Patent Publication Number: US-2007099150-A1

Title: Dental drill device with a stop element

Description:
FIELD OF THE INVENTION  
      The present invention relates to a dental drill device.  
     BACKGROUND OF THE INVENTION  
      U.S. Pat. No. 5,890,897 discloses a dental drill device with a stop element held on a drill. The stop element engages completely around the drill in the circumferential direction and is held on it so as to be displaceable in the axial direction.  
      The drill has an exposed drill end on a cutting part, and a cylinder shank with an exposed shank end face. Located between the drill end and the shank end face there is a holder portion with several spherical-cap-shaped fastening recesses spaced apart from one another in the axial direction and oriented toward one another.  
      The stop element has a circular-cylindrical shape with a drill abutment surface. In the axial direction, the stop element is designed with a central through-opening which corresponds substantially to a diameter of the drill. In the radial direction of the stop element, an insert opening runs through the stop element. A spring-loaded, pin-like engagement element is arranged in the insert opening.  
      The stop element can be fitted onto the drill from the direction of the drill end and can be fixed with a force fit on the drill by means of the engagement element engaging in one of the fastening recesses.  
      Consequently, the drill abutment surface is arranged at a defined and desired distance from the drill end, as a result of which a maximum drilling depth is defined. During drilling of a hole in a jawbone, the drill abutment surface bears on the jawbone or gum when the desired drilling depth is reached.  
      U.S. Pat. No. 5,890,897 also discloses an alternative embodiment of the stop element. In this embodiment, the engagement element is provided with an outer thread and is screwed into the insert opening. By orienting the engagement element with one of the fastening recesses and then turning the engagement element, the latter comes into form-fit engagement with the relevant fastening recess.  
      EP 0 643 567 B1 discloses a drill having annular markings arranged around the circumference and spaced apart from one another in the axial direction, these markings differing in color from the surface layer of the drill. During drilling, the annular markings are used to estimate the actual drilling depth. The rings are produced by surface treatment of the drill.  
      U.S. Pat. No. 5,941,706 discloses a drill which has colored rings extending in the circumferential direction and spaced apart from one another in the axial direction. For this purpose, the drill has annular grooves spaced apart from one another in the axial direction and filled with colored material. During drilling, the actual drilling depth can be read off with the aid of these colored rings.  
      U.S. Pat. No. 6,514,258 B1 discloses a dental drill device comprising a drill and a stop element. The drill has a drill end and a cylinder shank. At an end area of the cylinder shank directed toward the drill end, it has a cuff-like thickened area. This thickened area is limited in the direction of the drill end by a narrowing truncated cone surface. The stop element has a sleeve-shaped design and has a drill abutment surface at one of its end faces and, adjoining another end face, a clamp area which is intended to engage around the thickened area. The stop element can be pushed onto the drill from the direction of the drill end, by which means the clamp area is fitted onto the thickened area in the manner of a snap-fit closure. The stop elements are designed in different lengths corresponding to different drilling depths.  
      U.S. Pat. No. 6,739,872 B1 discloses a dental drill device composed of a drill and of a stop element engaging in the manner of a sleeve around the drill. The drill has a cutting part with an exposed drill end, and a cylinder shank. A holder portion is formed between the cutting part and the cylinder shank. The holder portion has a thread which is designed running in the opposite direction to the turn of the chip grooves of the twist drill. The stop element is first fitted with an inner thread onto the drill from the direction of the drill end and is screwed onto the thread. Toward the drill end, the stop element has an exposed drill abutment surface. In order to set a maximum drilling depth, the stop element is turned to the desired axial position. As soon as the drill abutment surface is stopped, during drilling, by interaction with a material into which the drill is being drilled, or as soon as it is prevented from turning together with the drill, the effect of the thread is that the drill is automatically moved out of the drilled hole.  
      The known dental drill devices and dental drills have different disadvantages. Those drills designed only with visual elements for determining the drilling depth have the disadvantage that, during use, the actual drilling depth cannot be defined with precision, and the visual markings can become soiled and thus unreadable.  
      In dental drill devices with a stop element, handling can prove to be complicated, for example in the one according to U.S. Pat. No. 6,514,258 B1, because the length of the stop element has to be adapted individually to the respective drilling depth of the hole that is to be drilled, and because a drill stop element, once it has been used, cannot be used again.  
      During the use of the dental drill device disclosed in U.S. Pat. No. 5,890,897, when the drill abutment surface of the stop element is resting on the jawbone or gum, the force-fit connection can be overcome, which would lead to a drilled hole that was too deep.  
     SUMMARY OF THE INVENTION  
      In accordance with various embodiments of the present invention, a dental drill device is provided in which the position of the drill abutment surface relative to the drill, and thus the depth of the hole to be drilled, can be defined in a reliable and simple manner.  
      In one or more embodiments, all the elements of the dental drill device may be re-usable.  
      In one embodiment, a dental drill device has a drill and a stop element arranged thereon, the drill having, at one end, a cutting part with a front drill end and, at the other end, a shank part with a receiving end area which is intended to be received in a drill-holder device, the shank part having a holder portion for the stop element, and the stop element having a drill abutment surface which is exposed in the direction of the drill end and which is held on the drill at a desired distance from the drill end, wherein several fastening recesses spaced apart from one another in the axial direction (A) of the drill are arranged within the holder portion of the drill, and the stop element has an engagement element engagable in one of the fastening recesses, wherein the fastening recesses, on their side directed toward the receiving end area, are limited by an abutment surface extending at least approximately at right angles to the axial direction (A), and the engagement element has a counter-abutment surface which cooperates in a form fit with the relevant abutment surface.  
      In another embodiment, a dental drill device has a drill defining an axial direction (A), with an extension element, and with a stop element arranged on the latter, the drill having, at one end, a cutting part with a front drill end and being intended, at the other end, to be held on the extension element, the extension element having a receiving end area receivable in a drill holder device, and a holder portion for the stop element, and the stop element having a drill abutment surface which is exposed in the direction of the drill end and which is held on the extension element at a desired distance from the drill end, wherein several fastening recesses spaced apart from one another in the axial direction (A) of the extension element are arranged thereon within the holder portion, and the stop element has an engagement element engagable in one of the fastening recesses, said fastening recesses being limited, on their side directed toward the receiving end area, by an abutment surface extending at least approximately at right angles to the axial direction (A), and the engagement element having a counter-abutment surface which cooperates in a form fit with the relevant abutment surface.  
      In accordance with various embodiments, by means of the abutment surface being oriented at least approximately at right angles to the axis of the drill, and by means of the engagement element which has a counter-abutment surface cooperating with the abutment surface in a form-fit manner, it is ensured that, when a force acts on the stop element in the axial direction and away from the drill end, the stop element is held immovably on the drill or extension element.  
      In one embodiment, the stop element has a radially outward, circular-cylindrical guide surface. This makes it possible to guide the stop element, and therefore the drill, on a drill jig for example, by which means the position and direction of the hole that is to be drilled can be defined with precision.  
      In another embodiment, the dental drill device comprises a drill jig which can be fixed in a stationary position relative to the oral cavity of a patient. The drill jig has a circular-cylindrical recess with a mating guide surface which is intended to cooperate with the guide surface. By means of this cooperation, the drilling direction and the position of the drilled hole are defined by the drill jig. An incorrect orientation and incorrect position of the drilled hole are avoided.  
      In another embodiment, the drill jig also has a shoulder which projects radially inward relative to the mating guide surface and which is intended to cooperate with the drill abutment surface of the stop element. In this embodiment, a maximum drilling depth is defined by the cooperation between the shoulder and the drill abutment surface.  
      In another embodiment, the stop element is designed with a sleeve shape, and the engagement element is preferably arranged on a spring element designed as a resilient finger. This embodiment permits a compact structure in the radial direction. This embodiment also makes it possible for the stop element to be fitted from the direction of the receiving end area, since a stop element mounted on the holder portion, with the engagement element engaging in one of the receiving recesses, can be displaced in the direction of the drill end if a certain force is overcome and, in this way, the engagement element can be brought to another of the receiving recesses.  
