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Can We Pass The Zygomatic Implant Through The Infratemporal Fossa

What happens if I partially pass the zygomatic implant through the infra-temporal fossa?


The violation of the infratemporal fossa during the performance of osteotomies for the zygomatic implant can happen due to two situations:

1) Perforation error

2) Intentionally planned maneuver


Given this, some questions are unavoidable: will it bring us any problems? Is there any risk in this maneuver? What are the advantages and disadvantages of positioning the zygomatic implant in such a region? Before answering these questions, let's understand when this situation happens.


1) Perforation error


When the surgeon finishes the mucoperiosteal detachment and has the maxillozygomatic region exposed, it is time to define where our perforation's initial position will be.

Intuitively, we tend to choose regions where there is a bulky bone, which would probably denote more bone volume.


The problem is that such areas do not always represent where maximum zygoma bone availability exists.

The region with the bulk external bone topography can "be hollow," that is, after the initial perforation, the drill falls directly into the maxillary sinus.


Once inside the maxillary sinus, the drill must continue until it finds the entrance to the zygoma body. It is here where the problems begin.

As it is a region without direct visualization, the surgeon can progress with the drill only in the "feeling" and end up drilling the maxillary sinus's posterior wall and entering directly into the infratemporal fossa. In these cases, the lack of bone resistance is evident.



zygomatic implant surgical technique
Axil view of an ideal and wrong osteotomy for a zygomatic implant.


When removing the drill, you will notice soft tissue in the drill grooves, instead of bone. When it happens, you need to recognize that your clinical judgment is wrong. As much as the clinical judgment by analyzing the external bone topography of the maxillozygomatic region indicates that the zygomatic implant position should be in that location, the result of the drilling process is telling you with absolute certainty that it is not. You are mistaken. It is not uncommon in zygomatic implant surgery.



But then, where should I do the new drilling?


At this point, some surgeons decide to take a more invasive approach, trying to understand what is happening more visually.

The solution is to open a window in the upper-superior-anterior part of the maxillary sinus to identify where exactly the entrance of the zygoma body is. In this way, the exact point of entry of the drill bit can be inspected, which significantly facilitates identifying the precise location of drilling.


Zygomatic implante surgical technique
Antrostomy for direct visualization of the zygomatic bone.


For a long time, I have always used this approach as a surgical protocol. In the most challenging cases, I would always open this window to optimize the drill's positioning.


But is this ideal?


NO! Large maxillary sinus openings contribute to a decrease in the capacity of the sinus mucosa's ciliary motility, contributing to the possible development of sinusitis.

It is worth reading this paper (1), which, despite not focusing on zygomatic implants but zygoma fractures, brings great insight concerning our surgical technique and the potential consequences of wide sinus openings.


anterior maxillary sinus


Nowadays, with the possibility of 3D virtual planning, it is clear that the zygomatic implant can be installed with a single precise perforation directly in the optimal region without the need for any sinus opening. Even though some are still reluctant to take this new approach, this is the new era of zygomatic implants!.

zygomatic implant technque
Large Antrostomy Vs. Single Point Osteotomy

Precise virtual planning allows us to know precisely where we should do our initial drilling and anticipate all synesthetic perceptions. All of it without doing any anthrostomy.


The fact is that when you enter the infratemporal fossa due to perforation errors, depending on the magnitude of the error, the implant can reach more posterior locations of the infratemporal fossa, and this can damage soft tissue structures.

However, a partial and more anterior violation of the infratemporal fossa can be intentional, as we will see now.


2) Intentionally planned maneuver


When planning the installation of zygomatic implants in cases where the zygoma body has a thin thickness, the position of the implant passing equidistant from the internal and external cortical of the zygoma body can cause the external cortical to become very thin. During the installation of the zygomatic implant, this cortical may crack, but the implant may remain stable, or the worst, which may be a total fracture of the outer cortical of the zygoma body, may happen. I wrote a post explaining more details about it.


In such situations, a displacement of the drill further towards the zygoma's internal cortical is not only desirable but also fundamental in some cases. In this way, the implant will anchor in four cortices and maintain the external cortical of the zygoma body extremely robust and free of risk of fracture.


What is the chance that you can identify and have that kind of clarity without using virtual planning? Zero. That's why many surgeons try to learn zygomatic implants and give up—lack of clarity and an individualized understanding of each case.


But after all, is there a problem with the partial violation of the infra-temporal fossa?

To answer this question, we need to understand what is the content of the infratemporal fossa.


What we have in this region is the insertion of the temporal muscle and fatty tissue. During the drilling process, you will feel a change in drilling pressure, and, when removing the drill, you will notice that you will have fragments of fascia, fat, and / or muscle in the drill grooves. Some facial soft tissue vibration occurs, and the drill lost its bone cut capacity because of soft tissue attached to the drill's groove. It's advisable the clean it.

Below, a case in which I pass implant through in the infratemporal fossa.


zygomatic implant CT
Zygomatic implant passing through infratemporal fossa


Even authors (2) even suggest this maneuver to increase the number of cortical affected by the implant, and complications or sequelae of it have not been reported.


In our virtual planning, we will also have this degree of detail to place the implants and make this fine adjustment, moving our implant slightly towards the inner cortical of the zygoma to protect the outer cortical and optimize our surgical success. Our planning will always seek maximum bone availability to increase the implant's BIC.


Some studies have tomographically evaluated the BIC of zygomatic implants, and the variation is immense, ranging from 4.9mm to 32.9mm (3). Indeed, the individual differences in the amount of bone also interfere with this BIC variation, but we firmly believe that the implants' three-dimensional positioning can be even more relevant.


Imagine a 4 mm thick zygoma in which a zygomatic implant was installed with its head in the most anterior position possible in the alveolar ridge, which leads to a perforating the zygoma body from anterior to posterior. In this situation, you can easily get around 15mm of implant-bone insertion.


Imagine a bulky 7mm zygoma, but a zygomatic implant was installed with the head far posterior on the alveolar ridge, making it crossing the zygoma almost perpendicularly. In such a position, we would do have a 7mm bone insertion. You can already figure out these findings in the virtual planning, visualizing the tomographic slices along the implant axis.


bone insertion zygomatic implant
The more anterior the zygomatic implant's head the bigger is the bone insertion into zygoma


In summary, passing the zygomatic implant through the infratemporal fossa has its purpose and indication in cases of the thin zygomatic bone.


However, this must be part of pre-established surgical planning and not the result of an inability to conduct surgeries according to plan.

Please, share your thoughts and experiences with us on comments.



References

(1) Ballon A, Landes CA, Zeilhofer HF, Herzog M, Klein C, Sader R. The importance of the primary reconstruction of the traumatized anterior maxillary sinus wall. J Craniofac Surg. 2008; 19 (2): 505-509. doi: 10.1097 / SCS.0b013e318163f2ea https://pubmed.ncbi.nlm.nih.gov/18362733/


(2) Jensen, OT, Brownd, C. & Blacker, J. Nasofacial prostheses supported by osseointegrated implants. Int J Oral Maxillofac Implants 7 , 203-211 (1992). https://pubmed.ncbi.nlm.nih.gov/1398837/


(3) Balshi, TJ, Wolfinger, GJ, Shuscavage, NJ & Balshi, SF Zygomatic bone-to-implant contact in 77 patients with partially or completely edentulous maxillas. J Oral Maxillofac Surg 70, 2065-2069, doi:10.1016/j.joms.2012.05.016 (2012). https://pubmed.ncbi.nlm.nih.gov/22907109/


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