Dental Impression Materials

• Dental impressions are the focus
• Mrs. Priti Songra is the tutor
• FCSP is the module

GDC Learning Outcomes

• Scientific principles behind dental materials and biomaterials, including their limitations and selection in dentistry, should be understood and described
• Performing special investigations and diagnostic procedures, including radiography, is required
• Effective decontamination and infection control procedures following current guidelines should be implemented and performed
• Maintaining contemporaneous, complete, and accurate patient records following legal requirements and best practices is essential

Intended Learning Outcomes

• Ideal impression material features are outlined
• Impression uses and steps are described
• Available impression material types are outlined
• Alginate clinical properties are recognized and identified

Glossary of Terms

• Exothermic: Heat production occurs upon mixing, accelerating setting
• Hydrophilic: Water-attracting, absorbing, or saturating
• Hydrophobic: Water-repelling
• Tear strength: Material's resistance to tearing
• Working time: Duration from mixing until material develops elastic properties, usually at room temperature
• Setting time: Duration from mixing until material fully sets, usually at mouth temperature
• Dimensional stability: Material's ability to maintain original dimensions despite temperature and humidity changes
• Polymerization: Chemical bonding of small molecules (monomers) into large chainlike structures (polymers)
• Viscosity: Resistance to flow or 'thickness'
• Elasticity: Material's ability to return to its original shape after stretching
• Mucostatic: Material doesn't displace mucosa, ideal for impressions of tissues without load, common for flabby ridges
• Mucocompressive: Material displaces mucosa, enabling recording of oral tissue in a functional state
• Thermoplastic: Materials that soften to liquid at high heat, hardening upon cooling
• Wash impression: Special technique using thin, low viscosity material for fine details, often a second stage for crown and bridge work

Impressions

• Record the shape of teeth
• Create negative imprints
• Variety of materials can be used
• Record teeth
• Record soft tissue contours
• Record soft tissue reflections
• Record spaces and voids

Uses of Impressions

• Orthodontics
• Prosthodontics (removable and fixed)
• Oral Maxfax
• Prevention
• Aesthetics

Types of Impressions

• Preliminary
• Final or second stage

Qualities of a Good Impression Material

• Appropriate mixing and insertion proportion, biocompatible, and adequate working time is required
• Short setting time, low setting and thermal shrinkage, flexible and elastic, and high tear resistance for setting and removal
• Dimensional stability, resistance to distortion during casting, and chemical compatibility for storage and casting
• Nontoxic, non-irritant, easy to use, acceptable taste and smell, long shelf life, and relatively inexpensive are additional requirements

Types of Impression Materials

Non-Elastic

• Impression Compound
• Impression Plaster
• Impression Wax
• Zinc Oxide Eugenol

Elastic

• Hydrocolloids
• Synthetic Elastomers

Non Elastic Impressions

Zinc Oxide Eugenol

• Composition: Two pastes, a white base (ZnO) and a brownish transparent activator (eugenol)
• Uses: Typically a secondary impression for complete dentures
• Advantages: good surface detail and dimensional stability, good shelf life
• Disadvantages: Not suitable for deep undercuts, sets quickly in thin sections, may cause eugenol allergy

Impression Compound

• Composition: Mix of thermoplastic resin/waxes with fillers (talcum)
• Properties: Solid at mouth temperature, softens between 55-60°C
• Advantages: Suitable working time, can be modified by reheating, good shelf life
• Disadvantages: Poor surface detail, high thermal expansion coefficient, distorts when removed, not suitable in undercut areas, poor dimensional stability
• Mucocompressive

Plaster

• Composition: (CaSO4)2.H2O with accelerators, retarders, and coloring agents
• Advantages: Good surface detail, excellent dimensional stability, quick setting
• Disadvantages: Exothermic, setting expansion, fractures with undercuts, and its taste and roughness may cause vomiting
• Quick setting

Impression Wax

• Properties: Thermoplastic, flows at mouth temperature, soft at room temperature
• Uses: Primarily for inlay wax, can be used directly in the mouth but more commonly in the lab, used for bite registration
• Disadvantages: Readily distorted

