Instrument and method for making dental impressions

A gun-like instrument for making dental impressions, comprising an outer air nozzle and an inner nozzle for impression material within the outer nozzle, the inner nozzle projecting beyond the tip of the outer nozzle so that any tendency of the impression material to plug the outer nozzle is eliminated. The air emanating from the outer nozzle first removes debris from the operative area, and then causes the impression material to impinge on the tooth in such a way as to form an accurate impression. The instrument includes a hand grip having a finger operable trigger forwardly thereof for discharging impression material from the inner nozzle, a valve for discharging air from the air nozzle, and thumb operable valve actuators on opposite sides of the instrument for opening the air valve. With this construction, the fingers can be used to control the discharge of impression material, while the thumb is used to control the discharge of air independently. Equipping the instrument with thumb operable valve actuators on opposite sides thereof renders the instrument usable by either a left-handed or a right-handed operator.

BACKGROUND OF THE INVENTION 
The present invention relates in general to an instrument for making dental 
impressions and, more particularly, to a gun-like instrument which first 
cleans the area in which an impression is to be made with compressed air, 
and which then applies the impression material thereto. Still more 
particularly, the present invention relates to a gun-like instrument 
similar in a general sense to that disclosed in U.S. Pat. No. 3,530,587, 
issued Sept. 29, 1970, to Robert Leo Anderson, reference to which is 
hereby made for further background. 
Dentist's impression material is prepared by mixing base and catalyst 
materials just prior to the time at which an impression is to be taken. 
Depending upon a number of minor variables, such as temperature, the 
particular chemicals and the amount of catalyst used, a limited amount of 
time is available for taking the impression. Prior to this time, a dentist 
has usually completed preparation of the patient for taking the 
impression, which involves both cleaning the area and adequately exposing 
the tooth at or below the gum line, as necessary, for reception of the 
impression material. The groove defined between the tooth and gum in this 
region is usually referred to as the "sulcus". In addition, it is 
important that each other concave and convex surface on which the 
impression material is to be placed be dry, because the impression 
material does not otherwise adhere. The presence of seepage and the 
physical characteristics of the impression material tend to introduce 
voids, bubbles, and incompletely filled areas into the impression. The 
more intricate the concavities and convexities, the less likely it is that 
these critical regions will be adequately filled. 
Consequently, when a casting is to be made it is often necessary for the 
dentist or technician to study the matter very carefully and to 
interpolate, extrapolate or actually "fake" the margin line and the 
contours needed for the final casting. If the edges and margins of the 
final casting do not precisely match the prepared area of the tooth at or 
below the gum line, the process of decay can quickly be renewed and the 
useful life of the filling can be substantially shortened. 
Major difficulties arise with present extrusion type impression 
instruments, because the impression material is flowable under pressure, 
but has a rubbery and elastomeric characteristic even while setting. The 
impression material will take the shape of something against which it is 
pressed, but adequate and equal pressure should be exerted on all sides to 
insure conformance to complex shapes. Consequently, the sulcus around the 
gum line of a tooth being prepared for receiving a casting cannot be 
filled simply by pressing an adequate amount of material toward it. Other 
concavities and some convex portions also will create problems unless they 
are precisely defined by an initial layer or film of adherent impression 
material. 
The characteristics of the impression material can be particularly 
troublesome when seepage of blood or saliva occurs, as very readily 
happens because of the circumstances under which the impression is taken. 
To obtain clear access to the sulcus and the margin line which the casting 
base is to follow, a packing material is often used to separate the gum 
from the tooth in this region. Seepage begins as soon as the packing 
material is taken out, or can be continuous if no packing is used. The 
impression material will not adhere to a wet surface but instead, slips to 
another region. This, together with the rubbery characteristic of the 
impression material, contributes further to the uncertainties in the 
location of margins and contours which require interpolation and 
extrapolation to attempt to define the proper shape. It will be borne in 
mind that an accurate impression must be taken as expeditiously as 
possible, for the benefit of both the patient and the dentist. To 
accomplish this a versatile instrument capable of being used in different 
ways to overcome different problems is highly desirable but has not 
heretofore been available. 
