Rubber Impression Research Articles

Accuracy of pouring mercaptan rubber impressions at various intervals after separation

Accuracy of pouring mercaptan rubber impressions at various intervals after separation

Minimum acceptable laboratory procedures for satisfactory fixed partial dentures

Diagnostic casts should be made of hydrocal stone poured into the impressions. Dies may be copper-plated (if the impressions are in compound), or they may be made of improved stone, or silver-plated (if the impressions are made of an elastic material) or they may be made of silver amalgam or epoxy resin. Working casts should be made of hydrocal stone after the dies are properly placed, if full plaster impressions have been supplied. When castings are placed in the impression, they are treated to permit the use of low-fusing metal in them and hydrocal stone is poured in the remainder of the impression to form the cast. Impressions made in elastic materials may be silver-plated or hydrocal stone can be poured directly into them. The cast of the opposing arch may be poured in stone, or a combination of low-fusing metal can be used in the imprints of the teeth, and the remainder of the cast can be made of hydrocal stone. Casts should be poured immediately after impressions made in alginate (irreversible colloid) and agar (reversible hydrocolloid) in]pression materials are removed from the mouth. Thiokol and silicone rubber impressions should have casts poured in them within two hours after removal from the mouth. Casts made of hydrocal stone should be placed in a humidor until the set is complete (see manufacturer’s directions).

Accuracy of a Mercaptan Rubber Impression Technique Using a Stock Tray

The accuracy of a relined mercaptan rubber impression technique, in which a stock tray is used for the preliminary impression, was investigated. Casts made with this technique were compared with those made with the double-mix injection method. Vertical and horizontal deviations from the master die were determined. Both impression methods produce casts larger than the master die, although casts made with the relined impressions were slightly more accurate than those produced from the nonrelined technique.

The accuracy of stone dies made from rubber impression materials

The accuracy of stone dies made from rubber impression materials

A NOTE ON THE MEASUREMENT OF STOMATAL APERTURE

SummaryCellulose acetate replicas were made from silicone rubber impressions of the abaxial surfaces of perennial ryegrass leaves. Apertures between 1 μ and 4 μ (mean 2 μ) were measured in replicas from leaves which had been exposed to conditions expected to close the stomata. This discrepancy is explained by observations of the ventral walls of guard cells in transverse sections of stomata, and by Araldite impressions of the cut ends of ryegrass leaves. These show that when a stoma is closed the ventral walls make contact below the paradermal walls of the guard cells and consequently a small depression is left between the cells. These depressions are similar in width to the apparent apertures in the cellulose replicas which may be wrongly interpreted as slightly open stomata. In some species the silicone impression method is incapable of giving an accurate measurement of stomatal aperture. Consequently, in attempts to relate such measurements to stomatal function or rate of transpiration it should be established that small apertures shown in cellulose acetate replicas are not the result of depressions between the external surfaces of guard cells in closed stomata.

The Borehole TeleviewerA New Logging Concept for Fracture Location and Other Types of Borehole Inspection

Zemanek, J., Mobil Research and Development Corp. Caldwell, R.L. Mobil Research and Development Corp. Glenn Jr., E.E., SPE-AIME, Mobil Research and Development Corp. Holcomb, S.V., Mobil Research and Development Corp. Norton, L.J., Mobil Research and Development Corp. Straus, A.J.D., Mobil Research and Development Corp. The Borehole Televiewer logging tool takes an acoustic picture in the form of a well log, it invaluable for formation evaluation and borehole inspection. The log, which is run continuously, can define both induced and natural fractures, and can reveal vuggy porosity, the size and distribution of perforations in casing, and casing failures. Introduction A new and unique logging tool, called the Borehole Televiewer (BHTV), has been developed to inspect boreholes and to evaluate formations. Even though geologists and engineers have had only about 3 years' experience with the BHTV, the thinking of many of them has been radically influenced by the fascinating and revealing "log-picture" recorded with the tool. The BHTV fills a need for a logging tool that can produce a direct and descriptive record of the produce a direct and descriptive record of the physical properties of the borehole environment. Although physical properties of the borehole environment. Although primarily developed to evaluate fractured reservoirs, primarily developed to evaluate fractured reservoirs, the BHTV has been used successfully to solve a variety of problems related to formation evaluation and borehole inspection. Geologists and petroleum engineers have been confounded for many years by the problems of locating and evaluating fractures. Interpretation of the usual resistivity, acoustic or radioactivity logs, as well as the analysis of cores, for evaluation of fractured reservoirs is extremely difficult and often not definitive. This is understandable since analysis of cores from fractured formations has reported variously: low porosity, no effective permeability, lack of porosity, no effective permeability, lack of any matrix oil saturation and oil stains on fracture planes as the only indications of potential production. In recent years acoustic amplitude logs production. In recent years acoustic amplitude logs have been introduced and used with varying degrees of success to locate fractures. Conventional amplitude logs at best give only qualitative answers where quantitative ones are desired. The logs reveal nothing of the orientation of the fractures. In addition to these logs, various types of cameras, television, and rubber impression packers have been used for borehole inspection. (See Appendix.)The BHTV logging tool supplies both the quantitative and the orientation answers about fractures. The borehole can be filled with any homogeneous, gas-free liquid such as fresh water, saturated brine, crude oil or drilling muds. This tool takes an "acoustic picture" of the borehole wall. The resulting log is a picture" of the borehole wall. The resulting log is a representation of the borehole wall as if it were split vertically and laid flat. The log is oriented with respect to magnetic north. Any physical changes in the borehole wall are seen as changes in picture intensity. In this way, fractures, deformation or pits are reflected on the log. pits are reflected on the log. Tool Description The fundamental parts of the BHTV are shown in Fig. 1. A piezoelectric transducer probes the borehole wall with bursts of acoustic energy. A flux-gate magnetometer senses the earth's magnetic field and provides the means for determining the orientation of the log. JPT P. 762

Stomate Density and its Relationship to Water‐Use Efficiency of Blue Panicgrass (Panicum antidotale Retz.)1

Six clones of blue panicgrass (Panicum antidotale Retz.) representing three diverse sources of germ plasm were used to evaluate the association between stomate density and water‐use efficiency. Silicone rubber impressions were taken on the abaxial and adaxial leaf surfaces of four plants from each clone. Leaves were selected from the top, middle, and base of the culm and impressions were taken at the base, middle, and tip of each leaf.Stomate density of blue panicgrass clones ranged from 78 to 165 per mm2. Leaves adjacent to the inflorescence had significantly lower stomate density than those at the middle and base of the culm. No difference was found among stomate densities at the three positions on a leaf.A nonsignificant association was obtained when wateruse efficiency and stomate density were correlated for the six clones. Drouth tolerant clones had fewer stomates per unit area than drouth susceptible clones.

Disclosure and reproduction of a fistula tract in the routine impression procedure by use of silicone rubber: report of case

Although rubber impression material should not be used exclusively, it would have been impossible to discover this abnormality by use of an impression compound.

Microscopic and macroscopic investigation on results of mechanical preparation of root canals

Sixty extracted canine teeth and sixty lower incisors were prepared mechanically, and the root canals were flushed with saline solution, sodium hypochlorite, or EDTA. Canine teeth were enlarged with Maillefer instruments up to No. 100, while incisors were enlarged with Kerr instruments up to No. 6. One group of teeth extracted canine teeth enlarged with reamers only and in thirty such teeth enlarged and EDTA was enlarged with reamers only, whereas another group was enlarged with both reamers and files. Models of the root canals were made with Permlastic (Kerr). No difference was noted between canal walls enlarged with reamers only and those enlarged with reamers plus files. The smoothest root canals were those irrigated with EDTA. Root canal models made with mercaptan rubber impression paste demonstrated that a completely erroneous concept of internal anatomy of root canals and of mechanical preparation has been commonly accepted. In general, a high incidence of prolongations of the root canals, closely resembling the fins of a fish, were never touched by root canal instrumentation. Saline solution, sodium hypochlorite, and EDTA solution oversaturated in root canals and left a heavy crystalline deposit, making root canal obturation more difficult.

Mechanical Properties of Hydrocolloid and Rubber Impression Materials

Mechanical Properties of Hydrocolloid and Rubber Impression Materials

Properties of die materials: A comparative study

A comparative study of the pertinent properties of die materials used for the indirect materials has been made. Eight classes of materials were evaluated. No one material proved to be superior in all properties. The stones were superior from the standpoint of dimensional accuracy but their abrasion resistance was low. All of the dies, with the exception of those made from stone or low-fusing alloy, were undersize at the cervical margin of the simulated full cast crown preparation. An abrasion apparatus, designed to duplicate certain of the conditions to which such dies are subjected, was devised. On the basis of these tests it was not always possible to predict the abrasion resistance from the corresponding hardness. The dies made from the ceramic material, silicophosphate cement, one of the resins and by electrodeposition were superior in abrasion resistance. The surface of the electroplated dies, the ceramic material, stones and silicophosphate cement provided excellent duplication of detail. Differences were observed in the compatibility of certain die materials and rubber impression products, as compared to the duplication produced when the die material was poured against an inert surface.

