Irreversible hydrocolloids

BY FATEEMA PRIYAM FEROZ

1. IRREVERSIBLE HYDROCOLLOIDS FATEEMA PRIYAM 1 ST YR P.G DEPT OF PROSTHODONTICS

2. CONTENTS CLASSIFICATION IDEAL REQUIREMENTS OF AN IMPRESSION MATERIAL ALGINATE HISTORY COMPOSITION SETTING REACTION PROPERTIES DIMENSIONAL CHANGES PERMANENT DEFORMATION DISINFECTION COMPATIBILITY WITH GYPSUM

3. ALGINATES SELECTION OF THE TRAY DISPENSING AND STORAGE MANIPULATION MIXING MAKING IMPRESSION COMMON CAUSES OF REMAKING MANAGING A GAGGING PATIENT MODIFIED ALGINATES BIOHAZARDS DUE TO ALGINATES RECENT ADVANCES DISCUSSION SUMMARY REFERENCES

4. CLASSIFICATION OF IMPRESSION MATERIALS BASED ON SETTING MECHANISM Reversible : Impression compound,dental waxes ,agar hydrocolloids Irreversible Alginate,Zinc oxide eugenol and elastomers

5. BASED ON FLEXIBILITY Inelastic / rigid: Plaster of Paris,impression compound,zinc oxide eugenol Elastic : Elastomers,Alginate,Agar hydrocolloid BASED ON THE AMOUNT OF PRESSURE Mucostatic impression materials: Zinc oxide eugenol impression paste,Impression plaster Mucocompressive impression material impression compound,impression waxes,Alginate

6. BASED ON THE TYPE OF TRAY Perforated metal tray: Alginate hydrocolloid Water cooled metal tray: Agar hydrocolloid Custom tray: Zinc oxide eugenol,Impression plaster,Elastomeric impression material

7. IDEAL REQUIREMENT OF IMPRESSION MATERIALS They should be fluid enough to adapt to the oral tissues. They should be viscous enough to be contained in the impression tray. They should have a pleasant door,taste and color. Satisfactory consistency,texture and should wet the oral tissues. They should set within a suitable amount of time once seated in the mouth. The set material should not distort or tear during removal from the mouth.

8. It must be dimensionally stable atleast till the cast is poured. It should be cost effective. It should be stable for a long period of time long enough to permit pouring of the cast. It should be readily disinfected without any loss of accuracy ***No impression material fulfils all the ideal requirements.

9. THE SIX IMPORTANT STEPS INVOLVED IN CREATING A DUPLICATE CAST OF THE ORAL TISSUES PREPARATION OF THE TRAY PREPARATION AND LOADING OF THE IMPRESSION MATERIAL ONTO THE TRAY MAKING AN IMPRESSION REMOVAL OF THE IMPRESSION FROM THE ORAL CAVITY DISINFECTION OF IMPRESSION PREPARATION OF THE CAST,MODEL /DIES

10. ALGINATES

11. HISTORY The making of impressions to construct dentures have always been difficult. Most failures were due to the fact that compound wax would usually distort and plaster impressions had to be removed in fragments and put together with sticky wax. This would result in  inaccurate reproduction of the tissues and undercuts around the teeth. Only a material that was sufficiently elastic so that it could be removed from the mouth without distortion could solve this problem . As a result, flexible impression materials which remain elastic after setting were developed.

12. The concept evolved from the use of jelly mould for making impressions of still life objects such as statues. In 1925,Alphonse Poller ,an Austrian  invented and patented a material called Nogacoll . In 1931, after the inventors death, the formula was acquired by a company that sold it under the name of Kelco . Within a few years a dozen competing brands were in the market,mainly reversible hydrocolloids, with the main ingredient being agar, which is the vegetable colloid derived from   seaweed.This jelly like substance softened when heated and set when cold.

13. The technique of using this was complicated because of the need for special heaters, syringes and water cooled trays. When the types of agar used for the manufacture were no longer available in America during the Second World War the need for brown algae increased.

