Dental Impression Materials and Methods

• Impronte refers to impressions taken of a patient's dental arches to record their shape

Impression Functions

• Impressions record the shape of the patient's dental arches, as registered by the clinician

Impression Contents

• Includes the function of impressions
• Preliminary impression treatments
• Rigid and elastic impression materials
• Closure areas
• Impressions made with intraoral scanners

Impression Objectives

• Be able to safely prepare impressions for pouring
• Understand the characteristics of the main impression materials
• Know how to recognize the morphological characteristics present in an impression

Impression process explained

• Impressions result from an odontiatrist or dentist and are developed by a dental technician
• It is taken from a patient
• It has to be disinfected

Impression materials

• Includes impression material delivered using a dental impression tray
• Used for registering the dental arches of a patient to create a model upon which to build dental prosthetics

Impression Treatment and Potential Errors

• If the impression material is not treated properly in the lab, it can lead to an inaccurate model, which won't be a faithful reproduction of the patient's mouth
• This inaccurate model will then result in a prosthetic device that is also inaccurate and doesn't fit well

Impression Materials Impact

• Adequate handling results in an accurate model that faithfully represents the patient's situation, leading to a congruent prosthetic device
• Inadequate handling leads to an inaccurate model that doesn't faithfully represent the patient's situation, leading to an incongruent prosthetic device

Preliminary Impression Treatment

• All impressions and devices coming from the clinic can be potential sources of infection
• It's crucial to wear PPE (single-use gloves, masks, and protective eyewear) before handling any devices or materials from the clinic in the lab
• Once PPE is on, disinfect the impressions using appropriate methods and products based on the materials they're made of, such as sprays or disinfectant baths

Material Characteristics and Importance

• Understanding impression material characteristics is important for the dental technician to accurately replicate a patients mouth.
• Some impression materials are also used in the lab i.e duplicating models or making masks for stamping aesthetic materials
• Choosing the most appropriate method is important for creating the most accurate model possible

Incompatibilities and Contraindications

• Impression materials can have incompatibilities and contraindications with development materials
• Incorrect working methods can affect the success of the model (eg. alginate impressions deteriorate if not poured at the correct time)

Rigid Impression Materials: Plaster of Paris

• Was widely used in the first half of the 1900s
• Its extreme rigidity led to its abandonment, due to it's difficult nature of working with undercuts, sometimes needing breakage to extract

Undercuts Explained

• Undercuts are concave, recessed parts of an anatomical structure, like a tooth or ridge, that resist prosthetic device insertion
• The extent of an undercut is always evaluated in relation to the prosthetic insertion axis

Undercuts and Impressions

• Teeth naturally have undercut areas due to their morphology, but a material's elasticity helps it overcome these during impression disinsertion
• Undercuts aren't always undesirable, as they provide retention for partial dentures via clasps on abutment teeth

Thermoplastic Materials

• Materials that become plastic when heated
• Heated by immersion in a hot water bath with a temperature indicated by the manufacturer between 50 and 60 degrees celcius

Impression Process

• An impression is taken while the material is still soft and plastic, before it cools down to mouth temperature (37 degrees celcius) and hardens
• Once solidified, the impression is removed from the mouth

Thermoplastic Uses

• Able to be used for impressions of single pieces or small cavities, which will allow for the creations of inlays.
• Their rebase is possible with precision materials like zinc-oxide eugenol pastes.

Thermoplastic Downsides

• The use has decreased to other materials due to new materials that are quicker and more elastic
• Does not risk deteriorating details, especially in subquad areas.

Thermoplastic Uses Today

• Used in mobile prosthetics
• Used to define portaimpronte borders
• Precise remoddeling of soft tissues

Elastic Materials: Alginates

• Belong to the family of irreversible hydrocolloids because they can only be used once
• Supplied as powders that are mixed with water that will be used inside the dental impression tray
• Some alginates, called chromatic alginates, change colors during the various work phases to communicate stages

Mixing and Setting

• Unlike gypsum, put water into powder when mixing
• A common problem with alginates is their dimensional variation as they dry

Storage and Usage

• Impressions should be developed as soon as possible(i.e, within 30min)
• Due to reduced cost alginate is more useful in study models but also used to duplicate other models

Elastomers: Silicones

• Generally grouped under the classification of silicones
• Divided into groups with their own characteristics
  • Silicones for addition (Polivinilsilossani - VPS):
    • Composed of 2 masses
    • Consists of a base and a catalyst
    • Very smooth and hydrophilic
    • Very precise detail
    • Used for pretty much all types of prosthesis
  • Silicones for condenstation:
    • Also 2 masses to be mixed for a 1:1 ratio
    • Distinguished from silicones for addition by its greater strength
    • Suited for use of labor and supporting more fluids
  • Polyethylenes:
    • Very hydrophilic
    • Elastic and precise
    • Difficult to remove than other elastomers
    • Precise adherece

Importance of Precautions

• Never use the catalyst with another silicone base
• Can result in low polymerization/nonhardening
• Elastomers are the most used material for definitive impressions as they are stable and possess good mechanical properties
• Have elastic memory

Use of Different Viscosities

• Materials of higher visosity are more cohesive, resistant but not very fluid
• Materials of low viscosity are fluid but are able to reach the most sensitive zones in the oral cavity.

Combination Techniques

• The materials will adapt to oral structure, this means it results in lower fluidity.
  • Monophase Technique:
    • Only one material is used
    • medium visocity
    • per individualized portaipromp technique
  • "Sandwhich" technique:
    • Uses 2 materials.
    • Varied viscosity that clinic can use in a single phase

Two Step Technique

• Records a first impression, one in which the material becomes polymnerized.

Closure Zones

• When creating fixed prosthesis, closure zones are one of the important areas that are revealed in the impressions in which there is contact
• An extremely important thing to note is that this shift in the material
• Must happen in a linear fashion such that it matches how a healthy gumline of a person with natural teeth would

Managing Closure Zones

• Requires perfect detail that is hard to correctly replicate saliva and potential blood tend to stagnate thus covering border preparation
• These drawbacks can be avoided with elastomer of a varied consistency
• A gingival opening can resolve this using the following:
  • Surgical incision
  • Copper rings:
    • In combo with thermoplastic masses
    • Tends to reveal the closing in accurate fashion
  • Retractor Wire: This method is popular
    • Places dual file in between gingiva and the tooth

Digital Intraoral Scanners

• Development of new digital scans has made it easier to scan impressions with interoral machines
  • This allows for a digital 3D print
• Allows easy data and internet delivery, saving money and time
• Lets medical staff easily check the quality of impressions and allows digital saving in 3D digital form
• Can scan interoral root canals

Proper selection and handling of dental impression materials are crucial for accurate models and suitable prostheses. Dental impressions should always be treated as potentially infectious and disinfected appropriately. PPE must be worn when handling impressions.