Parallel-pin splints for periodontally involved teeth

A simplified technique for the construction of parallel-pin splints has been described. A matrix with metal guides is used to insure parallelism of tooth preparations. Patterns for the castings are made on investment casts poured into mercaptan or silicone rubber impressions. The finished castings are cemented permanently into the mouth with oxyphosphate of zinc cement.

Mixing Thiokol rubber impression materials

Mixing Thiokol rubber impression materials

Physical properties and manipulation of rubber impression materials

The polysulfide rubber and the silicone impression materials compare favorably as to accuracy with the reversible hydrocolloids. Advantages of the silicone materials include improved esthetics, and greater cleanliness in handling. The polysulfide polymers are more standardized from batch to batch, and have a superior shelf-life. The use of the rubber impression materials in many phases of dentistry should continue to expand.

Copper tube, acrylic resin, and thiokol rubber-base impressions for full veneer preparations

A new method for the use of rubber impression materials has been described. It has the following advantages: (1) no gingival retraction is necessary, but gingival margins can be registered adequately; (2) there is reasonable assurance that an acceptable impression will be made; (3) the impression of as many teeth as there are prepared in the arch can be made; (4) the margins of the prepared teeth can be corrected if indicated by the preliminary impression; (5) a satisfactory impression can be obtained in the presence of a wet or bloody field; (6) the inexperienced dentist or one who has not mastered gingival retraction can achieve better results than otherwise possible for him by the use of the laboratory-prepared band; (7) the technique is versatile and may be adapted to many situations. The procedure has the following disadvantages: (1) The technique seems complicated and time consuming until it is mastered. (2) The dentist must be able to work rapidly and have a well-trained assistant for making the final impression. (3) The use of the acrylic-resin impressions made in the mouth adds the amount of time required to handle the acrylic resin to the over-all chair time.

Clinical and physical studies of the silicone rubber impression materials

Clinical and physical studies of the silicone rubber impression materials

The Properties and Manipulation of Mercaptan Base and Silicone Base Impression Materials

The presently available rubber impression materials can be classified as mercaptan base and silicone base materials, according to their composition. The sub-classes of each type can be designated as “heavy type,” “regular type” and “syringe type” according to their viscosity after mixing and their general specialized uses. “Thiokol Polysulfide Rubber,” a polyfunctional mercaptan, is the chief constituent of the mercaptan base materials. A polymerization to a synthetic rubber is effected by means of lead peroxide and sulfur as accelerators. Both the base and the accelerator are supplied in paste form containing plasticizers and fillers. One of the products of the reaction is water. The principal ingredient of the silicone rubber impression materials is thought to be polydimethyl siloxane, which is formed into a paste with a carefully compounded filler. The accelerator (an organic tin compound) is usually supplied as a liquid. Hydrogen and other gases may be evolved during polymerization and may cause pitting of the stone model unless eliminated by a hydrogen acceptor or by the use of a more complex dimethyl siloxane. Volatiles of some nature are always evolved during the vulcanization reactions. It has been shown that the working time of various products varies between 3 and 9 minutes, and the setting time varies between 6 and 13 minutes; the silicone base materials generally set faster than the mercaptan base materials. An increase in temperature accelerates the setting time, particularly in the case of the mercaptan base impression materials. The setting time of the silicone base materials can be controlled by the amount of accelerator employed, but the relation is not in direct proportion. The control of the setting time of the mercaptan base materials can be effected by the mixing temperature, or by the addition of a drop of water for acceleration or a small amount of fatty acid for retardation. The better rubber impression materials may possess elastic properties equal or superior to those of the hydrocolloid impression materials. In general, the strength of these materials is comparatively high. All of the rubber impression materials shrink after setting; the present silicone base materials tend to shrink more than the mercaptan base materials. Although the materials cannot be considered to be dimensionally stable, in some instances the change may be within the allowed tolerance of error. In all instances they are superior in this respect to the hydrocolloid impression materials. Rubber impressions can be electroplated successfully with silver. In general, the electroplated die may not be quite as accurate as a stone die constructed within 30 minutes after the removal of the impression from the mouth. Techniques were suggested for the proper procedures based upon the research findings. The importance of a uniform mix of the base and accelerator was emphasized, as well as the necessity for complete retention of the material in the tray during withdrawal from the parts impressed. The rubber impression pastes are virtually universal impression materials for any dental procedure. The silicone materials at present generally set too rapidly and exhibit poor dimensional stability in comparison to the mercaptan base materials. On the other hand, the silicone materials present the advantages over the mercaptan materials of cleanliness in handling, less tendency to stain, less sensitivity to temperature change, and less toxicity when in continuous contact with the tissues. Once these important disadvantages are eliminated, it is predicted that the silicone base impression materials will supplant the mercaptan base materials.

