2Today’s ClassDriving Question: How are diagnostic cast utilized in the dental office?Learning Intentions: We will be able to describe various methods of constructing custom trays and demonstrate creating a light-cured custom tray.Anchor: What personal protective equipment should be worn by the dental assistant when pouring a stone cast?
3Diagnostic Cast Models Duplicate patient’ s teeth and mouth structures for diagnostic purposesMade from quality dental impressionsUsed as models for further fabricating dental prosthesesUsed as education toolFrom initial casts dental prostheses are made that fit patient’s jaw structure and resemble other teeth
4Gypsum MaterialsUsed in dentistry to create diagnostic cast models of maxillary or mandibular archMost common are plaster, stone, and high-strength stoneComposed primarily of calcium sulfate dihydrateSupplied as powderDuring setting process gypsum gives off heat in an exothermic reaction
5Strengths of Gypsum Products Plaster of ParisDental stoneDie stoneTo learn more about gypsum products andother dental materials, click here or go toDentMat/default.asp
6Plaster of ParisUsed for pouring cast models for preliminary study, diagnostic reasons, to attach casts onto articulators, and for general use in the dental lab when strength is not importantBecause of porous and irregular particles, plaster requires more water when being mixedInitial setting time is from 5 to 15 minutes and is completely set within 45 minutesRemoval of cast from mold too soon can result in fractures to the cast
8Stone Available in yellow or buff color Requires less water when mixing, and sets more slowly than plasterWhen set, stone is harder, denser, and has a higher crushing strength than plasterHarder stone casts provide excellent master casts for fabrication of dentures, bleach trays, athletic mouth guards, and temporary crown splints
9Stone Spatulation is completed in 30 to 60 seconds on a vibrator Initial setting time for artificial stone is usually 8 to 15 minutes and final setting time is approximately 45 minutes
10Die Stone Strongest gypsum product Used to create working casts for fixed prostheses and partial denturesMost often poured by the dental laboratory technicianMix must not be too thick or too thin so that it flows into the dentition easily and yet is thick enough to maintain strength
12Steps to Pouring a Dental Model Use a clean, dry mixing bowl and spatulaMeasure volume of water and weigh powderAlways add powder to water and not water to powderSpatulate thoroughly by hand, incorporating all the powder evenly throughout the mix until creamyAvoid whipping the mix
13Steps to Pouring a Dental Model Vacuum mixing with a power mixer-investor helps eliminate incorporation of air into the mixHold bowl against a vibrator for a few minutes to cause trapped air to rise to the surfaceNever add water to a mix that is too thick
16Parts of a Cast Model Click here for a question to consider Anatomic portion:includes teeth and oral structuresthe baseshould make up two-thirds of the modelArt portion:makes up one-thirdClick here for a question to consider
17Question to ConsiderWhat is the difference between the maxillary and mandibular trimmed models?