Dental Crowns and Abutment Tooth Contours

Exam Format

• 20 multiple-choice questions (MCQs): 10 fixed, 10 removable; each worth 1 mark. Each MCQ has 5 options, only one correct answer.
• 10 short-answer questions (SAQs): 5 fixed, 5 removable; each worth 4 marks. SAQs are mainly clinical-based. Review year 3 notes and clinical guidelines. Read questions carefully before answering.

Crowns

• Indications for a dental crown: Protect remaining tooth structure, alter aesthetics, alter crown form for removable partial dentures (act as abutments), alter occlusal plane.
• Crowns (conservative to destructive): Zirconia (monolithic), all-metal crown, all-ceramic crown, ceramo-metal crown, porcelain fused to zirconia.

Tooth Reductions

• A table showing various biomaterials and tooth reduction amounts (occlusal/posterior, incisal/anterior, axial) for different types of crowns is included. Refer to the provided table for specific data.

Crown Preparation (steps)

• Take shade of crown (for porcelain or zirconia).
• Take 2-3 putty indices.
• Apply local anesthetic (if required).
• Prepare tooth appropriately (using indices as guides).
• Construct temporary crown.
• Place retraction cord with hemostatic agent.
• Take impression.
• Place temporary crown.
• Check occlusion and adjust if needed.
• Complete records and lab card.

One-stage Impression Technique

• Choose appropriate tray.
• Apply adhesive to tray (following manufacturer's recommendations).
• Ensure undercuts are blocked (using wax if needed).
• Clinical assistant loads heavy-bodied material into the tray (using green/blue mixing tip).
• Simultaneously, syringe wash material (light-bodied) around prepared teeth (using yellow mixing tip and intra-oral yellow tip).
• Firmly place loaded tray into mouth.
• Hold tray firmly until impression sets.
• Remove impression, rinse, and disinfect (following manufacturer's instructions).

Inspection of Impression Quality

• Rinse impression with water to remove saliva and blood.
• Dry impression using 3-in-1 device.
• Check under light +/- magnification.
• Disinfect impression (following manufacturer's instructions).
• Complete and submit lab form, signed by supervisor.

Crown Cementation (steps)

• Check lab work (fit and shade).
• Remove temporary restoration.
• Clean underlying prepared tooth.
• Try-in the restoration.
• Check marginal fit (using probe), contact points, and occlusion.
• Confirm patient satisfaction with fit and appearance.
• Remove crown, clean crown and tooth surfaces.
• If needed, sandblast with aluminum oxide (50μm).
• Cement crown with appropriate cement.
• Check and remove excess cement.
• Recheck occlusion.

Cements or Luting Agents

• Soft (temporary) cements: Zinc Oxide with/without eugenol (used for provisional and definitive restorations if required/symptom or trial assessment).
• Permanent (hard) cements: Definitive cementation (conventional cements), acid-base reaction (resin cements), polymerization reaction (hybrid cements), combination of above.

Choosing the Right Cement

• Weaker restoration material requires stronger cement.
• Bonded cements spread forces away from tooth-restoration interface, whereas non-bonded cements concentrate forces.
• Amount of retention needed (preparation form, tapers, length of crown/walls) influences cement choice.

Non-silicate ceramics (especially zirconia): Problems and Solutions

• Difficulty in achieving suitable adhesion with synthetic substrates or natural tissues.
• Traditional adhesive techniques used with silica-based ceramics do not effectively adhere to zirconia.
• Current efforts focus on surface modification of zirconia to enable chemical functionalization for achieving adhesive bonding.

Physical Properties of Zirconia

• The composition and physical properties of zirconia differ from silica-based materials (e.g., porcelain)
• Zirconia is less readily etched and requires more aggressive mechanical abrasion

Recommended Cements for Zirconia

• Resin cements and primers containing 10-MDP (methacryloyloxydecyl dihydrogen phosphate) are recommended for zirconia bonding.
• Examples of such materials include: Panavia V5, SE Bond, SA Luting Cement (Kuraray, Osaka, Japan), Scotchbond Universal adhesive.
• Other primers such as: Metal/Zirconia Primer (Ivoclar), Z-Primer (Bisco), and AZ Primer (Shofu) also contain phosphoric acid monomers to promote adhesion.

