Impression Materials and Laboratory Materials and Procedures

Question 1

Dental labortory

Answer 1

making impression, take place in dental office and require expertise in using a dental laboratory.

The laboratory could be in house and will help with
-making models from preliminary impressions.

-Trimming and finishing diagnostic models

-Preparing custom trays

-polishing
*provisional coverage
*partial or full dentures
* Indirect restorations

Question 1

Laboratory rules

Answer 1

• no eating and drinking or smoking
• keep all cosmetics out of area
• wear personal protective equipment when working in laboratory
• keep hair back
• report all accidents to dentist immediately
• follow the manufactures instructions for the operation of equipment.
• clean the work area before and after every procedure.

Question 2

Laboratory Safety Lab

Answer 2

safety requires attention to several key areas. Review the safety guidelines here:

• Physical safety: Know the location of the fire extinguisher and fire-escape routes
• Chemical safety: Take care in the handling of corrosive, toxic, and carcinogenic substances
• Biohazards: Be aware that items brought into the laboratory can harbor blood and saliva that might be infective

Question 3

Laboratory equipment

Answer 3

• Heat source: torches and bunsen burners and used to heat wax carving instrument, smooth wax surfaces, and perform tasks that require constant and controlled.

-Vacuum former: machine that uses heated plastic and suction to fabricate customs trays, high guards, bleaching trays, athletic mouth guards, and splints for temporary crowns.

-Articulator: a-mechanical device to which casts of maxillary and mandibular teeth are attached to simulate the position of the maxilla to the mandible. The articulator assists in the fabrication of orthodontic appliances, bridge, crowns, inlays, and onlays. The articulator might or might not be used with a facebow.

• Dental lathe: piece of dental laboratory equipment that uses grinding and polishing attachments to polish dentures and crowns.
• vibrator: A speed adjustable machine that vibrates to promote the easy pouring or plaster into. dental impression while preventing bubbles from forming in the plaster.
• Model Trimmer: An instrument that uses an abrasive wheel and water to trim and contour casts and models made ofgypsum.

Question 4

Equipment : spatulas and Bowls

Answer 4

• Wax spatulas: wax spatulas are used to control hot wax used in prosthodontic procedures.
• Mixing spatulas: Maxing spatulas include broad blade spatulas used for mixing alginate impression materials. The broad blade helps push the materials against the bowl to eliminate air bubbles.

-Rubber Bowls: are soft and fleible and used for mixing alginate, plaster, stone, and other dental materials.

Question 5

Final impression

Answer 5

Final impression , provides that most accurate reproduction of the teeth and surrounding tissues.

Final impression are used to make:
- Indirect restorations
- partial or full dentures
-implant

Final impression are taking by the dentist

Question 5

preliminary impression

Answer 5

three different types of impression
- preliminary impression
- Final impression
- bite impression

preliminary impression are used for
- diagnostic models
- customs trays
-provisional coverage
- orthodontic appliances
- preliminary and prettreatment records.

preliminary impression are taken either by the dentist or the expanded function dental assistant..

Question 6

Basic Impression technique

Answer 6

impression are made using following sequence steps:

1. The dentist chooses the material based on personal presences and the types of impression for the procedure
2. dentist preparew the tooth or the teeth for the impression
3. The light bodied material is prepared and loaded into the syringe and transferred to the dentist.
4. The dentist the light bodied material over and around the prepared teeth and on the surrounding tissues.
5. the heavy material is prepared and load into the tray and transferred to the dentist.
6. when the impression material has reached its final set, the impression is removed and inspected for accuracy.
7. The accuracy is disinfected, placed in a biohazard bag, labeled, and readied for the laboratory technician.

Question 7

Impression trays

Answer 7

Impression trays must be sufficiently rigid to

• carry the impression material into the oral cavity
• hold the material in close proximity to the teeth
• avoid being broken during removal
• prevent warping of the completed impression.

Different Impression trays are used for different purpose.

• Quadrant Tray: covers one half of the arch
• section tray: covers the anterior portion of the arch

-Full arch tray: covers the entire arch.

• perforated tray: has holes in the tray to create mechanical lock to hold the material in place.

-Smooth tray: has an interior that is painted or sprayed with an adhesive to hold the impression material.

Question 7

Tray selection criteria

Answer 7

1.Dell comfortable to the patient.

2. extend slightly beyond the facial surface of teeth.
3. Extend approximately 2-3mm beyond the third molar, retromolar, or tuberosity area of the arch
4. Have enough depth to allow 2-3 mm of material between the tray and incisal or occlusal edges of the teeth

Question 8

Tray Adhesives

Answer 8

Tray Adhesives should be applied after the tray’s has been tested in the patient’s mouth.

