US3811432A - Device for operating a pump so as to produce therefrom a pulsating jet of liquid - Google Patents

Abstract

Device for operating a pump so as to produce therefrom a pulsating jet of liquid for feeding to a hand-piece for medical care, in particular for tooth and mouth care, in which the frequency of the liquid impulses, are capable of being modulated while maintaining a nearly constant amplitude of the liquid pressure.

Description

United States Patent [1 1 Moret DEVICE FOR OPERATING A PUMP SO AS TO PRODUCE THEREFROM A PULSATING JET OF LIQUID Michel A. Moret, 39, Peillonnex, K 5791 BOFIFSLSWI'IZBIIQQFI Filed: Jan. 15, 1973 Appl. No.: 323,742

Related US. Application Data Continuation-impart of Ser. No. 100,755, Dec. 22, 1970, abandoned.

Inventor:

[30] Foreign Application Priority Data Dec. 24, 1969 Switzerland 19302/69 Int. Cl A61h 9/00 Field of Search 128/66, 62 A, 230

References Cited UNITED STATES PATENTS 3,547,110 12/1970 Balamuth 128/62 A US. Cl. 128/66 1 [111 3,811,432 [451 May 21, 1974 3,227,158 1/1966 Mattingly 128/66 3,401,690 9/1968 Martin 128/62 UX FOREIGN PATENTS OR APPLICATIONS 1,225,547 2/1960 France 128/62 A Primary Examiner-Lawrence W. Trapp Attorney, Agent, or Firm-Pennie & Edmonds [5 7 ABSTRACT Device for operating a pump so as to producetherefrom a pulsating jet of liquid for feeding to a handpiece for medical care,- in particular for tooth and mouth care, in which the frequency of the liquid impulses, are capable of being modulated while maintaining a nearly constant amplitude of the liquid pressure. I I

15 Claims, 10 Drawing Figures PATENTEDHM 2 1 91.4

SMLU 1 0F 3 QmL & W N

INVENTOR MICHEL A. MORET PATENTEB M21 \974 SHEET 2 OF 3 @w an mm m m m km m H vdE INVENTOR MICHEL A. MORET PATENTEBIAY 21 1914 3.81 1.432

SHEET 3 BF 3 FIG. 7 HQ 8 T FIG. 9 F l G. 10

Ra a 0w PUMP UNIT INVENTOR MICHEL A. MORET DEVICE FOR OPERATING A PUMP SO AS TO PRODUCE THEREFROM A PULSATING JET OF LIQUID This is a continuation, division, of abandoned application Ser. No. 100,755, filed Dec. 22, 1970.

This invention relates to devices for operating a pump so as to produce therefrom a pulsating jet of liquid utilizable, usually by means of a suitable handpiece, for general medical care of the body but more particularly for oral hygiene especially of the teeth and gums.

Certain such devices are already known in which the piston ofa pump is driven by a motor (U. S. Pat. No. 3,536,065) and are intended for use with-hand pieces which can be provided with a (power operated) toothbrush or with ajet diffuser out of which a pulsating liquid jet is ejected by means of the'pump. In these devices the frequency of the pulses of liquid is constant, since the motor which drives the pump has a predetermined and. in general, a constant speed of revolution.

Also, other devices are known which have a handpiece suitable only for cleaning and massaging by means of a pulsating liquid jet. Such a known device (U. S. Pat. No. 3,227,]58) provides jet pulsations ofa constant frequency which is determined by predetermining the speed of rotation of an electric motor as the prime mover. the speed of rotation of the electric motor being variable.

Modern hygiene of the mouth implies two substantially different operations. First the cleaning of dental surfaces, the gingival surfaces, and the interproximal spaces, by the elimination of food deposits and, secondly by a massage and reactivation of the gingival tissues in order to stimulate circulation of the blood, particularly in the capillaries. When using known devices for carrying out these operations by means of a pulsating jet of liquid, such known devices are'subject to the following disadvantages.

IN order to obtain a good cleaning effect, one cannot simply increase the pressure of the jet ofliquid because of the risk of passing the pain threshold or even causing injury to the gums. An efficient cleaning effect with a limited liquid pressure can be obtained only according to the principle of the pneumatic hammer" in order to remove remaining particles of food.

on the other hand, an efficient massage of the gum can be obtained only by means of low frequencies of the pulsating jet of liquid for the following reasons: The gums form a thin cover without muscle over parts of the jaw bone and over the roots of the teeth which thin cover, in consequence, is of very reduced elasticity. In particular, the capillaries of the gums are like an inelastic tube, the diameter of which is only about that of a blood particle (7 I Micron). The gums and the capillaries thereof are submitted to the cleaning and massaging treatment.

The arteries and veins which are located deeper and which are like elastic tubes by comparison with said capilliaries, are not affected directly, but only indirectly by said cleaning and massaging treatment. Because of the reduced elasticity of the gums, the tendency for the retration of the tissue, as a consequence of the successive liquid inpulses, does not occur. Instead, a sufficient period of time must be given in order that the gums are able, between two successive liquid impulses, to go back to their nonnal form. One can only speak of a real massage when the gums are really moved by the pulsating jet of liquid, that is to say, when a changing compression to. decompression is achieved, which can be visually verified by the alternative change from a pink to a white colour.

' Experience has shown that (low) frequencies under 3,000 or even 1,000 impulses/min. are necessary to achieve an efficient massage of the gums. About 70 impulses/min. corresponding to the pulsations of the heart are not sufficient for a' good cleaning, whereas the high frequencies for an optimal cleaning, in particular above 3,000 impulses/min. are not sufficient for the massage of the gums, given the fact that with high frequency impulees, the gums remain pressed all the time when submitted to the liquid jet. I

In order to con ciliate, at least partially, these two opposite requirements for both cleaning and massage of the gums, it has already been proposed (U. S. Pat. No. 3,696,809)-to modulate the pressure amplitude of the impulses of a pulsating liquid jet with a relatively high frequency of impulses for cleaning an'by means ofa re]- atively low modulation frequency for impartinga satisfactory massage.

Although better results are to be obtained with the latter proposed device than with known devices having a constant impulse frequency and a constantpressure amplitude, this solution presents certain drawbacks: Only two different impulse frequencies are effective, namely the basic or support frequency of the liquid impulses and the frequency of the amplitude modulation.

The optimum impulse frequency for massage can vary according to the individual'and, moreover, beneficial specific physiological and neurological effects can be obtained particularly wth several various frequencies. A single fixed massage frequency is thus in general insufficient to obtain a satisfactory result. On the one hand, the-rate of modulation must be high in order to obtain effects, about percent for example,

, whereas, on the other hand, the maximum pressure amplitude must not surpass the pain threshold of the user; these requirements domean that the minimal pressure amplitudes are very low and thus, in the minima ofthe modulations the impulses have no practicaleffect, thus reducing the total rate of efficiency of the device. Moreover, the great fluctuations of amplitude cause disturbing noises and unpleasant vibrations for the user.

According to the invention there is provided a device for operating a pump so as to produce therefrom a pulsating jet of liquid for feeding to a hand-piece for medical care, in particular for tooth and mouth care, in which th frequency of the pump motor movement and thus the frequency of the liquid impulses, are capable of being modulated while maintaining a nearly constant amplitude of the liquid pressure.

Preferred embodiments of the invention are hereinafter described by way of an example, reference being made to the accompanying drawings, in which:

FIG. I is a cross-section of a first embodiment of a device according to the invention; FIG. 2 is a cross-section taken on the line II II of FIG. 1;

FIG. 3 is a more detailed view of that part of FIG. 1

indicated by the arrow III;

FIG. 4 is a cross-section of a second embodiment of a device according to the invention;

FIG. 5 is a cross-section taken on the line V V of FIG. 4;

FIG. 6 is a schematic view of the oscillating mechanism of the internal gear according to a third embodiment of the invention;

FIGS. 7 and 8 are diagrams showing the liquid impulses to be obtained with known devices with the pressure P of liquid impulse plotted against time t, and

FIG. 9 is a diagram which shows, with a device according to the invention, the modulation of the frequency of liquid impulses obtained, and

FIG. 10 shows the overall combination of reservoir, pump unit and jet nozzle connected thereto by a conduit.

According to FIG. 1, a toothed wheel 4 on a shaft 2 of a motor 1 mounted on a frame-24 is turning with a toothed-wheel 5 and a sun-wheel 3 of a planet gear.

Parts of that planet-gear are: the three planet-wheels 8a, 8b, 80, with their shafts 9a, 9b, 9c (FIG. 2,) turning at the periphery of sun-wheel 3, the plate 7 on aside of which the shafts 9a, 9b, 9c of said planet-wheels are fixed and which forms an integral part of ahollow coaxia shaft an i er a seam), s erna tLthed surface of which rneshes with the planetwheels Saftib, 8c freely iimunted on motor shaft z a &ll er bearing 21 being introduced between said shaft and said internal gear. The hollow shaft ltlis freely rotatable on a shaft 11 by means ofbearir gs lg andjj and formsii feffect an extension of the motoi" shaft 2, the bearing 14 being mounted an aperture of a support 13 fixed on frame 24.