      Other configurations of the dental drill device according to the invention are set forth in the following detailed description and claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  shows a perspective view of a dental drill device according to the invention in a first embodiment, comprising a dental drill with five grooves spaced apart from one another in the axial direction within a holder portion of a cylinder shank, and a stop element designed as a clamp ring and fitted in one of the grooves;  
       FIG. 2  shows a perspective view of a dental drill device according to the invention in a second embodiment, comprising a dental drill and a stop element, with three thickened areas spaced apart from one another in the axial direction within a holder portion of a cylinder shank, and a stop element mounted on one of the thickened areas;  
       FIG. 3   a  shows a perspective view of a dental drill device in a third embodiment, comprising a dental drill and a sleeve-shaped stop element, with three grooves formed in a holder portion of the dental drill, and the stop element being able to be fixed in the axial direction on these grooves;  
       FIG. 3   b  shows a side view of the dental drill according to  FIG. 3   a , with the stop element shown in cross section;  
       FIG. 4   a  shows a perspective view of a dental drill device according to the invention in a fourth embodiment, comprising a dental drill fitted into an extension element, and a stop element held on the extension element;  
       FIG. 4   b  shows a perspective view of the dental drill device according to  FIG. 4   a , with the stop element being shown as if transparent;  
       FIG. 4   c  shows the dental drill device according to  FIG. 4   a  and  FIG. 4   b , the dental drill being shown in a side view, and the extension element and the stop element being shown in longitudinal section;  
       FIG. 4   d  shows the dental drill device according to  FIG. 4   a ,  FIG. 4   b  and  FIG. 4   c  in a side view; and  
       FIG. 5  shows a cross sectional view of a dental drill device according to  FIG. 2 , in which the dental drill is guided in a drill jig. 
    
    
     DETAILED DESCRIPTION  
       FIG. 1  shows a first illustrative embodiment of a dental drill device  10  according to the invention. A dental drill  12  has, at one end, a cutting part  14  with an exposed drill end  16 , and, at the other end, a shank part  18  with an exposed receiving end area  20 . The receiving end area  20  is intended to be received in a generally known drill holder device and has a rotation-preventing means  22  configured as a surface, and an axial securing means  24 ′ designed as a groove  24  extending partially in the circumferential direction. The rotation-preventing means  22  and the axial securing means  24 ′ means that the dental drill  12  can be brought into a fixed connection with the drill holder device, which for example is part of a drill drive or a hand drill.  
      The shank part  18  has a holder portion  26  for a stop element  28 . This holder portion  26  is formed by a circular-cylindrical thickening of the shank part  18  into which five fastening recesses  30  designed as circumferential grooves  29  are formed. In the axial direction A of the dental drill  12 , all the grooves  29  have the same width and, in the radial direction of the dental drill  12 , they have the same depth. In the axial direction A, each of the fastening recesses  30  is limited at one end, in the direction of the receiving end area  20  of the shank part  18 , by a circular abutment surface  32  at right angles to the axial direction A. Each fastening recess  30  is limited, in the direction of the drill end  16 , by another likewise circular limit surface at right angles to the axial direction A.  
      The stop element  28  of the dental drill device  10  is formed by a circular and open, and therefore C-shaped, clamp ring. The stop element  28  is intended to be inserted into one of the fastening recesses  30 , clamping in the radial direction. The stop element  28  forms an engagement element  58 .  
      In the text that follows, the stop element  28  is described as if in the state, shown in  FIG. 1 , in which it is inserted into one of the fastening recesses  30 .  
      The external diameter of the stop element is chosen to be greater than the external diameter of the holder portion  26  and also greater than the drill diameter of the cutting part  14 . The width of the clamp ring, measured in the axial direction A, is chosen at least slightly smaller than the distance of the abutment surface  32  from the opposite limit surface of the fastening recess  30 . By means of this configuration, the stop element  28  fitted into one of the fastening recesses  30  protrudes radially past the holder portion  26  and past the cutting part  14 . A counter-abutment surface  35  of the stop element  28 , facing toward the abutment surface  32 , is at right angles to the axial direction A and is intended to cooperate with the abutment surface  32 . In the axial direction A, directed away from the counter-abutment surface  35  and toward the drill end  16 , the stop element  28  has a drill abutment surface  36  lying at right angles to the axial direction A.  
      The stop element  28  is preferably designed symmetrically with respect to a plane lying at right angles to the axial direction A, so that the drill abutment surface  36  and the counter-abutment surface  35  are of the same design.  
      In order to set the drilling depth of a hole that is to be drilled into the jawbone, the stop element  28  is inserted into the relevant recess of the fastening recesses  30 . The maximum drilling depth is defined by the distance of the drill abutment surface  36  from the drill end  16 . If another maximum drilling depth is desired, the stop element  28  can be removed from the fastening recess  30  and can be inserted into another of the fastening recesses  30 .  
