Treatment Planning Dental Implants for the Fully Edentulous Patient
The fully edentulous patient represents a group of individuals who may be missing teeth, teeth and gums, or, teeth, gums and bone.
A denture is a prosthesis which can replace teeth, gums and / or bone. The tooth part is obvious. It is the “white” portion of the denture. The gum and bone are replaced by the “pink” portion of the denture. The more resorbed the maxilla or the mandible, the thicker the pink portion of the prosthesis. In treatment planning the fully edentulous patient, it is essential to identify and quantify the soft and hard tissue defects. Several different prosthetic designs are available for treatment of this group of patients. The types of prosthesis available to treat the composite defects are: the overdenture, PFM Bridge, and the Hybrid Bridge.
Prosthesis available to reconstruct the composite defects have specific biomechanical properties. It is essential to understand the biomechanics of the prosthesis before treatment planning. I will define the IRTS and the IRIS designs.
IRTS ( Removable Prosthesis):
IRTS is the acronym for the Implant Retained, Tissue Supported prosthesis. This prosthesis is essentially a denture. The IRTS is also known as the overdenture. When the patient occludes, the prosthesis is supported by the gingiva and the bony structures, such as the alveolus, palate, and the buccal shelf. The implants should be only involved in retention. When the denture is lifted off the alveolus, the implant’s retentive components play their role.
The most common retentive components of an over-denture is the gold or plastic clip. The implants are connected to each other by a bar, The clip should be fabricated with a spacer in place so that there is no contact of the clip with the bar at rest or centric occlusion. The clips engage the bar and are in “function” as the denture is pulled away from the alveolar ridge. The placement of the clip is critical so that it only contacts the bar as the denture is lifted sway from the alveolar ridge. During all other loading of the denture, the denture should only contact and be supported by the soft and hard tissues. To accomplish this goal, a single clip is placed parallel to the hinge axis. Therefore, the prosthesis rotates around the bar with no loading of the implants. Disadvantage of this type of prosthesis is one of continuous resorption of the alveolus as minimal internal loading is introduced within the edentulous ridge. This presents an ongoing clinical evaluation and relining of the denture base.
IRIS (Fixed Prosthesis):
The IRIS prosthesis is usually a fixed prosthesis. The gold screws retain the prosthesis to the abutments. During centric occlusion, only the implants are supporting the bridge, as there is no soft or hard tissue contacts between the base of the prosthesis and the edentulous ridge. The loading of the implants introduces internal forces to the edentulous ridge and results in maintenance of the residual alveolus similar to the dentate patient.
This type of prosthesis provides the most stable functional appliance with minimal long-term maintenance.
How many implants to place?
The number of implants for either type of prosthesis depends on the ridge being reconstructed.
The Fully Edentulous Mandible:
The anterior mandible represents type I bone. For the IRTS prosthesis, 2 implants are placed in positions 22 and 27. For the IRIS prosthesis, 5 implants are placed between the mental foramanae.
The Fully Edentulous Maxilla:
The anterior maxilla is type III bone. For the IRTS prosthesis, 4 implants are placed in positions 6, 7, 10 and 11. For the IRIS prosthesis, 6 implants are distributed between the first bicuspids. The limiting factor in this arch is the anterior extension of the maxillary sinus.
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