Elastomeric impression material

Question 1

Why do we take dental impressions and pour a gypsum model? (5)

Answer 1

🧠 Purpose of impressions:

🧐 Study the case – understand occlusion, arch shape, and individual characteristics.
🧬 Diagnose dental conditions – malocclusion, caries, wear patterns, soft tissue evaluation.
🦷 Treatment planning – for crowns, bridges, implants, dentures, ortho.
🧑‍🏫 Educate the patient – visual aid to explain treatment needs.
🧱 Fabricate indirect restorations – inlays, onlays, crowns, bridges, complete/partial dentures.
🔁 Link between dentist and technician – accurate communication via model.

Question 2

What factors influence impression material selection? (5)

Answer 2

Clinicians consider:

🧁 Consistency – putty, medium, or light body
💧 Flow properties – ability to adapt around fine details
⏱ Setting time – shorter for patient comfort, long enough for working
📐 Dimensional stability – minimal shrinkage or deformation
✋ Ease of handling – mixing, tray loading, and placement

Question 3

3. What are elastomeric impression materials?

Answer 3

Definition:

A class of rubbery materials (natural/synthetic) used when high accuracy is essential 📏
🧲 Elastomers deform under force and return to shape when force is removed.
Structure:

🧬 Long-chain polymers that form a 3D crosslinked network
Upon stretching, chains uncoil but return to original once relaxed 🌀

Question 4

Ideal properties of elastomeric materials? (9)

Answer 4

🚫 Non-toxic, non-irritant
😌 Acceptable taste and odour for patients
⏳ Optimal setting time (not too fast, not too slow)
🧈 Consistency suitable for different applications
🧼 Excellent surface detail reproduction
🧍 Dimensional stability over time
🛠 Easy to mix and use
🤝 Compatible with gypsum for model pouring
💰 Cost-effective & long shelf life

Question 5

Types of Elastic Impression Materials (2)

Answer 5

Elastic Materials are divided into:

Aqueous Hydrocolloids (Water-based):
🌀 Agar (reversible)
🌊 Alginate (irreversible)

Non-aqueous Elastomers (Rubber-based):
🧴 Polysulfide
🧪 Silicones – Condensation (C-Silicone) and Addition (A-Silicone/PVS)
🌧 Polyether

Question 6

Why not use alginate for precision impressions?

Answer 6

🧻 Tears easily
❌ Dimensionally unstable – must pour immediately
📸 Single-use cast
🔍 Low detail – unsuitable for crowns/bridges
🧽 Difficult to disinfect
💥 High permanent deformation after removal

Question 7

Forms of Elastomeric Materials (3)

Answer 7

Light-body (wash/syringe) – flows into fine details
Medium/regular-body – used in tray, provides support, thicker materials and stiffness forces light bodied materials to close contact wit prepared teeth to ensure a accurate impression
Putty – kneaded by hand, often used in putty-wash technique
💡 Viscosity is determined by the filler content.

Question 8

What are the 3 Stages of Setting in Elastomers

Answer 8

Initial Set – material stiffens, not elastic yet
Final Set – becomes elastic; manipulation must stop
Final Cure – occurs over 1–24 hrs; full strength achieved

Question 9

What should clinicians check in an elastomeric impression? (9)

Answer 9

🔎 Clinical checklist:

🦷 Detail reproduction – sharp margins, fine anatomy
📐 Dimensional accuracy – no distortion or tray separation
🫧 No voids or bubbles – especially at margins
📏 Full coverage – teeth + soft tissues
🧽 Consistent thickness – even material distribution
🚫 No drag or pulls – no movement during setting
⏱ Proper setting time – fully cured before removal
📏 Tray fit – rigid tray + good retention
🧼 Infection control – properly disinfected before lab

Question 10

Summary: What makes the perfect impression material?

Answer 10

✅ Smooth-flowing
💧 Hydrophilic
🧵 Good tear strength
📉 Low shrinkage
🔁 Can be poured multiple times
😊 Pleasant taste
📆 Long shelf life
🚫 No toxic by-products
📤 Easy to mix and use
🧪 Compatible with gypsum

Question 11

What are future trends in impression taking?

Answer 11

🚀 Digital impressions are gaining popularity due to:

🖥 Intraoral scanners: iTero, 3Shape, LAVA COS
🧼 More hygienic – no materials in mouth
🧠 Better patient experience
📤 Instant digital communication with labs
📸 High-resolution images for diagnosis & planning

Question 12

What are some examples of digital impression systems?

Answer 12

💻 iTero
📸 3Shape
🧠 LAVA COS

Question 13

What are the benefits of digital impressions?

Answer 13

🎯 High precision
🚫 No distortion
📦 Easy storage/sharing
😌 More comfortable for patient
📉 Reduced chairside errors

Question 14

What is the composition of polysulfide materials?

