DEN 135 1 O - Dental Materials II & Lab- Ch 46

Impression Materials and Techniques

Learning Objectives

  • Lesson 46.1: Impression Types, Trays, and Hydrocolloid Impression Materials

    • Pronounce, define, and spell the key terms.

    • Identify the three types of impressions taken in a dental office.

    • Describe the types of impression trays and their characteristics of use.

    • Discuss hydrocolloid impression materials, their uses, mixing techniques, and applications.

Introduction

  • Impression materials are utilized to obtain a reproduction of teeth, surrounding oral tissues, or both.

  • Impressions serve as a negative reproduction of dental structures.

Classification of Impressions

  • Three classifications of impressions in dental procedures:

    1. Preliminary Impressions

    2. Final Impressions

    3. Occlusal Registration (Bite Registration)

  • The type of dental material selected for impressions is contingent upon what will be constructed from the impression.

Preliminary Impressions

  • Taken by either the dentist or the expanded-function dental assistant (EFDA).

  • Used for:

    • Diagnostic models

    • Custom trays

    • Provisional coverage

    • Orthodontic appliances

    • Pretreatment and posttreatment records

Final Impressions

  • Taken by the dentist to produce the most accurate reproduction of teeth and surrounding tissue.

  • Provide essential information needed for the creation of:

    • Indirect restorations

    • Partial or full dentures

    • Implants

Bite Registrations

  • Taken by the dentist or EFDA to reproduce the occlusal relationship of maxillary and mandibular teeth when the mouth is occluded.

  • Provide an accurate registration of the patient’s centric relationship between the maxillary and mandibular arches.

Impression Trays

  • Used to hold the impression material during the taking of impressions.

  • Must be sufficiently rigid to:

    • Carry the impression material into the oral cavity.

    • Hold the material close to the teeth.

    • Avoid breaking during removal.

    • Prevent warping of the completed impression.

  • Two basic types of impression trays:

    1. Stock Trays

    2. Custom Trays

Stock Trays

  • Manufactured in various ways and available in a range of sizes/styles.

Characteristics of Impression Trays (Slide 1 of 2)

  • Supplied as:

    • Quadrant Tray: Covers half of an arch.

    • Section Tray: Utilized to cover the anterior portion of the arch.

    • Full-Arch Tray: Covers the entire arch.

Characteristics of Impression Trays (Slide 2 of 2)

  • Can be characterized by whether the surface of the tray is perforated or smooth:

    • Perforated Surface Tray: Impression material oozes through holes creating a mechanical lock.

    • Smooth Surface Tray: Requires adhesive to hold the impression material securely in the tray.

Sizing of Impression Tray

  • The proper tray must be:

    • Comfortable for the patient.

    • 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.

    • Sufficiently deep, allowing 2 to 3 mm of material between the tray and incisal or occlusal edges of the teeth.

Adaptation of Tray

  • Length can be extended with utility wax, necessary for complete coverage of the third molars.

  • Softened utility wax can be added for patients with a high palate.

Custom Trays

  • Constructed to fit the mouth of a specific patient.

  • Made in the laboratory from a diagnostic model obtained from a preliminary impression.

  • Can be constructed with acrylic resin, light-cured resin, or thermoplastic resin techniques.

Tray Adhesives

  • Specific adhesives for impression materials include:

    • VPS Adhesives (Blue): For polyvinyl siloxane and polyether materials.

    • Rubber Base Adhesive (Brown): Used with rubber base materials.

    • Silicone Adhesive (Orange-Pink): For silicone materials.

Hydrocolloid Materials

  • Used for both preliminary and final impressions.

  • Hydro: Means water.

  • Colloid: Refers to a gelatinous substance.

  • Physical changes from sol (solution) to gel can be:

    • Irreversible (changed by chemical factors).

    • Reversible (changed by thermal factors).

Irreversible Hydrocolloid: Alginate

  • Cannot revert to the sol state once it becomes gel; widely used for preliminary impressions.

Composition and Chemistry (Slide 1 of 2)

  • Main ingredients of alginate:

    • Potassium Alginate: Derived from seaweed; acts as a thickening agent in some ice creams.

    • Calcium Sulfate: Interacts with potassium alginate to form the gel.

    • Trisodium Phosphate: Added to slow the reaction time during mixing.

Composition and Chemistry (Slide 2 of 2)

  • Additional ingredients include:

    • Diatomaceous Earth: Filler to add bulk.

    • Zinc Oxide: Adds bulk.

    • Potassium Titanium Fluoride: Ensures setting and surface strength during model creation.

Physical Phases of Alginate

  • Two physical phases:

    • Sol Phase: Liquid or semi-liquid form.

    • Gel Phase: Semi-solid form, akin to pudding.

  • Gel strength is lower compared to elastomeric impression materials.

Strength of Alginate

  • Must be sufficiently strong to resist tearing during removal from the mouth.

