US2759266A

US2759266A - Dental and surgical abrasive jet apparatus

Info

Publication number: US2759266A
Application number: US354185A
Authority: US
Inventors: Renato E Cassani
Original assignee: Individual
Current assignee: Individual
Priority date: 1953-05-11
Filing date: 1953-05-11
Publication date: 1956-08-21
Anticipated expiration: 1973-08-21

Description

Aug. 21, 1956 R. E. CASSANI 2,759,266

DENTAL AND SURGICAL ABRASIVE JET APPARATUS 3 Sheets-Sheet 1 Filed May 11, 1953 INVENTOR.

Aug. 21, 1956 R. E. CASSANI 2,759,266

DENTAL AND SURGICAL ABRASIVE JET APPARATUS Filed May 11, 1955 3 Sheets-Sheet 2 IN V EN TOR.

DENTAL AND SURGICAL ABRASIVE JET APPARATUS Filed May 11, 195:

Aug. 21, 1956 R. E. CASSANI 5 Sheets-Sheet 3 FIG.7-

INVENTOR.

FIG. 8

Unitfid States Patent) Thisinvention .relates to apparatus for providing a jet of finely divided abrasive solidstsuspendedina propelling gas suitable for impingement uponarestricted area of hard ectodermal and mesodermahtissue, for cutting-boring, cleaning orpolishing the :same. indentistryandin such surgical operationsas .trephining, .the jet .contains abrasives of sufiicient hardness to .cut awayatooth'or a bone, while in oral hygiene the vjetcontains .softer abrasives. 'Such jets are .usedrasan adjunct .to,.or, in some instances, asireplacement for rotary .drills,-burrs,. and .related power-driven equipment. .Forexample, indentistry such a jet is used to cut away tooth enamel inpreparing a cavity; in most cases the cavity isfurther shaped and softer dental caries is removed by conventionalrotary or-other implements.

Apparatus for forming a jet of finelydivided abrasive solids are already known, butarecomplex and'expensive due to the need to entrain the solidsinthepropelling-gas at a regular rate, this regular entrainment .beingparticularly diflicult in the case of jets for dental .and-.surgical apparatus because of the small quantitiesinvolved for producing narrowjets usually less than ,onemillimeter in .diameter. Abrasive cuttingjets in dentistryand surgery .in particular must bedirected against a corifinediargetarea and must maintain a uniform cutting action over sufficient periods of time to complete ade'sired cut except insofar as 'thecutting actionis deliberately varied :by the operator. The intensity of the cutting action depends, apart from the hardness .and shape of the solid abrasive material, upon the kinetic energy of thetindividual solid particles, that is, .upon their velocity when the particle sizes are substantially uniform, and upon the number ofparticles strikingthe'toothin unit time; .for a jet wherinuthe particles move with a uniform speed the particlestimpinge on the target area at a ratethat is proportional to the solids content of the jet per unit of volume ,of propellan't gas at the conditions .ofthejet. This solids con'tenhis'for brevity herein referred to as the,jet density.

With a regulatedsupply .o'f propellant',.gas the velocity of the gas and, hence, of the entrained solids'inthejet can usually beheld more orfless constantunlessthe solidsentrainment unit is of a typethat ofiersa'yariable-or surging resistance to the passage of the gas or theisdlidsiare fed into the gas at afluctuatingra'te. IThe'entrainment "of'the solids by the gas in small'amoun'ts at a regular rate, has; however, been difiicult,*and'rnechanicalsolids feed devices have "been unreliable and/or expensive. When'astream of gas is passed through or in proximitytoa sourcebody of finely divided solids 'to'eftect direct'entrainment with a view to eliminating the mechanical feed "device, two "difficulties manifest themselves: surging "and dwindling. By surging is meant the periodicchange in thedensity=of the jet; this is believed to be "due to uncontrolled periodic movement of the source body of solids *which'causes a periodic change in the'surface of such 'body exposedto the current of entraining gas. By dwindling is meant 'a progressive, usually gradual decrease in the "density or the jet as the-supply of solids becomes depleted, continu- 2 ing until the reservoir 10f solids is rreplenished or, in some cases, shaken .to cause "a rearrangement of 'the solids. These difiiculties have heretofore ma'de itnecessary .touse special devices ,for. insuring -.the regular entrainment 'of the solids.in.the propellingwgas stream.

