Sonic dental tool
US 3124878 A
Description (OCR text may contain errors)
March 17, 1964 A. G. BoD|N|:,`JR., ETAL SONIC DENTAL TOOL 'Filed April 12, 1961 United States Patent O 3,124,378 SNlQ DENTAL T001'.
Albert G. Eddine, Jr., Sherman Oaks, Calif. (7377 Woodley Ave., Van Nuys, Calif.), and Ernest A. von Seggern, Burbank, Calif.; said Von Seggern assignor to said Bottine nnen Apr. i2, 19er, ser. No. masia s Ciaims. (ci. .a2- 26) This invention relates generally to sonic vibratory dental tools, applicable to such purposes as tooth drilling, scaling, amalgam and gold foil compaction, etc.
Electrically powered resonant vibratory or sonic drills are known, but have certain shortcomings, such as inherent danger to the patient, and the difficulty of maintaining resonant operation with variations in loading of the tool by the work A general object of the invention is the provision of an improved sonic dental tool, using a mechanical oscillator, preferably fluid driven, and having certain important advantages, such as improved working characteristics, adequate power for all purposes, safety, ease of operation and control by the dentist, ability to operate at resonance notwithstanding variations in loading by the work, and all around practicability.
The tool provided by the invention has a bar Which is capable of lateral elastic wave transmission. That is to say, the bar is subject to lateral elastic bending through a limited range, and is capable of elastic bending vibration. One end of this bar carries a dental tip, which is turned or bent, in the plane of the elastic bending vibration, i.e., of the lateral vibration pattern, through an elfective angle which may approach 90 and presents a working extremity facing away from the longitudinal axis of the bar.
At the other end of the bar is a mechanical oscillator or vibration generator adapted for creating and applying to that end of the bar a rotating force vector which rotates in the plane of the lateral or bending vibration of the bar, and about an axis at right angles to said plane and to the longitudinal axis of the bar. Preferably, this oscillator is of a fluid driven type, many examples o-f which are disclosed in United States Patent No. 2,960,314. "ille oscillator is driven at a speed corresponding approximately to a lateral resonant frequency of the bar, i.e., to a frequency at which the bar vibrates primarily in an elastic bending mode. An idealized oase, which is merely illustrative, and not restrictive on the invention, is the full wave length lateral bending mode, wherein the bar has two standing wave nodes spaced a halfwave length apart, with each node at a quarter wave length distance from the corresponding end of the bar. The dental tip actually comprises the working end portion of the bar, and its extremity is at a velocity antinode of the standing wave. The oscillator is at a velocity antinode at the opposite end of the bar.
The tool as thus briefly described forms a closely coupled resonant acoustic circuit, having a vibratory output means (the dental tip) which, in service, is either unloaded, or loaded, to a variable extent, and by loads of differing impedance characteristics, such that the resonant frequency of the circuit varies, in service, to an appreciable degree. The impedance loading of the tool varies with the class of service, and may be predominantly reactive, or predominantly resistive. In the illustrative tooth scaling or cleaning application, the impedance loading is predominantly resistive.
It is a characteristic of a bar vibrating elastically at resonance in a lateral bending mode that the resonant performance is highly sensitive to the resistive loading, and the resonant frequency tends to shift materially with such loading. In particular, the node nearest the tip shifts ice toward the tip with increase in resistive loading, and the resonant frequency drops perceptibly. However, instead of going out of resonance, the present tool continues to operate at resonance, but at a lower resonant frequency. This performance is characteristic of the mechanical oscillator employed in combination with the bar, which automatically tends to operate on the low side of the resonance curve, below the frequency for peak resonance. With increased resistive loading on the tool, the frequency drops, but resonance is preserved. In accordance with the disclosure in the aforementioned Patent No. 2,960,314, the oscillator is automatically constrained to operate on the low side of the resonance curve, below the frequency for peak resonance, and this continues to be the case even if the frequency for peak resonance is shifted downward by increase in loading.
