US2566596A

US2566596A - Method of preparing dental investments and the like

Info

Publication number: US2566596A
Application number: US2406A
Authority: US
Inventors: Jacob J Cantor
Original assignee: Individual
Current assignee: Individual
Priority date: 1948-01-15
Filing date: 1948-01-15
Publication date: 1951-09-04
Anticipated expiration: 1968-09-04

Description

J.*J. CANTOR Sept. 4, 1951 METHOD OF PREPARING DENTAL INVESTMENTS AND THE LIKE Filed Jan. 15, .194e

INVEN TOR.

Patented Sept. 4, 1951 'This invention `relates to a method for preparing dental investmentsrand similar molds.

It has long been recognizedinthe preparation of dental investments that air bubbles'in th'ein- .vestrnent mix linterfere with the ,production o'f castings which are Vin exact conformity with ythe `pattern and attemptsheretoforehave been made lto `eliminate these airbu'bbles vso'that vmore pre- `cise castings can be obtained.

Generally speaking, vtechniques endeavoring to eliminate such bubbles may 'be divided into Vtwo classes. `In the first class, the plaster or similar self-hardening material used to form the investment or mold was mixed with its liquid such as water and then subjected to vacuum `with 'the intention of extracting from the mix all of the gases existing therein vincluding air and water vapor. When the mix Was'thus prepared it was thenpoured in the flask about the vpattern and .allowed lto-set. An objection to this method resided in the .fact that Yin the vcourse of pouring the mix afterithad'been evacuated `around the ,pattern ,them'ix usually had adequate opportunity to lpick upor absorb new air which became `entrained therein and prevented or greatly retarded the abilityof securing.liighlyprecise cast- ,.ings. 'IJhecseoond method consisted of rst mixvving the plaster and subjecting it to vacuum,

,pouring it into the 'flaskaround the pattern and then "subjecting the .poured plaster to a second Vvacuum designed to extract the air from the poured material. A generalrevie'w of these procedures is Lto be .found .in the article entitled Principles of Vacuum Investing by K. -W. Ray appearing in the DentaTLaboratory'Review for September 1946, page 27.

A.Both of the above outlined procedures are still subject to a number of objections. One such objection exists in the fact that when the 'plaster ,and water have been mixed to form a paste or slurry the ability of the Vacuum to draw outk the air bubbles from the paste or slurry is highly restricted in that the high viscosity of the mix retards the passage of the air bubbles therethrough. Furthermore, if the pattern is quite Iintricateit may form pockets in which the air bubbles maybe disposed and these are held from escape through the plaster by the pattern itself. Another Iand more serious objection resides in -the fact 'that after the Water and dry plaster lhave'been mixed together the plaster immediately begins to set. Consequently, the creation of 2 heretofore employed -'have :been largely 4restricted intheir use to'castings-of small'size.

An object'of'the presentinvention is toprovide a method proceeding upon a different *theoryfrom those heretofore `developed wherein the dry plaster is placed in 'a suitable `'flask around vthe kpattern andthenis subjected'to vacuum "to remove the air therefrom. As the plaster is dry or substantially so, the extraction of vthe air therethrough is accomplished in amuch easier manner than endeavoring4 to 'extract `air bubbles through a moist paste vor slurry. AWhen the air 'has been thus extraote-dfrom thedryplasterand preferably while Yit lis still subject to vacuum, wateror other liquid, which may y"or may-notbe but which is preferably iree lof vair or oxygen, is admitted to the vacuum chamber yand allowed to wet the plaster 'causing it Ato commence to set. As soon as the'pl'aster has beenthorough'ly'we't ambient air 'pressure is allowed to enter v4the Vacuum chamber and ir Athere -are any remaining air bubbles or Vapor vbubbles `within the'investment these are immediately compressed Yor collapsed by -the air pressure. The result yobtained is 'an investment which'is remarkably L'free of pockets `produced'by air `and vapor bub'blesso `that highly precise castings "are 'obtainable -with the plaster canta-ke place at anytime andthere the appended claims, reference is Ihad 'to 'the accompanying 'drawings 'for van nillustrative embodiment ofthe invention, wherein:

Fig. l is la verticaljsection through the apparatus 'designed and used in vaccordance 'with vthe `present invention;

Fig. 2 is a horizontal section taken substantiaily upon the line'Z--2 upon'Fig. 1;'and

Fig 3 is a -partial view in vhorizontal Sectio-r1 taken substantially upon Vthe line 3-3 upon Fig. '1.

