Impression Taking By Alginate

Impression Materials and Tecniques in Orthodontics

1. IMPRESSION MATERIALS AND TECHNIQUES IN ORTHODONTICS By , Dr. Rifat Waliullah

2. In orthodontics, impression gives a negative imprint 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 - STUDY PURPOSE FABRICATION OF APPLIANCES MAINTAINING RECORDS

3. 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. 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

4. Classification of the Impression materials based on: Se t t in g T h e r m o pla s t i c T h e r m o set Reaction Elasticity Elastic Non-elastic Reversible I rreversible Nature of the setting reaction Pressure Exerted on the tissue M u c o c o mp r e s s i ve M u c o sta t ic D e n t i t i o n status E d e n t u l o u s D e n t u l o us

5. In orthodontics we require impression materials that are elastic since we deal with dentulous patients The most commonly employed materials include Hydrocolloid – Agar Agar (reversible) - Alginate (irreversible) Elastomeric impression materials.

6. IRREVERSIBLE HYDROCOLLOID ALGINATE : A SODIUM SALT ANHYDRO-ß-D-MANURONIC ACID / ALGINIC ACID TYPES: TYPE I – RAPID OR FAST SETTING TYPE II – NORMAL SETTING

7. Pr oper ties # Alginates are sufficiently flexible to record fine detail in the mouth.. # 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. # The material is sufficiently elastic to be withdrawn over undercuts; occasionally tearing of the impression materials may occur with serious undercuts.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 # Short shelf life.Alginate impression material deteriorates rapidly at elevated temperature and The material should be stored in cool dry place.(not above 37c ) # 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.

8. • 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 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)

9. 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)

10. Impression Trays They are used to carry the impression material to the mouth in its plastic state till it sets.

11. T R A Y S S T O C K C UST O M PERFORATED NONPERFORTED

12. Disposable impression trays

13.  MAXILLARY TRAY The tray must completely cover the tuberosity Must be 4mm wider than the most apical portion of the alveolar process at the molar region. The tray must cover the anteriors with the incisors contacting the flat portion of the tray about 4 mm from the raised palatal part of the tray. Selection Of Impression Tray The tray should cover all the teeth as well as the retromolar pad The tray should be 4-6 mm wider than the buccal and lingual portion of the anterior teeth It must be possible to center the tray  MANDIBULAR TRAY

14. Prepration Of The Patient Explain the procedure to the patient in the simplest of terms so that the patient is aware of the procedure and therefore the fear of the unknown is over come. Seat the patient upright so as to prevent the gagging due to the backward flow of the excess material into the throat . Advice the patient to breath through the nose and in case of gagging try and distract the patient’s attention and ask the patient to look down wards . Practice the placement of the empty tray into the patient’s mouth

15. MANIPULATION The recommended water powder ratio should be used. In general it is 38 ml of water per 16 gms of powder but slight variation can be presented depending on the manufacturer. The weighed power is incorporated into the water by carefully mixing with the spatula. Care should be taken to ensure that air is not incorporated into the mix by spatulating the mix against the side of the bowl while using the vigorous figure of 8 motion till a smooth creamy mix is obtained.

16. SEQUENCES OF IMPRESSION MAKING It is advisable to make mandibular impression first as there is less chance of the patient to gag .This allows the patient to become accustomed to the taste and the feeling of the material in the mouth which in turn reduces the chances of gagging while making an impression of the maxillary arch.

17. SEATING THE IMPRESSION TRAY Mandibular Impression Operator position at 7 O’clock Patient seated such a way that the occlusal plane placed parallel to the floor. Use the thumb and the index finger of the free hand to retract the cheek. Grasp the handle of the tray and rotate the tray into the mouth by using the front of the tray to deflect the other cheek . Once inserted straighten the tray so that the tray is in line with the patient’s midface Note the position of the tray in relation to the anteriors . Using the index finger of both the hands press the tray downwards Manipulate the patients cheeks and lips to create a more detailed anatomy of the facial and vestibular area. Ask the patient to raise the tongue and then move it from side to side. Allow the material to set and then remove. Using a firm grip on the tray handle, use a side ways lifting motion to remove the tray.

18. Maxillary Impression Operator position at 11 O ' clock position Patient seated such a way that the occlusal plane placed parallel to the floor. A blob of material may be placed in the palatal vault of the patient just b e h ind the inci s o rs, to eli m inate the trapped air and t o e nsure the faithful reproduction of palatal tissue . Use the thumb and the index finger of the free hand to retract the cheek . Once inserted straighten the tray so that the tray is in line with the patient’s mid face . Begin to apply light pressure upwards till the light resistance is felt.

19. Impression Taking Technique

20. Disinfecting The Impression Disinfection of impression is a concern due to viral diseases such as Hepatitis B,A I D S and herpes simplex Gently rinse the impression under the tap water to remove any debris that may be retained in the impression. Gently shake the excess water. Spray the entire impression with an O.S.H.A. (occupational health and safety administration) approved disinfecting solution. OR May immerse the impression in a disinfectant such as : gluteraldehyde solution Iodophors 1:10 dilution of sodium hypochlorite synthetic phenols

21. Criteria For Accessing The Impression Lack of voids. No distortion , clear and distinct impression Adequately extended. Free of debris and extraneous material. Adequate details and all structure must be recorded. Stable material which is sufficiently attached to the tray.

22. CAUSES OF FAILURE 1. Grainy material 2. Tearing 3. External bubbles Improper mixing Prolong mixing Undue gelation Water : powder ratio too low Inadequate bulk Moisture contamination Premature removal from mouth Prolong mixing Undue gelation, preventing flow Air incorporated during mixing

23. 4. Irregularly shaped voids Moisture or debris on tissue 5. Rough and chalky stone model Inadequate cleansing of impression Excess water or potassium sulfate solution left in impression Premature removal of model 6. Distortion Impression not poured immediately Movement of tray during gelation Premature removal from mouth

24. CONCLUSION One must not depend on a material to provide good impressions. A n y m a t e r i a l is g ood an d s h ould b e used till the operator is familiar with its characteristics Selecting the impression material depends on the convenience of the dentist and clinical situation. ALL WE NEED IS AN ACCURATE IMPRESSION. Thank You