Tray Adhesives vary in color and type. The specific type of Tray Adhesives used depends on the type of impression materials

Types Tray Adhesives

-VPS Adhesives (blue): for polyvinyi siloxane and polyether impression materials.

-Rubber base Adhesive (brown): used with rubber base impression materials

• Silicone Adhesive (orange-pink): used with silicone impression materials.

Question 9

Packaging and storing Alginate

Answer 9

the most common packaging for alginate impression materials is a reusable tub with a measuring scoop.

Distoration and dimensional chnage can occur with alginate impressions if the are improperly stored. Two types of conditions can result from improper storage:

-Imbibition: Expansion and distortion resulting from the alginate impression being stored in water or a very wet paper towel absorbing water.

• Syneresis: shrinkage and distortion resulting from the alginate impression remaining in the open air allowing its moisture evaporate.

Question 10

Hydrocolloid Impression Materials

Answer 10

Hydrocolloid Impression Materials: are used to obtain preliminary and final impressions.

Irreversible hydrocolloid materials: cannot return to solid state after it become a gel.

Alginate: the Hydrocolloid most widely used to take preliminary impressions.

Fasts: Hydro= water
colloid=gelatin substance.

Question 11

Alginate composition

Answer 11

Alginate consists f elements:

-Potassium alginate: comes from seaweed, also used in food such as ice cream as a thickening agent.

-Calcium sulfate: reacts with Potassium alginate to form the gel.

• Trisodium phosphate: added to slow the reaction time for mixing.
• Diatomaceous earth: A filler that adds bulk to the material

-Zinc oxide: adds bulk to the material.

-Potassium Trisodium fluoride: added so as not to interfere wt the setting surface strength.

Two physical phases of alginate are

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

-Second phase: in the gel phase, the material is semisolid, similar to gelatin dessert.

Question 12

Alginate settings

Answer 12

Alginate settings are effected by working time and setting time.

working time refers to the time allowed for mixing the alginate, loading the tray, and positioning the tray in the patient’s mouth.

Setting time refers to time required for the chemical action to be completed.

In terms of setting time, alginate can be divided into two types.

The setting time of alginate can be altered by adding:

• cooler water to increase the setting time if additional time is needed for the procedure.
• warmer water to reduce or shorten the setting time of the procedure.

Normal set Alginate: working time of 2 minutes, and a setting time of up to 41/2 min after mixing.

fast-set alginate: working time of 1 min and 15 sec and a setting time of 1 to 2 min.

Question 13

Mixing Alginate

Answer 13

when mixing the alginate, the water to powder ratio varies, depending on whether the material is for a mandibular or maxillary impression.

The ratios are
- For an adult mandibular impression, mix two scoops of powder and two measures of water.

-For an adult maxillary impression, mix three scoops of powder and three measures of water.

Question 14

Taking an alginate impression

Answer 14

It is important to explain the procedure
- the material will feel cold, there is unpleasant taste and the material will set quickly.

-The patient should breathe deeply through his or her nose to help relax and fell more comfortable.

• The patient should be use hand signals to communicate any discomfort.

*** Never leave the patient alone during this procedure.

• The impression tray is centered
• The “peripheral roll” including all of the vestibular areas is competed
• Tray is not overseated
• impression is free of tears or voids.
• sharp anatomic detail of all teeth and soft tissues is captured
• The retromolar area, lingual frenum, tongue space, and mylohyoid ridge are reproduced in the mandibular impression.
• The hard palate and tongue space are recorded in maxillary impression.

Question 15

Reverible hydrocolloid

Answer 15

Reversible Hydrocolloid Reversible hydrocolloid impression material changes its physical state from a solid to a gel and then back to a solid. Its chemical makeup includes 85% water and 13% agar. Additional chemical modifiers are added to improve the substance’s handling characteristics.

A conditioning bath is used to change the state of the reversible hydrocolloid material. The bath has three compartments:

• A “conditioner” bath liquefies the semisolid material at 212° F and then is cooled to 150° F
• A “storage” bath readies the material for the impression
• A “tempering” bath keeps material at 110° F in the syringe and tray

Reversible hydrocolloid tray material is packaged in plastic tubes, each with enough material to fill a water-cooled, full-arch tray. Syringe material is packaged in plastic or glass cartridges that fit a syringe. There are also preloaded syringes or preformed sticks that are used to refill special hydrocolloid inlay syringes.

