<PAGE>   1
                                                                   EXHIBIT 10.42


UNITED STATES PATENT [19]               [11]  PATENT NUMBER:           5,525,058

GALLANT ET AL.                          [45]  DATE OF PATENT:     *JUN. 11, 1996
--------------------------------------------------------------------------------

[54]    DENTAL TREATMENT SYSTEM

[75]    Inventors:  BEN J. GALLANT, Portland, Tex.; ALAN N.
                    GLEEMAN, Mountain View, Calif.;
                    WILLIAM S. PARKER, Ann Arbor, Mich.

[73]    Assignee:   AMERICAN DENTAL TECHNOLOGIES, INC., 
                    Southfield, Mich.

[*]     Notice:     The term of this patent shall not extend
                    beyond the expiration date of Pat. No. 
                    5,330,354.

[21]    Appl. No.:  276,964

[22]    Filed:      JUL. 19, 1994

                        RELATED U.S. APPLICATION DATA

[63]    Continuation-in-part of Ser. No. 859,158, Mar. 27, 1992,
        Pat. No. 5,330,354, and a continuation-in-part of Ser. No.
        29,732, Mar. 25, 1993, Pat. No. 5,350,299.

[51]    INT. CL.(6) ....................................A61C 3/02
[52]    U.S. CL. .................................433/88; 451/101
[58]    FIELD OF SEARCH ..............433/88; 451/75, 451/101,102

[56]                            REFERENCES CITED

                            U.S. PATENT DOCUMENTS

        2,661,537  12/1953  Angell .........................32/58
        2,696,049  12/1954  Black ..........................32/58
        3,852,918  12/1974  Black ..........................51/12
        3,882,638   5/1975  Black ..........................51/12
        3,971,375   7/1976  Hill .......................128/173.1
        4,276,023   6/1981  Phillips et al ................433/85
        4,492,575   1/1985  Mabille .......................435/88
        4,494,932   1/1985  Rzewinski .....................433/88
        4,635,897   1/1987  Gallant ........................251/5
        4,708,534  11/1987  Gallant .......................406/75
        4,767,404   8/1988  Renton ........................604/48
        4,826,431   5/1989  Fujimura et al. ...............433/29
        4,893,440   1/1990  Gallant et al. ................51/436
        4,901,758   2/1990  Cook et al. ................137/487.5
        4,940,411   7/1990  Vassiliadis ..................433/215
        5,055,048  10/1991  Vassiliadis ..................433/215
        5,205,743   4/1993  Ludvigsson et al. .............433/92
        5,330,354   7/1994  Gallant .......................433/88
        5,350,299   9/1994  Gallant .......................433/88

                              OTHER PUBLICATIONS

7 pages of advertising material of Proportion-Air of McCordsville, IN, entitled
"Proportion-Air Applications". 8-page brochure (including cover) entitled
"QB1/QB2T Servo Control Valves"; Proportion-Air, Inc., McCordsville, IN.

2-page advertisement entitled "BB Applications" Proportion-Air, Inc.,
McCordsville, IN, Nov. 23, 1991.

1-page advertisement entitled "Web Tensioning Using Dancer Arm Feedback",
Proportion-Air, Inc., McCordsville, IN, Mar. 16, 1992.

2-pages of advertising, headed Proportion-Air, Inc. Article entitled "Servo
Valves" by Eddie Harmon, in Motion Control, Apr. 1993, pages 37, 38, 41.

Primary Examiner-Ren Yan
Attorney, Agent, or Firm-Synnestvedt & Lechner

[57]                                ABSTRACT

Treating teeth or associated tooth structure by the use of an abrasive-laden
fluid stream which provides fluid at high pressure to a manifold with
selectively operable valves, delivers fluid at a selected pressure to a mixer
for fluid and abrasive and delivers the mix to a handpiece for application of
abrasive-laden air to a tooth or tooth structure.  Low pressure priming air
pressurizes the air abrasive device.  A path for pure air bypasses the
air/abrasive device. A control allows for delivery of air or air and abrasive 
as desired.  Fluid pressure is controlled by a  manually-operable servo system. 
Following treatment with the air/abrasive, a purge line purges the system
downstream from the abrasive device of excess abrasive particles.  A vacuum
removes abrasive particles and debris from the patient's mouth.  The abrasive
delivery device may include a hand-held nozzle having fluid ports operable by
the fingers of the operator to control system functions.  The vacuum includes a
ridge, disposable collection chamber for sterile disposal of abrasive and
debris and may include a common filter for the purge circuit and the system for
removal of abrasive particles and debris.  Connection to the existing suction
system in the dental office or use of a water powered venturi to provide
suction is disclosed.  Pressure regulating and relief means insure
instantaneous change of pressure levels.

                         5 CLAIMS, 10 DRAWING SHEETS



                             [SCHEMATIC DRAWING]

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FIG. 1


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FIG. 2


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FIG. 3

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FIG. 4


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FIG. 5


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FIG. 5A


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FIG. 5B


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FIG. 6


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FIG. 6A
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FIG. 7


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FIG. 8


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FIG. 9


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FIG. 10


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                                   5,525,058

                                       1
         
                            DENTAL TREATMENT SYSTEM

                              RELATED APPLICATION

     This application is a continuation-in-part of application Ser. No.
07/859,158, filed Mar. 27, 1992, now U.S. Pat No. 5,330,354 and of application
Ser. No. 08/029,732, filed Mar. 25, 1993, now U.S. Pat. No. 5,350,299 both of 
Ben J. Gallant, the specifications of which are included herein by reference.

                             FIELD OF THE INVENTION

     The present invention relates to systems used in the practice of dentistry,
and more particularly, to systems for cutting, excavating and etching teeth or
associated tooth structure by means of finely divided abrasive materials carried
in a fluid stream.

                          BACKGROUND OF THE INVENTION

        The use of abrasive-laden fluid streams to treat teeth has long been
known. For example, U.S. Pat. No. 2,661,537 to Angell describes equipment for
treating teeth with a relatively high-pressure stream laden with abrasive
particles. While the use of such equipment has gained a significant degree of
success in connection with the cleaning of teeth, there has heretofore been an
overall lack of success in the dental industry with respect to the use of such
equipment for cutting, excavating or etching teeth. Applicant has found that
this lack of success can be attributed to several heretofore unrecognized
disadvantages associated with equipment of the type described in Angell.

     For example, cutting or etching of teeth with gas/abrasive streams
frequently requires a source of fluid at pressures of at least about 120 psig.
Unfortunately, however, compressed air in the range of about 60 to 80 psig is
generally the highest pressure available in dental operatories. In order to
overcome this limitation, the Angell patent describes the use of cylinders
containing CO gas at a pressure of about 800 psig as a source of pressurized
fluid.  Applicant has found that there are numerous disadvantages associated
with the use of pressurized gas in this form. For example, applicant has found
that one important factor in successfully achieving cutting, etching and/or
excavating tooth enamel is proper regulation and control of the pressure at
which such operations are carried out. Such precise control and regulation is
difficult to achieve in the system described in Angell. One reason for this
difficulty is the very large pressure differentials between the pressure needed
to operate the system (e.g. 100 to 120 psig) and the pressure at which the gas
is delivered (800 psig). In particular, the accuracy of pressure regulation
equipment is frequently inversely proportional to the pressure differential
across the regulating device. Thus, the precision of the regulated pressure
frequently decreases as the pressure differential increases.

     Another disadvantage of the equipment described in Angell is that it is
capable of providing only two pressure levels for the fluid utilized to operate
the system. Applicant has found that this is another reason for the lack of
success achieved by prior devices. It is highly desirable to operate at more
than two distinct and different pressure levels because of the multiplicity of
dental procedures performed by the dentist. The equipment described in Angell,
however, is capable of supplying fluid at only two distinct pressure levels. As
a result, the required precision in operating the dental instrument is
deficient. Another disadvantage arises on account of the provision for the
supply of gas in compressed form in cylinders. In view of the considerable
volume of gas being used, cylinder replacement becomes a severe inconvenience.
Thus, applicant has found that the use of equipment as described in Angell is a
disadvantage in treatment operations involving the use of abrasive-laden fluid
streams.

