Research update: digital workflows

digital workflowImplant Dentistry Today presents the latest abstracts published on the burgeoning complexities of digital implant workflows.

Papaspyridakos P, Vazouras K, Chen YW, Kotina E, Natto Z, Kang K, Chochlidakis K (2020)

Digital vs conventional implant impressions: a systematic review and meta-analysis

J Prosthodont 29(8):660-678

Purpose

To systematically review in vitro and clinical studies comparing quantitatively the 3D accuracy (global implant deviations) of digital vs conventional implant impressions for partially and completely edentulous patients.

Materials and methods

Electronic and manual searches were conducted to identify in vitro and clinical studies, reporting on the 3D accuracy between digital and conventional implant impressions. Secondary outcomes were the effect of implant angulation, type of conventional impression technique, and type of intraoral scanner on the accuracy of implant impressions.

Results

The inclusion criteria were met by nine in vitro studies and one clinical study reporting on completely edentulous impressions, while six in vitro and two clinical studies reported on partially edentulous impressions. Quantitative meta-analysis was performed for five completely edentulous and six partially edentulous studies.

The studies exhibited high values for heterogeneity. A random effects model was conducted to estimate the effect size. Based on five in vitro studies on completely edentulous impressions, the mean 3D implant deviation between conventional and digital impressions was 8.20µm and the digital impressions had nominally less deviation (p = 0.72).

Based on one clinical and five in vitro studies on partially edentulous impressions, the mean 3D implant deviation between conventional and digital impressions was 52.31µm and the conventional impressions had nominally less deviation (p = 0.03). Five in vitro and two clinical studies were not included in the quantitative analysis due to heterogeneity in the methodology.

Implant angulation affected accuracy in favour of the partially edentulous conventional impressions. The effect of different scanners was not statistically significant on the completely edentulous impressions (p = 0.82).

Conclusions

Digital scans appear to have comparable 3D accuracy with conventional implant impressions based mainly on in vitro studies.

However, clinical trials are recommended to investigate the clinical accuracy of digital scans and digitally fabricated interim or prototype prostheses, before digital implant scans can be recommended for routine clinical use.

Burkhardt F, Strietzel FP, Bitter K, Spies BC (2020)

Guided implant surgery for one-piece ceramic implants: a digital workflow

Int J Comput Dent 23(1):73-82

Background

Accurate implant placement is key to successful implant treatment. Once inserted, it can be difficult to correct the orientation of the implant axis, especially of a one-piece implant. Prosthetic-driven digital implant planning in combination with fully guided implant surgery can offer additional safety in such cases.

Case presentation

The patient presented with a wide, edentulous interdental space extending from sites 13 to 16, which was to be restored with three one-piece zirconia implants supporting a zirconia fixed partial denture comprising a cantilever to the mesial aspect. Digital planning based on DICOM and intraoral surface data was performed to ensure optimal positioning. Guided implant placement was executed using a contra angle handpiece with special attachments and a compatible, sleeveless drill guide. Impressions of the implants for the final restoration were acquired using an intraoral scanner.

Reflection-related errors were compensated for by using the given digital abutment geometry. The DICOM and STL datasets were superimposed and used as the basis for fabricating a monolithic zirconia restoration through a subtractive milling process. The final restoration was adhesively cemented.

Conclusions

By using a prosthetic-driven implant planning strategy, it was possible to place the one-piece ceramic implants without an available implant manufacturer’s guide-based solution. This was accomplished using a contra angle surgical handpiece with special attachments and a compatible drill guide.

This approach is particularly recommended for the placement of one-piece implants, which otherwise require irreversible abutment grinding for the adjustment of the implant axis orientation after placement. To increase the precision of the digital impressions of the implants, the ideal abutment geometry was imported and superimposed onto the scan data.

The results demonstrate that the proposed method can dispense with the need for gingival retraction when acquiring impressions for implants of this type in the future.

Prpić V, Schauperl Z, Ćatić A, Dulčić N, Čimić S (2020)

Comparison of mechanical properties of 3D-printed, CAD/CAM, and conventional denture base materials

J Prosthodont 29(6):524-528

Purpose

To evaluate and compare the mechanical properties (flexural strength and surface hardness) of different materials and technologies for denture base fabrication. The study emphasised the digital technologies of computer-aided design/computer-aided manufacturing (CAD/CAM) and three-dimensional (3D) printing.

