Dentist drill

[57] ABSTRACT

A dentist drill which includes means for introducing a coolant, such as water, through a passageway in the drill and the working burr to the work piece. The burr, either in an air bearing, journalled, or mounted within a ball bearing assembly within the head of the dentist’s drill, has an axial passageway which co-operates with a concentric water inlet tube. A radially extending flanged device is attached to and radially extends from the head of the burr or extended shank holding the burr. The water inlet tube passes through an aperture, in a non-contacting relationship, in the center of the flanged device into the end of the burr. An air pressure source introduced from the drill creates an air pressure system about the water inlet tube. A housing, enclosing the flanged member, the head of the burr, and the water inlet tube, includes passageways whereby excess water and air may be discharged into the atmosphere. In operation, the water is forced through the water inlet tube into the burr and passing down the axial cavity will exit through the burr at appropriate exit ports. The air pressure system will tend to exhibit the discharge of water from the head of the burr. Any water which does discharge will contact the flanged device. The flanged device is radially sufficient to cover the width of the journal or ball bearings. Any discharge water tending to flow along the flanged device will be subjected to a centrifugal force exerted by the rotation flanged device and be discharged through the housing passageways. By a combination of air pressure and centrifugal force, the discharge water is inhibited from entering the journal or the ball bearings with subsequent deleterious results to the bearing surface.

Claims, 7 Drawing Figures

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PATENTED» 21973

3.762,052

SHEET 1 OF 4

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33 ZC L5 31 30 LI 22

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PATENTED OCT 21973

3,762,052

SHEET 2 OF 4

5Z. 51 54 59 49 50 55

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patented on era

3,762,052

SHEET 3 OF 4

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PATENTED 21973

3,762,052

SHEET U OF 4

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<img file="US3762052A_D0007.tif" />

3,762,052

DENTIST DRILL

The present invention pertains to dental hand pieces incorporating a coolant flowing through the burr to a work piece.

In prior art devices employing a coolant, several approaches have been attempted to segregate or maintain a separation between a coolant and the burr-bearing surfaces. In one of the better of such devices, a sleeve is fitted about the water injection tube in close tolerance with but not contacting the interior walls of the axial passageway extending through the burr. Due to the requisite non-contacting relationship, some water is formed between the passageway and the sleeve. This force is primarily the centrifugal force acting upon the water as the burr rotates at high speed, that is, 300,000 to 500,000 revolutions per minute. The seepage of water is generally in an upward direction, that is, away from the working part of the burr and may affect or interfere with the journal or bearing members of the burr and its attached turbine. A method of attempting to prevent the water from interfering with the journal or the bearings incorporates the use of the exhaust air from the turbine to pass through the bearings and exit through radially extending channels. These channels intersect the point of which the seeping water exits from the passageway. The exhaust air, acting upon the seeping water, tended to but did not wholly successfully force the water outwardly through the radial passageways and to the exterior of the drill where no damage will occur. A problem which also exists in this method is that occuring when the air, causing the turbine to rotate, is shut off as there will still be some water droplets, if not a stream of water, in the radial passageways. This water may tend to seep downwardly into the bearing surfaces and cause the oil or lubricant lodged therein to dissipate or run off. When the turbine is once again energized, the lack of lubricant within the bearings may ruin the bearing. Additionally, the force of the exhaust air through the bearings may not be fully effective to force water through the passageways during operation of the drill. Thus, some water may seep into the working bearings and cause extensive damage, possibly ruining the drill.

It is therefore a primary object of the present invention to provide a means for inhibiting the coolant in a dentist’s drill from coming into contact with the bearing surfaces of the burr.

Another object of the present invention is to provide a combination of a coolant and a gas to force the coolant through a burr to the work piece while inhibiting the coolant from interfering with the bearing surfaces of the burr.

Another object of the present invention is to provide a combination of pressurized gas and centrifugal force to inhibit a coolant from interfering with the surfaces of the bearing members.

