Dental curet and sharpening machine system

Abstract: A dental curet (8) and sharpening machine system (50) has been developed for complete mechanical guidance of the instruments during the sharpening procedure. Double-ended dental curets (8) comprising cutting blades (10), shanks (18), and a handle (20) have been designed so that regardless of the instrument's rake angle, the arc center (22) of the toe (16) on the face of the cutting blade which is to be sharpened lies on the longitudinal center axis (24) of the instrument and at a constant distance from reference points (32,34,36,38) on the instrument handle. The sharpening machine comprises a base (60), an electrical motor (52) with a rotating sharpening stone (56), and an instrument guide unit (54). The instrument guide unit can position the blade face of a curet of any rake angle in a horizontal plane with the arc center of the toe on the blade's face coincident with a vertical axis about which the guide unit is swung while the blade edge is engaged with the rotating stone during the cutting procedure. The invention comprises three aspects: 1) the curets (8); 2) the sharpening machine (50); and 3) the method of sharpening the curets.

Description: Background of the Invention Scaling and root planing for the removal of calculus and contaminated root cementum are essential procedures in the treatment of periodontal diseases. For this purpose, dental curets are used for orthogonal cutting of the root surfaces, a method that removes thin chips of contaminated cementum. This root planing procedure dulls the cutting edges of the curets which, for proper cutting action, have to be sharpened at frequent intervals. Up to now, such sharpening has been done as a freehand procedure, with or without guide plates, resulting in edges of inferior sharpness and incorrect edge angles with serious aberrations from the ideal shape of the cutting blade. A variety of dental curets of different shapes are available on the market, but there is not one single set of curets that in a systematic and logical way guides the operator in optical efficiency in the different areas of the oral cavity. The invention provides a dental curet and sharpening machines system that allows both professional and non-professional personnel to sharpen dental curets with the utmost precision. US-A-4 509 268 discloses a dental curet in accordance with the prior art portion of claim 1. This is a conventional dental curet and is disclosed in describing a guide to be used to facilitate sharpening of the dental curet. However, some skill is required to maintain proper alignment during sharpening. The present invention, as defined in claim 1, provides a dental curet which is so-shaped as to facilitate sharpening regardless of the rake angle of the cutting blade. This is achieved by having the centre of the semicircular distal edge portion of the cutting blade lying on the longitudinal axis of the curet handle. With this construction the entire sharpening operation can be achieved by a single rotational movement of the cure about each axis while maintaining a guiding wheel or other sharpening element in contact with the blade of the curet. The curets themselves are later described as being designed to provide a series of instruments with different rake angles in regular increments. The rake angle of each instrument is identified by the handle having a colour code which also serves as a guide for the setting of the sharpening machine. Each instrument has two cutting blades, one at each longitudinal end. The two blades are of the same rake angle but are mirror images of each other in that one is "right-handed" and the other "left-handed". The handles of the later illustrated curets contain reference points that are in a particular relationship to the cutting blades. These reference points are used to locate the instrument in a fixture portion of the sharpening machine. In the particular example of the double-ended curet that is to be illustrated and described, the reference points are advantageously arranged in a symmetrical pattern. Specifically, four reference points are contained in the handle of the double-ended curet, and they may be considered to constitute two pairs. One pair of reference points is nearer to one blade, while the other pair of reference points is nearer to the other blade. This results in the two pairs of reference points being spaced apart from each other along the main longitudinal axis of the instrument. The two reference points of each pair are equidistant from the arc-centre on the face of the nearer blade's semi-circular shaped cutting blade tip. Therefore, the two reference points are also equidistant from the arc centre on the face of the farther semi-circular shaped cutting blade tip. Moreover, the two reference points of each pair are 180° apart about the longitudinal axis of the handle. However, their circumferential locations about the axis are the same so that two of the four reference points, namely one of each pair, lie on one side of the handle while the other two of four reference points, namely the other of each pair, lie on the opposite side of the handle. The longitudinal axis of the instrument passes through the arc centres on the faces of its cutting