14. STRUCTURAL FORMULA OF ALGINIC ACID Derived from brown seaweed (algae) A linear polymer with numerous carboxyl acid groups and named anhydro -β-d mannuronic acid-also called as alginic acid. Alginic acid and most of the inorganic salts are insoluble in water ,but the salts obtained with sodium,potassium and ammonium are soluble in water.

15. Easy to manipulate Comfortable for the patient Patient  acceptability is high Inexpensive Hydrophilic,hence can displace blood and saliva Easy to pour and retrieve cast Compatible with gypsum Does not require elaborate equipment  Elastic in nature ADVANTAGES OF ALGINATE

16. Might tear on removal from mouth Must be poured immediately because - dimensionally unstable due to syneresis and imbibition Can pour the cast only once Cannot be electroplated Limited detailed reproduction DISADVANTAGES

17. COMPOSITION SODIUM / POTASSIUM ALGINATE-18% Main reactive ingredients Forms sol with water and becomes cross linked to form gel after reacting with calcium ions. CALCIUM SULFATE DEHYDRATE-14% Reacts with potassium alginate to form an insoluble calcium alginate gel,source of calcium ions which form cross linking of the alginate chains which provides calcium ion reactor. POTASSIUM SULFATE,ZINC FLOURIDE,SILICATE AND BORATES-10% Counteracts the inhibiting effect of hydrocolloid on the setting of gypsum,thus ensuring that the surface of the stone cast poured in the alginate impression will be of good quality. DIATOMACEOUS EARTH/SILICATE-50-60% Acts as a filler to increase the strength and stiffness of the gel,produces a firm gel surface that is not tacky

18. SODIUM PHOSPHATE-2% Reacts preferentially with calcium to provide ample working time before gelation GLYCOLS To make the powder dust free PIGMENTS-traces to provide colour PEPPERMINT CHLORHEXIDINE-traces To produce a pleasant taste QUATERNARY AMMONIUM SALTS-1-2% Disinfection of micro-organisms SODIUM SILICA FLUORIDE-4% Controls pH (gives a color change when setting is complete)

19. SETTING REACTION

20. When mixed with water, chemical reaction occurs that cross-links the polymer chains. Simultaneously a physical change is also taking place, forming a three-dimensional network structure. This is an irreversible process, therefore this can be used only once. (chemical reaction-irreversible) SOL GEL

21. Sol-gel reaction can be explained as Soluble alginate+Calcium sulphate Formation of insoluble calcium alginate gel. (This forms rapidly thus reducing the working time) To prevent this Trisodium phosphate is added to prolong the working time (thus calcium reacts with this rather than reacting with the soluble alginate) When the supply of trisodium phosphate is exhausted ,the calcium ions begin to react with the potassium alginate to produce calcium alginate The setting time can be observed from the time of mixing until the material is no longer tacky or sticky when it is touched with a clean,dry,gloved finger

22. Later, when the phosphate ions are consumed , the calcium ions react with the soluble potassium alginate to form an insoluble calcium alginate gel. The reaction results in tying altogether a chain of molecules of the salt into a network structure typical of gels. The calcium ions that are released from the calcium sulphate ,  act as a cross-linking agent.

23. The temperature of water controls the rate of the setting reaction. Warm water increases the setting rate and cooler water slows the setting reaction. Alginate is supplied by most manufacturers in the regular set and fast set variety . Regular set gels in 3 to 4.5 minutes where is fast set materials gels in 1.5 to 3 minutes.

24. PROPERTIES Working time-defined as the period from the beginning of mix till the impression material no longer is able to adapt and reproduce finer details of the surface. The impression must be thoroughly mixed, loaded into the tray and seated in place during this period of time.

25. CONTROLLING THE SETTING TIME Fast setting-1. 5 to 3 minutes Slow setting-3 to 4.5 minutes  The setting time can be altered by altering the temperature of water. Materials exhibit different degrees of sensitivity to temperature. In hot weather special precautions should be taken to provide cool water for mixing so that premature gelation does not occur. It may be necessary to pre-cool the mixing bowl and spatula.

