Digital Synergy for Full-Arch Hybrid Solutions

In the early days of this predominantly hand-processed technique, the surgeon, restorative dentist, and dental laboratory technician all played integral yet largely detached roles in the process. This disconnect between the surgical and restorative processes often resulted in various problems; however, during the past two decades, technology-driven concepts such as digital diagnostic design, analog and digital data merging, and digital communication have been critical in linking the surgeon, dentist, and technician so that they can function as a very efficient and synergistic team. As technology further evolves, it will continue to strengthen this teamwork, improve workflows, and ultimately lead to less invasive surgeries with more predictable prosthetic outcomes.

Reestablishing a lost vertical dimension of occlusion (VDO) has proven to be one of the biggest and potentially most costly challenges that the restorative team faces when processing full-arch hybrid prostheses.² Restorative success with the fixed hybrid technique is reliant on accurate implant placement, but in many cases, it is even more dependent on being able to effectively establish a correct VDO.

Without an accurate analog link, a digital workflow offers no true restorative value. In modern-day All-on-X workflows, the historically inaccurate process of conversion is replaced by a more predictable digitally planned one involving a latched prosthesis. This device provides the crucial accuracy during the jump between the design and the restorative processes. Contemporary chairside conversions can thus be diagnostically designed and precisely executed without placing additional pressure on the surgical team. Employing a latched instead of stackable surgical solution allows a true digital workflow to be brought to an analog process.

Traditionally, surgical solutions mostly utilized protocols involving stackable surgical guides; however, these solutions often failed to establish a repeatable pathway to create an accurate, diagnostically driven, surgically converted interim prosthesis. The most common problems were bite inaccuracies caused by the lack of predictability associated with the seating of the base guide. These inaccuracies were also influenced by the large amount of tissue reflection required to seat a buccolingual-type base guide. In many cases, extensive and often unnecessary bone reduction was planned to hide the smile line. This, in turn, required extensive FP3-style hybrid restorations to restore. The need for the surgeon to maintain or set the patient's VDO during these demanding surgical procedures, particularly when patients were orally intubated, often resulted in lengthy surgeries with restoratively worthless chairside conversions.

Today, technology allows us to record and maintain the occlusal starting point in a digital format using a combination of different software applications. This digital workflow facilitates diagnostic design, digital restorative review, planned bone reduction, guided implant placement, and, ultimately, fabrication of a latched, diagnostically driven conversion prosthesis. To begin, the presurgical VDO is recorded in the form of cone-beam computed tomography (CBCT) scans (DICOM data), digital intraoral scans (STL files), bite indices, and patient smile photographs. Model matching permits a transitional prosthesis to be designed from the preoperatively established centric occlusion or, if required, an established centric relation position. The preoperative records are used to inform the diagnostic design, which results in a diagnostically driven chairside converted prosthesis.

Figure 1 shows a case in which the clinician, Jeffrey Ganeles, DMD, was able to not only reestablish the patient's VDO but also satisfy her esthetic concerns with this transitional conversion prosthesis. After healing, this device will become a very valuable starting prototype for the processing of the final prosthesis. Oftentimes, this enables the restorative team to process a full-arch hybrid in as few as two or three clinical appointments.

FP1 Prosthetic Design

With advancements in digital diagnostic design and improvements in the transfer accuracy between the digital design process and the analog surgery, dentistry has seen a definite shift toward more conservative surgical procedures. Among other benefits, these more conservative surgeries are enabling the delivery of more hygienic FP1-style prosthetic designs. Figure 2 and Figure 3 show a case in which the clinician, Mark Ludlow, DMD, collaborated with the laboratory team to diagnostically plan and deliver a conservative, FP1-style final zirconia prosthesis.

When preoperatively planning an FP1-type case, accurate transfer of the digital data to the analog surgery is vital. The accuracy of this data transfer is predicated on achieving an exact seating of the base guide intraorally. Therefore, choosing a surgical solution that allows for predictable base guide seating (eg, Smile in a Box^®, Straumann Group; NDX^® nSequence, National Dentex Labs; CHROME^™, CHROME Guided Systems; IBUR^®, IBUR^® BioSystems; NavaGation^™, NavaGation Precision Guidance^®) can improve the success of this restorative process.

Too little planned or surgically established clearance will negatively influence the strength and severely complicate fabrication of this type of final prosthesis, and too much planned clearance will result in unnecessary bone reduction and potentially create an unsightly prosthetic-to-gingival transitional junction in the patient's smile. Ultimately, accurate base guide seating is the link between planning, surgery, conversion, and a predictable final prosthetic delivery.

Data Gathering and Planning

After the DICOM data are model matched with STL files acquired from intraoral scans or digitally converted vinyl polysiloxane impressions of the patient, the first step in processing a guided workflow for an implant-supported full-arch prosthesis is creating a digital diagnostic wax-up (Figure 4). The restorative team then collaborates through this digital media to plan the ideal final prosthesis before reverse engineering the surgical and bone reduction guides.³

In cases involving severely broken-down teeth and/or a collapsed bite, the diagnostic file can be milled into a PMMA tooth overlay (Figure 5). This cemented transitional "shell" prosthesis provides the clinician with an intraoral prototyping phase for bite adjustments and more. Once the bite is confirmed, an intraoral impression and a CBCT scan are performed. This tooth setup then becomes the diagnostic/preoperative starting point, which minimizes potential issues after surgery.

Surgical Planning

Once the restorative team approves the digitally planned prosthesis, the design is imported into the surgical planning software.⁴ The data are then model matched with the DICOM file and used to determine suggested implant positions. These implant positions are related to the final prosthetic position, not to the preoperative existing dentition. A suggested surgical plan is designed, and a digital review is scheduled with the surgeon. Although the surgical plan is guided by the final prosthesis, all surgical decisions, including any necessary adjustments to the plan, need to be approved by the surgeon.

