Principles of tooth preparation Flashcards
What is an indirect restoration? 🧱🦷
An indirect restoration is a dental restoration that’s fabricated outside the mouth 🛠️ — either in a dental lab or via CAD/CAM — and then cemented or bonded to the tooth. Examples include:
Crowns 👑
Veneers 💅
Inlays/Onlays 🧩
Implant-retained restorations ⚙️
What are the steps involved in providing an indirect restoration? 🔄
Tooth preparation to create space 🦷✂️
Impressions or scans 📸
Lab work – cast models, wax-ups, fabrication 🏗️
Try-in of the restoration 🤓
Final cementation 🪄
What are the advantages of indirect restorations? 💎
✅ Aesthetics – perfect shape, color, and alignment ✨
✅ Cuspal coverage – protects fractured/weakened teeth 💪
✅ Restores function – chewing, speaking, occlusion 🗣️🍽️
✅ Stability – prevents drifting or over-eruption ⚖️
✅ Comfort – better fit, less irritation 😊
✅ Implants – essential for restoring implants 🛠️🦷
What are the disadvantages of indirect restorations? 😩
⚠️ Multiple appointments 🗓️
⚠️ Higher cost 💸
⚠️ Longer chair time ⏰
⚠️ Involves more professionals 👩⚕️👨🔬
⚠️ Technically sensitive 🔬
Why do we prepare the tooth before an indirect restoration? 🔧
To create space for the material (ceramic, metal, etc.) ✂️
To conform to the patient’s occlusion 👄
To ensure path of insertion (no undercuts) 🚪
To give the crown its ideal shape and fit 📐
To prevent high spots or occlusal interference ⚙️
What happens if we don’t prepare the tooth properly? 😬
Crown will be too high 🏔️
Patient may experience pain when biting 😣
Crown may fracture 💥
Impression errors due to undercuts 📉
Risk of pulpal exposure if overprepared 😱
What is the ideal taper or TOC (Total Occlusal Convergence) for a prep? 🧊📏
🔹 6–12° is optimal
🔹 Maintains retention and resistance
🔹 Too much taper = less retention 😓
🔹 Achieved by holding the bur parallel to the long axis of the tooth 🪥
Why is retention and resistance important in indirect restorations? 🎯
🔒 Retention = resists pulling off along path of insertion
🔁 Resistance = resists tipping or lateral forces
Both are crucial for keeping the crown securely seated during function!
What factors affect retention and resistance? 🧮
✔️ TOC (Taper)
✔️ Height of the prep (minimum 3mm!) 📏
✔️ Surface area – larger tooth = more retention 🔄
✔️ Preparation design – grooves & boxes for extra resistance 🧩
✔️ Cement selection – active vs passive luting agents 🧪
How does tooth height influence retention/resistance? 📐
📏 Minimum height = 3mm
🦷 Taller teeth = more surface for bonding
🧱 Short preps may require grooves or boxes for stability
💥 Short height = increased risk of crown dislodgement
What is the purpose of grooves or boxes in prep design? 🧩
They increase resistance to torque or lateral forces 🔁
📌 Grooves should be parallel to the path of insertion
⚠️ Must be at least half a bur’s diameter to avoid filling with die spacer
What are the different crown materials used? 🪙🧱💎
Metal-ceramic crowns (MCC) – strong + aesthetic
Gold crowns – kind to opposing dentition, durable
Non-precious metals – cheaper, still functional
All-ceramic crowns – best for aesthetics, but brittle
Why is structural durability important for a restoration? 🦾
🦷 It must withstand:
Occlusal forces 💪
Temperature changes 🌡️
Moisture, pH & bacteria 🌊🦠
Poor durability = cracks, wear, failure 💥
🧱 Need enough thickness and correct prep to support the material!
What is marginal integrity, and why is it important? 🔍
🧼 A well-fitting margin:
✔️ Prevents plaque accumulation
✔️ Reduces cement washout 🧴
✔️ Protects against perio and caries 🦷🦠
🪚 Should be placed on sound tooth structure, either supragingival or equigingival
What are the types of prep margins? ✂️
🔹 Shoulder (horizontal) – common in MCC, needs ≥1.2mm
🔹 Knife edge (vertical) – thin metal, fades into tooth
📍 Finish line should follow the contour of gingiva and be in a healthy position
What are the biological considerations during tooth prep? 🌿
🧠 Preserve periodontium – no bulky restorations
🧼 Supragingival margins if possible (easier to clean)
🩸 Avoid violating biological width – can cause recession & inflammation
🧬 1mm subgingival margins ↑ recession risk ×2.65!
🛑 Preserve pulp vitality – 1/5 teeth become non-vital after crown prep!
What is biological width and why does it matter? 📏🧬
The space between the base of the sulcus and the alveolar crest, needed for soft tissue health. Violating it can cause:
Chronic inflammation
Recession
Loss of attachment
What if there’s not enough tooth structure above the gingiva? 🧱
You may need crown lengthening surgery 🦷🔪
👉 Removes bone and repositions the gingiva more apically
👉 Increases the height of clinical crown = better retention/resistance!
What is the final principle in tooth preparation? 🧑🎨
🎨 Aesthetics!
Patient consent is key 📝
Material choice affects how much tooth you need to remove
MCC needs at least 1.2mm to allow for multiple material layers (metal, opaquer, ceramic)
Smooth, natural-looking results = happy patient! 😁💕
What are the 7 principles of tooth preparation for indirect restorations?
- Preservation of tooth structure 🛡️
- Retention and resistance 🔒
- Structural durability 🧱
- Material
- Marginal integrity & position 🎯
- Biological considerations: Preservation of the periodontium 🌿 Preservation of pulp tissue 💓
- Aesthetics ✨
Why is preserving tooth structure during prep important?
Balances the need for material space with the goal of protecting the pulp and periodontium 🧠🫀
Prevents weakening the tooth or exposing pulp ⚠️
Under-preparation = bulbous, unaesthetic crowns or poor material thickness 😬
Over-preparation = pulp exposure risk (👀 pink hue shining through = danger!)
✅ Goal: Conserve as much healthy tooth as possible while making room for the restoration
What is the difference between retention and resistance form in prep?
Retention ➡️ Prevents crown removal along the path of insertion 🧲
Resistance ➡️ Prevents dislodgement by lateral or apical forces during function 🛑
Influenced by:
Taper of the walls: ideal 6–12° convergence 📐
Surface area: More contact = better grip ✊
Prep height: ≥3mm for good retention ⬆️
Prep design: grooves/boxes = more stability 📦
Cement selection: type & technique matter 🧪
Why is structural durability critical in indirect restorations?
Restoration must survive occlusal forces, temperature, pH changes, and moisture 💥🌡️
If there’s inadequate reduction, the material (e.g., ceramic or metal) could be too thin → cracks or perforation 😵
Need enough bulk in functional areas (e.g., cusps) to ensure long-term survival 🔧
✅ Reduce tooth following natural contours & planes = better strength & fit! 🦷🧩
What’s the role of margin design and position in prep?
Accurate margins = better fit, less cement exposure, fewer plaque traps 💥
Shoulder margins (horizontal) = great for ceramic/porcelain-fused-to-metal 🦷
Knife-edge/Chamfer (vertical) = good for metal 💫
Margins should be:
On sound tooth 🧱
Equi-/supra-gingival if possible for hygiene 🧼
Smooth and continuous 🎯
Incorrect margins = bulky restorations, open margins, or increased caries risk 🦠
