Pretend you are a teacher preparing a quiz for the text I will provide. 
            Each quiz question should follow the format below. 
            Ensure that you carefully recheck the questions and answers for accuracy. 
            The output should be a ready-to-use list of dictionaries for the Python eval function:

            [

                    "question": "WRITE THE QUESTION HERE",
                    "options": ["A) OPTION_1", "B) OPTION_2", "C) OPTION_3", "D) OPTION_4"],
                    "answer": INDEX_OF_CORRECT_ANSWER_IN_OPTIONS_LIST,
                    "explanation": "EXPLAIN WHY THE ANSWER IS CORRECT"

            ]

            Text:
            lternative to cord.  
✓ AlCl3-containing paste is injected into the dried sulcus with a special delivery gun. 
✓ Advantages: Good hemostasis with less discomfort than with the cord.  
▪ However, less tissue displacement is achieved than with cord, → 
may make subsequent laboratory steps e.g., die trimming more problematic. 
✓ Improved displacement may be achieved if the paste is directed into the sulcus by 
applying pressure with a hollow cotton roll (Roeko Comprecap).  
 
2) Other displacement pastes rely on volumetric expansion, as 1st described by 
Feinmann & Martignoni, who combined a polydimethylsiloxane with tin 
catalyst → release gas → a 4-fold volumetric expansion.  
✓ When the paste was applied into the sulcus, → quick seating of a prefabricated 
interim crown, → the volumetric expansion resulted in an apically directed flow 
that enlarged the gingival sulcus → allowed impression making.  
✓ A contemporary material (Magic FoamCord, polyvinyl siloxane tissue 
displacement system) is based on the identical principle, but a hollow cotton roll  
(Roeko Comprecap) is used to apply pressure to the expanding polymeric foam.  
• It provides tissue displacement with minimal discomfort or gingival trauma. 
• The patient closes on the cotton roll, maintaining pressure for 5 minutes.  
• Hemorrhage control with Fe2(SO4)3 can be used if bleeding is noted.  
 
87
 
 
 
 
 
✓ Occlusal Matrix Impression Technique 
The volumetric expansion pastes are effective, as resistance in an occlusal direction 
exerted by either an interim restoration or hollowed-out cotton roll →   
an apically directed flow of the impression material.  
Using an occlusal matrix→ the clinician takes advantage of the identical principle.  
It’s 1st reported by LaForgia, & subsequently with more contemporary materials by 
Livaditis. 1) An index is fabricated from a rigid material (e.g., polyether or putty) 
directly over the prepared teeth → trimmed short of the margin by about 1 mm. 
2) On intraoral verification, the index is filled with medium-bodied impression 
material → seated over the tooth preparations →  
ensures an apically flow of the impression material  
3) A medium-bodied impression material is then seated in  
a suitable impression tray over the index. 
88
 
 
 
 
A, Maxillary anterior teeth are prepared for complete crowns.  
B, Matrix is made in the carrier with elastomeric impression material putty  
before soft tissue is displaced. Registration of the gingival crest is the 1ry objective.  
C, F & L sides of matrix are trimmed with a scalpel. 
Matrix should extend 1/2 - 2/3 of the tooth beyond prepared teeth & close to G crest.  
Black lines indicate sulcular extension.  
 
 
D, Matrix in place in the mouth. A stock tray is selected to fit over matrix  
& any remaining teeth not covered with matrix.  
E, Matrix is painted with adhesive & filled with medium-viscosity impression 
material.  
  
F, Matrix impression is seated with light pressure. The stock tray filled

            Quiz: