Dowel receiving core for casting dental restorations

Models for dental restoration work are provided with a plurality of elongated openings through which dowels secured to individual tooth members may be reached. The openings are formed by resilient cores cast in the models. The tooth members may thus be removed and replaced from the model easily and accurately. Two or more dowels may be used in each tooth member without need for careful spacing because of the slotted construction of the cores.

BACKGROUND OF THE INVENTION 
It has been known in the casting of models for dental restoration work to 
employ brass dowels or pins secured to individual tooth members in the 
casting. After the casting is completed the individual tooth members are 
separated by cutting slots into the model between them. The tooth members 
are then individually removed from the model together with their attached 
dowels and worked on. Thereafter, they are replaced in the model using the 
dowels and the dowel receiving bores in the model to insure accurate 
positioning. 
In order to remove individual tooth members from the model it is desirable 
to apply pressure to the free end of the dowels and thus force the tooth 
members free of the casting. U.S. Pat. No. 2,851,728 issued to Spaltan et. 
al. employed a wax plug placed within the wax box in contact with each of 
the dowels. The casting material was then poured around the plugs and 
after the casting hardened the wax was melted out leaving an elongated 
opening through which the dowels could be reached. 
U.S. Pat. No. 3,286,350 issued to Cooper disclosed a two piece, pipe shaped 
core which was secured to the end of a dowel for each tooth in the casting 
and the casting material poured around it. This process eliminated the wax 
melting step. 
In U.S. Pat. No. 3,461,562 issued to Cooper there was disclosed the use of 
a jig to support the cores and improve dowel alignment during casting of 
the model. 
U.S. Pat. No. 3,871,804 issued to Cooper showed still another jig and means 
for placing two dowels in each tooth member to improve the accuracy of 
positioning. 
In present day dental restoration work, it is often preferred to cast a 
model of the dental impression, grind the cast model down until it is 
substantially thin, and thereafter drill holes in the model to receive the 
dowel pins. The dowel pins are cemented into holes and additional casting 
material is poured around the dowel pins to form a base for the model. 
Employing this technique, it is still desirable to provide elongated 
openings in the model to reach the ends of the dowels so that individual 
tooth members can be ejected from the model. 
Accordingly, it is an object of the present invention to provide core 
members which can be incorporated into the casting of a dental model to 
give access to the ends of the dowels after the casting has hardened, 
without the need for jigs. 
Another object of the present invention is to provide core members which 
lend themselves to the use of two or more dowels in a single tooth member 
without the need for accurate spacing of the dowels. 
A further object of the present invention is to provide a core structure 
which may be used for posterior as well as anterior teeth. 
Still another object of the present invention is to provide a core 
structure which is easy to remove from the casting and which will maintain 
its position during casting operations without the need for special jigs. 
SUMMARY OF THE INVENTION 
In one embodiment of the present invention there is provided a two-piece 
core assembly made of some suitable resilient material consisting of an 
outer sleeve portion and an inner dowel retaining member. The dowel 
retaining member is telescopically received within the sleeve and is 
formed with a slot at its outer end having a plurality of spaced 
transverse bores therein. The bores are interconnected by an elongated 
slot which makes it possible to receive the ends of the dowels without 
regard to their spacing. 
In another embodiment of the invention, the sleeved portion is omitted and 
the dowel receiving member is reduced in width to accomodate for use on 
anterior teeth which are small in size and closely spaced.

