apparatus, the supported movement of the tool can suitably be a translational movement of the tool in the relation to the tooth, such as preferably a translational movement independently in three directions. A preferred embodiment is illustrated by Figures 1-5; the supported movement in this case comprises a combination of both translational movement and angular rotational movement, with three degrees of freedom.

In a certain embodiment, the supported movement is further a rotational movement of the tool in relation to the tooth, around a least one rotational axis, such as an axis essentially parallel to the row of teeth comprising a teeth to be treated, such the tooth treatment instrument may reach said tooth at a varying angle relative to the occlusal surface. Such rotational movement may be obtained by a simple pin and hole interface, or preferably by means of an interface with an arch-shaped lip and corresponding groove, e. g. adjacent to a slidable interface for horizontal movement, such that the rotational axis is at or in close proximity to the operating member of the tool such as the bur on a turbine.

The guiding means for controlling the movement and/or function of the tool to within a pre-determined space comprise in useful embodiment a shoe with a guiding space, which shoe is supported by said base, and a guiding member. The guiding member is connected to said tool in a defined geometrically related location to said tool when the tool is connected to the base, and the member is guided by said shoe to thereby control the movement of the tool. The shoe is adjustable to a selected fixed position with respect to the base, and/or optionally the guiding member is adjustable to a selected fixed position with respect to the connected tool, such that the movement of the tool is limited to a pre-determined space corresponding to the guiding space, and such that the pre- determined space is suitably positioned in the tooth to be treated. Controlling the movement is to be understood in this context as limiting the allowed movement such as to a pre-determined space, and not necessarily effecting the movement within that space. The term shoe refers in this context to a body of any suitable outer shape made from any suitable material, to define the guiding space within the shoe.

One example of said geometric relation is simply that the guiding member is in a fixed position to said tool when the tool is connected to the base.

In one embodiment the shoe comprises a body with a model cavity essentially defining said pre-determined space. It is critical for such a described functionality to precisely position the shoe and/or guiding member for the correct position of the pre-determined space, which determines e. g. the material to be removed. This may be accomplished by fine-adjustment of the shoe with the tool and the tool guiding member in place, e. g. , by placing the guiding member at the edge of the guiding space and adjusting the position of the shoe such that the operating member of the tool (e. g. , a turbine) is at the corresponding edge of the pre-determined space to be cleared. For accuracy of the guided movement, it is highly preferable that the tip of said guiding member has essentially the same width as the tip of the operating member of the tool (e. g. tip of a turbine). Preferably, the engagement of the shoe to the base allows for such fine- adjustment in three independent directions. Alternatively, the position of the guiding member is fine-adjusted after approximate positioning of the shoe such as e. g. by sliding the shoe in a shoe seat along parallel members of a frame comprised in the base as described above.

A selection of shoes with different guiding spaces is further provided to allow for suitable different sizes and shapes of the predetermined space. An important utility of the invention is the possibility to create cavities of a pre-determined size and shape, into which a pre-fabricated filling fits. Thus, a dentist may after inspection of a tooth to be treated, select a suitable filling and its corresponding guiding shoe to create a cavity for the filling.

Shoes are also provided for guiding the shaping of tooth stumps for the insertion of dentures and artificial teeth, including crowns and bridges. Preparation of a tooth stump typically involves creating a flat surface just below the gum line and leaving a stump of a particular shape (e. g. semi-conical or boss shaped), which fits a corresponding hollow in the crown. A shoe for such shaping will thus have a guiding space with a flat bottom with a protrusion corresponding to the desired stump shape. Said bottom will need to be at least the size of the cross-section of the tooth at the created surface; the guiding space of such a shoe may further comprise edges limiting the operating space such as to protect adjacent teeth. Optional protection (both in preparation for dentures and in creating cavities) may be obtained by placing a thin foil (e. g. of thin, flexible stainless steel) between the tooth to be treated or removed and an adjacent tooth.

Preferably, for such controlled movement of the tool, the operating member of the tool may be operated essentially in a vertical position, or at a selected fixed angle to the occlusal surface.

It should be noted that the defined geometric relation between the tool and guiding member may also include other implementations than the above described fixed relation.

