A dental impression material helps to replicate an accurate negative reproduction of the oral cavity.
This includes the teeth surrounded by the tissues and dental arch.
The dental impression is a part of several daily tasks in the clinic however, the material for each can be different.
In order to avoid mistakes in the procedure, you should be able to aptly choose the best material for the impressions.
This article discusses the different types of dental impression material along with their pros and cons for better judgment.
Keep reading below to know more!
Types of Dental Impression Material
There are four main types of materials used in making dental impressions.
However, these four are further divided into two categories.
- Rigid
- Elastic
Rigid impression material consists of zinc oxide eugenol and impression compound.
Whereas elastic impression materials are silicone and alginate.
Dental impressions help to make the model of the dental equipment the patient and dentist need.
For instance, if the patient needs retainers or Invisalign, the impressions can help to make the equipment that molds directly over it and then fits your teeth.
This way you get an accurate mold that the teeth seamlessly fit into.
Therefore, getting the suitable material for the impression is important because it will impact the mold and the final equipment.
If it doesn’t fit the patient’s teeth, it may as well be useless.
When you are choosing the material, it is also important to consider few of its characteristics.
These include:
- The texture, consistency and handling of the material
- Its dimensional stability with regards to temperature and humidity, strength and elasticity
- It should have a pleasant odor and flavor as it goes into the mouth of the patient and stays there for a while
- The accuracy of how correctly it captures the mold and the results time is integral
- Look for its component toxicity
- Check its compatibility with molds and modeling materials
- What is its shelf life? What is the susceptibility to infection?
- Check its compatibility with water
The most popular material for dental impressions is the elastic ones.
These are alginates and silicone.
Usually, these characteristics are parts of the alginates and silicone.
Though rigid materials such as zinc oxide eugenol and impression compound are also in use for taking impressions of edentulous arches.
Let’s find out about the advantages and disadvantages of each.
Rigid Dental Impression Material
This material specifically records impressions of the edentulous arches, whether it is zinc oxide eugenol or impression compound.
Zinc oxide eugenol is modified with other properties to form the impression paste.
In order to make it, the dental staff will need to mix two tubes.
One contains the white zinc oxide mixture while the other consists of a red eugenol mixture.
Mix equal amounts of each paste on a pad using a spatula.
Load the mix on an impression tray in order to obtain secondary impressions of the edentulous arches.
This creates a mixture with a different color with no apparent red or white streaks visible.
On the other hand, the impression compound works differently.
In the process, the compound heats up in a water bath and molds on the impression tray.
However, compared to zinc oxide eugenol, it does not flow as well.
Thus, it will not record fine detail.
Its use in recording primary impressions of the edentulous arches rather than the secondary ones.
Though, impression paste has its set of advantages and disadvantages too.
Pros
It provides an improved fit for the patient.
Moreover, if it is not that accurate then you can retake the impression.
This is usually done by adding the fresh paste. Next, the dentist will insert it into the patient’s mouth until it is set.
Cons
The material is stick so it can attach to the surrounding skin and the lips.
Do not let it stick by using petroleum jelly beforehand.
Eugenol can cause a burning sensation in some patients.
Hence, those who are sensitive to such materials should avoid it.
While this material can take secondary impressions of edentulous arches, it is not the best for reproducing undercuts.
Hence, it cannot take partial denture impressions.
Elastic Material: Silicone
Among the elastic materials, there is dental silicone or putty wash.
This material is moldable so it allows for deformation and easy removal after solidification in the mouth.
This in return makes the entire procedure easier as it does not deform the mold.
Additionally, it does not stick to the lips or skin of the patient so there is no danger to them by using it.
A silicone impression material has a base and a catalyst in a putty consistency.
The classification of this material depends on its polymerization speed, method of polymerization setting, chemical formulation including addition silicone and condensation silicone as well as consistency.
Besides that, there is a range of viscosities in light, medium or very high viscosity.
A putty impression is one with a high viscosity.
To take this impression, it is combined with a low viscosity silicone i.e. a putty wash technique.
Recording a putty wash impression is done using three ways.
In the one-stage impression, the putty and the wash are recorded simultaneously.
This is the most effective way to record the impression in a rigid metal tray.
The others are a two-stage unspaced and spaced impressions.
In a spaced impression, the space is made for the wash using materials such as a polythene spacer over teeth to make the impression, scooping the putty away and giving escape channels or recording the putty impression before the tooth preparation.
In a two-stage un-spaced impression, the impression is recorded first.
Once it sets, the impressions is relined using a thin layer of wash material.
More on it uses, advantages and disadvantages below.
What are Alginates?
Alginates are the most widely used elastic material for dental impressions.
It is technically a hydrocolloid material.
In simple terms, it is made of seaweed or precisely the soluble salts of alginic acid that is found in marine algae.
Essentially a hydrocolloid material is a gelatinous substance that disperses in water.
Alginates are irreversible as they cannot become a solution once after being set.
Besides the soluble salts, it also contains:
- Calcium sulphate
- Diatomaceous earth
- Coloring & Flavoring agent traces
- Ester salts of alginic acid
- Potassium titanium fluoride
- Zinc oxide
- Sodium phosphate
While alginates usually come in a powder form, some have different colors.
Moreover, some alginates have color changing properties.
That helps during mixing, setting and loading times.
It can ease the procedure for a less experienced team and a nervous patient with a gag reflex.
Once the alginate mixes with water, it forms a paste.
This has a solid elastic mass that makes the negative reproduction and is then processed to form the positive reproduction later.
Use, Advantages and Disadvantages
Dental impressions usually come in use in specialties such as surgery and prosthetics.
It mainly comes in handy to make primary impressions for partial, removable or total dentures.
It is also commonly used in the assembly of articulators and the design of orthodontic study models.
Pros:
- It is easy to handle
- Alginates have good hydrophilic properties
- Affordable and cheaper than other options
- Have a good shelf life
- It is non toxic
- Available in fast setting and standard varieties
- Has a neutral taste
- Limited working time based on temperature and water
- It is easy to mix
Cons:
- Elastic recovery
- The entire impression is washed out
- Messier to work with
- Poor dimensional stability
- The impressions can distort easily
- Excess water gain can cause swelling and water loss shrinkage
Which Dental Impression Material is Better?
Since silicones are a more elastic material, they have a greater use than alginates in dentistry.
For impressions, a silicone material is used in:
- Implants
- Root canal
- Functional impressions of complete prostheses
- Soft structure and bone tissue
- Reproduction of fractured teeth by using impression procedures
- Total jaw impressions, with teeth and also without teeth
- Recording occlusal relationships due to its dimensional stability and accuracy
- Partial impressions for a particular part of the arch i.e. for crowns, bridges and inlays or overlays
Advantages
- Has a high recovery from deformation
- Good dimensional stability
- Guaranteed print stability
- One of the most accurate material available
- Is easily disinfected
Disadvantages
- You should not use latex dental gloves while handling it
- It is sensitive to pollutants
- The emptying is not immediate as there is release of hydrogen during polymerization
- It is harder to remove from the mold
- Refrain from using astringents with silicone as it affects its setting time
Silicones are the most stable material and will retain their shape for a long time.
It has different grade of thickness so is often used when more accurate impressions are needed.
Though, they are best suited in a dry environment hence, may not be as workable in the presence of saliva.
On the other hand, alginates are flexible and flowy.
It can record fine detail but it is also prone to distortion in damp conditions.
While alginate is versatile, most commonly used and cheap, it is not as accurate as silicone.
Thus, both the materials have their set of pros, cons and uses.
The dentist will use the type of dental impression material according to the requirement since both are effective and still in common use in dentistry.
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