Screw Retained Restoration
To clarify the terminology: most implant restorations are screw-retained because the transgingival abutment is screwed into the implant, including cement-retained restorations. A screw-retained restoration is one in which the crown and abutment are fixed and directly screwed to the implant.
It should be noted that a minimum height of 4 mm is required between the implant head and the opposite occlusal surface.
This type of implant restoration can be performed for simple crowns as well as full arch rehabilitation. The advantage of screw-retained crowns or bridges is that they can be removed for maintenance (peri-implantitis treatment, re-screwing) or for esthetic modifications (re-doing of the prosthesis). The choice of materials ranges from gold to all-ceramic restorations.
To ensure the success of this type of restoration, it is important to emphasize the importance of the position of the implant, which must be almost perfect. The access hole for the screw must go through the lingual surface for anterior teeth and through the center of the occlusal surface for posterior teeth. To protect the screw head and for esthetic reasons, it is necessary to place Teflon in the access channel and seal the access hole with composite.
The screw-retained prosthesis on implant has certain advantages such as the fact that the restoration is removable, but also the possibility of avoiding the use of cements and the risks of resorption at the head level. However, certain clinical situations argue for the choice of a cemented restoration. If the implant axis is too divergent, cemented restorations should be used. Also, if the prosthetic height is too high, the forces exerted on the abutment may be significant and the risk of fracture increases considerably. This may also lead the clinician to choose a cemented prosthesis.
The screw-retained restoration may take more time because of the need to adjust the proximal and occlusal contacts. One reason for this is that no temporary restoration was fabricated and the adjacent teeth may have moved between impression taking and placement.
In addition, the occlusal contact must be very light and just outside the occlusion. Unlike implants, which do not have a periodontal ligament, the remaining natural teeth have the ability to sink slightly into their bone sockets during masticatory movements. Therefore, it is recommended to establish only one occlusal contact directly on the implant.