      By means of the abutment surface  32  which lies at right angles to the axial direction A and which cooperates with the counter-abutment surface  35  of the stop element  28 , also lying at right angles to the axial direction A, inadvertent changing of the drilling depth is avoided by means of a form fit connection. It is still possible, however, to adapt the maximum drilling depth in a very simple manner—by radial withdrawal of the stop element  28  from one of the fastening recesses  30  and insertion of the stop element  28  into another of the fastening recesses  30 .  
      In further illustrative embodiments and configurations described below, the same reference numbers are used for the same or similar elements.  
      In a second illustrative embodiment of the dental drill device  10  shown in  FIG. 2 , the dental drill  12  has principally the same design as the dental drill  12  of the first illustrative embodiment, except for the form of the holder portion  26 .  
      In the holder portion  26 , the shank part  18  has three circumferential, cuff-like thickened areas  40 . The thickened area  40 ′ lying nearest to the cutting part  14  in the axial direction A is spaced apart from the cutting part  14 . Each of the thickened areas  40  has, facing toward the drill end  16 , an abutment surface  32  at right angles to the axial direction A of the dental drill  12 . Directly adjoining the abutment surface  32  and in the direction of the receiving end area  20 , each of the thickened areas  40  initially has a constant diameter. Thereafter, each of the thickened areas  40  narrows to the diameter of the cylinder shank  18 . The narrowing is effected via a truncated cone-shaped clamp surface  42 .  
      Fastening recesses  30  are formed between the individual thickened areas  40 . A further fastening recess  30  is formed between the cutting part  14  and the thickened area  40 ′ lying nearest to the cutting part  14 . In the direction of the receiving end area  20 , each of the fastening recesses  30  is limited by the abutment surface  32 .  
      The stop element  28  has a rectilinear, circular hollow cylinder configuration with a C-shaped cross-sectional surface area, designed principally as an open clamp ring, and is intended to be pushed in the radial direction onto one of the thickened areas  40 . An outer jacket surface of the stop element  28  lies on a circular cylinder with a diameter that is greater than a drill diameter of the cutting part  14 . One of the end faces of the stop element  28  forms a drill abutment surface  36  and, if the stop element  28  is pushed onto one of the thickened areas  40 , lies at right angles to the axial direction A and is exposed in the direction of the drill end  16 .  
      The outer jacket surface of the stop element  28  forms a guide surface  37  intended to cooperate with a mating guide surface  106  of a drill jig  100 , which is described further below.  
      In the text that follows, the stop element  28  is described as if in the state in which it is mounted on one of the thickened areas  40 .  
      The stop element  28  is held on one of the thickened areas  40  in the holder portion  26  of the dental drill  12  by two ridges  44 ,  46  which are spaced apart from one another in the axial direction A, protrude from an inner jacket surface of the C-shaped cylinder and extend in the circumferential direction. For this purpose, the ridge  44  directed toward the receiving end area has a mating clamp surface  48  that cooperates with the clamp surface  42 . The other ridge  46  forms an engagement element  58  and has a counter-abutment surface  35  cooperating with the abutment surface  32 . The counter-abutment surface  35 , like the abutment surface  32 , is at right angles to the axial direction A. The width (in the axial direction A) of the ridges  44 ,  46  is chosen smaller than the axial spacing of the thickened areas  40  from one another.  
      The stop element  28  mounted on one of the thickened areas  40  lies with its inner jacket surface on the thickened area  40  lying directly after in the direction of the drill end  16 , as a result of which the stop element  28  is supported on this thickened area  40 .  
      If the stop element  28  is mounted on the thickened area  40 ′ lying nearest to the cutting part  14 , the stop element  28  bears on the cutting part  14 . For this purpose, the cutting part has a truncated cone jacket surface facing toward the thickened area  40 ′ and designed to match a support surface  110  on the stop element  28 . The support surface  110  narrows, starting from the drill abutment surface  36 , to the diameter of the inner jacket surface of the stop element  28 .  