SUMMARY OF THE INVENTION 
A primary object of the invention is to provide an instrument for making 
dental impressions which includes an outer air nozzle and an inner nozzle 
for impression material within the outer nozzle. With this construction, 
after cleaning the area in which an impression is to be made with one or 
more air blasts, additional air blasts or a continuous air blast 
surrounding the impression material discharged by the inner nozzle may be 
used to cause the impression material to impinge on the tooth which is 
being worked on. Causing the impression material to impinge on the tooth 
in this manner results in a dense and accurate impression, which is an 
important feature. 
It is important to note that the air impinging on the tooth removes debris, 
dries the tooth, and permits the application of elastomeric impression 
materials to the tooth. The impression material will not adhere if the 
tooth is not clean and dry. It is blown away and replaced with material 
which does adhere to a clean and dry tooth. 
Another and important object related to the foregoing is to provide 
generally coaxial nozzles wherein the inner nozzle for the impression 
material projects beyond the tip of the outer air nozzle. With this 
construction, any possibility of plugging of the air nozzle by the 
impression material is eliminated, which is an important feature. 
Impression instruments in accordance with the invention satisfy the various 
requirements imposed by this delicate work, by concurrently flowing a 
cylindrical shell of pressurized air about an interior extrudable column 
of impression material that is separately controllable. The pressurized 
air emanates from the nozzle with concentrated flow of sufficient volume 
and velocity to eject seepage at the target area and to thoroughly and 
substantially immediately dry the prepared target area. Impression 
material is fed along the center of the air flow sheath and is attenuated 
into a thin converging and protruding column. Using concurrent material 
feed and air flow, the tip of the protruding column separates at a certain 
distance from the nozzle tip, causing small globules of the impression 
material to be directed into the target region. Alternatively the 
protruding material may be deposited directly on a desired accessible area 
simply by contact. Concurrently or subsequently the air flow spreads the 
globules or deposited mass into an adherent thin film. Thus, with 
receiving surface area dry, and with a readily controlled and precisely 
directed supply of impression material, the dentist has excellent control. 
He can often readily observe the proper buildup of the adherent thin film 
upon the complex surfaces of the immediate target region, or where there 
is no visibility he can assure development of an adherent film by repeated 
applications of material. He can quickly move along the sulcus all about 
the periphery of the tooth and insure that all of the least accessible and 
most critical regions have been filled. In doing this he can apply 
material and air flow in various modes best suited to the specific 
conditions he encounters. When a larger mass of impression material is 
then overlaid in position on one or a number of teeth, and allowed to set 
into its cured elastomeric state, the result is an impression which 
requires substantially no interpolation or extrapolation. 
The present invention may be summarized as including, and another important 
object is to provide an instrument for making dental impressions which 
includes: a gun having a hand grip and having a finger operable trigger 
forwardly of the hand grip for discharging impression material from the 
impression nozzle; valve means for discharging air from the air nozzle; 
and a thumb operable valve actuator for the valve means mounted on one 
side of the instrument adjacent the upper end of the trigger. With this 
construction, compressed air and impression material may be discharged 
selectively and/or simultaneously with one hand, using the fingers for the 
impression material and the thumb for the compressed air, which is an 
important feature. 
Yet another important object is to provide a second thumb operable valve 
actuator for the air valve mounted on the opposite side of the gun from 
the first valve actuator mentioned, whereby the instrument may be readily 
operated by either a left-handed or a right handed operator. 