     The prior art use of abrasive-laden fluid streams for treatment of teeth
has also suffered from the disadvantageous of having significant excess and/or
post-use abrasive particles in the area of the mouth during operation. The
presence of such abrasive particles is not only uncomfortable to the patient
being treated, but it may also constitute a hinderance to the dentist conducting
the operation. This disadvantage is particularly relevant for cutting and
abrading of teeth since the relatively high pressures required for such
operations sometimes result in a cloud or mist of excess or post-use abrasive
particles which make it difficult for the dentist to see the area being 
treated. This difficulty has heretofore not been fully overcome.

                      OBJECTS AND SUMMARY OF THE INVENTION

     In view of the deficiencies of the prior art, it is thus an object of the
present invention to provide improved dental systems which utilize pressurized
fluid streams containing abrasive particles for effectively and efficiently
abrading, etching and cutting teeth or associated tooth structure. As used
herein, by associated tooth structure is meant fillings, composites, facings,
crowns, caps, amalgam and the like.

     It is a further object of the invention to bring together the components
needed to produce a novel and effective dental tool capable of overcoming past
deficiencies of systems using abrasive-laden fluid streams.

     It is a further object of this invention to provide dental apparatus for
treating teeth via an abrasive-laden stream of high pressure fluid, such as
air, in which the disadvantages associated with the presence of excess 
abrasive particles are eliminated or substantially reduced.

     It is a further object of the present invention to provide dental apparatus
which utilize pressurized fluid streams containing abrasive particles wherein
the apparatus is capable of operating selectively at two or more precisely
controlled pressure levels.

     Yet another object of the invention is the use of a common suction system
for purging the equipment of excess abrasive particles and collection of
post-use abrasive particles. The common suction system may include connection 
means for connection to the office suction and waste collection systems 
pre-existing within the dental office. Advantageously, suction may be provided 
by a water venturi which draws off abrasive particles and debris into the 
water stream passing through the venturi.

     These and other objects are satisfied by the preferred system aspects of
the present invention. The present system is directed to the treatment of teeth
by means of abrasive particles carried by a gas stream. According to one
preferred embodiment, the system comprises, in combination which a source of
air: means for increasing the pressure of said air to an initial pressure; a
pressure selection means for selectively  providing said air at at least a
first or a second pressure, each of said first and second pressures being less 
than about said initial pressure; an abrasive delivery means for combining the
abrasive particles with said air at one of said first or second pressures to
provide an abrasive-laden air stream; and nozzle means for delivering said
abrasive-laden air
      
<PAGE>   13
                                   5,525,058

                                       3

steam to the teeth to be treated. According to another preferred embodiment,
the system comprises, in combination with a source of air at an initial
pressure: a pressure selection means for selectively providing said fluid at 
least a first, a second, or a third pressure, each of said first, second and
third pressures being less than about said initial pressure; an abrasive
delivery means for combining finely divided abrasive particles with said air at
one of said pressures to provide an abrasive-laden air stream; and nozzle
means for delivering said abrasive-laden air stream to the teeth to be treated.

     Another aspect of the present invention, which is preferably used in
combination with the treatment system aspects hereof, is directed to evacuation
systems especially well adapted for removing excess and/or post-use abrasive
particles from in and around the area of the mouth during dental operations.
Such systems preferably comprise a vacuum conduit having a first, relatively
large diameter outer conduit member and a second, relatively small diameter
inner conduit member, wherein said first and second members are moveable in a
longitudinal direction with respect to one another. In this configuration, the
outer conduit member may be placed adjacent to the chin, cheek, or lips of the
patient receiving treatment while the inner conduit member may be selectively
positioned within the mouth of the patient being treated.

     The evacuation system may include integral vacuum means and may optionally
and additionally include means for connection to the dental office suction
system for the evacuation of particulate debris and abrasive.

     Another aspect of the present invention, which is optionally but not
necessarily used in combination with one or more of the other aspects hereof,
is directed to a system for controlling the pressure of the abrasive/air mixture
leaving the delivery nozzle means. Such control systems preferably include
pneumatic control means, such as fluid discharge ports on the handle of the
dental apparatus for activating or deactivating the flow of pressurized fluid
therein.

     In another preferred aspect, the system includes as the pressure control
means a servo valve system comprising a servo valve through which the fluid is
supplied to the nozzle, the servo valve being settable to any of a plurality 
of selectable conditions by manually-operable controls, to select any of        
a corresponding set of pressure for the fluid supplied to the nozzle;
preferably also included are means for sensing the pressure of the fluid
leaving the servo valve and visual display means controlled by the sensing
means for indicating the pressure of fluid selected.

                       BRIEF DESCRIPTION OF THE DRAWINGS

     FIG. 1 is block diagram showing the elements of one embodiment of the
delivery system of the present invention.

     FIG. 2 is a block diagram showing one embodiment of the pressure selector
means 11 illustrated in FIG. 1.

     FIG. 3 is a block diagram showing one embodiment of one aspect of the 
pressure selector means shown in FIG. 2.

     FIG. 4 is a block diagram showing a second embodiment of one aspect of the
pressure selecting means illustrated in FIG. 2.

     FIG. 5 and 5A are block diagrams showing a preferred embodiment of the
treatment systems of the present invention, including the control systems
therefor.

     FIG. 5B is a view showing the abrasive delivery system with attendant
controls.

     FIG. 6 is a block diagram illustrating one embodiment of the treatment
system of the present invention in combination with one embodiment of the
evacuation system of the present invention.

     FIG. 6A is a block diagram illustrating a second embodiment of an
evacuation system of the present invention.

     FIG. 7 is a cross-sectional view of a two-stage evacuation nozzle according
to one embodiment of the present invention.

     FIG. 8 is a schematic block diagram showing the locating and general
arrangement of a presently-preferred servo valve system for controlling and
indicating the pressure of the fluid supplied to the jet.

     FIG. 9 and 10 are more detailed schematic diagrams of parts of the servo
valve pressure control system.

                 DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

     The present invention is directed generally to dental treatment systems and
dental components adapted for use in connection with such systems. As the term
is used herein, "treatment" refers to any operation for altering the physical
condition of the teeth or gums by impacting same with an abrasive-laden fluid
stream. As the term is used herein, "teeth" refers to teeth in their natural
state as well as teeth that have been filled or otherwise modified by earlier
dental treatment.

     FIG.1 is a schematic representation of a system embodying the present
invention and utilizing a stream of operating fluid delivered through a conduit
100. The illustrated system comprises the following components: fluid supply
means 101 connected to the conduit 100 for providing a stream of said fluid in a
second conduit 102 at an initial pressure; pressure selection means 103
connected to the stream within conduit 102 for selectively providing a fluid
stream within a conduit 104 at least at a first or second pressure, each of said
pressures being less than about the initial pressure of the stream in conduit
102; means 105 connected to conduit 104 for combining said fluid stream within
conduit 104 with abrasive particles to produce an abrasive-laden fluid stream
within a delivery conduit 106; and handpiece means 107 connected to conduit 106
for discarding or delivering a stream or fluid jet 108 against the tooth or
tooth structure of the patient to be treated.

     Preferably, pressure selection means 103 also comprises means for
selectively providing a substantially abrasive-free stream of pressurized fluid
to said handpiece means 107 by means of a conduit 109. Thus, preferred systems
of the type disclosed in FIG. 1 may alternatively and selectively be operated
in a first mode wherein the abrasive-laden stream is provided to handpiece
means 107 or a second mode wherein a substantially abrasive-free stream is 
provided to the handpiece. Applicant has discovered that highly desirable and 
beneficial characteristics are associated with dental treatment systems
having such a pressure selection means. For example, the systems of the present
invention are designed to provide abrasive-laden fluid streams for cutting of
teeth, such as is required in preparation for filling of cavities with amalgam
or the like. As the cavity is expanded by the abrasive-laden steam, the
abrasive particles may sometimes tend to settle or collect in the cavity and
produce a layer of abrasive particles in the cavity. The presence of this
layer, in turn, may reduce the effectiveness of the cutting operation under
certain conditions. Accordingly, it is a highly desirable aspect to the present
invention that the
<PAGE>   14
                                   5,525,058

                                       5

dental treatment system of the present type be selectively operable between an
abrasive-laden mode and an abrasive-free mode so that such layer can be readily
removed by blowing with a stream of air. It has been found that the use of
abrasive-free air acts to dry the tooth undergoing treatment which allows for
better cutting and abrading efficiency.