      The handling of the dental drill device  10  according to the second illustrative embodiment is principally the same as the above-described handling of the first illustrative embodiment of the dental drill device. The maximum drilling depth is once again determined by the distance of the drill abutment surface  36  from the drill end  16  of the cutting part  14 . The maximum drilling depth can be changed by radial withdrawal of the stop element  28  from the holder portion  26  and by mounting the stop element  28  on the desired thickened area  40 . Inadvertent changing of the maximum drilling depth in axial direction A is once again avoided by the form-fit connection between the abutment surface  32  and the counter-abutment surface  35  that cooperates with this abutment surface  32 . A secure fit of the stop element  28  in axial direction A is ensured by the cooperation of the clamp surface  42  and the mating clamp surface  48 , by which means the counter-abutment surface  35  is pressed firmly onto the abutment surface  32 . In the radial direction, the stop element  28  is fixed with a force fit on the dental drill  12  by its being designed as a clamp ring.  
      The third illustrative embodiment of the dental drill device according to the invention is shown in  FIG. 3   a  and  FIG. 3   b.    
      Except for the form of the holder portion  26 , the dental drill  12  is once again principally designed the same as the dental drill  12  of the first illustrative embodiment.  
      The shank part  18  has a constant diameter and, in the holder portion  26 , has three fastening recesses  30  designed as circumferential grooves  52 . The holder portion  26  directly adjoins the cutting part  14 . Each of the fastening recesses  30  is limited, at one end, by an abutment surface  32  directed toward the receiving end area  20  of the shank part  18  and at right angles to the axial direction A of the dental drill  12 , and, at the other end, by a ramp-like clamp surface  42 .  
      Each of the fastening recesses  30  has a circular cylinder surface of constant diameter between the abutment surface  32  and the clamp surface  42 . The clamp surface  42  lies on a truncated cone jacket surface, and rises like a ramp from the circular cylinder surface of the fastening recess  30  in the direction of the drill end  16 . The diameter of the shank part  18  is chosen smaller than a drill diameter of the cutting part  14 .  
      The stop element  28  has a sleeve-shaped design and is intended to be fitted onto the dental drill  12  from the direction of the receiving end area  20  of the shank part  18 . In the text that follows, the stop element  28  is once again described in the state in which it is fitted onto the dental drill  12 .  
      Except in the area of engagement elements  58  that are intended to engage in one of the fastening recesses  30 , the internal diameter of the stop element  28  is substantially equal to the drill diameter of the cutting part  14 . The stop element  28  has, at one end in the axial direction A, toward the drill end  16 , a front drill abutment surface  36  at right angles to the axial direction A and, at the other end, has an end surface  60 . An axial end area adjoining the drill abutment surface  36  and belonging to a radially inner jacket surface of the stop element  28  bears on the cutting part  14 . An outer jacket surface of the stop element  28  lying on a circular cylinder jacket surface forms a guide surface  37  and can cooperate with the mating guide surface  106  (see  FIG. 5 ) of the drill jig  100 . If appropriate, to make it easier to insert the stop element  28  into the drill jig  100 , the stop element  28  has, adjacent to the drill abutment surface  36 , a jacket surface area formed by a truncated cone surface.  
      Starting from the end surface  60 , the stop element  28  has six recesses  62  which extend in the axial direction A along approximately two thirds of the length of the stop element  28  and open in the direction of the end face surface  60 , as a result of which three spring elements  64  designed as resilient arms are formed on the stop element  28 . The spring elements  64  are arranged at regular intervals from one another in the circumferential direction. At its free end area, each spring element  64  has an engagement element  58  which is intended to engage in one of the fastening recesses  30 . Each engagement element  58  has a counter-abutment surface  35  which is exposed in the direction of the receiving end area  20  and which is intended to cooperate with the abutment surface  32  by which the fastening recess  30  is limited.  
      A mating clamp surface  48 , directed away from the counter-abutment surface  35  on the engagement element  58  in the axial direction A, is intended to cooperate with one of the clamp surfaces  42  of the fastening recesses  30  and, upon engagement of the engagement element  58  in one of the fastening recesses  30 , bears on the clamp surface  42  of the respective fastening recess  30 . By the cooperation between the mating clamp surfaces  48  and the clamp surface  42 , and by the force of the spring elements  64 , the counter-abutment surfaces  35  are pressed so as to bear on the abutment surface  32 . The counter-abutment surfaces  35  are likewise at right angles to the axial direction A.  
      The dental drill device  10  according to the third illustrative embodiment is used in the following way.  
