Gypsum: dental models Flashcards
what are dental models
- 3D reproductions of the teeth and the surrounding soft tissues of a patient’s max and mand arches
- also referred to as study casts
what are uses of dental models
- diagnosis for a fixed or removable prosthetic
- diagnosis for orthodontic treatment
- visual presentation of dental treatment
- making custom trays
- making orthodontic appliances
- making provisional coverage
- making mouth guards or bleaching trays
what are gypsum products
- used extensively in dentistry to make dental models
what are the chemical properties of gypsum products
- a mineral that is mined from the earth
- in its unrefined state, gypsum is the dihydrate form of calcium sulfate
- converted into a powdered hemihyrdate
what are the physical forms of gypsum
- model plaster
- dental stone
- high-strength stone
what are model plasters of gypsum used for and how much water is needed
- commonly called plaster of Paris
- used primarily for pouring preliminary impressions and the making of diagnostic models
- 45-50 ml
what is dental stone of gypsum used for and how much water is needed
- for use as a working model when a more durable diagnostic cast is required
- examples are in the making of custom trays and orthodontic appliances
- 30-32 ml
what are high strength stone models used for and how much water is needed
- also known as density or improved dental stone
- its strength, hardness, and dimensional accuracy make it ideal to create the dies used in the production of crowns, bridges and indirect restorations
- 19-24 ml
what are the 2 part that a model consists of
- anatomic portion: created from the alginate impression
2. art portion: forms the base of the model
what are the 3 different pouring methods for dental casts
- double-pour method: the anatomic portion of the model is pouring first. then a second mix of plaster or stone is used to prepare the art portion
- box and pour method: the impression is surrounded with a “box” made of wax and poured as one unit
- inverted-pour method: consists of mixing one large mixture of plaster or stone and pouring both portions of the model in a single step
what are voids and what are they caused by
- tooth or teeth not captured in the model
- under vibration
- over vibration
- pouring speed: hasty pouring, slow pouring
how do you separate the impression from the cast
- wait 45-60 mins after the base has been poured
- use plaster knife to: remove excess material from the edge of the impression tray; gently separate the margins of the tray from the cast
- first: release the ant portion by gently pulling downward and forward at one time
- make a firm, straight pull upwards - do not apply lateral pressure or rock tray
- if tray does not separate, check to see where the tray may be locked by the stone; use plaster knife to free the ray from the stone
how do you handle removing the impression from the cast with Mal-aligned teeth
- remove tray first, then impression material
what are post separation procedures
- label the bottom of the base with client’s name. permanent marker
- keep the wax bite with the model to prevent chipping of teeth during storage and transportation
how do you prepare the model for trimming and finishing
- soak in water for 5 mins
- no teeth
- cut excess gypsum away: retromolar pad, tuberosities
- remove small bubbles with old instrument: occlusal surfaces, gingival margins
how do you trim the maxillary model
- trim the base
- trim the posterior area
- trim the sides
- trim the heel cuts
- trim the angled portion from canine to canine
how do you trim the mandibular model
- trim the posterior portion of the mandibular model until is it even with the maxillary model
- trim the base
- trim the lateral cuts to match the maxillary lateral cuts
- trim the back and heel cuts
- trim from canine to canine in a rounded form
how do you finish the model
- mix a slurry of gypsum and fill any voids
how do you polish a plaster model
- use model polish and a soft buffing cloth (soak the model in a soapy solution for 24 hours)
