An article for dentists by Dr Nissit Patel
Screw retained dental implant crowns
The great advantage of screw retained dental implant crowns is that there is no cement at all. Therefore any of the potential problems of excess cement extruding beyond the crown margin and instigating peri implantitis is negated.
Another advantage is that if the crown needs to be removed, it is relatively easy to do so and there is no damage to the porcelain work by forcibly removing the crown.
Planning for screw retained implant crowns
In general, the screw access hole should be down the long axis of the implant. This is important in relation to ease of placement, avoiding damaging lateral tension forces when torquing the screw which could lead to screw loosening and avoiding the issue of possibly threading the screw if proper access has not been made.
Therefore, prior to placing the dental implant, it is important to plan what type of restoration is to be placed. However, recent advances in prosthetic design have evolved and Nobel Biocare now have an angulated screw channel. This allows a angulation difference of 25 degrees, which is significant. This can be applied to the posterior and anterior regions. This is possibly a game changer in dental implant prosthetics.
Placing screw retained dental implant crowns
The placement is generally quite simple. The crown and abutment is a one piece prosthetic device. The crown is then placed within the dental implant. There is only one path of insertion and therefore a placement jig is not required.
Initially, screw down gently until the crown is stable and in it's fully seating position. Check the marginal adaptation, contacts, embrasure space and occlusion. Take a peri-apical radiograph to ensure correct seating. If so, make any necessary adjustments.
Once all of the relevant checks have been made and verified, torque the screw to 20Ncm using a prosthetic torque wrench. The screw should be covered with sterile cotton wool and the access cavity restored with composite.
Tip: for metal based substructures, to avoid a grey shadow use an opaque flowable composite around the periphery and on the base. Voco have an excellent one which I routinely use to block out dark areas whilst placing composites.
Removing screw retained implant crowns
Simply remove the composite and cotton wool carefully and unscrew the abutment screw. Simple.
Tip: be very careful not to damage the abutment screw! Use an ultrasonic to remove the final layer of composite.
In many cases, screw retained implant crowns are the desired option. With the evolution of the Nobel Biocare angulated screw access, the scope for these restorations has increased hugely.
With the huge advantage of no cement, I would suggest considering screw retained restorations for single implant crowns as the first choice option.