At the external extremity of hollow shaft I0, a disc 10a is placed, which supports an eccentric pin 15 which engages freely in a longitudinal slot 17a of a slide 17 7 (FIG. 3) that is fixed on a rod 18 of 'a piston 19 of a water pump 16. The lower free extremity (FIG. 1) of pistonrodlS is introduced in an aperture ofan horizontal arm 13a of a support I3 of the frame 24. With this arrangement. the piston 19 of the pump 16 is given a to-and-fro movement-by the eccentric pin 15 upon rotation of the plate 7. Of course,the length of the longitudinal slot 17a must be at least equal to the diameter of the largest circle described by the pin 15 during a of a-pulsating liquid jet.

Assuming for the moment that internal gear 20 is fixed against rotation and the pin 6'is not provided. when the motor shaft 2 and sun-wheel 3 turn with a constant speed of rotation the plate 7 and disc 10a are driven at areduced constant speed of rotation which depends on the ratio of the diametre of planet-wheels 8a, 8b, 80 to the diameter of sun-wheel 3. Thus the piston I9 is given a reciprocatin movement of a constant frequency which defines the frequency of the impulses delivered by the pump 16. This frequency will be referred to herein as the intermediate impulse frequency.

However, because in reality pin 6 engages slot 22 on internal gear 20, which is freely mounted on shaft 2, the internal gear 20 is given an oscillating movement as toothed wheels 4 and 5 rotate. Consequently the speed of rotation of plate 7 is regularly increased and decreased and the impulses delivered by pump 16 will vary between a minimum and a maximum impulse frequency. I

In this way, a modulation of the impulse frequency is achieved. The limits between which the impulse frequency changes during a period of modulation, in other words the variation of frequency as an average between the minimum and the maximum impulse frequency, correspond to the amplitude of the impulse frequency and depends, in addition to the number of revolutions to the toothed-wheel 5, on the eccentricity of pin 6 in relation to the axis of rotation of toothed-wheel 5, and the distance between the pin 6 and the axis of rotation of internal gear 20. Given the fact that this last distance is different for both half oscillations of internal gear 20, as a result, the modulation of the frequency occurs in a slighty asymetric way in relation to the intermediate impulse frequency.

The throw or amplitude of the piston 19 remains constantduring such modulation, so that the maximum pressure of each liquid impulse, in other words the pressure amplitude of each liquid impulse, remains constant too, when the outflow aperture of the pump or jet diffuser is sufficiently small in comparison with the cross-section of the piston 19 or pump reservoir.

With reference to the embodiment of FIGS. 4 and 5 all numerals having a prime in FIGS. 4 and 5, refer to the same parts as in FIGSql and 2. in FIGS. 4 and 5, the plate 37 of the planet gear, whichsupports the shafts of the three planet wheels 38a, 3811, 380, is fixed on the motor shaft 2, whereas the sun-wheel 33 is placed on a separate shaft 40 coaxial with motor shaft 2', said shaft 40 being rotatably mounted in an aperture in support 43 fixed to the frame 24' and having at its outer extremity a disc 40a which supports the eccentric pin 15' in order to drive the piston 19' of pump 16.

A bifurcated member having parallel arms 53a and 53b is pivotable about pin 54 secured in a protrusion 55 of the frame 24. Engaging in a longitudinal slot 52 formed by said parallel arms is the eccentric pin 6' mounted on toothed wheel 5 and eccentric pin 51' mounted on internal gear 50. With the arrangement of this embodiment, revolving of the toothed-wheel 5 effects an oscillating movement of the internal gear 50, the assymmetry-of such oscillating movement being highly reduced in comparison with the example of FIGS. 1 and 2. When the distance between the pivot axis of said bifurcated member and the axis of rotation of toothed-wheel S is large in comparison with the eccentricity of pin 6, that is to say compared with the radial distance of the pin -6' from the-turning axis'of toothed-wheel 5, the form and speed of bothhalf oscillations of the bifurcated member are about the same during a revolution of toothed-wheel 5, which in turn leads to an almost symmetric modulation of the impulse frequency. Thus the direction and' speed of reduction of frequency in comparison to the average value of the impulse frequency are approximately equal to the direction and speed of increase in frequency in comparison to this intermediate value (see FIG. 9).

