3D printed temporary crown: modelling protocol

A provisional restoration obtained by additive manufacturing allows the case to be resolved within the same appointment, eliminating laboratory involvement and the variability inherent to the direct technique. The protocol comprises seven stages whose sequence must be observed.

Prerequisites

• STL file of the arch containing the prepared tooth.
• STL file of the opposing arch for occlusal verification.
• Preferably, a pre-preparation scan or reference wax-up permitting reproduction of the original anatomy.

Scan quality conditions the outcome to a greater extent than subsequent processing. A poorly recorded finish line does not admit recovery during modelling: its position must be estimated, with consequent loss of marginal adaptation.

Stage 1 — Mesh preparation

Once the file has been imported, the Inspector (I) is run and the reported defects corrected. Modelling upon a discontinuous mesh generates errors that manifest only at the slicing stage, once the preceding work has already been invested.

The region of interest is then isolated. Displaying the complete arch slows navigation and impedes reading of the marginal contour.

Stage 2 — Marginal delimitation

This stage determines the final result. Using Select Faces (S), the prepared surface is delimited up to the finish line. The recommended procedure consists of approximate delimitation followed by incremental adjustment with < and >.

Stage 3 — Internal relief

With the prepared surface delimited, Offset (Ctrl+D) is applied. This displacement constitutes the space allocated to the luting agent. Its absence prevents complete seating or generates stress compromising the integrity of the restoration upon removal.

The appropriate value depends on the material, the printing equipment and the resin employed. It is recommended to establish an initial value, print, verify clinically, and adjust until the calibrated parameter for the given system is obtained, thereafter maintained constant.

The result is consolidated with Make Solid, yielding a closed solid from the shell.

Stage 4 — Anatomical reconstruction

Two alternatives are available, the choice depending on the availability of references.

Alternative A — Reproduction of the original element

Where a pre-preparation scan is available, this procedure yields the optimal result, reproducing the patient's original anatomy. The original crown is isolated, positioned over the preparation with Transform (T), refined with Align (N) and consolidated by Boolean Union.

Alternative B — Library or sculpting

In the absence of prior reference, a library element of compatible morphology is imported or the volume is generated with the Volume Brush (3), with Hold Boundary (B) active to preserve the established marginal contour.

Where the contralateral element is intact, mirroring constitutes the more efficient procedure and affords greater morphological harmony.

Stage 5 — Occlusal and proximal adjustment

The antagonist is brought into the scene and its visibility alternated via the Object Browser. Rotating the model permits identification of contact points. Excesses are removed with the Volume Brush in subtractive mode; deficient proximal contacts are compensated by addition.

Stage 6 — Segmentation and validation

Using Separate Shells (Shift+Y), the objects are disaggregated and only the restoration retained. The Inspector (I) is run again, verifying:

• Closed mesh, without discontinuities.
• Single component; the presence of multiple shells indicates residual fragments.
• Minimum thickness throughout, with particular attention to the incisal edge and cuspal inclines.

Insufficient thickness constitutes the most frequent cause of fracture in provisional restorations produced by additive manufacturing.

Stage 7 — Export

Export in binary STL, a format of lower file size and universal compatibility. Nomenclature should identify patient and dental element according to the notation used within the practice.

From file to restoration

At the printing stage, three decisions determine the result: orientation, support placement and layer height. Crowns are customarily positioned at an angle, reducing the cross-sectional area per layer and permitting supports to be kept away from the occlusal surface and the marginal contour. Support scarring in the marginal region necessitates manual adjustment with consequent loss of adaptation.

The post-curing protocol must be executed in accordance with the resin technical data sheet. A restoration with incomplete polymerisation exhibits reduced mechanical properties and residual monomer release.