Why plan in 3D before a bone graft and an implant?

What cone beam CT reveals, and a panoramic X-ray does not

Cone beam CT (CBCT) reconstructs the jaws in three dimensions. The clinician scrolls through slices in every plane, above all cross-sections cut at right angles to the ridge, which show the bone “in section”.

These slices reveal:

• the bone height available, from the top of the ridge to the nerve or sinus;
• the width of the ridge at several levels (wide at the base, it may taper to a knife edge at the top);
• the angle of the ridge relative to the opposing teeth;
• the apparent density of the bone and any lesions (retained root, cyst, infection).

A review of recommendations judges cone beam CT justified for diagnosis, planning and intraoperative transfer in implant dentistry ^[1]. After an extraction, the ridge loses on average 3.8 mm of width within six months ^[2]: that very loss, invisible on a panoramic X-ray, is precisely what 3D imaging brings to light.

Two structures to respect: the nerve and the sinus

In the lower jaw, the inferior alveolar nerve runs through a bony canal beneath the roots of the premolars and molars. It is what gives the lower lip and chin their sensation; injuring it risks numbness or abnormal sensations. On the cone beam CT, the canal is identified and traced from end to end, together with its exit (the mental foramen) and any loops.

In the upper jaw, the sinus is an air-filled cavity lined with a thin membrane, just above the roots of the molars. Cone beam CT shows the bone height beneath it, the thickness of the membrane, any internal walls (septa) and the state of the sinus lining. All of these point towards a crestal or a lateral sinus lift. During a lateral sinus lift, membrane perforation is the most frequent complication, in 19.5% of cases on average in a systematic review ^[3]: knowing the anatomy before opening is already a way of anticipating it.

Starting from the tooth, not the bone

For a long time the implant went wherever bone was left, and the crown had to make do, sometimes at the cost of an oblique axis or a neck impossible to clean properly. Prosthetically driven planning reverses the order of decisions, in four steps:

• a digital impression of the teeth (taken with an intraoral scanner) is superimposed on the cone beam CT: visible teeth and invisible bone appear in the same space;
• the future crown is modelled in the place that chewing, appearance and cleaning demand;
• the virtual implant is slipped beneath that crown, along the axis of the chewing forces;
• only then is it checked whether bone surrounds this implant along its whole length. Where it is missing, the volume to rebuild is defined around the implant as it should be, not the other way round.

From plan to mouth: guide and mesh

A plan is only worth something if it is faithfully reproduced in theatre. Two tools build that bridge between the screen and the mouth.

The surgical guide is a splint that steers the drills along the planned axis. Its accuracy has been measured: on average, the placed implant deviates from the plan by a little over a millimetre (1.2 mm at the entry point, 1.4 mm at the tip) and by 3.5° ^[4]. Guiding every step, rather than only the first drill, tightens these deviations further: against freehand placement, the angular deviation drops from 7.5° to 2.6° and the deviation at the tip from 2.2 mm to 0.9 mm ^[5]. The comparison table of the three techniques and the principle of placement are on the page Placing an implant and guided surgery.

For large reconstructions, the custom titanium mesh is born of the same file: it gives physical form to the bone volume drawn around the implants. A 2025 meta-analysis reports, with these meshes, a mean bone gain of 6.4 mm in width and 5.1 mm in height ^[7]. Design and manufacture are described in the article on 3D printing, and the treatment steps on the Custom titanium mesh page.

What 3D does not solve

• Dose. Cone beam CT delivers more radiation than a panoramic X-ray, and very unevenly from one machine to another: the equivalent of 2 to 200 panoramic images ^[1]. The field of view is therefore kept to what is needed, and the scan is repeated only if it could change the decision.
• Artefacts. Metal crowns, old implants or patient movement draw streaks that hide the neighbouring bone ^[1].
• Measurement accuracy. It reaches 0.2 mm on the best-performing machines, but can be several times poorer depending on the machine and its settings ^[1]. Figures read on screen are not measurements to the tenth of a millimetre.
• Transfer. Even with a guide, a deviation of about 1 to 1.5 mm persists on average ^[4]; and the guide must sit perfectly still in the mouth.
• Biology. A perfect plan ensures neither gum healing nor bone formation. With custom meshes, exposure still occurs in close to one case in five ^[7].

Finally, greater accuracy does not automatically mean better clinical outcomes: when the available systematic reviews are pooled, implant survival is the same after guided surgery and after freehand placement; the benefit of guidance would lie chiefly in reducing surgical risk in difficult cases ^[8]. 3D planning is a tool for decision-making and safety, not a promise.

In which situations is 3D planning useful?

In a straightforward situation with bone to spare, planning is still useful but can be lighter. At Dr Hazout’s practice in Levallois-Perret, its level is matched to the difficulty of the case: never maximal as a matter of routine, never cut back when the nerve or sinus are close.

Frequently asked questions

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