In a particularly useful embodiment the tool and guiding member are connected via a pantograph. In one such embodiment, the tool is connected to the base by a pantograph that holds the guiding member, which pantograph may be connected to the frame via a pivotal joint on a joint member or through other engaging means, such that the pantograph is adjustably lockable to the base. In such an embodiment, the guiding means suitably comprise the aforementioned guiding means comprising a shoe and guiding member, wherein the model cavity of said shoe is scaled up by a pre-determined ratio compared to the pre-determined space, and wherein said pantograph scales down the movement of said tool compared to the movement of said guiding member by the same ratio such as to guide said tool to within said pre-determined space.

This is illustrated in Figure 1 showing an overview of an apparatus of this type, with more detailed illustrations in Figures 2-5. The apparatus comprises a base shown mounted on a jaw of teeth, with a joint member (43) lockably connected to a support member (41) of the base. A pivotal joint (61) connects a joint connection (47) to the joint member (43), holding the pantograph (48), which on one end holds a tool (51) such as a turbine, and on the other end (the farther end) holds the guiding member (53). The pantograph itself is a generally well known device, the ratio of the pantographic front and rear rhombi defined by the placement of the central joint on the pantographic crossed arms define the ratio of the movement of the far ends of the rhombi. In one embodiment the pantograph is designed such that the tooth treatment tool follows the mirror image of the movement of the guiding member, but scaled down by a factor of three. This factor, may however vary depending on the design of the pantograph, but is suitably in the range of about 2-5, such as about 3-4, e. g. about 3.

As seen in Figure 2, the model cavity of the shoe is mirrored in relation to the pre- determined space in the tooth, such that when the guiding member is moved upwards toward the bottom of the model cavity (which is turned upside-down), the tool moves down towards the bottom of the pre-determined space, and when the guiding member is moved outwards away from the mouth of the patient, the tool moves inwards deeper inside the mouth.

Other useful embodiments utilize other mechanisms for obtaining a scaled-down movement of the tool in relation to the guiding member. Certain preferred embodiment allow non-path limited movement in the x-y plane (i. e. the plane perpendicular to the operating member of the tool) while movement of the tool in the z-direction is accomplished with stepwise height adjustment of the tool relative to the guiding shoe.

Examples of such embodiments are shown in Figures 7-10. In these embodiments the apparatus comprises a gear mechanism (suitably a rack-and-pinion gear mechanism such as shown in Figure 6, but may also be a belt-driven gear mechanism or other type) for movement of the tool in one direction (x-direction), while angular rotational movement is allowed to allow essentially free movement in the x-y plane (limited by the guiding space though) the x-y plane being the plane perpendicular to the direction of the operating member of the tool. Movement of the tool in the z-direction, adjustment of the "height"of the tool, is however accomplished with step-wise adjustment via a height adjustment mechanism, typically a simple arrangement with a threaded axis joining the

tool and the shoe-holding member, the axis being connected to an adjustment screw or threaded adjustment ring, as shown in Figures 7-10.

In the case where the tool is a dental turbine, the turbine is in certain embodiments a conventional dental turbine and the said seat is shaped to firmly support said turbine. In this context, firm support is to be understood such that the operating member of the tool is in a fixed position with respect to the seat, and the positioning of the tool in the seat further needs to be accurate such that the position of the operating member of the tool with respect to the seat is always the same, such as after disconnection and re- connection of the tool and seat.

In other embodiments, the tool is specially constructed for operation according to the invention, e. g. by not having a conventional handle for holding the tool, but merely a lighter and smaller handle for guiding of the tool. The handle may further have a joint such that when moving the tool and seat upwards, less of a torque will affect the part of the tool joined to the seat, if a torque is unintentionally applied to the handle.

In a yet a further embodiment of the apparatus, the supported movement of the tool is remotely controlled movement. Such movement is suitably affected by micro-actuators such as micro-motors, hydraulic or pneumatic systems, interacting with said computer system. The apparatus may further comprise a user interface, such as a mouse, joystick or keyboard, to steer said movement. Thus, for tooth treatment such as the removal of tooth material, the computer system will store collected image data and create and store a digital geometric representation of the tooth, subtract a pre-determined space corresponding to tooth material to be removed to create a new geometric model which defines the space within which the operation of the tool is allowed. The computer system further receives positional information from location sensors within the seat and/or bearing unit and will override the input signal steering the movement of the tool when the operative member of the tool reaches a boundary of the operating space.