Scalloped Guided Bone Reduction

The true measure of a modern-day surgical solution is found in its ability to limit unnecessary bone reduction and tissue reflection while allowing for a conservative restoration. In many cases, bone reduction is now performed with a scallop-style guide. This type of guide, which was described by Salama et al⁵ several years ago, directs the surgeon in accurately scalloping the bone contour to exactly match the cementoenamel junction of the planned final prosthesis. Scallop-style bone reduction, as seen in this guided surgery performed by Ganeles (Figure 6), eliminates many of the hygiene issues caused by overlapped concave hybrid designs. This type of bone reduction is not only more hygienic due to the cleansable nature of the convex tissue contact surface but also more esthetic due to the reduced amount of artificial pink tissue required on the prosthesis.

Surgical Guide and Conversion

Following approval, the surgical plan is imported into the build software to facilitate the design of the surgical guide. The bone-stabilized base guide is designed with jack key latches to carry the guide components, and the components, including the scalloped bone reduction guide, surgical implant placement guide, and multi-unit abutment rotational index guide, are all designed to latch securely into the base guide.

Regarding the diagnostic conversion prosthesis, it is milled in a highly esthetic, double cross-linked PMMA material and latched in relation to the base guide position (Figure 7). This device will be converted into the interim temporary prosthesis chairside.⁶ After surgery, the conversion prosthesis predictably establishes the preplanned VDO with the digitally created bite. This type of latched conversion solution simplifies the process of resetting the VDO and greatly reduces the time required for the chairside conversion process by eliminating the need for the surgeon to check occlusion or set the bite with the arduous nose-chin measuring process.

Base Guide Seating and Fixation

Although surgical solutions for implant-retained prostheses share many components and general procedures in common, most of the modern-day innovations and technological advancements have focused on more efficient fixation methods to secure the base guide to the patient's bone. Accurate fixation plays an integral role in the overall efficiency and predictability of the surgery because accurate seating of the base guide is the link between the digital planning and successful surgical execution. If this link is broken, the digital workflow is disrupted, and surgical and final prosthetic delivery issues can occur.

Fixation Methods

Traditional surgical systems mostly utilized buccal-lingual engaging base guides or some variation of a stackable design. In addition, large tissue reflections are not only arduous but also capable of causing pushback on the base guide, making it difficult to determine seating and significantly complicating accurate fixation.

Newer systems have solved many of these surgical complications with very innovative, proprietary, base guide seating techniques. One such system engages the buccal bone using tissue depth indicators and requires no buccal tissue reflection. The workflow, which utilizes unilateral key fixation (minimally invasive, buccal bone engaging fixation), simplifies the surgical procedure and reduces historically required buccal tissue reflection by more than 80%.

Every surgical case is unique; therefore, it is important to have a fixation solution available that can overcome these individual challenges. The great differentiator between surgical solutions today is the efficiency and accuracy with which the base guide can be seated. Base guides used in surgery by Ludlow can be seen in Figure 8 and Figure 9.

A Synergistic Restorative Process

From the patient's perspective, these surgical advancements are only as good as the final prosthesis is beautiful. Scott Ganz, DMD, eloquently summed this up in an interview with Osstell when he stated, "My goal is always to understand that patients are not coming to me to have implants, they are coming to me to replace missing teeth."⁷

For challenging cases, planning preoperatively with restorative, technical, and surgical input is crucial to success. In the case depicted in Figure 10 through Figure 14, Ludlow collaborated with the guided surgery team and the laboratory team to plan for a successful surgery with a predictable final prosthesis.⁸ This collaboration, combined with an accurate data jump between planning and execution, was the foundation for a diagnostically driven transitional, chairside converted hybrid (Figure 11). After a period of healing, the transitional hybrid was removed from the mouth and digitized, and the STL files were sent to the laboratory for a biocopy with requested changes. To eliminate a clinical appointment, this step in the restorative process is often accomplished by the surgeon at the time of implant integration verification, but it can also be performed by the restorative clinician. The transitional hybrid was returned to the mouth, and the patient was released to the restorative dentist for final processing of the case. For the final try-in, the laboratory imported the STL data and fabricated a prototype hybrid prosthesis. This prototype can be a disposable, 3D printed (nonfunctional) prosthesis (Figure 12) or a dual-use PMMA (functional) prosthesis (Figure 13). The highly esthetic PMMA device can be worn by the patient for an extended transitional period to help determine if any occlusal or esthetic changes are necessary before continuing to the final restoration (Figure 14).

Conclusion

When restoring with a monolithic zirconia material, adjustments to the material after sintering should be limited. Therefore, all required modifications are performed chairside on the prototype, patient sign-off is acquired, and the file is sent to the laboratory for copy-milling. The laboratory will perform all artistic adjustments to the prosthesis while it is in the green state prior to sintering.

This modern-day digital workflow facilitates predictable surgery, allows for diagnostically driven conversion, and ultimately results in a stress-free restorative process.

Acknowledgments

The author would like to acknowledge the contributions, superb surgical abilities, restorative skills, and photography of Mark Ludlow, DMD, and Jeffrey Ganeles, DMD; the technical contributions of the Absolute Dental Lab Advanced Restorative Team in Durham, North Carolina, under the leadership of Jack Marrano, CDT, director of signature prosthetics; and the surgical design and continued research and development of Matt Vrhovac and Brian Lee from the NavaGation Precision Guidance^® team.

About the Author

Conrad J. Rensburg, ND, NHD
CEO and Head of Implant Division
Absolute Dental Services
Durham, North Carolina