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Gingival displacement forfixed partial denture impression techniques

Author: akil, Posted on Wednesday, September 08 @ 20:32:32 IST by RxPG  

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Dental

Critical sulcus WIDTH-0.2 mm ..lateral displacement less than this value results in increased incidence of voids in impression.

The critical position of PREPARED CERVICAL MARGIN-0.5mm from healthy free gingical margin or 0.3- 0.4 mm from alveolar crest.

RULES OF THREE IN GINGIVAL DISPLACEMENT…..

3 causes of difficulties in gingival displacement

1. inflamed gingival tissues
2. inadequate attached gingival
3. the too deep location of prepared cervical margin in the sulcus

3 techniques of gingival displacement

1. mechanical
2. chemical
3. surgical

(a combination of the two or more techniques is also used)

most common used method-the mechano-chemical method -gingival cord used with homeostatic medicaments.

3 mechano-chemical gingival displacement techniques
1. single cord technique
2. double cord technique
3. infusion method

3 basic designs of the gingival retraction cords

1. twisted
2. knitted
3. braided

(no proof of superiority of any single type of cord.so left to the discretion of dentist)
**but acoording to Rosentiel –large braided cords whould be avoided since they have a tendency to “double up”and become to too thick to be atraumatically placed.

3 points to note choice of size of retraction cord

1. THE LARGEST CORD THAT CAN BE PLACED IN THE SULCUS ATRAUMATICALLY IS CHOSEN.
2. smaller cords cause little trauma but the lateral displacement is inadequate.
3. larger cords can cause trauma and even lead to recession(iatrogenic cause)

3 safe homeostatic medicaments**

1. aluminmium potassium sulphate
2. aluminium sulphate
3. aluminium chloride

**Rosentiel lists ferric chloride, and the sympathomimetic amine containing eye wash or nasal decongest!
** Rosentiel says these medicaments cause a transient ischemia, shrinking the gingival tissue. the sulcus closes quickly ( less than 30 seconds) after the cord is removed, so the impression must be taken immediately.

Epinephrine is NOT FOR ROUTINE USE.
3 category of patients in whom epinephrine is c/I (list may not be complete)
1. diabetics
2. hyperthyroid patients
3. CVS patients

3 classes of drugs which C/I concomitant use of epinephrine (list may not be complete)
1. MAO tricyclic antidepressants
2. Beta blockers
3. Cocaine

3 reasons to avoid routine use of epinephrine

1. routine dental examination involves measurement of the resting BP and resting pulse rate only and many latent CVS problems are missed.
2. Evidence of systemic absorption is there and this combined with the endogenous epinephrine due to stress and other factors may cause adverse effects of great magnitude.
3. The other 3 homeostatic medicaments have virtually no side effects and equally effective in gingical displacement.

SINGLE CORD TECHNIQUE
Simple efficient and most common method
The largest cord that fits atraumaically into the sulcus is chosen
Length of cord cut according to anatomy of tooth
Cord soaked in medicament, the excess bloated and placed in the sulcus
Gingival cord is left in place for atleast 8 – 10 minutes.
3 reasons for this-
a. Gingival displacement
b. Control of haemorrhage
c. Control of crevicular fluid
Removed after soaking the cord in water(removal of the cord without drying results in tearing fo the inner epithelium and leads to haemorrhage.
Preparation is dried and then impression is taken

DOUBLE CORD TECHNIQUE

Indicated mainly in compromised tissue health of gingival tissues and impression procedure cannot be delayed.
Dry 2-0 surgical suture WITHOUT SOAKING IN MEDICAMENT is packed in the sulcus depth such the the ends meet end to end around the tooth.(little deficient and gap remaining or little long and slightly overlapping of the cord causes the cord to be impregnated in the impression causing difficulties in pouring the impression)
Second cord is chosen which is largest cord that can be placed in the sulcus atraumatically.
The second cord is removed after 8-10 minutes after soaking in water.The small cord is left in place.
Then the preparation is dried, and the impression is taken.
Then the small cord is soaked in water and removed.

The main use of this technique is in multiple preparation when the gingial fluid can seep over the prepared margin of the last tooth to be impressed

INFUSION METHOD.(written from memory and hence requires referring)

This method is radically different from the previous two techniques.
First a specilaised instrument called a dento infusor is used to apply 15% or 20% ferric sulphate in the sulcular area. This is done with firm pressure with burnishing action..this causes a very good haemostatic effect. Then the cord is dipped in the ferric sulphate solutuion and packed into the sulcus. It is left in the sulcus for 1 to 3 minutes( leaving it longer has NOT proved to be safe!)
Some belive that the short time is not enough to cause adequate gingival displacement.

The 20% soluition of ferric sulphate than 15% solutions of ferric sulphate is preferred since its lower acidity will NOT cause the removal smear layer over the prepared surfaces.



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