Another object of the present invention is to provide a first air pressure source to rotate a burr and using the exhaust air in combination with a second air pressure source to inhibit a coolant from interfering with the bearings of the burr.

Another object of the present invention is to provide a dentist’s drill which can selectively provide a coolant, or air, or both through a temporarily non-rotating burr to flush or dry the work piece being reduced.

Still another object of the present invention is to provide egress means on a burr whereby a coolant will be ejected onto the work piece.;

These and other objects of the present invention will become apparent to those skilled in the art as the description thereof proceeds.

In describing the invention with more specificity, reference will be made to the following drawings, in which:

FIG. 1 illustrates a dental hand piece suitable for incorporating the invention.

FIG. 2 illustrates the basic structure taught in accordance with the present invention.

FIG. 2a illustrates a modification of a burr that may be used for a particular application of the present invention.

FIG. 3 illustrates a modification of the structure taught by the instant invention.

FIG. 4 illustrates a further modification of the structure taught in the instant invention.

FIG. 5 illustrates a modification of the instant invention which may be incorporated in existing dental hand pieces.

FIG. 6 illustrates an air and water valve system.

Referring to FIG. 1, there is shown a dental hand piece including head 1, shank 2, and handle 3. Extending from handle 3 may be a plurality of tubes to be connected to the air and water pressure sources. The head 1 includes a burr 4 extending therefrom suitable for operating upon a work peice. A cap 5 constructed in accordance with the invention is attached to the opposite side of head 1.

Referring to FIG. 2, there is shown a cross section of head 1 and a portion of shank 2 of the dental hand piece. Burr 4 having a shank and a working portion is frictionally fitted within the hollow cylindrical member 6. The relationship between member 6 and burr 4 should be such that the burr may be removed and inserted within the member 6 without undue physical strain, yet provide sufficient friction whereby rotation of member 6 will cause burr 4 to rotate. Member 6 is positioned within head 1 by two rotary bearings 8 and 9. These bearings may be any of several different designs; however, it has been found that caged ball bearings rotating within an inner and an outer race have proven quite satisfactory. Disposed between ball bearings 8 and 9 and frictionally fitted to member 6 is a turbine 10. The design of this turbine may be of any several known configurations; however, a design which is particularly suitable for dental hand pieces is that known as a bucket turbine, that is, a plurality of depressions about its circumference in radial alignment with and for co-operation with a fluid source point. The fluid, which may be air, emanating from the source point, or orifice, is directed toward the buckets in a direction not normal to the circumference of the turbine and imparts a force causing the turbine to rotate. The exhausted air may be transported away from the turbine through an opening in the turbine housing circumferentially displaced about the air input source 2'. As there is a finite space between the edges of the turbine 10 and the circular turbine housing, there will be some air exhaustion toward either edge of the turbine through this finite space. This air will flow around the turbine edges and outwardly through ball bearings 8 and 9 to cavities 16 and 19.

3,762,052

The previously mentioned ball bearings are attached to the head 1 by O-rings 11. As these points of attachment 11 are circumferential and cause the ball bearings 8, 9 to be finitely displaced from the inner wall of head 1, there will exist an annular cavity 15 between the outer race of the ball bearing and the inner surface of the housing of head 1. The turbine exhaust air flowing about and axially along the outer surface of the turbine will escape through this annular cavity if the O-rings 11 are perforated and thence to cavities 16 and 19.

The design of head 1 includes an inwardly directed flange 12 attached onto the bottom of head 1 and partially covering the side of ball bearing assembly 8. A similarly designed circular inwardly pointing flange 13 is attached to the upper portion of head 1 whereby most but not all of the side of ball bearing 9 is covered. Each of flanges 12 and 13 do not contact their respective ball bearings 8 and 9, whereby the previously discussed annular cavity extends from the outside of ball bearings 8 and 9 inwardly along lateral edge of the ball bearings toward the burr 4 through lateral cavities 16, 19. At the bottom of the head 1 there is disposed an outwardly directed circular flange 14 about member 6. The width of flange 14 is such that it overlaps but does not contact flange 12. Thus, the escaping exhaust gases pass through cavities 15, 16, and 19 and through space 17 between flange 14 and flange 12.