26. FACTORS AFFECTING THE SETTING TIME Changing the water powder ratio The setting time can be modified to some extent by controlling the temperature of the mixing water Decreasing the water temperature increases the setting time  Using water at an elevated temperature reduces the working time and setting time

27. Alginate material adjacent to the oral tissues sets more rapidly, while that adjacent to the cooler tray sets more slowly. Hence one must ensure that the impression tray is not moved during setting else distortion occurs .

28. Setting time is detected by the loss of surface tackiness. Colour changing alginates provide a visual indication of working and setting time. The mechanism of colour change is the pH related change in the colour of the dye. How to check setting of the material???

29. CAUSES OF DIMENSIONAL CHANGES IN ALGINATE Alginate loses or gains water which is trapped within the gel by syneresis, imbibition and evaporation. Since the impression is removed from the mouth and exposed to the air at room temperature, some shrinkage will take place due to syneresis and evaporation.  If immersed in water, swelling will take place due to imbibition. Thermal changes also contribute to dimensional changes. With alginates, impressions shrink slightly because of the thermal difference between the mouth temperature (37℃)and the room temperature(23℃)

30. METHODS TO AVOID DIMENSIONAL CHANGE  For best results the impression should be exposed to air for as short as possible The cast can be poured immediately The impression should be stored in hundred percent relative humidity in a plastic bag /wrapped in a damp cotton.

31. STRENGTH Maximum gel strength is required to prevent fracture and to ensure elastic recovery of the impression upon its removal from the mouth. Insufficient spatulation results in failure of the ingredients to mix properly. Overmixing can break up the calcium alginate gel network as it forms and weakens its strength.

32. Spatulation time Spatulation done insufficiently-results in failure of the ingredients to dissolve sufficiently and decreases the strength Overspatulation-breaks off the calcium alginate gel network by incorporating  air bubbles and reduces its strength

33. Permanent Deformation It mainly depends on Degree of undercut Thickness of material between the tissue and the tray Time duration for which it remains  compressed Recovery time after the release of the load

34. Precautions to reduce permanent deformation of impression Ensure that there are no deep undercuts, greater it is greater the amount of compression leading to permanent deformation Sufficient bulk of material between the tissue and the tray approximately 5 mm Remove the impression in a snapshot manner The degree of cross-linking continues to increase after the material has apparently set. Waiting a minute or two before removing the impression enhances the elastic nature of the material. Long recovery time results in lower permanent deformation

35. Flexibility ADA specification limits a range of 5 to 20% at the stress of 1kg/ cm². Typical values for commercial alginates, are between 12 to 18%, whereas hard setting alginates are 5 to 8 %. Thicker mix this results in lower flexibility.

36. Disinfection Since the hydrocolloid material must be poured within a short time the disinfection procedure should be relatively rapid to prevent dimensional changes. Studies have shown that test viruses have been inactivated in alginate impression by 10 minute soak in 0. 5% sodium hypochlorite   or a 10 minute wait after spraying the impression with this solution ,or a 10 minute immersion in gluteraldehyde .

37. Clinical significance Alginate impression must be removed from the mouth after breaking the peripheral seal. When gelation is complete ,the impression is removed with a sudden pull. Avoid torquing or twisting the impression in an effort to remove it quickly  Permanent distortions due to viscoelastic effects and tearing are reduced slightly by using a large bulk of material. It is better to have approximately 3 to 5 mm of material between the tissue and the tray.

38. Compatibility with gypsum The impression must be rinsed well in water to remove saliva and blood as it interferes with the setting of the gypsum model. After disinfection all the free water should be removed before pouring in stone, as residual water  will dilute the model material and result in a soft, chalky surface of the model which will be easily damaged. SODIUM SULPHATE???

39. A rough stone will result if excess rinsing water has collected on the surface of the impression at the time the stone mixture is poured. Excessive dehydration can also cause syneresis and dehydration of the impression.The surface of the impression should be shiny but with no visible water film or droplets at the time the impression is poured with model or die material. The stone cast should be kept in contact with the impression for a minimum of 30 minutes ,preferably for 60 mins,before the impression is separated from the cast.

40. Objectives for taking alginate impressions All teeth in the upper and lower arch The entire alveolar process The retromolar area of the lower arch The area of the hamular notch in the upper arch A detailed ,undistorted and bubble free reproduction of the oral tissues.

41. Selection of the tray Completely cover the tuberosity Be 4 mm wider than the most apical portion of the alveolar process at the molar region Cover the anterior teeth with the incisors contacting the flat portion of the tray about 4 mm from the rest palatal part of the tray FOR MAXILLARY TRAY

42. CRITERIA FOR MANDIBULAR TRAY Cover all teeth and the retromolar pad Be 4 millimetre wider than the buccal and lingual portions of the anterior teeth 

43. Modification of the tray To be sure the alginate flows into the labial vestibule when the impression is added,rope wax may be added to the anterior surface . The rope wax may be added to other borders to make sure that any extensions of the alginate are well supported.

44. Dispensing and storage    Alginate is made available in either a sealed pre weighed packet/ or in bulk form For correct proportioning of the powder and water ,the manufacturer supplies a suitable measuring spoon. Individual pouches are preferred because there is less chance for contamination during storage.

45. Shelf life is affected by storage temperature and moisture. The powder should be mixed thoroughly before use to eliminate the segregation that may occur during storage and to incorporate the surface layer,which is often contaminated with moisture picked up from the atmosphere. Material should be stored in a dry place with the lid tightly closed in bulk packing.

46. MANIPULATION EQUIPMENT REQUIRED ALGINATE PLASTIC MEASURING CYLINDER FOR WATER(with special markings provided to measure the correct amount of water) SUPPLIED SCOOP FOR POWDER RUBBER MIXING BOWL STIFF WIDE BLADED STEEL SPATULA PERFORATED TRAY IS SELECTED.

47. PROPORTIONING Measure cool (18℃/24℉) water for required number of scoops. Amount of alginate powder depends on the size of the arch. Normally 18-20 grams of powder is sufficient for an impression of one arch. When dispensing the powder,the scoop is used to remove the appropriate amount of powder by filling it and levelling it with the blade of the spatula.

48. Fluffing is required as materials supplied in large quantities have a tendency to undergo separation as the dense ingredient falls to the bottom of the container. This must be overcome by inverting the container before use so it prevents impaction of the powder and ensures that the reproducible volume of material is used in each mix. Correct amount of water is emptied into the mixing bowl first ,then the alginate is carefully dispensed onto the surface of the water.

49. Mixing the alginate Stir powder and water vigorously to wet powder completely,care should be taken to avoid whipping air into the mix-to avoid this problem a vacuum mixer can be used. Vigorous figure of eight motion is best,with the mix being swiped against the sides of the rubber mixing bowl with intermittent rotations of the spatula to press out air bubbles. Wipe the mix against the side of the bowl for 60seconds to homogenise and remove air bubbles.

50. The entire spatulation should take approximately 1 minute,fast setting should be accomplished in no more than 45 seconds. Care should be taken not to overmix ,because this limits the working time and breaks up the gel that is forming,thus reducing the strength of the final alginate. Inadequate mixing procedures produces a grainy material with low strength. Mix should be creamy , thick,smooth consistency that does not drip off the spatula when it is raised from the bowl.

51. Making the impression  Push the left corner of the mouth away with the side of the tray Insert the tray with the rotary motion Place the left heel of the tray in contact followed by the anterior and then the right heel Have the patient lift the tongue and with the free hand pull the lip down gently. Seat the tray in the direction of the long axis of the anterior teeth, and alginate should flow into the vestibule Apply the seating force moderately slowly to allow the alginate to flow properly For lower arch

52. At final seating the incisal edges and cuspal tips should be atleast 1 to 2 mm from the metal surface of the train The tray is held in position until the alginate has set, which is about one minute after it has lost its tackiness testing by touching two persons with the finger. The set impression is removed with the rapid ,firm pull.

