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ePaper created 2017-08-30, 10:20:50 | version 1.38.0
implants_industry Fig. 7a Fig. 7b Fig. 7c Fig. 8a Fig. 8b Fig. 8c Fig. 7a: Implant overdenture: Attachments provide a spatial location of the prosthodontics. Fig. 7b: Peripheral mucosal support provides prosthetic stability. Fig. 7c: Retentive devices prevent the removal of the prosthesis from the tissues. Fig. 8a: Implant-supported overden- ture ensures retention and allows support during the application of the occlusal forces. Fig. 8b: The insertion axis perpendicular to the occlusal plane will produce a continuous and correct relocation of the prosthodontics that mandible.8 There is no doubt that implants, particu- larly in the mandibular bone, allow to better anchor dentures and thus improving their stability and reten- tion (Fig. 6). The question that arises may be this: How many im- plants do we have to insert in the jaw? Better splint them or not? The satisfaction the patient declares with the simplest prosthetic project, i.e. an overden- ture with two direct spherical attachments, is not sig- nificantly different from that given by two or four im- plants with connecting bar (Figs. 9a & b). The choice of connecting implants between bars may be the lack of parallelism; and, if in presence of bars, it is neces- sary to make some distinctions. The second group of overdentures are supported by implants, typically anchored on a milled bar; the latter receives all the functional loads so that there is no di- rect contact between the prosthesis and the soft tis- sues. The prosthesis is removable but seats rigidly on the bar, so that all the lateral and rotational move- ments are limited. In addition, the full distribution of the masticatory loads on the fixture only is useful to the preservation of the bone and also positively af- fects the implant integration (Figs. 8a–c). Contrary to the resilient prosthodontics supported by the mucosa and retained by the implants, a milled bar prevents rotational movement of the prosthesis.14 Aside the different conception and construction of the two types of overdenture, a further differ- avoids tensions to implant structures. Implant-retained vs. implant-supported Fig. 8c: The peripheral seal prevents accumulation of food under the dentures. 48 2_2017 48 implants A classification10, 11 divides overdentures in im- plant-retained and implant-supported overden- tures. The first represents the best choice for those patients that have already a complete but instable and with no retention removable denture. In this case, both the implants (from 2 to 4) and the soft tissues contribute to the retention and stability with a more economic project compared to the milled bars and counter-bars. Different types of attachments allow the overden- ture to be retained to the implants; those resilient anchoring systems guarantee moderate vertical and rotational movements of the prosthesis (Figs. 7a–c). To achieve this kind of result, Dolder bars are usually used. Both bars and the ball attachments, not con- nected to each other, showed no clinical differences in the patient’s satisfaction and implant survival rates.12 Also the maintenance of the systems shows no difference between the bars and the ball attach- ments.13 Fig. 9a Fig. 9b