Anatomic Customization of Root-Analog Dental Implants With Cone-Beam CT and CAD/CAM Fabrication: A Cadaver-Based Pilot Evaluation
Existing root-analog dental implant systems have no standardized protocols regarding retentive design, surface manipulation, or prosthetic attachment design relative to the site's unique anatomy. Historically, existing systems made those design choices arbitrarily. For this report, strategies were developed that deliberately reference the adjacent anatomy, implant and restorable path of draw, and bone density for implant and retentive design. For proof of concept, dentate arches from human cadavers were scanned using cone-beam computed tomography and then digitally modeled. Teeth of interest were virtually extracted and manipulated via computer-aided design to generate root-analog implants from zirconium. We created a stepwise protocol for analyzing and developing the implant sites, implant design and retention, and prosthetic emergence and connection all from the pre-op cone-beam data. Root-analog implants were placed at the time of extraction and examined radiographically and mechanically concerning ideal fit and stability. This study provides proof of concept that retentive root-analog implants can be produced from cone-beam data while improving fit, retention, safety, esthetics, and restorability when compared to the existing protocols. These advancements may provide the critical steps necessary for clinical relevance and success of immediately placed root-analog implants. Additional studies are necessary to validate the model prior to clinical trial.
Figure 1. Virtual tooth extraction: Each tooth of interest was selected and volumetrically modeled. Shown is a tooth #9 virtually extracted from the cone-beam computerized tomography along with the tooth model on the right. Once confirmed, .stl models were created and exported to computer aided design software. Figure 2. Removal of root prominence: .stl models of virtually extracted teeth were assigned a central axis which was aligned in the computer aided design software to the y-axis. Areas of prominence were defined and removed, providing the basis for implant design. Left to right: aligned .stl, edge of prominence marked, volume of prominence highlighted, prominence removed and new surface defined.
Orthographic projection of the implant body and retentive element design based upon a modified-buttress thread design and nomenclature. On the lower right are the intended relationships between cone-beam computerized tomography measured bone-density and the dimensions of the retentive element parameters.
Analysis of bone and adjacent anatomy: axial slices showing implant tooth/site of interest #22. Areas in green on the bottom row represent the defined zones safe for retentive element intrusion beyond the root to be extracted. Left to right: 3 mm from the crest of bone, mid-root, and 3 mm from apex.
Retentive element design: Elements were placed relative to the defined safe zones in the alveolus. Left: mesial view of a whole implant with the middle element crest marked in blue. Top right: expanded view. Bottom right: final offset angle set to allow the element crest to be perpendicular to the implant long axis.
Virtual preparation of the prosthetic attachment: margin placement was at the estimated natural cementoenamel junction and the abutment was aligned with the restorative path of draw. Left to right: facial view, distal view, occlusal view.
Implant design: left to right for natural tooth #7: .stl surface mesh images of the extracted tooth, .stl images of the designed implant, and photograph of the implant. Top: distal view. Bottom: lingual view.
Case 1. Panel photographs on the top 3 rows from top to bottom showing labial, occlusal, and lingual views of implant site #9. From left to right: pre-op, extraction, and implantation. On the bottom row left to right: periapical radiographs taken pre-op, after extraction, and after implantation. Implant .stl surface mesh models and matching implant photographs distal and lingual are shown.
Case 2. Panel photographs on the top three rows from top to bottom showing facial, occlusal, and lingual views of implant site #5. From left to right: pre-op, extraction, and implantation. On the bottom row left to right: periapical radiographs taken pre-op, after extraction, and after implantation. Implant .stl surface mesh models and matching implant photographs distal and lingual are shown.
Implant stability: box plot and data point representation for Periotest M stability measurements in total and for maxillary and mandibular implants. For implant stability mandibular vs maxillary arches, no significant difference found (P > .05).
Contributor Notes