  • Strength increases post-setting; following manufacturer’s recommendations is crucial for achieving maximum strength.

Dimensional Change

  • Alginate impressions are susceptible to distortion:

    • Imbibition: Absorbing excess water when stored in saturated conditions—causes swelling.

    • Syneresis: Evaporation of water when left in open air—causes shrinkage.

  • An impression must be poured up within an hour to prevent distortion.

Packaging and Storing of Alginate

  • Available in different packaging, commonly in coffee can-sized containers or premeasured individual packages for convenience.

  • Flavoring and color-changing properties upon setting may be included.

  • Shelf life is approximately 1 year.

Types of Setting (Slide 1 of 2)

  • Alginate available in two setting times:

    • Normal-Set Alginate: Working time of 2 minutes; setting time up to 4.5 minutes after mixing.

    • Fast-Set Alginate: Working time of 1.25 minutes; setting time 1-2 minutes.

Types of Setting (Slide 2 of 2)

  • Working Time: Time allocated for mixing, loading the tray, and positioning it in the patient's mouth.

  • Setting Time: Duration required for the chemical action to complete, post which the impression is ready for removal.

Altering Setting Time of Alginate

  • Room temperature water is ideal for mixing.

  • Cooler Water: Increases setting time for extended procedures.

  • Warmer Water: Reduces or shortens setting time.

Water-to-Powder Ratio

  • Accurate measurements are crucial for mixing:

    • Adult Mandibular Impression: Typically requires two scoops of powder and two measures of water.

    • Adult Maxillary Impression: Typically requires three scoops of powder and three measures of water.

Mixing Techniques

  • Commonly involves:

    • Manual Spatulation: With a rubber bowl and wide spatula.

    • Alginator: An electrical component with a rubber flexible bowl.

Taking an Alginate Impression

  • EFDA competently performs:

    • Mixing the alginate.

    • Loading the tray.

    • Ensuring patient comfort during the impression-taking process.

Explain Procedure to the Patient

  • Inform the patient about:

    • The material's cool temperature, absence of unpleasant taste, and quick setting time.

    • Suggest deep nasal breathing for relaxation.

    • Use of hand signals to communicate discomfort.

Evaluating Alginate Impression

  • Check for:

    • Centering of the impression tray.

    • Complete peripheral roll, including vestibular areas.

    • Avoidance of over-seating of the tray.

    • Absence of tears or voids.

    • Clear anatomical detail of all teeth and soft tissues.

    • Adequate recording of relevant anatomical features.

Impressions of Edentulous Arches

  • Differ from regular impressions in two respects:

    • Absence of tooth height requires capturing extensive tissue details.

    • Use an edentulous tray that is less deep than standard trays.

Reversible Hydrocolloid (Slide 1 of 3)

  • Changes physical state from sol to gel and back upon temperature variation.

  • Hysteresis: Refers to the temperature change required for reversible hydrocolloid transformation.

Reversible Hydrocolloid (Slide 2 of 3)

  • Composition:

    • 85% Water

    • 13% Agar: Derived from seaweed.

    • Additional modifiers improve handling characteristics.

Reversible Hydrocolloid (Slide 3 of 3)

  • Requires specialized conditioning baths for temperature control:

    • Conditioner Bath: Liquefies material at 212º F and cools to 150º F.

    • Storage Bath: Prepares the material in tubes for use.

    • Tempering Bath: Keeps material at 110º F post tray filling.

Reversible Hydrocolloid Tray Material

  • Packaged in plastic tubes, sufficient for a full-arch tray.

  • Must maintain viscosity to prevent flow-out when dispensed.

  • Impression tray requires immersion in a 110º F bath to increase viscosity and reach patient comfort level.

Reversible Hydrocolloid Syringe Material

  • Dispensed directly onto teeth with less viscosity than tray material.

  • Comes in plastic/glass cartridges or preloaded syringes.

  • Must be prepared in similar storage bath as tray material.

Application of Reversible Hydrocolloid Impression Material

  • Steps include:

    • Select a stock water-cooled tray.

    • Place plastic stops in the tray.

    • Connect tubing to facilitate drainage.

    • Prepare and liquefy materials for dispensing.

    • Apply light-bodied material followed by seating the tray.

Learning Objectives - Lesson 46.2: Elastomeric Impression Materials and Occlusal Registration

  • Discuss elastomeric impression materials, their uses, mixing techniques, and applications.

  • Explain importance and use of occlusal registration in procedures.

Elastomeric Materials

  • Used for impressions requiring high accuracy; elastomeric indicates rubber-like qualities.

Characteristics of Elastomeric Impression Materials

  • Self-Curing: Comes in base and catalyst forms.

  • Base: Available as paste in tubes/cartridges or putty in jars.

  • Catalyst: Available as paste or liquid for mixing.

