Preparation Margin Extra sulcular Intra sulcular Esthetic Good Retention Prevent Radicular Caries Control Ferula Effect
The weak link between the tooth and the restoration is the correct impression
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
the techniques used for gingival displacement surgical method mechanical method chemico-mechanical method
Chemico-Mechanical Method Retraction Cord Chemical drug Epinephrine Aluminum Chloride Alum(aluminum potassium sulfate) Ferric Sulfate Aluminum Sulfate
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:
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).
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
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
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