Control of the cutting .or polishing operation can be effectively attained only .byajetin-which-the density and the velocity of the solids .remain constant unless deliberatelyaltered by the-operator. Variations in the density of .theLjet .aifectthe-cutting speed-also in that too higha density undersome conditions causes solids to accumulate in the .cut, e. g., in the tooth cavity, forming an obstruction to succeedingsolids whereby the latter-are prevented from striking theintendedpart-of the hard tissue directly.

It is an object of thisinvention to provide a simple dental .and surgical apparatusifor-forming a-controlled jet of finelydivided abrasive solids suspended-in a propellant gas wherein the jet densityand the particle velocitycan be kept substantially 'free'from random variations as-considered above. .Ancillarythereto, it isan object to provide i. an apparatus .wherein the rate .at which solids are entrained :andthe cuttingrate-canbe readily altered by variation in the rateofflow .ofthev gas, Without-theinterpositiontof mechanical .or electrical devices that act on the solids .admitted .to ithe gas stream.

Afurther object is .to .provide apneumatic solids entrainment device suitable for use in .dental and surgical apparatus of the type described .whereinsolids 'are'stored in .a .canister that forms areservoirand the solids are entrained in.a propellantgas at a rate thatis determined substantially solely byttherate of gas fflowltoform a suspension, suitable .fordischarge from .a nozzle.

Further objects will be apparent from the following description. I

In summary, the apparatusaccording to the invention includes, preferably in the sequence recited, .a source of gas underpressure, an :entrainment deviceincluding va canister forming a reservoir for the "finely divided abrasive solids and .anentrainment chamber communicating with the canister, flow controlmeans for the gas, and a discharge nozzle adapted for use in'the mouth or onother parts .o'f'th'e body for directing .the suspension formed in the entrainment device .as a confined jet toward a restricted areadf atooth, bone, or "thellike. "The improved entrainment deviceincludes the said canister, an'entrainment chambeflformedby-a tubenr the likezand situated preferably within thecadister; said 'chamberbeingin communication with a lower part of the canister through one or more 'solids intake ports and having a gas inlet that provides*a-restrictedpassageway fordirecting the gas are high velocity through the "chamber "past 'the intake ports and generate a low pressure region Within the chamber near the ports, the chaniberhavin'g an outlettoaconduit adapted totransportthe suspension of solids formed in the'chamber, and the cariister being furtherin communication with the esouree df -'gas through 'a passageway arranged *to agitate the supply-of solids within the canister, said communication lbe'ing preferably through 'the said entrainmentcharnber.

Having thus described the invention in a general *way, the *following-detailed 'tlescription at certain specific embodiments is made withireferenee to the accompanying drawings r forming a =part 'of this specification, wherein:

Fi-gure 1 is a diagrammatic'view of the apparatus;

FigureZiis a vertictil sectional view through the "entrainment device; I

Figure 3 'is 'a'h'orizontal sectional view taken on the line Iii- 3 of ..Figure '2;

Figure A isa*horizontal-seetional 'view takenpn the line Figure 5 is avertical sectional view through an en trainment device according to a modified construction;

Figure 6 is an enlarged horizontal sectional view taken on the line 6-6 of Figure Figure 7 is a vertical sectional view through another modified embodiment of the entrainment device; and

Figure 8 is a horizontal sectional view taken on the line 88 of Figure 7.

