Why Dental Laboratories Reject Intraoral Scans: A Chairside Checklist Before Your Patient Leaves

An intraoral scan can upload successfully, look impressive on screen and still be unusable for manufacturing a predictable restoration. The software confirming that a file has been sent does not mean that the preparation margin, occlusion and surrounding anatomy have been captured accurately enough for the laboratory.

When a laboratory asks for a rescan, it is not rejecting digital dentistry or questioning the clinician’s ability. It is identifying a risk before that risk becomes an inaccurate crown, an unsuccessful fit appointment or a remake. The best time to find a scanning problem is while the patient is still in the chair and the tooth remains isolated.

This guide explains what makes an intraoral scan unusable, what the laboratory checks when the file arrives and how the dentist or dental nurse can complete a practical 60-second inspection before dismissing the patient.

A successful upload is not the same as a usable scan
An intraoral scanner creates a three-dimensional model by capturing many images and joining them together. The software can often produce a complete-looking model even when some of the underlying clinical information is unclear, distorted or missing.

The laboratory does not simply need a recognisable tooth. The technician needs sufficient information to identify the preparation boundary, design the restoration, establish appropriate contacts and reproduce the patient’s occlusion.

A scan may therefore be rejected when:

• Part of the preparation margin is missing or obscured
• Blood, saliva or gingival tissue covers the finish line
• The preparation contains holes, blurred surfaces or duplicated anatomy
• Important neighbouring teeth have not been captured
• The opposing arch is incomplete
• The buccal bite scan has not related the arches reliably
• The scan contains stitching or alignment errors
• The prescription and scan do not correspond
• There is insufficient clearance for the prescribed restoration

These are not minor cosmetic imperfections in the digital model. Each one can affect the technician’s ability to design a restoration that fits accurately and functions correctly.

The preparation margin must be visible all the way around
For a crown or other indirect restoration, the technician must be able to follow the finish line continuously around the entire preparation. If the margin disappears beneath the gingiva, blends into adjacent tissue or becomes unclear on one surface, the technician is being asked to estimate where the preparation ends.
That estimate can affect the emergence profile, marginal seal and seating of the restoration. Although software can help display the scan, it cannot reliably recover anatomy that was never recorded.
Before approving the scan, rotate the preparation slowly through 360 degrees. Inspect the buccal, lingual or palatal, mesial and distal surfaces individually. Do not rely solely on the scanner’s automatic margin suggestion or colour map.

Ask three questions:

• Can I trace the finish line without interruption?
• Is the margin represented by clear tooth structure rather than soft tissue or fluid?
• Would another clinician who did not prepare the tooth identify the same boundary?

If the answer to any of these is no, improve the isolation or tissue management and rescan before the patient leaves.
Research comparing digital and conventional workflows has shown that the finish line recorded by an intraoral scanner can differ vertically from the reference geometry in some areas. This reinforces why direct inspection of the captured margin remains important rather than assuming the digital boundary is exact. Research on finish-line location in intraoral-scanner workflows.

Saliva, blood and soft tissue change what the scanner records
Intraoral scanners capture visible surfaces. They cannot scan through saliva, blood or gingival tissue.

A reflective pool of saliva may create an irregular surface, introduce noise or obscure a fine finish line. Blood can interfere with capture and make it difficult to distinguish the preparation from the surrounding tissue. Mobile gingiva can move between scan passes, causing the software to combine anatomy recorded in different positions.

Good soft-tissue management is therefore part of the impression procedure, even when no conventional impression material is used. Retraction, haemostasis, moisture control and a clear field remain essential.
Practical measures may include:

• Achieving haemostasis before starting the definitive scan
• Using appropriate retraction where the margin is equigingival or subgingival
• Drying the preparation without excessively desiccating the tissues
• Using high-volume suction or an assistant to control saliva
• Scanning the preparation promptly once the field is clear
• Rechecking any area where tissue moved during capture

If bleeding restarts or tissue collapses over the margin, repeatedly scanning the area is unlikely to solve the underlying clinical problem. Stop, regain control of the field and then continue.

Look for holes, soft detail and invented-looking surfaces
A visible hole in the digital model is an obvious warning, but not every problem appears as an empty space. A surface may look rounded, melted, rippled or unusually smooth because the scanner did not capture enough reliable information.

Pay particular attention to:

• The finish line and axial walls
• Sharp line angles
• Deep proximal boxes
• Distal surfaces of terminal teeth
• Interproximal areas beside the preparation
• Occlusal anatomy on the opposing arch
• Edentulous spaces needed for the proposed design

Do not assume the software has accurately filled every apparently complete surface. Compare the model with what you can see clinically. If the shape on screen does not resemble the mouth, investigate it.

Why duplicated anatomy and stitching errors occur
The scanner must repeatedly recognise where it is and join each new image to the existing model. This process is often described as stitching.

Errors can occur when the scanner loses its position and attaches new information to the wrong place. Long smooth edentulous areas, repeated tooth shapes, limited landmarks, rapid movement, contamination and repeated scanning over the same region may make alignment more difficult.
Possible signs include:

• A tooth appearing twice
• An unnatural step or bend in the arch
• Gingiva that appears stretched or folded
• A sudden change in tooth width
• Overlapping or floating anatomy
• A bite that looks correct on one side but separated or penetrated on the other
• An arch form that changes after additional images are added

A large digital model is not automatically a more accurate one. Continuing to pass over an unstable area can add conflicting information and make the dataset harder to assess.
Following the scanning strategy recommended for the particular scanner is important because scanner design, software and scan path can all influence accuracy. A systematic review of intraoral-scanner accuracy identified several factors that can affect performance, including the scanner system, scan strategy and characteristics of the area being scanned. Systematic review of factors affecting intraoral-scanner accuracy.