53. For upper arch impressions Start seating the tray by positioning it's posterior border and  then continue seating parallel to the axis of the central incisors so that most of the excess alginate flows both in labial or buccal direction but not in a palatal direction. Break the peripheral seal by running a finger around the edge and remove the impression with the rapid firm full,and use a downwards sideways flipping motion to remove the impression.

54. A thick,pasty consistency can sometimes cause some patients to gag.Although gagging has a physical component,it is atleast as much psychologically as well as physically induced. Therefore how you approach patients has a bearing on whether they gag or not. To prevent gagging,avoid anxiety producing actions or words,be gentle and practice patient distraction.Very occasionally you may need to use topical anaesthetic,a lozenge etc. Educate the patient regarding the upcoming procedure. Just say "I am going to take a duplicate of your teeth rather than saying I am going to take a bowl full of material and put in your mouth till it hardens".This will increase their tendency to gag, PREVENTION OF PATIENT GAGGING

55. Pleasant conversations distracts the patients. Tipping the patients head back slightly for mandibular impressions and forward for upper impressions helps loosen the muscles. Some patients will gag despite your best intentions.Having these patients lift their leg off the chair helps distract them.Remind them to breathe deeply through their nose and tell them not to swallow their saliva. In worst cases nitrous oxide helps relax the patient and can be administered to allow an impression to be taken.

56. COMMON CAUSES OF REMAKING HYDROCOLLOID IMPRESSIONS GRAINY MATERIAL Improper mixing Prolonged mixing Excessive gelation Water/powder ratio too low TEARING Inadequate bulk Moisture contamination Premature removal from mouth Prolong mixing

57. EXTERNAL BUBBLES Undue gelation preventing flow Air incorporated during mixing IRREGULARLY SHAPED VOIDS Moisture or debris on the tissue ROUGH OR CHALKY STONE MODEL Inadequate cleaning of the impression Excess water left in the impression Premature removal of the impression Model left in impression for too long Improper manipulation of stone DISTORTION Impression not poured immediately Movement of tray during gelation Premature removal from mouth improper removal from mouth

58. MODIFIED ALGINATES ALGINATES IN THE FORM OF SOL Traditional alginate material is used as a 2 component system of powder and water in which no reaction occurs till the powder is added to the water to initiate the reaction. However,the alginate can be purchased in the form of a sol ,containing water but no source of calcium ions. A reactor of plaster of Paris can then be added to the sol.

59. SILICONIZED ALGINATES Considered as hybrids of alginate and silicone elastomers. Alginates modified by the incorporation of silicone polymers. Supplied as 2 paste which are mixed together. One alginate sol and the other calcium reactor. Impression materials of this type may be supplied both in tray viscosity and in syringe viscosity. They are resistant to tearing when compared to modified alginates.

60. DUST FREE ALGINATES Alginate powder contains silica dust,a potential biohazard when inhaled. Modern alginate powders are coated with glycerin so that the particles agglomerate ,which keeps them from generating dust when the can is shaken just before being opened.

61. CHROMATIC ALGINATES The main purpose of adding indicator is to show the different stages during manipulation and helps the operator during impression making.Chemical reaction takes place and it is shown by change in color in each stage. Pink colour - during spatulation Orange colour -during loading White colour -when the material sets

62. LAMINATE TECHNIQUE The hydrocolloid in the tray is replaced with a mix of chilled alginate that bonds to the syringe agar.The agar gels by means of contact with the cool alginate ,rather than water circulating through the tray and alginate gels by a chemical reaction. ADVANTAGES Good surface details recorded by agar. Preparation time is less. Cost effective.

63. DISADVANTAGES The higher viscosity alginate may displace the agar during setting. Bond between agar and alginate is not always strong.

64. BIOHAZARDS DUE TO ALGINATE SILICOSIS It is important that care is taken to avoid inhaling the dust especially when opening the container after shaking it to fluff up the powder. Now dustless alginates have been emulated to reduce this risk. It can also result in pulmonary fibrosis which can be progressive and may lead to death. INGESTIONS - may result in intestinal obstructions.

