In fixed prosthodontics, the finish line plays an important role in crown and veneer preparation. The selected margin design can influence marginal adaptation, restorative material thickness, tooth preservation and esthetic outcomes.
Two commonly used designs are the chamfer and shoulder margin. Their selection should depend on the restorative material, tooth anatomy and clinical objective.
Just as important is the instrument used to create the preparation. The FG diamond bur defines the geometry, while the high-speed dental handpiece provides the cutting performance, cooling and visibility needed to guide the bur accurately.
Understanding Finish Line Geometry
The finish line forms the cervical boundary between the prepared tooth and the final restoration.
A well-prepared finish line should support:
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Clear marginal definition
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Adequate restorative thickness
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Tooth structure preservation
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Smooth restorative contours
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Accurate scanning or impression taking
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Healthy surrounding tissues
There is no single margin design suitable for every restoration. Material requirements and manufacturer preparation guidelines should always be considered.
1. Chamfer Margin
A chamfer creates a smooth, rounded transition between the axial wall and the tooth surface.
Common Characteristics
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Rounded internal geometry
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Smooth sloping finish line
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Relatively conservative tooth reduction
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Clearly identifiable margin when properly prepared
Common Clinical Applications
Chamfer margins may be considered for:
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Full metal crowns
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Monolithic zirconia crowns
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Lingual surfaces of selected PFM crowns
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Posterior restorations
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Cases where tooth conservation is important
The exact margin depth depends on the restorative material. A zirconia crown, for example, may require a different preparation depth compared with a full metal restoration.
Bur Selection for Chamfer Preparation
A tapered round-end FG diamond bur is commonly used to form a chamfer because its geometry naturally creates a rounded cervical transition.
The clinician should control:
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Bur angulation
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Preparation depth
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Axial wall convergence
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Finish-line continuity
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Cutting pressure
Handpiece Role During Chamfer Preparation
The handpiece does more than rotate the bur. During crown preparation, it influences cutting stability, water cooling, visibility and overall control.
For higher-load restorative preparation, the Kaneiko Master Torque Model M9K Friction Grip High-Speed Dental Handpiece can support demanding cutting procedures.
Key features include:
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Up to 38 W cutting power
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300,000 to 400,000 rpm
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Ø1.6 mm FG bur compatibility
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Four-point water spray
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Fibre-optic illumination
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German ceramic ball bearings
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DLC-coated titanium body
When combined with an appropriate chamfer diamond bur, the workflow becomes:
Handpiece → FG Bur → Controlled Reduction → Defined Chamfer
2. Shoulder Margin
A shoulder creates a broader cervical ledge compared with a traditional chamfer.
Common Characteristics
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Wider cervical reduction
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Clearly defined margin
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Greater space for restorative material
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Suitable for restorations requiring more cervical bulk
For modern ceramic restorations, the internal angle should generally be rounded rather than sharply defined, helping avoid unnecessary stress concentration and supporting smoother CAD/CAM preparation geometry.
Common Clinical Applications
A shoulder or rounded shoulder may be selected for:
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Selected all-ceramic crowns
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Lithium disilicate restorations
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Layered ceramic crowns
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Porcelain facial margins of selected PFM crowns
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Cases requiring greater cervical restorative thickness
The required width should follow the specific restorative material and manufacturer recommendations rather than a fixed measurement for every case.
Bur Selection for Shoulder Preparation
A suitable tapered flat-end or shoulder-preparation FG diamond bur may be used to establish the cervical ledge.
During preparation, avoid:
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Excessive tooth reduction
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Sharp internal angles
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Irregular margin depth
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Unintended undercuts
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Damage to adjacent teeth or gingiva
Handpiece Control During Shoulder Preparation
Because shoulder preparation may require greater reduction, cutting stability and water cooling become especially important.
The Kaneiko M9K is suitable for demanding crown preparation where stronger cutting performance is needed.
For routine restorative workflows, the Kaneiko Model 100 Integrated High-Speed Dental Handpiece offers another option.
Key features include:
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Integrated M4 connection
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Built-in LED illumination
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330,000 to 400,000 rpm
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Four-point water spray
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Ø1.6 mm FG bur compatibility
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Titanium alloy handle
The Model 100 is designed for clinicians who prefer a direct M4 connection without a separate quick coupling.
Chamfer or Shoulder: What Determines the Choice?
The margin should be selected according to the planned restoration, not simply the bur available.
Restorative Material
Different materials require different minimum thicknesses.
A preparation that is too conservative may not provide enough restorative bulk, while excessive reduction sacrifices healthy tooth structure.
Tooth Anatomy
Remaining enamel and dentine, pulp size, existing restorations and tooth position can all affect preparation design.
Restoration Location
Posterior restorations often emphasize strength and conservation, while anterior restorations may require greater consideration of esthetics and translucency.
Digital Workflow
Smooth, clearly defined margins are easier to identify during intraoral scanning and CAD/CAM design.
Rounded internal transitions can also support more predictable digital restorative workflows.
A Controlled Crown Preparation Workflow
Tooth preparation should be considered as a sequence rather than a single cutting step:
Assess → Reduce → Define Margin → Refine → Verify
Assess
Confirm the restorative material, minimum thickness, tooth anatomy, margin location and manufacturer guidelines.
Reduce
Use an appropriate FG diamond bur for occlusal, incisal and axial reduction.
Define the Margin
Select bur geometry according to the planned finish line.
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Tapered round-end bur → Chamfer
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Suitable flat or modified-end bur → Shoulder or rounded shoulder
Refine
Switch to a finer diamond when needed to smooth preparation surfaces and improve finish-line continuity.
Verify
Check for:
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Continuous finish line
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Adequate restorative clearance
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Smooth axial surfaces
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Rounded internal transitions
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Appropriate convergence
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Absence of unintended undercuts
What About Veneer Preparation?
Veneers should not automatically be classified as shoulder preparations.
Preparation design depends on:
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Enamel availability
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Tooth position
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Ceramic thickness
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Esthetic correction
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Incisal reduction
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Laboratory or manufacturer requirements
The preparation should therefore follow the intended veneer design rather than one universal margin type.
Which Kaneiko Handpiece Fits the Workflow?
For crown and veneer preparation, two Kaneiko options can support different clinical needs.
Best suited for:
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High-load crown preparation
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Enamel reduction
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Veneer preparation
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Resistant restorative material removal
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Procedures requiring stronger cutting performance
Best suited for:
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Routine crown preparation
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General restorative procedures
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Integrated M4 setups
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Clinicians preferring built-in LED illumination
Margin Design as Part of the Full Preparation Workflow
Chamfer and shoulder margins should not be viewed as competing techniques where one is always better.
The correct finish line depends on the restorative material, tooth anatomy, clinical objective and preparation requirements.
The bur determines the cutting geometry, while the handpiece provides the cutting platform needed to control that geometry.
By matching finish-line design, FG bur selection and dental handpiece performance, clinicians can create a more controlled crown and veneer preparation workflow.
Plan the restoration → Select the margin → Match the bur → Control the handpiece → Refine the preparation
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