The authors have questioned the accuracy of intraoral scanning when restoring the full arch implant patient. Yet clinicians use intraoral scanning (IOS) for this purpose due to the many efficiencies that the IOS workflow offers. This article describes a workflow that is used to enhance the accuracy of the intraoral scan without the need to use photogrammetry. It uses a design file for the provisional prototype restoration to create both a one piece prototype prosthesis and a segmented verification prosthesis. This verified workflow has the efficiency and comfort of the IOS workflow and the accuracy of the traditional workflow.
Key points
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This article describes a complete digital workflow using intraoral scanning (IOS) for the restoration of the full arch implant patient.
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The verified workflow combines the speed and comfort of IOS with the accuracy of traditional approaches.
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The verification protocol can be accomplished with minimal additional chair time and laboratory expense.
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The protocol may serve as a viable alternative to photogrammetry.
Introduction
Intraoral scanning (IOS) has been confirmed accurate for data collection and restoration of individual teeth, implants, and small span fixed partial dentures. , IOS has not been uniformly accepted for the manufacture of rigid full arch splinted implant restorations. Despite this, many clinicians have gravitated toward the use of IOS in the restoration of the full arch implant rehabilitation patient due to the efficiency and comfort of IOS. Still some authors question the accuracy of this approach for the restoration of the full arch implant patient and have added photogrammetry to IOS ( Box 1 ). ,
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Advantages of IOS
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IOS is ubiquitous, many dentists already own IOS.
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Efficient data collection and scan alignment.
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Patient experience and comfort.
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Data are highly accurate in single units and short spans.
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Data can be merged with the preexisting condition, creating multiple datasets.
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Disadvantages of IOS:
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Initial costs, start up.
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Requires understanding, learning curve, and mastery of scanning technique.
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Scan accuracy in question for full arch/cross-arch.
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Challenges of bleeding surgical sites.
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Challenges in mandible and mobile tissue bed.
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This study addresses these concerns and presents a comprehensive IOS protocol called “the verified IOS full arch implant workflow.” This protocol combines the efficiency of IOS with the predicability of traditional approaches. It uses a complete IOS data collection protocol and a digital design and manufacturing strategy along with an efficient digitally designed physical verification process. It requires a slightly modified scan strategy with several clinical and laboratory confirmation steps. Each part of this proposed treatment protocol sequentially builds upon itself and serves to verify the prior step adding confidence and efficiency to the design and restoration delivery process.
The workflow combines multiple confirmation steps including the delivery of a digitally designed splinted provisional prototype. , Additionally, a second duplicate segmented prototype is manufactured from the same design file. The segmented prototype is assembled intraorally and occlusally adjusted and is related to the opposing arch with a silicone interocclusal registration. This is used to create a mounted verification index. A definitive restoration created from this workflow can be effectively confirmed for fit and confirmed for occlusal accuracy prior to delivery independent of the eventual prosthetic design. , The verified IOS full arch workflow is designed to minimize concerns of inaccuracy while maintaining the comfort and efficiency that IOS data collection and digital design and manufacturing offers ( Box 2 ).
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Protocol: The verified IOS full arch implant restoration workflow comprises:
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The verified scan strategy
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The verified provisional prototype
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The assembled segmented prototype
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The mounted verification index
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Restorations are designed and manufactured in a completely digital environment benefiting from the ability to perfectly merge the preexisting data and diagnostic data with the newly prescribed restorative design. Provisional restorations delivered using this protocol serve to confirm the preceding scan data accuracy and design accuracy as well. Additionally, the occlusal relationship is confirmed in addition to other factors like tooth form, tooth color, hygiene access, and overall esthetics. If distortion is suspected in the data and in the provisional prototype one may proceed with the correction of the provisional prototype by adapting it to the verification index. The definitive restoration can also be adapted to the verified implant positions and occlusion on the assembled and mounted verification index.
The index may serve as merely a confirmation and refinement of accuracy, or it may be used as an analog backup for a redesign if needed. If significant differences in fit or occlusal anomalies are detected in the prototype, the mounted verification index could be scanned into the design software. The restoration design could be modified and adapted to the corrected data from the index. The laboratory can use the index data as a source for a redesign without requiring multiple additional patient visits or chair time. Definitive restorations can be fitted to the index or Ti bases can be seated and cemented into the prosthesis using the index for seating and verification.
This protocol has all the efficiencies of the digital approach and all the accuracy of traditional techniques. It bypasses some of the challenges and inefficiencies of traditional impression making and confirmation techniques. It allows the laboratory to use traditional methods to insure the fit and complete seating and occlusal adjustment of the prosthesis. It also provides a backup data source in the event it is needed without the burden of additional visits and chair time. The protocol represents an effective novel method for collecting and verifying data for digitally designed restorations. It allows for the confirmation of the esthetics, occlusion, and accurate fit of the restoration made for the full arch splinted implant condition.
Each of the components of the validated IOS full arch workflow is designed to provide the clinician with confidence that the data collected is accurate and confirmed. This allows the next step to proceed unencumbered by any concerns of inaccuracy. It is designed to provide the patient with a comfortable experience. It also provides that the clinician and the laboratory team will be confident that each progressive step which is built upon the prior step will be accurate from scanning to delivery.