Question 16

Reversible hydrocolloid Application steps.

Answer 16

1. Impression material is placed into the tray
2. Eject the syringe material around the treatment area in the oral cavity
3. place and seat the tray in the mouth
4. The tray should be cooled with the water in the tubes for 3-5 min.
5. Remove the tray and pour gypsum into it.

Question 17

Elastomeric Impression materilas

Answer 17

The base can be packaged as:

• Paste in a tube
• putty in a jar
• a cartridge

The catalyst or “accelerator” can be packaged as

• paste in a tube
• A cartridge
• liquid in a bottle with a dropper top.

Question 18

Polysulfide material

Answer 18

Polysulfide material provide excellent reproduction of detail, and are composed of a catalyst and a base.

The chemical makeup of the Polysulfide impression material is

• fillers : zinc sulfate, lithopone or calcium sulfate dihydrate
• crosslinking agent: sulfer, lead peroxide m or both
• catalysts: copper hydroxides, zinc peroxide, organic hydrogen peroxide.

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Question 18

Three stages of elastomeric impression materials

Answer 18

common types of elastomeric materials includes:

• Polysufide
• polyether
• silicone
  -polyvinyI siloxane

the material sets after the base and catalyst are mixed. they can be found in a syringe-type application that automatically/extrudes and mixes the material.

The curing stage of elastomeric materials occurs in three stages

• Initial set: paste stiffens and does not exhibit elastic properties. This is only time the material can be manipulated.
• Final set:s second stage, the material becomes more elastic and gradually changes to a solid rubberlike mass. The material must be in place in the mouth before the elastic properties of the finals et begin to develop.
• Final cure: during last stage, which take to 24 hours only slight changes details of the impression.

Question 19

Polysulfide material mixing steps

Answer 19

to mix Polysulfide material steps:

-step 1: dispense pastes at the top of the mixing pad.

-step 2: mix pastes with the tip of a spatula to incorporate the material first

-step 3; transfer the material to fresh surface of the mixing pad.

-step 4: notes that water, saliva, blood affect polysulfide material.

-step 5: remove the impression quickly after setting ; do not rock the tray.

-step 6: make sure the adhesive is thin and dry before adding the impression material.

-step 7: wait 20-30 min before pouring the impression to allow stress relaxation to occur in the material.

-step 8: be careful to avoid glove powder contamination.

Question 19

Mixing silicon materials

Answer 19

When mixing silicone material, note that

• The material has a limited shelf life.
• The tray requires a special tray adhesive
• Silicone material is not subject to syneresis
• silicone material is not subject to syneresis or imbition, but it does shrink over time.
• The material is more flexible, so the chance of distortion during removal is grater.

-You should wait with 20 to 30 min before pouring models to allow stress relaxation to accur.

Question 20

Polyvinyl siloxane material

Answer 20

for dimensional stability, Polyvinyl siloxane is the best impression material pouring of the model can be delayed as long as 7 to 10 days. stiffness of the material makes removal of the tray difficult, the material is dispensed with the use of an auto of an auto-maxing unit and mixing tips.

The chemical makeup of Polyvinyl siloxane impression material is listed:
1. filler: silica
2. catalyst: chloroplatinic acid
3. base: silicone polymer

Question 21

Bite Registration

Answer 21

Bite Registration provide a reproduction of occlusal relationship between the maxillary and mandibular teeth. they provide an accurate registration of the patient’s centric relationship between the maxillary and mandibular arches.

Bite Registration are taken by the dentiist or dental assistant.

Occlusal registration is an accurate registration of the normal centric relationship of the maxillary and mandibular arches. It also commonly referred to as the Bite Registration.

Question 22

silicon material

Answer 22

silicon impression materials are used for complete denture impression and fabrication of crown and bridge. They come in light, medium and heavy bodies; and a very high viscosity putty material.

The chemicals make up the silicone impression materoal is listed:

-Base: polydimethylsiloxane

• Crosslinking agent: alkI orthosilicate or organo hydrogen siloxane
• catalysts: organo tin compounds
• fillers: sillica

Question 23

Types of occlusal registration

Answer 23

one type of Types of occlusal registration is the wax bit, which is useful when the diagnose casts are trimmed. The most common technique involves the use of the softened baseplate wax.

other type of occlusal registration include polysiloxane bite-registration and zinc oxide-eugenol (ZOE) bite-registration paste.