The invention may be further summarized as including, and an additional 
object of the invention is to provide an instrument for making dental 
impressions which includes: a gun having a housing and a hand grip and 
having a cylinder terminating in a nozzle for discharging impression 
material; a plunger in the cylinder for expelling impression material 
through the nozzle; a rack in the housing and connected to the plunger; a 
pinion in the housing and meshed with the rack; a ratchet wheel in the 
housing and connected to the pinion; a trigger pivotally mounted on the 
gun adjacent and forwardly of the hand grip; a pawl pivotally mounted on 
the trigger and engageable with the ratchet wheel to rotate the ratchet 
wheel in a direction to advance the plunger; and a second pawl pivotally 
mounted on the housing and engageable with the rachet wheel to prevent 
rotation of the ratchet wheel in the opposite direction. 
A further object is to provide an instrument of the foregoing nature 
wherein the housing includes a pivoted cover openable to provide access to 
the rack, the instrument including means responsive to opening of such 
cover for disengaging the second pawl from the ratchet wheel so that the 
plunger may be returned to its starting position. 
The foregoing objects, advantages, features and results of the present 
invention, together with various other objects, advantages, features and 
results which will be evident to those skilled in the dental impression 
art in the light of this disclosure, may be achieved with the exemplary 
embodiment of the invention described in detail hereinafter and 
illustrated in the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to the drawing, the gun-like instrument of the invention is 
designated generally by the numeral 10 and includes a housing 12 shown as 
formed in two halves secured together by screws 14. The housing 12 
includes a hand grip 16 much like a pistol grip. 
The upper, rear portion of the housing 12 includes a cover 18 which is 
connected to the body of the housing by a transverse pivot 20. As will be 
apparent from a comparison of FIGS. 2 and 7, the cover 18 may be pivoted 
upwardly for access to the interior of the housing 12. 
Clamped between the two halves of the housing 12, at the forward end of the 
housing and at the upper end of the hand grip 16, is a tubular member 22 
which carries a nozzle assembly 24. This assembly includes an outer air 
nozzle 26 containing an inner nozzle 28 for impression material. The outer 
nozzle 26 is provided with an external annular flange 30 clamped against 
the forward end of the tubular member 22 by a knurled nut 32 threaded onto 
this tubular member. 
The inner, impression nozzle 28 is spaced inwardly from the outer, air 
nozzle 26 to provide an air passage therebetween. The outer and inner 
nozzles 26 and 28 terminate in curved tips 36 and 38 which are also spaced 
apart to provide for compressed air flow therebetween. Preferably the 
spacing between the tips 36 and 38 is maintained by circumferentially 
spaced, longitudinally extending ribs 40, shown in FIG. 6. 
As previously discussed, an important feature of the invention is that the 
inner tip 38 for the impression material projects beyond the outer tip 36 
for the compressed air. With this construction, any possibility of 
plugging of the air nozzle 26 by the impression material is eliminated, 
which is an important feature. 
The inner nozzle 28 includes a cylinder 42 which contains a supply of 
impression material 44. Disposed in the cylinder 42, and movable from the 
rearward end thereof toward the forward end thereof to expel impression 
material 44 through the inner tip 38, is a plunger 46 carried by a rack 
48. The latter is coaxial with the plunger 46 and is supported by a guide 
50 on the tubular member 22 and a guide 52 on the housing 12. The rack 48 
is provided at its rearward end with a knob 54 for manual retraction of 
the plunger 46 upon opening of the cover 18. 
As will be apparent, displacement of the plunger 46 toward the forward or 
outer end of the cylinder 42 will result in expelling the impression 
material 44 through the inner tip 38, which impression material may be 
caused to impinge on a tooth being worked on to form the desired 
impression. The plunger 46 is advanced in this manner by a pinion 58 
meshed with the rack 48 and fixed on a transverse shaft 60 rotatably 
mounted in the housing 12, as best shown in FIG. 3. Also fixed on the 
shaft 60, adjacent the pinion 58, is a ratchet wheel 62. The ratchet wheel 
is rotated in the counterclockwise direction, as viewed in FIG. 2, to 
advance the plunger 46, by a pawl 64 pivotally mounted, at 66, on the 
upper end of a trigger 68, the pawl 64 being biased toward the ratchet 
wheel 62 by a spring 70. The lower end of the trigger 68 is pivotally 
connected, at 72, to the hand grip 16. The trigger 68 projects forwardly 
of the hand grip 16 so that it can be pivoted rearwardly readily by the 
operator's fingers when the operator is grasping the hand grip 16. The 
trigger 68 is biased forwardly by a spring 74 within the hand grip 16. 