Elastic Impression Materials

Synthetic Elastomers

• Polysulphide
• Polyether
• Addition Silicone ( used for restoring class IV restorations on anterior teeth)
• Condensation Silicone

Hydrocolloids

• Agar-agar (reversible)
• Alginate (irreversible)

Hydrocolloids

• Colloid: A substance where one component is dispersed but not dissolved in another
• Hydrocolloid: A dispersion of a substance in water, existing in two phases: a liquid sol and a semisolid gel

Hydrocolloids - Agar

• Derived from seaweed
• Reversible: Can be repeatedly converted between sol and gel by heating and cooling
• Hydrophilic
• Poor dimensional stability

Hydrocolloids - Alginate

• Derived from seaweed
• Irreversible: Once set, cannot revert to its original state
• Hydrophilic
• Poor dimensional stability
• Accuracy is best when casting quickly.

Alginate Composition

• Potassium alginate: Derived from seaweed and functions as a thickening agent (e.g., in ice cream)
• Calcium sulfate: Reacts with the potassium alginate to form the gel
• Trisodium phosphate: Slows reaction time for proper mixing
• Fillers: Diatomaceous earth and zinc oxide

Alginate Reaction

• K alginate + CaSO4 • 2H2O yields Ca alginate gel + K2SO4

Alginate Properties

Advantages

• Elastic
• Nontoxic and non-irritant
• Good surface detail
• Easy to mix and use
• Affordable with good shelf life (approximately 1 year)
• Setting time can be somewhat controlled

Disadvantages

• Poor dimensional stability
• Incompatibility with some dental stones
• Setting time and operator handling issues
• Messy
• Storage concerns related to moisture and temperature
• Tears easily

Impression Materials

Impressions trays

• Stock trays: Ready-made, available in different sizes, can be metal or plastic, perforated or solid
• Custom trays: Accurate and more comfortable, less material used, material in more even thickness for increased accuracy

Impression Trays: Types

• Full arch (whole arch)
• Sectional (anteriors)
• Quadrant (covers one half of the arch)

Impression Trays: Properties

• Essential for adhering the impression material to tray
• Carry impression material into oral cavity
• Hold the material close to the teeth surfaces
• Prevents breaking during removal
• Prevents the completed impression from warping

Adhesives

• For adhering impression material to tray
• Different materials need different adhesives.
• Alginate adhesive: 10-12% toluene dissolved In 45-50% isopropanol
• Maximum adhesion with adhesive and perforated trays

Tray Selection

• Should feel comfortable to the patient
• Should extend slightly beyond the facial surfaces of the teeth
• Extend approximately 2 to 3 mm beyond the third molar, retromolar, or tuberosity area of the arch
• Be sufficiently deep to allow 2 to 3 mm of material between the tray and incisal or occlusal edges of the teeth while extending into the sulcus

Adhesive Placement

• Apply 2 thin coats
• Dry between coats
• Do not place impression on pooled adhesive
• Apply adhesive to the internal surface of the tray as well as over the margins to ensure the binding of the outer edge of the impression material to the tray

Stages and Considerations

• Signed treatment plan
• Consent
• MH & allergic reactions
• Full PPE
• Ability for patient to open mouth widely
• Gag reflex & retching
• Positioning patient in chair
• Clinician's posture

Alginate Placement

• The patient should be seated upright
• For a lower impression, the clinician should be in front of the patient
• For an upper impression, the clinician should be behind the patient
• Check the appropriate tray size
• Be sure to place an adhesive
• Have the alginate and water ready for mixing
• Ensure no air bubbles when mixing
• Load the tray
• Place into pt mouth’s - sideways first
• Reassure your patient
• Remove the tray
• Check if the impression adequate, and if not repeat the process if necessary
• Disinfect the impression
• Wrap in moist tissue/gauze
• Ensure required paperwork is filled

More Recent Developments in Impressions

• Digital impressions/Scanners (e.g., iTero or Cerec) using CAD/CAM
• Similar to intra-oral photography—scans the dental arch and surrounding tissues, which is then used to create a model
• Literature on this topic is not conclusive

Assessment

• Formative
• Practical task
• Summative

Questions about dental materials used for taking impressions in dentistry. Covers terminology and characteristics. Includes material properties, reactions, and GDC learning outcomes related to dental materials.