lec:8 dental material dr. aseel mohammed · web viewhybrid impression (combination of addition...

Lec:8 Dental Material dr. Aseel Mohammed

Elastomeric impression materialIn addition to hydrocolloids there is another group of elastic impression materials. They are soft and rubber like and are known as elastomers or non aqueous impression material. Elastomers are flexible cross-linked polymers when set. They are synthetic polymers which can be converted to solid rubber at room temperature by mixing with a suitable catalyst they undergo polymerization and /or cross linking (by condensation or addition) reaction to produce firm elastic solid.

Types of elastomers (According to the chemistry):

1. Polysulphide.2. Condensation polymerizing silicones.3. Addition polymerizing silicones.4. Polyether.5. Hybrid impression (combination of addition silicon and polyether).

Presentation:

Regardless of type all elastomeric impression materials are supplied as two paste systems (base and catalyst) in collapsible tubes. While the Putty consistency is supply in jars.

Each type may be further divided into five viscosity: In increasing order of filler content

Extra low or very low bodied. Low or light bodied (Also referred to as syringe type, or wash type. This material is

used because of its ability to flow in and about the details of the prepared tooth. A special syringe is used to place the light-bodied material immediately around the prepared teeth.

Medium or regular bodied (used with special tray). Heavy bodied or tray consistency (Often referred to as tray - type materials, they are

much thicker. they are used to fill the special tray. Their stiffness helps to force the light-bodied material into close contact with the prepared teeth and surrounding tissues to ensure a more accurate.

Very heavy or putty consistency.


Extra-low and very heavy (putty) forms are available only for condensation and addition silicones. There is no heavy-body product for condensation silicone.

The light bodied and the very light bodied classes are used as a syringe material in combination with a tray material or with putty type, and the regular material is used alone with special tray. While the putty consistency used with stock tray either use alone as primary impression or use with light body or with very light body as final impression. Tray adhesive is needed for adherence of the impression material to the tray.

Uses : generally used in all cases1. Crown and bridge impressions.2. Partial and complete denture impressions.3. Implant.

1. Polysulphide impression material:

This was the first elastomeric impression material to be introduced. It is also known as Mercaptan or Thiokol.

Presentation: paste in collapsed tubes as base and accelerator or catalyst. Base is white colored; accelerator is brown or gray.Available in three viscosities (by controlling the filler in its composition). Light bodied, medium bodied, heavy bodied.

Composition: Base:

1. Liquid polysulphide polymer with terminal and pendant thiol (-SH) groups (this is further polymerized and cross linked to form rubber).

2. Inert filler (silica or titanium dioxide); (to give body, control viscosity and modify physical properties.


Catalyst:

1. Lead dioxide (react with thiol groups causing setting).2. Dibutyl phthalate (plasticizer).3. Sulfer (to enhance reaction).4. Magnizium stearate (retarded and deodorants).

Setting reaction Equal length of base paste and acceleration paste are mixed, it undergoes a chemical reaction. The liquid polymer sets to form solid but highly elastic and flexible rubber like material.

The lead dioxide reacts with the polysulphide polymer causing

Chain lengthening by oxidation of terminal –SH groups Cross linking by oxidation of pendant –SH groups.

The reaction is exothermic 3-4 c rise in temperature. The reaction is sensitive to heat and moisture increase in either one will accelerate the setting reaction.

Mercaptan + lead dioxide polysulphide +water (by product)

Properties: 1. Unpleasant odor and color. It stains the clothes and it is messy to work with it.2. It has long setting time about 12.5 min (discomfort to the patients).3. Excellent reproduction of detail.4. Dimensional stability; the curing shrinkage is highest permanent deformation

among the elastomers. this improve with time so pouring of the model should be delay by half an hour, further delay is avoided to minimize curing shrinkage, loss of the by product (water) is also causing shrinkage.

5. It has high tear strength and Low hardness.6. It has good flexibility.7. It is hydrophobic, so the mouth should be dried before making an impression.

Care should also be taken while pouring the stone to avoid air pockets.8. The half life is good 2 years.9. Inexpensive to use.10.Requires a special tray (2 mm spacer).11.The tray is painted with adhesive before putting the impression.12.These materials are extremely viscous and sticky, mixing is difficult, however they

exhibit pseudoplasticity (if sufficient speed and force is used for mixing the material will seem easier to handle).