      The stop element  28  is fitted onto the dental drill  12  from the direction of the receiving end area  20 , with the drill abutment surface  36  to the front. As soon as the mating clamp surfaces  48  of the engagement elements  58  come to bear on the shank part  18 , the spring elements  64  are deflected in the radial direction, as a result of which the counter-abutment surfaces  35  are forced by elastic deflection into a position that is not at right angles to the axial direction A. As soon as the radially inward end edges of the counter-abutment surfaces  35  have passed the abutment surface  32 , the spring elements  64  shoot into a parallel orientation to the axial direction A, as a result of which the engagement elements  58  are brought into engagement with the fastening recesses  30 , and the counter-abutment surfaces  35  are brought into the position at right angles to the axial direction A. By the spring force of the spring elements  64  and by cooperation between the clamp surface  42  and the mating clamp surfaces  48 , the counter-abutment surfaces  35  are pressed into contact against the abutment surface  32 . By means of the force fit acting between the abutment surface  32  and the counter-abutment surfaces  35 , the stop element  28  is held in one of the fastening recesses  30  and is not displaceable in the direction of the receiving end area  20 .  
      By applying a minimum force oriented in the direction of the drill end  16 , the stop element  28  can be displaced in the direction of the drill end  16 , so that the engagement elements  58  of the stop element  28  can be brought into the fastening recess  30  lying next in the direction of the drill end  16 . By means of the ramp-like clamp surface  42  and the mating clamp surfaces  48 , the spring elements  64  are deflected in the radial direction upon a movement of the stop element  28  toward the drill end  16 . The engagement elements  58  engage in the next fastening recess  30  in the manner described above. If no further fastening recess  30  is present, the stop element  28  can be drawn off via the cutting part  14 . The engagement elements  58  are in this case guided in the chip grooves of the cutting part  14 .  
      If the engagement elements  58  are engaged in one of the fastening recesses  30 , the stop element  28  of the third illustrative embodiment too is held on the dental drill  12  by a form-fit connection so as to be non-displaceable in the direction of the free end area  20 . In this way, an inadvertent increase in the distance of the drill abutment surface  36  from the drill end  16  is avoided. By contrast, the distance of the drill abutment surface  36  from the drill end  16  can be reduced by displacing the stop element  28  in the direction of the drill end  16 .  
      A fourth illustrative embodiment of a dental drill device according to the invention is shown in  FIG. 4   a ,  FIG. 4   b ,  FIG. 4   c  and  FIG. 4   d.    
      This dental drill device  10  comprises a dental drill  12  of analogous design to the dental drill of the first illustrative embodiment, the dental drill  12  of the fourth illustrative embodiment having no holder portion. A drill shank  70  is formed integrally on the cutting part  14  of the dental drill  12 , and this drill shank  70  again comprises, on an exposed assembly end area  76 , an axial securing means  24 ′ and a means  22  for preventing rotation, analogously to the dental drill of the first illustrative embodiment. The drill shank  70  is shorter than the shank part of the dental drill of the first illustrative embodiment. The assembly end area  76  is intended to be received in a corresponding receiving recess  72  of an extension element  74 .  
      The extension element  74  comprises a shank part  18  with one radial step. The area of the stepped shank part  18  that has a greater diameter forms a holder portion  26 . Within the holder portion  26 , the shank part  18  is provided with the receiving recess  72 . Lying at the opposite end from the receiving recess  72 , the shank part  18  has a receiving end area  20 . The receiving end area  20  is intended to be received in a drill holder device. For this purpose, the receiving end area  20  has an axial securing means  24 ′ and a means  22  preventing rotation, which are designed analogously to the axial securing means  22  and the means  24 ′ preventing rotation of the dental drill  12 . A sleeve-shaped stop element  28  can be fitted onto the holder portion  26 .  
      In the text below, the dental drill device  10  is described in a state in which the assembly end area  76  of the dental drill  12  is held in the receiving recess  72  by a spring element, preferably a spring arm  77 , that engages in the axial securing means  24 ′. Moreover, the stop element  28  is pushed onto the holder portion  26  from the direction of the drill end  16 .  
      The holder portion  26  principally has a radially outer, circular-cylindrical jacket surface which serves as a guide surface for a sleeve-shaped stop element  28 . The external diameter of the holder portion  26  is chosen slightly greater than the drill diameter of the dental drill  12 . A channel-like structure formed by grooves is let into the holder portion  26 . A guide groove  78  extends in the axial direction A of the dental drill  12  and is open in the direction of the drill end  16 . Three fastening recesses  30  designed as circumferential grooves  80  run in the circumferential direction from the guide groove  78 , all of them in the same direction.  