The upper end of the shank of burr 4 is machined to form a shoulder 20 whereby a cap 20' may be fitted thereon. A circular member 21 with a circular flange 22 extending therefrom is fitted on cap 20'. When member 21 is fitted on cap 20', the flange 22 should just clear flange 13 whereby rotation of member 21 due to rotation of the burr 4 or shank 6 if extended will not cause flange 22 to engage flange 13.

Cap 5 is threadably fitted onto head 1. Disposed within cap 5 is an air passage 23 connected to air passage 23', the latter being disposed within shank 2 and extending out through handle 3. Additionally, a water passage 24 is disposed within cap 5 and connects to passage 24' disposed within the shank 2 and ultimately extends from handle 3. The water passage 24 extends through cap 5 to a generally axially centered point 25 and thence downwardly through an attached tube 26 whereby it will be axially aligned with the center line of burr 4. The dimension of tube 26 is such that it will be concentric within the passageway 27 axially extending through burr 4. The cap 20' has an aperture 28 at its approximate center point which is of only slightly greater diameter than that of tube 26 in order to form a relatively small annular cavity 29 between tube 26 and aperture 28. In this manner, the axial cavity 27 need not be bored to obtain a close tolerance with tube 26 and may be bored larger than would otherwise be desired provided that aperture 28 is maintained as small as possible. Thereby, lower machining costs will be incurred to obtain cavity 27. The member 21 has an aperture extending therethrough at the approximate center point whereby tube 26 may extend therethrough without contacting member 21. The cavity 30 of member 21 may be somewhat larger than aperture 28. The upper edge 31 of aperture is somewhat larger than tube 26 in order to prevent physical contact therewith but should be smaller than the diameter at the center of aperture 30; thereby, a spherelike cavity is formed within member 21.

The air passageway 23 extends into the approximate center portion of cap 5 and opens into a cavity 33. The lower orifice 34 of cavity 33 is somewhat smaller in diameter than that of the cavity but of greater diameter than tube 26, whereby air flowing through passageway 23 and into cavity 33 may flow between the orifice 34 and tube 26. The cap 5 includes a further concentric cavity 35 about member 21 and opens to the atmosphere whereby the air discharged through orifice 34 may vent through cavity 35 into the atmosphere.

In one embodiment of cap 5, the cap is designed with a lower circular portion threadably fitted onto head 1 and having three or four ribs extending upwardly therefrom to the top central solid portion. One of these ribs may carry the air and water passageways 23, 24 respectively.

