Direct answer
They are long implants, larger than conventional implants, that gain anchorage in the zygomatic bone instead of the maxilla. They make it possible to support a fixed prosthesis in maxillae where there is no longer enough bone for conventional implants, doing away with extensive bone regeneration.
The zygomatic bone, also known as the malar bone, is not part of the alveolar process — the portion of the maxilla that houses the roots of the teeth and that resorbs once these are lost. It therefore keeps its volume regardless of the presence of teeth, and remains available once maxillary support has been lost. That is the principle on which the technique rests.
The quality of the bone matches this availability. A micro-computed tomography study compared, in the same atrophic maxillae, the different anchorage sites possible, and concluded that the zygomatic bone offers an implant bed equivalent to that of the anterior sector of the maxilla and superior to that of the posterior sector [2] — which is precisely the region where atrophy and expansion of the maxillary sinus most limit the placement of conventional implants.
The clinical results are consistent with this rationale. An overview of systematic reviews reported survival rates between 95.2% and 100% in atrophic maxillae [1]. In the quad zygoma configuration, a meta-analysis that brought together eleven studies and 166 patients reported an aggregate survival of 98% (95% CI: 97–99%) [3].
The relevant differences lie in the length of the implant and in the path it takes to its fixation in the bone structure. A conventional implant typically measures between 8 and 15 millimetres and is placed in the maxillary bone. A zygomatic implant is larger, and can reach 55 millimetres: it passes through the maxilla and gains anchorage in the body of the zygoma.
From the patient's point of view, the final result does not differ from a rehabilitation on conventional implants.
The number of zygomatic implants needed for the rehabilitation depends on the bone remaining in the maxilla. Depending on the distribution of that bone structure, conventional implants and zygomatic implants can be combined in the same rehabilitation.
The most frequent pattern of maxillary atrophy is a lack of bone structure in the posterior sector, with remaining bone persisting in the anterior sector. In these cases we usually place two zygomatic implants, one on each side, combined with conventional implants in the anterior region.
When the deficiency is very severe and the maxillary bone is so residual that it does not allow the placement of conventional implants, use is made of the quad zygoma configuration: four zygomatic implants, two anchored in each zygomatic bone, on which the rehabilitation rests entirely.
In certain anatomies, zygomatic anchorage is combined with pterygoid or transnasal implants, so as to distribute the support of the prosthesis along the arch [4].
Historical background
Zygomatic anchorage was developed in the 1990s by Per-Ingvar Brånemark, the researcher responsible for introducing modern osseointegrated implantology. It therefore has scientific literature accumulated over several decades.
This is an advanced surgical rehabilitation of atrophic jaws, usually carried out under sedation, with local anaesthesia.
It rests on rigorous planning, prepared beforehand on cone beam computed tomography — CBCT — from which three-dimensional models of the patient's anatomy can be obtained. It is that study which defines, before the procedure, the path of each implant and its relationship with the anatomical structures of the region.
Fitting a provisional fixed prosthesis in the hours following the surgery is the aim of this type of procedure. The definitive prosthesis is made later, once osseointegration has been confirmed.
References
The indication is determined by imaging assessment, case by case.
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