      The circumferential grooves  80  all have the same length and have a locking recess  82  at their end areas remote from the guide groove  78  in the circumferential direction. The cross sections of the guide grooves  78  (in the circumferential direction) and those of the circumferential grooves  80  (in the axial direction) are substantially the same and, adjacent to the jacket surface, have side walls  83  extending parallel to the radial direction. A groove base of the guide groove  78  and also of the circumferential grooves  80  is of a cylindrical design. The locking recesses  82  are made deeper in the radial direction than the remaining area of the fastening recesses  30 , the side walls  83  being continued in the radial direction and the groove base thus being lowered farther in the area of the fastening recess  30 .  
      Each fastening recess  30  has an abutment surface  32  which is at least approximately at right angles to the axial direction A and is formed by a portion of the side wall  83  that limits the fastening recess in the direction of the receiving end area  20 .  
      The stop element  28  that can be fitted onto the holder area  26  has a sleeve-shaped design. In the axial direction A, the stop element  28  has, at one end toward the drill end  16 , a front drill abutment surface  36  lying at right angles to the axial direction A, and, at the other end, it has an end face  60 . An outer jacket surface of the stop element  28  lying on a circular-cylindrical jacket surface forms a guide surface  37 .  
      When using a drill jig  100 , described in more detail in connection with  FIG. 5 , the guide surface  37  cooperates with a mating guide surface  106  of the drill jig  100 .  
      A spring element  84  arranged in the circumferential direction and designed as a resilient finger is formed by a slit-like recess  86  on the stop element  28 . The recess  86  starts from the end face  60  and extends first in the axial direction A and then in the circumferential direction.  
      Secured at the free end area of the spring element  84  there is a pin-like engagement element  58  which protrudes radially inward and which is intended to engage in the grooves  78 ,  80 . Directly adjacent to a radially inward surface of the spring element  84 , the engagement element  58  has a circular-cylindrical portion and, adjoining the latter in the radial direction, a hemispherical portion which is intended to cooperate with one of the locking recesses  82 . The circular-cylindrical portion forms a counter-abutment surface  35  which is intended to cooperate with one of the abutment surfaces  32 . The diameter of the hemispherical portion and of the cylindrical portion is chosen such that the engagement element  58  in the fastening recess  30  has little play in the axial direction A.  
      The dental drill device  10  according to the fourth illustrative embodiment is used in the following way.  
      The dental drill  12  is inserted, with the assembly area  76  leading, into the receiving recess  72  of the extension element  74 , as a result of which the spring arm  77  comes into engagement into the axial securing means  24 ′ of the dental drill  12 .  
      With the end face  60  leading, the stop element  28  is fitted onto the dental drill  12  from the direction of the drill end  16  and is moved in the axial direction A toward the holder portion  26 . When fitting the stop element onto the holder portion  26 , care must be taken to ensure that the engagement element  58  is aligned with the guide groove  78 . When the stop element  28  is moved farther, the engagement element  58  is guided in the guide groove  78 .  
      A radial deflection of the spring arm  77  is made impossible by the stop element  28  being pushed on, as a result of which the dental drill  12  is secured in the receiving recess  72  of the extension element  74 .  
      Once the engagement element  58  has been brought into alignment with the desired fastening recess  30  by displacement of the stop element  28  in the axial direction A, the stop element can be turned in the circumferential direction, as a result of which the engagement element  58  engages in the locking recess  82  of the fastening recess  30 .  
      When the engagement element  58  engages in one of the fastening recesses  30 , the stop element  28  is secured in the axial direction A, in particular in the direction of the receiving end area  20  of the cylinder shank  18 , by a form fit connection between the abutment surface  32  and the counter-abutment surface  35 . When the engagement element  58  engages in one of the locking recesses  83 , the stop element  28  is held secure against turning in the circumferential direction by means of a force fit.  
      The desired maximum drilling depth of the dental drill device  10  according to the fourth illustrative embodiment is once again defined by the distance of the drill abutment surface  36  from the drill end  16 .  
