06 — Troubleshooting
Diagnosis,
not trial
and error.
A guide to identifying, interpreting and correcting failures in intraoral scanning and dental 3D printing. A visually similar defect can have different causes; diagnosis follows process evidence, not appearance.
Premises
Diagnosis, not guesswork
Digital workflow failures rarely have a single cause. Before changing several parameters at once, isolate one hypothesis, test it, record it, and only then move on.
Less rework
The goal is to recognise early signs: duplicated mesh, areas without data, delamination, poor adhesion, base distortion, excessive washing and incorrect post-curing.
Process control
Scanner, computer, resin, temperature, FEP film, orientation, supports, washing and post-curing form a chain. Correcting only the last step can mask the real error.
Investigation method
Use a stable analysis sequence. In digital dentistry, changing scanner, software, resin, orientation and post-cure simultaneously makes it impossible to know which variable actually fixed the problem.
Define the signal
Describe the observable defect: a hole in the mesh, a step, an adhesion failure, a loose layer, a widened margin, a brittle part or poor fit.
Locate the stage
Sort the defect into acquisition, CAD, slicing, printing, washing, post-curing or finishing.
Isolate the variable
Change only one condition per test: exposure, temperature, supports, orientation, FEP film, cleaning or scanning strategy.
Record
Note the resin batch, temperature, exposure time, orientation, layer height, solvent, wash time and cure.
Validate
Confirm on a functional part, not only by visual inspection. For clinical use, fit, stability and biocompatibility matter.
A visually similar defect can have different causes. A part stuck to the FEP film may result from weak initial adhesion, a degraded film, cold resin, insufficient exposure, poor orientation or excessive cross-sectional area per layer. Diagnosis must follow process evidence, not appearance alone.
Possible scanning errors
The intraoral scanner rebuilds a mesh through sequential image acquisition. Over large areas, small alignment errors can accumulate. Field control, anatomical references and scanning strategy reduce the likelihood of distortion.
2.1Loss of tracking Medium
- Observed signal
- The software freezes, interrupts capture, raises an alert, or the mesh stops advancing even while the wand keeps moving.
- Likely causes
- Movement that is too fast or erratic.
- Absence of stable anatomical references.
- Saliva, blood, tongue or cheek covering surfaces.
- Highly reflective or repetitive surfaces.
- Recommended action
- Return to an already-scanned region, preferably occlusal, recover tracking and continue with continuous movement. If the mesh became confused, erase that stretch and rescan with a dry, well-retracted field.
2.2Steps, overlap or duplicated mesh High
- Observed signal
- Teeth with “steps”, double-layered gingiva, overlapping areas or anatomy that looks flattened after several passes.
- Likely causes
- Excessive repetition over the same area at incompatible angles.
- Software attempting to merge images captured at different moments with mobile tissue.
- Insufficient retraction of mucosa, tongue or lip.
- Automatic hole filling without sufficient real data.
- Recommended action
- Do not try to “fix” it by scanning indefinitely. Use the trim tool, remove the unstable area and capture again in a short, clean and coherent sequence.
2.3Holes in the mesh Medium
- Observed signal
- Interproximal areas, the preparation margin or cervical regions appear with holes, shadows or artificial filling.
- Likely causes
- Insufficient wand angulation.
- Subgingival margin without adequate retraction.
- Moisture or blood in the area of interest.
- Field of view blocked by cheek, lip or tongue.
- Recommended action
- Increase retraction, dry without over-desiccating, angle the wand mesially and distally, and capture real data. For a subgingival preparation, the scan will only be reliable if the margin is visible.
2.4Failure on metal, polished ceramic or shiny surfaces Low
- Observed signal
- The mesh shows unstable or empty areas over amalgam, metal, abutments, polished restorations or very wet surfaces.
- Likely causes
- Intense specular reflection.
- External light source interfering with the reading.
- Smooth surface with few reference points.
- Recommended action
- Reduce direct light from the operating light, change the reading angle, capture adjacent structures first and advance gradually. Where the material and software allow, reflective-surface settings can help.
Physical barriers can be useful on the scanner body and cable, provided they do not cover the wand or lens, nor obstruct ventilation. Overheating and fogging can occur when air outlets are blocked. The wand must follow the manufacturer's official cleaning and sterilisation protocol.
Possible 3D-printing errors
Most resin-printing failures come from the interaction between initial adhesion, peel force, viscosity, exposure, orientation, supports and the condition of the FEP/nFEP/PFA film.
3.1Part stuck to the bottom of the vat High
- Observed signal
- The build plate rises empty or partially empty; a sheet of cured resin is stuck to the FEP film.
- Likely causes
- Insufficient bottom-layer exposure.
- Poorly levelled plate or contaminated surface.
- Cold or viscous resin increasing suction force.
- Excessive layer area or inadequate orientation.
- Cloudy, marked or mistensioned FEP film.