Referring to Figure l, the apparatus comprises a source of propelling gas, preferably dry, e. g., air or carbon dioxide under pressure, represented by a pressure cylinder 10, optionally provided with a pressure regulator 11 for maintaining a constant discharge pressure. It will be understood that other suitable sources of gas may be employed, such as a compressor which is commonly available as an accessory to a dental unit, which may be supplemented by a drying unit. The propelling gas passes through a supply pipe 12 to an entraining unit 13, wherein it becomes laden With abrasive solids. The resulting suspension is discharged through an outlet conduit 14 that advantageously has a sufiicient small bore to insure a sustained high velocity to maintain the solids dispersed in the gas, whereby it is adapted to transport the suspension of solids without sedimentation. The conduit 14 is connected to a flexible hose 15 which is provided with a flow control device 16 of any suitable type, c. g., a pinch device, and is connected to a discharge nozzle 17 which is preferably provided with a rigid hand part and a discharge part 170 of small external size suitable for manipulation, e. g., within the mouth of a patient. Such a nozzie, being known per se, will not be described in detail. It may be said, however, that such a nozzle may, for example, have a bore with a diameter of about 0.5 mm. (millimeters), although bores of other diameters may be used in certain cases, e. g., for oral hygiene, where somewhat larger bores are suitable, or for making exceptionally fine cuts, when smaller bores can be used. The bore in the discharge part 17a should preferably be streamlined to emit a jet that maintains its diameter for distances several times the diameter thereof, e. g., from 1 to 3 mm., without appreciable divergence. The flow controller 16 may be operated to permit gradations in the flow rate by a treadle, for convenient operation by the dentist or surgeon and connected by any suitable mechanical, electrical or pneumatic connection, indicated diagrammatically by the dashed line 19. It will be understood that the pressure regulator valve 11 may, if desired, be omitted or combined with the flow controller, and that the latter may be placed ahead of the entraining unit or operated manually from the nozzle. It was found, however, that rapid control of the jet can be achieved by placing the flow controller as near to the nozzle as practicable.

The nozzle is used in a known manner to direct the abrasive jet against the tooth or other hard tissue while a suction device, not shown but known in the art, is placed into or near the mouth of the patient or other target area to remove spent solids.

The entrainment unit 13 may be constructed as shown in Figures 2-4, wherein 20 represents a canister of cir cular cross-section and of sufiieient strength to Withstand the pressure of the gas. The canister has a threaded neck by which it is secured to a knurled coupler 21 that is threaded to an elbow pipe 22. The latter is connected to and supported from the pipe 12 through a swivel joint that includes an externally threaded, flanged tube 23 and a knurled ring 24 having a flange 24a that may be spun over the flange 22a of the elbow. By loosening the ring 24 the elbow 22 can be rotated to bring the coupler 21 to a position beneath the. pipe 12, permitting a canister containing finely divided abrasives to be attached. Thereafter the canister and elbow can be rotated to the operative raised position shown and clamped by the ring 24.

The canister contains a central tube 25 defining within itself an entrainment chamber and secured within a bushing 26 that is threaded within the coupler 21. The tube or pressed fixedly to the tube and is held against the bushing by a coupling ring 23 that is threaded to the bushing. The bottom of the tube is closed by a circular floor plate 29 and the top is closed by a cap 30 that has a central positioning boss 3011. Near the bottom of the tube are a plurality, e. g., four solids intake ports 31. Gas is admitted into the bottom of the chamber above the floor plate through a constriction to insure a high upward velocity past the ports 31. According to the preferred embodiment shown, a separate gas stream is provided for each port, and this may be attained by mounting a corresponding number of fine capillary tubes 32, e. g., having diameters from 0.2 to 2 mm., depending upon their number and the total gas flow, in holes in the plate 29. For example, four capillary tubes with 0.5 mm. bores are suitable when the tube 25 is 1 cm. in internal diameter. For high velocity jets, approaching the critical sonic velocity, it is desirable to use convergent-divergent bores, as shown in Figure 5.

The canister is placed in communication with the source of gas through a passageway including a flow director for agitating the solids therein. In this embodiment the passageway includes a plurality of helical tubes 33 and 34 that are mounted on the tube 25 in communication with the upper end thereof and extend downwardly so as to discharge gas downwardly and slightly outwardly, toward the periphery of the canister bottom with a whirling motion, the helical tubes in this constituting the said flow director.