blades' semi-circular shaped tips. US-A-2 578 309 discloses a machine and sharpening method in accordance with the prior art portions of claims 9 and 8, respectively. While this prior machine enables the holding of a curet in a particular orientation with respect to a grinding wheel, it in general requires different positions and adjustment at different times during sharpening as compared with the machine and method of the invention as defined in claims 9 and 8 where the entire sharpening operation can be carried out in one motion once the dental curet has been mounted in the support structure without intermediate adjustments being required. In the later described machine, a grinding stone, in the form of a wheel, is mounted on the shaft of an electric motor, which is positionable along a guide in the base of the machine. The grinding wheel is disposed at a fixed angle, which guarantees the restoration of a sharp cutting edge of the correct edge angle when the motor is positioned to bring the wheel into contact with the blade, and the fixture is swung in an arc to cause the cutting edge to be passed against the rotating wheel, first at one side of the blade, then along the semi-circular shaped tip, and finally at the other side. The foregoing features, advantages and benefits of the invention, along with additional ones, will be seen in the ensuing description and claims which should be considered in conjunction with the accompanying drawings. The drawings disclose a preferred embodiment of the invention according to the best mode contemplated at the present time in carrying out the invention. BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1A, 1B and 1C are respectively a front elevational view, a top plan view, and a side elevational view of a preferred embodiment of the dental curet and sharpening machine system of the invention. Fig. 1D is an enlarged fragmentary view of a portion of Fig. 1A; Fig. 1E is a fragmentary cross sectional view in the direction of arrows 1E-1E in Fig. 1A; Fig. 1F is an enlarged fragmentary view of a portion of Fig. 1B; and Fig. 1G is an enlarged fragmentary view of a portion of Fig. 1C. Fig. 2A is a view similar to Fig. 1B but showing a different position; Fig. 2B is an enlarged view of a portion of Fig. 2A. Fig. 3A is a longitudinal view of a curet shown by itself. Fig. 3B is an end view of Fig. 3A, and Fig. 3C is an enlarged view of Fig. 3B. Fig. 3D is a fragmentary perspective view of a curet blade. Fig. 3E is an enlarged transverse view taken in the direction of arrows 3E-3E in Fig. 3D. Fig. 3F is a fragmentary view in the same direction as Fig. 3E, but on a reduced scale and illustrating a step in the sharpening procedure. Fig. 4 is a view of three curets with different rake angles. Note that the configuration of the lower shank in the cutting blade is identical for all three instruments. Fig. 5A is a view showing the adjustments of the fixture unit needed to put the three different curets of Fig. 4 in proper positions for the sharpening procedure, and Fig. 5B is a close-up of a portion of Fig. 5A. Figs. 6A, 6B and 6C are fragmentary views illustrating a series of steps in the sharpening procedure for purposes of explanation. Figs. 6D1, 6E1 and 6F1 are close-up views of portions of Figs. 6A, 6B and 6C respectively, and Figs. 6D2, 6E2, and 6F2 are bottom end views of Figs. 6D1, 6E1, and 6F1, respectively. Figs. 6G and 6H are close-up views of other portions of Figs. 6B and 6C. DESCRIPTION OF A PREFERRED EMBODIMENT Curets Fig. 3 shows that the cutting blade 10 of each curet 8 has a flat top surface 12 (the face), a rounded bottom surface 14 (the base), and a circular tip 16 (the toe). A shank 18, which has several bends, connects the blade to the handle 20. The curet is double-ended, i.e. has cutting blades in both ends. When viewed in a working position, each blade is the other's mirror image in that the toe of one blade will point to the left whereas the other will point to the right. The shank can have various configurations, but the arc center 22 of the toe on each blade's face is always located on the longitudinal center axis 24 of the instrument, i.e. the longitudinal center axis of the handle. The configuration of the lower half 18a of the shank is identical for all instruments regardless of the instrument's rake angle, i.e. the angle between the face of the cutting blade and the long axis of the handle. The configuration of the upper half 18b of the shank determines the rake angle of the curet, and a set of curets of different rake angles facilitates access to hard-to-reach sites in the oral cavity. The upper portions of the shanks are designed to provide sets of instruments of different rake angles in regular angular increments, which are indicated by a color code on the instrument handle. Figs. 3F and 4 show three different rake angles. The handle 20 has a circular cross-section interrupted by two opposing flat surfaces 28, 30 along almost its entire length. These flat surfaces are parallel with the side edges of the cutting blade. The handle has four circular conical depressions 32, 34, 36 and 38, which form a symmetrical pattern of reference points for the two blades. Depressions 32, 34 constitute one pair of reference points and depressions 