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Gypsum Products, 8. Denture Resins and Polymers, 9. Restorative Resins, Dental Amalgam, Direct Filling Gold, Dental Cements, Liners and Varnish, Model, Cast and Die Materials, Waxes in Dentistry, Dental Casting Investment Materials, Casting Procedures, Dental Casting Alloys, Dental Ceramics, Wrought Alloys, Soldering, Brazing and Welding, Abrasion and Polishing Agents, Tarnish and Corrosion, Dental Implant Materials.
Download Here http: You just clipped your first slide! Clipping is a handy way to collect important slides you want to go back to later. When a direct flame is used, the compound should not be allowed to boil or ignite, otherwise, the plasticizers are volatilized. Cakes When a large amount of compound is to be softened, it is difficult to heat the compound uniformly over a flame.
The compound is softened in warm water in a thermostatically controlled water bath Fig. After the compound is removed from the water bath, it is usually kneaded with the fingers in order to obtain uniform plasticity throughout the mass. A thermostatically controlled water bath.
Removal of Impression The impression is removed from the mouth only after it has completely hardened. Pouring the Cast and Cast Separation The cast should be poured without delay. The cast is separated from the impression by immersing it in warm water until it is soft enough. Excessively hot water is avoided as it can make the material sticky and difficult to remove from the cast. The material can be reused a number of times for the same patient only in case of errors.
Inaccurate portions can be remade without having to remake the entire impression. Accuracy can be improved by flaming the surface material. The material has sufficient body to support itself to an extent especially in the peripheral portions. It does not collapse completely if unsupported by the tray. Difficult to record details because of its high viscosity. Compresses soft tissues while making impression. Distortion due to its poor dimensional stability.
Difficult to remove if there are severe undercuts. There is always the possibility of overextension especially in the peripheral portions. Fixed vegetable or mineral oil acts as plaslicizer and also aids in masking the action of eugenol as an irritant. It is sometimes used in preference to eugenol because it reduces burning sensation. Gum or polymerised rosin speeds the reaction. Canada and peru balsam improves flow and mixing properties.
Calcium chloride acts as an accelerator of setting reaction. Other accelerators are: Zinc acetate 2. Primary alcohols 3. Glacial acetic acid.
This reaction is also known as chelation and the product is called zinc eugenolate. The chelate is thought to form as an amorphous gel that tends to crystallize giving strength to the set mass. Formation of crystalline zinc eugenolate is greatly enhanced by zinc acetate dehydrate accelerator which is more soluble than Zn OH 2 and can supply zinc ions more rapidly.
Setting Time Once the material is in place, it should set fast. Why should an impression material set quickly in the mouth? Any material which takes a long time to set in the mouth: In a busy practice, this could lead to a lot of stress. Initial setting time is the period from the beginning of the mixing until the material ceases to pull away or string out when its surface is touched with a metal rod of specified dimensions.
The impressions should be seated in the mouth before the initial set. The final set occurs when a needle of specified dimension fails to penetrate the surface of the specimen more than 0.
If the particle size is small and if it is acid coated, the setting time is less. It increases speed of formation of the zinc hydroxide. A paste of thick consistency can compress the tissues. A thin free flowing material copies the tissues without distorting them. Type I pastes — 30 to 50 mm Type II pastes — 20 to 45 mm Clinically, these materials have a very good flow.
Occasionally one does come across poor quality impression pastes, which thicken unduly and have a poor flow. Detail Reproduction It registers surface details quite accurately due to the good flow. Rigidity and Strength The impression should resist fracture and be unyielding when removed from the mouth. Dimensional Stability The dimensional stability is quite satisfactory. A negligible shrinkage less than 0. Biological Considerations Some patients experience a burning sensation in the mouth due to eugenol.
It can also cause tissue irritation. This may be overcome by using a non-eugenol paste. Two ropes of paste of same length and width, one from each tube are squeezed onto the mixing slab Fig. A flexible stainless steel spatula is used. The two ropes are combined with the first sweep of the spatula and mixed until a uniform color is observed Figs 4.
Mixing time 1 minute. Mechanical mixing A rotary mixing device can also be used Fig. Special circular mixing pads are available. These are attached to the circular table of the device. After dispensing the material, the machine is switched on. As the table rotates, the operator first collects the material using the sides of the spatula.