(Normally, the user interface is connected to the micro-actuators trough the computer system.) A further embodiment uses such micro-actuators for effecting the movement of the tool, wherein the micro-actuators interact with the computer system and the computer system steers the movement based on the pre-determined space. The computer system in this

case uses a program, which uses the digital geometric model defining the operating space to calculate a suitable path that the tool is moved by, by the micro-actuators when an operator (i. e. the dentist) runs the program.

In another aspect of the invention, a method is provided for treatment of a tooth in a patient, such as for removal of tooth material, comprising the steps of : arranging a base inside the mouth of the patient in a fixed position with respect to the tooth to be treated; connecting a tooth treatment tool to the base, wherein the connection between the base and the tooth treatment tool allows a supported and preferably non-path limited movement of the tool in relation to the tooth; performing the treatment by supported movement and operation of the tool. The tool is any dental tool as described above, and in useful embodiments comprises a dental turbine, and the base is preferably as described above. The tool is preferably connected with a seat and bearing unit assembly as described above, such as with a sliding member for slidable movement along a member of the base, as described above. However, in presently preferred embodiments, the connection between the base and the tooth treatment tool comprises a pantograph device holding the tool at one end, and a guiding member at the other end, wherein the guiding member is in contact with a guiding shoe adjustably lockable to the base, to thus allow the supported movement of the tool on relation to the tooth, for performing the treatment according to the method of the invention, by supported movement and operation of the tool in a pre-defined space within the tooth to be treated, which pre-defined space is defined by the guiding space of the guiding shoe.

It will be appreciated that the method, is particularly useful for removal of tooth material from a tooth of a patient, wherein the method comprises the steps of: determining at least one characteristic of said tooth, such characteristics being location and approximate shape of tooth material to be removed; determining-based on the determined characteristic of the tooth, the size and shape of an appropriate space-operating space-within which a tooth treatment tool as defined above is to be operated; arranging a supporting base such as any of the above described, inside the mouth of the patient and in fixed position with respect to said tooth; connecting said tool to said base such that said connection allows for supported movement of the tool, allowing the operation of said tool within said operating space;

preparing the tooth with the use of said tool essentially to clear the pre-determined operating space.

The connection of the tool to the base is preferably such as described above. It will be appreciated that the above method may readily be realized with the apparatus described herein.

In a useful embodiment, the method according to the invention comprises repairing tooth decay in a tooth such as removal of caries, wherein: said characteristics being location and approximate size of the decay to be removed; said appropriate space-operating space-is determined such that an appropriate filling may be inserted into said space; and wherein the method further comprises the steps of: optionally applying fastening means such as dental cement into said cavity and/or onto the filling to be inserted into said cavity; and inserting said filling into said operating space; and optionally finishing the surface of said filling. This method thus allows a dentist to readily and quite quickly prepare a cavity into which a pre-formed filling will fit, e. g. a pre-formed porcelain or plastic filling. Note that the terms dental fillings and dental inserts are used herein interchangeably. The use of such pre-made fillings has been severely limited due to the difficulty of preparing cavities of exact size and shape to fit the filling, with currently available prior art methods.

In a preferred embodiment, an appropriate filling is selected such it will fit in a cavity created such that all caries is removed and the amount of healthy tooth tissue material removed is minimized.

Preferably, during said preparing, the location and/or function of said tool is controlled to within the pre-determined operating space, with an apparatus as described above.

Such controlling of the location of the tool may in a useful embodiment of the method be effected by adjusting and fastening a shoe with a guiding space onto said base such that when a guiding member-which is fixed, or in a non-fixed but geometrically defined related position, relative to the connected tooth treatment tool-is inserted in the guiding space, the location of the operating member of the tool is limited to within the operating space. This is accomplished with an apparatus as described above.

Where the method is used for repair of tooth decay, the appropriate preformed filling may suitably be fabricated such that the periphery and inclination of said filling essentially matches said operating space, i. e. the exposed surfaces of the filling need not be perfectly aligned with the surfaces of the tooth as the filling may be finished in a further optional step of the method with any appropriate finishing means well known to the person skilled in the art such as a turbine, an ultrasonic bur, or a file.

It is a particularly noteworthy feature of the method according to the invention that a pre- fabricated filling may be selected based on the size, shape and location of said tooth decay, and said operating space is then pre-determined such that the periphery and inclination of said operating space essentially matches the periphery of said filling. The invention thus offers the possibility for a dentist to have a stock of pre-fabricated fillings of the most commonly needed shapes and sizes (it is estimated that only 9 different fillings would be suitable and sufficient for the repair of about 90% of caries infections which appear in molars (Ericsson, Yngve et al., Kariologiska principer, 1980, Lagerblads AB).

