Considering how costly implant surgery can be, patients, for the most part, will have exceedingly high expectations for the treatment outcome. If the patient meets all the prerequisites to be eligible for digitally-guided implant surgery, he or she can benefit from a highly-customized digital workflow. The digital aspect is not limited to design and manufacturing of the surgical guides and provisional prostheses only, it starts with record taking and diagnostics. This in itself, comes with its own advantages as well as limitations.
What does digital workflow entail?
Most digital workflow steps fall into of 4 distinctive phases; these are:
- Record taking phase
- Treatment plan phase
- Surgical template manufacturing phase
- Surgical phase
Record taking phase
This is the data collection phase where all the required records can be taken in a single visit and compiled for processing. In this phase, we mainly need 2 types of file, namely DICOM and STL files. The DICOM file is a radiographic image in the form of CBCT or CT scans. The STL file can be either an intraoral scan or a scan of the model cast/dental impression. Bone and teeth segmentation of the CBCT image can be performed either manually or automatically.
Treatment plan phase
In this phase, the files are imported into an implant planning software. The STL image is superimposed on the CBCT image using anatomical landmarks. In the case of any mismatch, cross section imaging of the aligned images can be easily employed to analyze and correct the misalignment.
Following that, a digital wax-up is generated in the software (or an analog version thereof is scanned and imported). Backward planning is carried out to achieve the desired functional and esthetic outcomes. Prosthetically-driven implants are digitally positioned after vital intraoral structures have been delineated. A recommended distance of 1.5 mm away from the inferior alveolar canal should be left in order to protect the nerve.
In 360dps, for example, there is a comprehensive library of the most commonly-used dental implants. According to the available remaining bone and the implant provider’s indications, implants’ length and diameter can be chosen. Screw axis, implant shoulder relative position as well as mucosa thickness are all taken into account at this stage. Depending on the proposed plan. teeth extraction or bone augmentation may also be required.
After the virtual implant placement, 3D surgical/bone reduction guides are designed. Surgical placement of implants can be either partially-guided or fully-guided. In the first approach, only the pilot drill is guided, whereas in the latter, surgical guide sleeves are included in the surgical guide depending on the chosen implant system. Once the treatment plan is approved, a drill protocol is automatically generated; detailing the proper sequence of the surgical procedure.
Surgical guide manufacturing phase
Following the completion of the surgical guide design, the resulting STL file will be used to mill or 3D the guide with CAM technology. Other rapid prototyping techniques may also be used such as; stereolithography (SLA), digital light processing (DLP), or selective laser sintering (SLS).
All surgical guide components are checked for accuracy inside the patient’s mouth. Proper execution of the implant placement procedure depends on how accurately the guide is seated intraorally. A surgical flap may have to be raised to gain access to the bony tissue (e.g. in cases of bone reduction). A flapless approach can also be used; in which case, the tissue needs to be punched. As mentioned earlier, teeth extraction may be necessary at this stage. Manufacturer-specific drill protocol is then followed to prepare the implant recipient area. The secured surgical guide may hinder the proper irrigation and subsequently affect visibility. Immediate loading of temporary restoration is then carried out, or in some cases, suturing or healing abutments can be used.
Advantages of digital workflow
- Virtual visual evaluation of intraoral anatomy in 3D.
- Comprehensive assessment of the quality and quantity of the bony ridge.
- Accurate diagnosis and detection of potential abnormalities.
- Predictability and protection of vital anatomic structures.
- Reduced rates of free-hand error during the surgical phase.
- Higher success rates of implant surgery and enhanced prognosis of the final restoration.
Factors affecting digital workflow
Any single or a combination of the factors included in each phase of the digital workflow can lead to poor prognosis and subsequent failure– for example:
- 3D imaging and intraoral scanning quality.
- Accuracy of digital/analog dental impression.
- Precision of the digital pre-surgical planning of the implants.
- Quality of surgical guide manufacturing.
- Implant drilling protocol.
- Skill and experience of the oral surgeon.
Record taking factors
Obtaining the best quality DICOM and STL files will depend on the CBCT scanning process which is limited by the type of device available. It is recommended that only higher-end systems are to be used and the correct scanning procedure is to be followed. Scattering effect can occur due to the presence of restorations with high ratios of radiopacity; which can affect the scan quality. To decrease this effect, the use of radiographic markers is advised.
Analog dental impressions are slightly preferred in full arch rehabilitation cases in order to keep the deviation in superimposable data sets less than 100 microns. Larger deviation ratios will cause poor fit of surgical guides and resulting prostheses. That said, for the purposes of digital workflow, intraoral scanning has been shown to be adequate.
Surgical guide manufacturing factors
Computer-aided manufacturing of the surgical guide is largely dependent on the type of technique employed. Generally speaking, subtractive methods have been shown to be more accurate than additive methods (typical accuracy is 0.1 – 0.2 mm). Consumer-grade 3D printing devices (i.e. fused filament fabrication) produce significantly inaccurate guides compared to digital light processing (DLP) printers.
Surgical phase factors
For the long-term prognosis of the treatment of choice, the implant system is as important as the guided surgery solution. For example, axial deviations caused by the space between the drill and the sleeve can affect the overall placement accuracy. The space between the implant sleeve and the bone or soft tissue needs to be adequate; high sleeve position makes for decreased drill accessibility, whereas low sleeve position pinches the mucosa rendering flapless surgery impractical.
Fully guided implant surgery has been shown to be more accurate than partially-guided protocol. Although guided surgeries performed by advanced oral surgeons seem to have more accurate outcomes, surgeons with varying skill levels can also significantly increase the accuracy rates of their performance using this technique.
In conclusion, compared to traditional free-hand implant surgery, guided surgery can be demonstrated to be more accurate, reliable and predictable. Although the difference between the planned and actual positions of the placed implants is lower in fully guided protocols, the overall success rates seem comparable. 3D virtual treatment planning produces surgical and bone reduction guides that have superior accuracy and fit. Preplanning has the advantage of customizing the treatment procedure according to quality of information available, giving the patient an accurate representation of the overall procedure as well as the ability to discuss alternative treatment options at an early stage.
Implant dentistry, like many other fields, is becoming increasingly digitized. We have been witnessing one breakthrough after another, with less and less time between each one. Computer-aided design and manufacturing has firmly established itself as a solid solution for implant placement procedure. With an ever increasing variety in techniques, materials and powerful systems, digital dentistry seems to be here to stay.