He then spreads the material by flattening the spatula. The process of collecting and flattening is repeated alternately until a uniform mix is obtained.
Mechanical mixing gives a faster, uniform mix with less voids and bubbles. It has sufficient body so as to make up for any minor under extensions in the tray itself during impression making. It has enough working time to complete border moulding. It can be checked in the mouth repeatedly without deforming.
It registers accurate surface details. It is dimensionally stable. It does not require any separating media since it does not stick to the cast material. Minor defects can be corrected locally without discarding a good impression.
Manipulation of zinc oxide eugenol paste: Paste dispensing: Paste dispensing is an important aspect of the manipulation of all impression materials dispensed in tubes that are of equal length. A—both the ropes should be of equal length and width in order to ensure the correct proportioning. It requires a special tray for impression making. It is sticky in nature and adheres to tissues. Eugenol can cause burning sensation and tissue irritation. It cannot be used for making impression of teeth and under-cut areas as it is inelastic in nature.
Mixing is done with a stainless steel spatula using circular motions until a streak free mix is obtained Manufacturers usually provide such materials in contrasting colors to aid in visually ascertaining completion of mix FIGURE 4. A rotary automixing device for pastes and cements 4 5 Rigid Impression Materials may be placed over the wound to aid in the retention of the medicament, to protect the wound and to promote healing also known as periodontal pack.
These surgical pastes are less brittle and weaker after hardening. The setting time is longer. The paste is mixed and formed into a rope that is packed over the gingival wounds and into the interproximal spaces to provide retention. The final product after setting should be sufficiently strong so that it is not readily displaced during mastication. These pastes may also contain more eugenol and the accelerator content is less.
Some patients find the taste of eugenol disagreeable and in cases where the surgical pack is worn for several weeks chronic gastric disturbance may result. Hence non-eugenol pastes were developed. Here, the zinc oxide is reacted with a carboxylic acid. Bactericides and other medicaments can be incorporated. This reaction can be substituted for the zinc oxide eugenol reaction to form any type of dental paste. ZOE pastes used for this purpose have slightly different properties.
ZOE registrations are more rigid than registrations made in wax. They are more stable, and offer less resistance to the closing of the jaw. Teeth or severe undercuts if present, would make the removal of such impressions difficult. The impression could distort or fracture on removal.
The ideal impression material for accurately reproducing tooth form and relation- ship would be an elastic substance which can be withdrawn from the undercut area and would return to its original form without any distortion. By definition, an elastic impression material is one that can transform from a semisolid, nonelastic state to a highly elastic solid state. Hydrocolloids 2. Thus, a solution exists as a single phase because there is no separation between the solute and the solvent.
Suspensions and emulsions are two phase systems. Colloids They are often classed as the fourth state of matter known as colloidal state. A colloid is a two-phase system. The two phases of the colloidal sol are: Types of Colloids Colloidal sols may be: Hydrocolloids Basically they are lyosols.
They consist of gelatin particles suspended in water. Since water is the dispersion medium it is known as hydrocolloid. There is no clear demarcation between solutions, colloids and suspensions emulsions.
A Sol has the appearance and many characteristics of a viscous liquid. A Gel is a jelly like elastic semi-solid and is produced from a sol by a process called gelation by the formation of fibrils or chains or micelles of the dispersed phase which become interlocked. Gelation is thus the conversion of a sol to gel.
The dispersion medium is held in the interstices between the fibrils by capillary attraction or adhesion. Gelation may be brought about in one of the two ways: Alginate Gel Strength The gel strength depends on: Greater the concentration, greater will be the number of micelles and hence greater the brush heap density. Addition of fillers also increases the viscosity of the sol.
Reversible hydrocolloids They are called reversible because their physical state can be reversed. This makes them reusable. Irreversible hydrocolloids Once these set, it is usually permanent, and so are known as irreversible. Agar hydrocolloid was the first successful elastic impression material to be used in dentistry. It is an organic hydrophillic colloid polysaccharide extracted from certain types of seaweed.
It is a sulphuric ester of a linear polymer of galactose. Although it is an excellent impression material and yields accurate impressions, presently it has been largely replaced by alginate hydrocolloid and rubber impression materials.
USES 1. Widely used at present for cast duplication during fabrication of cast metal removable partial denture, etc. For full mouth impressions without deep undercuts.
