Chapter 15 and 16 Flashcards
Diagnostic casts
positive replicas of the teeth and surrounding oral tissues and structures produced from impressions that create a negative representation of the teeth; commonly called study models and used for diagnostic purposes and numerous chairside and laboratory procedures
Preliminary impression
an impression of the dentition and surrounding tissues taken as a precursor to other treatment; often used to make casts (models) of oral structures for planning, and to construct custom trays or provisional restorations
Final impression
a detailed impression of oral structures used to make an accurate cast from which restorations or protheses are made
Bite registration
An impression of the upper and lower teeth in the patients normal bite relation
Hydrocolloid
A water based colloid used as an elastic impresion material
Reversible hydrocolloid
An agar impression material that can be heated to change a gel into a fluid sol state that can flow around the teeth, and then cooled to gel again to make an impression of the shapes of the oral structures
Agar
A powder derived from seaweed that is a major component of reversible hydrocolloid
Alginate
A versitile irreversible hydrocolloid that is the most used impression material in the dental office; it lacks the accuracy and fine surface detail needed for impressions for crown and bridge procedures
Syneresis
A characteristic of gels when let standing to contract and squeeze out some liquid that then accumulates on the surface
Imbibtion
act of absorbing moisture
Surfactant
chemical that lowers the surface tension of a substance so that it is more readily wetted; for example, oil beads on the surface of water, but soap acts as a surfactant to allow the oil to spread over the surface
Polysulfide
An elastic impression material that has sulfur containing (mercaptan) functional groups; it has also been referred to as rubber base impression material
Polyvinyl Siloxane (PVS)
Very accurate addition silicone elastomer impression material; it is used extensively for crown and bridge procedures because of its accuracy, dimensional stability, and ease of use
Casts
Hard replicas of hard and soft tissue of the patients oral cavity, made from gypsum products; also referred to as models
Diagnostic casts
casts generally made from dental plaster or stone and used for patient education, treatment planning, and tracking the progress of treatment, as with orthodontic models; these casts are also known as study models
Working casts
casts generally made from one of the dental stones that are strong enough to resist the stresses of fabricating an indirect restoration or prothesis; these casts are also known as master casts or working models
Dies
replicas of the prepared teeth that are generally removable from the working casts
Model plaster
the weakest, most porous form of gypsum product used in dentistry
Dental stone
a stronger, less porous form of gypsum product used in dentistry
Die stone
the densest form of gypsum product used in dentistry
Pouring
pouring the cast refers to the process of vibrating the flowable gypsum product into an impression; this process must produce a cast that is an exact replica of the impression
Trimming
the process of removing excess hardened gypsum from the cast for ease in working with the cast and appearance and presentation
Melting range
a range of melting points of the individual components of wax
Flow
the movement of wax as it approaches the melting range
Excess residue
a wax film that remains on an object after the wax is removed
Wax pattern
a duplicate of a restoration carved in wax
Most common impression material
alginate
Alginate
irreversible inexpensibe no special equipment easy to manipulate fairly accurate
Composition of alginate
Agar (seaweed)
Working time for alginate
Fast: 1.25-2 min
Regular: 2-3 min
Trays used for alginate
Metal perforated trays
Maxillary perforated trays
1-6; 1 largest and 6 smallest
Mandibular perforated trays
20-26; 20 largest
most common 22 or 24
Idenitec
put powder in bowl first then put water
Positive air bubbles
Blebs
Negative air bubbles
Voids
Two portions of a diagnostic study model
Anatomical portion and Art portion
Anatomical portion
Contains the registration of the oral anatomy. It compromises 2/3 of the total height of each trimmed study cast
Art portion