In yet a further embodiment, finishing of an inserted filling and/or prepared tooth surface may be performed by the tool of the apparatus as described above, wherein during said finishing step the active member of said device may optionally be exchanged for an appropriate finishing-active member, such as a bur or file. When the location and/or function of the tool is controlled by the use a digital geometric model and computer system as described above, such finishing may suitably be performed such that the function of said tool is limited to a space determined by the surface of the geometric representation of the tooth, prior to the treatment, with similar methods and means as described above. Essentially, a new operating space is determined for this step, which is defined by the surface of the tooth as it was prior to the treatment, or optionally by another desired surface.

MORE DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS WITH REFERENCE TO THE FIGURES Adjustment of guiding member and guiding shoe: By adjusting the position of the clamp (15), the height of the guiding member (14) and the position of the guiding shoe (22), the

exact location of the pre-determined space is set. The adjustment is suitably done by, e. g. placing the tool where an edge of the prepared cavity should be and adjusting the guiding member and guiding shoe such that it contacts the corresponding edge of the guiding space of the shoe. The guiding member has essentially the same diameter as the operating member of the tool such that the position of all edges of the operating member will correspond to the corresponding edges of the guiding member.

Figure 2: The lower portion of the figure shows a preferred embodiment of a base frame, as described above, comprising a fork shaped frame (40) shaped such as to fit inside the mouth of a patient, substantially following the arch of the jaw. A fixed supporting member (41) extends out from the mouth when the base is in place. Flexible holders (42) that can be affixed to the teeth by use of quick-hardening molding paste, are slidably mounted on the frame (40). When providing sufficient amount of molding paste in the space between the holders and adjacent teeth, the hardened paste and holders create rigid fixtures keeping the base in a fixed position relative to the teeth. A lockable joint member (43) slides onto the supporting member (41) allowing lockable adjustment of a shoe-holding member (44), which on one end has a fixture (45) for a guiding shoe (46), and on the opposite end has a joint connection (47), which connects a pantograph (48) to the shoe-holding member (44). The shoe-holding member (44) is fastened on a pivot member (61) by a quick-release mechanism (55).

The pantograph (48) holds on one end a dental tool, illustrated here as a dental turbine (51) and on the other end a guiding member (53). The joint connection (47) and the pantographic joints (49,50) allow essentially free movement in three directions of the dental tool (i. e. , a combination of translational and angular movement, with a total of three degrees of freedom).

By this arrangement, the dental tool stays in a defined geometrically relation to the guiding member, defined by the pantograph design (ratio of length of front and rear pantographic rhombi). In the embodiment shown, the guiding member has an extended joystick handle (54), by which an operator of the instrument (the dentist or dental assistant) steers the movement of the tool (51). The movement of the tool's active member (52) essentially follows the mirror image of the movement of the endpoint (56) of the guiding member (53), but scaled down by a factor determined by the design of the pantograph. As shown in the illustrated embodiment, the pantographic factor is about 3.

For improved precision, the width of the guide member endpoint (56) should correspond to the width of the active member (52) of the tool, multiplied with the pantographic factor.

Adjustment of the position of the guiding shoe: The guiding member (53) can be locked in a certain position by the guiding shoe (such as at the far edge of the guiding space within the shoe, e. g. by a simple hook mechanism (57); then, by loosening the joint member (43) and the pivot member (61), movement of the joystick handle (54) will move not only the tool and guiding member but also the shoe-holding member (44) and guiding shoe (46). When the tool's active member (52) is suitably positioned at a suitable point location by a tooth to be treated, i. e. the point of the edge of the desired operating space, which corresponds to the point of the edge of the guiding space at which the guiding member is positioned, the shoe- holding member (44) is locked in place by fastening the joint member (43) and pivot member (61). Thereby, the guiding space of the guiding shoe now defines the desired operating space within a tooth.

Adjustment of the pivot member (61) further allows suitable adjustment of the angle of tool, before the pivot member is locked in position. The quick-release mechanism (55) allows removal of the shoe-holder and pantograph, without changing the positional and angular adjustment of tool relative to the base.

By exchanging the tool for a positioning plate tool (a tool with an affixed plate perpendicular to the tool direction), the angle of the tool can be readily adjusted to be perpendicular to the occlusal surface of the tooth to be treated.