36 and 38 another pair. These four reference points are arranged in the manner described earlier. The four reference points are identical, both in the pattern in which they are arranged relative to the blades and in their specific details, in all curets regardless of the configuration of their shanks, i.e. regardless of rake angle. The junction between the face 12 and the base 14 of the blade constitutes the cutting edge 40. For proper cutting action of the curet, the edge portions 42, 44 along the sides and the end edge portion 46 around the toe must be sharpened at frequent intervals. The grinding is always done on the base surface 14 of the cutting blade, never on the face, for an edge angle of about 80 degrees. It is important to maintain the proper edge angle as well as the shape of the blade, i.e. a circular toe. In order to meet all these requirements, the guide unit of the sharpening machine, to be described in the next section of the text, is designed to provide mechanical guidance for the curets during the sharpening procedure. Sharpening Machine Refer to Figs. 1A-1G, and 2A-2B. The sharpening machine 50 supports two units: the electric motor 52 and the instrument guide unit 54. The electric motor, on the shaft 51 of which is fitted a circular rotating sharpening stone 56, is disposed atop a support block 53 with the shaft at a fixed angle to the horizontal plane in order to achieve the proper edge angle of the curet's cutting blade. The motor and support block can be moved along a straight guide 58 in the base 60 of the machine toward and away from the instrument guide unit 54. It is moved away from the instrument guide unit to facilitate both the placement of the curet in the instrument guide unit before sharpening, and the removal of the curet from the instrument guide unit after sharpening. It is moved toward the instrument guide unit for the sharpening procedure. The instrument guide unit is mounted in a ball bearing 62 housed in the base of the machine which allows the instrument guide unit to rotate in the horizontal plane about a vertical axis 64. The lower portion 66 of the instrument guide unit (the support portion), comprises one horizontal member 68 and one vertical member 70, the latter one fitted with a horizontal shaft 72 and color-coded dial 74 having a series of uniquely colored, pointed markers 75. The upper portion 76 of the instrument guide unit (the fixture portion), rotates around the horizontal shaft 72 of the support portion, has a center line mark 78 in its lower end, and can be locked in fixed positions by means of a wing nut 80. The fixture portion of the instrument guide unit has a lid 82 that swings around two hinges 84, 86 attached to a base 88 of the fixture portion. The opposing surfaces of lid 82 and base 88 each have a groove of semi-circular cross-section along their common longitudinal axis when the lid is closed and secured with a clamp 90, that form a tube that can securely hold and house the curet handle 20 in the fixture portion. Proper placement of the curet is accomplished by conical pins 92, 94, 96, 98 in the lid and base of the fixture unit. The pins are arranged in a pattern matching the pattern of the reference points in the curet's handle. When the lid is clamped in a closed position, the pins fit tightly into the conical depressions 32, 34, 36, 38 in the curet handle. These reference points will guarantee a reproducible placement of the curet so that the arc center of the toe on the face of the blade to be sharpened lies on the center of the horizontal rotation axis of the fixture portion (axis of shaft 72) as well as on the center of the vertical rotation axis of the entire guide unit (axis 64). These integrated design features of the curets and sharpening machine make it possible to place a curet of any rake angle with the face of a cutting blade, which is to be sharpened, in the horizontal plane and with the center of the toe of that blade at the same time being on the rotation axis 64 of the guide unit. This will guarantee that the sharpening procedure will give exactly the same edge angle along the entire perimeter of the cutting blade and that the shape of the cutting blade, i.e. a rounded toe, will be maintained. Each unique marker color corresponds to the color of a curet of a particular rake angle so that, when a given color curet is placed in the fixture and the corresponding marker 75 aligned with marker 78, the face of the blade being sharpened is in the horizontal plane. The electric motor unit contains a circular rod 100 which has a knob 102 at its top end. The rod 100 passes through a hole in the motor support block, and the rod's lower end contains an eccentric 104, which is cooperatively associated with a slot 106 in base 60, and parallel with guide 58. An electro-magnet 110 is housed in the motor support block and a ferrous block 112 is mounted on base 60 for cooperative association with electro-magnet 110. Operation The electric motor 52 with the sharpening stone 56 is moved away (position at Fig. 6A) from the instrument guide unit 54. A curet is clamped in the instrument guide unit, and the fixture portion is rotated around the horizontal shaft 72 in order to position the face 12 of the curet blade in the horizontal