In operation, the ejection of the water through tube 26 through cap 20' and into passageway 27 of burr 4 will continue down passageway 27 to the working portion of burr 4 generally shown as 36. It has been found that the best results are obtained when the Water is discharged both axially and laterally from the working portion of burr 4. However, the lateral ejections must be through passageways 37 located within the lower half or third of the working portion 36 of the burr. Unless this precaution is followed, the water will discharge through the lateral passageways 37 without also discharging through the axial passageway, that is, the extension of passageway 27. In some dental reduction operations, the grinding operation of the burr is performed by the upper portion of the working portion 36. For these operations, additional lateral passageways 37' (see FIG. 2a) may be incorporated in the burr 4. These lateral passageways are located within the upper half or third of the working portion 36 and cause all the water passing through passageway 27 to be discharged therethrough. Thus, the water is discharged onto the area being worked and not below it. The air entering cavity 33 through passageway 23 will be collected and forced out through orifice 34 at an accelerated rate. This accelerated air is forced into the sphere-like cavity 30 and maintains a pressure differential therein greater than that within the passageway 27. In this manner, the water ejected into passageway 27 by tube 26 will be inhibited from flowing upwardly to cavity 30. At the speeds at which these type of burrs normally rotate (300,000 to 500,000 revolutions per minute), there is a sharply increased centrifugal force on the water, causing a high pressure gradient to exist toward the outer boundary of passage 27. Thus, the water tends to flow therealong both upwardly and downwardly. The upwardly flowing water will, unless otherwise inhibited, pass through the annular cavity 29. Total containment of water within passageway 27 is generally extremely difficult in practical applications. Thus, provisions must be made for disposing of that overflow of water before it can affect other critical elements within the head 1. One such critical element is that of the ball bearings 8 and 9. If water were to flow into either of these bearings, the lubricating medium may be lost and immediate damage to the bearings would result. The water escaping through the annular cavity 29, entering the cavity 30, and flowing therefrom along the outer edge of member 21 could, if not otherwise inhibited, find its way to bearings 9. At the water emanates from cavity 30 and enters the upper surface of member 21, it is subjected to centrifugal force as the water is, of course, ro3,762,052 tating within cavity 30. The water on the surface of member 21 will continue to rotate and be forced to the periphery of flange 20 and thence slung off and through the openings in cap 5. Portions of that water which is slung off will undoubtedly strike one of the solid portions of cap 5 and flow down the inner side 38 of the cap 5. This water will run inwardly along flange 18 to its inner edge and possibly drop into bearing 9 unless precautions therefor are taken. The spacing between flange 18 and rotating flange 22 is maintained at a minimal distance whereby all but the very thinnest film of water could flow therebetween without contacting flange 22. Thus, any water of greater teickness than a thin film would contact flange 22 with the latter imparting a centrifugal force to again sling this water out through the openings within the cap 5. Any remaining thin film of water not acted upon by flange 22 would be subjected to the turbine exhaust air flowing through cavity 19 and ultimately outwardly through the spacing between flanges 18 and 22. This air flow would act upon the thin film of water and tend to inhibit it from creeping inwardly toward the inner edge of flange 18 and thus drop into bearing 9.

The cap 20' serves an additional purpose in that the aperture 28 therein co-operating with the tube 26 may be designed to be of lesser diameter than passageway 27 whereby the water acting under centrifugal force at the outer edges of passageway 27 would be inhibited by the shoulder of cap 20' extending into passageway 27 from flowing upwardly between the tube 26 and the edge of the aperture 28.

In many dental reduction operations, there is a periodic requirement to flush and/or dry the work area. By a modification to the head 1 and the dental piece actuating control system, such a requirement may be satisfied. A brake 90, connected by a plunger 91 to a solenoid within a housing 92, will serve to brake the rotating burr 4 without otherwise affecting the operation of the dental piece. The braking of burr 4 will not impede the flow of water through passageways 27 and 37 and the burr 4 may then be used to flush the work area with water. By turning control valve 69 (see FIG. 6), the water may be shut off and air flowing through passageway 27 may be used to dry the work area.

The solenoid 92 may be attached to any physically convenient spot on the dental piece and may be actuated by either a hand or a foot control (not shown). It is anticipated that other braking mechanisms may also be utilized.

For slow speed dental hand pieces, the means for driving the burr and the means for providing support for the rotating burrs is usually of a different design than previously discussed. FIG. 3 illustrates in cross section the head 1 of such a burr. The drive means, which is shown to be a belt 46 operating through the shank 40 and about a receiving member 43, in concentrically attached to and arranged about a sleeve 44. The sleeve 44 may be journalled within journals 45. A burr 4 is frictionally handfitted within sleeve 44. The fit should be such that the burr may be easily extracted and inserted and yet have sufficient frictional resistance so that it will turn with sleeve 44 in response to movement of belt 46. Other air or electric low speed drive means may also be used.

In order to provide a satisfactory injection of water into the axial passageway 47 of burr 4 and ultimately emanating through the axial and lateral passageways 47 and 48 of the working part Of burr 4, the following modifications need to be made to a standard low speed drill.