- Recommended action
- Check levelling, clean the plate, inspect the FEP film, control the temperature where indicated, and adjust bottom exposure incrementally. Avoid raising exposure without reviewing orientation and cross-sectional area per layer.
3.2Horizontal lines or delamination Medium
- Observed signal
- The part prints, but shows lines, separating layers, horizontal “scars” or regions with weak bonding between layers.
- Likely causes
- FEP film with inadequate tension or wear.
- Lift speed or height incompatible with the resin.
- Insufficient or poorly positioned supports.
- Settled or poorly homogenised resin.
- Normal exposure insufficient for that colour, batch or temperature.
- Recommended action
- Homogenise the resin, reduce lift aggressiveness where needed, add support in critical areas and calibrate normal exposure. If the problem appears only after many prints, replace or re-tension the film.
3.3Elephant's foot and distorted margin Medium
- Observed signal
- Widened first layers, deformed base, a die with poor fit or a distorted margin on a critical part.
- Likely causes
- Excessive bottom-layer exposure.
- Critical part printed directly on the build plate.
- Base compensation disabled or inadequate.
- Excessive compression at the Z-axis zero point.
- Recommended action
- Do not place critical margins directly on the plate. Tilt restorative parts, use adequate supports, reduce bottom exposure if excessive and consider the slicer's elephant-foot compensation feature.
3.4Incomplete or warped part, or broken supports High
- Observed signal
- Part of the piece exists, part is missing; supports break, tips stay stuck to the FEP film, or the part warps during printing.
- Likely causes
- Support insufficient for the mass and geometry.
- Unsupported islands in the slice.
- Orientation producing a large cross-section per layer.
- Support contact too small for a viscous or highly filled resin.
- Recommended action
- Check for islands in the slicer, reduce cross-sectional area with proper orientation, increase supports in non-critical zones, and keep margin and fit surfaces free of excessive marks.
Post-processing errors
Washing, drying and post-curing alter mechanical properties, dimensional stability, degree of conversion and biocompatibility. The protocol must match the material, not only the printer.
4.1Cloudy, brittle part or micro-cracks Medium
- Likely causes
- Bath too long, incompatible solvent, resin-saturated alcohol, aggressive brushing or insufficient drying before curing.
- Recommended action
- Follow the manufacturer's solvent and time. Use a clean bath where needed, avoid over-immersion and dry completely before post-curing.
4.2Brittle, under-converted or distorted part High
- Likely causes
- Incompatible time, temperature, wavelength, intensity or curing chamber. Under-curing and over-curing can produce different problems.
- Recommended action
- Use a curing unit validated or compatible with the resin. Avoid extrapolating time and temperature without evidence. For clinical parts, respect the instructions for use, the batch and traceability.
Studies on printed dental resins show that post-curing conditions can alter degree of conversion, microhardness and colour stability. “Cure it longer” is therefore not a sufficient technical criterion; the answer depends on the material and the curing unit.
Environment, maintenance and routine
Organisation reduces failures, contamination and equipment wear. The goal is not improvised protection, but a standardised clean, traceable and safe bench.
- Clean hand / dirty hand
- Decide which hand handles parts and resin and which touches the mouse, screen, laptop, lid and clean tools. Change gloves whenever contamination occurs.
- Equipment protection
- Plastic film can protect external areas, buttons and the bench, but must not block ventilation, sensors, moving lids or the optical area.
- FEP / nFEP / PFA
- Inspect for cloudiness, marks, tension and micro-punctures. If a leak is suspected, empty the vat, clean it and test before printing again.
- Resin
- Shake it, filter when needed, avoid excessive ambient light, and never mix resins or batches without traceability.
- Build plate
- Keep it clean, dry and free of cured residue. Residue from a previous print is a frequent cause of failure and of damage to the FEP film.
- Records
- Note parameters, batch, opening date, solvent, wash time, cure time and temperature, and any failures that occurred.
Liquid resins and solvents must be handled with PPE, adequate ventilation and compatible disposal. Nitrile gloves are generally preferred for handling liquid resin, but the final choice should follow the material's safety data sheet. A surgical mask is not a respirator for organic vapours.
Essential references
References selected to support claims on safety, accuracy, dental printing and post-processing.
- Aktug Karademir S, et al. Effects of post-curing conditions on degree of conversion, microhardness, and stainability of 3D printed permanent resins. PubMed
- Falih MY, et al. Trueness and precision of eight intraoral scanners with different finishing line configurations. PMC
- Hassanpour M, et al. Effects of post-processing parameters on 3D-printed dental materials. PMC
- Kwon M, et al. Full-arch accuracy of five intraoral scanners: in vivo analysis. PMC
- NIOSH. Approaches to Safe 3D Printing: a guide for makerspace users, schools, libraries, and small businesses. CDC/NIOSH (PDF)
- Oğuz F, et al. An evaluation of the performance of low-cost resin printers. PMC
- Vafaee F, et al. Accuracy, precision and trueness of dental scanners. PMC
- Zingari F, et al. Predictability of intraoral scanner error for full-arch implant impressions. PMC