Vertical dimension being verified using a Willis Gauge
Using the removable prosthesis, a rapid-set silicone impression is made to identify the implant locations. [The following image] depicts a complete denture containing a polyvinyl siloxane bite registration material demarcating the implant sites. The removable prosthesis should be relieved around these marked sites to allow a passive seating of the prosthesis relative to the anatomical indices (Figs. 9.2, 9.3 and 9.4).
Temporary cylinders are to be seated at this point. Radiographs should be taken to verify seating if at implant level. Parallelism between the temporary cylinders should be visually checked and any multi-unit abutments necessitating repositioning should be completed. Once parallelism is deemed acceptable, the removable prosthesis may be tried in for passivity while indexed to the selected anatomical reference(s). The removable prosthesis should be tried in over one temporary cylinder at a time to ensure that the trajectory of any single cylinder does not interfere with seating of the prosthesis. Temporary cylinders should not be in contact with any surfaces of the removable prosthesis; if contact is visible, further relief of the prosthesis is necessary. It is imperative that there is sufficient relief around the temporary cylinders to ensure that there is no interference in seating and that there will be sufficient space for pickup resin to flow (Figs. 9.5, 9.6, 9.7, 9.8, 9.9 and 9.10).
Prior to using any pickup resin, measures must be taken to avoid allowing resin to flow into undesired areas. A rubber dam or rubber dam pieces should be adapted around all temporary cylinders to prevent resin from flowing onto sutures or into the surgical site. To prevent potential screwdriver access issues, temporary cylinder access holes should also be plugged with removable block-out material, such as rapid-set silicone or Teflon. The removable appliance should be placed ensuring that it is seated in the palate area (Figs. 9.11, 9.12 and 9.13).
Self-curing acrylic resin can be used to carefully pick up the temporary cylinders. It is recommended that temporary cylinders be indexed into the prosthesis individually to maintain passivity and ensure that sufficient resin is used to secure the position. Once one cylinder has been secured the patient must be viewed for accurate tooth position and occlusal plane. Once this is deemed satisfactory the remaining cylinders can be attached. Once all temporary cylinders have been indexed into the denture and the resin has been allowed to sufficiently set, it may be removed from the mouth for finishing procedures (Figs. 9.14, 9.15 and 9.16).
Once the prosthesis is detached from the patient, polishing protectors should be connected to the temporary cylinders to prevent over-finishing the implant fixture contact surfaces. Flanges should be reduced to allow direct visibility of the analogue abutment collars from a lateral view; this will aid in fabricating a hygienic, convex gingival surface. Additional acrylic resin can then be added to firmly fixate the temporary cylinders, provide resin bulk, and finalize the shape of the fixed restoration. Temporary cylinders should also be adjusted to remove occlusal or contour interferences (Figs. 9.17, 9.18, 9.19 and 9.20).
Upon insertion of the finished converted prosthesis, passivity should be verified by tactile sensation when tightening screws and seating verified with radiographs, followed by occlusal adjustment. Care should be taken to verify a fair distribution of occlusal forces, especially if there are any cantilevers. There should be no active gingival blanching or tissue pressure (Figs. 9.20 and 9.21).
The mandibular arch is much more challenging to load utilizing the direct technique. When a significant amount of bone reduction has been done, the prosthesis is usually not very stable and obtaining adequate centric relation records can be difficult. This is compounded by the numbness of the patient post-surgery.
The prosthodontist must work diligently with the surgeon and laboratory technician to determine approximately the amount of bone reduction that is required and this must be approximately replicated on the casts.
The following are necessary for an optimal outcome:
Approximation of bone reduction on casts
Fabrication of a bone reduction guide with a reference from which the surgeon can measure
Fully extended denture
The following illustrates the clinical sequence:
A silicone bite registration is placed in the intaglio of the denture and the denture is placed intraorally over the healing caps.
The patient is guided into maximal intercuspal/CR position. This can be attained with the use of a silicone index also.
This position is verified for repeatability.
A section of the silicone material is removed in the anterior area of the denture and a temporary cylinder placed intraorally. A hole is made in the intaglio of the denture corresponding to the marking of healing cap. The denture is seated over the temporary cylinder intraorally.
Self-cured acrylic resin is used to pick up the temporary cylinder.
The denture with attached temporary cylinder is removed.
The adjacent section of silicone is removed from the intaglio of the denture and a temporary cylinder is placed intraorally. A second hole is made in the intaglio of the denture corresponding to the position of the second temporary cylinder.
The denture is placed back into the mouth screw retained by the first picked-up cylinder. The rigid silicone material in the posterior aspect provides anteroposterior stability. The second temporary cylinder should not interfere with the seating of the denture. The temporary cylinder is picked up with self-cured acrylic resin.
A similar sequence is followed to attach the third and then the fourth temporary cylinders.