A cap 49 is threadably or press-fitted to head 1. The design of the cap 49 should be similar to that described with respect to FIG. 2. The cap 49 has a lower circular portion with ribs extending therefrom inwardly and outwardly to form an upper central portion. Disposed within the cap 49 is a water passageway 50 suitably connected to a water pressure source and extending downwardly from the cap at its approximate center. At the central point of the cap, there may be a cavity 51 into which passageway 50 leads and emanating downwardly therefrom there may be a water injection tube 52. The water injection tube 52 co-operates with an aperture 53 disposed within a cap 54, the latter attached to the head of burr 4. The cap 54 is axially displaced from burr 4 such that a cavity is formed between the upper extremity of burr 4 and the apertured portion of cap 54.

The cap 49 also contains a second passageway 55 connected to a suitable air pressure source for injecting air into a cavity 56, centrally disposed about water injection tube 54. A second air passageway 57, which may be partially disposed within shank 40 and connected to a suitable variable air pressure source, exhausts at either side of journals 45. The purpose of this air pressure system is primarily that of inhibiting the water flowing out through water injection tube 52 from coming into contact with and thereafter destroying the journals 46 and accomplishes that purpose in the following manner.

Centrally disposed about the lower portion of sleeve 44 is a circular flange 58. A second circular flange 59 is disposed about the upper portion of sleeve 44. Each of these flanges 58, 59 are generally in close proximity to the solid portions 60, 61 of the head 1 whereby passageway therebetween, respectively, is of a restricted nature. The air through air passageway 57 exhausts at the outer side of journals 45, thereby creating an increased air pressure adjacent the sleeve 44 and causing air to flow therefrom outwardly between flange 58 and portion 60 of head 1 and flange 59 and portion 61 of head 1. Any foreign substances, such as water, existing therebetween will be inhibited from flowing counter to the air flow. Additionally, any foreign substance therebetween which contacts the rotating flanges 58, 59 will have imparted thereto a centrifugal force forcing it away from the sleeve 44. Thus, the journals 45 are protected from the incursion of foreign substances. The air pressure system created by air passing through air passageway 55 into cavity 56 will inhibit the water, passing through passageway 50 through water injection tube 52 and into the cavity at the upper end of the axial passageway 47, from flowing through the annular cavity 53 about injection tube 52 in cap 54. Any water that does in fact leak out through the annular cavity 53 will flow along the upper edge of cap 54 to the sleeve 44 downwardly therefrom and onto flange 59. The rotating motion of cap 54, sleeve 44, and flange 59 would tend to impart a centrifugal force to this seepage of water and sling the water off the flange 59 before the water has a chance to flow downwardly from the edge of the flange 59, inwardly along the bottom portion and ultimately toward journals 45.

As the cap 49 is vented due to its rib-like construction, the water which has been slung off flange 59 will

3,762,052 be ejected from the head 1. Any water contacting one of the ribs and thereby stopped from leaving the head 1 will be inhibited from flowing toward journals 45 between the flange 59 and portion 61 on the head 1 due to the aforementioned air pressure exhaust therethrough.

FIG. 4 illustrates the head of the dental hand piece generally similar to that of FIG. 2; however, substantial modifications have been made in the means by which the combination of the air and water are introduced to the central passageway disposed within the burr. The following discussion will generally center on these differences without repeating the common constructional features.