13.The reaction yields water as a by-product. Loss of this small molecule from the set material has a significant effect on the dimensional stability of the impression so we should pour the impression with gypsum product not more than 30 min.

Manipulation: Equal length of base paste and acceleration paste are mixed on the paper pad by using stiff bladed spatula, the mixing is continued until the mix is free from steaks and uniform in color. A special tray (with 2mm spaced) are used and the inside of the tray is painted with a layer of adhesive and allow to dry before put the impression material in the tray (otherwise the polysulfide impression may separated from the tray during removal from the mouth). Some time holes are drilled through the tray to provide mechanical retention of the impression material. When the material has set it remove with a steady force (a snap removal not necessary because it have high tear strength). We pour the impression with gypsum product After 30 minutes after removal from the patient mouth. No separating medium is needed before pouring the gypsum products.

Silicone impression materialsTwo types of silicon impression materials based on the type of polymerization reaction occurring during its setting: 1. Condensation silicon impression materials.

2. Addition silicone impression materials.

2. Condensation silicon impression materials

It was the earlier of the two silicone impression materials, available in four viscosities. (Very low, light bodied, medium bodied and putty).

Presentation: The materials are supplied as- base paste and a low-viscosity liquid catalyst.

- base putty and a low-viscosity liquid catalyst.

- base putty and paste catalyst.

- two-paste system. (Not equal in size)

- two-putty system.


Composition: Base:

1. polydimethyl siloxane (hydroxyl-terminated).2. Inert filler colloidal silica or metal oxide filler.3. Color pigments.

Accelerator:

1. Orthoethyl silicate (cross linking agent) 2. Stannous octoate as a catalyst.

Setting reaction: It is condensation reaction, polymerization occurs as a result of cross linkable between the orthoeyl silicate and the terminal hydroxyl group of dimethyl siloxane to form a three-dimensional network. The reaction is exothermic (1 C) rise. Ethyl alcohol formed as by product evaporates gradually form the set rubber leading to shrinkage.

Dimethyl siloxane + orthoethyl silicate stannous octoat silicone rubber + ethyl alcohol

Properties: 1. Pleasant color and odor.2. Direct skin contact should be avoided to prevent any allergic reaction.3. Setting time is (6-9) min. (shorter than polysulphide).4. Excellent reproduction of surface details.5. Dimensional stability is comparatively less because of high curing shrinkage (0.4-0.6)

% and shrinkage due to evaporation of ethyl alcohol by product. To avoid this cast should be poured immediately.

6. Tear strength is lower than the polysulphides.7. Elasticity develops earlier than polysulphide.8. It is stiffer and harder than the polysulphides. The hardness increase with time. The

spacing in the tray is increased to 3mm to compensate for the stiffness.


9. It is hydrophobic. The impression field should be dried well before making an impression. Care should also be taken while pouring the stone to avoid air pockets.

10. Shelf life is slightly less than polysulphide.11. Slightly more expensive than polysulphide.12. Need to paint the tray with adhesive.13. The putty consistency mostly widely used with stock offering an advantage over the

polysulphide which are used with special tray only.

3. Addition silicone impression materials: They have better properties than condensation silicone and the polysulphide. This material is often called a polyvinyl siloxane (PVS) or vinyl polysiloxane (VPS) impression material. Addition silicone is available in extra low, low, medium, heavy, and very heavy (putty) consistencies. Presentation: The materials are supplied as- Two-paste system: The base and catalyst pastes come in equal size tube (unlike condensation silicones). - two- putty system (jars): Two equal size jars, one containing the base and the other the catalyst.

Composition: Base:

1. Poly methyl hydrogen siloxane.2. Other siloxane prepolymers.3. Fillers.

Accelerator:1. Divinyl polysiloxane.2. Other siloxane prepolymers.3. Platinum salt (chloroplatinic acid), catalyst.4. Palladium or hydrogen absorber.5. Retarders.6. Fillers.