     As described above, an important consideration in achieving successful
operation of dental treatment systems is the degree to which the system permits
precise control and regulation of the fluid operating pressure. This
consideration is important because the regulation of fluid operating pressure.
this consideration is important because the regulation of fluid pressure helps
to control the action of the abrasive-laden stream on the tooth. However, the
rate at which abrasive particles are delivered to the fluid stream is also
frequently an important variable in achieving successful system operation. That
is, fluid pressure and abrasive delivery rate each have an influence upon the
cutting or abrading characteristics of the fluid stream. Moreover, it has been
discovered that a specific correspondence or relationship between fluid pressure
and abrasive delivery rate each have an influence upon the cutting or abrading
characteristics of the fluid stream. Moreover, it has been discovered that a
specific correspondence or relationship between fluid pressure and abrasive
delivery rate should exist in order to achieve results which are consistently
commercially acceptable. Improper matching of these two operating parameters can
preclude effective operation of the dental system. The pressure selection means
103 of the present invention preferably includes means for providing a control
signal 110 for controlling the rate at which abrasive delivery means 105
provides abrasive to the fluid stream within conduit 104. The present system
preferably operates such that the  control signal 110 be modulated according 
to the pressure selected. In this way, the systems of the present invention are
capable of producing an abrasive delivery rate which is precisely matched
to the pressure selected and hence to the desired operation. In general, it can
be said that at relatively low pressures, abrasive powder tends to accumulate
at relatively low pressures, abrasive powder tends to accumulate at relatively
low points in the system, whereas by moving air at a faster rate, higher
pressures above a given pressure, depending upon the design of the systems,
will be effective to move all of the powder available.

     The present system optionally includes means 112 (illustrated in FIGS. 6
and 7) in juxtaposition to the mouth of the person being treated for removing
excess and/or post-use abrasive particles from in and around the mouth.

     The present systems also optionally may include or are associated with a
dental laser of the type described, for example, in U.S. Pat. Nos. 5,055,048,
issued Oct. 8, 1991 and 4,940,411, issued Jul. 10, 1990. According to such
preferred embodiments, the present treatment systems further include means for
directing a beam of laser light toward the teeth of the patient being treated.
In this way, the dentist or other dental professional may utilize the present
system to alternatively and selectively treat the teeth of the patient with an 
abrasive-laden fluid stream or a dental laser.

     The components of the present systems may be housed, either together or
separately, in one or more suitable housings. In certain embodiments, however,
it is preferred that the dental treatment systems be incorporated into a
stand-alone, portable unit which can be transported to numerous locations and
connected to the appropriate local power supply and fluid source. In such
embodiments, it is preferred that the components are housed together on or in a
relatively compact housing.

                            A. Fluid Supply Means

     The nature and character of the fluid supply means 101 of the present
invention may vary widely, depending upon numerous factors, such as the
particular operating fluid being used. The material which comprises the
fluid stream supplied through conduit 100 may also vary widely within the scope
hereof, depending upon such factors as cost and availability, and the use of a
wide variety of materials are within the scope hereof. It is preferred,
however, that the fluid of the present invention comprise a gaseous material,
and even more preferably air.

     It will be also appreciated that the construction of fluid supply means 101
may vary depending upon factors such as the pressure of the operating fluid
being used. For example, it is contemplated that in certain embodiments the
fluid source within conduit 100 is provided at a pressure which is sufficiently
high to operate the dental systems of the present invention without further
compression. In such embodiments, the fluid supply means 101 may simply
comprise, for example, a supply conduit for transporting the fluid from its
source to  the pressure selection means 103. As mentioned above, however, the
preferred fluid, i.e., air, is generally only available in dental operatories
at pressures limited to about 60 to at most about 90 psig. This source of
operating fluid is preferred because of its ready availability and low cost.
While air at such pressures may be acceptable for numerous dental applications,
applicant has found that such pressures are insufficient to perform the
preferred etching and cutting operations for which the present system is
especially well adapted. In particular, applicant has found that successful
cutting, abrading and etching operations require a source of gas at a pressure
of from about 80 to 200 psig. According to preferred embodiments, therefore, the
preferred fluid source comprised operatory air at a pressure of less than about
80 to about 90 psig and the fluid supply means 101 comprises means for
increasing the pressure of the operatory air to greater than about 80 psig, and
even more preferably to a pressure of from about 80 to about 200 psig.

     The pressure increasing means of the present invention may comprise any one
of several well known structures for increasing the pressure of the selected
fluid medium. The selection of any particular pressure increasing means will
depend upon numerous factors such as flow rate, pressure differentials, sealing
methods, methods of lubrication, power consumption, serviceability and cost. It
is contemplated, therefore, that the pressure increasing means may take
numerous forms within the scope hereof. For embodiments in which the
operating fluid is a gas, it is contemplated that the pressure increasing means
may comprise, for example: fans, both axial and centrifugal; compressors, both
axial and centrifugal; rotary blowers; reciprocating compressors, both single
stage and two stage; and ejectors. For embodiments in which the preferred fluid
is air, the preferred means for increasing the fluid pressure comprises an air
pressure intensifier of the type sold, for example, by Haskel Incorporated of
Burbank, Calif. 97502, under Model No. MAA-2.5.

     The fluid supply means 101 according to preferred embodiments also includes
means for storing the pressurized fluid. The fluid supply means 101 also
preferably includes means for stabilizing the pressure of fluid stream with in
conduit 102. According to simple and effective embodiments of the present
invention, the means for storing the pressurized fluid also acts as the means
for stabilizing the pressure of fluid stream 102. For example, the air exiting
the pressure increasing means in the preferred embodiment is transported to a 
fluid supply tank adapted to maintain a reservoir of the pressurized air. This
fluid supply tank not only provides a high pressure reservoir, it also
serves to buffer or dampen the pressure spikes or fluctuations frequently
encountered with dental operatory air. For preferred 
<PAGE>   15
                                   5,525,058

                                       7

embodiments, especially those in which the present system is a substantially
portable system, the fluid supply tank comprises an air storage bottle capable
of maintaining at least one cubic feet of air at a pressure of about 250 psi.
In this way, fluctuations in the pressure of the fluid exiting the fluid supply
means is minimized.

              B. Means For Selectively Reducing the Fluid Pressure

     With reference to FIG. 2, an important aspect of the present dental
treatment systems resides in the provision of means 103 for selectively
reducing the pressure of the fluid stream within conduit 102. In particular,
means 103 makes the operating fluid selectively available at least at two and
preferably at least three discrete pressure levels, said discrete pressure
levels each preferably being less than about the initial pressure level of the
fluid provided by the fluid supply means 101 but substantially above
atmospheric. While it is contemplated that numerous structures may be adaptable
for use as the pressure selection means, it is preferred that the pressure
selection means 103 comprise inlet manifold means 114 connected to said fluid
supply means 101 for providing at least first and second flow paths 116 and 117
for the operating fluid. Each of said first and second flow paths 116 and 117
preferably include pressure regulating means 118 and 119 for precisely
regulating the pressure in a downstream portion of the flow path. Unless the
context clearly indicates otherwise, the term "downstream" refers to that
region of the flow path downstream of the pressure regulating means and
"upstream" refers to that region of the flow path upstream of the pressure
regulating means. Each flow path is thus divided by its respective pressure
regulating means into a high pressure upstream portion and a low pressure
downstream portion. According to highly preferred embodiments, the flow paths
are connected in parallel configuration. That is, the manifold means 114 is
configured such that the upstream pressure in said first flow path 116 is
substantially equivalent to about the upstream pressure in said second flow
path 117.