The burr 62 is frictionally fitted within sleeve 6 whereby it may be easily inserted and removed by hand. The design of the burr 62 is such that a portion of it is a thin-walled cylinder extending from a solid piece having a passageway 63 axially extending therethrough. At the working tip of the burr, a plurality of lateral passageways 37 generally configured to be within the lower half or lower one-third of the working tip extend therethrough. Two concentric tubes 64, 65 are attached to cap 5; these tubes are inserted through cap 20' into the hollow portion of burr 62. The inner one of these tubes 64 forms a passageway for the water flowing through passageway 24 in the cap 5. The larger concentric tube 62 forms a passageway for the air flow from the passageway 23 of cap 5. Tube 64 is so designed that water exiting therefrom in the form of a stream will be directed into the passageway 63 and thence to the working portion of the burr 62. The end of tube 65 terminates somewhat short of tube 64 whereby air emanating therefrom creates a pressure chamber within the hollow cylinder of the burr 62. Any water emanating from tube 64 and not passed directly to passageway 63 would form a pool of water about the lower portion of the hollow cylinder of burr 62. The air pressure within the hollow cylinder would tend to force this water out through passageway 63. As the burr 62 may rotate at high speeds (300,000 to 500,000 revolutions per minute), a portion of the water emanating from tube 64 and not flowing to passageway 63 may, through the centrifugal force pressure gradient, creep upwardly along the edge 66 of the hollow cylinder. At the upper portion of the hollow cylinder, the water would ultimately contact cap 20' and normally be retained thereby. However, if the thickness of the cylindrically shaped column of water about the outer edge 66 of the hollow cylinder would approach the distance between the inside edge 66 of the hollow cylinder and the outer edge of aperture 28, there is a possibility that water would flow through the annular cavity 29 formed about tube 65. Should water flow through this annular cavity 29, it will flow through the annular cavity 30 within member 21 as the latter is designed to be approximately the same circumferential size as the cavity 29. Any water flowing therethrough will ultimately seep out from the upper edge 31 of the annular cavity 30 in member 21 and thence along its upper surface. A centrifugal force is imparted to the seeping water due to the rotation of member 21. The centrifugal force on the water will be great enough to cause the water to rapidly accelerate radially and be slung through the apertures within cap 5 and into the surrounding atmosphere. Any water which may strike the inside edges of the ribs in cap 5 and flowing downwardly will be inhib8 ited from flowing toward bearings 9 between flanges 18 and 22 by the evacuated air flowing opposite thereto as previously discussed with respect to FIG. 2.

FIG. 5 illustrates the head of a dental hand piece generally similar to that of FIG. 2; however, substantial modifications have been made in the means by which the combination of the air and water are introduced to the central passageways disposed within the burr. The following discussion will generally center on these differences without repeating the common constructional features.

The burr 73 is frictionally fitted within sleeve 6 whereby it may be easily inserted and removed by hand. The burr 73 includes an axial passageway 27 extending therethrough and a shank 72 extending upwardly from the sleeved portion of burr 73.

A cap 5 is threadably or otherwise securely fitted to head 1 of the dental hand piece. The cap 5 includes an air ingress passageway 24 opening into the upper portion of a generally vertically oriented cavity 71. Considerations of machining costs may dictate that this cavity 71 be a cylinder with a vertical axis. Cap 5 also includes a water ingress passageway 23 opening into a lower portion of cavity 71. An inwardly extending radial flange 74 is fitted within the lower portion of the cavity 75 within cap 5. This flange 74 includes an upwardly projecting lip 76 about the aperture 77 at the center of flange 74. The diameter of the aperture 77 and its lip 76 is greater than the diameter of shank 72, whereby the shank 72 extending from the mounted burr 73 will not be in a contacting relationship with flange 74.

A circular flange 79, having a downwardly oriented lip 78 at its periphery, is frictionally fitted to shank 72. The relationship of the respective lips 76 and 78 is that of an interlocking arrangement whereby lip 78 extends diametrically beyond lip 76 and overlaps it in the vertical direction, but without any contact therebetween.

