Engaging vs. Non-Engaging Abutments

One of the most common questions we receive about implant restorations is the difference between engaging and non-engaging abutments. In this article, implant specialist Alex Rugh, CDT, covers the differences between engaging and non-engaging dental implant abutments and when to use one over the other.

Implant Interface Shapes

Almost every modern implant has 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.

Engaging abutments lock into the implant’s interface’s specific anti-rotational shape (hex, star, etc.). However, non-engaging abutments do not have this anti-rotational feature. Rather, the design doesn’t quite “interact” or lock the same way between the abutment and 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.

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.

Cement-Retained Restorations:
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.

Restorations such as e.max® and full zirconia crowns/bridges require titanium bases to create them so that they’re screw-retained. That’s great for single units, but the titanium bases aren’t widely available for 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!