     The preferred selective pressure reduction means 103 is readily adaptable
and well suited for selectively providing the operating fluid at three or more
pressure levels, with each of said pressure levels being less than about the
initial pressure of the fluid provided by the fluid supply means. Applicant has
found that such an embodiment is especially beneficial for the provision of a
dental treatment system well adapted for use in each of the following three
dental operations: cutting, etching and abrading. Thus, it is highly preferred
that the inlet manifold means 114 include means for providing a first flow path,
a second flow path and a third flow path, each of said flow paths being
connected in a parallel configuration. The use of such a configuration according
to the preferred aspects of the present invention permits the utilization of
three distinct, precisely controllable operating pressures for the dental
instrument. Applicant has found that this is an important feature of such
preferred embodiments since it allows flexibility of use while simultaneously
preserving precise control and regulation of the necessary fluid stream. For use
in applications where the cleaning of the teeth is contemplated, a fourth 
parallel flow path may be provided with pressure in the fourth flow path being 
regulated to a level which is lower than the other pressure levels.

     With particular reference now to FIG. 3, the selective pressure reduction
means 103 of the present invention also preferably includes selective valve
means 120 and 121 in a portion, and preferably a downstream portion, of each
of the flow paths 116 and 117 for selectively blocking and unblocking the flow
of fluid through the respective flow paths. It is contemplated that numerous
valves of the type known and available in the industry are adaptable for use
for this purpose, and all such valves are within the scope of the present
invention. According to preferred embodiments hereof, as disclosed more fully
hereinafter, the valves of the present invention are preferably high pressure
solenoid operated valves of a type well known in the art. Each of the flow
paths also preferably includes in a downstream portion thereof, means 124 and
125 for preventing back flow of said pressurized fluid. The back-flow
prevention means are preferably located in a portion of said flow path which is
downstream of said valve means 120 and 121. In a typical arrangement, means 124
and 125 each comprise a check valve in the flow path immediately downstream of
valve means 120 and 121, respectively, each such check valve being of any type
and construction well known in the art. Additionally, a filters 122 for
removing unwanted debris or particles from the fluid should be included in a
downstream portion of the flow paths. The filters are of particular importance
in the prevention of the migration of abrasive back into the solenoid operated
valves and the check valves, thus avoiding equipment failure.

     Another aspect of the invention illustrated in FIG. 1 involves the supply
of gas at a pressure close to but somewhat below the lower of any of the
operating pressures established by the selective pressure reduction means,
directly to the inlet of the abrasive particle delivery systems. For reasons
which will become apparent in the following, it is of importance that at start
up, prior to the selection of any particular operating pressure level, the
abrasive particle delivery system be immediately activated by the supply of
regulated air under pressure. For this purpose, in systems where operatory air 
at pressures of about 80 psig is available in conduit 100, a branch conduit 123
delivers regulated air directly from line 100 to air/abrasive unit 105. In order
to regulate the pressure of this air supply, a pressure regulator 126 is
provided which maintains the pressure in line 123 at a preset limit, for
example, between about 60 and about 80 psig.

     The selective pressure reducing means 103 preferably comprises control
means 127 for providing a control signal (indicated by dashed lines) to the
valve means 120 and 121, thereby selectively opening and/or closing the valve
means. In the preferred embodiments in which the valve means is a solenoid
operated valve, the control means comprises a solenoid for each of said valves 
and an electrically operated circuit for opening and closing the solenoid 
valve, as more fully described hereinafter.

     The pressure reducing means 103 also preferably includes an exit manifold
means 128 connected to flow paths 116 and 117. The function of the exit manifold
means 28 is to provide a source of fluid 104 at the selected pressure to the
air/abrasive means 105. Thus, the exit manifold means 128 preferably comprises a
conduit connected between a downstream portion of each of said flow paths 116 
and 117 and said abrasive delivery means.

     The selective pressure reduction means 103 also preferably includes
pressure relief means for relieving fluid pressure in excess of that selected 
for the particular operation. Important functions of the pressure relief means 
are to ensure that pressure of the fluid is immediately adjusted to the selected
pressure and, in addition, that it does not unexpectedly and unwantedly rise,
because of a malfunction in the system, substantially beyond that pressure
selected by
<PAGE>   16
                                   5,525,058

                                       9

the dentist or other dental professional.  Control means is also preferably
provided for selectively controlling the relief means such that the activating
pressure of the relief means corresponds to or is slightly greater than the 
maximum pressure in the pressure range selected by the dentists. As the term 
is used herein, "activating pressure" refers to the pressure at which the 
pressure relief system relieves the build-up of pressure in the system.

     It will be appreciated that the provision of such pressure relief means
according to the present invention constitutes an important aspect of certain
embodiments hereof. For example, the relief means provides a way of immediately
establishing a selected pressure and gives the health professional a confidence
that the desired pressure level is reliably at the pressure selected. In
addition, it would be undesirable and potentially detrimental to the patient
if the operating pressure in the dental treatment system was suddenly and
unintentionally raised above the selected operating pressure. If such were to
occur, the rate of flow and the pressure of the jet stream leaving the dental
handpiece would unexpectedly increase beyond the desired pressure range. This
unexpected and undesired increase may not only reduce the efficacy of the
desired dental treatment, it may also, depending upon the extent of the pressure
increase, cause harm and injury to the patient being treated. Accordingly, it is
important and highly desirable that the dental treatment systems of the present
invention include mechanisms for ensuring that desired pressure is reliably
established and that such an unexpected pressure increase does not occur.

     An preferred configuration of the downstream portion of pressure
selection means 103 is illustrated in FIG. 4. According to the embodiment of
FIG. 4 and  also indicated in FIG. 1, the system includes means for providing a 
substantially abrasive-free stream 109 to handpiece 107. Applicant has found 
that the provision of such means, particularly when such means is operable 
separately and independently of remaining portions of the pressure selection
means, is highly desirable, as described hereinbefore. Accordingly, with
reference to FIG. 4, the substantially abrasive-free delivery means comprises,
for example, conduit 129 leading from a downstream portion of flow path 116 and
selective valve means 131 in the flow path for selectively blocking and
unblocking the flow of fluid therethrough. The conduit 129 also contains a
pressure regulator 130 to  regulate the pressure of the abrasive-free air
flowing to the nozzle. Control means 127 is connected to valve means 131 for
selectively and independently operating the valve means 131. A check valve 132
and filter 133 are preferably located downstream of valve means 131 for
preventing the back flow of fluid or contaminants and abrasives therethrough.

     As further illustrated in FIG. 4, the pressure relief means comprises a
pressure relief means associated with each selectable pressure range. For
example, relief means 134 and 135 are connected to exit manifold means 128 for
relieving fluid pressure in the exit manifold to the extent such pressure is in
excess of the fluid pressure selected. The exit manifold 128 will, depending
upon the operating pressure selected, be subject to at least a relatively high
pressure and a relatively low pressure. When the relatively low pressure is
selected, no difficulty is presented. On the other hand, the presence of the
low pressure relief means in fluid communication with the exit manifold would,
in the absence of the pressure relief blocking means of the present invention,
prevent operation in the relatively high pressure mode. Accordingly, each
pressure relief means 134 and 135 is preferably connected to control means 127
such that the relief means is operative  when the pressure range of its
associated flow path is selected and inoperative when a higher pressure range
is selected. Thus, each pressure relief means 134 and 135 preferably includes a
valve means connected to control means 127 for selectively blocking and
unblocking flow of pressurized fluid to the respective pressure relief
mechanism, depending upon the pressure selected for operating the system. In
operation, therefore, the valve means for each relief mechanism is activated to
the unblocked position when the operating pressure range associated with that
relief means is selected. Conversely, the valve means remains in the
unactivated, blocked position when all higher pressure ranges are selected, 
thus assuring that the desired pressure will be immediately and reliably 
available to the operator.

