Hydrocolloid impression materials

hydrocolloid impression materials, agar and alginate impression materials and properties of the same.
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1. Hydrocolloid Impression Materials In Dentistry Presented by – Piyali bhattacharya 1 st year PGT Dept . Of Prosthodontics Crown & Bridge HIDSAR

2. What is An Impression ? a negative likeness or copy in reverse of the surface of an object ; an imprint of the teeth and adjacent structures for use in dentistry (GPT-9) I mpression area : The surface that is recorded in an impression Impression Material: Any substance or combination of substances used for making an impression or negative reproduction.

3. Ideal Requirements Of An Impression Material Dimensional Stability Adequate Strength Satisfactory Texture And Consistency Easy To Disinfect Without Loss Of Accuracy Compatible With Die And Cast Material Good Elastic Properties Easy Manipulation Adequate Setting Characteristics

4. 9.High Reproduction Of Details 10.Should Not Release Any Gas 11.Should Not Be Technique Sensitive 12.Economical 13.Not Contain Any Toxic And Irritating Component 14.Adequate Shelf Life 15.Pleasant Smell And Taste

5. CLASSIFICATION OF IMPRESSION MATERIAL RIGID ELASTIC A.IMPRESSION PLASTER B.IMPRESSION COMPOUND C.METALLIC PASTE HYDROCOLLOIDS REVERSIBLE IRREVERSIBLE SYNTHETIC ELASTOMERS A.POLYSUFIDE B.POLYETHER C.SILICONE (ADDITION, CONDENSATION) Ref: Anusavice 11 th edition 209

6. What is Colloid Solution or Sol ? 4 TH state of matter.. It is somewhere between solution and suspension 2 phases- i) dispersed phase(primary or secondary forces) ii) dispersion phase If the dispersion phase of the colloidal system contains water, it is called hydrocolloid. Ref: Anusavice 11 th edition 231 INTRODUCTION

7. Based on the mode of gelation, they are classified as: i ) reversible hydrocolloids agar ii) irreversible hydrocolloids alginate Ref: Sanjay Madhavan et al /J. Pharm. Sci. & Res. Vol. 7(9), 2015, 704-707

8. AGAR(ADA Sp. No . 11 ) Reversible hydrocolloid was introduced to the dental profession in 1925 by Alphons Poller , an Austrian as impression material . Agar was first introduced into dentistry for recording crown impressions in 1937 by Sears . Sanjay Madhavan et al /J. Pharm. Sci. & Res. Vol. 7(9), 2015, 704-707

9. Type I: High Consistency(Tray Material) Type II: Medium Consistency (Tray/Syringe Material) Type III: Low Consistency (Syringe Material) Classification (ISO 1564:2001)

10. Uses: 1.Full mouth impression without deep undercuts 2.As a tissue conditioner 3.As duplicating material 4.Earlier it was extensively used for FPD impression prior to elastomers

11. Composition & Functions Of Each Components: Agar (13%-17%)- Brush-heap structure Borate(0.2%-0.5%)- Strength Sulfate(1%-2%)- Gypsum Hardener Wax(0.5%-1.0%)- Filler Thixotropic materials(0.3%-0.5%)-Thickener Water –Reaction medium

12. Brush –Heap Structure Of Hydrocolloid

13. Agar Conditioning Unit

14. Rim Lock Tray

15. Tray Selection for Agar http://www.juniordentist.com/agar-reversible-hydrocolloid-impression-material.html

16. STEPS OF MANIPULATION Preparation And Conditioning Of The Material Tempering The Material Making The Agar Impression

17. Working time: 7-15 minutes Setting time: 5 minutes

18. Accuracy : One of the most accurate impression materials which has a long history of successful use in dentistry. Viscosity of The Sol: The material must be viscous enough even after it has been liquefied in order to prevent itself from flowing out of the tray when it’s inverted e.g.; while making a mandibular impression.

19. Even when the material is viscous enough to stabilize the tray it does not offer much resistance to seating Also patient may “bite through” the impression material.. With a “ Triple Tray Technique ” the oral impression of the maxillary ,mandibular arches as well as occlusal relationship can be recorded although it is technique sensitive procedure.

20. Distortion during Gelation: As the material undergoes physical change from Sol to Gel contraction occurs (usually in the center of the tray, resulting in larger dies) As the Sol is a poor conductor of temperature , rapid cooling of the tray causes stress concentration near the tray where the gelation first occurs. Ideally water at 20 ℃ is most suitable for cooling the impression tray than ice water.