Mercaptan Rubber Impression Technique for Single and Multiple Restorations

The mercaptan rubber should be used for the impression when making indirect single and multiple tooth restorations. For the impression of the full crown preparation, the use of a tube is often the method of choice, but the tray technique is advocated for other types of preparations. Accurate results can be expected if the basic properties of the materials used are understood and correlated with practical application. Rigidity, stability, and a rubber adhesive must be provided in the tray or tube. When the tray method is used, a uniform 2 or 3 mm. thickness of rubber is recommended; also, a double mix technique utilizing a syringe is advised, and the surfaces to be impressed should be exposed to view and dry. Mixing of the base and accelerator pastes must be thorough. Care must be exercised to allow for the development of sufficient elastic property before withdrawing the impression. The impression should be poured as soon as practicable, preferably within a few hours, but if the taper of the preparation is not minimal, a day or two delay is allowable. Two pours are permitted in the tray impression, and any one of several methods may be employed to make the first pour a split model, where desired. A strip method is recommended.

Clinical uses of rubber impression materials and electroforming of casts and dies in pure silver

DIGEST OF THE LITERATURE pertaining to the physical properties of the rubber impression materials shows agreement among the investigators as to its accuracy, dimensional stability, and ability to recover after deformation in removal from severe undercuts. The research of Skinner and Cooper,1 Jorgensen,” Rosenteil, Fairhurst and others,’ and the Thiokol Chemical Corporation” confirms the belief of the author that the synthetic rubber base is a desirable impression.material which possesses qualities equal to those of the hydrocolloids. Variables inherent to the hydrocolloids are not found in the synthetic rubber impression materials which may lay claim to some valuable properties of their own. Notable among them is the surface density and fine detail imparted to stone casts and individual dies recovered from such impressions. Casts and dies need not be processed immediately as in the case of the hydrocolloids but may be poured at a convenient time. The rubber base neither gives up nor takes water from the hydrocal material during setting. This property results in an extremely accurate cast that exhibits a harder surface than casts poured in the hydrocolloid impressions. The ability of the Thiokol base synthetic rubber material to take a plate of pure silver to electroform casts and dies enhances it as an impression material for most prosthodontic procedures, including the making of individual crowns and inlays of either gold or porcelain. A comparison of electroformed silver with stone dies for processing inlays favors the metal type of die because of the better marginal definition, strength, ease of waxing, and finishing. The detail and accuracy of the silver dies produced by electrodeposition over rubber impressions is unsurpassed. Undercuts that have not been eliminated in the preparation are faithfully reproduced in the impression and die and, if they are not recognized and eliminated in the wax-up, they will prevent the precise seating of the crown or inlay. The circular gouging by diamond and cross-cut cylindrical instruments in the preparation of parallel walls constitutes small but precise undercuts that may prevent the proper seating of the casting. Attention to detail in the elimination of undercuts and other shortcomings in our preparations will be rewarding in the satisfaction one receives from the production of superior restorations. The rubber base material may be used for impressions in most clinical and laboratory procedures where hydrocolloid, alginate, modeling compound, or zinc oxide and eugenol pastes have been the materials of choice. For single and multiple inlays and crowns, multiple abutments for fixed and removable partial dentures, and for complete dentures, this versatile material may be used for the production of

A simple technic for making dental porcelain jacket crowns

6. A rubber impression in a compound lined tray must be poured within three hours; if compound is not used to line the tray, the impression may be poured days later. 7. Sufficient setting time for the rub­ ber material should be allowed to achieve resiliency. At least ten minutes from start of mixing is recommended as being sufficient. 8. The enamel portion of the proxi­ mal buccal and lingual walls of the cav­ ity preparation should be flared well into the buccal and lingual embrasures, wherever compatible with esthetics. 9. The tray method of impression taking is recommended. 10. Salivation must be controlled by profound local anesthesia for the tray impression technic. 11. The rubber material is remark­ ably stable. 12. The surface of dies from the rub­ ber impression is superior to that of dies from reversible hydrocolloid. 13. A rubber impression of the tray type permits a second pouring. 14. It is not recommended that an attempt be made to correct a rubber impression by adding newly mixed rub­ ber and reseating. 15. An impression technic is recom­ mended which revolves around the simul­ taneous use of two rubber materials of different viscosities, and a newly designed plastic tube or plastic tipped syringe.