impression materials and techniques for fixed prosthodontic

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Impression materials and techniques for fixed prosthodontic

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The ideal impression material should possess multiple characteristics: 1- The hydrophilicity of impression material, which is defined as having a high affinity for moisture, providing good surface wetting, and allowing for greater surface detail.

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Page 1: Impression materials and techniques for fixed prosthodontic

Impression materials and techniques for fixed prosthodontic

Page 2: Impression materials and techniques for fixed prosthodontic

Impression: is a negative likeness or copy in reverse of the surface of an object .

. A variety of impression materials exists in order to capture the surface detail and dimensions of hard and soft tissues for fabrication of prosthesis. Also the impression used for diagnosis (e.g. in orthodontic).

Page 3: Impression materials and techniques for fixed prosthodontic

The ideal impression material should possess multiple characteristics:

1 -The hydrophilicity of impression

material, which is defined as having a

high affinity for moisture, providing

good surface wetting, and allowing for

greater surface detail .

Page 4: Impression materials and techniques for fixed prosthodontic

2- The dimensional stability of the material, which is critical for

accurate replication of the intraoral structures.

Dimensional changes may occur due to (1) contraction

from polymerization, (2) liberation of a by-product or

accelerator component, (3) water absorption from a wet or

humid environment, (4) a change in temperature and (5)

incomplete recovery of deformation because of viscoelastic

behavior. . Materials with good dimensional stability can

remain unchanged for a period of approximately 7 days and

resist temperature extremes during shipping.

Page 5: Impression materials and techniques for fixed prosthodontic

Overcome dimensional change:

1. Delay pouring the impression after half to one hour until byproduct (hydrogen gas) volatile. 2. Manufactures often add a noble metal, such as platinum or palladium, to act as a scavenger for the released hydrogen gas.

Page 6: Impression materials and techniques for fixed prosthodontic

3- Tear resistance and elastic

recovery. These are important for

preserving the accuracy of the

impression during removal from the

mouth and after cast separations.

Materials with sufficient tear

resistance and elastic recovery will

withstand multiple pours.

Page 7: Impression materials and techniques for fixed prosthodontic

4- Other properties for an ideal impression material

would have a pleasant odor, taste, and acceptable color.

Absence of toxic or irritant constituents, adequate shelf

life for requirements of storage and distribution,

setting characteristics that meet clinical requirements,

compatibility with cast and die material, readily

disinfected without loss of accuracy.

Page 8: Impression materials and techniques for fixed prosthodontic

According to the elasticity:

Page 9: Impression materials and techniques for fixed prosthodontic

Elastomers are a group of elastic impression

materials. They consist of polymers that bind

together in a network of chains that give material a

rubber consistency. They are widely used in fixed

and removable prosthesis because of their good

properties

Page 10: Impression materials and techniques for fixed prosthodontic

1- ViscosityViscosity describes the flow characteristics of an unset impression material. Materials with low viscosity have high flow and those with high viscosity have low flow. The low viscosity material can be referred to as light body, syringe, or wash material. These lower viscosity materials can flow easily into and record fine details; however, they are usually not used alone. Instead, they are generally used in conjunction with a second more viscous material to push and support the lower viscosity material.

Page 11: Impression materials and techniques for fixed prosthodontic

2- Hydrophilicity

Impression materials are characterized by their degree

of hydrophilicity. Surface wetting describes the relative

affinity of a liquid for a solid and can be quantified by

measuring the contact angle. A contact angle of zero

would indicate complete wetting of the surface;

whereas, a high angle would indicate less wetting.

Page 12: Impression materials and techniques for fixed prosthodontic
Page 13: Impression materials and techniques for fixed prosthodontic

Hydrophilic materials have a high affinity for

moisture (low contact angle), provide good surface

wetting, and allow for a high degree of surface detail.

Hydrophobic impression materials have a low

affinity for moisture (high contact angle), provide

poor surface wetting, and a lower degree of surface

detail. Hydroactive impression materials are normally

hydrophobic and are rendered hydrophilic through

the addition of surfactants.

