CAD/CAM-Driven Full-Arch Restorations

The prevalence of edentulism is thought to be increasing worldwide due to advances in medicine leading to an increase in life expectancy.¹ Considered the “end-stage of oral disease,” edentulism is a multifactorial condition that is often the result of untreated oral problems such as caries, periodontal diseases, and/​or trauma.² As oral health declines, the dentition undergoes irreversible structural and functional compromise, culminating in terminal dentition. This necessitates extensive prosthetic intervention to restore function, speech, and esthetics.^2,3

With the success of implant therapy, coupled with the advances in computer-aided design/​computer-aided manufacturing (CAD/​CAM) technologies, fixed full-arch implant-supported restorations are a reliable treatment for edentulous patients or those with a terminal dentition.⁴ Complete digital workflows have been described to facilitate the diagnosis, planning, and execution of full-arch implant restorations.

Diagnosis and Treatment Planning

As with any dental treatment, the first step is thorough documentation of the patient’s chief concern in addition to medical, social, and dental history. For patients indicated for full-arch implant therapy, a restoratively driven approach that starts with identifying the ideal position of teeth in the oral cavity based on facial esthetics and phonetics is appropriate. This requires obtaining accurate scans or impressions of the existing soft and hard tissues, extraoral photos, and/​or facial scans. Accurate articulation and merging of all diagnostic information using dental design software are critical to the treatment planning process.⁵

Data from facial and intraoral scans, two-dimensional photography, and radiographic images can be accurately combined to provide a complete representation of the patient’s intraoral and extraoral surfaces.⁵ An example of this process is the dual scan technique for implant planning in the edentulous patient, in which a cone-beam computed tomography (CBCT) scan is obtained of the removable prosthesis intraorally and extraorally (Figure 1). This allows the diagnostic process to be thorough, precise, and enables the clinician to visualize the relationship of the desired tooth position to the anatomical structures of the oral cavity. It also helps identify deficiencies in soft and hard tissues.

Pollini et al⁶ discussed a classification system to identify and treatment plan for deficiencies in the lip-tooth-ridge complex. Correction of such deficiencies, as described by Pollini et al, can be done prosthetically through the use of pink restorative materials such as porcelain or acrylic. However, surgical implant site development procedures are needed when vertical and/​or horizontal deficiencies limit the proper positioning of implants, or in order to modify the anatomical deficiencies so that pink porcelain or acrylic is no longer necessary.

Implant Planning

Once all the diagnostic information has been gathered and rendered digitally, implant planning can begin with the final restoration’s design and material in mind. Implant planning software combines and overlays anatomical data from the CBCT, intraoral scans, and the desired location of the dentition, to properly position the implants ensuring the fulfillment of both biological and biomechanical requirements. Software features — including measurements, three-dimensional (3D) rendering, and the ability to visualize prosthetic components — can aid in the proper positioning of implants (Figure 2). A critical factor to address when planning for full-arch implant restorations is the necessary restorative space; this is determined by the definitive restorative material.⁷ Pre-operative measurements of the available restorative space allows for adjustments of the implant position, potentially mitigating both biological and prosthetic complications.^7,8

Digital rendering also aids clinicians in designing the emergence profile of the final restoration, ensuring the development of biologically sound and esthetically pleasing gingival tissue surrounding the restoration.⁸ Furthermore, implant planning software packages routinely offer digital libraries with a variety of prosthetic components that can be readily identified and visualized at this early stage.⁹ Given the common use of angle-correcting abutments in implant therapy, their determination is achievable during the planning phase (Figure 3).

Combined with designing capabilities, several software programs use surface scans of the existing anatomy, alveolar bone, gingival tissue, or teeth to design a surgical guide for the implant placement.⁹ Specific surgical guides can also help facilitate accurate bone reduction when additional restorative space is required for the restorative material strength (Figure 4). A comprehensive implant planning approach integrates diagnostic data, implant positioning considerations, and advanced software tools, optimizing the outcome of implant therapy.

Surgical Execution and Provisionalization

After determining the definitive position of the teeth and the necessary implants to support them, the plan must be transferred to the operating room. Computer-aided implant placement can be divided into two categories: static and dynamic navigation.¹⁰ Static navigation involves the stereolithographic fabrication of a rigid stent with guide sleeves or tubes that direct the placement of the implant.^10,11

The position and angle of the guide sleeves are based on the planned position of the implant within the implant planning software (Figure 5). Once the implant location is determined, and the guide is fabricated, the planned position of the implant can no longer be modified; hence, this type of guide is described as being “static.”^10,11

In contrast, dynamic navigation allows for the implant plan to be changed in real time.¹⁰ It involves fiducial markers on the patient to provide calibration between the patient and the obtained imaging, as well as positioning sensors on the handpiece and jaw tracker (Figure 6).^10,11 This permits continuous feedback of the drill position relative to the planned implant position. Real time feedback enables the provider to modify the implant plan intraoperatively, including implant position, angulation, and type.^10,11 While there is not a significant difference in accuracy between static and dynamic guides, both dynamic and static navigation have significantly greater accuracy when compared to freehand surgery.^12–14

After implants are placed, a full-arch implant-supported restoration is fabricated. One common method is to have a provisional fabricated in advance. The prefabricated provisional is indexed and retained by using anchor pins or supported by a foundation guide. After implant placement, titanium temporary cylinder abutments are attached to the prefabricated provisional prosthesis using resin.¹⁵ Supporting struts are removed, and contours are refined extraorally (Figure 7).

Another frequently used method of fabricating a provisional is via 3D printing or milling after implant placement. The location of the implants can be recorded using an intraoral scan or photogrammetry. Full-arch digital impressions of implants in the edentulous patient have not been found to be consistently clinically acceptable.¹⁶

Photogrammetry, on the other hand, has been shown to provide a more accurate representation of implant positioning when compared to splinted open tray impressions, the current gold standard.^17,18 Photogrammetry involves making precise measurements between reference points in photographs; it can provide the location of implants relative to one another (Figure 8). These data are merged with an intraoral scan to provide soft tissue information. The data obtained is aligned to the previously developed digital wax up to design and fabricate the provisional on the day of surgery using a 3D printer or mill.

Definitive Restoration

The final step, after osseointegration of the implants, is fabrication of the definitive prosthesis. Soft tissue development and occlusion is finalized in the provisional phase and used as a guide for fabricating the definitive restoration. CAD/​CAM technology allows us to replicate the contours of the interim restoration, ensuring that the definitive restoration requires minimal modification during insertion.

Following similar protocols used in the provisional phase, the final registration of the implant positions, soft tissue contours, and provisional restorations are used to fabricate the final restoration. In cases where modification of the provisional was not significant, the same records obtained during provisionalization can be used for fabrication of the definitive prosthesis. The ease of storage of digital data also facilitates the replication of these prostheses in case of complications, such as fractures.

Conclusion

Advancements in CAD/​CAM technology have led to an increase in reliability and predictability of full-arch implant-supported treatment. With careful planning and execution of implant placement and restoration, the dental clinician is able to efficiently treat the growing edentulous population.

References

1. Lin M, Griffin SO, Gooch BF, et al. Oral health surveillance report: trends in dental caries and sealants, tooth retention, and edentulism, United States: 1999–2004 to 2011–2016. Available at: stacks.cdc.g/​v/​view/​cdc/త. Accessed April 14, 2024.
2. Al-Rafee MA. The epidemiology of edentulism and the associated factors: A literature ReviewJ J Family Med Prim Care. 2020;9:1841.
3. Papaspyridakos P, Chronopoulos V. Transition from failing dentition to complete-arch implant rehabilitation with a staged approach: A 3-year clinical report. J Prosthet Dent. 2014;112(3):423-8.
4. Papaspyridakos P, Bordin TB, Kim YJ, et al. Technical complications and prosthesis survival rates with implant‐supported fixed complete dental prostheses: a retrospective study with 1‐to 12‐year follow‐up. J Prosthodont. 2020;29:3-11.
5. Hassan B, Gonzalez BG, Tahmaseb A, et al. A digital approach integrating facial scanning in a CAD-CAM workflow for complete-mouth implant-supported rehabilitation of patients with edentulism: A pilot clinical study. J Prosthet Dent. 2017;117:486-492.
6. Pollini A, Goldberg J, Mitrani R, et al. The lip-tooth-ridge classification: a guidepost for edentulous maxillary arches. diagnosis, risk assessment, and implant treatment indications. Int J Periodontics Restorative Dent. 2017;37:835–841.
7. Carpentieri J, Greenstein G, Cavallaro J. Hierarchy of restorative space required for different types of dental implant prostheses. J Am Dent Assoc. 2019;150:695-706.
8. Nagni M, Pirani F, D’Orto B, et al. Clinical and radiographic follow-up of full-arch implant prosthetic rehabilitations: retrospective clinical study at 6-year follow-up. Appl Sci. 2023;13:11143.
9. Flügge T, Kramer J, Nelson K, et al. Digital implantology—a review of virtual planning software for guided implant surgery. Part II: Prosthetic set-up and virtual implant planning. BMC Oral Health. 2022;22:1-1.
10. Block MS, Emery RW. Static or dynamic navigation for implant placement — choosing the method of guidance. J Oral Maxillofac Surg. 2016;74:269-277.
11. Mandelaris GA, Stefanelli LV, DeGroot BS. Dynamic navigation for surgical implant placement: overview of technology, key concepts, and a case report. Compend Contin Educ Dent. 2018;39:614-621.
12. Kaewsiri D, Panmekiate S, Subbalekha K, et al. The accuracy of static vs. dynamic computer-assisted implant surgery in single tooth space: A randomized controlled trial. Clin Oral Impl Res. 2019;30:505-514.
13. Gargallo-Albiol J, Barootchi S, Marqués-Guasch J, Wang HL. Fully guided versus half-guided and freehand implant placement: systematic review and meta-analysis. Int J Oral Maxillofac Implants. 2020;35:1159-1169.
14. Aydemir CA, Arisan V. Accuracy of dental implant placement via dynamic navigation or the freehand method: A split-mouth randomized controlled clinical trial. Clin Oral Impl Res. 2020; 31:255-263.
15. Chen C, Lai H, Zhu H, Gu X. Digitally prefabricated versus conventionally fabricated implant-supported full-arch provisional prosthesis: a retrospective cohort study. BMC Oral Health. 2022;22:335.
16. Zhang YJ, Shi JY, Qian SJ, et al. Accuracy of full-arch digital implant impressions taken using intraoral scanners and related variables: A systematic review. Int J Oral Implantol (Berl). 2021;14:157-159.
17. Ma B, Yue X, Sun Y, Peng L, Geng W. Accuracy of photogrammetry, intraoral scanning, and conventional impression techniques for complete-arch implant rehabilitation: an in vitro comparative study. BMC Oral Health. 2021;21:636.
18. Hajjar LG. Accuracy of photogrammetry, intraoral scanning, and conventional impression techniques for full-arch implant-supported prostheses: An in-vitro study. Master’s thesis. Boston University; 2022.

From Decisions in Dentistry. April/May 2024; 10(3):18,20-22