         C. Control System, Abrasive Delivery and Pressure Relief Means

     With reference now to FIGS. 5 and 5A, a preferred embodiment showing
details of the selective pressure reducing means, including control systems and
pressure relief means thereof is disclosed. As fully explained hereinafter, the
system illustrated provides for selective delivery of air and abrasive at three
discrete pressure levels or a supply of air free of abrasive. Turning first to
FIG. 5, the illustrated system includes a source of fluid, preferably air, at
a pressure of about 60 to about 90 psig and air supply means 101 which includes
means for increasing the pressure of the air so as to supply a stream of air
through line 102 at a pressure of from about 80 to about 200 psig. A valve 138
operated by a solenoid 139 is positioned upstream from the supply means 101.
Valve 138 is a normally closed valve (hereinafter an NC valve) which is
actuated to the opened position by the solenoid 139 upon the closing of a main 
switch 140.  The opening of valve 138 allows the flow of air to a pressure 
regulator 141 in conduit 123 and to supply means 101 and conduit 102, a check 
valve 142 to an inlet manifold means comprising the common manifold conduit 
143 which  corresponds to manifold 20 in FIG. 2 and manifold branch conduits 
144 through  146 and the connections therefor.

     Each branch conduit 144 though 146 comprises a flow path for the
pressurized air and includes therein pressure regulators 148 through 150 for
regulating the pressure in a downstream portion of the respective conduit.
Although the downstream pressures in conduits 144 through 146 may vary depending
upon the particular operations contemplated, it is preferred that they be
regulated to a pressure within  a high pressure range, a mid pressure range and
a low pressure range, respectively. More particularly, a high pressure range of
about 160 to 180 psig is preferred for cutting and excavating of tooth enamel, a
mid pressure range of about 120 to 140 psig is preferred for etching tooth
enamel and a low pressure range of about 80 to 100 psig is preferred for
cleaning teeth. In addition, manifold branch line 152, in which a pressure
regulator 153 is located, provides for delivery of a supply of regulated air 
free of abrasives and a manifold branch line 154 in which a regulator 155 is 
located, provides for delivery of air free of abrasive to the teeth or for the
evacuation of abrasive from the system downstream from the abrasive unit, as 
will be explained hereinafter.

     Immediately downstream of the pressure regulators 148 through 150 and 153
are NC valves 148A through 150A operated by solenoids 148B through 150B,
respectively. Downstream of the valves 148A through 150A are found check valves
156 through 158, respectively.

     Exit manifold means comprising manifold conduit 160 and pressure gauge 161
is connected to  and in fluid com- 

  
<PAGE>   17
                                  5,525,058


                                      11

munication with a downstream portion of each of the conduits 144 through 146. 
Also connected to and in fluid communication with manifold conduit 160 is a
pressure relief means comprising three relief valves 162 through 164 protected
by NC valves 166 through 168 operated by solenoids 169 through 171,
respectively.

        Exit manifold conduit 160 leads from each of conduits 144 through 146
to abrasive delivery means 105 for producing a stream of abrasive-laden gas at
the desired pressure to a handpiece 107 through a conduit 172.

        From the foregoing, it can be seen that upon closure of main switch
140, NC valve 138 is opened.  This allows operatory air to flow through
pressure regulator 141 directly to manifold 160 to pressurize the air abrasive
delivery system which is preferably of the kind illustrated and claimed in U.S.
Pat. No. 4,708,534 and as generally disclosed in FIG. 5B.

        The system may further be provided with a switch 101A located in
conjunction with the air reservoir within fluid supply means 101.  Switch 101A
prevents operation of the system, except when there is an adequate pressure 
level within the reservoir.

        With particular reference to FIG. 5B, the preferred form of abrasive
delivery system 105 will be described briefly.  The system includes a sealed
lower chamber 175 mounted on a base 176 and an abrasive powder supply vessel
177 which is bolted or otherwise fastened to the top of chamber 175.  Located
within chamber 175 is an upwardly open cylindrical particle feed receptacle 178
which is mounted on a vibratory device 179, as particularly described in the
aforesaid U.S. Pat. No. 4,708,534.  Cylindrical feed receptacle 178 is provided
on its inner surface with a helical feed groove 180, the lower end of which
communicates with the bottom of the cylinder and the top of which is in
communication with a feed tube 181 which delivers the particulate material
through a section of resilient, flexible tubing 182 to an exit tube 183 which
passes through the wall of vessel 175.  Joined to tube 183 is a second section
of resilient flexible tubing 184 which is in turn connected to a duct 172 which
leads to handpiece 107, as is illustrated in FIG. 5.

        Powder supply receptacle 177 is adapted to receive and contain a supply
of particulate abrasive matter, generally indicated by the reference character
P and to supply the same in a uniform manner to the bottom of cylindrical feed
device 178 through a feed tube 186 in a manner more particularly described in
U.S. Pat. No. 4,708,534.

        In order to bring the powder delivery system up to a pressure at which
it is primed for operation, air under pressure, for example, of about 80 psi,
is delivered to chamber 175 by way of a connection 187 which is connected to
line 160 which is pressurized upon closure of valve 138 when main control
switch 140 is closed.  A branch conduit 188 also supplies air at the same
pressure to the powder supply chamber 177 by means of a connection 189 which
communicates with the interior of the supply chamber 177.

        Vibratory device 179 is an electrically operated device which is
preferably activated off handpiece 107 by means to be described hereinafter. 
In general, the rate of vibratory feed is controlled by way of a preset
adjustable control device 190 mounted on the equipment control panel in a
convenient location.  Device 190 may be set manually by the operator to a
desired vibratory rate or optionally may be a pressure responsive device which
automatically adjusts through connections to switch 191 so that an appropriate
rate is provided for the operating pressure level as selected on switch 191.

        The abrasive delivery system is also preferably provided with a
normally closed value 192 which is preferably a pinch valve of the kind
illustrated more particularly in FIG. 10 of the aforesaid U.S. Pat. No.
4,708,534.  Pinch valve 192 is controlled by a solenoid 193 either directly or
through a fluid pressure device.  The solenoid 193 is preferably energized upon
closure of a switch activated off the handpiece to maintain pinch valve 192 in
the open position whenever vibrator 179 is in operation.

        In summary, when the main switch 140 is closed, chambers 175 and 177
are immediately pressurized at the low end of the operating pressure range so
that the abrasive delivery system is readied for the delivery of a
particulate-laden air stream through resilient tube 184 to conduit 185 when
desired by the operator.  Upon activation of the vibrator and opening of pinch
valve 192 by the control circuitry, described hereinafter, particulate material
advances upwardly within spiral groove 180 through duct 181 where it enters
resilient, flexible tubing 182 and exit tube 183, where it exits container 175
and passes through tube 184 to join conduit 185.

        It will be appreciated by those skilled in the art that it may be
desirable to use different abrasives and/or different particle size abrasives
for different dental operations.  For example, it may be desirable to utilize
abrasive particles having one set of characteristics for a first dental
operation and a second set of characteristics for a second dental operation. 
While it is possible to manually change the type of abrasive being used, it is
preferred that the abrasive delivery system of the present invention include
means for selectively providing either a first abrasive particle or a second
abrasive particle for mixing with the fluid stream.  One apparatus capable of
achieving this result is disclosed in U.S. Pat. No. 2,661,537 to Angell, which
is incorporated herein by reference.

        As explained above, closure of main switch 140 also allows the
operatory air to be delivered to the air pressure intensifier 101 which
preferably increases the pressure of the available air to be supplied to a
level of approximately 200 psig.  Air at this pressure is then delivered
through conduit 143.

        FIG. 5 further illustrates the system provided for controlling the
selective pressure reduction means and for selective delivery to the handpiece
of pure air under pressure or a pressurized air and abrasive mix as required. 
The control system preferably involves the use of separate pressure selector
switch 191 and additionally includes controls on the dental handpiece 107,
operation of the selective pressure reduction means being described first.

        The pressure selector switch 191 is located in any convenient position
on the control panel or optionally and/or additionally may be incorporated in a
foot actuated switching device of a type well known in the art.  As is
illustrated in FIG. 5, when switch 191 is in the open position (as shown), the
NC valves 148A through 150A remain closed and the flow of operating fluid
through any one of valves 148A through 150A is thus blocked.