When to rescan a small area
A local rescan may be appropriate when the rest of the model is stable and the defect is clearly limited. Examples include a small patch of missing anatomy, a saliva-covered area on one surface or a margin segment that became visible after further retraction.

Use the scanner’s delete or cut-out function to remove the unreliable information rather than simply scanning repeatedly over it. Then dry and isolate the site before recapturing it from a stable landmark into the missing area.
A small-area correction is most suitable when:

• The surrounding teeth and tissues look accurate
• The scanner remains correctly oriented
• There is no duplicated anatomy
• The error has an identifiable boundary
• The arches and bite remain correctly aligned
• The new images merge cleanly with the existing scan

After rescanning, rotate the model and make sure the correction has not created a ledge, overlap or second version of the same anatomy.

When it is safer to restart
Restarting can feel wasteful after several minutes of scanning, but it may be faster than trying to repair a corrupted dataset.
Consider starting again when:

• The scanner has lost tracking repeatedly
• There is duplicated or distorted anatomy across a wide area
• The arch form appears inaccurate
• Numerous patches require deletion and rescanning
• The preparation was contaminated throughout the original scan
• The bite is clearly inconsistent with the patient’s clinical occlusion
• The scan strategy was interrupted and the software cannot recover reliably
• You no longer trust which parts of the model are accurate

The decision should be based on confidence in the complete dataset, not on how much time has already been invested.

Do not forget the opposing arch
A beautifully captured preparation scan cannot produce a predictable restoration without an adequate opposing scan. The laboratory needs enough opposing anatomy to assess occlusal contacts, functional space and the relationship of the restoration to the antagonist.

Common problems include:

• The opposing scan stopping too close to the antagonist
• Missing distal teeth
• Holes in the opposing occlusal surfaces
• Saliva creating false anatomy
• An appliance or removable prosthesis being scanned when it should have been removed
• The wrong opposing arch being attached to the case

The clinically relevant opposing teeth should be captured clearly, together with enough stable anatomy for reliable alignment.

The bite scan needs more than a few random images
The buccal bite scan tells the software how the two arches relate. If this relationship is wrong, a well-designed crown may still return high or out of occlusion.

Before recording the bite, ensure the patient closes naturally into the intended intercuspal position. Avoid guiding the mandible inadvertently unless a specific jaw relationship has been prescribed.
Capture adequate buccal anatomy across both arches without excessive soft tissue. Depending on the case and scanner workflow, additional bite information may be helpful when there is limited posterior support, a long-span restoration, a terminal tooth or uncertainty about mandibular stability.

After alignment, inspect the virtual articulation rather than accepting it automatically. Look for:

• Unexpected posterior separation
• Excessive penetration between opposing teeth
• Contact only on the prepared side
• A visible shift in the mandibular arch
• A bite that does not match the clinical appearance
• Differences between left and right relationships

I
f the digital bite appears wrong, delete and repeat the bite scan while the patient is still present.

What the laboratory checks when the scan arrives
At Bremadent, a digital case must be assessed as clinical manufacturing information, not simply opened as a file.
Depending on the prescription, the laboratory may check:

• That the correct patient and practice details match the prescription
• That the prescribed tooth and restoration are clear
• Whether the preparation margin can be followed completely
• Whether the preparation and neighbouring contacts are accurately captured
• Whether there is sufficient occlusal and axial reduction
• Whether the opposing arch includes the relevant anatomy
• Whether the bite appears stable and clinically credible
• Whether the scan contains holes, overlaps, distortion or stitching errors
• Whether implant scan bodies and surrounding tissues are recorded appropriately
• Whether shade information, stump shade, photographs or material instructions are present
• Whether the requested design can be manufactured from the information supplied

If essential information is absent, contacting the practice is the responsible action. Designing through uncertainty may save a telephone call today but create a much more expensive fit problem later.

The final 60-second chairside scan checklist

Before the patient leaves, the dentist or nurse should complete one final review.

First 15 seconds: inspect the preparation

• Rotate the preparation through 360 degrees
• Trace the complete finish line
• Look for blood, saliva, tissue coverage, holes and blurred areas
• Confirm proximal and occlusal surfaces are complete

Next 15 seconds: inspect the wider arch

• Check the neighbouring teeth and contact areas
• Confirm adequate anatomy has been captured around the working site
• Look for duplicated teeth, overlaps, steps or distorted gingiva
• Confirm the scanned arch matches the mouth

Next 15 seconds: inspect the opposing arch and bite

• Confirm the correct opposing arch is present
• Check the antagonist and surrounding occlusal surfaces
• Inspect the aligned arches for unexpected gaps or penetration
• Confirm the virtual bite resembles the patient’s clinical bite

Final 15 seconds: check the prescription

• Confirm the patient, tooth number and restoration
• Record the material, shade and required design
• Add photographs and stump shade where relevant
• Include bruxism, implant, occlusal or appliance information
• Make sure every required file has uploaded

This short review can prevent a second appointment, an avoidable laboratory query and days of delay.

Digital dentistry works best when both teams inspect the same risks
The strongest digital workflow is not the one with the fewest clicks. It is the one that transfers accurate, complete and clinically meaningful information from the chairside to the laboratory.

Dentists control tissue management, preparation, scanning and jaw records. Technicians control interpretation, design, manufacturing and laboratory quality assurance. Predictable results depend on both teams refusing to guess when essential information is missing.

A scan should therefore be treated like any other clinical impression. It must be checked before the patient leaves, not merely sent and assumed to be suitable.

We provide a trusted laboratory service delivering consistent quality, saving chairside time, and supporting predictable patient outcomes.

Thank you for reading, if you or you know anyone that needs help with Digital dentistry and needs a reliable dental laboratory, please get in touch: 

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