Alginate Impresions Diagnostic Casts

Alginates Alginate Member of Hydrocolloid impression materials Hydro – water Colloid – gelatin substance Creates negative mold of pt teeth Common Uses Study models Opposing Arch model Bleach trays

Alginate - Hydrocolliod Solution in which water is used as the mixing agent Physical Phases of Hydrocolloids Sol – (as in solution) material is in liquid or semi-liquid form Gel – the material is semi-solid (as in gelatin dessert)

Alginate - Hydrocolliod Irreversible vs. Reversible Irreversible – Materials not able to return to the sol state after they become a gel example: cake mix Reversible – materials that change physical state from sol to gel then back to sol example: Ice cream

Alginate Irreversible hydrocolliod Not very accurate – not used for final impressions Recommended when accuracy is not important Easy to mix/use – little equipment Less expensive

Alginate Ingredients Potassium Alginate Main ingredient Comes from sea kelp (seaweed) Acts as a thickening agent (also in Ice Cream) Calcium sulfate Reacts with potassium alginate to accelerate the set

Alginate Ingredients Potassium titanium fluoride Added to resist interference of the set and strength of the alginate when making cast Trisodium phosphate Added as a retarder (slows down time it takes to form a gel Diatomacious earth Zinc Oxide – these are added as bulk

Impressions Ideal mixing temperature 70 degrees Alginate dispensment Coffee can size Premeasured – packages more expensive 1 year shelf life

Alginate Impressions Working Time Time allowed for mixing the alginate, loading the tray, positioning in mouth Setting Time Time required for the chemical action to be completed and when the impression is ready to be removed from pt’s mouth

Alginate Impressions Regular Set Working time – 2 minutes Setting time – 41/2 minutes Fast Set Working time – 11/4 minutes Setting time – 1-2 minutes

Alginate Impressions Fast set vs Regular set There is no difference in final product Use determined by: Difficulty in seating impression Sometimes easier to use when working alone Children and pt’s w/gag reflex – faster set can be easier

Alginate Impressions Dimensional Stability Serious problem associated w/alginate is loss of accuracy when impression is stored before pouring Will deteriorate w/elevated temperatures or in presence of moisture Alginate stored in water or a very wet paper towel will absorb & expand (this absorption is called imbibitions)

Alginate Impressions Dimensional Stability Exposure to open air – water will evaporate – causing impression to shrink and distort Optimum dimensional stability store in a damp paper towel for no more than 1 hour before pouring, your book says _?__ minutes.

MATERIALS Many brands – many techniques Common Ratio – 1 scoop of powder to 1 level of water 1=1 Maxillary 3=3 Mandibular 2=2 Usually

QUALITY OF MIX Quality of mix – creates Quality impression – combined w/quality pour creates Awesome models IMPORTANT: DO NOT ADD MORE WATER This takes away from strength of impression

MATERIALS - Trays Perforated trays Allows alginate to ooze through holes as it sets Forms a lock and keeps alginate from pulling away from tray Two types: Plastic – disposable Metal – sterilized after use

Selection of Trays Try in pt’s mouth after rinsing Check for comfort and fit Should extend below facial surfaces Should extend 2-3mm beyond molars Deep enough to allow 2-3mm of alginate between tray & incisal/occlusal Utility wax may be added to extend

Procedure – explain to Patient Plastic drape or bib Material will feel cold Not an unpleasant to taste Material will set quickly Mouth may feel full Hand signals – Gag reflex – tilt forward and breathe through nose

Evaluating the Impression Impression centered over centrals Complete peripheral roll to include vestibular areas Tray was not over seated (pushed down to far) Tray was seated evenly Impression free of tears & voids/holes

Evaluating the Impression Retromolar area, lingual frenum, tongue space – mandibular Hard palate & tuberosities are recorded – maxillary IMMEDIATELY after removing impression rinse & disinfect, damp paper towel – until poured

WAX BITE/UTILITY WAX Impression wax is used to show occlusal relationship between arches Soften wax – place over occlusal surface of mandibular teeth – have pt close gently but firmly Utility wax may be used to enlarge impression tray

GYPSUM PRODUCTS Model plaster Dental stone High strength stone

Model Plaster Plaster or paris Sets fast More porous White Weakest 20 – 30 minute set

Dental Stone More durable Yellow Finer grains 40 – 60 minute set

High Strength Stone Used for dies and final working models Very hard cast Very fine grains Green, Pink, Blue Takes longer to set Strongest 60 – 80 minute set

GYPSUM Gives off exothermic reaction as it sets (heat) Warmer water used to mix faster material will set

PARTS OF DENTALCAST Anatomic portion Created from the alginate impression Reproduction of teeth, muscle & frenum attachments Art portion Forms the base of cast (1/3 of overall height)

POURING METHODS Stone must be vibrated to remove bubbles Double Pour Anatomic portion poured first Another batch mixed for base/art portion Box & Pour One mix for both portions Poured into box made of wax

POURING METHODS Inverted Pour One mix for both portions then turned over Anatomical portion filled Base made by continuing pour Common

TRIMMING MODELS Soak models 5 min. Better for wheel on grinder Models should have ½ inch base Models should have 1 inch anatomic portion ALWAYS have gloves, goggles, mask ALWAYS use trim shield

ARTICULATOR Frame that holds the patients models in occlusion as the TMJ would Used commonly