        With switch 191 in any one of the closed positions, the appropriate
solenoid 148B through 150B is energized, thereby allowing fluid to flow through
the appropriate conduit 144 through 146.  As seen in FIGS. 5 and 5A, conduit
144 through 146 deliver air to manifold 160 at a pressure established by the
respective pressure regulator 148 through 150.

        Since the pressure in conduit 160 can be within any one of the three
above described pressure ranges, the pressure
<PAGE>   18
                                  5,525,058


                                      13

relief means includes first, second and third relief valves for relieving
pressure in excess of said first, second and third pressure in excess of said
first, second and third pressure ranges, respectively.  The first relief valve
162 is calibrated with an activation pressure which corresponds to or is
slightly greater than the maximum operating pressure in the downstream portion
of flow path 144, while relief valves 163 and 164 are calibrated to have
activation pressures which correspond to or are slightly greater than the
maximum operating pressure in the downstream portions of flow paths 145 and
146, respectively.  When a control signal is transmitted to solenoid 148 to
open valve 148A, solenoid 169 is activated by the same control signal, thereby
opening blocking valve means 166.  However, blocking valves 167 and 168 remain
closed, thereby isolating the relief valves 163 and 164 from the operating
fluid when the system is operated in the high pressure mode.  It will be
understood that similar operation occurs in the mid- or low-pressure modes.

        As indicated above, means are provided to deliver air at relatively low
pressure as established by pressure regulator 153 through the conduit 152. 
This conduit bypasses the abrasive supply unit 105, delivering a regulated
supply of air at a relatively low pressure directly to the inlet of the
handpiece 107 to provide the operator with a stream of abrasive-free air useful
for drying the region of the tooth as is frequently desired.  For this purpose,
normally closed valve 151A in line 152 is opening by energization of a solenoid
151B which is preferably controlled by a pressure operated switch activated by
closure of one of a group of control ports on handpiece 107, as described
below.  Line 152 is further provided with a filter 152A and check valve 159 to
isolate the valve components from the air and abrasive mixture.

        In one condition of operation of the system, as will be described
subsequently, the air delivered through line 152 may also be used to create a
vacuum downstream from the abrasive delivery system so as to effect removal of
the mixture of abrasive and/or debris from the interior of the handpiece.

        As indicated just above, a plurality of control ports provided on the
handpiece 107 enable certain functions of the system of the present invention. 
According to the preferred embodiment of the invention, shown in FIG. 5, the
handpiece is preferably provided with four fluid control ports 194 through 197,
each of which is conveniently located to be closed by a finger of the operator. 
Ports 194 through 197 are located in series-circuit relationship with a
relatively low pressure supply of air, supplied for example, through branching
conduit 154 and regulated by pressure regulator 155 (FIG. 5).  The ports 194
through 197 control three normally open diaphragm operated pressure switches
198, 199 and 201 and one diaphragm operated latching switch 200, each of which
receives pressurized air from conduit 154.  So long as handpiece ports 194
through 197 are uncovered, air at a relatively low pressure passes through the
diaphragm chamber of each of the switches 198 through 201 and exits through the
ports.  However, upon closure of a selected one of ports 194, 195 and 197, one
or more of the normally open switches 198, 199 and 201 will be closed on
account of the increase in pressure to which the diaphragm in the switch is
subjected.  In the case of latching switch 200, momentary closure of port 196
is effective to latch switch 200 in the closed position if initially opened and
to return it to the open position if closed.

        As illustrated in FIG. 5A, port 194 is a lamp activation port which
communicates with the diaphragm chamber of switch 198 which, when closed,
energizes a circuit which lights a lamp 202 (which may include a fiber optic
device) which casts a beam of light through an opening in the distal end of
handpiece 107 for the purpose of illuminating the area of a tooth or related
tooth structure being worked on by the operator.  So long as port 194 is
closed, the lamp 202 remains illuminated.

        Port 195 is a light and air activation port which is in communication
with normally open lamp switch 198 through a conduit 204 and 205 and in
communication with the diaphragm chamber of normally open diaphragm operated
switch 198 by means of conduits 204 and 205 so as to effect closure of switches
198 and 199 when port 195 is closed, thus turning on lamp 202 and activating
solenoid 212 so as to close valve 213 to deliver air free of abrasive from
conduit 152 to the handpiece.

        Port 196 is a powder evacuation activator port which is in
communication with latching switch 200 by means of conduit 206 and may also be
in communication with the light switch 199 by means of a branch conduit 207. 
Upon closure of port 196, the light will be turned on and switch 200 closed to
energize a solenoid 191A which activates switch 191 to turn on vacuum 221, as
described hereinafter in reference of FIG. 6.

        Port 197 is the port for activation of the powder delivery system and
is in communication with normally open diaphragm operated switch 201 via lines
208 and 211.  Closure of switch 201 by placing a finger over port 197 energizes
solenoid 193 to open pinch valve 192 and turns on vibrator 179. 
Simultaneously, solenoid 212 is energized to close normally opened purge valve
213.  The relatively high pressure air abrasive mixture is directed through
conduit 172 and out through nozzle 107A.  Since the pressure of the air and
abrasive mix is high relative to the pressure of the air in line 152, check
valve 159 blocks flow of pure air through line 152.  However, as soon as the
user removes his finger from port 197 to terminate the delivery of the air and
abrasive mix, pure air again flows past the check valve 159.  Opening of the
switch deenergizes solenoid 212 to open pinch valve 214 so that air flows out
through purge line 214.  Because there is a small orifice in the tip of
handpiece 107 relative to the cross-section of the purge line, the rush of air
creates a vacuum.

        As indicated in FIGS. 5 and 5A, the various branch circuits are
provided with check valves to insure that closure of a particular port
activates only through switches which are required to perform the functions
indicated.  In addition, filters 152A and 217 provided in lines 152 and 160
insure that abrasive does not enter the manifold system.

        Although the use of the above-described fluid ports constitute a
preferred method of control, it should be understood that electrically operated
switches positioned on the handpiece and utilizing a low voltage power source
could be employed without departing from the scope of the invention.

                          D. Dental Handpiece Means

        It will be appreciated by those skilled in the art that the particular
form of the handpiece 107 may vary widely, depending upon factors such as cost
and portability.  In general, it is preferred that the handpiece be adapted to
be carried and manipulated by the dentist or other dental professional.  For
this reason, handpiece 107 is generally formed in the shape of an elongate
cylinder connected to the abrasive/fluid delivery means 105 by way of the
conduit 172 (see FIG. 5), which conduit should be flexible for ease of
manipulation.  A central bore in the handpiece transports the

<PAGE>   19
                                   5,525,058

                                       15

abrasive-laden fluid to a nozzle means 107A disposed at the distal end thereof.

        In addition, the handpiece is provided with a fiber optic channel to
accommodate lamp 202 and a fiber optic device which terminates at the distal
end of portion 107A for the purpose of directing light in the area of impact of
the abrasive particles.  The nozzle means 107A may be, for example,
frusto-conically shaped, thereby providing a cross-sectional flow area which
reduces gradually from that of about the central bore to a relatively small
opening in the end of the nozzle.  This reduction in flow area results in a
concomitant increase in fluid velocity, thereby producing a stream or jet of
abrasive-laden fluid 108 which is effective for cutting, etching or cleaning
teeth or related tooth structure, depending upon the operating pressure of the
system.  The particular configuration and construction of such handpieces is
generally well known, and all such constructions are within the scope of the
present invention.  One such handpiece is shown in U.S. Pat. No. 2,696,049,
which is incorporated herein by reference.  As illustrated in the '049 patent,
the nozzle portion of the delivery means is preferably readily removably
attached to the handpiece.  Such removability is beneficial in several
respects.  First, it will be appreciated that the flow of high velocity
abrasives through the nozzle 107A of the present dental treatment systems will
tend to cause wear and abrasion of the internal channel of the nozzle.  This
could, in turn, reduce the efficacy of the system.  Accordingly, the provision
of a removable nozzle permits replacement of the nozzle as needed to maintain
the efficacy of the system.  In addition, applicant contemplates that the
nozzle 107A may, in certain embodiments, be comprised of a relatively
inexpensive material, such as plastic.  In such embodiments, it is expected
that the nozzle would be discarded after each use.  The provision of such a low
cost, inexpensive replaceable nozzle has the obvious advantage of reducing a
likelihood of the spread of infectious disease from one patient to the next.
It is contemplated that the removability of the present nozzle may be achieved
by providing the nozzle with a threaded portion, as disclosed in the '049
patent, or other means, such as providing a bayonet type attachment between the
nozzle and the remainder of the handle portion.  In addition, the entire
handpiece should be separable from conduit 172 and from its associated control
lines to permit autoclaving.

