DEN 135 1 O - Dental Materials II- FINAL EXAM

Includes: 46, 47

What is the main purpose of the dental laboratory?

Procedures that take place away from the patient treatment area.

What are some common uses of the dental laboratory?

Making models, preparing custom trays, polishing, provisional coverage, and indirect restorations.

What safety precautions must be followed in the dental laboratory?

No eating or drinking, wearing personal protective equipment, and reporting all accidents.

What are the three basic types of custom impression trays?

Tray must be rigid, fit and adapt well to the arch, and maintain an even distribution of impression material.

Define gypsum products in the context of dental models.

Used extensively in dentistry to make dental models and are characterized by their mineral composition and properties.

What is the significance of powder-to-water ratios in gypsum products?

Significant effect on the setting time and strength of the gypsum product; must be accurately measured.

What are the physical forms of gypsum used in dental models?

Impression Plaster (Type I), Model Plaster (Type II), Dental Stone (Type III), Die Stone (Type IV), High Strength Stone (Type V).

What is the purpose of a separating medium in custom impression trays?

To ensure the completed tray can be readily separated from the cast.

What materials are used to construct custom impression trays?

Self-curing acrylic resin, light-cured resin, and thermoplastic material.

What are the classifications of dental waxes?

Pattern waxes, processing waxes, and impression waxes.

what are impression materials?

Impression materials are used to obtain an impression of teeth, the surrounding oral tissues, or both

Impressions are a negative reproduction of dental structures

Classification of Impressions

The three classifications of impressions taken in dental procedures consist of preliminary, final, and occlusal, also referred to as a (bite) registration

The type of dental material selected by the dentist to take these impressions will depend on what will be constructed from the impression

Preliminary Impressions

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

Used for the following reasons:

Diagnostic models

Custom trays

Provisional coverage

Orthodontic appliances

Pretreatment and posttreatment records

Final Impressions

Taken by the dentist and are used to produce the most accurate reproduction of the teeth and surrounding tissue

Provide the dentist and the dental laboratory technician the essential information needed for creation of:

Indirect restorations

Partial or full dentures

Implants

Bite Registrations

Taken by the dentist or EFDA to produce a reproduction of the occlusal relationship of the 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 when impressions are taken

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 the completed impression

Impression trays are of two basic types

• Stock trays

• Custom trays

Stock Trays

Manufactured in several ways

Available in a range of sizes and styles

Characteristics of Impression Trays

Supplied in one of the following ways:

Quadrant tray

• Covers half of an arch

Section tray

• Used to cover the anterior portion of the arch

Full-arch tray

• Covers the entire arch

Also characterized by whether the surface of the tray is perforated or smooth

When a perforated surface tray is used, the impression material oozes through the holes in the tray, creating a mechanical lock to hold the material in place

When a smooth surface tray is used, there is no mechanical lock, so the interior of the tray is painted or sprayed with an adhesive to hold the impression material securely in the tray

Sizing of Impression Tray

The correct tray:

• Is comfortable to the patient

• Extends slightly beyond the facial surfaces of the teeth

• Extends approximately 2 to 3 mm beyond the third molar, retromolar, or tuberosity area of the arch

• Is sufficiently deep to allow 2 to 3 mm of material between the tray and incisal or occlusal edges of the teeth

Adaptation of Tray

Length of the tray can be extended by adding utility wax to the border of the tray

• May be necessary if the tray does not completely cover the third molars

For a patient with an unusually high palate, softened utility wax can be added to the palate area of the impression tray

Custom Trays

A custom tray is constructed to fit the mouth of a specific patient

The custom tray is constructed in the laboratory from a diagnostic model made from a preliminary impression of the arch before the dentist has prepared the teeth

A custom tray may be constructed by using acrylic resin, light-cured resin, or a thermoplastic resin technique

Tray Adhesives

Specific adhesives used with specific impression materials are:

VPS adhesives (blue)

• For polyvinyl siloxane and polyether impression materials

Rubber base adhesive (brown)

• Used with rubber base impression materials

Silicone adhesive (orange-pink)

• Used with silicone impression materials

Hydrocolloid Materials

These materials are used to obtain preliminary and final impressions

Hydro means “water”

