1. Tissues Treatment before Impression Department of Prosthodontics Dr. Lan Jing

3. Biologic Width review

4. Preparation Margin Extra sulcular Intra sulcular  Esthetic  Good Retention  Prevent Radicular Caries  Control Ferula Effect

5. The weak link between the tooth and the restoration is the correct impression

6.  Definition: the deflection of the marginal gingivae away from a tooth  Purpose: expose the finish line provide a space for impression material gingival displacement gingival retraction

7. the techniques used for gingival displacement surgical method mechanical method chemico-mechanical method

8. Chemico-Mechanical Method Retraction Cord Chemical drug Epinephrine Aluminum Chloride Alum(aluminum potassium sulfate) Ferric Sulfate Aluminum Sulfate

9.  Double Cord Technique: using two cords I like use #00 and #0  Single Cord Technique: using only one thick cord I like use #1 Techniques:

10. Double Cord Technique  First cord--------thin cord  at bottom of the gingival crevice （龈沟）  vertically and horizontally displace gingival margins  It is not removed during impressing  Second cord--------thicker cord  on top of the first cord  achieve horizontal tissue displacement  removed immediately before impressing (sulcus closes in less than 30 sec).

11. 1.Clean the preparative tooth 2.Place the #00 cord 3.Complete preparation 4.Place the #0 cord 5.Take the impression after 5- 10minutes removing the #0 cord Double Cord Technique Procedure: Contraindication （禁忌症） : Patient with thick periodontal tissue

12. Attentions: Select an appropriate size of cord The strength is softly, and the angle between cord packer and tooth axis is an acute angle Firstly place the cord in the proximal area, then to lingual or buccal area Moisten the cord before remove it to prevent gingival injury

13. surgical method mechanical method chemico-mechanical method

14. Questions:  What is the purpose of gingival displacement?  How many methods could retract gingivae? Grasping Content: Double cord technique

15. Wassell RW, Barker D, Walls AWG. Crowns and other extra-coronal restorations: Impression materials and technique. British Dental Journal 2002,192;679 - 690 References:

16. Thanks for your attention Jing Lan E-mail: jinglan@sdu.edu.cn Tel: 88382058