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Preparation Margin
Extra sulcular
Intra sulcular
Esthetic Good Retention Prevent Radicular Caries Control Ferula Effect
Definition: the deflection of the marginal gingivae away from a tooth
Purpose:• expose the finish line • provide a space for
impression material
gingival displacementgingival 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 cordat bottom of the gingival crevice (龈沟) vertically and horizontally displace gingival margins It is not removed during impressing
Second cord--------thicker cordon top of the first cordachieve horizontal tissue displacementremoved immediately before impressing (sulcus closes in less than 30 sec).
Very importan
t
1. Clean the preparative tooth2. Place the #00 cord3. Complete preparation4. Place the #0 cord5. Take the impression after 5-
10minutes removing the #0 cord
Double Cord Technique
Procedure:
Contraindication (禁忌症) :Patient with thick periodontal tissue
Very import
ant
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
Questions:What is the purpose of gingival
displacement?
How many methods could retract gingivae?
Grasping Content:Double cord technique
Wassell RW, Barker D, Walls AWG. Crowns and other extra-coronal restorations: Impression materials and technique. British Dental Journal 2002,192;679 - 690
References: