November 23, 2016
by Natalie Y. Wong
This article discusses a novel protocol to deliver a full-arch immediate fixed provisional prosthesis, which is clinically accurate and predictable. Detailed steps are outlined and documented that enables conversion of the provisional into a fixed screw-retained final prosthesis after healing and the osseointegration of the dental implants.
A 58-year-old female patient was referred to the office for “a new smile”. A comprehensive clinical and radiographic examination along with a full history including medical, dental and social information was performed. The results of the combined assessments revealed that the patient had a terminal maxillary dentition. Various treatment options were presented to the patient and the patient elected to proceed with a full-arch implant supported prosthesis for his maxilla (Figs. 1a, 1b).
Digitally Guided Surgery and Digitally Guided Provisional Prosthesis
The patient’s treatment planning and clinical procedure was pre-planned, visualized and discussed ahead of time with the patient. The digital protocol employed facilitated the fabrication of the fixed final prosthesis after the healing phase had taken place.
As part of the protocol, the practitioner must obtain the following clinical information and provide it to the laboratory (nSequence®).
Using this information, the information is then digitized and a digital treatment plan is created (Fig. 2). In this way, the dentist and patient are able to visualize the outcome prior to surgery and make any minor changes that may be required or anticipate any challenges ahead of the procedure.
Digitally Guided Surgical Phase
The digitally guided surgical phase has been previously described in detail in an earlier article by the author (Fig. 3).
Digitally Guided Final Prosthetic Phase
After the initial placement of the implants and for the duration of the healing phase, the provisional prosthesis was not removed. The rationale for this is that the provisional prosthesis acts as a “splint” and stabilizes the implants during osseointegration and healing.
A. Evaluation of the Provisional Prosthesis
The patient presented for evaluation after a six-month healing period for evaluation of the polymethlmethacrylate (PMMA) provisional prosthesis. This assessment examined the vertical dimension of the patient, as well as the phonetics and esthetics. As predicted, her occlusion was well-balanced, stable and showed no changes from the immediate post-operative position of the prosthesis. She was satisfied with both the phonetics and esthetics of the prosthesis. The prosthesis appeared to be in good condition (Fig. 4a, 4b).
B. Evaluation of the Underlying Tissues
The access holes of the provisional were uncovered and the screws were untorqued. Upon removal, the prosthesis was disinfected with chlorhexidine. Inspection of the tissues under the prosthesis revealed they were in good general health with some areas of mild inflammation given the patient had been wearing the provisional for a prolonged period of time since its initial insertion (Fig. 5).
C. Evaluation of the Implants and Abutments
To test the stability of each implants, a torque wrench with a multi-unit adapter was used (Fig. 6). This is an essential step for two reasons. Abutments can loosen over time and as such, any loose abutments are tightened against the implant using the torque wrench. Additionally, this also allows the practitioner to evaluate the strength of the bone-implant interface under strain at a force of 30Ncm (BioHorizons Implant System). If the interface is unstable, the implant will rotate. In this case, all implants and abutments were stable at 30Ncm.
D. Placement of the Clear Duplicate
The initial laboratory case was returned with a clear duplicate that was stored to be used at a later date. The clear duplicate was retrieved and inserted in the patient’s mouth. The duplicate was hand-tightened over the multi-unit abutments (MUA) (Figs. 7a, 7b). As anticipated, the fit was accurate and no adjustments were required. The fit resulted from the splinting and stabilization of the implants during the healing phase when the patient wore the PMMA provisional prosthesis. Radiographs were also taken to ensure the duplicate was seated properly prior to taking the next steps.
A gap was noted between the clear duplicate and the alveolar ridge due to tissue shrinkage during normal healing (Fig. 8a, 8b). The gap on the intaglio surface of the duplicate also allows impression material to flow into this area to capture the accurate surface of the ridge. (If there is inadequate clearance, the intaglio side of the duplicate provisional must be relieved using an acrylic bur.)
E. Impression of the Soft Tissues and Bite Registration
After seating the clear duplicate provisional, the seating was confirmed to ensure the esthetics and phonetics remained unchanged. The intaglio surfaces of the duplicate and the soft tissues were air-dried prior to capturing the impression with polyvinylsiloxane (PVS). PVS was injected into the gap area between the duplicate and ridge from the palatal and buccal aspects by gently extruding the material while carefully pulling the tip of syringe out (Fig. 9a, 9b). The bite registration was taken simultaneously while the patient was in centric relation (Fig. 10). This process aids in accurately capturing the soft tissues, which has changed during healing to enable an accurate and stable fit of the final prosthesis.
Once the materials have fully set, the bite registration and clear duplicate were gently removed from the mouth (Fig. 11a, 11b). The impression was examined for deficiencies and it was noted that it had accurately captured the underlying gingival contours.
At the point, the PMMA provisional prosthesis was re-inserted and radiographs were taken to ensure it was fully seated in the patient’s mouth as before (Figs. 12a-d). The patient was given another appointment and departed the office.
F. Laboratory Fabrication of the Final Fixed Prosthesis
The PVS impression taken with the clear duplicate prosthesis was then shipped to the laboratory where MUA analogs were attached and a master model was poured up. This master model, cross-mounted with the bite registration and the mounted mandibular cast, now serves as an accurate representation of the patient’s mouth.
At the lab, a full contour zirconia fixed implant supported prosthesis is fabricated following the size and shape of the provisional prosthesis, as shown in the clear duplicate. This
final prosthesis is made with access holes that correspond to the location of the implants and is screw-retained (Figs. 13a-c).
G. Try-In of the Final Prosthesis and Final Delivery
The patient returned to the clinic approximately two weeks after the impression was taken. The PMMA provisional was removed and the zirconia fixed implant supported prosthesis was inserted at this appointed (Figs. 14a-c). The final prosthesis must have a passive fit and to this end, a screw test was done and radiographs were taken to ensure the framework was accurately seated (Figs. 15a-c). The patient’s occlusion and VDO were also checked and the shade was confirmed. The prosthesis screws were torqued to 15Ncm (Biohorizons Implant System). Teflon tape and Cavit were used to close the access holes (Fig. 16). The occlusion was verified and the patient was given post-insertion care instructions. The patient was very pleased with the esthetic and phonetic result (Figs. 17a, 17b).
nSequence® (Reno, NV) uses a novel and integrated digital approach to aid practitioners achieve a predictable prosthetic result. The prosthetic phase was predicated on the stability and fit on the initial PMMA prosthesis. As noted in this paper, upon return after the healing process, the patient’s duplicate clear prosthesis fit precisely the same as the PMMA provisional prosthesis. As a result, the accuracy of the sequential prosthetic steps was also anticipated. Additionally, the final esthetics and function of the final fixed prosthesis were predictable and unchanged from the provisional. This certainty builds confidence in the patient and reduces the stress for the practitioner as both parties have discussed and worked together to achieve the final treatment result.
Overall, the combined guided surgical and guided prosthetic technique allows for a more accurate and efficient means of placing implants predictably and creating an accurate fit for both provisional and final prostheses. The involvement of the patient is essential during the treatment planning phase to ensure patient expectations are met and the final outcome is acceptable. For the practitioner, the protocol is very time efficient and eliminates any guesswork required in placing implants and adjustments of provisional and final prostheses.
Additionally, as a result of the stability of the osseointegrated implants and the predictable fit of the clear duplicate provisional, the fabrication of the final prosthesis requires fewer appointments. The clear duplicate serves as an impression tray and verification jig to ensure the accuracy of the implant/MUA positions in the master model while it also mirrors the size and shape of the teeth at the correct VDO required for the final prosthesis. Hence, this protocol eliminates several clinical steps including the verification jig, occlusal rim and wax set-up. Again, this is a clear advantage for the patient, as three possible appointments are not needed. With experience, in many instances, the framework try-in appointment may also be eliminated due to the high accuracy of the master model.
Several restorative materials may be used to fabricate the restorations for the final prosthesis. In this instance, the author chose to use a full contour zirconia restoration for its durability, strength and esthetics.
With the advent of digital technology and CAD-CAM solutions, the practitioner has highly accurate and predictable methods to place and create prosthesis for his/her patients. This not only results in a superior functional and esthetic result for the patient, but it also instills confidence and decreases the stress for the practitioner. The practitioner can work with the laboratory, technicians and his/her patients to create a final outcome that meets or exceeds the patient’s expectations. The guided surgical phase forms the foundation for the pre-planned prosthetic phase as it helps determine the ideal sites for successful implant placement. The use of the clear duplicate provisional in the guided prosthetic stage eliminates the inaccuracies of impression materials for the implant/MUA positions. The result is an accurate and passive fitting final prosthetic with predictable esthetics. This leads to an ideal outcome for both patient and practitioner. OH
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Read Part 1 here: https://www.oralhealthgroup.com/features/1003918999/
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About the Author
Dr. Natalie Wong graduated from the University of Toronto with her Doctor of Dental Surgery in 1996 and received her Certificate in Prosthodontics from the University of Michigan, Ann Arbor in 2007. She is the only dentist that has attained a combination of the U.S. Board Certification in Implant Dentistry, U.S. Board Certification in Prosthodontics, and Canadian Board Certification in Prosthodontics. She is a Diplomate of the International Congress of Oral Implantologists (ICOI), and holds Fellowships with the Academy of General Dentistry (AGD), American Academy of Implant Dentistry (AAID), and the Misch International Implant Institute Canada for which she is also a Faculty Member. Dr. Wong currently serves as a clinical instructor in the Implant Prosthodontic Unit in the Graduate Prosthodontic Department at the University of Toronto. Dr. Wong lectures nationally and internationally on implant dentistry while maintaining a private implant surgical and prosthodontic practice in Toronto. She also does one-on-one mentorships with doctors at her practice.