Some Tips

• Avoid contact between phosphoric acid and zirconia during cementation. Phosphate ions in acid greatly reduce bonding.
• Avoid use of prophy paste for cleaning tooth preparations. Use pumice powder and water.
• Resin modified glass ionomer (RMGI) cement is recommended for zirconia restorations when tooth preparations are near-optimum (at least 4mm).
• Parallelism of preparation walls should be less than 20 degrees.

Cement Types

• A table listing recommended uses, primary strengths, and primary weaknesses of various cement types (Zinc Phosphate, Polycarboxylate, Glass Ionomer, Resin Modified GIC, Resin based).

Articulating Papers

• Normal articulating paper (70-200 microns), used mainly for dentures.
• GHM articulating paper (12-20 microns), ideal for occlusal contacts in restorative dentistry.
• Shimstock (8 microns), also used for crowns and implant crowns.

Treatment Planning Process

• Emergency phase.
• Investigation/Stabilization phase.
• Rehabilitation phase.
• Maintenance and Monitoring phase.

Clinical Case Scenario

• Patient with acute pain from tooth #46 (irreversible pulpitis due to extensive caries).
• Advanced periodontal disease and other carious cavities present
• How to manage described case (Steps for Emergency, Stabilization, Rehabilitation, and Maintenance phases).

Common Errors Affecting Marginal Fit

• Tight proximal contacts.
• Casting blebs on fit surfaces.
• Over/under-extended crown margins.
• Impression distortion (no die spacer).

Checking Fit of Crown

• Visual: Margins, direct view/mirror, magnification
• Instruments: Explorer (straight probe), proper tip size and angle for subgingival evaluation

Types of Defective Margins

• Over-extended (poor impression, surplus wax/ceramic, improperly trimmed die)
• Under-extended (poor impression, over-polished casting, improperly trimmed die)
• Over-contoured (over-waxed casting)
• Open margin (casting not completely seated, poor impression)

Evaluating Crown Prior to Cementation

• Check proximal contacts (flossibility).
• Check marginal fit (explorer).
• Check aesthetics (shape and shade).
• Check occlusion (GHM articulating paper).

Semi-precision Attachments

• Information about these attachments was contained within the file. Refer to the slides for details.

Objectives in Modifying Abutment Tooth Contours (Advantages of Milled Crowns)

• Develop an acceptable path of insertion.
• Promote favorable biomechanical properties (retention, support, stability).
• Improve aesthetics.
• Improve structural durability, especially important for heavily restored teeth.

Options for Replacing Teeth (Removable, Resin-Bonded, Implant, Conventional Bridge)

• Removable options (Partial, complete): Acrylic, Cobalt Chrome, Valplast.
• Fixed options: Resin-bonded bridge, Implant, Conventional bridge.
• Different options/approaches offered when describing replacement methods, along with a description of each.

Factors Affecting Prognosis of Teeth

• Patient factors: Restorative status, medical/dental history, social factors, expectations, financial status, and behavior.
• Dentist factors: Skills, training, experience, available equipment, materials.

Prognosis

• Structural Integrity: Needs at least 1.5 mm of ferrule to support fixed prosthesis. Dentin thickness should be >1mm especially if root-treated.
• Endodontic Integrity: Predictable outcome requires a healthy pulp or properly cleaned/obturated root canals. Coronal seal success is key in root canal treatment.
• Periodontal Integrity: Bone loss and mobility negatively affect prognosis. A large amount of bone loss and associated higher mobility will result in a lower tooth prognosis.

Strategic Value of a Tooth

• Aesthetics.
• Medical.
• Occlusal.
• Prosthodontic.
• Functional.
• Financial.

What is RCP?

• Bilateral, unstrained mandible position.
• Condylar disc assembly is in superior anterior position.
• First 20mm of incisal opening is pure hinge axis.
• Initial contact of teeth.
• Reproducible position of occlusion, used for large changes to occlusion or when restoring multiple teeth.

What is ICP?

• Position with most tooth-to-tooth contact in that individual’s occlusion
• Used when restoring or confirming to patient's present occlusion.

