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ePaper created 2017-12-06, 12:03:50 | version 1.38.0
| industry thesis from the last pillar represents the power arm, the last implant acts as a fulcrum, and the AP spread represents the strength arm. When a force acts on a cantilever zone, force transmission occurs in the un- derlying systems in two different ways: compression on the most distal implants and traction on the more mesial ones.25 The literature demonstrates how, by applying a load to a prosthetic arch supported by four or six implants, there are no stress differences at the fixtures if the more mesial and more distal implants are placed in the same respective locations.12, 15 Although tilted im- plants show a higher concentration of stress at the bone–implant interface, the literature shows that there are no statistically significant differences in peri-implant bone loss when compared with vertical implants.13, 24 In the present study, the insertion of tilted implants enabled implanting of the implant neck in a more distal position compared with an im- plant positioned vertically. With Co-Axis implants, the angled connection from the longitudinal axis represents a valuable aid in cor- recting divergences and allowing more appropriate prosthetic positioning for the case. The ability to insert low-profile OT Equator attachments from the begin- ning without having to remove these during subse- quent prosthetic phases is of remarkable biological benefit because it avoids damage to the epithelial lig- ament and the circumferential connective fibres around the implant neck. This achieves a bio logical seal and plays a key role in preventing and avoiding propa- gation of infections to the deep supportive tissue.26 When connecting the implants through a bar, passivity of the structure is a problem, since tension can be transmitted to the implants and lead, in par- ticular, to incorrect fitting of the prosthesis and im- plant failure.27 In order to achieve a bar with good passivity, several try-in tests with the patient are required, and corrections are not always easy. In the present study, the passivity of the bar was obtained by inserting Elastic Seeger rings between the bar and the OT Equator attachments. This device over- comes the equator of the attachment and compen- sates for the space between the bar and the attach- ment itself, creating a solid connection with the guarantee of absolute passivity.19 The tolerance between the bar and OT Equator at- tachments is intended to compensate for the small inaccuracies that can arise between impression tak- ing and plaster casting. The function of the screw is to improve the contact of the Elastic Seeger rings on the walls of the bar by improving its anchorage. Muscu- loskeletal analysis showed that the patients treated did not fall into the brachycephalic class in which the masticatory load is very high. This analysis appears to be very important during the prosthetic design be- cause it is directly related to the occlusal load exerted on the implant–prosthesis structure.28 In Case 2, it was possible to perform immediate loading of the two maxillary anterior implants by in- serting retentive caps with a gummy consistency and capable of anchoring the prosthesis to the spherical attachments and acting as a shock absorber. This al- lowed the distribution of the masticatory forces to the ridges, avoiding the overload of the two implants. In order to achieve this, however, the temporary pros- thesis had a full palatal flange in order to have all the possible support on the palate, a non-compressible area, that provides support in the distribution of the occlusal load and improves retention and prosthetic stability. Fig. 17: Lingual surface of the prosthesis; screw holes allowed the prosthesis to be transformed into a fixed device by screwing on the overlying structure bearing the teeth. Fig. 18: The lateral cephalometric radiograph confirmed the position of the central incisor of the definitive prosthesis in relation to the alveolar ridge. Fig. 17 Fig. 18 28 implants 4 2017