Step 1: the verified scan strategy
The first step in the verified IOS workflow is the verified scan. The verified scan refers to a modified scan data collection process that confirms the dental arch scan prior to post-processing and sending. It includes an extra step at the completion of scanning each dental arch to confirm accuracy of the arch data prior to proceeding. While scanning an arch, audible clicks can be heard as the scanner is progressing. The clicking indicates that the scanner is accepting data and stitching images. If the data have defects, distortions, or discontinuation, there will be audible interruptions in the clicking sounds while scanning.
When a dental arch scan is initially completed and appears to be finished, it is difficult for the user to confirm that the data are accurate and acceptable for the fabrication of prosthetic restorations. The gathering of additional occlusal scan data can be used to minimize scan data distortion and to verify the scan. To confirm that an intraoral scan is verified, the user continues scanning from the occlusal aspect of either posterior quadrant. The user then continues advancing the scanner and passes the scanner tip from the posterior to the anterior and then to the contralateral posterior side and back. This process should occur without audible interruptions in clicking and without the scanning process being stopped or stalled during data acquisition. If audible interruption occurs, it indicates possible defects in the scan. Additional scanning at this point adds data and corrects errors in the scan. Areas with interruptions are noted and the data collection process is continued until audible clicks are continuous and uninterrupted.
Once the dataset is complete and well stitched, a continuous stream of audible clicks can be heard while passing the scanner tip throughout the dental arch. Therefore, the occlusal pass serves to add data to correct and to verify the data collection process. Next, a slightly buccal occlusal angulation can be utilized for additional data for confirmation and repeated with a slightly lingual occlusal angulation. Palatal data in the maxillary arch are added from anterior to posterior and can be important for cross-arch accuracy. Lastly and finally, an occlusal angulation scan is once again repeated for finalization of the process. This additional data accumulation can be completed in a minute and will add confidence in the scan data for use in the manufacture of prosthetic restorations. This protocol has been utilized successfully for many years to validate scan accuracy prior to post-processing and sending for prosthetic design and manufacture.
Additionally, it is critical to align the scans with the opposing arch. The buccal tissue and the buccal sulcular architecture have a unique shape that is used to align the dental arch scan with the interocclusal bite scans and the opposing arch scan. When finalizing a dental arch scan, extra attention is paid to capture the buccal, lingual, and peri-implant sulcular tissue areas during scan data collection. When making interocclusal bite scans, extra data are gathered following the initial scan alignment. Minimal or insufficient interocclusal scan data in the digital bite scan can lead to interocclusal alignment inaccuracies and an inability to align and confirm the opposing arch orientation.
Confirmation of opposing arch scan alignment is critical for occlusal scheme design and occlusal accuracy of the interim and final prosthesis. To verify scan alignment, the scan alignment data are inspected and confirmed while making and finalizing the bite scans. The opposing arch scan alignment can be made from either the preexisting condition “pre-preparation scan” or following the removal or the patient’s preexisting condition the scan alignment can be made from the edentulous condition “preparation scan.” Occasionally, bite scan data are difficult to collect when the patient’s prosthesis is removed and there is excessive space between the treatment arch and the opposing arch.
If the patient’s prosthesis is removed, interocclusal scan alignment can be difficult to achieve due to the void between opposing arches that are far from each other. To overcome this problem, an option exists to create a silicone interocclusal registration at the desired vertical dimension of occlusion. This interocclusal registration can serve to stabilize the prescribed treatment position. It can be trimmed to expose the buccal tissues that are used for interocclusal bite scan alignment while supporting the treatment position during scanning. Usually only an anterior silicone jig is needed for this purpose, but a full arch registration can be used to eliminate this problem and may serve the laboratory to confirm the alignment of printed casts. In summary, the silicone interocclusal registration can serve as a stable scanning base upon which the interocclusal bite scan data can be made of the arches. With this step, all data are inspected and confirmed. Shade selection can also be confirmed with the patient at this time. The data are then post processed and sent to the laboratory.
Step 2: the segmented prototype
Laboratory Phase
The second step in the verified IOS workflow is to design and manufacture the CAD/CAM full-arch prototype provisional restoration and an exact duplicate segmented prototype provisional restoration. In the design software, the preexisting tooth position or pre-preparation and opposing scans can be used as a guide to facilitate the esthetic and functional/occlusal digital design processes. The prescribed tooth position and arrangement is completed, and the design is approved. Two identical stereolithography (STL) design files are output and nested for manufacturing regardless of whether a milled or printed manufacturing process is used. A suitable high-strength restorative material is required. Once manufacturing is completed, the laboratory adds the Ti bases and verifies the complete seating of the Ti bases into both restorations. They are then cemented with a light-curing resin. Alternatively, if the restorations are designed to fit directly to the abutments, screw and abutment analog seating are confirmed prior to the clinical phase. Once both provisional prototypes are complete, one of the restorations is carefully segmented interproximally at each implant site by the laboratory with a thin flexible metal cutting disk. The splinted prosthesis and segmented prototype are disinfected and delivered to the clinical team.