        According to another preferred embodiment of the present invention, the
portion of the nozzle which comes in contact with the abrasive-laden fluid
stream may be formed of a hard, abrasion-resistant material, such as carbide.
Thus, the nozzle itself can be formed of such carbide material, or formed of
less expensive materials which are lined with carbide or similar
abrasion-resistant materials.

                E.  System for Evacuating Abrasive Material

        In its preferred form, the dental treatment system of the present
invention includes the provision of means for effectively and efficiently
evacuating excess abrasive particles from the area of the mouth after
treatment.  As noted, above, the failure of prior art dental treatment systems
to effectively deal with the continued removal of abrasive particles from the
mouth has contributed to the lack of acceptance of the systems.  With
particular reference to FIGS. 6, 6A and 7, the invention preferably includes a
two-piece vacuum nozzle means, generally indicated at 220, adapted to be placed
in the mouth of a patient and a means for creating a vacuum within the nozzle
means so as to draw away the abrasive particles and debris.

        According to FIG. 7, nozzle means 220 preferably includes an outer
tubular housing section 222 and an inner tubular section 223 co-axially mounted
within section 222 by means such as a support plate 224.  Preferably, inner
tubular member 223 has an outwardly flared portion 225 which is intended to be
positioned adjacent to the region of the patient's mouth during treatment.  A
plurality of spaced apart openings 226 are located in a plate 224.

        Preferably, inner tubular conduit section 223 is frictionally fitted
within a sleeve or collar 227 which is joined to support plate 224.  The
frictionally interfitting portions provide a means permitting longitudinal
adjustment of inner tubular member relative to the outer section 222 so as to
permit movement of the flared portion 225 to accommodate patients having
different sized mouths and/or to allow for adjustment to bring the flare
portion into different areas of the mouth.

        Evacuator nozzle 220 is connected to a flexible hose 230 which is
coupled onto the end of the outer tubular housing section 222.  Preferably, the
cross-sectional area of the openings 226 and the cross-sectional area of the
inner tubular section 223 should roughly equal the cross-sectional area of 
tube 230 so as to avoid an unwanted choking down of the air drawn from the
patient's mouth.  As indicated in FIG. 6, conduit 230 preferably is connected
to the vacuum means 221 which comprises a conventional electric motor operated
vacuum system which, in one embodiment, includes a rigid, removable disposable
container 232 within which the used abrasive and debris is collected.  A valve
233 within conduit 230 blocks flow through the conduit.  As indicated in FIG.
6, valve 233 is manually operated.  In addition, pressure selector switch 191
operates electric motor for vacuum 221 so as to draw air from the nozzle 107A
and the patient's mouth area as soon as a particular pressure is selected,
thereby avoiding the possibility of excess abrasive escaping to the atmosphere. 
With the system described, substantially all abrasive delivered to the
patient's mouth, as well as the debris created by the cleaning, abrading and
cutting operations, is captured by the vacuum system and delivered to the rigid
disposable container 232 which is preferably readily sealable for separate
handling and disposable at a medical disposal waste site, if necessary.

        FIG. 6 also illustrates purge line 214 which, as explained above, is
opened so as to convey away abrasive from the system downstream from the air
abrasive means 105 when the operator removes his finger from handpiece port
197.  Desirably, a filter 233 filters out any abrasive drawn through conduits
230 or 214 by vacuum means 221.

        FIG. 6A illustrates an alternative form of means for creating a
vacuum.  According to FIG. 6A, the vacuum means comprises a water venturi shown
at 221.  Both conduits 214 and 230 are connected to the throat of the venturi.
The flow of water through the venturi creates a subatmospheric pressure in the
throat drawing excess abrasive from evacuator nozzle 220 and purge line 214.

        With reference back to FIG. 6, the system may also comprise a branch
passage 234 which has a connector 235 which permits connection to the standard
suction system 236 available in most dental offices.

        The operation of the illustrative embodiment of the invention will now
be briefly summarized with particular reference to FIGS. 5A and 5B.

        When main power switch 140 is turned on, solenoid 139 effects the
opening of valve 138 delivering air under pressure of between about 60 and 90
psig to the pressure
<PAGE>   20
                                   5,525,058

                                       17

intensifier 101.  Simultaneously, a regulated supply of air is delivered
through conduits 123 and 160 to the air abrasive delivery unit priming this
unit by pressurizing chamber 175 and power supply 177.
 
     The operator chooses the particular operating pressure for delivery of the
air-abrasive mixture through use of selector switch 191 which may be
conveniently located on the instrument panel or, alternatively, through a
four-position foot activated switch, not shown, having four actuating positions
which are connected in parallel with the contacts of switch 191.

     At this point, the device is fully primed for operation which is achieved
through selective control by closure of an appropriate port on the dental
handpiece 107.  If the operator wishes to only illuminate the tooth or related
tooth structure to be worked on, he closes finger port 194 which effects closure
of the lamp circuit to light lamp 202.  If the operator then wishes to direct a
jet of drying air to the tooth or tooth structure, finger port 195 is closed
which effects energization of the lamp circuit and a closure of purge valve 213.

     Closure of port 196 latches switch 200 in the closed position which
activates the vacuum system of FIG. 6. Finally, when the operator is ready to
apply the air abrasive mix to the tooth or tooth region, the covers port 197
which energizes solenoid 193 to open pinch valve 192, turns on vibrator 179 and
closes normally open purge valve 213.  When port 197 is uncovered, the flow of
air and abrasives stops, the purge valve 213 is opened and air through line 152
purges portions of the system downstream of abrasive unit 105 of abrasive
materials.

     In the illustrative embodiment, the vacuum system is activated whenever
pressure selection  switch 191 is turned on with the result that abrasive
particles and tooth debris are drawn from the region of the patient's mouth
whenever an air/abrasive mixture is delivered by the handpiece as well as when
drying air alone is delivered and when the operator is merely inspecting the
area being treated.

     Through the unique combination of pressure relief valves 162 through 164
and blocking valves 166 through 168, the pressure chosen for use in the
treatment of teeth may be readily and rapidly changed by use of selector switch
191. When switching from a higher to a lower operating pressure, the change
occurs immediately, enabling the operator to work confidently and without delay.
Still further, switch over from cutting and abrading to the use of air for
cleaning and drying the tooth region being worked on or the use of the light
only can be readily and rapidly accomplished by controls conveniently located on
the dental handpiece.

     FIGS. 8 and 9 show a more-recently developed and presently preferred
embodiment of the pressure-selection apparatus 103 of FIG. 1, now to be
described.

     The pressure-selection means 103 shown in the broken-line block in FIG. 8
contains a servo valve 300 of known form, as described below, supplied with the
high-pressure fluid from fluid supply means 101 over line 103 as shown in FIG.
1.  Also provided to the servo value 300, from system power supply 302 over line
304, is the operating supply power for the apparatus, and a ground connector 306
is also provided.  Servo valve 300 serves to provide fluid under pressure over
line 104 to the abrasive supply 105, whence the abrasive-laden fluid travels
over line 106 to operator's handpiece 107 to form operating jet 108, numerals
corresponding to those in FIG. 1 indicating corresponding parts.

