It's important to ensure proper cementation for implant crowns. The following ideas will help you achieve the best results:
1. Manage the opening for the abutment screw. Close the abutment screw hole with a PTFE tape (Teflon). The tape can be sterilized and does not pick up a bad odor. It is radiopaque and easy to clean and remove if needed.1 You should leave most of the screw hole/chamber in the abutment open. This acts as a reservoir for excess cement and does not adversely affect the retention.
2. Use an appropriate amount of cement. Remember there is just enough room for a thin cement layer between the abutment and crown - about two coats of nail varnish - that is all the cement needed. This is about 3 percent of the total internal volume of the crown. Apply the cement near to but not including the crown margin. As the crown is seating the cement will flow “upwards” towards the occlusal table of the abutment. Once it reaches the occlusal table the vector of forces will be now perpendicular to the horizontal plane of the occlusal table. At this point the cement will now start moving towards the prep margin and excess will be extruded out.
3. Use PVS copy abutment. Conducting a “trial cementation” on a duplicate of the abutment outside the mouth, can simplify the clean up process. Follow these steps:
- Paint KY jelly on the internal surface of the implant crown.
- Adapt PTFE (Teflon) to the inside surface. Use a dry brush and place the crown on the abutment to adapt the tape. This acts as a 50 micron thick spacer.
- Fill the inside of the crown with a fast setting PVS material. Overfill to make a handle as well. Make markings to ensure easy identification and orientation.
- Remove this copy of the crown abutment from the crown, remove the tape and clean the intaglio surface of the crown.
- This copy of the abutment, also known as a pre-extrusion device, is approximately 50 microns smaller than the abutment. It is now ready for use.
- Place the abutment and load it with correct torque.
- Load the crown with the cement, push the PVS copy abutment into the crown and clean the excess cement; which is easy since it is done outside the mouth
- Pull the crown off and inspect the intaglio surface. Add cement if you find any "bare areas." Now seat the crown in the mouth on the abutment.
- This technique limits the excess cement to an absolute minimum and makes clean up quick and easy.
4. Modify the abutment design. A design variation of creating an internal vent has been suggested. Vent is created 3 mm from the occlusal table.2 Two vents on the axial surface 180 opposite to each other are placed. The abutment screw access hole is closed with PTFE and remaining space left open as described above. Cement is loaded following the technique steps described above. Wadhwani and colleagues, in their study, showed that this modification results in better extrusion of excess cement and better seating.2
5. Use a retraction cord. In an earlier post Dr. Winter described a technique of using two pieces of retraction cord one from the buccal and one from the lingual to allow for easy clean up of excess cement.
1. Moraguez OD, Belser UC. The use of polytetrafluoroethylene tape for the management of screw access channels in implant-supported prostheses. J Prosthet Dent. 2010 Mar;103(3):189 – 91.
2. Wadhwani C, Pineyro A, Hess T, Zhang H, Chung KH. Effect of implant abutment modification on the extrusion of excess cement at the crown-abutment margin for cement-retained implant restorations. Int J Oral Maxillofac Implants. 2011 Nov-Dec;26(6):1241 – 6.
Vivek Mehta DMD, FAGD, Visiting Faculty, Spear Education