Referring to the accompanying drawings wherein similar 'reference characters designate similar parts throughout, the apparatus v'illustrated consists -oi' 'a base generally in rthe form of a transverse bar Ill on which is mounted a circular plate II. A suitable gasket such as rubber or rubber-like material indicated at I2 is recessed in the plate II to form an air-tight seal with the bottom edge of a bell jar I3. A ask I4 is adapted to be positioned on the base beneath the bell jar and this flask has at the bottom thereof the conventional crater forming member I5 and the gate or sprue forming member I5 on which the pattern I1 is positioned in the usual manner. In accordance with conventional dental practice the pattern is formed of wax. On top of the flask I4 there is positioned a ring I8 which is held down against the flask by means of an apertured plate I9. Studs extend upwardly from the base 2I that supports the flask and thumb nuts 22 are threaded thereon enabling the plate I9 to be tightened downwardly against the top of the flask so that the base, crater forming member, flask, ring, and plate I9 may be held together as a unit when these parts have been assembled. The flask I4 has openings in the side walls thereof some of which may be merely in the form of perforations 23 and others of which indicated at 24 may be in the form of horizontal slots. These openings are covered externally by means of gauze or equivalent material indicated at 25 which is retained in place in any suitable manner such as, for example, by rubber bands or split rings indicated at 26. 'Ihe bar I9 has a Water passage 21 formed therein that leads to the base of an upstanding stud 29 that is mounted on the plate II. This stud provides an outlet 29 for water that can be admitted through a supply pipe 30 past a needle valve 3I. Within the belljar there is also disposed an upwardly extending tubular stud 32 the top of which is open to the interior of the bell jar and the bottom of which communicates with a passage 33 that is adapted to be connected to a vacuum gauge 344 and. to a conduit 35 that leads to a vacuum producing or creating means. The vacuum creating means may be any conventional apparatus for this purpose such as a vacuum pump or a water aspirator and when operated serves to create a high degree of vacuum within the bell jar I3.

Collars

36 and 31 are adjustably mounted on the two

studs

28 and 32 such as by thumb screws 38. These collars may be tightened down against an apertured plate 39 which is positioned against the tops of the thumb nuts 22 to hold the entire flask assembly in place.

The method performed utilizing the above described apparatus is substantially as follows. The pattern I1 is mounted on the sprue providing member I6 in the conventional manner and the flask I4 with its applied gauze 25 and retaining elements 26 is positioned on the crater forming member I5. The ring I8 which may be regarded as an excess plaster retaining ring is then mounted on the ask and the entire assembly clamped together by means of the thumb nuts 22. This assembly can then be positioned on the plate I I and clamped thereon by means of the