-Polysiloxane:

*supplied both as a paste system and also cartridges

*Fast-setting
* No resistance to biting force

• No odor or taste for the patient
  *Gains dimensional stability over time
• convenient to use
• Zinc oxide:
• offers litter or no resistance to bite closure and is a facst-setting material.
• Is supplied in a paste system and dispensed onto a paper pad, mixed, and placed on a gauze tray for the ptient to bite into.

Question 24

Dental Models

Answer 24

Dental Models: also known as study casts, they are three dimensional reproductions of the teeth and the surrounding soft tissue of a patient’s maxillary and mandibular arches.

Dental models are the following for the following tasks:

• Diagnosis for a fixed or removable
• Diagnosis for orthodontic treatment
• visual presentation of dental treatment
• makeing of custom trays
• making of orthodontic appliances
• making of provisional coverage
• making of mouth guards.

Question 24

Gypsum products

Answer 24

Gypsum: a very soft mineral used in plaster castings. A
products are used extensively in dentistry to make dental models.

Gypsum is a mineral that is mined from the earth, Unrefined, gypsum is dihydeate form of calcium sulfate. A dihydrate is a substance made up of two parts water to one part calcium sulfate, It is converted into plaster of paris and artificial stone using a process called calcination (by heating the gypsum). This converts the calcium sulfate dihydrate crystals determine the water- to power rations for all three types of gypsum.

There are three types of gypsum:

• Model plaster: also referred ti a plaster of paris, it is used primarily for creation of preliminary impressions and the construction of diagnostic model.
• Dental stone: For use as a working model when a more durable diagnostic cast is required; example include making custom trays and orthodontic appliances.
• High-strength stone: Also known as dentist or improved dental stone, it is ideal because of its strength, hardness, and dimensional accuracy. IT is used for the creation of the dies used in the production of crown, bridges, and indirect restorations.

Question 25

Composition of gypsum products

Answer 25

The recommended power to water rations for gypsum products vary by type as follows:
-Model plaster (100g) to 45 to 50 ml of water

• Dental stone (100g) to 30 to 32 mL of water
• High strength stone (100g) to 19 to 24 of water.

Question 26

Pouring dental models

Answer 26

Pouring dental models involves two pats:
the anatomic portion and the art portion.

The anatomic portion is created from the alginate impression,

The art portion forms the base of the model.

There are pour methods for creating the base of the cast.

Those methods are listed here

-Double pour method:
The anatomic portion of the model is pouring first, then a second mmix of plaster or stone is used to prepare the art potion.

• Box and pour method: Impression is surrounded with a box made o wax and poured as on unit.
• one large batch of plaster or stone is mixed, and potions of the model are pouring in a single step.

Inverted pour method:

• begin pouring in small increments at the posterior of impression while holding the handle of the tray so that the impression rests on the vibrator to release air pockets.

-once the impression is filled, but not overfilled, set the impression aside. take the rest of the plaster, thicken it if need be with additional powder, and create a base. Shape the sides. invert the impression onto the plaster base you just created, and smooth and contour the side of the base. Do not bury the sides of the impression tray in plaster because you might not be alble to remove the tray later.

Question 27

Trim mandibular dental models

Answer 27

To Trim mandibular dental models:

1. Trim the posterior potion of the mandibular model until it is even with the maxillary model.
2. trim the base
3. Trim the lateral cuts to cuts to match the maxillary lateral cuts.
4. Trim the back and heel cuts.
5. trim from canine to canine in a rounded form.

Question 27

Trim maxillary dental models

Answer 27

when Trimming and finishing dental model, first prepare the model should by soaking it in water for 5 min. makings on the model should me made in pencil.

To trim the maxillary model
1. trim the base
2. trim the posterior area
3. trim the sides
4. trim the heel cuts
5. trim the angled portion from the canine to canine

Question 28

Finish maxillary and mandibular models

Answer 28

to finish model:

1. mix slurry of gypsum and sill in any voids.
2. polish a plaster model
3. soak the model in a soapy solutions for 24 hr.
4. Dry the model and then polish it with a soft cloth.

Question 29

Custom impression trays

Answer 29

Custom impression trays must:

• Be sufficiently rigid
• fit and adapt well to edentulous
• provide accurate adaptation to an edentulous or a partially edentulous arch
• Maintain an even distribution of impression material.

In addition, the maxillary tray must cover the teeth and hard palate, and extend slightly the gingival margin. The mandibular tray must cover the teeth and extend beyond the ginvival margin.

Consider the following when outling the tray

• The margins of the cast where the finished tray will be seated are outlined in pencil.

-The outline designate the area to be covered by the tray

• The outline extends over the attached gingiva to the mucogingival junction and 2 to 3 mm beyond the last tooth in the quadrant.

