Preparation & Scanning Guide

Preparation Guide

Ideal Tooth Preparation
for Zirconia Crowns

Zirconia crowns are unforgiving of inadequate preparation. Sufficient reduction, correct margin design, and a well-defined finish line are the three factors that most influence the final fit and aesthetics of the restoration.

Our preferred margin: Chamfer (0.5–0.8mm depth) for the vast majority of posterior and anterior cases. Vertical/feather-edge preparations are a valid alternative where tooth structure is limited — guidance for both is covered below.

Preparation Guidelines Overview — Posterior (left) & Anterior (right)

Zirconia preparation guidelines showing posterior and anterior cross-sections with reduction measurements

Image source: Oceanic Dental. Zirconia Preparation Guidelines. View source →

Posterior Teeth — Premolars & Molars

Posterior Preparation

Posterior zirconia crowns require adequate occlusal reduction to allow sufficient material thickness for strength. Monolithic full-contour zirconia is extremely strong but will fracture if the material is too thin at the occlusal surface.

Reduction Requirements — Posterior

Minimum and ideal reduction depths for each surface.

Surface	Minimum	Ideal	Notes
Occlusal (non-functional cusps)	1.5mm	2.0mm	Most common cause of failure is under-reduction here
Occlusal (functional cusps)	2.0mm	2.5mm	Buccal cusps upper / lingual cusps lower
Axial walls (buccal & lingual)	1.0mm	1.2mm	Uniform reduction, avoid over-tapering
Chamfer margin depth	0.5mm	0.8mm	Well-defined, smooth, continuous
Axial wall taper (total)	6°	10–12°	Avoid >20° total which reduces retention

A — Chamfer (conventional) · B — Vertical (knife-edge)

Illustration showing conventional chamfer (A) and vertical knife-edge (B) crown preparations

Image source: Mörmann, W. et al. (2022). Three-year clinical evaluation of zirconia and zirconia-reinforced lithium silicate crowns with minimally invasive vertical preparation technique. View paper →

Recommended Burs — Posterior

Use diamond burs throughout. Coarse grit for bulk reduction, fine for finishing the margin.

Stage	Bur Type	Purpose
Depth cuts	Round-end tapered diamond (medium grit)	Create occlusal orientation grooves before bulk reduction
Occlusal reduction	Flat-end tapered diamond (coarse)	Remove occlusal tooth structure following the anatomical contour
Axial reduction	Tapered flat-end diamond (medium)	Reduce buccal, lingual and proximal walls to 1–1.2mm depth
Chamfer margin	Chamfer diamond bur (fine, 0.8–1.0mm tip radius)	Create smooth, continuous chamfer 0.5–0.8mm deep
Margin refinement	Fine chamfer or flame-shaped diamond	Smooth any ledges — a clean margin is critical for scanner accuracy
Vertical margin (alternative)	Knife-edge tapered diamond (fine, pointed tip)	Feather the margin to a thin continuous finish — no horizontal ledge

⚠️ Avoid sharp internal line angles. All internal transitions should be rounded and smooth. Sharp angles create stress concentration and cast shadows during scanning that reduce margin accuracy.

Anterior Teeth — Incisors & Canines

Anterior Preparation

Anterior preparations require particular attention to incisal and labial reduction. Layered aesthetic zirconia requires slightly more space than a monolithic posterior crown.

Reduction Requirements — Anterior

Anterior preparations require more labial reduction than posterior to accommodate aesthetic layering.

Surface	Minimum	Ideal	Notes
Incisal edge	1.5mm	2.0mm	Insufficient incisal space = grey show-through
Labial surface	1.2mm	1.5mm	Follow the natural labial contour in two planes if possible
Lingual/palatal surface	0.8mm	1.0mm	Maintain cingulum area reduction
Chamfer margin depth	0.5mm	0.8mm	Especially precise on labial — smooth and continuous
Axial wall taper (total)	6°	10°	Anterior teeth are naturally more tapered — don't over-prepare

Anterior Crown Preparation — Cross-Section

Anterior tooth preparation cross-section showing 1.8–2mm incisal reduction, 1–1.5mm axial reduction and 0.5mm chamfer margin

Image source: Oceanic Dental. Zirconia Preparation Guidelines. View source →

Recommended Burs — Anterior

Anterior preparations benefit from two-plane labial reduction for a more natural emergence profile.

Stage	Bur Type	Purpose
Incisal reduction	Flat-end tapered diamond (medium, narrow)	Create 2mm clearance following the incisal angle
Labial — cervical plane	Tapered round-end diamond (medium)	First plane — follow the gingival third contour
Labial — incisal plane	Tapered round-end diamond (medium)	Second plane — follow the middle and incisal third contour
Lingual/palatal	Wheel or pear-shaped diamond	Clear cingulum and maintain uniform lingual depth
Chamfer margin	Fine chamfer diamond (0.8mm tip radius)	Smooth, continuous chamfer — especially precise on labial
Vertical margin (alternative)	Fine knife-edge tapered diamond	Feather to a thin finish — useful where crown-lengthening is not possible

General Principles

Key Principles for Both Arches

Preparation Checklist for a Scannable Preparation

A great preparation gives the scanner enough information to record it accurately.

