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:
            ative humidity. 
2.  ↓ tear strength. 
3. Borax present in this material 
retard setting of some gypsum 
compounds → so manufacturers add 
K2So4 & plaster accelerators  
to improve pouring. 
4. Requires purchasing a water bath. 
5. Infection control unfriendly. 
 
i) Undergoes syneresis & imbibition  
i.e it is dimensionally unstable. 
ii) ↓↓ tear strength. 
iii) ↓ flow→ cannot record fine details 
 
100
 
 
 
 
 
 
A, The water-cooled impression tray is loaded with heavy-bodied material.   
B, The wash hydrocolloid is squeezed onto the tray material in the area of the 
preparations. C, The filled tray is placed in a tempering bath for 3 minutes.  
D, The sulcus is flooded with water or a surfactant.  
Alternatively, some dentists prefer a  syringe technique.  
E, Water-cooling tubes are connected → then the tray is seated.  
F, The completed impression.  
Light-bodied material should have been displaced by the tray material.  
B) Elastomeric impression material: 
1) Polysulfide Polymer 
Composition: 
1) Base: 
• Polysulfide prepolymer.  
• Filler for strength. 
• Plasticizer for optimum consistency. 
• Sulfur as an accelerator.  
101
 
 
2) Catalyst: 
• In the past, Lead peroxide (PbO2 gives characteristic brown color). 
• Contemporary materials are generally polymerized by copper hydroxide (light green) 
• Filler,         plasticizers,             & retarders.  
     Chemistry: 
• Contain Mercapten group.  
• The polysulfide prepolymer reacts with lead oxide   
a condensation polymerization reaction  forming polysulfide rubber &  
water as by-product  so pouring immediately should be within 1 hour. 
     Presentation: 
• 3 viscosities:  heavy / medium / light 
• It is available in a two-paste system: base & accelerator. 
Advantages: 
1. High (excellent) tear strength, 
2. Least rigid (most flexible of all the elastomers), 
High elasticity  to facilitate intra-sulcular & pinholes impression, 
3. Most biocompatible, 
4. Excellent flow so good reproduction of details, 
5. Hydrophilic, 
6. The least expensive elastomer, 
7. It has improved dimensional stability over hydrocolloid. 
Disadvantages: 
1. Dimensionally stability inferior to that of polyether & addition silicone  
because of shrinkage due to water by-product. 
2. Hydrophobic   care should be taken to prevent hemorrhage / fluid seepage 
during impression making + need surfactant for pouring. 
3. PbO2: long setting time (10-15 min).     Cu (OH)2:  setting time.  
4. Unpleasant sulfide odour. 
5. Unpleasant taste. 
6. In the past, the unpolymerized product is sticky & should be handled carefully 
because it stains clothing permanently (lead peroxides). 
7. Requires a custom tray. 
8.  Long setting time (10 minutes). 
9.  Must be poured within half an hour. 
10. 
 Messy to work. 
102
 
 
 Silicones: 
(2) Condensation silicone: 
Composition:  
1) base: 
• Hydroxy terminated polydimethylsiloxane forms polymer.  
• Fillers controls viscosity. 
2) accelerator:  
• Tetraethyl silicate 
• Ti

            Quiz: