Dental Impressions Overview

Impression Types

• Impressions are negative reproductions of teeth and surrounding tissues.
• Preliminary impressions are used for initial diagnosis, treatment planning, and construction of provisional restorations.
• Final impressions are used to create replicas for permanent restorations.
• Bite registrations record the occlusal relationship between the upper and lower teeth.

Impression Materials

• Alginate (irreversible hydrocolloid) is a commonly used material for preliminary impressions.
• Elastomeric materials (e.g., polysulfide, polyether, silicone) are used for final impressions.

Tray Types

• Quadrant tray covers half of the dental arch.
• Perforated tray allows impression material to lock on mechanically for better retention.
• Custom tray is created to fit the patient's specific mouth shape.
• Utility wax can be used to modify and extend tray length.

Alginate (Irreversible Hydrocolloid)

• A fast-set alginate is preferred for patients with a strong gag reflex.
• The water-to-powder ratio for a maxillary impression is typically 3 scoops of powder to 3 measures of water.
• Alginate is mixed in a rubber bowl.

Reversible Hydrocolloid

• Stored in a conditioning bath prior to use.

Elastomeric Materials

• Supplied in three consistencies: light-bodied, regular-bodied, and heavy-bodied.
• Light-bodied material is applied around prepared teeth using a syringe.
• Heavy-bodied material is used for the bulk of the impression.
• Automix systems are available for convenience and accuracy.

Bite Registration Materials

• Polysiloxane paste is the most popular bite registration material.
• ZOE (Zinc Oxide Eugenol) paste is applied to a gauze bite tray.
• Wax bite registration material is warmed to soften it before placement in the mouth.

Impression Types

• Preliminary Impressions are negatively reproduced and can legally be taken by an EFDA
• Bite Registrations are used for occlusal relationships and legally taken by an EFDA

Tray Types

• Quadrant Trays cover half an arch
• Perforated Trays allow impression material to lock mechanically
• Custom Trays fit a specific patient's mouth
• Utility Wax lengthens a tray

Impression Material

• Alginate is the most common irreversible hydrocolloid for preliminary impressions
• Alginate is derived from seaweed and contains potassium alginate
• Fast-Set Alginate is used when a patient has a strong gag reflex
• Irreversible Hydrocolloid is mixed in a rubber mixing bowl
• Reversible Hydrocolloid is kept in a conditioning bath before taking an impression
• Elastomeric Materials are used for final impressions, not preliminary impressions
• Elastomeric Materials are supplied in light-bodied, regular, and heavy-bodied forms
• Light-bodied Elastomeric Material is applied around a prepared tooth with a syringe
• Heavy-bodied Elastomeric Material is placed on teeth after light-bodied material
• Automix Systems mix the final impression material

Bite Registration Material

• Polysulfide or Rubber Base is a term for polysulfide
• Polysiloxane Paste is the most popular bite registration material
• ZOE Bite Registration Paste is applied with a gauze bite tray
• Wax bite registration material is softened by warming before placement in the patient's mouth