2.impression material in orthodontics

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  • 1. IMPRESSION MATERIALS AND TECHNIQUES IN ORTHODONTICS By, Dr.Karan Purohit M.S.R.D.C

2. CONTENTSCONTENTS INTRODUCTION. HISTORY IDEAL REQUISITES OF AN IMPRESSION MATERIAL CLASSIFICATION OF IMPRESSION MATERIALS AND TRAYS IMPRESSION MATERIALS- ALGINATE,AGAR AND SILICONES IMPRESSION TECHNIQUE IMPRESSION FOR CLEFT PALATE PATIENT IMPRESSION FOR MYOFUNCTIONAL APPLIANCES ORA SCANNER CONCLUSION REFERENCES 3. INTRODUCTION Impression materials are used to make an accurate replica of oral tissues. The area involved may vary from a single tooth to the whole dentition or an impression of an edentulous mouth. Usually the impression material is carried to the mouth in a plastic state on a tray and removed from the mouth when the material has set. The accuracy, detail and quality of the final replica is of greatest importance. 4. There are a wide range of impression materials having its own advantages and disadvantages. When making impressions for orthodontic cast the hard and soft tissues should be accurately reproduced. The casts should include the teeth, palate and the alveolar process to the base of vestibule and to the floor of the mouth. 5. DENTAL IMPRESSION? An imprint or a negative likeliness of the teeth and or edentulous areas where the teeth have been removed, made in a plastic material which becomes relatively hard or set when it comes in contact with these tissues. IMPRESSION MATERIAL ? Any substance or combination of substances used for making a negative reproduction or a replica of the oral tissues 6. HISTORY PHILIP PFAFFS (1756) WAS THE FIRST TO DESCRIBE TAKING AN IMPRESSION OF THE JAW . DELABARRE (1820) INTRODUCED THE IMPRESSION TRAY HARLES STENT (1857) A LONDON DENTIST TESTED A COMBINATION OF DIFFERENT KINDS OF WAXES HARDENED AT ORAL TEMPERATURES, WHICH IS STILL USED TODAY UNDER THE NAME OF STENTS COMPOSITION. JOSEPH RICHARDSON (1860) SUGGESTED THE EARLY USE OF GUTTA PERCHA FOR OBTAINING IMPRESSION BECAUSE OF ITS ELASTICITY S. WILLIAM WILDING (1940) USED ALGIN AS DENTAL IMPRESSION MATERIAL S. L. PEARSON, (1955) LIVERPOOL UNIVERSITY DEVELOPED ELASTIC IMPRESSION MATERIALS FROM SYNTHETIC RUBBER AND RESIN BASES. 7. In orthodontics, impression gives a negative reproduction of the tissues and by filling it with dental stone or other model material a positive cast is made that can be removed after model material has set., which in turn are used for; 1. STUDY PURPOSE 2. FABRICATION OF APPLIANCES 3. MAINTAINING RECORDS 8. IDEAL REQUISITES OF AN IMPRESSION MATERIAL BE NON TOXIC TO THE TISSUES. SHOULD HAVE AN ADEQUATE SHELF LIFE . BE SUFFICIENTLY FLUID ON INSERTION TO GIVE ACCURATE SURFACE DETAIL. HAVE PLEASANT TASTE, SMELL AND APPEARANCE . HAVE NO DIMENSIONSAL CHANGES EITHER IN OR OUT OF THE MOUTH AT ALL NORMAL DEGREES OF TEMPERATURE AND HUMIDITY. 9. SET OR HARDEN, AT OR NEAR MOUTH TEMPERATURE . IT SHOULD HAVE SUITABLE WORKING AND SETTING TIME. BE COMPATIBLE WITH DIE AND MODEL MATERIALS BE INEXPENSIVE 10. No impression material fulfills all these requirements And the selection of the material best suited for a particular Clinical situation and technique rests with Dentists. 11. CLASSIFICATION OF THE IMPRESSION MATERIALS BASED ON: SETTING REACTION THERMOPLASTIC THERMOSET ELASTICITY ELASTIC INELASTIC NATURE OF THE SETTING REACTION REVERSIBLE IRREVERSIBLE PRESSURE EXERTED ON THE TISSUE MUCOCOMPRESSIVE MUCOSTATIC DENTITION STATUS EDENTULOUS DENTULOUS 12. COLLOIDS They are the fourth state of matter because of their differences in structure, constitution, and reactions . Particles size ranging from 1 to 200 nanometers. Colloid are Suspension of 2 phases Colloidal materials used for making impressions are either algin or agar dissolved in water. Hence the name HYDROCOLLOIDS 13. Colloids , have two distinct phases A dispersed phase + dispersion phase LIQUID COLLOIDS ARE CALLED SOL SOLID COLLOIDS ARE CALLED GEL 14. In orthodontics we require impression materials that are elastic since we deal with dentulous patients The most commonly employed materials include I. Hydrocolloid Agar Agar (reversible) - Alginate (irreversible) II. Elastomeric impression materials. 15. SYNERISIS The process of synerisis may be explained as the squeezing of water from between the polysaccharide chains. As a result of which one may often observe a small droplets of water on the surface of impression. Which results in shrinkage of the impression. 16. IMBIBITION In the presence of excess water the hydrocolloids may absorb water by a process, which is opposite of synerisis that will cause the separation of the polysaccharide chains and thus causes the swelling of the impression. 