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Alginate Dental Impressions NickyShanks Dental Advisor for Simulation and Quality NIMDTAAims To give an overview on the constituents, properties and use of alginate as a dental impression material and the technique for making accurate alginate impressions of dentate patients. Overview Why do we need impressions? Properties of alginate Clinical techniques impressionsclinical – taking alginate Learning Outcomes By the end of this session the successful student should be able to: •List the constituents and properties of alginate as an impression material •Describe those features that must be recorded in a preliminary impression •Select stock impression trays and modify them to make preliminary impressions in alginate •Demonstrate clinical skills in taking upper and lower alginate dental impressions.What is an impression? A negative replica of the teeth and surrounding tissues of the mandible or maxillaModels From an impression it is possible to produce an exact replica of the dental structures as a cast (or model) stone) for use in dental patientental management.What needs to be recorded? Impressions should be made of the teeth, palate, buccal and lingual sulcusal, regions. Reasons for taking impressions •Study casts – plan and monitor treatment (complex restorative, ortho, tooth wear) •Permanent record of the dental arches •Monitoring tool e.g tooth wear •Construct appliances – ortho / protective / bleaching •Construct prostheses – fixed / removable •Opposing arch model to record occlusal relation ALGINA TE Used for: •Study casts, opposing occlusal models •Preliminary impressions for partially dentate patients •Appliances – protective bite guards, occlusal splints, orthodontic appliances, bleaching traysProperties of an ideal impression material • Biocompatible – safe for patient and dental team • Easy to use • Elastic on removal from mouth • Accurate (ability to record fine detail and dimensionally stable) • Fluid on insertion • Adherent to tray • Tear resistant • Compatible with model and die materials • Suitable shelf life, working time, setting time • Able to sterilise Classification of impression materials Elastic Non-elastic (rigid) 1. Synthetic elastomers 1. Impression plaster Silicones (addition cured) 2. Impression compound Polyethers 3. Zinc-oxide / eugenol Polysulphides 4. Impression waxes 2. Hydrocolloids Reversible (agar) Irreversible (alginate)Fortunately we are using alginate! ALGINA TE:Properties •Irreversible hydrocolloid COMPOSITION: Sodium alginate + calcium sulphate + inert filler + water + added PH indicators (give a visual aid to setting process) FOR RETENTION : •Perforated tray •Adhesive - solutions of resins in alcohol, either bottle with a brush or an aerosol sprayALGINA TE:Properties •Hydrophilic •Elastic – 2 min set •Poor tear resistance easily distorted or torn •Poor dimensional stability •Syneresis – shrinks if dries •Imbibition – expands if wet •Not as accurate as PVS so not for crown bridgework or Co-Cr P/P’s •Non-toxic, non-irritant, cheap •Does not bond to tray •pH goes from 11 to 7 •Must pour quickly (10 mins)ALGINATE: Irreversible hydrocolloidMaking impressions ✓ consent - explanation ✓ care of patient ✓ selecting trays ✓ impression techniques ✓ assessing impressions ✓ infection control ✓ administration Making a good impression Operator: ◦Understands what is required ◦Chooses correct material ◦Selects correct tray ◦Uses correct techniques ◦Good patient management Impression trays •To carry material •Must support material entirely, must not flex TYPES •Stock trays – metal and plastic, plain and perforated •Custom trays – acrylic lab. madeBOX TRAYS When teeth presentPreparation Rubber mixing bowl Mixing spatula Alginate powder – shake! Water – room temperature 21 C 0 Water measure Impression trays + handles Adhesive Disinfectant Gauze Laboratory docket Sealable plastic bag T echnique- 1 •Patient in upright position •Head supported and at your elbow height •Select tray and try in, lower from front, upper from side/behind •Tray should cover all teeth and be 3-4 mm wider than arch •Modify tray for dead space / extension •Apply adhesive to whole surface tray (thin layer) – wait 5 minsOperatorPositioning Upper impression Lower impressionCustomisation of stock trays ‘dead space’Adapt (customise) tray extensionExtension into ‘dead space’ obtained using impression compound for partially dentate patients T echnique- 2 •Dry teeth prior to impression •Smear impression material onto occlusal / incisal surfaces of teeth to reduce risk of air blows •Rotate tray gently into mouth •Line up centre of tray with incisors •Seat tray posteriorly and rotate to engage anterior teeth •Mould tissues •test)ain even pressure until set (can keep small amount of material to T echnique- 3 •Impression material near lips will set quicker than the bulk of the material – ensure enough time is allowed for the material to set before attempting removal •Release air posteriorly to release tray •Remove with a ‘quick’ movement to minimise distortion •Rotate and slide out of mouth carefully •Check surface of material for any obvious defects •Ensure material is still attached to supporting tray •Trim back unsupported material especially distally T echnique- 4 •Rinse and inspect for quality •Disinfect, wrap in damp gauze and place in sealed labelled bag •Prepare to be transported to laboratory – should be ideally poured within 30 minutes! •Fill in laboratory card‘Read’ the impression Has it adequately recorded what was desired? Impressions should be discussed under the following headings: 1. Extension 2. Anatomical landmarks 3. Rolled borders 4. Surface detail Disinfection of impressions •Rinse cold water 30 secs •Immerse Perform 10 mins •Rinse in water, remove excess •Wrap in damp gauze, plastic bag, label as disinfected •Lab prescription card completed Errors ➢Poor manipulation of material – ➢Adhesive failure •Not enough / too much material ➢Air / contaminant defects •Already set •Not mixed correctly ➢Poor technique – •Wrong tray size •Tray in wrong place -(often) too close to front teeth •Not fully seated •Moved during setting •Removed too earlyGagging: Causes Somatogenic (physiological) – tactile irritation, varies patient to patient, drug therapy, alcoholism Psychogenic – apprehension, anxiety, fear, others Gagging: Management ✓Minimise presence of physical stimulus – load tray carefully, tip head forward ✓Divert patient’s attention - breathing advice, count down time ✓Reassurance ✓Calm, confident approach ✓Rinse with DifflamAny questions?