Colloid means “gelatin substance”

Depending on the type of hydrocolloid, the physical change from sol (solution) to gel (solid) can be irreversible (changed by chemical factors) or reversible (changed by thermal factors)

Irreversible Hydrocolloid: Alginate

Hydrocolloid impression materials that cannot return to the sol state after they become a gel are termed irreversible hydrocolloids

Alginate is the irreversible hydrocolloid most widely used for preliminary impressions

Composition and Chemistry

The main ingredients of alginate include:

Potassium alginate

• Derived from seaweed; also used in some ice creams as a thickening agent

Calcium sulfate

• Reacts with the potassium alginate to form the gel

Trisodium phosphate

• Added to slow the reaction time for mixing

The main ingredients of alginate include:

Diatomaceous earth

• A filler that adds bulk to the material

Zinc oxide

• Adds bulk to the material

Potassium titanium fluoride

• Added so as not to interfere with the setting and surface strength of the product used when making a model

Physical Phases of Alginate

Hydrocolloid impression materials have two physical phases

• In the sol (solution) phase, the material is in a liquid or semiliquid form

• In the gel (solid) phase, the material is semisolid, similar to a pudding dessert

The gel strength of hydrocolloid is not as great as that of elastomeric impression materials

Strength of Alginate

It is important for alginate to be sufficiently strong to resist tearing when the impression is being removed from the patient’s mouth

• The strength of the material will continue to increase even after it appears to be set

• Leaving the impression in the mouth for the full length of time recommended by the manufacturer is important toward achieving maximum strength

Dimensional Change

Because the alginate is made from water, a change in the environment can distort the impression and cause a dimensional change.

If an impression is stored in water or in a saturated paper towel, the alginate will absorb excess water and swell. This is called imbibition.

If an impression is stored in the open air, water will evaporate from the material casing it to shrink. This is called syneresis.

Because of this, an alginate impression must be “poured up” within an hour to prevent distortion.

Packaging and Storing of Alginate

Alginate can be purchased in a variety of ways

Containers about the size of a coffee can are the most common form of packaging

Premeasured, individual packages are more expensive, but they save time by eliminating the need for measurement of the powder

The material is also supplied with flavoring as well as changes in color when set

The shelf life of alginate is approximately 1 year

Types of Setting

Alginate is available in two setting times

Normal-set alginate

• Working time of 2 minutes and a setting time of up to 4½ minutes after mixing

Fast-set alginate

• Working time of 1¼ minutes and a setting time of 1 to 2 minutes

Working time

• The time allowed for mixing the alginate, loading the tray, and positioning the tray in the patient’s mouth

Setting time

• The time required for the chemical action to be completed, after which the impression is ready to be removed from the patient’s mouth

Altering Setting Time of Alginate

Room temperature water is best to use when mixing alginate

Cooler water will increase the setting time if additional time is needed for the procedure

Warmer water will reduce or shorten the setting time of the procedure

Water-to-Powder Ratio

It is important to accurately measure the alginate powder and the water to be mixed

• The manufacturer supplies a plastic scoop for dispensing powder and a plastic cylinder for measuring the water

Adult mandibular impression

• Generally requires two scoops of powder and two measures of water

Adult maxillary impression

• Generally requires three scoops of powder and three measures of water

Mixing Techniques

The most common mixing technique is manual spatulation with a rubber bowl and beavertail wide spatula

An additional technique is the use of an alginator, which is a rubber flexible bowl attached to an electrical component with a low or high speed

Taking an Alginate Impression

It is important for the EFDA to be competent in:

• Mixing the alginate

• Loading the tray

• Keeping the patient comfortable while taking the impression

Explain Procedure to the Patient

The patient needs to know that:

• The material will feel cool, there is no unpleasant taste, and the material will set quickly

• Breathing deeply through the nose will help the patient relax and feel more comfortable

• The patient can use some type of hand signals to communicate any discomfort

Evaluating Alginate Impression

The impression tray should be centered

There is a complete “peripheral roll,” including all of the vestibular areas

The tray is not “overseated”

