The "No BS Guide" to Allon4 Technique (Part II)
Along with the post The "No BS Guide" to Allon4 Technique (Part I), we have seen a lot of technical concepts about the Allon4 technique. Let dive into the clinical and surgical concepts
Surgical technique All-on-4 standard - Technical concepts
The local anesthesia can be done with the same technique as for a conventional protocol surgery. We are going to block the infraorbital nerve, upper posterior and middle alveolar nerves, nasopalatine and greater palatine nerves and/or infiltrative anesthesia at the vestibule sulcus.
The incision is made with the flap design more palatal to the ridge crest center so that we can have a greater amount of keratinized gingiva around the mini abutments. Two vertical incisions are made in the region of the zygomatic buttress.
The detachment is done in the usual way with the elevator, Freer, Molt surgical curette or similar, according to your preference. The nasopalatine nerve can be sectioned to facilitate visualization since the implants will often be installed very close to the incisive canal. The cut of this nerve does not produce negative consequences regarding the vascularization of the palatal region since there are anastomoses with the vascular coming from the greater palatine foramen. After complete detachment, we recommend the use of a temporary X-shaped suture on the palatal flap to keep the tissues retracted and improve the visualization of the operative field without the need for any manual retractor in position.
Then, the osteotomy for leveling the ridge begins, according to the initial planning (height of the residual bone and amount of gingival exposure during the patient smiling without the prosthesis). This leveling can be done with a Maxicut drill or, preferably, an inverted pear drill.
The initial drilling begins with the start drill with a palatal approach, making sure that this drilling is perpendicular to the bipupilar line; distal perforations are made in 45o with these initial perforations, placing immediately after the canine buttress region.
Next, these initial perforations have been made, checked, and adjusted with the face, the standard drill sequence is performed according to bone consistency and always keeping in mind the importance of a sub-drilling to optimize the stability of the implants.
It is better to drill less than too much. Too little, correction is possible if the torque is too high to the risk of generating cracks or even a fracture in the ridge.
However, too large drilling ends up being something with no possibility of circumventing, as it is not possible drilling in another location most of the time.
If you feel the implant may be partially out of the bone tissue, with possible displacement toward the region of the maxillary sinus, when in doubt, make a small lateral opening in the anterior lateral wall of the maxillary sinus and perform probing to orient yourself where it lies. After the osteotomies are finished, it's time to install the implants. It is best to start the installation of the implants using the handpiece with torque calibration on 30Ncm. Once it locks, you finish the installation with the manual device. If the torque is too high, you can make a counter-torque of a few millimeters and, in sequence, go down the implant, redoing this maneuver successively until the implant is fully inserted into the bone.
Then, we install the mini abutments in the anterior region, usually with a height of 2 or 3mm. If you have too much gingival tissue, you should gently remove and reshape it accordingly. The distal mini abutments (multi-unit) are generally 30o 3mm high.
Completely remove the positioning rods from the angled mini abutments and use the short prosthetic wrench 1.2mm. If you are unsure of the ideal position of these mini abutments, you can remove the stabilization sutures from the palatal flap and check through the surgical guide (or prosthesis with a palatal opening), which will be the best position with the emergence of the prosthetic screw.
From that point on, there is nothing new concerning the prosthetic technique. Installation of the mini abutment cover and suture (preferably, we use 4-0 silk and remove the suture in 7 days). Avoid nylon suture, as compression of the nylon not by the prosthesis can cause discomfort in the postoperative period. After the suture has finished, the mini-abutment cover is removed, and the mini-abutment transfers are installed (or titanium cylinders, if you choose to capture the patient's prosthesis). They are splinted with acrylic resin, and this whole complex is joined to the guide (or prosthesis).
We recommend using the short transfer screw to not interfere with the patient's occlusion. Three points of acrylic resin are added for the occlusal registration; the antagonistic teeth are isolated with petroleum jelly, and, after the occlusal registration, the silicone impression material is injected with the aid of an elastomer pistol or syringe.