21. Properties 1.Gelation, Liquefaction And Hysterisis Gelation at 37 ℃ Liquefaction at 60 ℃ - 70 ℃ 2.Syneresis And Imbibition Whenever immersed into water agar doesn’t imbibe the original amount of water as it loses by evaporation 3.Flexibility : Between 4-15% with application of 14.2 Psi pressure

22. 4.Elasticity and elastic recovery Highly elastic in nature, elastic recovery is about 98.8% Strength: Tear strength of agar 0.8-0.9 N/mm Shelf-life: One year.

23. Alginate(ADA Sp. No. 18 ) Introduction: In 1921 in England a chemist , sir William Wilding received a basic patent for using Algin as a dental impression material Was introduced as a substitute for agar when its’ supply became scarce after WW II. The material is based on substances extracted from certain brown seaweed (anhydro – β - δ - mannuronic acid/ alginic acid ).

24. Properties of Alginate Impression Material: Pleasant taste and smell Highly flexible good elasticity and elastic recovery Fine reproduction of details Compressive strength 0.33-0.70 MPa Tear strength 350-700 gm/cm ² Poorly adheres to the tray

25. Uses: Used for making preliminary impression to construct custom tray, make study models , help in treatment planning. As alginate is hydrophilic in nature, impression can be recorded even on moist oral tissues

26. Composition & Their Function Potassium Alginate (15%)- Soluble Alginate (Or Sodium Alginate) Calcium Sulfate(16%)- Reactor Zinc Oxide(4%)-Filler Particle Potassium Titanium Fluoride(3%)- Accelerator Diatomaceous earth (60%)- Filler Particles Sodium Phosphate (2%)- Retarder

27. Gelation Process: Typical Sol-Gel reaction . 1.Reaction between soluble alginate with calcium sulfate & formation of insoluble calcium alginate . This is a rapid reaction and thus doesn’t allow much w orking time. 2.Trisodium phosphate (water soluble salt) is added to prolong the working time. Calcium sulfate first reacts with this salt & reaction with alginate is deferred as long as the unreacted trisodium phosphate is left.

28. 1. K2n- alginate +n CaSO 4 Ca n-(alginate) +n k 2 SO 4 (powder) (gel) 2 . Na 3 PO 4 + 3 CaSO 4 Ca 3 (PO 4 ) 2 + 3 Na 2 SO 4

29. The final structure Sodium/potassium alginate cross- linked with calcium ions. The Final Gel Structure

30. Setting Time : Depending on setting time Fast setting (1.5-3 min) Normal setting Alginate(3-4.5 min) Controlling the setting time: W/P ratio: affects properties e.g.; tear strength and elasticity Amount of retarder Alteration of temperature of water: a 1 – min reduction in setting time occurs for each 10 ℃ of temperature increase

31. Effect Of Temperature On Setting Time * Setting time in minutes & temperature in ℃

32. Manipulation 1.Measured powder is sifted into premeasured water into a clean rubber bowl 2.The powder is incorporated into water by carefully mixing with a metal spatula in vigorous figure of 8 motion with intermittent rotations (180 ◦ ) of spatula to press out air bubbles powder should always be weighed not measured. Mixing time: 45 sec-1 min Ideal w/p ratio: 38 ml water/16 gm. powder

33. Making The Impression A perforated tray is usually used .if plastic or metal rim-lock tray is used , a thin layer of alginate tray adhesive is applied and allowed to dry before mixing and loading the tray. As alginate is weak the tray must fit into the patient’s mouth to provide sufficient bulk of material. The thickness of alginate between tray and oral tissue should be 3 mm.

34. The compressive strength of alginate doubles the first 4 mins but after 4 mins it does not increase much Alginate impression material should be kept in the mouth for at least 3 min after the gelation has already occurred . Removal of Impression: The tear strength of alginate increases if the impression is removed with a snap Avoid torqueing or twisting of impression

35. The tray must be filled with the impression material up to the tray border The tray is filled by forcing the material firmly into the tray to make sure voids are not trapped. A useful method is to start at the posterior of the tray and push the mix anteriorly by adding more and more to the posterior . The excess unsupported material at the periphery must be removed with the mixing spatula The surface of the mix should be wiped with gloved finger Tray Selection

36. Impression tray is positioned in the mouth by retracting the patient’s lip on one side with a mouth mirror /gloved finger ; and on the other side by rotating the tray into the mouth. The tray has to be centered in position in the mouth ; and with light pressure, so that alginate can flow properly and impression held in place. IMPRESSION MAKING

37. While making the impression, the tray should cover the entire impression area & provide a space of at least 3 mm on all sides.