plane. The amount of rotation needed is easily determined by the alignment of the mark 78 on the vertical member of the fixture portion with the particular color mark 75 on the dial 74 that matches the color of the curet handle. The rod 100 is pulled up out of the deep section 114 of the slot 106 and the motor with the sharpening stone is moved toward the instrument guide unit, the tip of the rod sliding along the base of the slot, until stopped by the rod hitting the end of the slot 106 (Fig. 6B). At that point, the sharpening stone is very close to, but not in contact with, the curet and the magnet 110 in the motor unit is pulling toward the metal block 112 on the instrument base. Then, the rod is rotated to relieve the rod from the wall in the slot, and the magnet will move the motor toward the instrument guide unit until the sharpening stone is in contact with one side edge of the curet's cutting blade (Fig. 6C). The motor is started and the instrument guide unit is swung 180 degrees to sharpen the edge, first at one of the side edge portions 42, next the toe edge portion 46, and finally the other side edge portion 44. The pull of the magnet provides adequate pressure of the sharpening stone upon the curet during the sharpening procedure. The circuitry is designed so that the power line to the electromagnet is routed through a rheostat, which is mounted between the base and the instrument guide unit. The magnet is supplied with maximum power when the sharpening stone is in contact with the side edges. During the rotation of the instrument guide, when the toe of the curet is in contact with the sharpening stone, less power is let through the rheostat to the electromagnet, which therefore will exert less pull. With proper design, the pressure of the sharpening stone on the curet's blade will be constant per unit length of cutting edge during the entire sharpening procedure. The motor is stopped and moved away from the curet which is then taken out of the instrument guide. Curets with the same rake angle are sharpened in sequence to minimize required adjustments of the fixture portion of the instrument guide unit for the most efficient use of the sharpening machine. Curet Usage Curets are used most efficiently when the instrument handle is parallel with the long axis of the tooth, i.e. when the instrument's rake angle is similar to the actual rake angle relative to the root surface. This mode of instrumentation is feasible in the anterior regions of the oral cavity whereas, when working in the posterior regions, the instrument will be at a considerable angle to the longitudinal axis of the tooth due to interference between the instrument handle and the opposing dental arch. Consequently, instruments of different rake angles are used in different regions of the oral cavity in order to establish the optimal working rake angle for the different curets. However, the shanks on dental curets heretofore available offer no guidance for proper angulation of the instrument relative to the longitudinal axis of the tooth to achieve the optimal working rake angle on the root surface. The innovation of this invention encompasses curets that, regardless of the instrument's rake angle, have an identical configuration of the cutting blade and lower portion of the shank, which should be positioned parallel with the root surface for optimal working rake angle. Heretofore, dental curets have been unavailable in sets of different rake angles in regular increments and there have been no indicators on the instruments giving the actual rake angle. Furthermore, the usually complex configuration of the shanks gives little or no guidance in positioning the curets for proper working rake angle on the root surface. This invention presents a new concept in the design of dental curets for their compatibility with a sharpening machine providing complete mechanical guidance during the sharpening of the instruments. CONCLUSION The foregoing disclosure has shown a new and unique curet and sharpening machine system characterized by a system of novel dental curets, a novel method of sharpening dental curets, and a novel sharpening machine for dental curets. It provides a set of dental curets having different rake angles to facilitate scaling and root planing procedures on patients. It provides for the expeditious sharpening of dull curets of the set by a single machine, which assures the consistent restoration of a sharp edge of the correct angle while preserving the shape of the cutting blade. Although Fig. 1A and 1D show nine different settings for nine different rake angles, the particular number of settings and dental curets in the system may be other than this particular number. Fig. 3F illustrates only three different rake angles. Likewise, Fig. 4 shows instruments of three different rake angles and Fig. 5A shows three different settings of the machine corresponding with those three different rake angles of Fig. 4. It is also to be appreciated that the relative proportions illustrated in Fig. 3D are merely representative. For example, the radius of the end edge 46 and the lengths of the side edges 42, 44 are merely representative. It is to be understood that these are merely illustrative of general principles of the invention.

