Composite injection technique: designing the models in exocad
How the lab designs the wax-up and the printable models for the composite injection technique in exocad, from the scan to a model the clinic can use.
The composite injection technique lets a dentist transfer a planned shape into the mouth with flowable composite and a clear silicone index. The clinical part takes place at the chair, but the result depends on the wax-up and on the model the index is made on. This post is for labs and clinics that want to plan these cases in exocad, and it covers the design, the model and the details that decide whether the index fits.
How the technique works
The lab designs the final shape of the teeth as a digital wax-up. The wax-up is merged with the scanned arch and printed as a model. On that model a clear, rigid silicone index is made. In the mouth the dentist isolates and bonds the teeth, seats the index, injects a flowable or injectable composite through small holes and cures it through the clear silicone. After removing the index, only excess and contacts need finishing.
The shape on the patient is the shape of the wax-up, so every millimeter that is wrong in the design shows up in the mouth. The clinic gets little help from the composite: it flows into whatever space the index leaves.
What the lab needs from the clinic
An intraoral scan of both arches and the bite is the minimum. For anterior cases, frontal photos with the lips at rest and in a smile help a lot, and a face scan helps further when the smile line changes. The clinician should also say what the plan is: closing diastemas, lengthening worn incisors, correcting a shape, or rebuilding a worn dentition with a new vertical dimension.
The intraoral scan checklist covers what makes a scan usable. For these cases the cervical areas and the interdental spaces matter most, because the index has to sit on them.
Designing the wax-up in exocad
The wax-up is designed over the existing teeth, usually as a mockup job in DentalCAD, with the same tooth libraries and free-forming tools used for crowns and veneers. A few rules help.
- Design additively. Composite is added on the tooth, so the wax-up should cover the existing surface and never go inside it, unless the clinician has planned a preparation.
- Keep the emergence smooth. A thin edge at the gingival margin makes a thin composite flash that is hard to clean.
- Leave the contacts open or very light where the clinician wants to inject teeth one at a time. Many clinicians inject alternating teeth, then the ones in between, and tight contacts in the design make that harder.
- Check the occlusion. A lengthened incisor or a new canine guidance changes function, and the virtual articulator shows the interference before the composite is in the mouth.
When the smile itself is the subject, Smile Creator brings the photos into the design so the clinician can approve the shape against the face.
From the design to a printable model
The index is made on a physical model, so the wax-up and the scanned arch must become one closed mesh. In exocad this needs the Model Creator module: after the step that merges and saves the restorations, the model design starts and Digital waxup model is chosen as the model type. The wizard then lets you pick which parts go into the model, the full anatomy or the merged parts, and checks that the result is watertight.
A few checks before printing:
- The merged model must be watertight, with no gap between the wax-up and the tooth surface.
- The base should be closed and stable. A hollow model saves resin, but the walls have to stay stiff, because the silicone is pressed onto it.
- Interdental spaces deeper than the index can reach should be blocked out, or the silicone tears when it is removed.
- The file name should state what the model is (anatomic, reduced, upper, lower), which avoids confusion when two models of the same case exist.
For printing, a model resin calibrated on the printer in use is enough. The guide on 3D printed models with Model Creator covers bases, hollowing and drain holes.
One layer or two
Many cases are injected with a single composite shade, using one model and one index. When the clinician wants a dentin core and an enamel layer, the lab prepares a second model with reduced anatomy from the same design. The two-layer injection workflow explains how the reduction is designed and how the two models are used.
Where the lab adds value
Any lab with exocad can export a wax-up. What the clinic actually pays for is a wax-up that fits the face, works in occlusion, respects the gingiva and comes with a model that gives a clean index on the first try. Labs that want to offer these cases without spending design time on them can send the case for outsourced CAD design: the design comes back as an STL ready to print, with the reduced model when it is needed.
Frequently asked questions
What does the lab deliver for the composite injection technique?
A digital wax-up approved by the clinician and one or more printable models made from it. The clinic, or the lab, makes the clear silicone index on the printed model, and the dentist injects the composite through it in the mouth.
Which exocad modules are needed?
The wax-up is designed in DentalCAD, for example as a mockup job. Turning the design and the scanned arch into one printable digital waxup model needs the Model Creator module.
Can the same design be used for a two-layer injection?
Yes. A reduced version of the same anatomy gives a second model for the dentin layer, while the full anatomy gives the model for the enamel layer. Both come from one design, so they line up.
How long does the design take?
It depends on the number of teeth and on how much the clinician wants to change the smile. A simple case of a few anterior teeth is quicker than a full arch with a new vertical dimension, which also needs an occlusal check.