Principles of tooth preparation Flashcards
What is an indirect restoration? ๐งฑ๐ฆท
An indirect restoration is a dental restoration thatโs fabricated outside the mouth ๐ ๏ธ โ either in a dental lab or via CAD/CAM โ and then cemented or bonded to the tooth. Examples include:
Crowns ๐
Veneers ๐
Inlays/Onlays ๐งฉ
Implant-retained restorations โ๏ธ
What are the steps involved in providing an indirect restoration? ๐
Tooth preparation to create space ๐ฆทโ๏ธ
Impressions or scans ๐ธ
Lab work โ cast models, wax-ups, fabrication ๐๏ธ
Try-in of the restoration ๐ค
Final cementation ๐ช
What are the advantages of indirect restorations? ๐
โ
Aesthetics โ perfect shape, color, and alignment โจ
โ
Cuspal coverage โ protects fractured/weakened teeth ๐ช
โ
Restores function โ chewing, speaking, occlusion ๐ฃ๏ธ๐ฝ๏ธ
โ
Stability โ prevents drifting or over-eruption โ๏ธ
โ
Comfort โ better fit, less irritation ๐
โ
Implants โ essential for restoring implants ๐ ๏ธ๐ฆท
What are the disadvantages of indirect restorations? ๐ฉ
โ ๏ธ Multiple appointments ๐๏ธ
โ ๏ธ Higher cost ๐ธ
โ ๏ธ Longer chair time โฐ
โ ๏ธ Involves more professionals ๐ฉโโ๏ธ๐จโ๐ฌ
โ ๏ธ Technically sensitive ๐ฌ
Why do we prepare the tooth before an indirect restoration? ๐ง
To create space for the material (ceramic, metal, etc.) โ๏ธ
To conform to the patientโs occlusion ๐
To ensure path of insertion (no undercuts) ๐ช
To give the crown its ideal shape and fit ๐
To prevent high spots or occlusal interference โ๏ธ
What happens if we donโt prepare the tooth properly? ๐ฌ
Crown will be too high ๐๏ธ
Patient may experience pain when biting ๐ฃ
Crown may fracture ๐ฅ
Impression errors due to undercuts ๐
Risk of pulpal exposure if overprepared ๐ฑ
What is the ideal taper or TOC (Total Occlusal Convergence) for a prep? ๐ง๐
๐น 6โ12ยฐ is optimal
๐น Maintains retention and resistance
๐น Too much taper = less retention ๐
๐น Achieved by holding the bur parallel to the long axis of the tooth ๐ชฅ
Why is retention and resistance important in indirect restorations? ๐ฏ
๐ Retention = resists pulling off along path of insertion
๐ Resistance = resists tipping or lateral forces
Both are crucial for keeping the crown securely seated during function!
What factors affect retention and resistance? ๐งฎ
โ๏ธ TOC (Taper)
โ๏ธ Height of the prep (minimum 3mm!) ๐
โ๏ธ Surface area โ larger tooth = more retention ๐
โ๏ธ Preparation design โ grooves & boxes for extra resistance ๐งฉ
โ๏ธ Cement selection โ active vs passive luting agents ๐งช
How does tooth height influence retention/resistance? ๐
๐ Minimum height = 3mm
๐ฆท Taller teeth = more surface for bonding
๐งฑ Short preps may require grooves or boxes for stability
๐ฅ Short height = increased risk of crown dislodgement
What is the purpose of grooves or boxes in prep design? ๐งฉ
They increase resistance to torque or lateral forces ๐
๐ Grooves should be parallel to the path of insertion
โ ๏ธ Must be at least half a burโs diameter to avoid filling with die spacer
What are the different crown materials used? ๐ช๐งฑ๐
Metal-ceramic crowns (MCC) โ strong + aesthetic
Gold crowns โ kind to opposing dentition, durable
Non-precious metals โ cheaper, still functional
All-ceramic crowns โ best for aesthetics, but brittle
Why is structural durability important for a restoration? ๐ฆพ
๐ฆท It must withstand:
Occlusal forces ๐ช
Temperature changes ๐ก๏ธ
Moisture, pH & bacteria ๐๐ฆ
Poor durability = cracks, wear, failure ๐ฅ
๐งฑ Need enough thickness and correct prep to support the material!
