INTRODUCTION
Full-arch, implant-supported reconstruction continues to provide viable solutions to restore and improve function, enhance aesthetics, and change the quality of life for our patients. All-on-X implant reconstruction has benefitted from new advancements and technical innovations. In this current edition, the authors continue the journey, navigating through new developments that impact the full-arch analog and digital workflows. Our previous articles introduced several elements to aid the clinician in both the surgical and restorative phases of full-arch replacement, including the use of CBCT guided surgical applications1 and how they have greatly improved the assessment for implant placements relative to the desired restorative positions for preliminary and definitive restorations while also reducing implant complications. The authors have previously described an ancillary surgical protocol that utilizes extracted teeth as an autologous solution2 to bone grafting. This has greatly enhanced healing and long-term alveolar stability and provided ample graft volume while significantly reducing biomaterial costs. Subsequent publications also reported on improving the restorative time and treatment outcomes utilizing iJig technology3 and employing small-hole technology (C2F) to enhance the physical integrity and anatomy of milled or 3D printed provisional restorations4 and improving inter-arch alignment and occlusion. The goal of these articles has been to improve time, efficiency, costs, and long-term results for the betterment of clinicians, laboratory technicians, and patients. This latest article endeavors to provide updates in the acquisition of data necessary to complete the restorations with an emphasis on addressing improvements in screw-retained full arches for monolithic restorations that incorporate multi-unit abutments.
Data Acquisition
As the dental industry continues to strive for fully digital solutions, the development and improvement of intraoral data devices and acquisition technology has continued to evolve. Intraoral scanning (IOS) speeds and accuracies have become a viable solution for replacing direct analog impressions. Native IOS software applications now provide several impressive features that enhance and streamline complete digital protocols. However, due to inherent logistical limitations, the difficulty and accuracy of IOS technology used for full-arch dental implant restorations has presented major obstacles requiring additional applications to achieve fully digital solutions.
All-on-X, fixed surgical and restorative protocols require the placement of 4 or more implants with a favorable anterior-posterior spread to achieve the necessary long-term support. Capturing the positions of these implants with accurate cross-arch intraoral scanning, especially in the mandible, has been one of the major struggles for clinicians and dental laboratory technicians to overcome. IOS technology requires a stable environment for data to be stitched and captured accurately. Several techniques have emerged to aid the clinician in scanning these difficult environments, including proper retraction; salivary flow; lack of stable, keratinized soft tissues; large distances between scanning objects; and more. The use of splinting scan bodies with bands or wires (Figure 1) has facilitated the ability of scanners to continue a scan without interruption by creating a linear path for data capture.5 Innovative techniques, such as the sigma composite curve (or surgical intervention of fiducial markers fixated to the bone), have also helped improve scanning flow.6 While these processes work for some and not for others, developers have created alternative workflows to aid in acquiring accurate intraoral data.
Photogrammetry (PG) in dentistry is a relatively new development that has revolutionized capture and positional analysis.7 PG is a diagnostic and research method using an extraoral capture device with specific photogrammetric scanning abutments to acquire measurements from 2D digital images (Figures 2a and 2b). PG scans allow dental clinicians to acquire precise measurements of individual scan bodies (Figure 2c) secured to dental implants as they are in their natural state8 either at the time of surgical placement or after the implants are uncovered. While extremely accurate for recording the spatial positioning of the implants, PG does not acquire the topography of the soft tissue. Therefore, a second scan is required with an intraoral scanner. The IOS data can then be used to fabricate a virtual 3D model used to measure various parameters of the implant analogs.9 The software correlation of these measurements can be used to assess and validate the correct positioning of implants and the alignment of a patient’s occlusion, size, distance, and angle. The combination of IOS and PG data provides the CAD software designer with all of the necessary information to virtually create a provisional prosthesis or a final restoration to be 3D printed or CAM-milled. The advanced capability of this highly accurate technology generates a fully digital workflow. There is little need for an analog model for production or verification purposes. While these impressive devices are extremely accurate, the initial purchase costs and availability of sensitive component materials have been an issue of concern.
To obviate the expense of PG, alternative fully digital workflows have been developed, such as the Abeniam XCell10 process, to facilitate and streamline data acquisitions, avoiding the need for PG. This proprietary workflow protocol requires education and the use of proprietary scan bodies. The XCell proven process is extremely efficient and paved the way for other intraoral technology to continue to be developed. To maintain consistency and accuracy, the protocol recommends a specific IOS device and CAM unit. Additionally, the workflow recommends the use of the “Abenaim powerball” screw to complete the production of the final restoration. While the recommendations are not mandatory, there is limited support when not utilizing the components as indicated within the protocols.
Another very recent workflow, termed Grammetry, has been developed as an open comprehensive surgical and restorative solution that offers a very similar and straightforward process with a significantly reduced cost and allows the use of existing IOS scanners. While PG requires the use of an expensive device and expensive scanning abutments, Grammetry requires the use of an existing IOS device along with special components provided to the clinician for each case. An analog-digital process utilizes MUA-compatible scan bodies (OPTISPLINT [Digital Arches]) designed to incorporate an aluminum mesh frame (Figure 3a) that can be customized chairside (with the included “snipping” tool) as required by the intraoral location of the implants. This mesh frame comes in small and large sizes to accommodate various mouth sizes and multi-unit abutment-implant positions. The workflow consists of inserting the scan bodies onto the MUAs intraorally (Figure 3b). The proprietary scan bodies have extensions (Figure 4) to allow the mesh to seat and rotate in close proximity, in turn, to allow luting using a resin base material (Stellar DC Acrylic [TAUB Products]). The structure can then be digitized by scanning intraorally with an IOS or extraorally with an IOS or a desktop scanner. The bonded splinting of the scan bodies to the mesh frame allows for a simple, uninterrupted scan path. The Grammetry process provides the clinician with the fully digital benefits of PG while also providing the capability to fabricate physical analog models that can be articulated as part of the prosthetic design process represented by the clinical workflow in Figure 5. Additionally, the Grammetry splint can be used as a model-verification jig. The fully digital Grammetry process communicates the necessary records workflow to design and fabricate a full-arch prosthetic at a significantly reduced cost to the dental laboratory. For those who have 3D printers and wish to design and print the provisional prosthesis, a calibration device is included in the Grammetry kit. This device will ensure that the specific printer settings based on the resin used will have a passive fit.
Ti-Base, or Not Ti-Base? That Is the Question
The desire for screw retention over fixed, cementable prostheses has been debated for some time.11 As restorative components have evolved and CAM software/hardware manufacturing capabilities have improved dramatically, screw retention utilizing multi-unit abutments has become the preferred choice for most full-arch restorations due to the passivity required with monolithic-zirconia-designed prostheses. The elimination of subgingival cement12 and the passivity of prosthetic seating can be attributed to the success of screw-retained, full-arch, cross-splinted restorations.
Screw-retained, fixed implant prosthetics have undergone many iterations over the past several decades.13 PMMA acrylic denture conversions proved too weak to withstand forces of occlusion long-term. In order to improve strength, metal-frame reinforcement was added to the acrylic. The end results still yielded a high level of long-term prosthetic failures. Improvements in ceramo-metal restorations yielded improved long-term aesthetics and longevity; however, the associated costs became a factor, and fractures continued to occur. With the strength and diversity of materials improving and CAD/CAM technology continuing to develop, other material choices have become more viable. Currently, monolithic zirconia has become the most widely used material for full-arch, implant-supported restorations.14,15 The milled and sintered zirconia structure could be fabricated with a standard multi-unit abutment coping, custom-milled titanium bar, or a Ti-base cap. These metal substructures are chemically luted to the zirconia structure (Figure 6). Fractures were still evident, most notably from poor design. The fractures tended to occur in distal extensions attributed to poor A-P spread and in locations of screw-access holes. Screw-access fractures could be contributed to the lack of zirconia thickness in the crown-abutment interface. Conventional prosthesis-retaining screws secured to the MUAs have a screwhead that is 2 mm in diameter, only allowing for 0.25 mm of screw surface to engage the crown portion (Figure 7). This leaves only 0.4 mm between the head of a conventional screw and the titanium base. Reports of screw loosening, screw fractures, and de-bonding of Ti-bases from the zirconia structure have become a source of difficulty and concern.16 Developers have searched for alternative solutions as these complications and avoidable remakes continue to persist.
To counter the effects of screw-loosening, Ti-base de-bonding, and screw-access-hole fracture, several screws have been developed. Over the past few years, the continued refinement of these screws has led to the evolution of metal-free, full-arch monolithic zirconia restorations. As a result, in many case presentations, the need for excessive bone reduction to accommodate the metallic portion has been eliminated, allowing for increased potential for FP1 vs FP3 restorations. Some of these screws allow for increased thickness of zirconia between the MUA and screwhead. Allowing increased thickness in this susceptible region further reduces the risks of zirconia fracture in the screw-access-hole location. Additionally, the design of the newer screws typically has a tapered or rounded screwhead, allowing for improved retention by applying pressure to the lateral walls in the apical direction, reducing incidences of screw loosening.
A few of these newer screw designs can accommodate “angled” screw channels. Angled screw channel correction has become widely incorporated in single-tooth implant restorations.17 Previously, correcting angulations for full-arch restorations on multi-unit abutments required using an MUA with an increased degree of angulation. When an MUA is secured to the implant and the scan data has been captured, altering the screw-access channel would then affect the angulation of the MUA, which would need to be replaced. This becomes problematic when provisional or final restorations have already been designed and a new desired positional tooth change is requested. Often, these changes can leave access holes in aesthetic or potentially vulnerable areas (Figure 8). Additionally, there are angular limitations of the MUAs, which vary with each component manufacturer. Rather than changing the MUA and dealing with the difficulties of temporization, some of the newer MUA screw technologies allow for the MUA to remain in place while the screw channel can be angulated as much as 25°. One screw in particular that is uniquely designed is the “La Vis Grammetry” screw (Figure 9). The La Vis screw can accommodate various vertical positional depths. This feature allows for accommodating directly to an MUA, Ti-base, or Ti-bar simply by adjusting the height position of the screw. The adjustable vertical position allows for more or less zirconia, if desired, depending on available interocclusal space. In addition to accommodating angled screw channels, the ideal screw-access position and depth can be achieved.
Therefore, by utilizing the innovative methods of data capture and validation, combined with newer screw technology, it is possible to accomplish increased efficiency and accuracy of the fabrication process. Additionally, it has been illustrated that screws that can accommodate an angled screw-access channel position will result in improved aesthetics. The benefits of these screws and driver are required for usage (Figure 10).
CASE REPORT
The following case exhibits the features and benefits of utilizing Grammetry in combination with innovative screw technology. A 63-year-old male patient with non-contributory medical history presented with failing dentition in both arches. The mandible contained an impacted canine as well as several mobile and painful teeth (Figure 11a). The maxilla was in similar condition with deteriorating, painfully mobile teeth, as well as extensive caries. While the bone loss was significant in the mandible, the vertical dimension allowed for both arches to be treated with an FP1 (fixed prosthetic 1 Misch classification18) manor.
Diagnostic records were collected, including intraoral digital impressions (i700w [Medit]) (Figures 11b and 11c), large FOV 3D CBCT imaging (CS 9600 [Carestream Dental]), full-mouth digital x-rays (Figure 11d) (RVG 6200 [Carestream Dental]), and intraoral and extraoral photographs (Figure 11e). Based on the assessment of the acquired data, several treatment plans were developed and presented to the patient. Conventional treatment concepts that were considered included salvaging those teeth deemed stable enough to be utilized to retain removable appliances, implant stabilization with a combination of fixed and removable prosthetics, implant-supported overdentures, and full-mouth reconstruction with implant therapy. After reviewing the various treatment proposals, the patient elected for full-arch, fixed replacement with implants. The collected data along with preliminary plans for potential implant receptor sites (Blue Sky Plan [BlueSkyBio]) were submitted to the laboratory (ROE Dental Laboratory) for review. The 3D data from the CBCT scan was then merged with the IOS data set to aid in determining a restoratively driven solution for both arches. The laboratory then designed transitional full-arch, screw-retained restorations utilizing CAD software at the designated vertical dimension required for the prostheses. The desired tooth position, as visualized with the 3D reconstructed volume of bone, helped to determine the most favorable implant receptor sites. A virtual remote planning session was held with the laboratory to finalize the “full-template” guided surgical plan (CHROME GuidedSMILE), which incorporated a 2-mm increase in VDO, and it was sent for production. The CHROME GuidedSMILE protocol consists of several component parts that provide a “stackable” solution with metallic scaffolding to control the bone reduction; the preparation of the osteotomies; full-template guidance of the implants into the bone; implant depth, trajectory, and rotational indexing; the positioning of the MUAs; and the delivery of the provisional restorations.1