collars

36 and 31. Dry plaster or other cementitious material which becomes self-hardening when mixed with a liquid such as water is then poured into the flask. As materials of this type usually contract on being moistened, an excess of the dry plaster is poured into the flask so as to partially ll the ring I8 and thus compensate for shrinkage. The bell jar I3 is thenapplied to its gasket I2 and the vacuum creating means connected to the conduit 35 is then operated. During the creation of the vacuum Within the bell jar the valve 3| is maintained in closed position. As the plaster or equivalent material within theV flask is dry the air contained therein can readily pass out through the interstices between the dry particles and the vacuum can be retained in the bell jar I3 for an indefinite period of time to assure complete extraction of the air. When it is desired to form the investment or mold the needle valve 3I is opened allowing water to enter from the conduit 30, pass the needle valve and go through the passage 21. This water enters the bell jar through the inlet 29 and is allowed to ll the bell jar up to a level Where it may wet the plaster within the flask through the perforations 23 and/or 24. In many instances the plaster will wet itself throughout by capillary action but if desired the vacuum chamber may be flooded with water so that the investment is completely submerged. In the preferred method the water or liquid used is characterized by the fact that it is free or substantially free of all dissolved air or oxygen and other objectionable gases. Such water may be water that has been retained under a vacuum over a prolonged period of time or may be water that has been thoroughly boiled to drive out air and other gases. In some instances the water may be from a supply containing dissolved air or oxygen and as this water is admitted to the vacuum chamber within the bell jar I3 very slowly it will have the dissolved air removed therefrom on admittance. Where the Water or liquid is rendered gas free prior to admittance the particular manner in which it is thus prepared is immaterial in so far as the present invention is concerned. It is merely desirable that the water that wets the plaster be substantially free of air or gases so that it will not reintroduce air or gases into the dry plaster that has just been evacuated. In this way the dryair-free plaster is wetted in situ around the pattern and while the Vacuum within the bell jar is maintained. When the plaster has been thoroughly wet the conduit 35 is quickly opened allowing air to enter the bell jar and the water therein can be either drained off through the conduit 30 such as by siphoning or the bell jar may be lifted from the gasket I2 allowing the water within the bell jar to ow off of the plate II. 'Ihe entrance of ambient air pressure into the chamber causes any water vapor bubbles or any remaining expanded air bubbles to be compressed into very small volume so that these do not interfere with the obtaining of a highly precise mold from the pattern. 'I'he flask can then be treated in any conventional manner to remove the wax pattern I1 leaving a clean dry mold cavity. l

In the course of removing the air from the dry plaster within the flask it may be advisable to vibrate or successively jar the entire apparatus so as to disturb the plaster and thus facilitate egress of air therefrom while the plaster ls in its dry condition. In most instances, however, the air will readily escape from the powderedv plaster without such vibration or jarring primarily because egress of air therethrough is not hindered by the liquid. When the water is admitted to wet the dried air-free powder, the plaster usually contracts and in so doing the level of the plaster within the flask I4 and the ring I8 may settle to a level approximately even with the top of the flask I 4. Y

In the above described manner a mold or ihvestment can be produced having high fidelity to the shape ofthe pattern and which when the vacuum could be created immediately after the plaster and Water had .been mixed together and the plaster started setting, no such limitations are presented herein. For this reason, much larger patterns may be employed if desired or necessary than those capable of being used with prior processes above referred to.

Various changes may be made in the details of construction without departing from the spirit and scope of the invention as deiined by the appended claims.

I claim:

1. The method of preparing a dental investment or similar mold which comprises placing dry plaster in a flask about a pattern and evacuating air from the same while dried and While evacuated wetting the plaster causing it to commence to set.

2. The method of preparing a dental invest- 3. The method of preparing a dental investment or similar mold which includes bringing into contact around a pattern dry plaster and water from which the air has been removed and after the plaster has been thus wetted allowing the plaster to set.

4. The method of preparing dental investments or similar molds which includes bringing into mutual contact dry plaster and Water around a pattern while under a vacuum.

5. The method of preparing a dental investment or similar mold which includes bringing into mutual contact around a pattern plaster and gas-free Water While under a vacuum.

6. The method of preparing a dental investment or similar mold which includes as a step thereof placing dry plaster in a flask about a pattern and evacuating the air from the same while the plaster is in a dry state.

JACOB J. CANTOR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 391,830 Zuber Oct. 30, 1888 1,152,964 Nielsen Sept. '7, 1915 1,585,348 Hck et a1. May 18, 1926 2,089,552 Harrison Aug, 10, 1937 2,249,890 Droge July 22, 1941 2,392,929 Lee Jan. 15, 1946 2,414,093 Cole et al. Jan. 14, 1947 2,416,506 Vest e Feb. 25, 1947 2,490,193 Barr Dec. 6, 1949