The impression is free from tears or voids

Sharp anatomic detail of all teeth and soft tissues is provided

The retromolar area, lingual frenum, tongue space, and mylohyoid ridge are reproduced in the mandibular impression

The hard palate and tuberosities are recorded in the maxillary impression

Impressions of Edentulous Arches

Taking an alginate impression of an edentulous arch differs from taking other alginate impressions in two ways

• The height of the teeth is missing

• It is important to include more extensive tissue details

An edentulous tray is used to take this impression

• This tray is not as deep as other trays used for alginate impressions

Reversible Hydrocolloid

This impression material changes its physical state from a sol to a gel and then back to a sol

A change in temperature causes the reversible hydrocolloid material to transform from one physical state to another

Hysteresis is a term used to describe the change in temperature that causes the reversible hydrocolloid material to transform from one physical state to another

85% water

13% agar

• Agar is an organic substance derived from seaweed

Additional chemical modifiers are added to improve the substance’s handling characteristics

For the reversible hydrocolloid to change from one consistency to another, a specialized conditioning bath is used

The following three compartments maintain water at three different temperatures:

• A “conditioner” bath liquefies the semisolid material at 212º F and is then cooled to 150º F

• A “storage” bath readies the material for the impression in its tubes

• A “tempering” bath keeps material at 110º F for tempering after it has been placed in the tray

Reversible Hydrocolloid Tray Material

Tray material is packaged in plastic tubes

• Each tube holds enough material to fill a full-arch, water-cooled tray

The material needs enough viscosity to keep the material from flowing out of the tray when dispensed at 150º F

An impression tray is filled and immersed in the 110º F bath for a few minutes to further increase viscosity and reduce the temperature to a comfortable level for the patient

Reversible Hydrocolloid Syringe Material

A conventional hydrocolloid is dispensed directly onto the prepared tooth and surrounding teeth

Less viscous than tray material

Packaged in plastic or glass cartridges that fit a syringe or in a preloaded syringe, or comes in preloaded syringes or preformed sticks that refill special hydrocolloid inlay syringes

Syringe material is liquefied by placing it in the same 150º F storage bath as the tray material

Application of Reversible Hydrocolloid Impression Material

A stock water-cooled tray is selected

Plastic stops are placed in the tray

Tubing is connected to the tray and to the water outlet for drainage

The material is liquefied and moved to the storage bath

The light-bodied material is placed in the syringe, and heavy-bodied material is placed in the tray

The light-bodied material is expressed around the prepared tooth; the dentist seats the tray

Elastomeric Materials

Elastomeric impression materials are used when an accurate impression is essential

• Elastomeric means “having elastic or rubber-like qualities”

Characteristics of Elastomeric Impression Materials

Self-curing

Supplied as a base and a catalyst

• Base: Packaged as a paste in a tube, in a cartridge, or as putty in a jar

• Catalyst (accelerator): Packaged as a paste in a tube, in a cartridge, or as a liquid in a bottle with a dropper top

Forms of Elastomeric Impression Materials

Light-bodied material

• Also referred to as syringe-type or wash-type

• Used because it can flow into and around the details of the prepared tooth

• A special syringe, or extruder, is used to apply light-bodied material immediately around prepared teeth

Regular and heavy-bodied materials

• Also referred to as tray-type materials

• Much thicker than light-bodied materials

• Used to fill the tray

• Their stiffness helps force the light-bodied material into close contact with the prepared teeth and surrounding tissues to ensure a more accurate impression and details of a preparation

Basic Impression Technique

The dentist prepares the tooth (or teeth) for the impression

Light-bodied material is prepared, loaded into the syringe, and transferred to the dentist

Dentist places the light-bodied material over and around the prepared teeth and on surrounding tissues

Heavy-bodied material is prepared, loaded into the tray, and transferred to the dentist

When the impression material has reached final set, impression is removed and inspected for accuracy

Impression is disinfected, placed in a biohazard bag, labeled, and readied for the laboratory technician

Elastomeric Materials Curing Stages

1. Initial set

First stage results in stiffening of paste without the appearance of elastic properties