Operation of the apparatus of Figure 2, for insertion of a pre-formed dental insert: A base with a suitably sized frame is selected to match the jaw size of the subject to be treated. The base is mounted in the subject by substantially filling the space underneath the curved flaps of the holders (42) with quick-hardening dental molding paste, and the holders are adjusted on the frame such as not to block access to the tooth to be treated.

The frame with paste-filled holders is pushed on to the jaw with the tooth to be treated and the paste is allowed to harden, thus fixing the base in relation to said tooth. Judged from inspection of the tooth, a guiding shoe is selected with a guiding space matching a selected suitable pre-formed insert, and the shoe is inserted in the shoe-holder (45). The joint member (43) is slid onto the support member (41) with the shoe-holding member (44) and pantograph (48) mounted. The guiding member (53) is set in locked position (by means of locking mechanism (57) ) at the outer edge of the guiding space and the position of the tool (51) adjusted such that the active member of the tool (52) is located at position by said tooth corresponding to the farther edge of the cavity to be made, i. e.

the point of the cavity to be made corresponding the locked position of the guiding member. Typically, the height of the height ring (64) and the angle of the pivot member (61) are preferably adjusted such the angle of the tool is parallel to the axis of the tooth when the active member of the tool is at the mid-height of the cavity to be prepared.

After positioning and adjustment of the tool, the tool is turned on and operated by moving the joystick handle to fully clear the pre-determined space of the tooth. For added safety and guiding, it is useful to insert a thin metal foil between the tooth to be treated and the next tooth adjacent to the side of said tooth being treated. The insert can then be inserted into the prepared cavity, typically after application of a thin layer of dental cement. The insert is finally finished, by conventional finishing means and/or by using a suitable finishing tool inserted in the apparatus.

Figure 3 shows the base (40,41) and shoe-holding member (44) in a rear view, as compared to Figure 12, with the pantograph and guiding shoe not mounted. Only half of the shoe fixture (45) is shown, into which the guiding shoe may be locked.

An exploded view of the lockable joint member (43) is shown in Figure 4 showing a locking screw handle (60) which locks the slidable joint member (43) onto the supporting member (41) of the base (not shown); a pivot member (61) which is lockable in a selected position by tightening of a locking screw (62). A threaded height ring (64) is screwed on a threaded portion (63) of the pivot member (61), for adjusting the height at which the shoe-holding member (44) is mounted on the pivot member. Thus by suitable adjustment of the height ring (64) and the angle of the pivot member (61), a suitable operation angle of the tool (51) at a given position is set.

Figure 5 gives a view of a portion of the apparatus, illustrating the locking mechanism (57) and showing the guiding space (58) of the guiding shoe (46).

Figures 6 a-b illustrate a another preferred embodiment of the invention, where linear displacement of the tool in one direction (the direction of the tool body axis; the'x'- direction) is realized with a geared rack-and pinion mechanism, which mechanism is preferably enclosed within an elongated body. Figure 16a shows the inside of the body while 16b shows the enclosed body. The mechanism comprises two axially joined cogwheels (92,96) each of which connects to a rack of teeth (93,94) fixed to the respective bars (102,103). The number of teeth on each cogwheel, the radii of the

cogwheels and the width of the rack teeth on each rack (i. e. teeth per cm) determines the gear ratio between the movement of the bar (102) connected to the guiding pin (53) and the bar (103) connected to the tool (51). When the guiding pin and thus the bar (102) is moved a distance x in the direction towards the tool, the bar (103) and the tool (51) will move in the opposite direction by a distance that is a gear ratio of x. In one preferred embodiment the gear ratio is Y2, i. e. , when the bar (102) is moved by a distance x, the bar (103) will move by a distance-0.5 * x. The gearing ratio may however as well be, e. g. , about 1/1, about 1/3, or about 1/4, Preferably, the cogwheels are of a backlash-free type, i. e. that each cogwheel is comprised of two equal size axially joined wheels having a spring mechanism such that the teeth of one of the two wheels can move slightly relative to the teeth of the other wheel, to create a backlash- free connection with the rack teeth. Note that in Figure 6a, the cogwheels are shown having a horizontal axis, but the mechanism may just as well be configured based on cogwheels with a vertical axis. In between the bars (102,103) and elongated body are preferably linear bearings to minimize friction.

