Dental Asia May/June 2018

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Behind the Scenes Simplified Dental Protocol for the Construction of Removable Prosthesis WITH IMPLANT AND MUCOSAL SUPPORT By Dr. Maurizio Sedda and Mr. Simone Fedi The removable prosthesis with implant - mucosal support combines the aesthetic advantages of a removable prosthesis with the stability given by the implants. The protocol for this type of prostheses may be intricate, both for the clinician and for the dental technician. This work illustrates a simplified dental protocol with, at its starting point, the recognition of a diagnostic prosthesis. This is used as a guide for the placement of implants and, once duplicated, for impression registration of occlusal relationships and for obtaining an aesthetic prototype. Also, the management of milled bar becomes simplified, thanks to the use of attachments with reduced dimensions, and the superstructure, made of PEEK (Polyether ether ketone - thermoplastic composite polymer). By following what is illustrated in the article, it is possible to provide the patient with an aesthetic prosthesis which is stable and easily maintainable from a hygiene point of view. Introduction Gradually, more edentulous patients are specifically asking clinicians for a fixed prosthesis. Mostly in the lower jaw, the implant prosthetic treatment presents no high technical difficulties. However, in the upper arch, there are a number of variables that are essential to keep in mind during the commencement of the treatment plan. If these elements are undervalued, potential failure may easily occur. The shape of the jawbone and soft tissues can hold the patient back during cleansing of the prosthesis that, too often, is fabricated trying to meet only the aesthetic requirements, ignoring the importance of hygiene and basic requirement for the long-term success of the treatment 1,2 . For these reasons, prosthesis with implants should be designed prior to their placement where insertion must be “guided” by the prosthesis itself 3 . Additionally, in the upper arch, more than in the inferior, the shape and the position of the lip strongly contribute to the aesthetics; indeed the perioral tissues must be correctly supported in order to restore facial harmony and the phonetics 4 . As mentioned above, the removable prosthesis with implant and mucosal support nds its application in dentistry. This type of prosthesis is called “hybrid”: on one hand the implants perform a supporting function (like a Toronto Bridge), and not only as retention (for overdenture), while the prosthesis remains removable from the patient. The Anglo-Saxon definition i s o f t e n “ m i l l e d b a r o v e r d e n t u r e ” o r “fixed - removable overdenture”. In particular, according to the classication of Misch, we speak of removable prosthesis “RP-4” when the prosthesis is completely implant supported and removable prosthesis “RP-5” when the prosthesis is implant and mucosal supported 5 . The latter type and the subject of this work, is indicated when simultaneously 1) the patient requests for an implant-supported and 2) there is a need for a good support for the lips with a ange. In fact, a vestibular xed ange will impede the patient’s ability to maintain a proper hygiene, causing the loss of the implants. Combining the use of implants and of a removable prosthesis, the clinician is able to oer the patient a stable, aesthetic and easily hygienic prosthesis without the palate ange. The purpose of this article is to provide a simplied technical protocol, compared to the classical one, with the intention to 58 DENTAL ASIA MAY / JUNE 2018
Behind the Scenes increase the accuracy of the restoration and to decrease the diculty of implementation and the necessary time of processing. Clinical case A 54-year-old, male patient, non-smoker with no major clinical diseases, came to the clinician with an upper edentulous arch with some lower teeth present (from 34 to 45). The upper total prosthesis was incongruous, and caused some diculties in chewing and phonation. The patient manifested a psychological discomfort due the prosthesis condition in relation to his age, which hindered his speech when socialising with his co-workers. He also expressed the wish to replace the removable upper dentures with implants, quoting his own words, “something that will stay xed in the mouth and without palate.” The clinician started constructing the upper jaw with a new provisional but still entirely removable prosthesis for diagnostic purposes, and with the periodontal treatment of the lower arch, with a provisional and removable partial denture. Once the aesthetics and correct occlusal plane was restored, it is fundamental to maintain the buccal flange to support the upper lip. Some diagnostic tests were performed to study the placement of implants with a panoramic radiography and a computed tomography. In accordance to the patient’s approval, the clinician proceeds with the following treatment plan: insertion of four implants, in 14, 12, 22 and 24 areas and the construction of an implant - mucosal supported prosthesis with a milled bar on the upper arch; and the lower jaw was maintained healthy and restored with a removable partial denture. Once the implants were placed, the position was established according to the availability of the bone and the prosthetic requirements, the patient waited for the successful osseointegration with the total temporary prosthesis, suitably modied. In this period, the patient was subjected to periodontal maintenance therapy. The same prosthesis was used as a base for the nal restoration. Implementation of the transparent acrylic resin replica The provisional prosthesis was positioned with a precision silicone with a hardness of 70 Shore-A. The prosthesis and model silicone obtained were placed in a ask and then an insulator (insulating silicone spray, Transformer) was applied. Another silicone was placed between the replica and the cover of the ask, which was closed and held in place until the full curing of the silicone. The prosthesis was removed from the ask and two holes through the upper silicon (a 0.5 cm diameter for the input channel along with a 0.3 cm for the output channel) to allow the injection of the transparent acrylic resin. The resin was mixed and injected inside the ask, which was maintained at 50°C for 25 minutes at a pressure of 2.5 bars. Once cured, the ask was opened and the replica was nished with rotary instruments mounted on a laboratory handpiece and delivered to the clinician. Fig. 1: Impression obtained with the prosthesis replica Fig. 2: Placing of the laboratory analogues and the articial gingiva Impression with the prosthesis replica The transparent resin replica was used in a single chairside appointment, as customised tray, as a reference of the teeth set-up (control of the vertical dimension, the masticatory plane and the relationship with the antagonist), and as a rst test of the aesthetics (smile line, midline, etc). The clinician proceeded with the insertion of the replica in the oral cavity, checking the occlusion and removing the wrong occlusal contacts. The precise occlusion was then recorded using an additional fast-curing silicone. The replica had been perforated in correspondence with the emergence of the implants and daubed with adhesive. For the impression an addition silicone has been used and the replica was maintained in position by the patient with his bite until the complete polymerisation occurs; before its removal, a face bow was recorded. After removing the replica from the oral cavity, the silicone inside the holes was removed with a scalpel to allow the insertion of the pick-up transfers. The replica was placed back into the oral cavity and the transfers were screwed on the implants. Keeping the prosthesis in place, the transfers were blocked on the replica using light curing resin with low shrinkage. The xing screws were removed from the transfers and the impression was delivered to the laboratory after the disinfection protocol (Fig. 1). Fabrication of the master model and aesthetic try-in A silicone reproducing the soft tissues was placed at the area around the transfers then a proper insulation was daubed (Fig. 2). The master model was poured by developing the impression obtained with the replica with a class IV plaster; according to the manufacturer’s instructions (Fig. 3-4). Once hardened, the transfers were removed and the master model was positioned on the articulator using the replica and the face bow. The antagonist model was placed on the articulator with the silicone bite. DENTAL ASIA MAY / JUNE 2018 59
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Dental Asia May/June 2018

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