As will be apparent, squeezing the trigger 68 repeatedly causes the pawl 64 
to rotate the ratchet wheel 62 and the pinion 58 incrementally. 
Consequently, the rack 48 and the plunger 46 are advanced in step-by-step 
fashion to expel the impression material 44 from the inner tip 38 
incrementally. As previously explained, contemporaneous air blasts from 
the outer tip 36 cause the impression material to impinge on the tooth 
being worked on. 
The housing 12 carries another pawl 76 which engages the ratchet wheel 62, 
opposite the pawl 64, to prevent reversed movement of the plunger 46 
during forward pivoting of the trigger 68. The cover 18 carries a cam 78 
which, as best shown in FIG. 7, engages the pawl 76, upon opening of the 
cover, to disengage the pawl 76 from the ratchet wheel 62. This permits 
manual retraction of the plunger 46 whenever a fresh charge of impression 
material 44 is required. 
Turning now to a consideration of how compressed air is delivered to the 
outer nozzle 26, the butt of the hand grip 16 is provided with a fitting 
82 to which a compressed air line 84 may be connected. The line 84 is 
connected to the usual compressed air source provided in a dentist's 
office. A tube 86 within the hand grip 16 leads to a T-shaped valve body 
88, FIG. 4, mounted in the housing 12 adjacent the upper end of the 
trigger 68. The T-shaped body 88 includes a leg portion 90 and a crossbar 
portion 92 extending transversely of the hand grip 16 adjacent the tubular 
member 22. 
Within the leg portion 90 of the valve body 88 is a rotary valve 94 having 
an interior conduit 96 which in the open position as shown provides a flow 
path between the inlet tube 86 and an outlet conduit 108. The rotary valve 
94 is sealed by O-rings 98. 
As will be apparent, by rotating the valve 94 90.degree., compressed air is 
directed through a passage 108, FIG. 2, into the space between the inner, 
impression nozzle 28 and the outer, air nozzle 26 for discharge through 
the outer tip 36 of the nozzle assembly 24. As previously indicated, such 
compressed air may either be used to clean the tooth area being worked on, 
or to cause the impression material 44 to impinge on such area in building 
up the desired impression. 
Considering the manner in which the valve 94 is opened to produce the 
desired air blast, or series of air blasts, the ends of the valve 94 are 
exposed on opposite sides of the housing 12 and have connected thereto, as 
by screws 112, thumb operable actuators 114 which are located on opposite 
sides of the housing 12 adjacent the upper end of the trigger 68. 
With the foregoing construction, compressed air and impression material may 
be discharged selectively with one hand, using the fingers on the trigger 
68 for the impression material and the thumb on one of the actuators 114 
for the compressed air. Also, since there are two of the actuators 114 on 
opposite sides of the housing 12, the instrument may readily be operated 
by either a left-handed or a right-handed operator, which is an important 
feature. 
The impression instrument may be used with a great majority of commercial 
available impression materials, such as those based on silicones, 
polyethers, polysulfides, vinylpolysiloxides and rubber base materials. 
Most of these materials have some adherent properties sufficient to form a 
thin film that is not carried away by subsequent air blasts. Some of the 
polyethers and silicones, on the other hand, have an excessively slippery 
characteristic and do not permit the instrument to be used to full 
advantage. The material is mixed together with a suitable catalyst just 
prior to application, and usually has a cure time of approximately four 
minutes. After mixing, therefore, a part of the material is placed in the 
receiving cylinder 42 in the impression instrument, and the remainder is 
used to fill a small form, called a tray, which is to be used in the final 
step of taking the impression. 
