Screw-retained crown on a Ti-base in exocad, step by step
How to design a screw-retained crown on a Ti-base in exocad: DentalDB setup, scan body matching, screw channel, emergence profile, thickness checks and export.
A screw-retained crown on a Ti-base is one of the most common implant restorations a lab designs today: a zirconia or ceramic crown bonded to a prefabricated titanium base and screwed to the implant. In exocad the workflow is guided, but a few decisions along the way decide whether the crown fits, lasts and can be screwed in. This post walks through a screw-retained crown on a Ti-base in exocad, step by step, with the checks I make on every case.
Before opening the case
Three things have to be known before design starts: the implant system and platform, the exact Ti-base with its gingival height and the scan body used in the mouth. They decide which library to use and the library has to match the components in the box, from the manufacturer of those components and in a current version. exocad implant library installation explains where the libraries go.
Check the scan too. The scan body must be fully seated and scanned completely, with the soft tissue around it recorded. Common errors are covered in implant scan body tips.
Setting up the job in DentalDB
In DentalDB, select the tooth and the restoration type, then under Implant based? choose the option for the construction. The exocad documentation describes the main ones: a custom abutment, a screw-retained construction mounted directly on the implant, a crown on a stock abutment and manual positioning. Under Additional scans set the scan body scan and add a gingiva scan if the model was scanned without it.
When a Ti-base must be positioned by hand instead of through a scan body, exocad switches to manual positioning and the screw channel is then set manually.
Matching the scan body and the screw channel
The wizard asks for the library and then matches the scan body to the scan. Check the match closely: the library shape should sit on the scanned scan body with no visible offset. A poor match moves the implant position and every step after it.
exocad offers several screw channel angulation options depending on the library. Angulated screw channels are available only when the implant library allows them for that component and the Ti-base manufacturer states the maximum angle. Use the angle to bring the access hole out of the buccal surface of an anterior crown, staying within those limits.
Emergence profile and crown shape
Shape the emergence profile from the Ti-base to the gingiva first, then the crown. The profile should support the soft tissue without compressing it and it has to respect the gingival height of the chosen Ti-base. The crown then gets contacts and occlusion as any crown would, with the screw channel in view so it does not weaken a cusp or a marginal ridge.
Thickness checks around the channel
The Ti-base instructions set the minimum wall thickness of the ceramic part, especially around the screw channel and at the connection to the titanium. Open the thickness view and check those areas before finishing. A crown that looks right on screen can still be too thin next to the channel, which is a common weak point of screw-retained crowns.
The material sets its own minimums as well. For zirconia they are summarized in zirconia minimum thickness and connector size. The choice between a crown on a Ti-base, a custom abutment and a multi-unit solution is discussed in implant abutment types.
Export and production
Export the crown with the interface to the Ti-base as produced by the library and send it to the mill with the right material. For multilayer zirconia, the position in the disc matters too (see multilayer zirconia disc positioning). Keep the design, the library version and the components used with the case. The lab is the manufacturer of the final device and the records matter, as explained in MDR and implant-compatible design files.
When the channel would exit on a visible surface, angled screw channels in exocad explains when the library allows moving it and what the components require.
Sources
- exocad wiki, Choose implant type for construction in DentalDB
- exocad wiki, Abutment design: angulated screw channels
Frequently asked questions
Which option do I choose in DentalDB for a crown on a Ti-base?
Under Implant based, choose the screw-retained or custom abutment option that matches the restoration and set the scan body scan under Additional scans. The choice decides the wizard steps that follow.
Can exocad angle the screw channel on a Ti-base crown?
Only when the implant library supports angulated screw channels for that component. The exocad documentation notes that the angulation feature depends on the library and the Ti-base manufacturer sets the allowed range.
What is the most common mistake in Ti-base crowns?
Designing the ceramic part thinner than the Ti-base manufacturer allows around the screw channel or at the connection. The instructions of the Ti-base set those limits and the design has to stay within them.