One of the most common questions we get about implant restorations is the difference between engaging and non-engaging abutments and why we would use one over the other.
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Implant Interface Shapes
Almost every modern implant has what we call an anti-rotational element built into its interface. The shape of this element is usually a hex, like what you’ll see on implant brands made by Zimmer Biomet, Nobel Biocare™ and BioHorizons®. Other implant brands have different shapes. For example, the Straumann is a square interface and Keystone Dental’s is star shaped.
Hex interface found on Zimmer Biomet, Nobel Biocare™ and BioHorizons®
The square interface found on Straumann
The star interface found on Keystone Dental
Engaging abutments are are designed to lock into the specific anti-rotational shape (hex, star, etc.) of the implant’s interface. However, a non-engaging abutment does not have this anti-rotational feature. Rather, the design doesn’t quite “interact” or lock the same way between the abutment and implant.
Non-engaging left and engaging on right
Engaging on implant
Non-engaging on implant
When an Engaging Abutment is Required
With a single unit screw-retained restoration, we need to use the engaging abutment. This measure will lock the individual crown into the correct orientation.
If a non-engaging abutment is used, the abutment can rotate on the implant. The contacts of the crown would be the only areas providing any type of anti-rotation properties.
An engaging abutment needs to be used for single unit crown so it can lock into the correct orientation
When a non-engaging abutment is used on a single unit, the crown can freely rotate
When a Non-Engaging Design is Required
When you have 2+ unit implant restorations side by side, they’re able to work together to prevent any individual abutments from rotating on the supporting implants. Having optional anti-rotational features built into them just isn’t needed. Because of this situation, non-engaging abutments are always used for splinted screw retained restorations.
But it’s important to also note that anti-rotation elements in splinted screw retained restorations can also cause problems if they’re used in some cases. For example, it can be nearly impossible to get a passive fit with them, or when implants aren’t completely parallel to one another, it may not even be possible to seat a bridge because of the interferences.
With engaging abutments, a passive fit of a screw-retained bridge may not even be possible if the implants aren’t completely parallel
Which Abutment Type to Use?
With cement-retained restorations, you always want to use engaging abutments, regardless of whether they are singles or splinted. Why? Because you’re placing the abutments first, without the restoration.
Without anti-rotation properties, it’s impossible to get an accurate orientation for the abutment and restoration. In other words, it probably wouldn’t seat correctly. When abutments are made specifically for cement-retained bridges, they’re designed to set parallel with one another, so that after the abutments are placed and the bridge can be seated passively.
For cement-retained bridges, the abutments are designed to be parallel with each other, and are installed before the bridge
A Note About Materials
Non-engaging interfaces are usually only available in UCLA castable gold abutments and can only be used to fabricate PFM or full-cast gold restorations.
Non-engaging interfaces have traditionally only been available on UCLA castable gold abutments which can only be used to make PFM and full-cast gold restorations
Screw-retained full-cast gold
Restorations such as e.max® and full zirconia crowns/bridges require titanium bases in order to create them so that they’re screw-retained. That’s great for single units, but the titanium bases aren’t widely available for the non-engaging styles. What that means for you as a provider, is that some implant systems are non-compatible with screw-retained e.max® or zirconia bridges. (We can’t even make them in the lab.)
Screw-retained e.max® and full zirconia require titanium bases. For bridges, we can’t make them screw-retained with some implant systems.
For more information on the compatibility and design of engaging and non-engaging implants and implant restorations, reach out to us at any time!