Page 14: Impression materials and techniques for fixed prosthodontic

3- Tear Resistance and Elastic RecoveryTear resistance and elastic recovery are important in

preserving the accuracy of the impression during intraoral

removal and after cast separation. Materials with sufficient

tear resistance and elastic recovery will withstand multiple

pours, producing several accurate casts, which is a major

advantage in contemporary restorative dentistry.

Page 15: Impression materials and techniques for fixed prosthodontic
Page 16: Impression materials and techniques for fixed prosthodontic

4- Working time – a period from the start of mixing to the final time at which the impression can be seated in the mouth without its distorsion.

5- Setting time – a period from the start of mixing till the impression becomes elastic enough to resist deformation during its withdrawal from the mouth.

Page 17: Impression materials and techniques for fixed prosthodontic

Advantage Disadvantage

1. Low price.2. Long working time.

1. Should be poured within 0.5 – 1 hour.

2. Unpleasant mercaptane smell.

3. Long setting time app. to 10 min.

4. Poor elastic recovery – prone to plastic deformation.

Page 18: Impression materials and techniques for fixed prosthodontic

Advantage Disadvantage 1. Naturally hydrophillic.

2. Accurate and high

dimensional stability.3. Good elastic recovery.

4. Low setting contraction.

5. Excellent surface detail

reproduction.6- Highly acceptable to

patient.

 

1-Swells in disinfectant or moist environment.

2- Rather stiff when set

material (difficult to remove from mouth).

3- Very expensive.

Page 19: Impression materials and techniques for fixed prosthodontic

Advantage disadvantage

1- Easy to disinfect. 2- Highly acceptable to

patient.

3- Accurate impressions when poured soon.

4- Good elastic recovery.

5- Lower price.

1- Must pour within one hour.

2- Low tear strength.

2- Hydrophobic.

3- Dimensionally unstable.

Page 20: Impression materials and techniques for fixed prosthodontic

Advantage Disadvantage

1- Good surface detail (dry surface ).

2- Good dimensional accuracy.

3- Low permanent deformation.

4- Highly acceptable to patient.

5- Good storage stability.

1- Hydrophobic ( unless surfactant added.

2- Low tear strength.

3- High cost.

Page 21: Impression materials and techniques for fixed prosthodontic

Manual mixing Auto mixing

Page 22: Impression materials and techniques for fixed prosthodontic

.The auto mixing result in fewer voids than hand mixes. . Equal mix without lefting any material unmixed. . Low material waste than hand mixing.

. automixing was used for all consistencies except putty to be used with this system. . cost.

Page 23: Impression materials and techniques for fixed prosthodontic

1- Dual-Viscosity Technique.

2-Single-mix Technique or Monophase Technique. 3- Putty-Wash Technique.

Page 24: Impression materials and techniques for fixed prosthodontic

. Dual-viscosity technique also called one step technique in which low-consistency material is injected with a syringe into critical areas and the high-consistency material is mixed and placed in an impression tray. After injecting the low-viscosity material, the tray containing the higher-viscosity material is placed in the mouth. the materials join, bond, and set together.

Page 25: Impression materials and techniques for fixed prosthodontic

In the single-viscosity or monophase technique, impressions are often taken with a medium-viscosity impression material. To overcome problems associated with using two different viscosities such as using two mixing guns and any difference between the viscosities, a monophase impression technique with medium viscosity was suggested

Page 26: Impression materials and techniques for fixed prosthodontic

The putty-wash technique is also called two-step technique whereby a preliminary impression is taken in high- or putty-consistency material before the cavity preparation is made. Space is provided for a low consistency material by a variety of techniques, and after cavity preparation, a low-consistency material is syringed into the area and the preliminary impression is reinserted.

Page 27: Impression materials and techniques for fixed prosthodontic

Gingival retraction is allowed to remain for 5 to 10 minutes, to allow water absorption by the superficial cord and increase crevicular width.(a); Excess moisture is eliminated and the second cord is removed (b) a low viscosity impression material is immediately injected into the sulcus (c).

Page 28: Impression materials and techniques for fixed prosthodontic

.All impressions should at least undergo a disinfecting procedure by immersion in 1% sodium hypochlorite for a minimum of ten minutes…

.Chlorine solution, Aldehyde solutions, iodine and phenol solutions…

Page 29: Impression materials and techniques for fixed prosthodontic