The bifurcated member pivoted on the frame 24 according to the embodiment of FIGS. 4 and 5 can be also used in a device according to FIGS. 1 and 2 in which the sunwheel shaft is the inpt shaft and the plate(7) shaft is the output shaft. Also the arrangement of FIGS. 1 and 2 including the longitudinal slot 22 in the internal gear which slot is engaged by the pin 6 of toothed-wheel 5, can be incorporated in an embodiment according to FIGS. 4 and 5, the plate wherein the plate 37 shaft is the input shaft and the sunwheel shaft 40 is the output shaft. In a third embodiment according to FIG. 6, the oscillating movement of the internal gear 60 is imparted by means of a wheel 61 driven by the motor shaft, both wheels being connected with each other by a rod 62 which is pivotally connected to each such wheel a an eccentric point thereof as shown. This arrangement can be dimensioned in such a way that the asymmetry of the oscillation amplitudes of internal gear 60 and thus the asymmetry of the modulation of the frequency are most reduced.

A numerical example, according to FIGS. 4 and 5, will be explained in detail: Suppose that diameter of planet- wheels 38a, 38b, 38:" is equal to that of sunwheel 33 and that the motor rotates at 750 revolutions/minute. The ratio between the number of revolutions of plate 37 and sunwheel being, in that case, I :4, the intermediate number of revolutions of the sunwheel 30 driving the piston (with a fixed internal gear 50) is thus 3,000 revolutions /minute and, therefore the intermediate impulse frequency is 3,000 impulses minute. In order to obtains a favourable modulation frequency of, for example 10 percent of the intermediate impulse frequency, in other'words 300 periods of frequency modification per minute, the reduction between toothed-wheel 4' and toothedwheel 5' is in that case I 0,4. By means ofan appropriate choice of the length of members 53a, and'53h, as

well as of the eccentricities of pins 6' and'SI, the modification of the impulse frequency can be achieved at the rate of 300 times a minute between a minimum impulse fequency of about 2,000 impulses per minute and a maximum impulse frequency of about 4,000 impulses per minute. That is, the amplitude of the impulse frequency varies between the intermediate impulse frequency 50 percent and the intermediate impulse frequency-50 percent.

When the pulsated liquid jet for the treatment of teeth and gums is used, preferably high impulse frequencies are chosen for efficient cleaning. On the other hand, lower impulse frequencies are preferred when it is desired to impart a particularly good massage effect to the gums and to stimulate at the same time the blood circulation in the tissue of the gums.

In general, the device, according to the invention, can be dimensioned in such a way that the impulse fre quency varies between a minimum of value of 600 to 2,500 impulses minute and a maximum value of 3,500v to 5,000 impulses minute and the number of periods of frequency modification between 70 and 600, preferably between 200 and 400 per minute. When advanta geously, the intermediate impulse frequency is situated between 2,500 and 3,500 impulses minute, preferably at 3,000 impulses min., the modification of the impulse frequency can be at least i 20 percent of the intermediate impulse frequency and the number of the periods of the frequency modificaton between 2 percent and 25 percent, preferably between 6 percent and 12 percent, of the intermediate impulse frequency. In addition, the user can adjust the maximum pressure of liquid impulses with a pressure valve according to his personal need.

The invention is not limited to the device described with a planet gear system, but can be extended to other, mechanic, electric, electronic or hydraulic systems for the frequency modulaton; however, the preferred use of a planet gear system should have cost-saving advantages compared with other solutions.

With the use of a planet gear system as described, the internal gear need not necessarily be driven by a toothed wheel gear but other devices are possible with which the internal gear can be give an oscillating turn-' ing movement.

The pump can also be constructed differently and, for example, instead of a reciprocating'piston as described, may be a membrane type pump or a rotary piston type pump in which latter case the mechanism for transforming the rotary movement of the output shaft of a device according to the invention in a to-and-fro movement is no longer necessary. I

I claim:

1. Apparatus for medical care, particularly oral hygiene, which comprises a pump unit, a' jet nozzle, and

a conduit for connecting said pump-unit with said jet nozzle, said pump unit including means for supplying a stream of spaced liquid pressure pulses through said conduit to said nozzle which rise and fall between a low pressure and an approximately constant peak pressure, and means for cyclically varying the pulse recurrence frequency of said pressure pulses.