Serves as a base (top or bottom) of the study model. It compromises 1/3 of the total height of each trimmed study cast
Depth of the vestibule
lies about 1/2 inch from the gingival margin
Parts of a model trimmer
Grinding wheel
Casing
Platform
Rigid impression material
Reversible
Composition of rigid impression material
Thermoplactic resin; 40% fillers and 10% chalk and plastisizes
Uses for thermoplastic resin
Border molding and bite registration
How thermoplastic resin comes supplied
Cakes and sticks
Ways to soften thermoplastic resin
Soften on heating (warm water and flame) and hardens when cooled
Uses of impression material
replicas of oral tissues
replicas of facial defects
reproduction of hard and soft tissues
Most impression material is made from
elastic
Classifications for impression materials
Elastic and Rigid
Elastic
impression material able to pick-up undercuts
Rigid
impression material will not pick-up undercuts
Classification of elastic impression
Irreversible
Reversible
Irreversible
will not return to its original state (powder/liquid)
Reversible
will return to its original state (only one impression is reversible)
Types of impression trays
Metal perforated trays Rim lock metal trays Disposable (stock) trays Bite registration Triple tray Custom tray (denture impression)
Hydrophobic
Doesn’t like water
Hydrophilic
water loving
Negative
impression of the patients mouth
Positive
Poured impression in the stone known as the diagnostic cast
3 different types of impressions
preliminary
final
bite registration
Elastic impression material
irreversible
Composition of elastic impression material
Polyvinyl siloxane (PVS)
Armamentarium needed for Polyvinyl siloxane
Delivary system, cartridge (will have catalyst and base)
Brand name of polyvinyl siloxane
3M express and Extrude
Pouring for polyvinyl siloxane
Requires doctor to pour in microstone
Trays for polyvinyl siloxane
triple trays
Polyether is the composition for what kind of impression material
Elastic
Brand name for polyether
Impergum
Polysulfide is the composition of what kind of impression material
Elastic
Armamentarium needed for polysulfide
Onion skin pad, diamond head spatula, catalyst and base in two tubes
Trays for polyether
Custom
Humidore
(tupperware container) a vessel that is used to store an impression (alginate)
This holds the stone in the lab
plaster pin
Dihydrate
CaSO4*2H20 Calcium sulfate which is mined as solid mass then heated to turn into a powder
Hemihydrate
CaSO4*1/2H2O the final product after the dihydrate has been ground up (calcination) the powder
Classification of gypsum products
impression plaster model plaster dental stone dental stone high-strenght/low expansion dental stone high-strengh/hight expansion
Manipulation of gypsum
by hand in a stone bowl
vibrator
mechanical (vac-u-spat)
Setting for gypsum
Working time: after 1 min
Initial time: 8-16 mins
final set: can no longer be manipulated
Methods of pouring casts
Double pour method
single step method
boxing method
Slurry water
Water coming out from the model trimmer being used instead of regular water because it speeds up the process of impressions setting
examples of organic materials that retard
blood and saliva
Uses of dental waxes
Blockout (missing teeth)
Boxing impression
Bite
Occlusal rims for making denture
Composition of waxes
Both natural and synthetic
Natural waxes produced from plants, used in carnauba wax; insects, used in beeswax; and minerals, used in paraffin and ceresin wax
Synthetic waxes; gums, fats, oils, resins, and coloring agents
Melting range for waxes
range of temperatures at which each component of the wax will start to soften and then flow
Flow of waxes
As the temp of the wax increases, the viscosity of the wax decreases until the wax becomes a liquid
Excess residue of waxes
May result in inaccuracies in the object being produced
Classification of waxes
Pattern
Processing
Impression
Pattern waxes
Inlay, casting, and baseplate
Processing waxes
Boxing, utiliy, and sticky
Impression waxes
Correction impression
Bite registration
Why should you not use idophors to disinfect impressions?
It can stain them brown
Common uses if alginate impressions
Diagnostic casts Preliminary impression for complete dentures Partial denture frameworks Opposing casts for crown and bridge treatments Repairs of partial and complete dentures Provisional restorations Custom trays Sports protectors and night guards Removable othrodontic appliances