     The pressure supplied to line 104 by servo valve 300 is controlled by
command signals supplied to it over command line 310 from control and display
circuit 314.  Operator control of circuit 314 is enabled by operator interface
316; the operator increases the pressure in steps by sequential pushing of the
UP button 320, and decreases it in steps by sequential pushing of DOWN button
322.

     The valve is preferably of the type QB1TFEE30 made by Proportion-Air Inc.
of McCordsville, Ind.  It contains a valving arrangement which can be set by a
command voltage to variety of states (in this example, 6 states) in which it
produces different pressures in its output flow of fluid.  The valve also
includes a sensor which senses the valve output pressures to produce an internal
feedback voltage indicative of output pressure, compares the feedback voltage
with the command voltage to produce an error signal, and moves the valving
mechanism in the direction to reduce this error to substantially zero, thus
assuring that the commanded output pressure is produced.

     FIG. 9 shows the preferred arrangement for controlling the servo valve 330
in accordance with the operator's commands.  The UP and DOWN pushbuttons are
electrically connected to a conventional 3-bit up-down counter 360, which has
seven output states (binary 0-6), of which only 1-6 are used.  A set of seven
fixed d-c voltage sources 366, 368, 370, 374, 376, 378 are provided, as from
taps on a regulated voltage divider; the zero voltage is not used, except before
initial selection of a pressure.  These fixed voltages are applied to a selector
390, which passes to the command voltage lead 310 a fixed voltage corresponding
to the count put out by the 3-bit counter in response to the operator's
operation of the UP-DOWN buttons; that is, for each of the counts 1-6 a
different corresponding one of the fixed voltages is supplied to command lead
310 by the selector.  The selected voltage then causes the servo valve to move
toward, and remain at, the desired condition for producing the desired valve
output pressure.  The selector may be a conventional type CD 4051 integrated
circuit, commonly a available commercially.

     The remainder of the circuit is primarily to display the next pressure
called for by the operator (the "target" pressure) as well as the pressure
actually at the servo valve output. For this purpose, the 3-bit counter 360
supplies its output to a display logic circuit 379, which functions as follows.
When the operator wishes to change the pressure to a new value, he operates the
UP-DOWN buttons while a corresponding one of the barograph LED lamps 382, 384,
386, 388, 390, 392 connected to the display logic circuit flashes, until it
reaches the desired pressure, at which time he stops pushing the buttons, and
all lamps up to and including the one representing the desired pressure stay ON.
To provide the flashing functions, each LED illumination circuit may be provided
with a gate through which intermittent voltage from a flasher-voltage generator
in the logic display circuit is provided to any open gate; the binary number
being supplied from the 3-bit counter, through a selector circuit in the logic
display circuit, determines which gate is open and hence which lamp flashes,
indicating the existing pressure.  The lamps 381 through 392 may correspond, for
example to 40, 80, 100, 120, 140 and 160 pounds per square inch of servo valve
output pressure, respectively, and if the pressure is initially at 100 psi, the
lamps for 40, 80 and 100 psi will all be lit; if the operator then presses the
UP button twice, the 140 psi lamp will flash until the servo valve output
pressure reaches 140, at which time all of the 40, 80, 100, 120 and 140 psi
lamps will be steadily illuminated.

     The change from flashing of the "target" lamp to the all-steady lamp
condition is accomplished in response to an analog monitoring voltage received
on line 400 from the servo valve.  This analog monitoring voltage is convention-

 
<PAGE>   21




                                   5,525,058

                                       19

ally available in servo valves, including the model specified above.  The
received monitoring voltage is applied to an input of each of a set of
comparators 540, 542, 544, 546, 548 and 550, one for each voltage level.

     Each comparator is also supplied with a fixed output voltage from the
respective sources 500, 502, 504, 506, 508 and 510.  The voltage of each such
source is somewhat above the corresponding fixed voltage in the command-voltage
set 366 through 378, but below the next higher fixed voltage in that set.  That
is, the fixed voltage for the lowest comparator 500 is 0.94 v., which is greater
than zero but less than the 1.25 v. of the command set, and so on for the other
fixed voltages.  As a result, as the monitor voltage increases from zero due to
increasing servo output voltage, the comparator output lines 540 through 552 are
progressively actuated; that is, all of lines 640 through 652 connected to
comparators which have fixed voltage inputs less than the monitor feed back 
voltage are activated at any time.  The display logic circuit 379 is thereby
enabled to turn on steadily all lamps corresponding to the actuated output
lines of the comparators, as desired for this type of display.

     The control and display circuit 314 of FIG. 8 may be located on a panel of
the main system cabinet, or in some cases in the handpiece itself for convenient
use. 

     A switch (not shown in FIGS. 8-10), actuated for example by a foot pedal,
may be used to supply the jet with clean abrasive-free air for the fluid jet
when desired, and simultaneously to shut off the flow from the abrasive tank.

     Referring now to FIG. 10 showing a preferred form of display logic circuit,
numerals corresponding to those in earlier figures designate corresponding
parts.  Shown are the 3-bit counter 360, the selector 390, the lamps 381-392,
the gates 540-550, the fixed voltage sources 500-510 and the analog monitor
voltage line 400 as shown also in FIGS. 8 and 9.  The display logic unit is
shown in more detail in the broken-line box 379.  Included therein is a flasher
700 which, when turned on, generates a pulsating current for flashing the lamps.
The flasher is turned on, by way of flasher control 710, when the bit-change
sensor 702 senses a change in the output of the 3-bit counter 360 due to a
change in command by an operator pressing an up or down control button 320 or
322.  Which lamp is flashed is determined by conventional selector 716, under
the control of the output signal supplied to it from 3-bit counter 360 over line
724.  In this way the desired "target" lamp is caused to flash.

     When the servo valve responds to the command voltage and adjusts itself to
the target pressure, the analog voltage returned from the sensor valve over line
400 corresponds with the command voltage; the voltage on line 400 is supplied to
one input of a comparator 750 over line 400A, the other input of which is
supplied with the command voltage from selector 390.  When the servo valve
pressure corresponds to the commanded value, the comparator senses this and
produces an output to flasher control 710 to shut off the flasher, as desired
upon attainment of the target pressure.  

     Also, one may employ additionally, in some embodiments, a suction system
for removing abrasive material from the mouth, as described and claimed in the
above cited application Ser. No. 08/029,732, of Ben J. Gallant, the description
of which is included herein by reference.

     While the invention has been described with reference to specific
embodiments in the interest of complete definiteness, it will be understood that
it may be embodied in a variety of forms different from those specifically shown
and described, without departing from the spirit and scope of the invention.

     What is claimed is:

     1. A system for performing a dental procedure on teeth or associated tooth
structure by means of abrasive particles carried by a fluid stream, comprising:

     (a) a source of fluid under pressure;

     (b) a source of abrasive particles;

     (c) abrasive-mixing means supplied with said fluid under pressure and said
         abrasive particles, for combining said fluid under pressure with said
         abrasive particles to produce an abrasive-laden fluid stream;

     (d) nozzle means for delivering said abrasive-laden stream to the teeth or
         tooth structure undergoing said dental procedure; and 

     (e) pressure control means supplied with said fluid under pressure for
         controlling the pressure of said fluid supplied to said abrasive-mixing
         means;

     (f) wherein said pressure control means comprises a servo valve having a 
         fluid inlet, a fluid outlet, electrically controllable valve means
         positioned between said fluid inlet and said fluid outlet, and an
         electrical control terminal, said valve means being responsive to
         changes in the level of an electrical command signal at said
         electrical control terminal for adjusting said valve means to any
         selected one of a plurality of selected conditions, to set said
         pressure of said fluid supplied to said abrasive-mixing means to any
         of a corresponding plurality of selected pressure values.

     2. The system of claim 1, comprising manually controllable means for
adjusting said command signal level to select said pressure.

     3. The system of claim 2, wherein said manually controllable means
comprises pushbutton controls for adjusting said command signal level.

     4. The system of claim 1, comprising means for visually displaying the
output pressure of said servo valve.

     5. The system of claim 1, comprising means for producing a flashing light
indicator of the selected target pressure level toward which the servo valve
output pressure is moving.

                                   * * * * *