The "No BS Guide" to Allon4 Technique (Part I)
"The No BS Concept" of the Allon4 technique was written for surgeons, for those who face atrophic jaw from a different perspective. If you do believe that the bone graft is the unique treatment option for atrophic maxilla, you could stop reading here. Otherwise, keeping reading and welcome to the more straightforward guide about Allon4 ever published.
Simplicity is the maximum degree of sophistication.
Leonardo da Vinci
Yes, the Allon4 is a simplified technique, but it is not simple. What we will see later are practical concepts of those who do what they teach and not just replicate what they've read.
It is possible to theorize, dive into the preambles of finite element analysis studies, biomechanics, clinical studies, peri-implant bone remodeling, among other factors. All this information is published and serves as a scientific basis for us to be able to execute the technique with a strong scientific basis. We will see it only superficially. If, for you, at this very moment, the most important thing is to fully master all this theoretical information, feel free to read all these articles that are available to you elsewhere.
But assuming that all of this publication do exist and what you want is to implement the result of it in your clinical practice, read on.
The objective of the Allon4 technique is to use only four implants strategically placed in regions of high bone density, enabling immediate loading.
The tendency of bone quality is quite different in distinct areas of the maxillofacial sites.
We all know that bone density is one of the main factors responsible for high insertion torques of dental implants and consequently allowing us to perform the immediate load safely. It is a predictable feat in the lower jaw because it is a movable bone with insertions of the powerful masticatory muscles, which stimulates bone corticalization.
In the maxilla, the challenge is more remarkable, especially when the dental implants are installed in a region of grafted bone or posterior part of it. It is because the maxilla is a fixed bone, and only insertions of the mimic facial muscles are attached to it.
Despite it, there are areas of dissipation of masticatory force where there is a tendency towards greater corticalization. These areas are located in the nasomaxillary, canine, and zygomaticomaxillary buttress regions. It is precisely in these regions where rigid internal fixations are performed to stabilize Le Fort I type fractures (either due to trauma or orthognathic surgery).
Zygomatic bone, on the other hand, has a peculiar characteristic. Despite being a fixed bone, it has the insertion of the most potent masticatory muscle - the masseter. It causes a high trend of corticalization in its insertion.
Even after the loss of all teeth with consequent alveolar resorption, the stimulus to the masseter muscle will always be present.
When it comes to bone consistency, the zygomatic bone is a kind of mandible bone in the middle third of the face.
It is the main reason for the high insertion torques in this bone. Anyone who has never had a zygomatic implant surgery has a false feeling that this implant is unstable and, therefore, can cause damage to the future prosthesis.
Only after feeling in practice the insertion torque and the final stability of an installed zygomatic implant, the surgeon started to believe what he has read.
The basis of the Allon4 concept is to prioritize the quality of the implants over the quantity of it. This better-quality bone will be present in the anterior region of the maxilla and through the whole zygomatic bone(1).
There are three basic modalities to rehabilitate atrophic maxilla without bone graft within the Allon4 concept, which will be indicated according to the bone availability of each case.
Allon4 types
Allon4 Standard. In this modality, we will install four normal implants in the anterior region of the maxilla. It is indicated when we have remaining bone below the piriform aperture and canine buttress region.
The distal implants need to be tilted around 45o tangent to the anterior wall of the maxillary sinus, and the emergence of the prosthetic screw will generally come out at the level of the 1st upper premolar or posterior. The central implants are installed using a palatal approach.
When we do not have the available bone structure to install these distal implants, but there is a condition to place two implants in the anterior region, usually adjacent to the incisive foramen, we will use the Allon4 Hybrid modality, where we will associate two zygomatic implants to these two central implants. Take a look at this post to know everything about zygomatic implants systems.
In cases of severe atrophy where there is no possibility of installing implants on maxilla, we will use the Allon4 Zygoma modality, where four zygomatic implants are placed in the zygomatic bone (quad zygoma).
When you perform zygomatic implants but do not understand the Allon4 philosophy, you often overtreat the patient, install zygomatic implants in cases that could be resolved with conventional tilted implants (Allon4 Standard).
Finally, understand that the patient is not interested in surgery; he wants to be rehabilitated with an aesthetic and functional implant-supported prosthesis. We should always put the patient first and think that if I can solve the case with Allon4 Standard surgery, why am I going to perform Allon4 Hybrid? Just to share one more case of the zygomatic implant on the Facebook group? Patient first, surgeon later. If it is possible to simplify, do not complicate it.
Take the phrase from my master prof. Carlos Eduardo Francischone and take this as a mantra in your planning - just put four implants (Allon4 standard) and solves the patient's problem soon. It is the basis of the ZYGOMA 2.0 concept. Case selection for a zygomatic implant with extreme caution and responsibility. Once indicated, we will learn to plan and perform with maximum safety and results for our patients.
From a marketing point of view, it is effortless to acquire new patients. Generally, these patients have already been evaluated by other professionals, and, most of the time, all of them spoke only about bone graft. You then propose to carry out the treatment without bone graft and with immediate loading, and certainly, this is a great differential. It's a kind of win-win treatment.
If we could say what the core, the essence, the heart of the Allon4 Standard technique is, I would say there are three pillars: the palatal approach; learn to position the posterior implants on the anterior wall of the maxillary sinus; and maintain the spatial relationship of the initial perforation with the center of the face.
Also, we have to take into account that the costs for the patient end up also being lower(2).
We will now dive into the Allon4 Standard Technique. You will now understand some technical details that will make a massive difference in the surgery and consequently, in your clinical results.
Allon4 Standard
If we could say what the core, the essence, the heart of the Allon4 Standard technique is, I would say there are three pillars: the palatal approach; learn to position the posterior implants on the anterior wall of the maxillary sinus and maintain the spatial relationship of the initial perforation with the center of the face.
If we could say what the core, the essence, the heart of the Allon4 Standard technique is, I would say there are three pillars: the palatal approach; learn to position the posterior implants on the anterior wall of the maxillary sinus, and maintain the spatial relationship of the initial perforation with the center of the face.
Palatal approach
After understanding this concept and experiencing it in practice, you will never look at an atrophic maxilla the same way again. There is an automatic impulse always to imagine implants being installed in the center of the alveolar bone crest. When the crest bone is thin, a bone graft is suggested, usually in a block.
However, with the palatal approach, we will install the implants by drilling the palatal cortical, paying attention so that no vestibular fenestrations occur, and we will leave the palatal cervical threads of the implant exposed.
But won't that be a problem? Not!3 Because the palatal mucosa is exceptionally thick, dense, and keratinized, there is no tissue dehiscence.
Exemplifying. Imagine a situation like this below. The "standard" planning would undoubtedly include at least a bilateral maxillary sinus lift and even block grafting in the anterior region. After wanting 6 to 8 months, installation of 6 to 8 implants. After the period of osseointegration, new incision to expose de implants and then the procedures to the final prosthesis. Anyway, three surgeries and more than one year of treatment.
But using the Allon4 concept, you will understand that the most central region in yellow is the region where there is a tendency to have a denser bone. The red part represents the place where the bone tends to be less dense.
You will then start the drilling process in the region of less dense bone and progress with the drilling, preferably until the drill transfixes the cortical of the floor of the nasal cavity.
That's right! There is no complication in this maneuver, but the fact that the implants being bicorticalize, especially when the bone height is reduced, can be the decisive factor between a high or low insertion torque of the implant.
In addition to these implants being installed in a region of greater bone density, it is prevalent to use longer distal implants, usually 17mm length.
Whenever I teach face-to-face classes, at that point in the class, a question always arises.
- But professor, will not be tilting these implants promote bone loss? The answer is: NO! Several studies are supporting that there is no bone loss in these tilted implants(4-12).
Understand:
Decreasing the cantilever is more important than keeping the implants straight.
But the most common question from patients (and also from professionals who do not know the Allon4 technique) is:
- Doctor, but only with four implants, does it work? Another dentist said that only four implants are dangerous because if I lose one implant, I will lose the entire rehabilitation, so it is better to place several more implants.
When implants are installed in grafted bone, it is common to lose some implants, so the strategy is to place as many as possible, around 6 to 8 implants. Some implants will be lost, and what is left is then used to anchor the prosthesis.
However, when we talk about Allon4, we are placing the implants in non-augmented bone, that is, bone that is well vascularized, alive, and of higher quality.
Osseointegration is a qualitative question of anchorages and not a quantitative one.
A study by Professor Brånemark published in 1995(13) evaluates the rehabilitation with 4, 5, or 6 implants. The patients were followed for 10 years. The result was that there was no statistical difference between the groups evaluated.
The studies of the Allon4 technique started in the early 90s, with the first case being performed in the mandible in 1993. The benefits of the decrease in the cantilever were found and a high success rate. In 1996, it was conducted in the maxilla, and they started to have a lower success rate. It drops to only 70%. Then the possible causes and solutions to optimize success in the maxilla began to be investigated.
The design of the dental implant was modified, where the Nobel Speedy™ implant was launched. The benefits of seeking bicorticalizations (on the floor of the nasal cavity and anterior wall of the maxillary sinus) and the concept of sub-drilling were established to promote osseocompression during implant installation and optimize insertion torque.
Anyway, it took ten years to structure the protocol, and from there, the cases were selected for scientific validation.
Sequentially, studies and evidence appeared, and, at the present date, we have a lot of literature supporting us for the success and predictability of this technique(2,7,8,13-33).
But the advantages of the Allon4 technique do not end there. We all know that the minimum distance between implants must be at least 3mm to minimize the chance of saucerization. When 6 to 8 implants are installed, according to the traditional protocol, sometimes there may be a decrease in the distance between these implants, which is not ideal.
In addition to potential damage to peri-implant tissue stability, such situations generate numerous areas between implants for the patient to floss, making it very difficult to clean these spaces. See below when using just four implants, the time and ease of cleaning are much better.
The biomechanics of the future prosthesis are greatly improved when the cantilever is decreased by the inclination of the distal implants(4-12). In the mandible, in most cases, it is possible to arrange the implant head above the mental foramen, and due to the tilting of these distal implants, it is also possible to use longer implants and still deviate from the mental nerve looping.
The passivity of the metal infrastructure of the prosthesis also tends to be easier when fewer implants are used. A simple example, which can be explained to the patient, would be to compare the stability of a table with four legs compared to a table with six legs. The latter tend to have more difficulty in attaining stability.
Sub instrumentation (under preparation osteotomy)
This strategy is common in implant surgery. In the Allon4 technique, it is taken very seriously. To install implants with a thickness of 3.75mm, we usually drill with the pilot drill, drill 2.0, a little bit of the pilot drill 2/3, and, depending on bone consistency, drill 2.8.mm. The implant design must be optimized for osseocompression. Ideally, it should have an active tip, such as a NobelSpeedy™ or NeodentEx™ implant, among many others available on the market.
In the preoperative sequence and prosthetic preparation, there is no difference concerning conventional protocols. Preoperative exams are routinely requested, reverse prosthetic planning is performed, and a complete prosthesis is made within the aesthetic and functional parameters.
This prosthesis can be used immediately as a temporary prosthesis, capturing that prosthesis on the titanium cylinders, or we can use it as a multifunctional guide and make the prosthesis with a metal infrastructure. After three months, if necessary, a reshaping can be done on the bottom of the prosthesis for a better relationship with the already healed soft tissues.
Does the immediate loading need to finish in 3 days?
There has always been this concern in the past. It was believed that it was necessary to splint these implants as early as possible. I have realized in practice that this is not the case. We used to remove the prosthesis routinely to remove the suture in 7 days, and we never had any problems because of that. We have to understand that the implants were locked with 35 Ncm or more and, despite the torque dropping in the postoperative period, to remove and reinstall the prosthesis, we will give a torque of only 10 Ncm on the prosthesis cylinder screw.
There is even a study that reports that there are no differences between the different types of protocols for immediate loading(8).
As our confidence in the technique has increased over the years, even in cases of low torque in some implants, we continue to maintain immediate loading, and this has not reduced our success rate. I have always believed that torque (turning) does not occur with the prosthesis in function, besides the union of all components acting as a whole system.
More recently, our clinical perception was as well perceived for others, which just published it, where it was evident that low insertion torques do not decrease the success rate(28).
Now let's look at the technical and clinical concepts for carrying out the standard Allon4 technique.
Bone leveling
After local anesthesia, incision (positioned more towards the palate), and total mucoperiosteal detachment, we must make a bone leveling. This leveling can be almost zero, just smoothing the sharp edges of the residual edge, or it can be quite bulky. How to define the magnitude of this cut?
As we are going to perform dentogingival prosthesis, the transition from artificial gums to natural gums must not be exposed during the smile. Because of this, the essential picture you should take in the preoperative period is an image of the patient smiling without the denture.
It is possible to evaluate and record the dynamics of the lip and quantify how much bone and gingival tissue will be necessary to remove at the time of surgery. This lack of leveling can also leave little space for the bar, pink resin and teeth, causing the prosthesis to have vestibular overextensions (such as small flanges), which makes the ability to maintain proper oral hygiene difficult.
In some patients, the vertical leveling of the ridge will be done up to the maximum limit, which, in the posterior region of the maxilla, will be until we find a bluish part that is the maxillary sinus.
An essential tip for you not to lose the reference of how much bone you have already removed with what you need to remove is to wear one hemiarch at a time, so the other hemiarch remains with reference.
Facial reference guide
Initial drilling reference
The establishment of spatial orientation is critical. If you lose your spatial reference of the perforations to the face, you can completely lose the three-dimensional control of the position of the implants.
In the image below, our student installed the straight central implants and tilted the distal implants. Then he called me to see if she could continue with the drilling. In her view, the initial perforations were accurate.
However, when we zoom out and see the patient's face as a whole, it is clear that the central implants are tilted to the left.
This lack of spatial orientation is widespread in those at the beginner level. Such an error in the maxilla can make it very difficult to correctly position the distal implants.
How to avoid mistakes like that?
We have two ways to stay spatially oriented during surgery:
1) Parallel pins
We are all used to using these straight pins. However, there are also these pins with angles of 17o and 30o.
2) Allon4 Guide
It is a specific Allon4 implant placement guide marketed by Nobel™.
After doing the initial drilling and installing the parallelize pin, you need to move away from the operating field and look at the patient's face from the front. Being ok, just move on, otherwise, just adjust. Getting it right is critical. It is through this reference that all other implants will be installed.
A vital tip to facilitate the initial drilling with the palatal approach is to invert the position of the handpiece and look at the maxilla from the bottom up. The drilling with the operator at 9 hours position does not give us an excellent spatial relation and an exact notion of parallelism.
With the initial perforations made, we will use the 2.0mm drill that will be deepened until we fall into the void, that is, until we feel that we have completed passed through the nasal cavity cortical floor. With the aid of a probe, we will precisely measure the size of the implant that we will be using.
Be aware that, in general, if you have drilled until you fall into the nasal cavity and in your measurement, you have identified that the implant is more than 13mm, you have likely leveled the ridge too little. In this case, level the ridge more and use a maximum 13mm implant.
Drilling the distal implants will be performed at 45o to previous implants. Even when the bone is available in the posterior region of the maxilla, there is a strong tendency for this bone to be of low quality.
Another way to orient yourself spatially is through the Nobel™ Allon4 drilling guide. After the initial drilling, you will install this guide and see how it is positioned concerning the face and whether it is perpendicularly positioned with the bipupilar plane.
This guide is flexible, and you can shape it according to the shape of the ridge and adjust the tilt in the sagittal direction. In this guide, there are vertical lines that will serve as a reference for the installation of central and distal tilted implants.
The most critical point for performing the Allon4 technique is the installation of posterior implants. Understanding how to drill these implants on the anterior wall of the maxillary sinus is an important maneuver. There are some strategies for this, and we will see it next.
How to tangent the anterior wall of the maxillary sinus
Where do we place the initial perforations of the distal implants?
In many cases, it is possible to identify a slight bony prominence of the canine buttress. If the canine tooth were in this region in the past, it means that if we enter our drill distally to this bony prominence, it is very likely that the emergence of the prosthetic screw will come out very close to the upper 1st premolar.
The apical direction of the drilling, in most cases, can be towards the parallel pin of the anterior implant because we know that in this region, undoubtedly, there is bone.
If you want to check the position of the initial perforations with the surgical guide (multifunctional guide), you can then use the angled guide pins of 30o (or 17o if you have not tilted too much the implants).
The drill sequence to be used will vary according to bone density and your tactile perceptions, always taking care to perform a sub-drilling.
How to tangent the anterior wall of the maxillary sinus
There are four strategies to do that:
1) For transparency
Immediately after total mucoperiosteal detachment, it might be possible to identify a more bluish region on the outer wall in the posterolateral part of the maxilla. It happens because of the thin thickness of the lateral bony lamina of the maxillary sinus. In such situations, it is easy to define the anterior limit of the maxillary sinus visually.
2) Drilling and probing
In cases where the outer cortical bone is thicker, and it is not possible to see a bluish region, we can make a small lateral opening in the maxillary sinus. We can use a probe or curette to touch where the anterior limit of the maxillary sinus is found. As we will not be placing particulate bone, there are no concerns regarding the integrity of the sinus membrane.
3) Post-extraction socket reference
When there are associated extraction procedures, it is possible to use the references of the position of the alveoli with surrounding bone availability so that we can define the position where it is possible to make the perforations.
4) Tactile perception
After the installation of the anterior implants, you can measure according to the tomographic exam and make the initial perforation inclined to the anterior one and notice if you have found bone resistance during the entire perforation or felt a sensation of "falling into the void" inside the maxillary sinus. If you have fallen into the void, you have to change the direction of the perforation toward the anterior until you find bone resistance.
Does the order of dental implants interfere with the result?
It could be yes or it could be no. When there is enough bone, the implants are far from each other, and the tip of these implants is not likely to touch each other. However, in borderline cases, the order of the implants can make a difference.
The distal implants are generally more critical and should have priority. The anterior implants, in the worst case, we can even empty the content of the incisive canal to install one of the implants.
Imagine that we have already installed two 11mm implants in the central region, and now we are going to drill the distal ones. It may be that one of these central implants made it impossible to install a distal implant with the desired size.
It was what happened in the case below, where I had to change the planning in the trans-surgical moment and put a smaller implant on the left side. So, when in doubt, leave the drills in position and make a probe to identify if there is a touch between the implants before to finish drilling.
Installation of prosthetic components.
As the distal implants are very tilted, we will use 30o angled mini abutments to compensate for these inclinations. However, it is prevalent for you to have difficulty fitting the mini-abutment because it usually ends up touching the bone surrounding the implant head.
For this reason, after finishing the preparation of the bone bed, I suggest that you wear the region where the implant head will be a little more. As much as you use the countersink drill, it still doesn't seem to be enough in most cases.
It is essential to make sure that the mini abutment is seated correctly during the installation otherwise, you may have some surprise on the control radiograph.
In the next post, I will cover some more clinical tips about Allon4 Standard. But before move forward, I would like to hear your opinion in the comments below.
REFERENCES
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