Cement Retained Dental Implant Crowns

When restoring dental implants, the choice is screw retained or cement retained. Cement retained crowns will often be used when the screw access hole is not positioned down the long axis of the implant. There may be angulation issues or aesthetic issues that arise from this. Cement retained crowns may also be preferred by the patient due to the unaesthetic appearance of the access cavity for screw retained crowns, which often looks grey and discoloured if the underlying crown has a metal sub structure. Patients now often regard premolar and molar teeth as being in the aesthetic zone and are highly dental aware. Quite rightly, they expect dental implant crowns to look like natural teeth.

In my experience, Atlantis abutments are far superior to any other system. Think about how you would prepare a tooth for a crown and amplify the precision ten fold. With the digital age we live in, technology should be used to enhance the outcomes for our patients. This is one system that certainly does that. There are also other scanning centres which produce excellent abutments. It is worth talking with your dental implant technician and using a few systems. Of course, there is a cost implication involved and Atlantis may not be suitable for all.

When fitting cement retained crowns it is imperative that excess cement does not exude the margins and act as a plaque trap. This is one the main causes of Peri-implantitis and is avoidable.

There is an excellent technique which will help you to avoid any issues with excess cement:

1. Once you have verified the margins, occlusion, contacts, embrasure space and aesthetics you are ready to cement the crown.

2. Use your PVS bite registration material and insert within the crown creating a tag at the end to act as a handle.

3. Remove this index.

4. Mix the cement, which is usually a temporary cement (Tempbond NE) or a dedicated implant cement and place within the crown. Do not overfill. Make sure the abutment screw is covered. I use pre sterilised cotton wool.

5. Insert the index into the crown to remove the excess. This will leave a very fine layer of cement.

6. Place the crown and wait for setting. There should be no excess at the margins.

7. Perform the usual checks and take a PA radiograph to verify. There should be no exudate whatsoever.

8. A useful tip for removing any fine smears of Tempbond on the crown is orange solvent. Spray some onto a ball of cotton wool and clean any fine residue.

9. Review as required.

There are times when implant crowns will need to be removed. For example, if the abutment screw loosens. This is why temporary cements are used. In my experience, cement retained crowns can be removed with minimal fuss. However, you must pre warn the patient that some force is required. I would over emphasise this fact. To avoid damage to the porcelain, use rubber coated crown removing pliers. GC have an excellent one. Grip the crown firmly and exert pressure in a bucco-lingual direction initially and then rotational. The crown should ease off within a few seconds.

Dental implant crowns, screw or cement retained, require maintenance just as natural teeth. However, your hygienist must be trained in this field. Regular scalers, hand or ultrasonic, should not be used for fear of scratching the titanium. Satelec have introduced some excellent ultrasonic tips for implants. We have invested in these with great success. Specific implant hand scalers can also be used. We are also keen on adjunctive methods of cleaning such as Philips Airfloss.

Article for dentists written by Dr Nissit Patel.

I hope this article has been of use. It comes from many years of experience of placing implant crowns, cement and screw retained. I welcome any feedback that you may have, please e-mail me: nissit@progressivedentistry.co.uk

My next article will focus on screw retained crowns.