65. RECENT ADVANCES IN ALGINATES PROBLEMS WITH ALGINATE Alginate is one of the most commonly used impression material but there are few disadvantages of this material It has poor dimensional stability ,must be poured within 10 to 12 minutes impression making or distortion becomes a major issue and can be poured only once. Tear strength of hydrocolloids is low ,it may capture sub gingival contours and anatomy but may tear upon removal.

66. They have a tendency to stick to the teeth,which occurs when alginate radicals in the impression material form chemical bonds with hydroxyapatite crystals of the enamel.On removal of the impression the alginate tears. It consists of silica dust in the form of diatomaceous earth which are highly toxic. Poor adhesion with tray.

67. ADVANCES EXTENDED POUR ALGINATE If the alginate is poured within 15 minutes ,it can be used as a final impression material but if not poured it can cause dimensional changes. CAVEX color change (extended pour alginate) is designed for use with alginate which enables to delay pouring up impression under specified storage conditions. A recent investigation reported that storage of alginate upto 100 hrs did not result in significant dimensional changes. Extend-A Pour from Van-R reportedly preserves the alginate impression for upto 4 weeks.

68. TRAY ADHESIVES FOR ALGINATE Conventional alginates do not exhibit retention to the impression trays and hence perforated trays are generally employed to achieve retention. Recently,a tray adhesive in the form of liquid and spray containing polyamide,ester gum and rosin in isopropyl alcohol or a combination of isopropyl alcohol with ethyl acetate has been introduced. Application of such adhesives prior to the loading of alginates was found to improve the bond strength of the alginate to the metal and plastic trays. Along with that Fix solvent is a spray to remove any remaining adhesive from the impression tray after making impressions.

69. DUST FREE ALGINATES Sepiolite,a natural mineral fibre containing magnesium silicate, about 20% was added to alginate as a substitute. When added it traps the alginate particles thus reducing dust generation.

70. INFECTION FREE ALGINATES To avoid dimensional inaccuracies associated with disinfection process,manufacturers have incorporated disinfectant materials into the alginate such as quaternary ammonium compounds,chlorhexidine etc without altering its properties.Further studies showed that Epimax showed the highest disinfection after 10 minutes.

71. MIXING DEVICE A mixer for alginate has a rotatable bowl and one or more nozzles positioned above the opening of the rotatable bowl for injecting water into the bowl. The dual-chamber package includes a first chamber containing a pre-measured volume of water and a second chamber attached to and isolated from the first chamber and containing a pre-measured quantity of alginate powder where in the quality of powder and volume of water are in a pre-determined ratio for making a dental impression paste when mixed together.

72. DISCUSSION

73. CONCLUSION

74. TEXTBOOK REFERENCES Anusavice KJ.Philips Science of Dental Materials.12th Edition,2013 John F.McCabe.Applied Dental Materials.9th Edition Gladwin M.Clinical Aspects of Dental Materials.3rd Edition Powers JM.Craigs restorative dental materials.12th Edition Noort RV.Introduction to Dental materials.3rd Edition,2007

75. JOURNAL REFERENCES Demajo K. Effectiveness of disinfectants on antimicrobial and physical properties of dental impression materials.Int J Prosthodont 2016:29:63-67 . Kaur G,Jain P,Uppal M. Alginate Impression material-From then….Till now.Heal Talk,2013;5(2). Amalan A,Kishore G.Evaluation of properties of irreversible hydrocolloids mixed with disinfectant liquids.J Dent Res.2013 ;10(1):65-73. Hamid B,Ehsan G,Navid K. The effect of three different disinfection materials on alginate impression by spray method.ISRN Dent.2012;6:1-5. Shushing G,Sanjeev M,Sanjay B.A study on imbibition and syneresis in four commercially available irreversible hydrocolloid impression material.Int J Prosthodont.2012:2(1):1-4.

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