Was used extensively for crown and bridge impressions before elastomers came to the market. As tissue conditioner. The former is used with a water cooled impression tray Fig. The syringe material has a different color and is more fluid than the tray material. A Liquefied agar being poured into a duplicating mould. Fillers affect the strength, viscosity and rigidity of the gel.
Other examples of fillers—zinc oxide, diatomaceous earth, silica, clay, rubber, etc. Examples are: Glycerine, and Thymol. Thymol acts as bactericide also. Liquefaction section Every time the material is reliquefied, three minutes should be added. This is because it is more difficult to break down the agar brush heap structure after a previous use.
It can be stored in the sol condition till needed. This is done to reduce the temperature so that it can be tolerated by the sensitive oral tissues. It also makes the material viscous.
The rim lock is a beading on the inside edge of the tray which helps to retain the material as agar does not adhere to the tray. It also has an inlet and outlet for connecting the water tubes Fig. The tray should allow a space of 3 mm occlusally and laterally and extend distally to cover all teeth.
Making the Impression The tray containing the tempered material is removed from the bath. The outer surface of the agar sol is scraped off, then the water hoses are connected and the tray is positioned in the mouth by the dentist. Rapid cooling e. To guide the tray into position, three stops of compound are prepared on non-involved teeth.
A post dam is constructed with compound to prevent distal flow of the impression material. In a deep palate case, compound is placed on the palatal aspect of the tray in order to provide a uniform thickness of the hydrocolloid. The mandibular tray is prepared by placing compound on the distal aspect to limit the impression material. Black tray compound is used as it is not affected in the tempering bath.
Removal of Impression When the agar has gelled, the peripheral seal around the impression is broken, and the impression is removed rapidly from the mouth with a single stroke or snap. The impression is rinsed thoroughly with water and the excess water is removed by shaking the impression. Storage of Agar Impression Storage of agar impression is to be avoided at all costs and no satisfactory medium for storage is available. The cast should be poured immediately.
Storage in air results in dehydration, and storage in water results in swelling of the impression. Separation from Cast When the gypsum product has set, the agar impression must be removed promptly since the impression will dehydrate, become stiff, and difficult to remove. Weaker portions of the model may fracture. In addition, prolonged contact will result in a rougher surface on the model. Syneresis and Imbibition Dimensional Stability Since hydrocolloids use water as the dispersion medium, they are prone for dimensional change due to either loss or gain of water.
If left in a dry atmosphere, water is lost by evaporation, and if it is immersed in water, it absorbs water by a process known as imbibition. Some of the more soluble constituents are also lost. During syneresis small droplets of exudate are formed on the surface of the hydrocolloid and the process occurs irrespective of the humidity of the surrounding atmosphere. Agar exhibits the properties of syneresis and imbibition.
However, when immersed in water they do not imbibe more than original content which was lost by evaporation unlike alginates. Importance Syneresis and imbibition can result in dimensional changes and therefore inaccurate casts. To avoid this hydrocolloid impressions should be poured immediately. Flow The material is sufficient fluid to record the fine details if it is correctly manipulated.
Gelation, Liquefaction and Hysterisis Most materials melt as well as resolidify at the same temperature. However, in agar this does not coincide. This temperature lag between liquefaction and gelation is known as hysterisis. Elasticity and Elastic Recovery Agar hydrocolloids are highly elastic in nature and elastic recovery occurs to the extent of However, prompt pouring of plaster or stone models is recommended.
Working and Setting Time The working time ranges between minutes and the setting time is about 5 minutes. Both can be controlled by regulating the flow of water through the cooling tubes. Since the cooling tubes are on the periphery, the material sets from the periphery towards the teeth surfaces. According to ADA sp. The above values are for tray materials. The syringe materials have poorer mechanical properties. The alginate gels by a chemical reaction, whereas the agar gels by means of contact with the cool alginate rather than the water circulating through the tray.
Advantage 1. The syringe agar gives better details than alginate. Less air bubbles. Water cooled trays are not required. It sets faster than the regular agar technique. The areas to be recorded are actually flooded with warm water. While the syringe material is still liquid, the tray material is seated.
The hydraulic pressure of the viscous tray materials forces the fluid syringe hydrocolloid down into the areas to be recorded. This motion displaces the syringe materials as well as blood and debris throughout the sulcus.