The outlet conduit 14 extends concentrically within the tube 25 from the boss 300 which fits into the top to close and position the upper end. The conduit extends through the floor plate 29 and the outer wall of the elbow 22, to which it is sealed by an O-ring 35 and gland 36. The conduit 14 is in flow communication with the entrainment chamber through a plurality of side discharge ports 37 situated above the solids intake ports 31 by a distance sutficient to cause the gas velocity to become substantially uniform over the cross-section of the entrainment chamber, whereby pressure recovery occurs and the pressure at the ports 37 is higher than that at the ports 31. The ports 37 are advantageously below the top of the tube 25 as shown when the latter is longer than the length required to satisfy the above-noted pressure effect, so that the gas Withdrawn from the entrainment chamber through the conduit 14 will contain a greater or a more uniform quantity of solids, particularly at low gas flow rates when a certain amount of settling of the solids in the tube 25 may occur.

The operation of the entrainment device is as follows: Finely divided abrasive, e. g., aluminum oxide or dolomite with particle diameters of about 10 to 50 microns is placed in the canister. These and other materials are suitable for cutting, but dolomite, being softer, is preferred for dental prophylaxis. The particles are advantageously graded so as to avoid a wide range of particle sizes. Gas under pressure, e. g., from 30 to lbs. per sq. in. gauge or higher is supplied from the pipe 12 and flows upwards at high velocity through the capillary tubes 32 and thence at reduced velocity through the tube 25. A part of the gas flows through the helical tubes 33 and 34 into the canister, impinging on the source body of solids therein to agitate them and form a dense cloud. Due to this agitation the solids are conditioned to be drawn into the entrainment chamber through the solids intake ports 31, together with gas from the canister. The passage of the solids through these ports is induced by the high velocity jets emitted from the capillary tubes 32, which causes a low pressure region within the tube 25 opposite each intake port. The gas moves at lower velocity in the upper part of the tube 25 and at still lower velocity in the canister, so that a progressive recovery of pressure occurs and the pressure in the canister outside of the entrainment chamber exceeds that. within the. chamber. In this: manner. a continuing: flow. of-solidsand gas intothe tube 25-is induced,.resulting in. the. upward entrainmentv of solids; inthe; gas to.- forma. suspension. A. part of this suspension: is. disi charged. through the discharge ports- 37 into the outlet conduit: 14. to formthe.jet emittedlfrom the nozzle 1:7; It' is evident that the'gasdischargedIthrOugh the. heliealt tubesiwillalso contain' suspended.solids; so that-.a circulation of solids occurs, and that the gas flow in the conduit 14 equals. that admitted fromthepipe. 12

The agitation of the solids-\within the canister constitutes an important'feature oiltheinvention. It-is only. by thisexpedient that the=regula-r=flow of solids: intothe" entrainment chamber is effected, without: surges and. without significant diminution-in: the density" of' the suspension as. the supply of solids in the: canister becomes depleted. Moreover, the. response ofthe systemto changes inthe. gasflow is rapid Whenthepedallfids released. to. stop'the flow of gas circulation'stops almost immediately, and only a second or lessis required to startthe circulationof sol-ids" after the pedalzisidepressed to start the flow of gas. The circulation of solids becomes less: at reduced gas velocity; resulting inthe dis charge of solids from the device through the conduitzll i at a lower rate when the. pedal 18% is. partially released. This reduces thecutting power o fithe'jet; It thereliy'be comes unnecessary to. provide'a rnechanicalor electrical: device: for determining therate at whichi solids are; admitted to the gas stream.

This. dispositionof the discharges ports 37: in'the side of the conduit 14 was found.to-giveexcellentresults While. discharge oil the suspension ithrouglr the upper end of an open discharge conduitcan' be used; this requires thesolids to. make a change of direction through 180" before entering the; conduit and results in the:discharge of a gas stream'containing a lower density ofisolidsthan in theembodimentrshown, whereinonlya190 ohange of direction occurs prior: towent'ering the ports; However; theinvention isnot restricted'tothefiarrangement shown.