Forms of Elastomeric Impression Materials (Slide 1 of 2)

  • Light-Bodied Material: Also known as syringe-type, flows well into prepared tooth details; applied with a special syringe or extruder.

Forms of Elastomeric Impression Materials (Slide 2 of 2)

  • Regular/Heavy-Bodied Materials: Thicker, filling trays; their stiffness helps force the light-bodied material into contact with teeth and tissues.

Basic Impression Technique

  • Process includes:

    1. Dentist prepares teeth for the impression.

    2. Light-bodied material prepared, loaded into syringe for dentist's application.

    3. Heavy-bodied material prepared and loaded into tray.

    4. Impression is inspected post-setting, disinfected, placed in a biohazard bag, labeled, and readied for lab.

Elastomeric Materials Curing Stages

  • Initial Set: Stiffening stage, prior to elastic properties appearing; manipulation possible.

  • Final Set: Appearance of elasticity until solid rubbery condition is achieved.

  • Final Cure: Occurs within 1 to 24 hours post-application.

Mixing of Elastomeric Materials

  • Various techniques available:

    • Sequence of preparing light-bodied first, then heavy-bodied.

    • Paste System: Manual mixing.

    • Automix System: Automatic mixing and dispensing via extruder.

    • Mixing Unit System: Saves time with various material capabilities.

    • Putty System: Higher consistency, kneaded manually.

Types of Elastomeric Materials (Slide 1 of 2)

  • Common types used in dentistry:

    • Polysulfide

    • Polyether

    • Silicone

    • Polysiloxane (Polyvinyl Siloxane)

Types of Elastomeric Materials (Slide 2 of 2)

  • Concerns involve:

    • Dimensional Stability: Ability to retain shape.

    • Deformation: Resistance to permanent change during removal.

    • Permanent Deformation: Indicates material will not regain its form post-stress.

Polysulfide Impression Material

  • Long-standing use as final impression material.

  • Offered in various forms (light-bodied, regular, heavy), supplied as a two-paste system (base and catalyst).

  • Notable characteristics:

    • Strong odor and potential staining ability.

    • Long working and setting times.

    • Low stiffness.

Guidelines for Using Material (Slide 1 of 2)

  • Dispense pastes at top of mixing pad; mix with a spatula for consistency.

  • Verify monitoring of setting time via excess material on the pad.

  • Be mindful of affects of water, saliva, and blood on material properties.

Guidelines for Using Material (Slide 2 of 2)

  • Impressions should be removed promptly after setting; avoid rocking the tray.

  • Ensure adhesive is applied thinly and adequately dried before impression material addition.

  • Allow impression stress relaxation (20-30 minutes) before pouring to ensure accuracy.

Polyether Impression Material

  • Superior mechanical properties over polysulfide with less dimensional change than silicone.

  • Requires a thinning agent for adjustments as the set material is quite stiff.

  • Supplied as a two-paste system with different tube sizes for precision.

Mixing Guidelines for Polyether Material

  • Difficult removal due to stiffness; use care to break seal first and rock slightly.

  • Monitor external conditions such as moisture impact on the setting process.

  • Impressions can be dispensed from automated extruder and mixer setups.

Silicone Impression Material

  • Characterized as odor-free, non-staining, with easier mixing.

  • Deformation mechanism is minimal, offering superior dimensional stability.

  • Supplied as base paste and liquid catalyst or as preloaded syringes.

Mixing Guidelines for Silicone Material

  • Limited shelf life noted with conditions for the tray adhesive required.

  • While not prone to syneresis or imbibition, it may experience shrinkage over time.

  • Flexible but distortion risk increases during removal.

  • Allow for stress relaxation before pouring (20-30 minutes).

Polysiloxane Impression Material

  • Noted for high dimensional stability but low tear resistance.

  • User-friendly during final impression take; devoid of taste or odor.

  • Available forms include light-bodied, regular, and heavy-bodied.

Mixing Guidelines for Polysiloxane Material

  • Renowned for dimensional stability; models can be poured after a delay of 7 to 10 days.

  • Stiffness makes removal challenging; typically dispensed using automixer technology.

Occlusal (Bite) Registration

  • Critical for registering the normal centric relationship of the maxillary and mandibular arches.

  • Commonly called bite registration.

Wax Bite Registration

  • Used to indicate the occlusal relationship of maxillary and mandibular teeth.

  • Common technique employs softened baseplate wax and is effective for trimmed diagnostic casts.

Polysiloxane Bite Registration Paste

  • Popular material for bite registration, offered in paste systems or cartridges.

  • Features include:

    • Fast-setting capabilities.

    • No bite force resistance.

    • Odorless and tasteless; stability improves over time.

    • Convenience in usage.

Zinc Oxide–Eugenol (ZOE) Bite-Registration Paste

  • Selected for durable bite registration material.

  • Fast-setting ZOE paste shows minimal resistance to bite closure.

  • Supplied in a paste system dispensed on a paper pad and mixed before patient use.