Clinical Phase
The next step is to appoint the patient for the clinical assembly of the segmented provisional restoration and to deliver the splinted one piece provisional prototype. In addition, it is valuable to make a silicone interocclusal registration on the segmented prototype prior to its removal from the patient. It is suggested to assemble the segmented prototype intraorally first before delivering the one piece provisional to avoid having to remove and replace the full arch splinted provisional restoration. As an alternative, one may choose to deliver the provisional at once and reappoint the patient for the assembly of the segmented prototype. This approach requires an extra step. These steps may be performed together or separately at the discretion of the dentist.
The patient is appointed for the assembly of the segmented prototype. Each of the individual implant segments is confirmed to be completely seated with hand torque and without interference. The remaining sections are sequentially added and tightened into place. Space between segments is confirmed with dental floss and adjustments are made to insure complete seating without interference between adjacent segments. The segments are joined using a bonding agent and a clear flowable light-cured resin. Once curing is complete, an additional strut is added at the posterior aspect of the prosthesis and light cured in place. The posterior strut strengthens the assembly and helps resist fracture and distortion. Once this step is complete, an occlusal adjustment may be performed and an interocclusal registration made. The assembled prototype is then removed and returned to the laboratory with the appropriate analogs added for and for the creation and mounting of a conventional stone verification index.
Step 3: the solid prototype
Once the assembly of the segmented prototype is completed, the clinician then proceeds with the delivery of the one piece splinted prototype restoration. The accurate seating of this restoration can serve to validate the original scan dataset and the digital design of the restoration. Special attention can be given to assess the tightening characteristics of the screws for complete seating and accuracy of the restoration. Other issues like the blanching of tissues upon seating and the ability of the patient to achieve hygiene access are also evaluated. Esthetic considerations as well as tooth form and occlusal contact pattern may be adjusted and assessed. All these steps help to verify the design data accuracy and the acceptability of the digital design choices and shade selection. The patient can be dismissed.
Following a period of functional use, the patient may be reappointed for occlusal check and for esthetic consultation and final shade confirmation of both the dental and gingival shades. It is suggested that the patient wear the prothesis and return to the clinic for these adjustments including evaluation of all aspects, the provisional prototype restoration. Necessary adjustments and future desired design modifications are noted. Once this has occurred, the patient is given the choice to approve the prescribed color and tooth arrangement.
In summary, these steps are complete when the assembly of the segmented prototype is performed and the silicone interocclusal registration is made along with the try-in and delivery of the splinted one piece prototype restoration. With this and with patient acceptance, the entire process is confirmed. The prototype restoration is used to validate the accuracy of the scan and to confirm that the design has the appropriate esthetics and occlusion. This confirms that the original dataset and the design data are appropriate before continuing to create the definitive restoration. The patient and the team can then decide to proceed to finalize the definitive design and to manufacture the restoration in zirconia.
Step 4: the mounted verification index
The laboratory receives the assembled segmented prototype and a silicone interocclusal registration. The appropriate laboratory analogs are inserted into the prototype with care so not to stress or fracture the acrylic and bonded composite construction. A low expansion stone index is used to pour the index and the analogs are placed into the stone and allowed to set. Then prior to disassembly of the matrix, the index is mounted on a suitable articulator using the silicone interocclusal registration. At this point, the clinical and laboratory team has all the data necessary to finalize the design and manufacture the restoration. This can incorporate esthetic and hygienic modifications as needed. Additionally, screw channels can be angled toward the cingulum areas and the away from interproximal areas to maximize strength and occlusion can be optimized. The reengineered final design is exported, nested, and ready for manufacture. Once milled, the definitive restoration can infiltrated, colorized, and sintered according the manufactures recommended firing process. The restoration is then adapted to the verification index and Ti bases until complete seating is confirmed. Occlusal adjustment of the prosthesis can also be accomplished. The ceramic shape, color, and texture and the final exterior enhancements can be made. Once completed, the Ti bases can be cemented into the restoration using the verification index as the guide. The prosthesis is complete and now ready for delivery to the patient.
Case presentation
This patient presented with multiple failing anterior implants and a failing porcelain fused to gold fixed partial denture. The 3 implants exhibited peri-implant inflammation and excessive bone loss. Extraction of the failed dental implants and bone grafting for site preservation were performed. This rendered the existing prosthesis insufficiently supported, maladapted, and no longer serviceable. A treatment plan was developed to design and deliver a 14 tooth implant-supported maxillary fixed complete denture. Multiple additional posterior implants were required to provide added implant support for prosthesis posteriorly. Following sufficient healing and bone regeneration, additional implants were placed utilizing a guided surgical approach with several vertical osteotome sinus lifts. The limited vertical bone height of the resultant maxillary arch also required positioning of the posterior implants into the posterior maxillary/pterygoid areas to maximize posterior support. The panoramic radiograph illustrates the condition of the maxilla following a period of healing with implants, abutment, with Ti bases in place ( Fig. 1 ).