Question 30

Cast preparation

Answer 30

When creating custom impression tray, the first steps in cast preparation is to fill undercuts with wax or other molding material. Air bubbles in the cast, the shape of the arch and ridge, carious lesions, fractured teeth, and deep interproximal spaces and malposed teeth can cause undercuts.

A spacer is placed on the cast to create room in the tray for the impression material. Baseplate wax, a folded moist paper towel, o a commercial nonstick molding material can be used for this purpose. To create the spacer, cut a length of wax, warm it, and place it on the cast over the area of the tray. A warmed plastic instrument is used to lute the wax to the cast.

Question 31

Spacer Stop Creation and Handle Formation

Answer 31

The next step of creating a custom impression tray is to create a spacer stop. Triangular or round holes are cut out of the spacer with the use of a laboratory knife or wax spatula. These cutouts are placed to prevent the tray from being seated too deeply onto the arch or quadrant. Allow for an adequate quantity of impression material around the preparations.

An edentulous tray requires a minimum of four stops, one each on the crest of the alveolar ridge in the area of the first or second molar. Additional stop can be placed on the crest of the ridge in the area of each canine. A tray used to take an impression of prepared natural teeth, as for a crown or bridge, has the stops placed near, but not on, the prepared teeth.

The prepared cast, spacer, and immediate surrounding area are painted with a separating medium so that the completed tray can be readily separated from the cast.

The next step of creating a custom impression tray is to form a handle. A handle adapted to the tray will allow easier placement into, and removal from, the patient’s mouth.

The handle should be placed at the anterior of the tray. It should be placed as close to the midline as possible, facing outward and parallel to the occlusal surfaces of the teeth. It can be formed from a piece of scrap acrylic that has been cut away from the tray. The end of the handle and the area where it will be attached to the tray are moistened with tray resin liquid.

After the tray has been formed, the spacer is removed, and the tissue side of the tray is cleaned. A small stiff brush, such as a toothbrush, is used to remove most of the wax at this time. The remainder of the spacer is removed, and the interior of the tray is cleaned after it reaches its final set.

Question 32

Finshing a customs impression tray

Answer 32

When finishing a custom impression tray, rough areas in the tissue side of the tray do not need to be removed removed; this surface will be covered with impression material. However, any rough outer edges of the tray should be smoothed so they do not injured the tissues of the patient’s mouth. A laboratory knife can be used to smooth miner rough areas. An acrylic bur in a straight handpiece can be used to remove major rough areas. An alternative is use the laboratory lathe to smooth the edges.

The tray should now be given a final rinse and disindected in accordance with the manufacture’s instructions.

Question 33

Dental Waxes

Answer 33

Dental Waxes are use for various procedures in dentistry. For example, they can be used to line the impression trays to make them larger. they are designed for different functions in the dental office and come in different colors to help differentiate their functions.

Boxing wax: is soft, pliable wax a smooth, shiny appearance. It is supplied in long narrow strips measuring 1 to 1 1/2 inches wide and 12 to 18 inch long. It is ised to form a wall or box around a perliminary perliminary when pouring.

Utillity wax: is supplies in various form depending on its composed of beeswax, , petroleum and and other soft waxes. Utillity wax is used to

• Extend the borders of an impression tray
• cover brackets in orthodontic treatment.
• Sticky wax: is supplied in skicks or blocks. Its main ingredients are beeswax and rosin. It is quite brittle; but because very tacky when heated. Skicky wax is usedful for creating a wax pattern or joining acrylic resin.
• Inclay casting wax: is a hard, britle wax made from paraffin wax, carnauba wax, resin, and beeswax. it is used to create a pattern of the indirect restoration on a model. It is classificed according to flow as follows:
• type A: hard inlay wax
• Type B: medium inlay wax
  -Type C: soft inlay wax

Question 34

Dental Waxes

Answer 34

• casting wax: is made of paraffin, ceresin, beeswax, and resins. It is supplied in sheets of various thicknesses and it used for single tooth indirect restorations, fixed bridges, and casting of metal portional of partal denture.

Baseplate wax: is made of paraffin or ceresin with beeswax and carnuba wax. It is hard and brittle at room temperature and supplied in sheets. there are three types of baseplate wax;

*Type I: softer wax used for denture construction

*Type II medium- hardness wax used in moderate climates

• Type III: harder wax for use in tropical climates.
• Bite registration waxes: are soft and very similar to casting waxes. Bite registration wax softens under warm water. The patient is instructed bite down, leaving an imprint of the teeth in the wax.