It has been mentioned above that the oscillator` which vibrates the bar creates and applies to the driven end of the bar a rotating force vector which turns in the plane of the desired lateral bending vibration of the bar. The lateral resonant frequency of the bar is lower than the frequency for longitudinal resonant vibration, so that as the oscillator is brought up to speed, the lateral bending mode is excited first, as the speed of the oscillator approximates the lateral resonant frequency of the bar. At this drive frequency, operation is substantially under the resonant frequency for longitudinal or compressional vibration. However, in View of the fact that the rotating force vector applied to the bar has a component of force longitudinal of the bar, the bar is also set into a certain degree of longitudinal or compressional vibration, i.e., an elastic vibration along the longitudinal axis. This longitudinal vibration results in a small amplitude longitudinal vibration of the dental tip (longitudinally of the bar) and in a cyclic stress in the bend region of the laterally turned tip, with the consequence that the dental tip does not merely vibrate generally laterally of the longitudinal axis of the bar (by reason of the lateral vibration of the bar itself), but vibrates also to a small but useful extent in a general direction longitudinal of the bar. This longitudinal component of vibration is attributable to two factors, rst, longitudinal vibration of the bar, and second, cyclic elastic tiexure in the bend region of the tip. The working extremity of the tip therefore vibrates with a primary component of motion generally laterally of the longitudinal axis of the bar, and with a lesser component of motion generally longitudinally of the bar. The compound motion so obtained is very effective in dental operations.
The invention will be better understood from the following detailed description of a present illustrative embodiment thereof, reference for this purpose being had to the accompanying drawings, in which:
FIG. 1 is a side view of the completely assembled tool, with a partial section showing the air hose connection.
FG. 2 is a section taken along the lines 2 2 of FIG. l, showing the air inlet and outlet passages, and Water passage.
FIG. 3 is a view taken along the line 3--3 of FIG. 2 showing the tool with half of the main case removed with the end caps and chuck in section and the internal vibrating member in vertical elevation.
FIG. 4 is a section taken along the line 4-4 of FIG. 3 showing the construction of the oscillator.
FIG. 5 is a horizontal section of the tool taken along the line 5--5 of FIG. 3, and
FIG. 6 is a vertical section taken along the line 6-6 of FIG. 4 showing the oscillator rotor and the pin about which it gyrates.
The tool, as shown in FIG. ll, is comprised of a central housing 20 and 2l made in t-wo halves split along the central plane of the tool, Kand a screw cap 22 at the front and a screwed on sleeve 23 at the rear which hold the two halves together. Enclosed in the two halves 2% and 21 is an elastic bar 24 which has an oscillator 25 at one end, and a tool chuck 26 at the other end which extends outside of the housing. A tool tip 27 is held rigidly by the chuck. This tip 27 has a straight shank 27a, with which merges a curved, hookdike portion 271:, terminating in a working end or extremity which faces away from the longitudinal axis of the bar. Preferably, and as shown, the tip is thereby given an effective turn or lateral bend approaching 90 relative to the longitudinal axis of the bar. In the speciiic case shown, the angle is somewhat under 90, which is presently preferred, but it will be understood that considerable latitude in this respect is allowable depending upon the specific use -to which the tool is to be applied. Broadly, the tip may be regarded as having an angle bend, or as projecting laterally from the bar.
The bar 24 is supported in the housing by an O ring 2S held in place by the screw cap 22, adjacent the chuck, and by a pair of O rings 2.9 and 30 on the sides of the bar near the oscillator 25.
Extending from the rear of the split housing are a pair of semi-circular channels 35 and 36 which together form a tube onto which the air hose 37 is attached, the attachment point being inside the rear sleeve 23. Also inside the sleeve is the end of an optional water tube 33, onto which a water hose 39 is attached. The Water t-ube extends through the housing Ztl-21, and connects by means of a short plastic tube 40 to a short tube 41 joined to the tip 27. This latter is bent so that water issuing therefrom is directed toward the end 42 of the tip 27. ln many instances this water feature is not needed.
