Future Trends in Implant Dentistry: Digitally Guided Surgery and Prosthetics

INTRODUCTION
This article discusses an innovative and clinically accurate protocol that will assist interested dental practitioners in the delivery of full-arch fixed immediate provisional prostheses. Additionally, the detailed steps involved in converting the provisional into a fixed screw-retained final prosthesis, following sufficient healing and the osseointegration of dental implants, are outlined.

CASE REPORT
Diagnosis and Treatment Planning

A 76-year-old male patient presented to the office with Kennedy Class I partial edentulism in the maxilla (Figure 1). He had 4 anterior teeth present with one that had fractured at the gingival margin. He expressed a desire for a fixed implant-supported solution. After appropriate medical, dental, and social histories were obtained, a full clinical and radiographic examination was performed. Subsequently, it was determined that the patient had a terminal maxillary dentition and he was presented with various options.

The patient elected to have a full implant-retained prosthesis for the maxillary arch. The treatment planning and clinical procedure involved digitally guided surgery and a digitally guided provisional prosthesis. The digital protocol simplifies the steps involved in fabricating a fixed final prosthesis after subsequent healing has taken place.

To employ this protocol, the practitioner provided the laboratory team with the following:

  • Models (conventional or digital) with a face-bow registration
  • A bite registration of the patient at his “idealized” vertical dimension of occlusion (VDO)
  • CBCT at the idealized VDO
  • A series of intra- and extraoral photographs of the patient.

The company, nSequence Center for Advanced Dentistry (Reno, Nev), then digitized this information, creating a digital treatment plan to allow the practitioner and patient to visualize the outcome prior to surgery (Figure 2).

Figure 1. Retracted preoperative presentation.
Figure 2. A digital treatment plan was requested and provided.

Digitally Guided Surgical and Prosthetic Phases
Check Bite—A hard acrylic bite was fabricated by the laboratory team, based upon the initial patient records (Figure 3). The “check bite” step verifies the accuracy of the merged data, and the practitioner can feel confident that the digital records correctly represent the clinical situation.

Placement of the foundation guide—Once the patient’s maxillary teeth were extracted and a full-thickness flap was raised to expose the entire alveolus, the “foundation” guide was placed to fit over the alveolus (Figure 4). This foundation guide remains in place until the time that the provisional prosthesis is inserted. The patient bites into the struts of the guide, which helps to stabilize and position the foundation guide.

Once fully seated, guided fixation pins were placed using depth control to secure the guide by engaging both the buccal and palatal bone.

After removal of the positioning struts, the foundation guide directed subsequent bone reduction. Bone reduction was achieved using a Rongeur’s forceps. Any larger bone fragments were preserved to fill the extraction sockets. A bur (Pikos bone block contouring bur [Salvin Dental Specialties]) was used to smooth the alveolus until flush with the foundation guide (Figure 5).

Figure 3. Lab-fabricated hard acrylic bite. Figure 4. After extraction of maxillary teeth and a full-thickness flap, the “foundation” guide was placed over the alveolus.
Figure 5. The alveolus was smoothed with a bur until flush with the foundation guide. Figure 6. An implant placement guide was indexed to fit into the foundation guide.
Figure 7. Implants were placed, and then the implant placement guide was detached from the foundation guide. Figure 8. Abutments were placed, and then the abutment placement guide was removed.
Figure 9. Pretrimmed temporary
titanium cylinders, hand-tightened to the multiunit abutments (MUAs). Block-out tubes were placed in cylinders to protect prosthesis screws.
Figure 10. A flexible silicone gasket was then placed over the temporary titanium cylinders.
Figure 11. The gasket blocked out undercuts and helped position the provisional. Figure 12. Picking up the provisional clear duplicate.


Placement of the implants—An implant placement guide (patented by the laboratory [nSequence Center]) was indexed to fit into the foundation guide (Figure 6). This assisted in the sequential osteotomy process, preparing the implant sites. Once the implants were placed, the implant placement guide was detached from the foundation guide (Figure 7).

Placement of the multiunit abutments (MUAs)—An indexed abutment placement guide was then fit into the foundation guide. A specific guide was created to assist in the placement of the angled MUAs to ensure correct positioning. The abutments were then placed and torqued per the manufacturer’s recommendations, and then the abutment placement guide was removed (Figure 8).

Placement of the temporary titanium cylinder—Pretrimmed temporary titanium cylinders were subsequently hand-tightened to the MUAs. Block-out tubes were then placed into these cylinders to protect the prosthesis screws (Figure 9).

Figure 13. The silicone maxillary gasket, fixation pins, and foundation guide were removed. Figure 14. The finished provisional prosthesis.
Figure 15. Panoramic radiograph of and anterior photo of the bar-supported provisional prosthesis.

Placement of the silicone gasket and fit of the provisional—A flexible silicone gasket was then placed over the temporary titanium cylinders, hugging the apical portion of the cylinders tightly (Figure 10). The gasket served to block out undercuts and to guide the apical and lateral position of the provisional (Figure 11), while taking into account the thickness of the underlying soft tissue. The provided silicone bite registration index was placed against the incisal edge of the provisional and indexed to the patient’s mandibular incisors, and thus stabilized the prosthesis at the patient’s idealized VDO.

Picking up the provisional prosthesis and clear duplicate—After stabilizing the prosthesis, a dual-cured polymer (Triad [Dentsply Sirona]) was used to “pick up” the cylinders after injecting material into the small buccal channels. After curing the polymer from the buccal, the silicone bite registration was removed. Next, any remaining voids were then filled with the polymer and light-cured from the occlusal aspect. Then, the block-out tubes were removed and the prosthesis was unscrewed and removed from the mouth. This step was then repeated using a second set of titanium cylinders and the clear duplicate prosthesis supplied by the laboratory team (Figure 12). This clear duplicate prosthesis was then stored for future use after the healing period elapsed to help fabricate the final fixed prosthesis.

Removal of guide and closure—The silicone maxillary gasket was then removed along with the fixation pins and foundation guide (Figure 13). The alveolus was then smoothed and contoured and the earlier harvested autogenous bone used to fill the remaining sockets. Closure was achieved by placing individual interrupted sutures between the implants.

Finishing and insertion of the provisional prosthesis—After adding acrylic to fill any remaining voids around the titanium cylinders, the provisional was further cured with heat and pressure before giving its final polish. Next, the finished provisional prosthesis was placed onto the MUAs and torqued into place per the manufacturer’s specifications (Figure 14). Teflon tape and Cavit [3M] were then used to close each access hole before verification of the patient’s occlusion. This bar-supported, monolithic polymethyl methacrylate acrylic (PMMA) prosthesis would then be worn for approximately 6 months (Figures 15 and 16).1

Digitally Guided Final Prosthetic Phase
During the healing phase, the provisional prosthesis was not removed. It served as a “splint” for the implants, helping to stabilize them during the healing process.2,3 After the 6-month healing period,1 the patient returned with his PMMA provisional prosthesis in place. Upon examination, his occlusion remained stable, well balanced, and unchanged from his initial immediate postoperative position (Figure 16a). The prosthesis, although a little worn and mildly stained, was still functional and showed good aesthetics (Figure 16b).

Figure 16. The provisional prosthesis was stable and unchanged at 6 months.
Figure 17. Some inflammation in the tissues was noted after wearing the provisional prosthesis continuously for an extended period of time.
Figure 18. Using a torque wrench with a multiunit adapter, the stability of each implant was tested. Figure 19. One implant did not
successfully osseointegrate and was subsequently removed.
Figure 20. The stored clear duplicate was retrieved and inserted. Figure 21. The prosthesis was
hand-tightened over the MUAs.
Figure 22. The intaglio surface of the clear duplicate and underlying soft tissues were air-dried.

Removal of the provisional prosthesis—The access holes of the provisional prosthesis, which had been closed off with Cavit and Teflon tape, were uncovered. The screws were untorqued, and the prosthesis was removed and cleaned with a chlorhexidine solution (Chlorhexidine Gluconate 0.12% Oro-Cleanse [Germiphene]). Upon inspection of the tissues underlying the prosthesis, the general health of the tissues was fair with some inflammation consistent with expectations having worn the provisional prosthesis continuously for a long period of time (Figure 17).

Verification of the stability of the implants—Using a torque wrench with a multiunit adapter, the stability of each implant was tested (Figure 18). This test serves 2 purposes: first, the abutments are tightened against the implant as they can loosen with time; and second, the bone-implant interface is placed under strain to evaluate its strength at a force of 30 Ncm. If the bone-implant contact is unstable, the implant will rotate. In this case, one implant did not successfully osseointegrate and was subsequently removed (Figure 19). There was no need to replace the failed implant. The design of the final prosthesis would be stable, balanced, and functional using the remaining 7 implants and their anterior-posterior spread.4 The original treatment plan accounted for the potential failure of one or 2 of the implants without the need for additional surgery.

Fit and use of the clear duplicate—The stored clear duplicate was retrieved and inserted into the patient’s mouth (Figure 20). The prosthesis was hand-tightened over the MUAs. The fit was found to be precise and required no adjustment (Figure 21). This predictable fit was a result of the stabilization and splinting of the implants after surgery while the patient wore his PMMA provisional prosthesis. There may be a gap between the clear duplicate and the ridge as some tissue shrinkage is a normal sequelae of the healing process. If there is not an adequate amount of clearance, the intaglio side of this duplicate provisional must be relieved using an acrylic bur to create the required space for the impression material.

Radiographs were then taken to ensure this duplicate was seated properly prior to the next steps.

Impression of the arch and pickup of the implant/MUA positions—Once the seating has been verified and prior to taking an impression, it is important to confirm that the clear provisional duplicates the aesthetics of the provisional prosthesis. (In this practitioner’s experience, this has never been an issue, as the clear duplicate and provisional prosthesis are fabricated together using the same digital technology and processes prior to the surgical procedure.)

Figure 23a. Using retractors, light-body vinyl polysiloxane (VPS) impression material (Examix NDS [GC America]) was injected into the gap area between the tissues and the clear duplicate from both the palatal and buccal. Figure 23b. The VPS material was extruded to record the facial and palatal contours of the ridge.
Figure 23c. A bite registration was taken simultaneously with the patient in centric relation.
Figure 24. Once the materials were fully set, the bite registration was carefully removed, the clear duplicate unscrewed and removed. Figure 25. The lab team (nSequence Center for Advanced Dentistry; Reno, Nev) then fabricated a metal framework with access holes where the implants are located for the final prosthesis.
Figure 26. The patient returned to the office at approximately 2 weeks for the metal framework try-in.

The intaglio surface of the clear duplicate and underlying soft tissues were air-dried (Figure 22). Using retractors, light-body vinyl polysiloxane (VPS) impression material (Examix NDS [GC America]) was injected into the gap area between the tissues and the clear duplicate from both the palatal and buccal. With the tip inserted inside the gap area, the impression material was gently extruded while the tip was carefully pulled out (Figure 23a). This process ensures that there is adequate impression material in this area to adequately capture the gingival tissues that have recontoured during the healing phase. The VPS material was also extruded to record the facial and palatal contours of the ridge (Figure 23b). The accuracy of the vestibular contours was not critical in this procedure, as a fixed prosthesis was treatment planned for the patient rather than a conventional full denture. A bite registration was also taken simultaneously with the patient in centric relation (Figure 23c).

Once the materials were fully set, the bite registration was carefully removed and the clear duplicate unscrewed and removed from the mouth (Figure 24). The impression was examined carefully to ensure that the intaglio surface of the denture had accurately recorded the gingival contours and there were no serious deficiencies. The PMMA provisional prosthesis was then re-inserted for the patient, and radiographs taken to ensure that the prosthesis was seated and fit appropriately.

Figure 27. Radiographs were taken and a screw test done to confirm an accurate and passive fit of the framework.
Figure 28. Completed maxillary implant-retained prosthesis.

Laboratory fabrication of the final fixed prosthesis—Next, the impression was sent to the laboratory, where the lab team would attach MUA analogs and pour a model to become an accurate representation of the patient’s arch and implant/MUA positions (master model). This master model was cross-mounted with the bite registration and the previous mounted mandibular cast. The lab team then fabricated a metal framework with access holes where the implants were located for the final prosthesis. On this screw-retained prosthesis, each final crown restoration was made to fit the individual crown preparations on the framework (Figure 25). In this case, milled lithium disilicate (IPS e.max CAD [Ivoclar Vivadent]) crowns were prescribed.

Try-in of the metal framework—The patient returned to the office in approximately 2 weeks to try in the metal framework (Figure 26). Radiographs were taken and a screw test done to confirm an accurate and passive fit of the framework (Figure 27).5,6 The occlusion and VDO were verified and a final shade selected.

Finalization of the prosthesis by the laboratory team—The laboratory finished the case by milling the lithium disilicate crowns, and then adding pink porcelain to the metal framework to mimic the gingiva and soft tissues. Access holes were created in the crowns where the screws were located. Finally, the crowns were then cemented onto the framework at the laboratory using permanent cement.

Insertion of the final fixed prosthesis—The patient returned to the clinic, and the provisional PMMA prosthesis was removed and the final prosthesis delivered. The access holes are filled with Cavit and Teflon tape, and the excess material removed. The aesthetics, occlusion, and VDO were verified. The patient was very pleased with the final outcome (Figure 28).

DISCUSSION
This innovative technique (patented by nSequence) uses integrated digital technology to achieve a predictable prosthetic result.7 As noted herein, each sequential step was guided by the initial treatment planning, ensuring accuracy of fit in each surgical and prosthetic phase. The aesthetics and function of the final prosthesis were predictable and unchanged from the provisional phase through the delivery of the fixed prosthesis. This instilled confidence between the clinician and the patient, as they worked together in the treatment planning and consultation phases to reach this outcome.

This technique is very time efficient for both the clinician and the patient. The guided surgical and guided prosthetic protocol enable a faster and more accurate placement of implants and provisional prosthesis without any guesswork, as is required in other “freehand” methods.8-10 Additionally, the fabrication of the final prosthesis requires fewer appointments as several clinical steps (including the verification jig, occlusal rim, and wax setup) are eliminated as a direct result of the digital solution provided by this methodology. The clear duplicate serves as an impression tray as well as a verification jig to ensure the accuracy of the implant/MUA positions in the master model. Also, the use of the clear duplicate mimics the size and shape of the teeth at the correct VDO for the final prosthesis; thus, there is no need for wax occlusal rims or a wax tooth setup. For the patient, this is advantageous as (potentially) 3 appointments are eliminated. It is noteworthy to mention that, with experience and developed expertise, the metal framework try-in appointment can often be eliminated given the high level of accuracy of the master model.

This protocol will support the use of various restorative materials for the final prosthesis. However, the main advantage of using a framework with individual CAD/CAM crowns is the ease with which replacement crowns can be fabricated in the event the patient fractures one since a digital record is kept. If one crown chips, it can be removed and provisionalized while the lab team is instructed to fabricate a replacement crown. It is unnecessary to remove and send the entire prosthesis back to the laboratory. Additionally, the lab team could even fabricate the replacement crown before the patient presents to the office, as long as the practitioner knows ahead of time which crown is compromised.

IN SUMMARY
The use of digital technology and CAD/CAM solutions creates a high degree of predictability for the practitioner. The preplanned surgical phase, including the foundation and implant placement guides, reduces the stresses involved in determining optimal implant placement sites for prosthetic rehabilitation.11 Using the clear duplicate protocol eliminates the inaccuracies of impression materials for the implant and/or MUA positions. This translates into a more passive fitting prosthesis5 along with predictable aesthetics. Ultimately, this is a win-win situation for the patient and the clinician.


References

  1. Brånemark PI, Albrektsson T. Microcirculation and healing of artificial implants in bone. In: Proceedings of the 2nd World Congress for Microcirculation. Cambridge, MA: Academic Press; 1979:59-60.
  2. Schnitman PA, Wöhrle PS, Rubenstein JE, et al. Ten-year results for Brånemark implants immediately loaded with fixed prostheses at implant placement. Int J Oral Maxillofac Implants. 1997;12:495-503.
  3. Wang TM, Leu LJ, Wang J, et al. Effects of prosthesis materials and prosthesis splinting on peri-implant bone stress around implants in poor-quality bone: a numeric analysis. Int J Oral Maxillofac Implants. 2002;17:231-237.
  4. Rodriguez AM, Aquilino SA, Lund PS. Cantilever and implant biomechanics: a review of the literature, Part 2. J Prosthodont. 1994;3:114-118.
  5. Sahin S, Cehreli MC. The significance of passive framework fit in implant prosthodontics: current status. Implant Dent. 2001;10:85-92.
  6. Kan JY, Rungcharassaeng K, Bohsali K, et al. Clinical methods for evaluating implant framework fit. J Prosthet Dent. 1999;81:7-13.
  7. Pikos MA, Magyar CW, Llop DR. Guided full-arch immediate-function treatment modality for the edentulous and terminal dentition patient. Compend Contin Educ Dent. 2015;36:116-128.
  8. Rosenfeld AL, Mandelaris GA, Tardieu PB. Prosthetically directed implant placement using computer software to ensure precise placement and predictable prosthetic outcomes. Part 1: diagnostics, imaging, and collaborative accountability. Int J Periodontics Restorative Dent. 2006;26:215-221.
  9. Pikos MA, Mattia AH. Implant surgery interventions: Three-dimensional reverse tissue engineering for optimal dental implant reconstruction. In: Jokstad A, ed. Osseointegration and Dental Implants. Ames, IA: Wiley-Blackwell; 2008:197-204.
  10. Worthington P, Rubenstein J, Hatcher DC. The role of cone-beam computed tomography in the planning and placement of implants. J Am Dent Assoc. 2010;141(suppl 3):19S-24S.
  11. Wong NY. Predictable immediate implant prosthetics using guided surgery and guided prosthetics: a case report. Oral Health. 2016;106:66-78.

Dr. Wong graduated from the University of Toronto with a DDS (1996) and received her certificate in prosthodontics from the University of Michigan (2007). She is the only dentist who has attained a combination of the US board certification in implant dentistry (Diplomate from the American Board of Oral Implantology [ABOI], 2003), US board certification in prosthodontics (Diplomate of American Board of Prosthodontics, 2008), and Canadian board certification in prosthodontics (Fellow of Royal College of Dentists of Canada, 2008). She is a Diplomate of the International Congress of Oral Implantologists and holds Fellowships with the AGD, American Academy of Implant Dentistry (AAID), and the Misch International Implant Institute in Canada, where she is also a faculty member. She has served as a clinical instructor in the implant prosthodontic unit in the graduate prosthodontic department at the University of Toronto. She is past president of the ABOI, the current treasurer for the AAID, president of the Association of Prosthodontists of Ontario, and founder and director of the Toronto Implant Institute. She lectures internationally on implant dentistry and continues to practice implantology in Toronto. She can be reached by email at the following address: This email address is being protected from spambots. You need JavaScript enabled to view it..

Disclosure: Dr. Wong is a consultant for BioHorizons.

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