Materials and methods

A total of 160 rectangular specimens were fabricated from three conventional heat-polymerised materials (Probase Hot, Paladon 65, and Interacryl Hot), three CAD/CAM produced materials (Ivobase CAD, Interdent CC disc PMMA, and Polident CAD/CAM disc), one 3D-printed material (Nextdent Base), and one polyamide material (Vertex Thermosens) for denture base fabrication.

The flexural strength test was the three-point flexure test, while hardness testing was conducted using the Brinell method. The data were analysed using descriptive and analytical statistics ( = 0.05).

Results

During flexural testing, the Ivobase CAD and Vertex Thermosens specimens did not fracture during loading. The flexural strength values of the other groups ranged from 71.7 ± 7.4 MPa to 111.9 ± 4.3 MPa. The surface hardness values ranged from 67.13 ± 10.64 MPa to 145.66 ± 2.22 MPa. There were significant differences between the tested materials for both flexural strength and surface hardness.

There were also differences between some materials with the same polymerisation type. CAD/CAM and polyamide materials had the highest flexural strength values. Two groups of CAD/CAM materials had the highest surface hardness values, while a third, along with the polyamide material, had the lowest. The 3D-printed materials had the lowest flexural strength values.

Conclusions

Generally, CAD/CAM materials show better mechanical properties than heat-polymerised and 3D-printed acrylics do. Nevertheless, a material’s polymerization type is no guarantee of its optimal mechanical properties.

Pol CW, Raghoebar GM, Cune MS, Meijer HJ (2020)

Implant-supported three-unit fixed dental prosthesis using coded healing abutments and fabricated using a digital workflow: a one-year prospective case series study

Int J Prosthodont 33(6):609-619

Purpose

To test the applicability of coded healing abutments, intraoral scanners, and monolithic zirconia for the fabrication of three-unit fixed dental prostheses (FDPs) on two dental implants.

Materials and methods

Patients with three missing teeth in the posterior region of either the maxilla or mandible received two dental implants. After healing, coded healing abutments were placed. Full-arch intraoral scans were made to produce individual titanium abutments and a three-unit FDP. Peri-implant tissues were assessed two weeks after placement of the FDP and again after one year.

Patient-reported outcome measures were registered prior to treatment and after one year. The quality of the FDPs was assessed using modified United States Public Health Service criteria after one year of service.

Results

A total of 54 patients were treated with 60 restorations, and 51 patients with 56 restorations were available at the one-year follow-up. Implant survival was 99.1%, and prosthesis survival was 100%. The peri-implant tissues remained healthy, and patient satisfaction was high.

However, the USPHS evaluation showed that some prostheses exhibited fit or colour issues that needed to be addressed, although most were rated as successful (80.4%).

Conclusion

The use of coded healing abutments and intraoral scanners to produce full-zirconia three-unit FDPs on two dental implants proved to be a feasible technique, with promising objective and subjective results.

However, technical challenges still impacted the treatment results. This resulted in a number of restorations having clinical or radiographic marginal gaps or reduced colour match.

Chochlidakis K, Papaspyridakos P, Tsigarida A, Romeo D, Chen YW, Natto Z, Ercoli C (2002)

Digital versus conventional full-arch implant impressions: a prospective study on 16 edentulous maxillae

J Prosthodont 29(4):281-286

Purpose

A prospective clinical study to compare for the first time the accuracy of digital and conventional maxillary implant impressions for completely edentulous patients.

Materials and methods

Sixteen patients received maxillary implant supported fixed complete dentures. After the verification of the conventional final casts, the casts were scanned with a desktop (extraoral) scanner. Intraoral full-arch digital scans were also obtained with scan bodies and STL files.

Extraoral and intraoral scans were superimposed and analysed with reverse engineering software. The primary outcome measure was the assessment of accuracy between scans of the verified conventional casts and digital full-arch impressions. The secondary outcome was the effect of the implant number on the 3D accuracy of impressions with Spearman’s rank correlation coefficient.

Results

The 3D deviations between virtual casts from intraoral full-arch digital scans and digitised final stone casts generated from conventional implant impressions were found to be 162 ± 77 μm. In the four-implant group, five-implant group, and six-implant group the 3D deviations were found to be 139 ± 56 μm, 146 ± 90 μm, and 185 ± 81 μm, respectively. There was a positive correlation between increased implant number and 3D-deviations, but there was no statistically significant difference (p = 0.191).

Conclusions

The 3D accuracy of full-arch digital implant scans lies within previously reported clinically acceptable threshold. Full-arch digital scans and a complete digital workflow in the fabrication of maxillary fixed complete dentures may be clinically feasible.

This article first appeared in Implant Dentistry Today magazine. You can read the latest issue here.

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