General Description 
Referring to the drawings and particularly FIGS. 1 and 2, 10 indicates a 
core assembly made in accordance with the present invention, consisting of 
a sleeve 11 and a dowel receiving member 12 slidable within the sleeve 11. 
The sleeve 11 consists of a body portion 13 in the form of a hollow 
elongated rectangulr shape. The body 13 is flanged at one end as shown at 
14 in FIG. 1 and open at its opposite end 15 to accept the dowel receiving 
member 12. A stop recess 16 is formed in the upper wall of the body 13 and 
serves to limit the travel of the dowel receiving member 12 into the 
sleeve 11. A transverse boss 17, shown in dashed lines in FIG. 1, is 
molded on the upper interior surface of the sleeve 11 and serves to 
yieldably lock the dowel receiving member 12 in place, as hereinafter more 
fully described. 
The dowel receiving member 12, as shown in FIGS. 1 and 2, consist of a body 
portion 18 of a shape which will freely slide within the sleeve 11. The 
body portion is preferably made of some resilient material such as vinyl 
which material is also suitable for the sleeve 11. One end of the body of 
18 is rounded as indicated at 19 and the opposite, or dowel receiving, end 
20 is stepped as shown at 21. The stepped portion 21 consists of a small 
platform like extension 22 having a rear bearing surface 23 which abutts 
the stop recess 16 in the sleeve 11 when the dowel receiving member has 
been inserted therein. At this juncture, a small rib 24 molded into the 
top surface 25 of the dowel receiving member 12 snaps under the boss 17 in 
the sleeve 11 to yiedably secure the sleeve and dowel receiving member 
together. 
The platform extension 22 and the stepped portion of the dowel receiving 
member 12 are slotted as indicated at 26 to form spaced jaw members 27, 28 
in the end of the dowel receiving member. In addition, a plurality of 
spaced bores 29 having a diameter somewhat smaller than that of the dowels 
30 which are to be received therein, are provided along the longitudinal 
axis of the dowel receiving member slot 26. FIG. 1 shows the slot 
connecting all but one bore while the embodiment of FIG. 2 shows all the 
bores so connected. 
Referring to FIG. 3, there is shown the manner in which a dental model is 
cast from an impression of the patient's mouth. This process is well known 
in the art and forms no part of the present invention. However, the nature 
of this process is felt to be important in understanding the present 
invention. 
After the dentist makes an impression of the patient's mouth by means of 
some suitable plastic material inserted therein, it assumes a shape 
generally indicated at 31 which shape, corresponds to the gums and teeth 
of the patient. The impression 31 is placed upon a small tray 32 and a 
quantity of some casting material 33 such as plaster of paris or stone is 
poured into and over the impression 31. Thereafter, the cast material 33 
is ground down to thin the amount of cast material to a suitable degree 
such as along the line 34. The thinned model is then placed beneath a 
drill or, in some instances on top of a drill. Small holes, indicated by 
the dashed lines 35 in FIG. 3, are drilled into the area represented by 
individual tooth members. As previously stated, it is preferred to put at 
least two such holes in each tooth member to prevent rotation of the teeth 
during the work of the technician in removing and replacing individual 
tooth members. The next step is to cement the dowels 30 into the holes 35 
with some suitable cement material. 
In practicing the present invention, the dowel receiving core members 10 
are next slipped upon the ends of the dowels as indicated in FIG. 4. The 
configuration of the slot 26 and the bores 29 as well as the resilience of 
the material of which the dowel receiving member 12 is made, permit the 
said receiving member to grasp the ends of the dowels and extend outwardly 
as shown in FIG. 4. At this juncture some suitable parting material such 
as soap or other lubricant 37 well known in the art, is placed upon the 
upper surface of the cast material and around the dowels 30. An additional 
amount of cast material 38 is then poured over the assembly to provide a 
substantial base for the dental model as indicated in FIG. 4. When the 
cast material has hardened, the sleeves 11 can be pulled out of the cast 
material and thereafter the dowel receiving member 12 withdrawn from 
around the dowels 30. The resulting model has the appearance shown in FIG. 
5 in which the ends 36 of the dowels 30 extend into the core cavity 38a so 
that, when the individual tooth members 38 are separated by sawing 
therebetween, pressure on the ends 36 of the dowels 30 will lift the tooth 
members free of the base 38 of the model. 
The locking action of the boss 17 and rib 24 prevents accidental 
dislocation of the sleeve 11 and dowel receiving member 12 during casting 
operations and prevents casting materials from flowing therebetween which 
might prevent the core assembly from operating. In addition, the stop 16 
and stepped portion 21 further serves to seal the space within the sleeve 
11 during casting operations. The flange 14 around the open outer end of 
the sleeve 11 permits any casting material which may enter the sleeve to 
be removed and aids in sleeve removal. 
Referring to FIG. 6 there is shown a further embodiment of the present 
invention which is useful in connection with anterior teeth. This 
embodiment is thinner than the dowel receiving member 12 so that the 
problem of small er teeth spaced closer together can be overcome. In this 
embodiment, the dowel receiving member 39 is used without a sleeve and the 
stepped portion 21 is not provided with a platform 22 for obvious reasons. 
In all other respects, the operation of the dowel receiving member 39 is 
similar to that of the first embodiment member 12. The end flange 14a aids 
in removing the dowel receiving member from the cast material. 
Since the dowels are cemented in place before the remainder of the casting 
material is applied, they are accurately disposed normal to the surface of 
the model parallel to each other and firmly cemented in place so that 
there is no need to use jigs or other supporting devices for the core 
assemblies. The core assemblies remain firmly on the ends 36 of the dowels 
during the casting procedures. Since the dowels are parallel to each 
other, having been drilled from the same location, there is no difficulty 
in removing the tooth member with the dowels attached. This procedure 
eliminates the need for accurate alignment of the dowels which was time 
consuming and difficult in prior art processes.