Claims: A dental curet comprising an elongate handle (20) having a central longitudinal axis (24) and a cutting blade at one end of the handle (20), said cutting blade comprising a cutting edge (40) defined by a flat face surface (12) having parallel side edge portions (42, 44) and a generally semi-circular distal end edge portion (46), characterised in that the arc centre (22) of said generally semi-circular distal end edge portion (46) lies on the central longitudinal axis (24) of the handle (20). A dental curet as claimed in claim 1, in which said handle (20) has a generally circular transverse cross-section terminating in parallel side surfaces (28, 30) on opposite sides and wherein respective imaginary planes, which respectively contain said two side edge portions (42, 44) and are parallel to said central longitudinal axis (24), are also parallel to said handle's side surfaces. A dental curet as claimed in claim 1 or 2, in which a second cutting blade is disposed at the other end of the handle (20) and is identical to the cutting blade at the one end of the handle except that it points in the opposite direction from the cutting blade at said one end of the handle. A dental curet as claimed in claim 3, including references points (32,34,36,38) on said handle (20) for said blades, said reference points being disposed in a symmetrical pattern with respect to the arc centre (22) on the face (12) of the generally semi-circular distal end edge portions (46) of the two blades. A dental curet as claimed in any preceding claim, wherein the handle (20) is provided with a colour code corresponding to the rake angle of a blade at the end of the curet. A set of dental curets, each being as claimed in claim 5, and being identical except for the fact that the blades at the ends of the handle (20) of different curets (8) have different rake angles with each handle (20) having a colour code unique to the particular rake angle of the curet. A set of dental curets as claimed in claim 6, in which the blades and lower shanks (18a) of the different curets (20) are identical and the different rake angles are achieved by differences in the configurations of the upper portions (18b) of the shanks that join the respective cutting blades and lower shanks (18a) with the respective handles (20). A method of sharpening the edge portion of a cutting blade of a dental curet (8) as claimed in any one of claims 1 to 5, by means of a sharpening machine, the method comprising: placing the curet (8), the blade of which is to be sharpened, in a fixture portion (76) of the machine such that the flat face (12) of the blade is disposed in a predetermined plane relative to the machine and contacting the cutting edge (40) of the cutting blade with a sharpening element (56), characterised in that a side edge portion (40, 42) of the cutting blade is contacted with the sharpening element (56), and in that the fixture portion (76) and the sharpening element (56) are relatively movable about the axis (64) which passes through the arc centre (22) on the face (12) of the semi-circular distal end edge portion (40) of the blade, said axis (64) being perpendicular to the face (12) of the cutting blade at said arc centre (22), to pass one of said side edge portions (42), then said distal end edge portion (46) and then the other said side edge portion across the sharpening element (56) without repositioning the curet (8) in said fixture portion (76) of the machine. A machine for sharpening a dental curet, said machine comprising: a base (60); a sharpening element (56) mounted to said base and disposed to yield a desired angle for a cutting edge (40,42,44) of a blade of said curet; and an instrument guide unit (54) mounted to said base; wherein said instrument guide unit comprises a support portion (66) secured to said base (60), and a fixture portion (76) for holding said curet (8) such that the face (12) of said curet (8) is at an angle and location to be sharpened by said sharpening element (56); wherein the instrument guide unit (54) and the sharpening element (56) are relatively rotatable about a first axis (64), and the fixture portion (76) is rotatably mounted (72) on the support portion (66) about a second axis; characterised in that, for sharpening a curet as claimed in any of claims 1 to 5, the machine is adjustable such that the first axis (64) passes through the arc-centre of the curet tip; that the second axis lies in the plane of the curet face and passes through the arc-centre of the curet tip, such that the face of the curet, having any rake angle, can be positioned orthogonal to the first axis (64); and that the relative movement of the instrument guide unit (54) and the sharpening element (56) about the first axis (64), with the face of the curet perpendicular to the first axis (64), causes the entire cutting edge (40) of the said curet (8) to be sharpened, without repositioning said curet (8) in said fixture portion (76), by passing one side edge portion (42), then a distal end edge portion (46), and then the other side edge portion (44), against the sharpening element (56). A machine according to claim 9, wherein the guide unit has discrete settings (75) corresponding to different positions of rotation of the fixture portion (76) relative to the support portion (66). A machine according to claim 9 or claim 10, wherein the guide unit (54) and the sharpening element (56) can rotate relative to each other approximately 180° around the first axis (64). A machine according to any of claims 9 to 11, wherein the sharpening element is a grinding wheel (56). A machine according to any of claims 9 to 11, wherein the sharpening element comprises a replaceable abrasive material. A machine according to any of claims 9 to 13, wherein the sharpening element (56) and its mounting (53) are displaceable relative to the guide unit (54) or the fixture portion (76), to facilitate the insertion and removal of the curet (8) from the fixture portion. A machine according to any of claims 9 to 14, wherein the fixture portion (76) comprises pins (92,94,96,98) adapted to hold the curet (8) in a specific orientation relative to the fixture portion.

Inventors: SVANBERG GUNNAR K, SVANBERG, GUNNAR K.
Applicants: SVANBERG GUNNAR K, SVANBERG, GUNNAR K.
Application year: 1988
Main classification: B24B3
IPC codes: B24B41, A61C3, B24B3, B24B51, A61C19