Clear, continuous margin. The finish line must be smooth and unbroken all the way around. Any ledges, notches, or rough areas create inaccuracies in the digital impression.
No undercuts. All axial walls must diverge occlusally. Undercuts prevent seating and cannot always be detected by design software automatically.
Rounded internal angles. All internal line angles should be rounded, not sharp. Use a round-end bur to finish these areas.
Adequate height. Minimum 4mm of axial wall height for acceptable retention. Contact us before proceeding with shorter preparations.
Tissue management before scanning. The margin must be fully visible and accessible. Retraction cord, astringent paste, or both should be placed before scanning.
Remove all temporary cement before scanning. Any cement remnants, blood, or saliva will affect scan accuracy. Clean and dry the preparation thoroughly.

⚠️ Contact us before preparing. If you have any doubt about whether a tooth is suitable — due to short clinical crown height, heavily broken-down tooth, or parafunction — contact the lab first. We would rather advise before preparation than after.

Scanning Guide

Intraoral Scanning
Best Practice

A high-quality digital scan is the foundation of a well-fitting crown. This guide covers the principles that apply to all major intraoral scanners — regardless of brand. Always follow your scanner manufacturer's specific protocol in addition to these guidelines.

Compatible scanners: We accept STL files from all major intraoral scanners including iTero, 3Shape TRIOS, Carestream CS 3600, Dentsply Sirona Primescan, Planmeca Emerald, and others. Export as STL and upload via our portal or send via WeTransfer.

Before You Scan — Preparation Checklist

Getting the preparation right before you pick up the scanner will save time and avoid rescans.

Tissue management. Place retraction cord (size 0 or 00 for thin tissue, size 1 for thicker tissue) at least 2–3 minutes before scanning. The margin must be fully visible and dry.
Isolate and dry. Moisture is the enemy of a good scan. Use cotton rolls, dry angles, and air to keep the preparation dry.
Check the preparation. Before scanning, visually confirm: the margin is smooth and continuous, no undercuts are present, there is adequate reduction, and all temporary cement has been removed.
Anti-fog. Allow the scanner to reach operating temperature before beginning. Most modern scanners have automatic anti-fogging.
Patient positioning. Recline the patient to a comfortable position. Posterior teeth scan best with the patient slightly upright to reduce salivary flow.

Scanning Protocol — Step by Step

These steps apply to virtually all intraoral scanners.

Scan the opposing arch first. Scan the full opposing arch before touching the prepared arch. This gives a reference for occlusion.
Scan the prepared arch. Begin posterior to the preparation and scan forward. Capture at least two teeth either side of the preparation.
Capture the margin in detail. Slow down when scanning over the preparation. Angle the scanner tip slightly to ensure the margin area is captured from multiple angles.
Buccal bite scan. Scan the buccal bite in at least two positions — anterior and posterior — with the teeth in maximum intercuspation.
Review before dismissing the patient. Check the on-screen model for any holes, voids, or poorly captured areas — especially at the margin. Rescan before removing retraction cord.

Common Scanning Mistakes to Avoid

These are the most frequent causes of scan failures that require remakes or adjustments.

Mistake	Result	Prevention
Margin not visible	Holes or voids at margin	Place retraction cord and ensure full tissue deflection
Moisture contamination	Rough or granular scan surface	Dry the preparation thoroughly before and during the scan
Moving patient	Stitch errors and misalignment	Ask the patient to keep still and avoid swallowing during the scan
Scanning too fast	Gaps and voids at the margin	Slow down over the preparation — speed is less important than coverage
Poor buccal bite	Crown too high or too low in occlusion	Ensure teeth are in full intercuspation when capturing the bite
Incomplete opposing scan	Missing occlusal contacts	Scan the full opposing arch — minimum 3 teeth either side

Exporting & Sending Your Files

All scanners can export STL files. Here is the standard export process.

Export as STL. You should have at minimum: upper arch STL, lower arch STL, and bite/occlusion STL. Some scanners combine these — that is fine.
Include all required files. We need: prepared arch, opposing arch, and buccal bite registration. Without all three we cannot design the crown accurately.
Name your files clearly. Include the patient identifier and tooth number — e.g. JS_UR6_upper.stl.
Upload to the portal. Log in to your case portal, complete the case submission form, and upload your STL files directly. Alternatively send via WeTransfer referencing your case number.
Include clinical photos where possible. Photos of the preparation, shade tab, and adjacent teeth help our technicians — especially for anterior cases.

Upload Files via the Portal →

Not sure if your scan is good enough? Send it anyway and we will review it. If there are issues with scan quality or margin visibility, we will contact you before proceeding. It is always better to check than to deliver a poorly-fitting crown.