17. IRREVERSIBLE HYDROCOLLOID ALGINATE (ADA no 18) At the end of 19th century the chemist from Scotland noticed that certain brown seaweed produced a mucous extraction that he termed as ALGIN. Later S William wilding used this algin as dental impression. This became the chief ingredient in our popularly used dental ALGINATE, which is A SODIUM SALT ANHYDRO--D-MANURONIC ACID/ ALGINIC ACID 18. The factors causing its successful use as an impression material include: Ease of manipulation Comfortable to the patients Relatively inexpensive not requiring elaborate armamentarium. TYPES TYPE I RAPID OR FAST SETTING TYPE II NORMAL SETTING 19. APPLICATIOS OF ALGINATE 1.Most communally used for making impression for orthodontic study models. 2.For duplicating models. 20. COMPOSITION NO COMPOSITION FUNCTION % I. Salt of Alginic acid Dissolves in water & reacts with calcium ions 15% II. Calcium sulphate Reacts with pottasium alginate to form calcium alginate 16% III. Tri sodium phosphate Reacts in preference with calcium sulphate - retarder 2% IV. Pottasium Titanium Gypsum hardener 3% V. Zinc oxide Filler 4% VI. Diatomaceous earth Filler 60% VII. Flavouring & coloring agents Makes the material more palatable TRACES 21. SETTING REACTION. Soluble alginate reacts with the calcium sulphate resulting in the formation of an insoluble calcium alginate. This process occurs quite rapidly and thus would not allow sufficient working time, so to compensate for this problem a water soluble salt namely Tri-sodium phosphate is added to prolong the working time. The basic idea behind adding this salt is to allow calcium sulphate to initially react with tri-sodium phosphate in preference to the soluble alginate 22. Properties WORKING TIME ;- for fast setting materials -1.25 to 2 min (mixing time-45 sec) for regular setting times is - 2 to 4.5 min (m.t.-60 sec) 23. Flexibility A D A specification permits a range of 5% to 20% at a stress of 1000 gmscm2 and most alginate have a typical value of 14%. Strength The compressive strengths range from 5000 9000 gmscm. The Tear strength vary from 380- 700 gmscm. Elasticity highly elastic but less when compared to agar and about 97.3% elastic recovery occurs. The amount of permanent deformation is more as compare to agar. 24. ACCURACY Alginates are sufficiently flexible to record fine detail in the mouth.. During setting of the material it is important that the impression should not be moved. The reaction is faster at higher temperature and so the material is contact with the tissues sets first. Any pressure on the gel due to movement of the tray will set up stresses within the materials which will distort the alginate after its removal from the mouth. 25. The material is sufficiently elastic to be withdrawn over undercuts; occasionally tearing of the impression materials may occur with serious undercuts. Alginate are not stable on storage because of evaporation Compatibility with plaster and stone can be good. Some alginates give powdery surface on casts from dental stones. SHELF LIFE;- Short shelf life.Alginate impression material deteriorates rapidly at elevated temperature and The material should be stored in cool dry place.(not above 37c) 26. DIMENSION STABILITY Alginate impression loses water by evaporation and shrinks on standing in air If it is placed in water it absorbs water and swells .Therefore, cast should be poured immediately after making the impression. If storage is unavoidable keeping in a humid temperature of 100% results in least dimensional changes. BIOLOGICAL PROPERTIES Some of silica particles present in dust are of possible health hazards. Presently some manufacturers supply Dust free alginate. 27. Inexpensive and hydrophillic (contact angle 37) Easy to manipulate Displace blood and saliva and pour well with gypsum stone) Minimum requirement of equipments Accurate if proprely handled 28. Disadvantages of alginate Low tear strength Poorer reproduction of surface detail as compare to agar Not as dimensionally acccurate as medium and light body silicone. Not dimensionally stable on storage due to syneresis and poured immediately.(triethanolamine modified alginates more stable in long life hermetically sealed bags impressions can be stored for 48 hrs) 29. Zelgan (densply) W:P 57 ml : 22 g Mixing time 45 sec Manipulation time 60 sec Time in mouth 45 sec 30. Dustless alginates:- Many materials have now been formulated which gives off little or no dust particles, so avoiding dust inhalation. This can be achieved by coating the material with a glycol Siliconised alginates:- Two pastes alginates have been developed, which incorporate silicon polymer component. These materials have superior resistance to tearing compared to unmodified alginates. However dimensional stability is reported to be poor A combination reversible hydrocolloid / alginate impression technique has been improved. 31. Modified alginates Fluorides or silicofluorides to improve surface of stone model(hexafluoro titanate in alginoplast and xantalgin) Chlorhexidine added to alginate powder (hydrogum plus chlorhexidine) inactive bacterial microorganism. Mint and vanilla flavour (