CAD/CAM international magazine of digital dentistry

18 I CAD/CAM 3_2012 was ready to be processed. The denture is processed in one of two ways: _In the laboratory technique, the female part T (made from pure Grade 4 titanium) is integrated into the denture and a complete prosthesis is re- turned to the clinic. Part T is contra-indicated for use on two implant bars (Figs. 11a & b). _In the chairside technique, the denture is processed and a window is cut in the denture, through which the dentist can pick up the female part E (made from Elitor—68.6 per cent gold alloy), using self-curing acrylic resin in the patient’s mouthafterseatingthespacerandblockingoutall undercuts (Fig. 10). The total width of the bar with the E clip seated is 4.3 mm (Fig. 12) and 3.6 mm with the T clip seated (Fig. 11a). This is relevant for treatment planning, as ridge reduction may be indicated to provide space for the denture. In the laboratory method, the denture is com- pleted with the female part T integrated into the denture.Thedentistthenchoosesthelevelofreten- tionrequiredbyselectingtheappropriateplasticin- serts and seating them in part T (Fig. 11b). The plas- tic inserts are designed to compensate for transfer inaccuracies during the impression, master cast fabrication and post-processing stages. The pres- enceofalaboratorytechnicianisrecommendedfor the chairside technique. A spacer is placed on the tube bar prior to seating the E clip to ensure vertical resilience. The spacer ensures a slight gap between the E clip and the tube bar so that when the patient bitesdown,theEclipdoesnotoverloadordistortthe barasthedenturebedsintothesupportingmucosa. All undercuts around the bar assembly, especially between the bar clip and tissues, were blocked out with a silicone material (Fig. 10). A window was then cut into the lin- gual aspect of the denture to expose the E clip (Fig. 13a). A small bead of cold-cure acrylic resin was then placed on the E clip, covering the re- tentiveelementoftheclip.The Eclipwasthenattachedtothe denturewithsmallincrements of resin (Fig. 13b). The resin was allowed to cure fully be- forethedenturewiththeEclip was removed from the mouth. The remainder of the void was thenfilledwithcold-cureresin and allowed to cure outside themouth(Figs.13c&d).Ideally,thisprocessshould take place in a pressure pot. A transfer jig that fits into the E clip and is ef- fectively a tube bar replica can be utilised if a large volume of acrylic has been used to house the E clip. The denture with the transfer jig seated in the E clip is bedded into a patty of fast-set plaster, similar to a denture-repair scenario. Once the stone has set, the denture is placed in a pressure pot with warm water and the self-curing resin is allowed to poly- merise. Once the acrylic has fully cured, it is sepa- rated from the stone base and the transfer jig and all excess acrylic is trimmed. At least 50per cent of the lamellae of the E clip must be clear of resin. Only the superior part of the E clip with the attachment portion and shoulder section is locked into acrylic (Fig. 13c). The lamellae must be free to flex over the tube bar during in- sertion and removal of the denture. If the resin is in direct contact with the lamellae, the denture may not seat, as the E clip cannot flex. Finally, the de- finitive prosthesis was seated (Figs. 14a & b). The level of retention of the E clip was adjusted usingtheactivationanddeactivationtoolsprovided intherestorativekit.Theocclusionwascheckedand adjusted after verifying that the denture had been properly seated, using pressure-indicating paste. Thebarassemblyisrequiredtoretainthedenturein the two-implant scenario. Support is derived from the conventional hard- and soft-tissue load, bear- ingareasliketheresidualridgeandthebuccalshelf. Thepatientwastheninstructedonappropriatecare of the implants and the prosthesis, and a routine recall and maintenance programme was instituted. Fig. 13a Fig. 13b Fig. 13c Fig. 13d I research _ SFI-Bar