The chuck 26 is of the conventional collet type having a threaded cap 43 which forces a split and tapered sleeve 44 against the shank of the tool tip 27 and holds it tirmily in the bar 24.
The oscillator 25 consists of a rotor 45 which is mounted loosely on a pin 50. The pin is supported by a pair of side plates 51 and 52 and these in turn are held in place in the bar 24 by a pair of threaded discs 53 and 54 which screw into the sides `of the bar, which is hollowed out at the end to accommodate the rotor. The side plates are held in accurate parallel alignment and separation by resting on annular Ifaces 55-56 in the bar and are rigidly held from moving laterally by the tapered seats 57-53 in the discs 53-54. Four nozzles, indicated by numeral 59, are drilled in each side plate, extending from the annular grooves 60-61 into the rotor race 52. These nozdfles are drilled, as shown in FIG. 4, so that air, entering the nozzles from the annular grooves Gil-61, simultaneously flows into the race in the same direction. FIG. 6 shows the radial symmetry of the nozzles in one side plate, whereby the entering air is directed to tlow in a circulating path around the central pin Sil.
The rotor 45 has a set of nine varies 63 on each side of its central disc 64, which are arranged to intercept the air entering the race from the nozzle and receive a driving vforce therefrom.
In operation, air from a source of pressure is supplied through the hose 39 and enters the passage formed by channels 35-36 as shown by the arrow 65. The passage is divided into two branches 70-71 (FIG. 5) which in turn connect with a pair of drilled holes '72--73 (FiG. 3), which terminate in short opening 74-75 in the inner wall of the housing -21. The entering air flows through these passages and enters the bar 24 via ports 24a at the points Where the bar is supported by O rings 29-30. These rings are seated in shallow matching grooves 76--77 in the housing and bar, and both support the bar in the housing and seal the air passage, Within the bar the air flows via bore 74h, as shown by' arrows 78, toward and into lthe annular spaces eil-6l between the side plates 51-52 and the respective threaded discs S15-54. There the air enters the nozzles 59 and is directed against the vanes 63 of rotor 45. After impinging on the varies the air escapes radially outward and leaves the bar `24 through the ports 81, 82, and 83 as shown by arrows S4. A pair of openings in each of the housing members Z0 and 21 allows the air to escape from the cavity in the housing enclosing the bar, and pass out to the atmosphere through the sleeve 23.
The rotor 4S is provided with a hole S6 through its center which is somewhat larger in diameter than that of the pin 50. As a consequence where the rotor rests on the pin as shown in FIG. 6, the c.g. 87 of the rotor is off-set slightly from the center line '38 of the pin 50. When rotated by the air stream the rotor does not spin on the shaft like `a wheel with a plain bearing, but rolls on the shaft without appreciable slippage, and gyrates. The c.g. 87 moves in a circular path around the center S3 of the pin 50 and the rotor exerts a centrifugal force on the pin in the direction of an :arrow 89 drawn from the center line 88 of the pin through the c g. S7 of the rotor. This force vector rotates about the pin as the rotor gyrates about it.
The relation between the rotation of the force vector or the movement of the point of contact between the rotor and pin, and the rotation of the rotor about its own center is defined as the gyration ratio of the rotor, and is expressed by the formula This number may vary, from values of from 2 to 12, but is usually taken at about 6, i.e., the force vector rotates six times `faster than the rotor itself. In practice, the force vector rotates about 7000 times per second while the air driven rotor turns at 7000/ 6 or 1166 r.p.s.
'Ilhe centrifugal force, or rotating force vector, exerted by the rotor on the pin is transmitted to the bar since the pin is rigidly xed in the bar. When a periodically varying force (in this instance, a constant force varying periodically in its direction) is exerted on an elastic member (the steel bar) the bar is caused to vibrate elastically at the frequency of the varying force. A bar has a number of possible modes in which it can vibrate, but will vibrate primarily in those modes whose resonant frcquenoies are excited directly by the varying force.