38. Properly Made Alginate Impression

39. Factors affecting the strength of the gel 1.Adequate w/p ratio: Too much or too less water weakens the gel 2.Adequet spatulation: over mixing breaks up the calcium alginate network and reduces the strength. Accuracy Alginates are sufficiently accurate for making impression for removable partial dentures. However, as compared to elastomeric impression materials, alginate do not produce finer details

40. Tear Strength The tear strength is a measure of force/thickness ratio needed to initiate or continue tearing. Ranges from- (0.37 to 0.69)N/mm Tearing occurs in the thin sections of the impressions and the probability of tearing decreases with the increase in rate of removal

41. Effect Of Rate Of Deformation On The Tear Strength Of Alginate Material

42. Properties of Alginate 1.Flexibility: About 14% at stress of 1000gm/cm2 .Some of the hard set materials have lower elasticity(5-8%)lower w/p ration results in lower flexibility 2.Elasticity & Elastic Recovery: Less elastic when compared to agar impression material.it Is about 98.2%.thus permanent deformation is more for alginate, but when set impression is removed early from mouth , permanent deformation is less 3.Reproduction of tissue detail: Lower when compared to agar.ADA sp. Requires this material to reproduce a line that is 0.075 mm in width 4.Strength: Compressive strength: 0.33-0.70MPa

43. Other Applications of hydrocolloids

44. Laminate Technique

45. Duplicating Material Both hydrocolloids can be used for duplicating casts or m odels to construct prosthetic appliances & orthodontic models But agar is more popular as it can be used many times With intermittent stirring agar can be kept liquid for 1-2 Weeks at a constant pouring temperature. Duplicating materials have the same composition as the impression material except, they have a higher water content & a lower agar / alginate content compromising its compressive strength & percent permanent set. This property requirement is identified as ADA specification no. 20

46. Hydrocolloids should be disinfected for a limited time period . Immersion is more secure than spraying and self-disinfecting materials are efficacious, but better accompanied by immersion. Most manufacturers recommend iodophor , gluteraldehyde , phenol as disinfectants E . k o t s i omi t i et al ., Dimensional changes of disinfected i m p r e s s i o n s, Journal of Oral Rehabilitation 2008 35; 291–299 Disinfection of hydrocolloids

47. The addition of 1% chlorhexidine di acetate to Alginate has decreased its compatibility with the dental stones when compared with its non-antimicrobial counterpart. In terms of gypsum compatibility, the non-antimicrobial Alginate was compatible with all disinfectant and gypsum combinations. King , Norling , and Seal, Compatibility /Antimicrobial Alginates, Journal of prosthodontics. Vol3, No 4 ( December), 1994:pp219-227

48. The current protocol from the CENTER for DISEASE CONTROL is to use house hold bleach, ( 1-10 dilution ), Iodophor , synthetic phenol as disinfectants . After impression is rinsed thoroughly under water, disinfectants can be sprayed . then impression is wrapped in disinfectant soaked paper towel & placed in a plastic bag for 10 minutes. Finally, impression Is taken out of bag unwrapped, rinsed, shaken to remove excess water and poured with stone.

49. Dimensional stability of Hydrocolloids In case of Agar, if the impression is left exposed in the air at room temperature shrinkage occurs due to syneresis. If the impression is immersed into water, swelling occurs due to imbibition 2% Potassium sulfate or 100% relative humidity are suggested to prevent dimensional change of agar. Alginate impression materials shrink slightly because of the thermal differential between mouth temperature (37 ˚c ) and room temperature(20 ˚ c ).While agar impression material shows a temperature shift in opposite direction , from chilled water to warmer room temperature makes the impression to expand and become less accurate

50. Linear contraction of reversible hydrocolloid in air(31%-42% relative humidity) & subsequent Expansion in water Percentage change in water content according to weight of agar hydrocolloid in Various storage medium, at 100% humidity The percent change is minimal

51. Compatibility With Gypsum Borax , which is a gypsum retarder is used as a filler in agar impression material which may cause surface of gypsum casts prepared from agar to be soft for using as dies. The gelation process of alginate impression produces calcium alginate & sodium sulfate which is a gypsum accelerator at low concentration & a retarder at high concentration . The amount of sodium sulfate produced becomes enough to retard the setting of gypsum cast

52. Means To Counteract: By immersing impression in accelerator such as 2% potassium sulfate solution prior to pouring impression with gypsum product 2. By using products that incorporate gypsum hardener or accelerator e.g.; sulfate in agar & potassium titanium fluoride in alginate. The S tone cast/Die should be in contact with the impression material for at least 30min or preferably 60 min.