Setting reaction: It is addition reaction. Base polymer is terminated with vinyl group and is cross linked with silane (hydride group). The reaction is activated by the platinum salt (chloroplatinic acid). There are no by products. Sulfur compounds retard the setting of silicones. One source of sulfur contamination is from latex gloves worn by the operator when mixing the impression (the vinyl gloves should be used).


Vinyl siloxane + silane siloxane chloroplatinic acid silicon rubber

Properties: 1. Pleasant odor and color.2. Direct skin contact should be avoided because of the allergic reaction.3. Excellent reproduction of surface details.4. Setting time is (5-9) min.5. It has the best dimensional stability among the elastomers even after 1 week

(dimensional stability), it has low curing shrinkage 0.17% and the lowest permanent deformation (0.05-0.3).

6. It has good tear strength.7. It is hydrophobic. Care should be taken while making the impression and pouring the

wet stone, some manufacture adds a surfactant to make it more hydrophilic.8. It has low flexible and harder than polysulphides. Extra spacing 3mm. should be

provided in the impression tray. Care should be taken while removing the stone cast from the impression to avoid any breakage.

9. Shelf life range from 1 to 2 years.10. More expensive.11. Need to paint the tray with adhesive.

4. Polyether impression material It has good mechanical properties and dimensional stability. Its disadvantages were that the working time was short and the material was very stiff. It is also expensive and bitter in taste. Polyethers remain popular among a large number of clinicians mainly because of their hydrophilic nature. The water-loving elastomeric material provides superior wettability and adherence to preparations, resulting in good surface detail. Their use is ideal in situations where it is difficult to maintain a dry environment.

Presentation:


Available as base and accelerator in collapsible tubes (the accelerator tube is usually smaller). A third tube containing a thinner was provided. It is available in three viscosities (light bodied, medium bodied and heavy bodied).

Composition: Base:

1. Polyether polymer.2. Colloidal silica (filler).3. Glycolether or phthalate (plasticizer).

Accelerator:1. Aromatic suffonate (cross linking agent).2. Colloidal silica (filler).3. Phthalate or glycolether (plasticizer).

Setting reaction: Polyether+ sulphonic ester cross linked rubber

The reaction is exothermic (4 to 5 C) rise.

Properties: 1. Pleasant color and odor.

2. Bitter in taste.3. Direct skin contact should be avoided (the sulphonic ester may cause skin reaction).4. Setting time is (3-5) min. heat decrease the setting time.5. Excellent reproduction of surface details.6. Dimensional stability is very good. Curing shrinkage (0.24) % and permanent

deformation is low. Polyether absorbed water and can change dimension (should not be stored in water or in humid climates).

7. Tear strength is good.8. It is extremely stiff and its hardness is higher than the polysulphides and increase

with time. Removing it from undercuts is difficult. So extra spacing (4 mm) should be given. Care should be also taken while removing the cast from the impression to avoid any breakage.

9. It is hydrophilic. So moisture in the impression field is not critical. It has the best compatibility with stone.

10. Shelf life is excellent (more than 2 years).11. Tray adhesive used before putting the impression in the tray.12. Expensive.


Light activated polyether impression material:

Available as two viscosities:1. Light body: packed in disposable syringe.2. Heavy body: packed in tubes.

Composition: 1. Visible light curing polyether (urethane dimethacrylate elastomeric resin.2. Visible light cured photo initiator.3. Photo accelerators.4. Silicon dioxide as filler: it has refractive index close to that of resin, in order to

provide translucency necessary for the depth of the cure.

Properties: 1. Excellent elasticity.2. Very low dimensional changes upon setting, it can be poured immediately or up to

two weeks.3. Polyether is very rigid (stiff) so undercuts should be blocked out for easy removal of

the impression.

Manipulation: no mixing is required, light body material is syringed into the impression area. The tray is loaded with heavy body material and placed inside the patient mouth. After the tray is seated in the mouth, both the viscosities are cured simultaneously using a visible light curing unit, having 8mm or larger diameter probe. The curing time is approximately 3 minutes.