The operation of the water purging action of the shank 72 and flanges 79, 74 may be described as follows. The air passageway 23 introduces an air pressure system about shank 72 within cavity 71. The water passageway 24 introduces a flow of water at a pressure less than that of the air to the upper portion of cavity 71 and about the extremity of shank 72. The axial passageway 27 opening into cavity 71 at the extremity of shank 72 is in a receiving relationship with respect to the water in cavity 71. The air pressure system developed about the shank 72, in conjunction with the water passageway 24, places the water within cavity 71 under pressure and as the axial passageway 27 is not pressurized, the water will flow therethrough to the working portion of burr 73 (not shown). The air pressure system, being at a higher pressure than the water, will tend to contain the water within the upper portion of cavity 71.

Should some water flow downwardly along the sides of cavity 71 or shank 72, it will contact the rotating flange 78. The flange 78 imparts a centrifugal force to any water disposed thereon and causes that water to be ejected through the ports or openings in cap 5 (previously discussed). Any water deposited on flange 74 is inhibited from flowing inwardly and contacting the lower portion 79 of shank 72 by the lip 76. In addition to this physical impediment, additional means may be used to impede any water creepage toward the bearings 9. In high speed air driven drills, the exhaust air (previously discussed) flows through the bearings 9 into cav

3,762,052 ity 19 and through the aperture 77 and the passageway defined by the interlocking lips 76 and 78, and thence exhausts through the openings in cap 5. This described flow of air will further impede any water flow or water creepage to the bearings 9. In low speed drills which do not have a flow of exhaust air through bearings 9, an additional air flow source 70 may be introduced. This air flow source 70 opens into cavity 19 and establishes an air flow path through the interlocking lips 76, 78 as discussed above.

The cap 5 modification discussed with respect to FIG. 5 has a further distinct important feature. Presently used dental pieces may easily be modified to incorporate the cap 5. Through a simple machining process, the head 1 may be modified to threadably or otherwise firmly engage the cap 5. External air and water sources are then attached to passageways 23 and 24. A burr designed in accordance with the configuration of burr 73 is inserted within sleeve 6 in head 1. The shank 72 penetrates and engages the aperture in flange 73, the latter being held in place by the interlocking lips 76, 78 and the edge 80 of cavity 71. If necessary, head 1 and shank 2 of the dental piece may be modified to receive air passageway 70, or air passageway 70 may be built into cap 5 without requiring any further alteration of head 1. Thus, presently used dental pieces may be modified to take advantage of the benefits obtained through the instant invention.

In order to use theinvention to its best advantage, the opening and closing of the air and water sources should be in a predetermined sequence. FIG. 6 illustrates a rotary valve arrangement which may be incorporated in the shank 2, handle 3, or it may be foot-operated (not shown). The water inlet passageway 67 is ported through a transverse passageway 68 in the barrel 69 of the rotary valve and into a water outlet passageway 84 which connects to passageway 23. Similarly, the air inlet passageway 81 is ported through a transverse passageway 64 in the barrel 69 and into each of the air outlet passageways 82, 83. The air outlet passageway 82 connects to passageway 23 in cap 5 while the air outlet passageway 83 connects to air input source 2'. The porting arrangement in the barrel 69 is designed so that as the drill is shut down by turning the rotary valve counterclockwise to the “off” position, the flow of water is first interrupted. The continuing flow of air through passageways 2' and 23 will purge the head 1 of any remaining water. Next, the rotary valve will interrupt the flow of air to passageway 23 and lastly the air to passageway 2'. In this manner, the air flowing through annular cavities 16 and 19 will be turned off last and thereby provide the greatest insurance against any water entering bearings 8 and 9 of FIG. 2.

When the rotary valve is turned toward the “on” position, an air flow, emanating from passageways 83 and 2' is initially established through annular cavities 16 and 19 to inhibit water flowing therethrough. Secondly, air pressure about the annular cavity 30 is established through passageways 82 and 23 to inhibit water from flowing therethrough. Lastly, the water flowing through passageways 84 and 24 is introduced to the head 1 of the dental hand piece. By this manner of activating and deactivating the dental hand piece, all precautions are undertaken to insure that the water will flow through and discharge from the burr without entering the bearings 8, 9 and cause damage.