In the present impression instrument a concentric sheath of air flowing at 
a substantial rate can be concentrated on the target area to provide 
immediate and concurrent drying. The flow rate is sufficiently high, with 
a source pressure of 30 psi typically being used, for the flow through the 
small outer nozzle (less than one-quarter inch in inner diameter) to force 
out excess seepage and dries off trace amounts of seepage. Because the 
inner tip 38 protrudes beyond the outer air tip 36, extrudate which moves 
past the end of the inner tip 38 is acted upon on all sides by the air 
flow sheath directed down into the concavity, when air flow is used. As 
best seen in FIG. 8, the rubbery and somewhat elastic characteristic of 
the impression material prevents the extrudate from separating from the 
extruded mass directly at the tip 38 of the inner nozzle. Instead, a 
length or column 120 of extrudate, typically one-quarter to three-eighths 
inches long, is formed that converges or is attenuated in the direction of 
air flow into a point. This point may be touched directly upon the target 
area to deposit a moderate mass of material, whether air is flowing or 
not. If more impression material is fed out, small globules of impression 
material separate off the protruding end of the extruded column 120 and 
move with the air flow to impinge on the dried target area. The small 
globules or deposited mass adhere where the target area is dry, but if it 
is not, the globules are displaced to one side or the other until the area 
is dried, at which point adherence begins. The accumulation of material 
is, very importantly, not a successive thickening or layering, which does 
not insure freedom from voids. Instead, when the material adheres the 
action of the air flow spreads it out into a thin film, as seen at 122 in 
FIG. 8. This film penetrates into and conforms to the interior of the 
concavity along the sulcus, as well as conforming to other concavities and 
convexities on the tooth. The dentist therefore can quickly move around 
the entire tooth, using various combinations of air flow and impression 
material feed control. The air flow can be used intermittently or 
continuously for drying purposes and the impression material can be 
deposited directly or advanced incrementally as needed for deposit. When 
the impression material has been formed into the desired band of deposited 
film about the gum line and the casting margin and onto and into the 
intricacies of the prepared tooth, for one or a number of teeth, the 
impression instrument need no longer be used. At this point the 
conventional tray that was previously filled with the remainder of the 
impression material is placed in position over the teeth and pressed down, 
urging impression material around the entire tooth. With the margins and 
concavities completely covered with a film of impression material, the 
application of the tray insures complete filling, because seepage is no 
longer a problem and because the added impression material readily adheres 
to that previously laid down. When the impression material is fully cured 
after a few minutes, it is removed for inspection and is thereupon ready 
for a dental technician. 
Impressions made in this fashion substantially eliminate the need for 
subsequent tailoring of dies made from the impression, or extrapolation or 
interpolation of the margin lines. The impression that is taken is clear 
and undistorted, and free of voids and bubbles when the instrument is 
properly used, whether the dentist is able to observe the integrity of the 
film as it is being laid down, or not. 
The tips can be reused if desired, but are of low cost molded plastic 
construction and typically are disposed of after one use or a limited 
continuous period of use. The detachable nozzle assembly can readily be 
rotated within the tightening ring on the housing, so that the curved tip 
points in any direction desired for depositing impression material on 
upper or lower teeth, while the handle remains in a convenient operative 
position. The convenience of operation and accessibility with this 
mechanism of all regions within the mouth of a patient enable the 
impression to be taken more rapidly, as well as more efficiently, than 
heretofore. 
Although an exemplary embodiment of the invention has been disclosed for 
illustrative purposes, it will be understood that various changes, 
modifications and substitutions may be incorporated in such embodiment 
without departing from the invention as hereinafter claimed.