2. Apparatus according to claim I in which said pulse recurrence frequency varies between a minimum value of 600-2,500 pulses per minute and a maximum value of 3,5005,000 pulses per minute at a cyclic rate of -600 cycles per minute. 7

3. Apparatus according to claim 2 in which said cyclic rate is 200-400 cyclesper minute.

4. Apparatus according to claim 1 in which said pulse recurrence frequency has an intermediate frequency of 2,500-3,500 pulses per minute and varies cyclically at least :20 percent of said intermediate frequency at a cyclic rate between 2 percent and 25 percent of said intermediate frequency.

5. Apparatus according to claim 4 in which said cyclic rate is between 6 percent and 12 percent of said intermediate frequency.

6. Apparatus according to claim 1 in which a said means for supplying a stream of spaced liquid pressure pulses includes a pump having a driven member, a driving motor having a shaft, and planet-gear mechanism for coupling said motor shaft with said pump driven member,

b said planet-gear mechanism including a sun-wheel,

an internal gear, planet wheels engaging said sunwheel and internal gear, and a planet-wheel carrier on which said planet wheels are rotatably mounted,

0 one of said sun-wheel and planet-wheel carrier being coupled to said motor shaft and the other to said pump driven member,

d and said means for cyclically varying the pulse recurrence frequency includes means for oscillating said internal gear about the axis thereof at a frequency substantially lower than the pulse recurrence frequency.

7. Apparatus according to claim 6 in which said means, for oscillating said internal gear includes a gear driven by said motor shaft and having an eccentric pin mounted thereon. and a radially disposed slot on said internal gear engaged by said eccentric pin.

8. Apparatus according to claim 6 in which said means for oscillating said internal gear includes a gear driven by said motor shaft and having an eccentric pin mounted thereon, an eccentric pin mounted on said internal gear, and a bifurcated member pivotally mounted for-oscillation about a fixed axis spaced from the axis of said internal gear, said eccentric pins engaging the bifurcation of said bifurcated member between said fixed axis and the axis of said internal gear.

9. Apparatus according to claim 6 in which said means for oscillating said internal gear includes a gear driven by said motorshaft and having an eccentric pin mounted thereon, and a connecting rod pivotally connected at one end thereof to said eccentric pin and at the other end thereof to said internal gear at a point spaced from the axis of the internal-gear.

10. Apparatus according to claim 6 in which said pump is a reciprocating piston pump driven by a piston rod, and including a slotted member fixed with said piston rod with the slot thereof extending transverse to the rod, said other of the sun-wheel and planet-wheel carrier having an eccentric pin attached thereto, said eccentric pin engaging said slotted member for reciprocating the piston rod.

11. In oral hygiene, the method of cleaning the teeth and massaging the gums which comprises forming a pulsating jet of spaced liquid pressure pulses which rise and fall between a low pressure and an approximately constant peak pressure and in which the pulse recurrence frequency of said pressure pulses cyclically varies, and directing said pulsating iet against the surfaces to be treated.

12. A method according to claim 11 in which said pulse recurrence frequency varies between a minimum value of 600-2,500 pulses per minute and a maximum value of 3,500-5,000 pulses per minute at a cyclic rate of -600 cycles per minute.

13. A method according to claim 12 in which said cyclic rate is 200-400 cycles per minute.

14. A method according to claim 11 in which said pulse recurrence frequency has an intermediate frequency of 2,500-3,500 pulses per minute and varies cyclically at least :20 percent of said intermediate frequency at a cyclic rate between 2 percent and 25 .percent of said intermediate frequency.

15. A method according to claim-l4 in which said cyclic rate is between 6 percent and l2 percent of said intermediate frequency.

p-17o4 DIV. Y W

22223 UNI'II'IU S'I'A'I'I'IS PA'II'I'N'I UFFH IE I Y CER'l.l|l(I/\'l.l OF CORREC'IION Pa tcnt No. 3 r '432 Dated May 19 74 lnvontoflgfi MICHEL A. MoRE'r It is certified that error appears in the abovo-'-idcntificd patent and that said Letters Patent; are hereby corrected as shown below:

Cover page, Item [63] "Continuation-impart s hould read Division Cover pag, add Assignee: Institut de Reohoi ohe W006,

o Geneva, Switzerland Column 1, line 5, "continuation! should be de iated.

line '41, "IN" should-be In li n e 4 8, "aiij" should be 0n Column 2, 11 15, "pulees should be 111995 lin; 54, "th" should be the I I Coluinn 3, line 49 "moon" should be means -----I lino 64, "rciprocatin" should be 'rociprocating Column 4, line, 47, "with the arrangement" should begin a 1 new paragraph. o

', lino "assymetry" should be asymmetry v Sign ed and sealed this 7th dyof January 1975.

(SEAL), Attesti Y McCOY M. GIBSON" JR. 0. I IL-TAR'JSHALL ,DANN

Attesting Officer Cornfiiigionet of Patents

Claims (15)

1. Apparatus for medical care, particularly oral hygiene, which comprises a pump unit, a jet nozzle, and a conduit for connecting said pump unit with said jet nozzle, said pump unit including means for supplying a stream of spaced liquid pressure pulses through said conduit to said nozzle which rise and fall between a low pressure and an approximately constant peak pressure, and means for cyclically varying the pulse recurrence frequency of said pressure pulses.

2. Apparatus according to claim 1 in which said pulse recurrence frequency varies between a minimum value of 600-2,500 pulses per minute and a maximum value of 3,500-5,000 pulses per minute at a cyclic rate of 70-600 cycles per minute.

3. ApparaTus according to claim 2 in which said cyclic rate is 200-400 cycles per minute.

4. Apparatus according to claim 1 in which said pulse recurrence frequency has an intermediate frequency of 2,500-3,500 pulses per minute and varies cyclically at least + or - 20 percent of said intermediate frequency at a cyclic rate between 2 percent and 25 percent of said intermediate frequency.

5. Apparatus according to claim 4 in which said cyclic rate is between 6 percent and 12 percent of said intermediate frequency.

6. Apparatus according to claim 1 in which a said means for supplying a stream of spaced liquid pressure pulses includes a pump having a driven member, a driving motor having a shaft, and planet-gear mechanism for coupling said motor shaft with said pump driven member, b said planet-gear mechanism including a sun-wheel, an internal gear, planet wheels engaging said sun-wheel and internal gear, and a planet-wheel carrier on which said planet wheels are rotatably mounted, c one of said sun-wheel and planet-wheel carrier being coupled to said motor shaft and the other to said pump driven member, d and said means for cyclically varying the pulse recurrence frequency includes means for oscillating said internal gear about the axis thereof at a frequency substantially lower than the pulse recurrence frequency.

7. Apparatus according to claim 6 in which said means for oscillating said internal gear includes a gear driven by said motor shaft and having an eccentric pin mounted thereon, and a radially disposed slot on said internal gear engaged by said eccentric pin.

8. Apparatus according to claim 6 in which said means for oscillating said internal gear includes a gear driven by said motor shaft and having an eccentric pin mounted thereon, an eccentric pin mounted on said internal gear, and a bifurcated member pivotally mounted for oscillation about a fixed axis spaced from the axis of said internal gear, said eccentric pins engaging the bifurcation of said bifurcated member between said fixed axis and the axis of said internal gear.

9. Apparatus according to claim 6 in which said means for oscillating said internal gear includes a gear driven by said motor shaft and having an eccentric pin mounted thereon, and a connecting rod pivotally connected at one end thereof to said eccentric pin and at the other end thereof to said internal gear at a point spaced from the axis of the internal gear.

10. Apparatus according to claim 6 in which said pump is a reciprocating piston pump driven by a piston rod, and including a slotted member fixed with said piston rod with the slot thereof extending transverse to the rod, said other of the sun-wheel and planet-wheel carrier having an eccentric pin attached thereto, said eccentric pin engaging said slotted member for reciprocating the piston rod.

11. In oral hygiene, the method of cleaning the teeth and massaging the gums which comprises forming a pulsating jet of spaced liquid pressure pulses which rise and fall between a low pressure and an approximately constant peak pressure and in which the pulse recurrence frequency of said pressure pulses cyclically varies, and directing said pulsating jet against the surfaces to be treated.

12. A method according to claim 11 in which said pulse recurrence frequency varies between a minimum value of 600-2,500 pulses per minute and a maximum value of 3,500-5,000 pulses per minute at a cyclic rate of 70-600 cycles per minute.

13. A method according to claim 12 in which said cyclic rate is 200-400 cycles per minute.

14. A method according to claim 11 in which said pulse recurrence frequency has an intermediate frequency of 2,500-3,500 pulses per minute and varies cyclically at least + or - 20 percent of said intermediate frequency at a cyclic rate between 2 percent and 25 percent of said intermediate frequency.

15. A method according to claim 14 in which said Cyclic rate is between 6 percent and 12 percent of said intermediate frequency.

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