This makes it an ideal mould material. The agar is broken into small chunks and loaded into the liquefying machine Fig. The liquid agar is poured into a mould former in order to create a mould. Later, investment is poured into this to create a refractory cast which is used in the fabrication of the cast partial denture framework.
Most manufacturers recommend a specific disinfectant. The agent may be iodophor, bleach or glutaraldehyde. Apparently little distortion occurs if the recommended immersion time is followed and if impression is poured promptly. Accurate dies can be prepared, if the material is properly handled. It has good elastic properties and reproduces most undercut areas correctly.
It has good recovery from distortion. As it is not hydrophobic, it gives good model surface. It is palatable and well tolerated by the patient. It is cheap as compared to synthetic elastic materials. It can be reused when used as a duplicating material reuse is not recommended when used as impression material. Disadvantages 1. Does not flow well when compared to newly available materials. It cannot be electroplated.
During insertion or gelation it may be painful to the patient. Tears relatively easily. Greater gingival retraction is required for providing adequate thickness of the material.
Only one model can be poured. Extensive and expensive equipment is required. A soft surface of the gypsum cast results unless a plaster hardener is used. Although it can be reused, it is impossible to sterilize this material. Also with repeated use there may be contamination of the materials and a deterioration in its properties. Algin was used for many purposes. In England 40 years later, another chemist, S.
William Wilding received a basic patent for the use of algin as a dental impression material. Alginate was developed as a substitute for agar when it became scarce due to World War II Japan was a prime source of agar.
Currently, alginate is more popular than Agar for dental impressions, because it is simpler to use. Type II- normal setting. A plastic scoop is supplied for dispensing the bulk powder, and a plastic cylinder, is supplied for measuring the water.
Modified Alginates Other forms are also available: A reactor of plaster of Paris is supplied separately. These materials are said to contain silicone and have superior resistance to tearing when compared to unmodified alginates. They may be supplied in both tray and syringe viscosity. Alginate is available in bulk packing or as small sachets for individual impressions.
It is used for impression making: For making preliminary impressions for complete dentures. For impressions to make study models and working casts.
For duplicating models. Functions 1. Coloring and flavoring agent Traces e. The final gel, i. However, this reaction proceeds too fast.
There is not enough working time. So the reaction is delayed by addition of a retarder sodium phosphate by the manufacturer. Calcium sulphate prefers to react with the retarder first. Only after the supply of the retarder is over does calcium sulphate react with sodium alginate. This delays the reaction and ensures adequate working time for the dentist. In other words, two main reactions occur during setting: Next, after the sodium phosphate is used up, the remaining calcium sulphate reacts with sodium alginate to form insoluble calcium alginate which forms a gel with water.
Gel Structure The final gel consists of a brush heap of calcium alginate fibril network enclosing unreacted sodium alginate sol, excess water, filler particles and reaction by products. It is a cross linked structure i. Calcium is responsible for cross linking. Over the years, manufacturers have added a variety of colors, odors and tastes to make it as pleasant as possible to the patient.
Flavors include strawberry, orange, mint, vanilla, etc. Thus permanent deformation is more for Alginate about 1. Permanent deformation is less if the set impression is removed from the mouth quickly. Reproduction of Tissue Detail Detail reproduction is also lower when compared to agar hydrocolloid. The ADA Sp. A number of products exceed this minimum value. Dimensional Stability Set alginates have poor dimensional stability due to evaporation, syneresis and imbibition. Therefore, the cast should be poured immediately.
Adhesion Alginate does not adhere well to the tray. Good adhesion is important for the accuracy of the impression. Retention to the tray is achieved by mechanical locking features in the tray or by applying an adhesive. Biological Properties Silica particles present in the dust which rises from the can after fluffing alginate powder, are a possible health hazard. Avoid breathing the dust. Dustless alginates contain glycol. It acts by coating the powder. Shelf Life and Storage Alginate material deteriorates rapidly at elevated temperatures and humid environment.
This ensures uniform distribution of the filler before mixing. The top of the can should be taken off carefully to prevent the very fine silica particles from being inhaled. It is better to use separate bowls for plaster and alginate as plaster contamination can accelerate setting. The water measure and scoop are supplied by the manufacturer.
