Elastomeric impression material Flashcards
Why do we take dental impressions and pour a gypsum model? (5)
🧠 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.
What factors influence impression material selection? (5)
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
- What are elastomeric impression materials?
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 🌀
Ideal properties of elastomeric materials? (9)
🚫 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
Types of Elastic Impression Materials (2)
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
Why not use alginate for precision impressions?
🧻 Tears easily
❌ Dimensionally unstable – must pour immediately
📸 Single-use cast
🔍 Low detail – unsuitable for crowns/bridges
🧽 Difficult to disinfect
💥 High permanent deformation after removal
Forms of Elastomeric Materials (3)
Light-body (wash/syringe) – flows into fine details
Medium/regular-body – used in tray, provides support
Putty – kneaded by hand, often used in putty-wash technique
💡 Viscosity is determined by the filler content.
What are the 3 Stages of Setting in Elastomers
Initial Set – material stiffens, not elastic yet
Final Set – becomes elastic; manipulation must stop
Final Cure – occurs over 1–24 hrs; full strength achieved
What should clinicians check in an elastomeric impression? (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
Summary: What makes the perfect impression material?
✅ 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
What are future trends in impression taking?
🚀 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
What are some examples of digital impression systems?
💻 iTero
📸 3Shape
🧠 LAVA COS
What are the benefits of digital impressions?
🎯 High precision
🚫 No distortion
📦 Easy storage/sharing
😌 More comfortable for patient
📉 Reduced chairside errors
What is the composition of polysulfide materials?
🧴 Base: Mercaptan polysulfide
🔁 Crosslinker: Sulfur or lead dioxide
⚗️ Catalyst: Copper hydroxide, zinc periodate
🧂 Filler: Zinc sulfate, calcium sulfate dihydrate
What is the polysulfide setting reaction?
🧪 Mercaptan + Lead Dioxide → Polysulfide rubber + Lead oxide + Water
What are the advantages of polysulfide?
💰 Lower cost
🕐 Long working time
🧵 High tear strength
🌀 Flexible
🔍 Good detail reproduction
What are the disadvantages of polysulfide?
💧 Poor dimensional stability
⏱ Pour within 1 hour
🧼 Messy handling
👃 Bad odor
🖌 Requires custom tray
What is the composition of polyether materials?
🧴 Base: Polyether
🔁 Crosslinker: Sulfonic ester
⚗️ Catalyst: Glycol plasticizers
🧂 Filler: Silica
What are the advantages of polyether?
🎯 High accuracy
📐 Excellent dimensional stability
🔁 Can pour multiple casts
💧 Hydrophilic – great in moist conditions
🧼 Good surface detail
What are the disadvantages of polyether?
💸 Expensive
🕐 Short working time
🧱 Very stiff – hard to remove
😖 Bitter taste
📉 Low tear strength
💧 Absorbs water – dimensional changes
What is the chemical composition of C-silicones?
🧴 Base: Polydimethyl siloxane
🔁 Crosslinker: Alkyl ortho silicate
⚗️ Catalyst: Organo tin compound
🧂 Filler: Silica
🔄 Byproduct: Ethyl alcohol (causes shrinkage)
What are the advantages of C-silicones?
✅ Better elasticity than alginate
🧼 Cleaner with pleasant odor
🕐 Good working/setting time
🪥 Can be used with stock trays (putty-wash)
What are the disadvantages of C-silicones?
📉 Poor dimensional stability
💨 Shrinks due to ethanol byproduct
⏱ Must be poured within 30 minutes
💧 Hydrophobic – poor wettability
📦 Limited shelf life
What is the composition of addition silicones?
🧴 Base: Vinyl polysiloxane
🧴 Catalyst: Siloxane prepolymer
🧪 Catalyst: Chloroplatinic acid
🧂 Filler: Silica
🧨 No byproduct (unless contaminated – may release H₂ gas)
What are the advantages of PVS (A-silicones)?
💯 Highly accurate
📐 Excellent dimensional stability
🧪 No byproduct
📆 Long shelf life
🔁 Multiple pours
🚚 Can be shipped without distortion
🧼 Easy to mix
😌 Pleasant odor
What are the disadvantages of PVS?
🧪 Sensitive to sulfur (latex gloves, retraction agents)
🕐 Short working time
📉 Lower tear strength
💨 Potential hydrogen gas release → air bubbles
🧲 Requires palladium to absorb gas
How should polyether impressions be handled?
🪨 Very stiff → Rock tray gently to remove
💧 Avoid water/blood contamination → causes discrepancies
🚫 Avoid undercuts → material may lock in
❓ How should PVS impressions be handled?
⏳ Allow proper setting → early removal = distortion
🧴 Use automix tips for uniform mix
🛠 For best results, use surfactant or hydrophilic types
❓ What causes most distortion in elastomeric impressions?
🕐 Removing impression too soon before cross-linking is complete
