Zygomatic Implants Length and Clinical Outcome
I could say that in no zygomatic implant book, you will see someone calling attention to this detail, which in my opinion, is one of the most critical factors for effective and predictable rehabilitation with zygomatic implants.
With virtual planning, it is currently possible to specify the zygomatic implant's maximum anchorage area in the zygoma body. From there, place the implant's head in the most favorable position concerning the residual ridge and screw prosthetic emergence. More advanced adjustment is possible about the distance between the osteotomy/implant and the internal and external bone cortical. It can be a crucial factor in implant stabilization.
The sizes of the zygomatic implants to be selected in each case do not depend only on each patient's anatomy, but also on the three-dimensional positioning of the implants. BIC (bone-implant contact) varies between patients and varies in the same patient, depending on the planning.
It is a basic mistake of those who start with zygomatic implants. They believe that only the zygoma thickness will determine precisely the amount of anchorage of the zygomatic implant, which is a mistake.
Some surgeons believe that although the zygomatic implant is long, its biomechanics is like a short implant. The zygomatic implant is around 47mm, but the bone's thickness in the region of the zygoma body is only 5mm. Bullshit!
I can say that this is one of the main basic errors in understanding the zygomatic implant and its relationship with the zygoma body. The problem is that many surgeons transmit the knowledge applied to conventional implants also to the zygomatic implant, which is a mistake.
Let's imagine the following: you will place an implant in the region of tooth 46. When you evaluated the CT scan of this region, you found that it has 6.5mm high and 5mm wide bone. You choose to install a 5mm high and 3.75mm wide implant. Once this implant is perfectly placed, we will have a 5mm bone insertion.
Let's assess the zygoma body CT. In the coronal view, we see that the thickness of the zygomatic bone is about 5mm.
The surgeon transfers the same form of reasoning to the zygomatic implant; that is, we will have 5mm of insertion into the bone. However, this premise does not apply to the zygomatic implant!
The implant position in the maxilla concerning the zygoma body will be from anterior to posterior; that is, it will transfix the zygoma body, from anterior to posterior, and from bottom to top.
This implant-bone insertion will be much larger than the thickness of the zygomatic bone and generate high torques, which allows immediate loading. These nuances will be clearly explained, and we will learn to evaluate this amount of bone insertion even before surgery. (a post about it is coming soon).
To supply the range of possibilities involving anatomical and planning issues, zygomatic implants must have several dimensions available. Because of it, companies produce various sizes of implants, and ideally, all must be available at the time of the surgical procedure.
As much as there is a possibility of preoperative planning, small changes in the initial angulation culminate in considerable differences in the zygomatic implant's final size needed. The ideal position concerning the implant head about the residual ridge and antagonistic teeth also contributes to selecting the exact size of the implant. Sometimes, we have substantial maxillomandibular discrepancies, which is better managed with the most prolonged zygomatic implants (implant's head as anterior as possible).
Among the sizes of zygomatic implants available, there is a wide variation from company to company. When it comes to the smallest zygomatic implants available, we have not found any difference by companies, which are zygomatic implants with a length of 30 to 32mm. However, when it comes to maximum size, things change completely.
Whenever we performed Allon4 Zygoma (Quad zygoma) cases, the anterior zygomatic implants generally needed to be very long implants to have a good relationship with the residual ridge. Sometimes, the head of the most anterior zygomatic implants is positioned close to the lateral incisor region.
From a surgical point of view, it is essential to note that the further anterior the head of the zygomatic implants in the alveolar ridge region, the more the zygomatic implant will cross the body of the zygoma from anterior to posterior, increasing the zygoma bone anchorage.
The opposite decreases bone anchorage. Understand that the more posterior the head of the zygomatic implant in the residual ridge, the more vertical the implant will have to be, and the more perpendicular the implant will transfix the body of the zygoma, decreasing the amount of bone anchorage.
Maybe these concepts sound a little abstract to you now, but these concepts are experienced and internalized intuitively in virtual planning.
The fact is that to have such cases well-conducted, longer zygomatic implants are essential. When I started using Neodent zygomatic implants, this was an aspect that I promptly realize because, in this zygomatic implant system, the longest implant was 52.5mm, very different from the system I had been using (SIN Implant System), which had the most extended implant of 62.5mm.
For this reason, I ended up returning to using the implant system from SIN Implant System. I always believed that these clinical perceptions were not seen or commented on among colleagues who work in zygomatic implants until I came across an interesting scientific paper.
The authors made a series of virtual planning of zygomatic implant surgery, placing the implants in the area of maximum bone availability in the zygoma body.
The authors' conclusion was exactly what I had already experienced in practice:
It is worthy to note that when the apex of the previous implant was placed at Point A3, the average lengths of the implant were 55.68 + - 63.41 mm, which were beyond the lengths of the commercial zygomatic implants. Therefore, to obtain the largest BICs, it is suggested to produce longer zygomatic implants.
Another study by Pelegrino (2020) also found a similar conclusion (2).
I think that the zygomatic implants' size is a crucial factor to be taken into account when deciding which zygomatic implant system you will use.
I have compiled all the information regarding zygomatic implant sizes and other important aspects of the world's main implant companies in this post.
I recommend that everyone read the article below. After all, the scientific basis is what drives clinical decisions. It is certainly what companies should prioritize when developing new solutions that meet the clinical needs of surgeons.
Short size zygomatic implants
The use of excessively short zygomatic implants can be used in two different situations.
1) Planning error
Take a look at this paper (3), where a virtual plan was made with the implant's head positioned more posterior region (which I do not recommend). Realize that in situations like this, zygomatic implants always end up having a smaller size. The clinical repercussion of it is the formation of a huge anterior cantilever.
2) patients with a short face
In patients of short size and short face, the length of the zygomatic implants is proportionally shorter. I had a case where I used the smallest zygomatic implant that I had available in the system I was using - 32.5mm - and the apex of the implant was beyond the external cortical of the zygoma body.
Fortunately, the implant's apex was rounded and, although it was possible to feel the prominence with the skin palpation, the patient did not present any complaints.
When a surgical planning and execution error is made, the zygomatic implant is installed with its head in a more posterior position to the ridge in short-faced patients; you could need shorter zygomatic implants than those available in the market.
The length of the zygomatic implants is critical information and tells us beforehand if the planning is consistent with our case's anatomical reality. Virtual planning (correctly executed) is fundamental not only for an excellent clinical result but also for the surgeon to understand such nuances to accelerate his learning curve regarding installing zygomatic implants.
REFERENCES
(1) Hung KF, Ai QY, Fan SC, Wang F, Huang W, Wu YQ. Measurement of the zygomatic region for the optimal placement of quad zygomatic implants. Clin Implant Dent Relat Res. 2017 Oct;19(5):841-848. doi: 10.1111/cid.12524. Epub 2017 Aug 1. PMID: 28766912.
(2) Pellegrino G, Grande F, Ferri A, Pisi P, Gandolfi MG, Marchetti C. Three-Dimensional Radiographic Evaluation of the Malar Bone Engagement Available for Ideal Zygomatic Implant Placement. Methods Protoc. 2020; 3 (3): E52. Published 2020 Jul 22. doi: 10.3390 / mps3030052 https://pubmed.ncbi.nlm.nih.gov/32707931/
(3) Duan Y, Chandran R, Cherry D. Influence of Alveolar Bone Defects on the Stress Distribution in Quad Zygomatic Implant-Supported Maxillary Prosthesis. Int J Oral Maxillofac Implants. 2018 May/Jun;33(3):693-700. doi: 10.11607/jomi.4692. PMID: 29763505.
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