The bar 24 is excited in the plane of the rotor and can therefore vibrate either in a bending lateral mode in the plane of the rotating force vector, or in a longitudinal compressional mode. The lateral mode has the lower resonance frequency, however, and will be excited first. The lowest lateral frequency is the fundamental mode, in which the bar has two nodes, with a 1/2 Wave length between the nodes and 1A wave length on each end beyond the nodes. In order for a bar to vibrate most freely `it should be supported at the nodes and the bar 24 is accordingly supported at its nodes bythe O rings 29-30 Vand 28. The tip 27 is rigidly held to the bar, being oriented such that the plane of its lateral bend coincides with the plane of lateral vibration; and the tip is a part of the vibrating system. Hence the distance from ring 28 to the end of tip 27 is 1/4 wave length and similarly yfrom rings 29-30 to the oscillator 25.
The frequency' at which the force vector rotates is directly related to the air pressure in hose 37. With increasing pressure (usually about 15-20 p.s.i.) the frequency of the rotating force vector reaches the resonant frequency of the lateral bar in its fundamental mode (about 7000 c.p.s. for the bar shown) and the amplitude of vibration increases rapidly. This causes the tip 27 at the end of the bar to vibrate as shown by double headed arrow a-b with an amplitude of about .005 inch.
At the same time, owing to non-resonant longitudinal vibration in the bar, and to elastic ilexure of the lateraliy turned tip owing to longitudinal vibration of the bar, the extremity of the tip has a small but useful component of vibration longitudinally of the bar, as represented by the short double headed arrow c-d. As mentioned hereinabove, the compound motion so attained is useful in dental operations.
It is to be understood that the drawings and description are merely illustrative of one present embodiment of the invention, and that various ohanges in design, structure and arrangement may be made Without departing lfrom the spirit and scope of the invention as dened in the appended claims.
1. In a Ivibratory dental tool, the combination of: a laterally elastically vibratory bar having a longitudinal axis, a vibration generating means coupled to an end of said bar operable at a frequency for lateral resonant elast-ic vibration 4of said bar, for applying to said bar at said frequency a rotating force vectorwhich turns in the plane of lateral vibration of the bar and turns about an axis `at right angles to said plane and to said longitudinal axis of said bar, and a `dental tip on the opposite end of said bar having a bend in said plane of lateral vibration, said tip terminating in a working extremity facing generallly iaway from the longitudinal :axis o-f the bar.
2. In a vbratory dental tool, the combination olf: a laterally elastically vibratory bar having a longitudinal axis, a vibration generating means coupled to an end of said bar for app-lying to said bar a rotating force vector which turns in the plane of laterali vibration of the bar and turns about an iaxis at night angles to said plane and to said longitudinal axis of said bar, and a dental tip on the opposite end of said bar having a lateral bend in said plane of lateral vibration terminating in a working extremity facing generally away from Ithe ilongitudinal axis of the bar, said generating means including a fluid-driven rotor and means on ysaid first mentioned end of said bar constraining said rotor to gyiation in said plane of lateral vibration, with its center of gravity eccentric to the axis of gyration, `said rotor being iluid-driVable at a rfrequency corresponding to an `elastic resonant lateral vibration `frequency of the bar.
3. In a vibrating dental tooll, the combination of: an elastic laterally' vibratory bar, a vibration generating means coupled to an end of said bar ffor appl-ying to said bar a rotating force vector whioh turns in the piane of lateral Vibration of the bar, and a dental tip on the opposite end of :said bar projecting generally llaterally tof the bar in said plane of lateral vibration, whereby the extremity of said tip vibrates generally laterally .of the .bar 1as a consequence of lateral vibration of the bar and generailly longitudinally of the bar as =a consequence of longitudinal vibration orf the bar, and means ffor driving lsaid generating means at a lateral resonant frequency of the bar, whereby the lateral vibration amplitude of the extremity of the -tip exceeds the iongitudinal vibration amplitude of the extremity of the tip.
References Cited in the file of this patent UNITED STATES PATENTS 1,224,008 Nelson Apr. 24, 1917 2,921,372 Bodine Jan. 19, 1960