Answer 14

🧴 Base: Mercaptan polysulfide
🔁 Crosslinker: Sulfur or lead dioxide
⚗️ Catalyst: Copper hydroxide, zinc periodate
🧂 Filler: Zinc sulfate, calcium sulfate dihydrate

Question 15

What is the polysulfide setting reaction?

Answer 15

🧪 Mercaptan + Lead Dioxide → Polysulfide rubber + Lead oxide + Water

Question 16

What are the advantages of polysulfide?

Answer 16

FIRST DENTAL ELASTOMERS
$ Lower cost
🕐 Long working time
🧵 High tear strength
🌀 Flexible
🔍 Good detail reproduction

Question 17

What are the disadvantages of polysulfide?

Answer 17

💧 Poor dimensional stability
⏱ Pour within 1 hour
🧼 Messy handling
👃 Bad odor
🖌 Requires custom tray

Question 18

What is the composition of polyether materials?

Answer 18

🧴 Base: Polyether
🔁 Crosslinker: Sulfonic ester
⚗️ Catalyst: Glycol plasticizers
🧂 Filler: Silica

Question 19

What are the advantages of polyether?

Answer 19

🎯 High accuracy
📐 Excellent dimensional stability
🔁 Can pour multiple casts
💧 Hydrophilic – great in moist conditions
🧼 Good surface detail

Question 20

What are the disadvantages of polyether?

Answer 20

💸 Expensive
🕐 Short working time
🧱 Very stiff – hard to remove
😖 Bitter taste
📉 Low tear strength
💧 Absorbs water – dimensional changes

Question 21

What is the chemical composition of C-silicones?

Answer 21

🧴 Base: Polydimethyl siloxane
🔁 Crosslinker: Alkyl ortho silicate
⚗️ Catalyst: Organo tin compound
🧂 Filler: Silica
🔄 Byproduct: Ethyl alcohol (causes shrinkage)

Question 22

What are the advantages of C-silicones?

Answer 22

✅ Better elasticity than alginate
🧼 Cleaner with pleasant odor
🕐 Good working/setting time
🪥 Can be used with stock trays (putty-wash)

Question 23

What are the disadvantages of C-silicones?

Answer 23

📉 Poor dimensional stability
💨 Shrinks due to ethanol byproduct
⏱ Must be poured within 30 minutes
💧 Hydrophobic – poor wettability
📦 Limited shelf life

Question 24

What is the composition of addition silicones?

Answer 24

🧴 Base: Vinyl polysiloxane
🧴 Catalyst: Siloxane prepolymer
🧪 Catalyst: Chloroplatinic acid
🧂 Filler: Silica
🧨 No byproduct (unless contaminated – may release H₂ gas)

Question 25

What are the advantages of PVS (A-silicones)?

Answer 25

💯 Highly accurate 📐 Excellent dimensional stability 🧪 No byproduct 📆 Long shelf life 🔁 Multiple pours 🚚 Can be shipped without distortion 🧼 Easy to mix 😌 Pleasant odor

Question 26

What are the disadvantages of PVS?

Answer 26

🧪 Sensitive to sulfur (latex gloves, retraction agents) 🕐 Short working time 📉 Lower tear strength 💨 Potential hydrogen gas release → air bubbles 🧲 Requires palladium to absorb gas

Question 27

How should polyether impressions be handled?

Answer 27

🪨 Very stiff → Rock tray gently to remove 💧 Avoid water/blood contamination → causes discrepancies 🚫 Avoid undercuts → material may lock in

Question 28

❓ How should PVS impressions be handled?

Answer 28

⏳ Allow proper setting → early removal = distortion 🧴 Use automix tips for uniform mix 🛠 For best results, use surfactant or hydrophilic types

Question 29

❓ What causes most distortion in elastomeric impressions?

Answer 29

🕐 Removing impression too soon before cross-linking is complete

Question 30

What is a base or catalyst in impression materials

Answer 30

Question 31

Name 4 types of elastomeric materials

Answer 31

Question 32

What are the indications for Polysuflide

Answer 32

- complete denture - removable fixed partial denture - crown and bridge examples: Permlastic Omnni Flex

Question 33

How do you manipulate Polysulfide

Answer 33

- Adhesive to try Uniform layer -equal lengths of paste Mix thoroughly- within one minute Setting time 8-12 minutes Pour within 1 hour - messy paste to paste mix bad odour may satin clothing H-S gives rotten egg smell

Question 34

Manipulations and technique considerations for Polyether materials

Answer 34

Question 35

What are the manipulations and technique considerations for C silicone material

Answer 35

Question 36

What are Polyvinyl siloxanes and how are they supplied

Answer 36

Question 38

Describe the different pastes and catalyst used In PVS

Answer 38

Question 39

Question 40

A silicone Properties 4

Answer 40

Question 41

Manipualtiyon and technique cosndieratiosn for PVS

Answer 41

Question 42