Simplified Dental Protocol for Construction of Removable Prosthesis with Implant/Mucosa Support
Inside Dental Technology delivers updates on digital workflows, materials, lab techniques, and innovation in dental technology through expert articles and videos.
September 1, 2016
Volume 7, Issue 9, September 2016
Page(s): p. 54
By Maurizio Sedda, CDT, DDS, MSc, PhD; and Simone Fedi, CDT
Edentulous patients increasingly present to clinicians with a request for a fixed prosthesis. In the lower arch, implant prosthetics usually are not technically difficult to treatment plan and fabricate. In the upper arch, however, a number of variables must be considered during treatment planning, and if they are underestimated then the potential for failure increases. The shape of the jawbone and soft tissues can impede the patient’s ability to clean the implants and prosthesis, which too often are designed and fabricated with only esthetic considerations in mind. The importance of hygiene is often ignored, despite being a basic requirement for the long-term success of the treatment.1,2 For these reasons, the prosthesis and implants should be designed prior to placement, with the insertion being “guided” by the prosthesis itself.3 Additionally, the shape and position of the lip strongly contribute to the esthetics, especially in the upper arch; the perioral tissues must be correctly supported to restore facial harmony and phonetics.4
The purpose of this article is to provide a simplified technical protocol to increase the accuracy of the restoration and decrease the difficulty of implementation and the necessary processing time.
Clinical Case
A 54-year-old man, a non-smoker with no major diseases, presented to the clinician with an edentulous upper arch. Some lower elements were present from teeth Nos. 21 to 29. The complete prosthesis for the upper arch was incongruous and caused difficulties with chewing and speech. The clinician started by constructing a provisional restoration for the maxillary arch, still using a complete removable prosthesis for diagnostic purposes. Periodontal treatment was performed for the lower elements, with a provisional removable partial denture.
Once the esthetics and a correct occlusal plane were restored, it was necessary to maintain the buccal flange in support of the upper lip. Diagnostic tests were performed to study the placement of the implants with panoramic radiography and computed tomography. The patient agreed to the following treatment plan: insertion of four implants in the areas of teeth Nos. 5, 7, 10, and 12; an implant- and mucosa-supported prosthesis with a milled bar on the upper arch; and a removable partial denture for the lower arch.
Once the implants were placed, with their position determined by the availability of the bone and the prosthetic requirements, the patient wore a modified temporary prosthesis until the osseointegration process was complete. During this time, the patient was subjected to periodontal maintenance therapy. The same prosthesis was used as a base for the final restoration.
Fabrication of the Master Model and of the Esthetic Try-in
The master model was achieved by developing the impression with a class IV plaster, using distilled water according to the manufacturer’s mixing ratios and with vacuum mechanical mixing (Figure 1). Once hardened, the transfers were removed and the master model was positioned on the articulator using the replica and the facebow. The antagonist model was placed on the articulator with the silicone bite. A light-curing resin was used to produce the esthetic prototype (Figure 2).
Fabrication of the Bar
Once cured, the prototype and the master model were removed from the flask and digitized using a laboratory scanner, and then the files were uploaded into the CAD software (DentalCAD, exocad, exocad.com) (Figure 3). The design of the primary bar was developed according to the teeth setup in order to put the attachments perpendicular to the occlusal plane. The bar surface facing the gingiva was made convex, to minimize the accumulation of plaque and food and to facilitate hygiene. The bar was milled from a solid titanium alloy block (Figure 4 and Figure 5). Four attachments, with their respective housings, were put on the bar. The attachment chosen (OT Equator, Rhein83, rhein83usa.com) had a reduced vertical dimension compared with spherical attachments, saving space with stronger retention. The attachments were screwed directly into the thread inside the bar that was created by the milling center, avoiding the necessity for adhesive materials or welding (Figure 6). Those threaded attachments allowed for quick and easy replacement without removing the bar. The retentive elastic cap made it unlikely that the attachments would need to be replaced. The bar, with the attachments screwed in, was delivered to the clinician.
Verification of the Bar
The clinician proceeded to screw the bar onto the abutments, verifying its passive seating (Figure 7). The distance between the gingiva and the bar, which is crucial to daily hygiene, was checked, and a test was performed to verify that the patient was able to brush and use floss. The compressive points on the gingiva were reduced. The bar was returned to the laboratory after the disinfection protocol, and the final prosthesis was fabricated.
Conclusion
A removable prosthesis with implant and mucosa support is a solution that combines the esthetics and lip support of a removable prosthesis with the stability of an implant-retained fixed prosthesis (Figure 8 through Figure 10). Furthermore, it allows for easier cleaning and eliminates the encumbrance of the palate.
The execution of the simplified protocol in this case allowed for a reduction of the processing times without any loss of quality and accuracy.
The use of low-profile attachments screwed directly into the bar without gluing or welding allowed for easy installation and an eventual replacement, and also ensured excellent retention within small spaces.
Maurizio Sedda, CDT, DDS, MSc, PhD, practices prosthodontics in Pistoia, Italy. Simone Fedi, CDT, owns a laboratory in Pistoia, Italy.