To prevent adventitioussolids" particles-front clogging the capillaries it is desirable touse a gasthat isfree from moisture, and a -drying unit is advan-tageouslvenn ployed when the gas is'atmospheric air-thatispressurized. The. use of dry gas is further" desirable for preventingagglomeration of the solids within the canister; such agglomeration may causeinterference with the regular circulation of thesolids in the 'rna-nner describedabove and may clog'the nozzle 17';

Referring to Figures 5" and 6;- tlr'e modified entraining device illustrates several variants that can be; applied individually or in combination to the embodiment previously described. This device includes a canister 40. which may be circular or rectangular in cross-.sectionand. has a removable top closure 41 with a: threaded filling: opening, that isnorma-lly, closedsby, an. inverted cap 42. The bottom.43.is thiclcenedzattthe center and has. atcen tral, internally threaded. hole into W-hlCllt the: tube. 44' forming the. entrainment'chamber is screwed. The. tube is closed. at. the bot-tom a permanently, fixediorifice: plate 45 having; small; convergent-divergent orifices 46= extending, therethrough; correspe-ndiugadn number: to and. situated adjoining; solids-intake: ports 47 1 inathe tube. just above the orifice plate. For example;.four suzrh-rports and oriiicesr may be. provided,:.the latter: having;;the: sizes: previously described. Thertopwf the tu'bea hastthreaded connection'with aihead:4'8'-having:aipair of: discharge: tubes 49 =and 50. the; outletsuof which i are directed dowm wardly and slightly outwardly; approximately, toward tthes bottom of the canister side wall. gas: box: 51. is" mounted'beneath =the tbottonr' lfinby scrcwseSiZ andlhas a partition: 53: dividing it. into an upper) and lhwer' gas! supplyzchamberz ThBfOImET."lS: supplied. with gaseunderpressure through aisupplypipe; 514 l andi the latter! comnmi nicates'. to'zan outlet conduitif'fi: that is. adapted to transport the suspension;

A rotatable: outlet: tube 56- extends. vertically through the box 5.1?andplate 45' and. concentrically into the tube 1 44 and has the upper: end thereofpositioned by adeflector cap'57- that may be integral with a. sleeve 58 fixed within the tube-44 by a screw 59: The deflector-sleeve structure:=provideslarge openings 60 for the upward flow 0f gasg la-rrd the tube: 56 isrotatable with respect-to the? deflector 57. As: shown in Figure 6, the deflector has twowings, and preferably has rounded edges so as. to have parts of each wing extend to progressively different-distances. beyond thetube. 56. The outlet. tube has a collar 61 bearingiagainst the partition 53 to prevent propellingzgas supplied from the pipe 54 flows upwards through-the orifices 46athigh velocity past the solids intake'pforts-47 to'draw'solids and gas from the canister into the tube 44'and form therein a suspension. A part.

of the gas-together with entrained solids, flows through the

tubes

49 and 50. to agitate the solids in the canister; however, in-this instance these tubes are situated in vertical-planeswandno swirling occurs. The remaining. part of the suspension enters the-ports 62, moves downward through. the tube 56; andemerges through the ports 63 and the conduit 55.

According to a'feature of this embodiment the density of thesuspension withdrawn from the device can be varied. It Will bexnoted-that the gas flowing from the tube:44vinto the ports" 62 makes a change in direction. Part of the suspended solids, will separate from the gas due". to inertia, unless: otherwise guided, resulting in a discharged suspension that has a density somewhat lower than that ascendingthe tube 44. The deflector 57 assists: indeflecting. the solids to enter the ports 62. The. effect of. the deflector can, however, be varied by rotation'of the tube:56 by means of the handle 66, bring-the ports into alignmentwith the deflector wings or'in positions. displaced therefrom entirely out of alignment withhthezdeflector wings, or into intermediate positions; With :therports displaced from the deflector wings the de flector: is. almost inefiective to deflect solids and the dis charged suspension has the lowest density; rotation to the positionshowrr in the'drawing, with the ports in alignment: with'the longest dimension of the deflector, the" density; is progressively increased.