• Material may be manipulated only during this first stage

2. Final set

Second stage begins with the appearance of elasticity and proceeds through a gradual change to a solid, rubbery mass

• Material must be in place in mouth before elastic properties of final set begin to develop

3. Final cure

• Last stage occurs within 1 to 24 hours

Mixing of Elastomeric Materials

Many different mixing techniques are available for use with impression materials

• Most common sequence involves preparing the light-bodied material first, then the heavy-bodied material

Paste system

Automix system

Mixing unit system

Putty system

Paste System

When working with an elastomeric material in a paste system, timing is the most important reason for having the equipment and material prepared and ready to mix when the dentist signals the go-ahead

Make sure you have enough of the material placed out for the type of tray you are using

Automix System

Provides a homogenous mix with the appropriate amount of material without waste

Extruder is used to automatically mix and dispense elastomeric impression materials

Can be used with light-bodied or heavy-bodied material and is operated with a trigger-like handle

Extruder is loaded with dual cartridges that consist of a tube of catalyst and a tube of base material

Mixing Unit System

In a dental office where a lot of impressions are taken, a table-top or wall-mounted mixing unit may save time

Several factors make this process easier

• Controlled dispensing: No excess material on the pad

• Infection control: Less time is spent cleaning and disinfecting tube” and cartridges

• Versatility: A variety of materials can be mixed and dispensed from this unit

Putty System

Putty has a higher consistency and insertion force than are seen with heavy-bodied materials

Material is kneaded with the hands

Types of Elastomeric Materials

The four types of elastomeric impression materials most often used in dental practice are:

• Polysulfide

• Polyether

• Silicone

• Polysiloxane (polyvinyl siloxane)

Of particular concern with these materials are:

Dimensional stability

• The ability of the material to keep its shape after it has been removed from the mouth

Deformation

• The ability to resist permanent change caused by stresses during removal from the mouth

Permanent deformation

• Means the material was changed and will not regain its previous shape

Polysulfide Impression Material

Has been used in dentistry as a final impression material for many years

Available in light-bodied, regular, and heavy-bodied forms

Supplied as a two-paste system; base and catalyst

Rubber base material has a strong odor and can easily stain clothing

Relatively long working and setting times

Stiffness is low

Mixing Guidelines for Polyether Material

The material is very stiff, making it difficult to remove without rocking

When removing the impression, break the seal and rock slightly to prevent tearing

Water, saliva, and blood affect the setting process of polyether material

Added moisture will increase the impression’s marginal discrepancy

Increased water absorption occurs if a thinning agent is used

Impressions can be dispensed from an automated extruder and mixer

Silicone Impression Material

Odor-free, nonstaining, and relatively easy to mix

The deformation is much less than that of polysulfide; the dimensional stability is superior

Supplied with the base as a paste in a tube and the catalyst as a liquid in a bottle or smaller tube of paste, with cartridges and putty

Mixing Guidelines for Silicone Material

Limited shelf life

Tray requires a special tray adhesive

Not subject to syneresis or imbibition, but it does respond with shrinkage over time

More flexible

• Chance of distortion during removal is greater

Wait 20 to 30 minutes before pouring of models for stress relaxation to occur

Polysiloxane Impression Material

High-dimensional stability and low tear resistance

• Easy to handle when taking final impressions

No taste or odor

Available in light-bodied, regular, and heavy-bodied forms

Mixing Guidelines for Polysiloxane Material

For dimensional stability, this is the best impression material

Pouring of the model can be delayed up to 7 to 10 days

Stiffness of the material makes removal of the tray difficult

Dispensed with the use of an automixer and mixing tips

Occlusal (Bite) Registration

An accurate registration of the normal centric relationship of the maxillary and mandibular arches

Also commonly referred to as the bite registration

Wax Bite Registration

Used to show the occlusal relationship of the maxillary and mandibular teeth

Particularly useful when the diagnostic casts are trimmed

Most common technique uses a softened baseplate wax

Polysiloxane Bite Registration Paste

One of the most popular materials for bite registration

Supplied as a paste system and as cartridges

• Fast-setting

• No resistance to biting forces

• No odor or taste for the patient

• Gains dimensional stability over time

• Convenient to use