What is marginal integrity, and why is it important? ๐
๐งผ A well-fitting margin:
โ๏ธ Prevents plaque accumulation
โ๏ธ Reduces cement washout ๐งด
โ๏ธ Protects against perio and caries ๐ฆท๐ฆ
๐ช Should be placed on sound tooth structure, either supragingival or equigingival
What are the types of prep margins? โ๏ธ
๐น Shoulder (horizontal) โ common in MCC, needs โฅ1.2mm
๐น Knife edge (vertical) โ thin metal, fades into tooth
๐ Finish line should follow the contour of gingiva and be in a healthy position
What are the biological considerations during tooth prep? ๐ฟ
๐ง Preserve periodontium โ no bulky restorations
๐งผ Supragingival margins if possible (easier to clean)
๐ฉธ Avoid violating biological width โ can cause recession & inflammation
๐งฌ 1mm subgingival margins โ recession risk ร2.65!
๐ Preserve pulp vitality โ 1/5 teeth become non-vital after crown prep!
What is biological width and why does it matter? ๐๐งฌ
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 thereโs not enough tooth structure above the gingiva? ๐งฑ
You may need crown lengthening surgery ๐ฆท๐ช
๐ Removes bone and repositions the gingiva more apically
๐ Increases the height of clinical crown = better retention/resistance!
What is the final principle in tooth preparation? ๐งโ๐จ
๐จ Aesthetics!
Patient consent is key ๐
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! ๐๐
What are the 7 principles of tooth preparation for indirect restorations?
- Preservation of tooth structure ๐ก๏ธ
- Retention and resistance ๐
- Structural durability ๐งฑ
- Material
- Marginal integrity & position ๐ฏ
- Biological considerations: Preservation of the periodontium ๐ฟ Preservation of pulp tissue ๐
- Aesthetics โจ
Why is preserving tooth structure during prep important?
Balances the need for material space with the goal of protecting the pulp and periodontium ๐ง ๐ซ
Prevents weakening the tooth or exposing pulp โ ๏ธ
Under-preparation = bulbous, unaesthetic crowns or poor material thickness ๐ฌ
Over-preparation = pulp exposure risk (๐ pink hue shining through = danger!)
โ
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 โก๏ธ Prevents crown removal along the path of insertion ๐งฒ
Resistance โก๏ธ Prevents dislodgement by lateral or apical forces during function ๐
Influenced by:
Taper of the walls: ideal 6โ12ยฐ convergence ๐
Surface area: More contact = better grip โ
Prep height: โฅ3mm for good retention โฌ๏ธ
Prep design: grooves/boxes = more stability ๐ฆ
Cement selection: type & technique matter ๐งช
Why is structural durability critical in indirect restorations?
Restoration must survive occlusal forces, temperature, pH changes, and moisture ๐ฅ๐ก๏ธ
If thereโs inadequate reduction, the material (e.g., ceramic or metal) could be too thin โ cracks or perforation ๐ต
Need enough bulk in functional areas (e.g., cusps) to ensure long-term survival ๐ง
โ
Reduce tooth following natural contours & planes = better strength & fit! ๐ฆท๐งฉ
Whatโs the role of margin design and position in prep?
Accurate margins = better fit, less cement exposure, fewer plaque traps ๐ฅ
Shoulder margins (horizontal) = great for ceramic/porcelain-fused-to-metal ๐ฆท
Knife-edge/Chamfer (vertical) = good for metal ๐ซ
Margins should be:
On sound tooth ๐งฑ
Equi-/supra-gingival if possible for hygiene ๐งผ
Smooth and continuous ๐ฏ
Incorrect margins = bulky restorations, open margins, or increased caries risk ๐ฆ
How do you protect the periodontium during prep?
Aim for supragingival margins when possible ๐ธ
Avoid bulky restorations that lead to plaque accumulation ๐ฆ
Consider biological width: distance from sulcus to bone (2-3 mm) โ donโt violate it! ๐ซ
If crown height is insufficient โก๏ธ consider crown lengthening surgery โ๏ธ๐ฆท
Soft tissue management (e.g., retraction cords for impressions) is crucial ๐งต
How can prep affect pulp health?
Over-prep or excessive heat can cause pulpal trauma ๐ฅต
1 in 5 crowned teeth become non-vital ๐จ
Follow natural tooth contours and use coolant spray to avoid thermal damage ๐ฆ
Get informed consent from patients โ they must know the risk of possible RCT later ๐๐ง
What aesthetic factors are considered during tooth prep?
Especially important for ceramic restorations in visible areas ๐
Requires 1.2โ2mm reduction to accommodate layering of materials (ceramic, opaquer, metal etc.) ๐จ
Contour and translucency of final crown depend on prep accuracy ๐
Margin placement and symmetry affect final look ๐
Discuss shade, material, and limitations with the patient โ