Referringto Figures 7 and 8, showing a further modificatiomzthe-entraining device'includes a canister 7d having aw-removable top-closure 71 and a vertical partitionwallJZ-separating. the. reservoir 73- for solids from the entrainment chamber 74. The partition has a plurality,

bottom of the canister beneath the entrainment chamber 74-has an opening into which is inserted an orifice plate propellinggas' under pressure bya supply pipe 79. The.

Wall 721s: breachedtabove the ports 75 to accommodate a flowdirector'having anxintake deflector 8t) and a down wardly'inclined. spout; 81; The top of the entrainment transport a. suspension.

In operation; finely divided. solids having been placed e. g., four, solids intake ports '75 at the bottom. The

chamberis closedby the curved, top part of the wall '72.. and. communicates with-an outlet'conduit 82 adapted to a low pressure region opposite each solids intake port 75 and causing solids and gas to be drawn in. This forms an ascending suspension within the entrainment chamber 74. A part of this suspension is directed out from the entrainment chamber by the deflector 80 and downwards against the solids by the spout 81 to agitate the solids. The remaining part of the suspension is discharged through the conduit 82. The principles considered above apply to this embodiment, with the change that the suspension is discharged from the entraining device above the passage through which agitating gas is admitted into the canister.

It is evident that other changes may be made in the configuration and arrangement of parts without departing from the invention as defined in the appended claims. Thus, the flow director for directing the agitating gas into the canister may take other forms, including baffles or swirler vanes.

I claim as my invention:

1. An entrainment device for forming a suspension of finely divided abrasive solids in a small stream of propelling gas for use in dental and surgical abrasive jet apparatus which comprises, in combination, a canister forming a reservoir for said solids, a wall structure defining an entrainment chamber communicating with the canister through a solids intake opening, a gas inlet to said chamber adapted for connection to a source of said propelling gas under pressure situated near said solids intake opening and providing a restricted flow passage small in relation to the cross-section of the entrainment chamber for directing the gas at high velocity in proximity to said openings to generate a low pressure within the chamber at said opening and to form a suspension of said solids in the gas within the chamber, an outlet for discharging said suspension from the chamber, and means for admitting agitating gas into said canister, said means including a flow director for directing said agitating gas into the solids within the canister and said solids.

2. An entrainnrent device for forming a suspension of finely divided abrasive solids in a small stream of propelling gas for use in dental and surgical abrasive jet apparatus which comprises, in combination, a canister forming a reservoir for said solids, a wall structure defining an entrainment chamber communicating with the canister through a solids intake opening, a gas inlet to said chamber adapted for connection to a source of said propelling gas under pressure situated near said solids intake opening and providing a restricted flow passage small in relation to the cross-section of the entrainment chamber for directing the gas at high velocity in proximity to said opening to generate a low pressure within the chamber at said opening and to form a suspension of said solids in the gas within the chamber, an outlet for discharging said suspension from the chamber, a passageway connected to said entrainment chamber to receive a portion of said suspension therefrom, and a flow director for directing the said portion of the suspension into the solids within the canister to agitate the said solids.

3. An entrainment device for forming a suspension of finely divided abrasive solids in a small stream of propelling gas for use in dental and surgical abrasive jet apparatus which comprises, in combination, a canister forming a reservoir for said solids, a wall structure defining an upright entrainment chamber laterally contiguous to said reservoir, said wall structure having a solids intake port interconnecting said entrainment chamber and a lower part of said canister, a gas inlet to said chamber adapted for connection to a source of said propelling gas under pressure and providing beneath said port and in proximity thereto a restricted flow passage small in relation to the cross-section of the entrainment chamber for directing said gas at high velocity with an upward velocity component in proximity to said port to generate a low pressure within the chamber at said opening and to form an ascending suspension of said solids in the gas within the chamber, an outlet for discharging said suspension from the chamber adapted for connection to a conduit suitable for transporting said suspension, and a passageway connected to receive gas from said source and including a flow director for directing said gas into the canister into the solids therein for agitating the solids.

