Why Manual Impressions Are Still Used in Implant Restoration Planning

Intraoral scanning has become the default for crowns, inlays, aligners and study models, and for good reason — it is quicker, more comfortable, and for single units it is at least as accurate as a conventional impression.

Implant restorations are the one area where the picture is genuinely more nuanced, and where conventional impression materials are still routinely chosen for certain cases. The reason is not nostalgia. It is that implant restorations have a requirement natural teeth do not, and the way the two techniques accumulate error across a span behaves differently.

A natural tooth sits in a periodontal ligament. That ligament allows perhaps fifty to a hundred microns of physiological movement, and it means a crown on a natural tooth that is very slightly out can still seat — the tooth accommodates it.

An implant is fused directly to bone. There is no ligament and essentially no movement. A restoration spanning two or more implants must therefore fit all of them simultaneously, in their actual positions, without being forced into place.

This is called passive fit, and the absence of it is not merely a matter of comfort. A framework that does not seat passively is tightened into position by the screws, which locks permanent stress into the assembly. That stress does not dissipate. It contributes to screw loosening, screw fracture, ceramic chipping, framework fracture, and — in the worst cases — bone loss around the implant.

Our article on how implants transmit chewing pressure differently covers the underlying reason implants tolerate less error than teeth do.

For a single implant crown, an intraoral scan is generally excellent. Only one position needs recording, there is nothing to span, and passive fit is not the same problem. Most single-unit implant restorations are scanned.

For multiple implants, the difficulty is different in kind. A scanner builds its model by stitching together many individual images. Each stitch introduces a very small error. Over a short span this is negligible. Over a long edentulous span — where there are few landmarks, because smooth mucosa gives the software little to align against — the errors can accumulate along the arch.

This is why the question is rarely "digital or conventional" in the abstract. It is a question of how many implants, how far apart, and what lies between them.

Our article on digital scans compared with conventional impressions covers the general comparison.

It is not the same procedure as an impression for a crown, and the difference matters.

Instead of recording the shape of a prepared tooth, an implant impression records the position and orientation of a component screwed into the implant.

Impression copings are attached directly to the implants and screwed down. These are precision components matching the implant connection.

Open tray (pick-up) technique. A tray with holes over each implant allows the coping screws to project through. The impression material sets around the copings, the screws are undone through the holes, and the copings come out embedded in the impression, held rigidly in the set material. Because nothing has to be re-inserted, this technique avoids a source of error and is generally preferred for multiple implants.

Closed tray (transfer) technique. The impression is removed leaving the copings in the mouth; they are then unscrewed and repositioned into the impression. Simpler, but the repositioning step introduces a possible error, so it is usually reserved for single units or where access is limited.

Splinting. For multiple implants, the copings are often joined together with a rigid material — commonly a resin pattern, sectioned and rejoined to compensate for its own shrinkage, or a metal bar. Splinted copings move as one unit, which preserves their relative positions during removal.

Material choice. Polyvinyl siloxane or polyether, both of which are dimensionally stable and record fine detail. Polyether is rigid and hydrophilic, which suits implant work.

A verification jig. For extensive cases, a rigid framework is made on the model and tried in the mouth. If it seats passively on all implants, the model is accurate. If it does not, it is sectioned and rejoined in the mouth, and a new record is taken. This step is what makes a full-arch case predictable, and it applies whichever impression method was used.

Full-arch and multiple-implant cases. The accumulation issue described above.

Long edentulous spans. Smooth mucosa provides few reference points for a scanner to stitch against.

Recording soft tissue at rest. Denture-supported and hybrid restorations depend partly on the mucosa. A conventional impression can record tissue in a functionally loaded or specific state in a way scanning does not.

Deeply placed or divergent implants. Where a scan body sits subgingivally or at an awkward angle, the scanner may not see enough of it to register its orientation reliably.

Limited mouth opening or restricted access, where a scanner wand may not reach but a sectional tray can.

Registering vertical dimension and jaw relationship in edentulous cases, where record blocks remain the practical approach.

It is worth being even-handed, because digital is the right answer more often than not.

• Single implant crowns, where accuracy is comparable and the experience is considerably more pleasant.

• Short spans between natural teeth, where the teeth themselves give the scanner good landmarks.

• Patients with a strong gag reflex, where a full-arch impression tray is genuinely difficult.

• Cases needing surgical guides, where the digital file integrates directly with the CT scan for planning.

• Any case where the record may need repeating — rescanning a section is trivial compared with retaking an impression.

• Storage and communication — files do not distort, do not need posting, and can be reused.

Many practices now work with both, choosing per case, and some use a hybrid approach in which a conventional impression is taken and the resulting model is scanned.

Not unpleasant, but worth knowing about.

The healing abutments or existing crown are removed, which takes a moment and is generally comfortable. Impression copings are screwed into place, and a radiograph is often taken to confirm each is fully seated — a coping that is not properly down produces an inaccurate model, and it is not always obvious visually.

If splinting is used, the copings are joined and the material allowed to set. The tray is tried in, the material loaded, and the impression taken. Setting takes a few minutes, during which breathing through the nose is the main thing to concentrate on.

For an open tray impression, the screws are undone before removal. The copings are then removed from the mouth and the healing abutments or temporary restoration replaced.

A bite registration and an opposing arch record are taken, along with photographs and shade information — our article on matching an implant crown to natural teeth covers that side.

The practical implications are few but worth knowing.

Being told an impression rather than a scan is planned is not a sign of dated practice. For full-arch and multi-implant work, it is a considered choice about where error accumulates.

A retake is not a failure. Impressions are checked for bubbles, drags and incomplete detail at the margins. Retaking one takes minutes; remaking a framework that did not fit takes months.

The verification appointment matters. For extensive cases, the try-in of a framework or jig is one of the more important appointments in the sequence, even though nothing much appears to happen at it.

Tell the team about a gag reflex in advance. There are ways of managing it, and a scan may be feasible instead.

Our guides on factors influencing implant stability and implant crown design and maintenance cover the stages either side of the impression.

Are conventional impressions less accurate than digital scans?

Not inherently. For single units they are broadly comparable. For long spans and full arches, conventional techniques with splinted copings currently remain the more predictable option, though digital workflows continue to improve.

Why do I need an impression when I already had a scan?

Scans taken for planning or for a surgical guide serve a different purpose from the record used to make the final restoration. The latter has to capture implant positions with considerably more precision.

What is passive fit and why does it matter?

It means the restoration seats fully on every implant without being forced. Because implants have no ligament to absorb discrepancy, a framework tightened into an ill-fitting position locks in stress that can cause screw loosening, fracture or bone loss.

Will the impression be uncomfortable?

Most people find it manageable. The material is soft going in, sets in a few minutes, and breathing through the nose is the main thing. Tell the team if you have a strong gag reflex.

Why was my impression taken twice?

Impressions are checked closely and retaken if detail is incomplete. It is far quicker to repeat it than to remake a restoration that does not fit.

If you are planning implant treatment, the impression stage is where the accuracy of the final restoration is largely determined — and which technique suits your case depends on how many implants are involved and where they sit.

You can contact our team at our Wimpole Street practice. Our dental implants page explains the full treatment sequence.

This article provides general information about impression techniques in implant dentistry and does not constitute individual dental advice. The appropriate technique for a given case can only be determined through clinical assessment. Wimpole Dental is regulated by the Care Quality Commission, and our clinicians are registered with the General Dental Council.

Next review due: 5 September 2027