53. Separation of Cast : Separation of cast should be done within a reasonable period of time . As desiccation of the hydrocolloid may cause abrasion of gypsum during removal

54. Biocompatibility Silica particles present in alginate may cause silicosis ,pulmonary hypersensitivity, The most common side effect of reversible hydrocolloid is thermal injury due to improper tempering or faulty equipment during impression making

55. The Bio Hazard from Alginate Impression Materials BRUNE AND BELTESBREKKE, Airborne Particles of Alginate , Scand.J . Dent. Res . 1978: 86: 206-210

56. BRUNE AND BELTESBREKKE, Airborne Particles of Alginate , Scand.J . Dent. Res . 1978: 86: 206-210

57. Dust -Free Alginate Dust –Free Aginate : In attempt to minimize the risk from the dust , alginate is coated with Glycerin , Glycol, Polypropylene Glycol or Polyethylene Glycol

58. Advances in Alginate: 1.Extended-pour Alginate: enables to delay pouring impression under specified condition for up to 100 hrs without much dimensional change. Some extended pour alginate allows to delay pouring up to 4 weeks Kaur et. Al., Alginate Impression Material: from then till now .. Heal Talk | November-December 2012|volume 05| issue 2

59. 2. High Viscosity Alginates: By incorporation of hydrophobic material(.01-.1 wt %) or surfactants (0.05-0.1 wt %) permeation of water is speeded, Kneading time is shortened , incorporation of polysaccharides prevent gagging 3.Color Changing Alginate: By adding pH indicator. Although most pH indicator changes color little above pH 8 before the actual gelation time.

60. 4.Two Paste system: Base paste contains soluble mix of Alginate , water and fillers . With paste fo rming materials e.g.; Gum arabican , carrageenan Reactor/ catalyst paste contains calcium salt with viscous liq. l ike paraffin & a pH stabilizing agent (magnesium hydroxide) 5.Tray Adhesive for Alginate: A tray adhesive in the form of liquid or spray containing polyamide or diethylene tetra amine ether , ester gum and rosin containing isopropyl alcohol.

61. Two Paste System

62. Color Changing Alginate

63. Infection Free Alginate: Alginate incorporated with disinfectant materials such as quaternary ammonium compounds , bisguanides , chlorhexidine without compromising its’ properties Epimax showed highest disinfection action after 10 mins

64. EFFECT CAUSE Grainy material Improper mixing Prolonged mixing Excessive gelation water/powder ratio too low Tearing Inadequate bulk Moister contamination Premature removal from mouth Prolonged mixing External bubbles Undue gelation preventing flow air incorporated during mixing COMMON CAUSE OF FAILED ALGINATE IMPRESSIONS

65. Irregularly shaped voids Moisture or debris on tissue Rough or chalky stone model Inadequate cleaning of impression Excess water left in impression Premature removal of impression Model left in impression too long Improper manipulation of stone Distortion Impression not poured immediately Movement of tray during gelation Premature removal from mouth Improper removal from mouth

66. Shelf Life Two factors affecting the shelf life of alginate: 1.Storage temperature 2.Moisture contamination It is best not to stock more than 1 year’s supply in dental office. The material should be stored in a cool, dry environment

67. References 1. Ref: Anusavice 11 th edition 209 2. Sanjay Madhavan et al /J. Pharm. Sci. & Res. Vol. 7(9), 2015, 704-707 3. http:// www.juniordentist.com/agar-reversible-hydrocolloid-impressionmaterial.html 4. E . k o t s i omi t i et al ., Dimensional changes of disinfected i m p r e s s i o n s, Journal of Oral Rehabilitation 2008 35; 291–299 5. King , Norling , and Seal, Compatibility /Antimicrobial Alginates, Journal of prosthodontics. Vol3, No 4 (December), 1994:pp219-227 6. BRUNE AND BELTESBREKKE, Airborne Particles of Alginate , Scand.J . Dent. Res . 1978: 86: 206-210 7. Kaur et. Al., Alginate Impression Material: from then till now.. Heal Talk | November-December 2012|volume 05| issue 2