Dental News - Digital workflows for conversion prostheses in full-arch implant dentistry

Dr Max Li

Thu. 17. April 2025

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Implant treatment for full-arch fixed restorations has been around for decades now.^1–3 The treatment usually involves four to six implants placed in either the maxilla or the mandible, which is then restored with a fixed denture.⁴ One of the benefits of this treatment is the ability to achieve a new fixed temporary set of teeth on the same day as implant surgery.^1–5 This temporary restoration is commonly known as a conversion prosthesis owing to its process of fabrication.⁵

Fig. 1: Initial situation.

Conventionally, a denture is converted to an immediate implant-supported temporary restoration after the implants are placed. Briefly, producing a traditional pick-up conversion prosthesis requires locating the implants relative to the denture, drilling holes in the denture at the implant locations and attaching the temporary abutments to the denture.^5, 6 Once the implant abutments have been luted to the denture, it is removed from the mouth. Flanges are cut, voids are filled and the intaglio surface is adjusted to accommodate any bone reduction that may have occurred and to mould the tissue in a certain shape, depending on the design of the prosthesis. Afterwards, the prosthesis is inserted into the mouth. This entire process can be very tedious, messy and time-consuming.⁷

With digital technology in modern-day dentistry, the process of fabricating an immediate conversion prosthesis can be much improved—in terms of both patient comfort and clinical efficiency. This article will present two cases to showcase a digital workflow for dentate (Fig. 1) and edentulous patients using intra-oral scanning and digital software to fabricate the conversion prosthesis.

Partially dentate case

The digital process starts with a digital wax-up long before the day of surgery. Proper planning for any case is vital to treatment success. Once the tooth positioning has been finalised, a surgical plan can be put in place for implant placement. The virtual wax-up is saved and will be needed on the day of surgery for the digital conversion (Figs. 2a & b).

Figs. 2a & b: Pre-op maxillary intra-oral scan (a). Pre-op scan with the digital wax-up (b).

An important factor for digital conversion on the day of surgery is sequencing of both the surgery (extractions and implant placement) and the intra-oral scans. One of the benefits of digital technology is the ability to merge common points from one scan to the next. The basis of the conversion is the proper merging of the implant scan on the day of surgery with the preoperative scan, thus locating the original wax-up on the new implant scan. If no reference points exist between the original scan and the implant scan, there will be difficulty in merging the two scans, and the new implant scan will be lost in 3D space with no way to reference it back. Thus, it is important to determine the reference points prior to surgery with a proper plan. For cases where the patient is still dentate or partially dentate, selective extractions and keeping of specific teeth for reference is an easy way to enable accurate merging of the scans with the preoperative scan.

Figs. 3a–d: Selective extraction left three teeth as common points between the pre-op (a), interim (b) and implant intra-oral scans (c) to enable the software to merge the files, locating the implant scan in the same 3D space as the pre-op scan which had the wax-up.

Figs. 4a–d: Pre-op maxillary intra-oral scan with the digital wax-up (a & b) converted to the prosthesis on the implant scan (c & d).

Once the scans have been merged (Figs. 3a-d), the original wax-up can be referenced to the new implant scan. Using dental software (DentalCAD, exocad), the conversion prosthesis can be designed by connecting the teeth in the wax-up to the implants. This process usually takes approximately 30 minutes because most of the design time goes into design of the wax-up prior to surgery (Figs. 4a-d). After the digital conversion, the prosthesis is 3D-printed, processed and inserted on to the immediately placed implants (Figs. 5 & 6).

Fig. 5: 3D-printed maxillary prosthesis after insertion on the day of surgery.

Fig. 6: Patient’s smile immediately after insertion of the conversion prosthesis.

Figs. 7a & b: Relined maxillary (a) and mandibular trial prostheses (b). Cutouts in the prosthesis allow it to be scanned intra-orally with reference points.

Edentulous case

For edentulous cases, a trial prosthesis is still necessary in order to test tooth positioning and vertical dimension prior to surgery like you would do with any other edentulous case. This trial prosthesis (which is fabricated from the digital wax-up) also doubles as a way to connect the implant scan back to the digital wax-up (Figs. 7a & b).

Since soft tissue is generally not reliable as a reference, especially during or after full-arch implant surgery, reference points must be placed for the purpose of merging. These reference points can be any form of temporary screw that can be embedded in the bone for surgery. Examples include temporary anchorage devices (TADs) or tenting screws. The teeth of the trial prosthesis can be merged with the second (interim) scan. The TADs in the interim scan can be merged with the third (final, implant) scan (Figs. 8a-c & 9a-c). Thus, the implant scan can be related back to the original scan. The same digital process as for the dentate patient is then repeated, and the prosthesis is 3D-printed and inserted on the same day as surgery (Figs. 10a-d, 11a & b).

Figs. 8a–c: Scan of the maxillary trial prosthesis (a). Scan of the trial prosthesis with three TADs in the centre of the palate (b). Intra-oral scan of the four maxillary implants with the three TADs (c).

Figs. 9a–c: Scan of the mandibular trial prosthesis (a). Scan of the trial prosthesis with three TADs (one in the midline, two on the buccal shelf; b). Intra-oral scan of the five mandibular implants with the three TADs (c).

Figs. 10a–d: Original digital wax-up overlayed on to the implant scan (a & b). Conversion prostheses designed by connecting the teeth to the implants (c & d).

Figs. 11a & b: 3D-printed prosthesis before processing (a). Finished prosthesis after removal of the printing supports and final staining and glazing (b).

Conclusion

The advancement of new digital technologies has enabled the conversion process to be cleaner, more streamlined and more predictable. The increased accuracy of intra-oral scanners, improved capabilities of dental software and increased strength of 3D-printed materials all play a role in these advancements. As the digital landscape continues to change, it is an exciting time to see what significant improvements in both patient comfort and care as well as dental clinical proficiency can be achieved.

Editorial note:

This article originally appeared in Oral Health Magazine, and an edited version is provided here with permission from Newcom Media. It was also published in digital—international magazine of digital dentisty vol. 6, issue 1/2025. The list of references can be found here.

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3D printing Dental implantology DentalCAD Digital dentistry Digital workflows Exocad Full-arch rehabilitation Intra-oral scanners

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