Management of Teeth with Extensive Tooth Loss

• Managing teeth with extensive tooth loss. Refer to slides for visualization.

Toothwear

• Presenting complaint.
• Medical, Social, & Dietary history.
• Extra-oral and intra-oral exams.
• Identifying wear type.
• Sensibility testing.
• Radiographs.
• Prosthodontic assessment.

Types of Tooth Surface Loss

• Attrition
• Abrasion
• Erosion/Acid Dissolution
• Abfraction
• Caries
• Iatrogenic
• Trauma

How Do You Manage Cases of Tooth Wear?

• Determine the type of wear.
• Monitor or treat.
• Restoration plans (articulated study casts, wax-ups).
• Materials to use.
• When to offer a splint.
• What types of splints (mentioning hard and soft splinting).

Clinical Features (Attrition and erosion)

• Attrition: Describes flat cusps, matching wear facets/loss, excessive fracture of restorations, hypersensitivity, loss not in articulation, masseteric hypertrophy/tenderness, prominent antagonistic notching, Pterygoid tenderness, TM joint clicking/crepitus/limitation, and scalloping/cheek ridging.
• Erosion: Describes loss of surface characteristics with smooth/shiny enamel and dentin, old fillings/fillings/ amalgams, cupping.

Management of TSL

• Active monitoring.
• Splint therapy.
• Composite build-ups.
• Various types of inlay/onlay restorations, crowns, bridges, various forms of full dentures/overdentures, and implants (ordered from least to most invasive, as stated).

How to Manage a Patient with TSL from Erosion

• Diet analysis and dietary changes.
• Use fluoride toothpaste for tooth repair/protection.
• Restore function and aesthetics using composite resin restorations.
• Plan to restore worn teeth with indirect lab-made restorations.

How a Wear Case is Managed

• Take articulated study casts in centric relation.
• Make wax-ups.
• Demonstrate to the patient.
• Create putty index or plastic retainer.
• Use composite to restore the teeth.

Role of Splints

• Testing occlusal vertical dimension.
• Checking for patient centric relation (RCP).
• Treating Temporomandibular joint (TMD) pain (muscle origin).
• Protecting teeth from wear/restoration.
• Used for patients wearing partial or overdentures/onlay dentures.

Posts and Cores

• Posts (dowels): Metal or rigid restorative material for non-vital teeth in the radicular portion.
• Cores: Substructure replacement that replaces missing coronal structures and retains the final restoration.

How to Decide on the Ideal Post (Direct/Indirect)

• Determine amount of ferrule present; minimum is 1.5mm.
• 2-3mm ferrule suggests an indirect cast post.
• 3–4mm ferrule suggests a direct post.
• Molar teeth may benefit from a Nayyar core instead of a post and core.

Differentiating Indirect and Direct Post Methods

• Indirect: Post and core fabricated in lab (usually involves a cast post).
• Direct: Post and core fabricated chairside (usually involves a fiber composite post and bulk-filled composite core). Use duralay/wax for detailed representation for the lab, which is then formed into a cast.

Tooth Restorability Index (TRI)

• A structured assessment method for determining the restorability of a tooth.
• Divide the tooth into 6 equal sextants (2 proximal, buccal, 2 lingual) and scores 0-3 for each.
• 0-None – No axial wall/dentine to support core or crown.
• 1-Inadequate – Dentine present, insufficient for holding and supporting a core or crown/restoration.
• 2-Questionable – More dentine present, but uncertain if sufficient to ensure predictable core/restoration.
• 3-Adequate – Sufficient dentine to predict and support a core/restoration.

Tooth Structure Remaining/Clinical Decision

• A table that relates various scores (0 to 12 or greater) to an acceptable/questionable or unacceptable clinical decision.
• Explains that the index is helpful in deciding if a post or crown and core can be placed and how to make clinical predictions if a crown and core can be placed.

This quiz covers essential concepts related to the assessment and evaluation of dental crowns and abutment tooth contours. Questions focus on defects, measurement practices, and biomechanical properties. Test your knowledge on the criteria for effective crown fit and restoration techniques.