After testing the bar and wax teeth set up, the prosthesis is finished within the aesthetic and functional parameters.
The prosthesis is then installed. Note the distal implants came out between the premolars, which is excellent from the biomechanics point of view.
On the final radiograph, it is possible to assess the magnitude of the inclination of the distal implants.
As we installed the implants at 45o with the anterior implants, these emergencies of the screws of the mini abutments of these posterior implants remain slightly distalized, since the mini abutments are of 30o. It does not bring any negative consequences. On the contrary, it tends to further distalize the emergence of the prosthetic screw, further decreasing the size of the cantilever.
A widespread situation in the clinical routine is that we have patients with severe periodontal disease with the indication for multiple extraction and implants. Many clinicians are still a little afraid to make implants in the same act due to the possibility of contamination, but there is evidence that this maneuver is possible, reiterating the need for control in the postoperative period(1).
Below, we have a case where the ideal tangential position of the implant in the anterior maxillary sinus was critical to achieving optimal anchorage for the All-on-4 Standard. Immediately, the two maxillary sinuses were opened.
The performance of the All-on-4 technique in the mandible also has advantages, especially about the distribution of implants and the reduction of the distal cantilever. The surgical sequence is similar to the upper jaw, but it is essential to visualize the emergence of the mental foramen.
Generally, the novice surgeon is a little afraid of detaching this region for fear of damaging the nerve; however, as long as the detachment is done with caution, this is not likely. For the treatment of parasymphysis fractures, it is common to dissect this nerve to place two mini plates. Although there is paresthesia in the postoperative period, the sensitivity returns later.
Leveling the residual ridge is also essential in the mandible. Although the possibility of the transition from artificial gingiva to natural gingiva is less critical, the lack of bone reduction can leave little space for the metal infrastructure and teeth set up. It can cause future prosthesis to have a small "flange," which will difficult the possibility of hygiene.
After the initial reference perforation, we check and adjust the ideal position of this perforation with the patient's face, and also we can use the All-on-4 guide or just the parallelizing pins.
As the distal implants will be tilted 45o with the central implants, the prosthetic emergency may be established just above the region of the mental foramen. This clinical situation is not viable in most of the time if straight implants were used in this region. Besides, with the inclination, we can use longer implants. Despite it, implants larger than 15mm are rarely needed. In most cases, we use 3.75x13mm implants in the central region and 3.75x15mm in the posterior part, but obviously, this depends on each case.
Many still question us why not put a 5th implant in the midline. The question I ask is: for what? The answer is: if you lose one of the five implants, you don't lose the prosthesis. Could it be? In the paramedian region, we have the highest corticalization. It is rare to loose implants, but when it does, it is usually one of the distal implants. Thus, this implant needs to be reinstalled anyway, regardless of having that extra implant in the anterior region.
Possible problems with the Allon4 technique in the jaw.
When you do Allon4 but do not work with a zygomatic implant, you are restricted to the All-on-4 Standard mode. Then I ask you:
If you have a loss of the distal implant (a rare but possible situation), how will you fix the case? The first option is to reinstall the lost implant in the same region. However, what if there is no bone to redo this distal implant?
There is no way; you do need to install zygomatic implants.
To master and be safe with the Allon4 Technique, it is imperative to learn to work with zygomatic implants.
The Allon4 philosophy tells us WHAT TO DO in the face of the atrophic jaw:
All-on-4 Standard, Hybrid, or Zygoma, but there is no clear methodology on HOW TO DO zygomatic implants.
With this in mind, we started working on the ZYGOMA 2.0 concept, an objective method of learning to plan and execute zygomatic implants.
REFERENCES
1 Malo, P., Nobre Mde, A., Lopes, A., Ferro, A. & Gravito, I. Immediate loading of implants placed in patients with untreated periodontal disease: a 5-year prospective cohort study. Eur J Oral Implantol 7, 295-304 (2014).https://pubmed.ncbi.nlm.nih.gov/25237673/
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