The measured quantity of the powder is sprinkled in the measured amount of water in the rubber mixing bowl and the lid of the metal can is replaced immediately. The mixing is started with a stirring motion to wet the powder with water. Once the powder has been moistened, rapid spatulation by swiping or stropping against the side of the bowl is done.
A vigorous figure— eight motion can also be used Fig. A Alginate is mixed by stroping or swiping the material against the sides of the bowl. Mechanical devices are available for spatulating alginate. Their main advantages are: A proper mix is smooth and creamy with minimum voids and does not drip off the spatula when it is raised from the bowl.
Mixing Time For fast set alginate 45 seconds. For normal set alginate 60 seconds. Over Mixing Results In — Reduction in final strength as the gel fibrils are destroyed. Under Mixing Results In — Inadequate wetting, lack of homogeneity and reduced strength. Working Time Fast set alginate: Normal set alginate: Type II normal: Even the mixing bowl and spatula can be cooled.
Alginate can be retained by: The tray should cover the entire impression area and provide a space of at least 3 mm on all sides. The surface of the alginate in the tray may be smoothened out by moistening the finger with water and running it over the surface of the alginate.
A small amount of material is taken on the index finger and applied on the occlusal surfaces of the teeth and on the rugae area. This help to reduce air voids and improve accuracy.
So once the tray is seated, it must be held in place firmly without any movement. Test for Set The material loses its tackyness when set. It should rebound fully when prodded with a blunt instrument.
The strength and elasticity of the alginate gel continues to increase for several minutes after initial gelation. The impression must be removed suddenly, with a jerk.
The brush-heap structure of a gel responds more favorably to a sudden force. A gentle, long, continued pull will frequently cause the alginate to tear or separate away from the tray. It also causes higher permanent deformation.
An alginate impression is displayed in Figure 4. After removal from the mouth, the impression should be: If it becomes necessary to store the impression, the following methods may be used: Note Even under these conditions storage should not be done for more than one hour.
However, the formulas of presently available alginates have been adjusted so that no hardening solution is required. For alginate, best results are obtained if the cast is removed at one hour.
The cast should not be left in the impression for too long a period either because: Removal can break the teeth and other thin portions of the cast. The viruses can contaminate the gypsum models and present a risk to dental laboratory and operating personnel. The irreversible hydrocolloids may be disinfected by 10 minutes immersion in, or spraying of, some antimicrobial agent e.
It is easy to mix and manipulate. Minimum requirement of equipment. Flexibility of the set impression. Accuracy if properly handled. Low cost. Comfortable to the patient. It is hygienic, as fresh material must be used for each impression. It gives a good surface detail even in presence of saliva. Cannot be electroplated so metal dies not possible.
It cannot be corrected. Distortion may occur without it being obvious if the material is not held steady while it is setting. Poor dimensional stability—it cannot be stored for long time. Poor tear strength. Because of some of the above drawbacks and because of the availability of better materials , it is not recommended when a high level of accuracy is required, e.
They are soft and rubber like and are known as elastomers or synthetic rubbers. As per ADA Sp. Elastomeric materials contain large molecules with weak interaction between them.
They are tied together at certain points to form a three dimensional network. On stretching the chains uncoil, and on removal of the stress they snap back to their relaxed entangled state. They are liquid polymers which can be converted to solid rubber at room temperature.
Synonyms Initially they were called rubber-base or rubber impression materials. Currently, they referred to as elastomers or elastomeric impression materials. According to Viscosity Each type may be further divided into four viscosity classes Fig. In fixed partial dentures for impressions of prepared teeth. Impressions of dentulous mouths for removable partial dentures. Impressions of edentulous mouths for complete dentures. Polyether is used for border moulding of special trays.
For bite registration. A success dentist has to combine technical skills together with sound clinical know-how. To the novice, the assignment may also appear formidable due to the wide array of substances to be had.
This is pretty everyday and thankfully disappears with use and familiarity. Basic Dental materials, first posted in , is now in its 18th yr. Its publication became inspired with the aid of the preference to assist students navigate the complex area of dental substances from the first actual year of the path. Being the primary published book on dental materials from India, it had set new standards, such as moving faraway from traditional formats. College students are recommended to read from a huge supply of substances for extra understanding and intensity of understanding.
It is encouraging to peer plenty of latest courses in the u.