Figures 7a and b show a more detailed version of the last-mentioned embodiment. The guiding member (53) is shown joined to the bar (102) having a joystick (54) for manually steering the movement of the guiding member within the guiding space (58) of the guiding shoe (46). The elongated body (90) is held with an adjustable clamp (110) shown here with hinges (111). A joint member (43) lockably connected with a locking screw with quick-lock handle (60) to a support member (41) on the base (40) holds the shoe holding member (44) such that it can be adjusted in a fixed position in relation to the base (40) and teeth (not shown). Preferably, the joint member (43) comprises a pivotal joint member (61) to allow angular displacement of the shoe holding member (44) and the clamp (110) to adjust the angle of the x-y plane of the tool. A screw axis (114) connects the clamp and elongated body (90) and a threaded plate (113) screwed onto the axis adjusts the height of the elongated body within the clamp. A spring coil (124) pushes the elongated body towards the plate (113).

A second threaded plate (112) screwed on a threaded end of the pivot member (61) allows height adjustment of the shoe-holding member (44) and clamp (110) relative to the joint member (43) and the frame (40). Further, the screw axis allows angular movement (i. e. rotating within the x-y plane) of the guiding member and tool. The ratio of the distance from the screw axis to the too on the one hand and to the guiding member

on the other hand determines the relative movement of the tool relative to the guiding member through rotational movement around the screw axis. In the embodiment as shown the distance ratio is about 1/2, i. e. the same as the gear ratio of the rack-and- pinion gear mechanism, thus the guiding space defining the pre-determined space to be operated within by the tool is about twice the size of the desired pre-determined space.

In the embodiment as shown, manual movement of the joystick does not allow linear or angular movement of the tool in the z-direction. Rather, the tool is operated in a first x-y plane (essentially on the surface of the tooth to be treated), then the tool is lowered by adjustment of the threaded wheel (113) and a lower x-y plane of the pre-determined space is cleared. This is repeated stepwise until the guiding member (56) has reached the bottom of the guiding space (46), when the tool has correspondingly reached the bottom of the pre-determined space.

The joystick handle may be provided with a force-dependent spring hinge to limit the torque on the guiding member when applying extensive force on the joystick handle.

Figure 8a-c shows a similar embodiment as in Figure 7, the difference lying in a different clamp (110), which is hooked onto the shoe holding member (44) in a fixed position (by bosses (131) on the shoe holding member that fit in corresponding dimples underneath the clamp). The height adjustment of the elongated body and tool is accomplished here with a horizontal screw (130) that connects to the screw axis (114).

Yet a further version is shown in Figures 9a-c having a split screw axis but where a clamp is not used. Instead, the first screw axis (114) through the elongated body (90) is joined to a plate (121), which fits snugly and can be fastened in a fixed position (shown with a boss and dimple arrangement similar as in Figure 8) onto an opposite plate (120) on the shoe holding member (44). A second screw axis (122) and threaded plate (112) allows height adjustment of the shoe holding member (44) and thus the plate (121) with the first screw axis (114) and elongated body (90).

A similar version to the one of Figure 8 is shown in Figure 10, where a different height adjustment mechanism for the elongated body within the clamp is shown.

Figures 11-12 show various embodiments of possible frames of the present invention.

The frames of Figure 11 b and c are designed such that they are fastened in either side of the mouth, depending on the location of the tooth to be treated.

Figures 13 and 14 show exploded views of different joint members (43) such as can be used with the above discussed embodiments of the apparatus.

Figure 15 shows an illustration of a different type of pantograph apparatus (a"belt- wheel"pantograph), where the tool and guiding member are connected via three belt- connected wheels (144, 145,146), creating a geared-down mirrored movement of the tool (51) relative to the guiding member (53). In the embodiment as shown, the movement ratio is 1/2. (See schematic illustration; when point a (the guiding member) is moved to right, point b moves half the distance to the left). The belt-wheel pantograph is connected via a joint connection (47) to the shoe-holding member (44), which is adjustably lockable onto the frame via a joint member (43) and a pivot member (61), allowing essentially free movement of the guiding member within the guiding space.

In figure 16 a similar belt-wheel pantograph is shown, but here the guiding member and thus the tool is moved via the joystick in the x-y plane, while movement in the z-direction is accomplished with stepwise adjustment of a pantograph holding member (150) with a height adjustment screw (130) such that the tool is operated in a single plane at a time, in a similar fashion as with the embodiments of Figures 7-10.