      The maximum drilling depth can once again be modified in a very simple manner. To do so, the stop element  28  is first turned in the circumferential direction and in the direction of the guide groove  78  so that, by overcoming the force-fit connection, the engagement element  58  is moved out of the locking recess  82  in which said engagement element  58  engages. The stop element  28  is then moved in the axial direction A, the engagement element  58  is aligned with another fastening recess  30  and, by turning the stop element  28 , the engagement element  58  comes into engagement in the fastening recess  30 .  
      It is likewise possible for the stop element  28  to be pre-fitted on the extension element  74  in the holder portion  26 . In this case, the spring arm  77  has such great freedom of movement relative to the stop element  28  that, when the assembly area  76  of the dental drill  12  is inserted into the receiving opening  72 , the spring arm  77  is able to deflect in order to lock in the axial securing means  24 ′.  
      In the illustrative embodiments described above, the desired drilling depth is defined by the distance of the drill abutment surface  36  from the drill end  16 .  
      When the desired drilling depth is reached upon drilling a hole in a jawbone, the abutment surface comes to rest on the jawbone or on the gum surrounding the jawbone.  
       FIG. 5  shows a further configuration of the dental drill device according to the second illustrative embodiment. This configuration comprises a drill jig  100  which guides the dental drill  12  with the stop element  28  arranged thereon.  
      The drill jig  100  is intended to be secured in a fixed position relative to the oral cavity of a patient. The drill jig  100  is preferably produced from an impression of the upper jaw or lower jaw. The drill jig  100  has a drill jig plate  102  with a fixed drill jig sleeve  104  positioned therein. A radially inward surface of the drill jig sleeve  104  forms a mating guide surface  106  for the guide surface  37  of the stop element  28 . At an axial end area, the drill jig sleeve  104  has an annular shoulder  108  that projects radially inward. The shoulder  108  forms a counter-abutment for the drill abutment surface  36  of the stop element  28 .  
      The dental drill device  10  shown in  FIG. 5  is used in the following way.  
      For treating a patient, the drill jig  100  is arranged in the patient&#39;s oral cavity, or in direct proximity to it, and fixed in position relative to the oral cavity. The shoulder  108  of the drill jig  100  is directed toward the hole that is to be drilled, that is to say toward the jawbone. The desired drilling depth is defined by means of the stop element  28  on the dental drill  12 , by fitting the stop element onto one of the thickened areas  40 . In this illustrative embodiment, the desired maximum drilling depth is determined by the distance of the drill abutment surface  36  from the shoulder  108 . The position and direction of the drilled hole are defined by the insertion of the stop element into the recess formed by the drill sleeve  104  in the drill jig, and by the cooperation between the guide surface  37  of the stop element  28  and the counter-abutment surface  106 .  
      Consequently, by means of the dental drill device  10  according to  FIG. 5 , it is possible, in a very simple way, to drill a hole at the desired position, in the desired direction and to the desired depth. An obstructed view during the drilling operation, caused by material from the drilled hole, has no effect on the precision of the hole that is to be drilled.  
      It is likewise possible to do without the shoulder  108  on the drill jig  100 . Consequently, the maximum drilling depth is again set by the distance of the drill abutment surface  36  from the drill end  16 . When the maximum drilling depth is reached, the drill abutment surface  36  rests on the jawbone or gum.  
      Of course, the use of the drill jig  100  is not limited to the dental drill according to the second illustrative embodiment. A dental drill according to the third illustrative embodiment, or a dental drill in combination with an extension element according to the fourth illustrative embodiment, can likewise be used with the drill jig.  
      If a hole is drilled without using the drill jig, the radial guide surface  37  of the third and fourth illustrative embodiments can still make guiding easier during drilling, by means of the guide surface  37  being rested laterally on an element.  
      The number of fastening recesses in all the illustrative embodiments can of course be varied almost in any desired extent and is not limited to the numbers cited in the illustrative embodiments.  
      Likewise, the first three illustrative embodiments, which do not have an extension element, can in fact be realized with an extension element, analogously to the fourth illustrative embodiment. The holder portion is then not arranged on the dental drill, but instead on the extension element. Consequently, the stop element is held not on the dental drill, but instead on the extension element.  
      The fourth illustrative embodiment can likewise be realized without an extension element. The holder portion is then arranged on the shank part of the dental drill, analogously to the dental drills of the first to third illustrative embodiments. The stop element is consequently held on the dental drill. The necessary adjustments are once again evident to a person skilled in the art.