Properties : 1. Infinitive working time and short setting time.2. Excellent physical, mechanical and clinical properties.3. Simplification of manipulation technique, i.e. no mixing is required.4. Need for special tray that are transparent to the visible light and are required to cure

material.5. The materials should not be used in patient mouth with known allergy or sensitivity

to urethane or methacrylate.6. The material should be stored in a dark place, away from the light.


hybrid impression (combination of addition silicon and polyether): The vinyl polyether silicon impression material (VPES) represents the next generation of impression material. It combined the benefits of polyether and the vinyl poly siloxane impression materials. It is available in two setting time (fast and regular) and in 4 viscosities (light body, medium body, heavy body and putty).

properties 1. Pleasant tasting (mint taste).2. Excellent tear strength 3. Adequate Bond of impression material to tray.4. Hydrophilic. Record the finer details of the tooth surface, even in a moist

environment.5. Superior elasticity – elasticity without distortion allows for easy removal 6. Multiple pours (allows for multiple pours due to the toughness and elasticity of

material) 7. Excellent dimensional accuracy.8. Exceptional reproduction of detail.9. Resistance to deformation (great recovery from deformation).

10. Excellent flow.11. Compatible with any disinfection procedure12. Little time in mouth. Fast setting time.

Technical consideration (for rubber impression material):


1. The regular body and heavy body are usually made in special tray. Perforated stock trays are used only for making impression in putty.

2. The spacing given is special tray between (2-4) mm.3. Elastomers do not adhere well to the tray. An adhesive should be applied onto the

tray and allow to dry before making impression except the hybrid type don’t need adhesive.

4. The bulk of the impression should be made with heavier consistency (to reduce shrinkage). Light bodied should only be used in a thin layer as a wash impression over the putty or heavy body.

5. The putty type and the heavy bodied rarely could be used alone as primary impression without light body or used with light body or very light body as final impression.

Methods of making impression: 1. Single mix technique: Tray used (resin special tray with 2 to 4 mm spacing). Viscosity

used (regular only). 2. Multiple mix technique: Tray used (resin special tray with 2 to 4 mm spacing). Viscosity

used (heavy bodied and light bodied). 3. Two stage putty wash technique: Tray used (perforated stock tray). Viscosity used (putty

and light bodied).

Manipulation of elastomer impression materials

The user should dispense the correct lengths of materials onto a mixing pad or glass slab. The catalyst paste is first collected by a stainless steel spatula and then spread over the base paste. The mixture is then spread over the mixing pad. The mixing process is continued until the mixed paste is uniform in color, with no streaks of the base or catalyst appearing in the mixture. If one of the components is in liquid form, such as the catalyst for condensation silicones, a length of the base is dispensed from the tube onto a graduated mixing pad and drops of the liquid catalyst corresponding to the length of the base are added. The two-putty systems that available for condensation and addition silicone dispensed by volume using an equal number of scoops of each material. The best mixing technique is to knead the material with fingers until a uniform color is obtained.

Each type of the impression is put in the tray and then inserted in the patient mouth. the impression should not be removed from the patient mouth until the curing has progressed


sufficiently to provide adequate elasticity, so that distortion will not occur. Typically, the impression should be ready for removal within at least 10 minutes from the time of mixing. Manufacturers usually provide the optimal time for removal after mixing. Finally we pouring the impression according to the type of the material (eather immediately or waiting for a period). No separating medium is needed before pouring the gypsum products. All the type of elastomeric impression material except the hybrid impression need tray adhesive.

DIGITAL IMPRESSIONS

Several digital impression systems are currently on the market that allows the dentist to make a digital impression in place of a traditional impression. Digital impressions offer a precise fit with fewer incidents of remakes and shorter adjustment time.

CAD/CAM, the abbreviation for computer-aided design/computer-aided manufacturing, describes a process in which digital images or models of objects are created and used for the design and fabrication of final products.

Properties poly sulphide condensation silicon addition silicon polyether

Setting time moderate- long short-moderate short-moderate short Shrinkage on setting high moderate-high very low low Elastic recovery after removal moderate high very high high Flexibility during removal high moderate low-moderate low-moderate Tear strength moderate-high low- moderate low- moderate moderate Wettability by gypsum mixed moderate poor good-very good very good Detail reproduction excellent excellent excellent excellent

lec:8 dental material dr. aseel mohammed · web viewhybrid impression (combination of addition...

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