4. An entrainment device according to claim 3 wherein said passageway interconnects a region of said entrainment chamber above the solids intake ports with the canister, wherein said gas directed into the solids contains suspended solids.

5. An entrainment device according to claim 3 wherein said flow director is situated at an elevated part of the canister and is disposed to direct gas downwardly.

6. An entrainment device according to claim 3 wherein said gas inlet to the entrainment chamber includes a capillary tube with a diameter of about 0.2 to 2 mm.

7. An entrainment device according to claim 3 wherein said gas inlet to the entrainment chamber includes an orifice having therein an orifice with a diameter of about 0.2 to 2 mm.

8. An entrainment device according to claim 3 wherein said wall structure provides a plurality of solids intake ports and said gas inlet provide a corresponding plurality of orifices, each orifice being situated in proximity to a solids intake port.

9. An entrainment device for forming a suspension of finely divided abrasive solids in a small stream of propelling gas for use in dental and surgical jet apparatus which comprises, in combination, a canister forming a reservoir for solids, an upright tube within said canister defining within itself an entrainment chamber, said tube having a plurality of solids intake ports near the bottom, a gas inlet to said tube at the bottom thereof adapted for connection to a source of said propelling gas under pressure and providing beneath said ports a restricted flow passage small in relation to the cross-section of the tube for directing said gas at high velocity upwards past said ports to generate a low pressure region within the tube and to form an ascending suspension of said solids in the gas within the tube, an outlet discharging said suspension from an elevated part of the tube adapted for connection to a conduit suitable for transporting said suspension, and a passageway interconnecting a part of the tube higher than the solids intake ports with the canister and including a flow director for directing a portion of said suspension into the solids in the canister for agitating the solids.

10. An entrainment device according to claim 9 wherein said outlet includes a vertical outlet conduit situated within said tube in communication with said tube at said elevated part of the tube.

11. An entrainment device according to claim 9 wherein said flow director is shaped to direct said suspension downwardly with a whirling motion.

12. An entrainment device according to claim 9 wherein said outlet includes a vertical outlet conduit situated within said tube and having lateral intake ports establishing communication with said tube at said elevated part of the tube, and a deflector immediately above said lateral ports for deflecting solids into the ports, said deflector occupying only a portion of the cross-sectional area of the tube for the continued passage of a portion of the suspension upwardly beyond the deflector, said deflector being lower than the communication to said passageway through which a portion of the suspension flows into the canister.

13. An entrainment device according to claim 12 wherein said deflector is circumferentially discontinuous and said deflector and outlet conduit are relatively rotatable, whereby the effectiveness of said deflector for deflecting solids into the lateral intake ports can be adjusted.

14. An entrainment device for forming a suspension of finely divided abrasive solids in a small stream of propelling gas for use in dental and surgical abrasive jet apparatus which comprises, in combination, a canister defining an entrainment chamber communicating with the canister through a solids intake opening, a gas inlet to said chamber adapted for connection to a source of said propelling gas under pressure situated near said solids intake opening and providing a restricted passage small in relation to the cross-section of the entrainment chamber and opening into the entrainment chamber in advance of said solids intake opening so as to direct a jet of propelling gas at high velocity past the said opening and to generate a low pressure within the chamber 10 at said opening, an outlet for discharging said suspension from the chamber, and means for admitting gas into said canister.

15. An entrainment device according to claim 14 wherein said wall structure has a plurality of solids intake openings and said gas inlet to the chamber includes a separate restricted passage for each intake opening situated to form a separate jet of propelling gas opposite each of said intake openings.

References Cited in the file of this patent UNITED STATES PATENTS