Zygomatic Implants Installation and Screw Fractures
During the insertion of the zygomatic implant, it is not uncommon to achieve high insertion torques. The insertion torque theme is something that will be discussed in a future post.
The insertion of the zygomatic implant with extreme high torque values, despite giving the surgeon the perception of security to perform the immediate loading, might negatively affect the installation procedure.
In the worst-case scenario, it is possible to fracture a segment of the zygomatic bone. It may happen when high installation torques are generated during the zygomatic implant screwing in a region where the complete osteotomy has left the zygoma external cortical very thin. This subject was described in detail in this post.
Another situation that can occur during the installation of the zygomatic implant with high torques is the fracture of the screw of the implant carrier (assembler). It is a complication that most surgeons have probably experienced at some point in their professional lives.
The fracture of the screw of the zygomatic implant carrier can occur due to the low resistance of the screw. As much as some companies can specify what the maximum strength value of the screw would be (defined through laboratory tests), in clinical practice, we were unable to have objective references as torque wrenches generally measure up to around 60N. There is no way to know, objectively, how much torque we are using.
The torque's clinical perception applied to the zygomatic implant is also quite different from conventional implants. It happens because of the zygomatic implant installation key, which is robust and heavy.
However, there are some precautions that the surgeon can take to avoid such an occurrence. The first one is to try to make the turning movement with apical pressure, always maintaining the force along the zygomatic implant axis.
The second is always to check the assembler screw in some moments during the installation process. It is expected that as soon as the insertion torque starts to increase, the assembler's screw starts to lose its initial torque. If that happens, then the assembler begins to detach from the zygomatic implant's head, generating motion and increasing the possibility of fatigue and fracture of the screw.
Thus, it is recommended to always check the screw's torque during the whole process of installation to the zygomatic implant.
Another detail that can lead to a screw fracture is what happened in the Allon4 Zygoma case below. All implants were installed with excellent anchorage and good prosthetic position, but when we were finishing the last zygomatic implant installation, there was an "unexpected surprise."
In addition to loosening the screw, the screw head in this zygomatic implant system has a positioning slightly external to the assembler.
It seems just a simple detail, but during the implant's installation, this small prominence touched the palatal cortical bone and generated additional stress to the screw that is already under the effect of high torque and torsional forces because it is loosening.
The result is this unpleasant surprise that creates stress for the surgeon and requires additional procedure time.
I had recurring problems with the SIN zygomatic implant assemblers, which, by the way, are excellent zygomatic implants for several reasons that I explain in another post. Not infrequently, the assembler's screw came from the factory with a possible excess of torque, which caused the screw to dust off when removing it. Because of that, I started to remove the assemblers previously out of the mouth for testing, and then I installed it to then proceed with the implant installation.
In 2020, SIN reformulated its line of the zygomatic implants with some modifications concerning the implants' design and surface (but this is a subject for another post). Let's wait for the performance of the assemblers.
Faced with such a situation, there is no alternative. We need to get around the problem. We have one of the alternatives.
1) removal of the fractured screw
2) removal of the zygomatic implant.
We always start with option number 1. It is common for the fracture to occur close to the head of the screw, leaving a remnant where it may be possible to mobilize with some instruments and perform the counterclockwise rotation.
Another alternative is to try to use specific devices for this purpose, such as this fractured screw retriever.
Once all methods were tried without success, it's to move on to the most radical maneuver—removing the zygomatic implant.
Removing a pre-installed zygomatic implant with high torque is no simple task without the help of the assembler. There is no instrument fully design for this purpose. The alternative we have is to use a dental forceps and turn the counter-torque counterclockwise. The procedure is time-consuming and tedious, but slowly, the implant is being removed.
In case of too high torque where it is impossible to remove the zygomatic implant with forceps, the final alternative would be to cut the implant and bury the apex.
Such complications are incredibly exhausting, and we should avoid them as much as possible.
For that reason, always look for a zygomatic implant system with better resistance of the assembler's screw. However, even so, fractures can occur in cases of extremely high torques.
In summary, we can say that our advice is always to keep the torque not too high. When that happens, complete removing the zygomatic implant and perform a little more osteotomy and insert it again. It will prevent a fracture of the screw and a possible fracture of the zygomatic bone segment.
When it comes to fracture screw removal strategies, each surgeon has his preferences, and it would be very helpful for surgeons to share their experiences with this type of complication below in comments and what maneuvers and devices they have used for the solution.
It is also interesting to share our experiences and to mention the trademark names of zygomatic implant systems. It generates benefits for better choices and exposes companies to improve their products to serve surgeons and, consequently, our patients.
What zygomatic implant systems have you been using?
What has your experience been? Were there any cases of fracture of the screw of the zygomatic implant carrier? What have you done to remove the screw?
If there is a need to remove the zygomatic implant, what has been your strategy?
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