When fitting dental implants in the upper molar area, the professional often finds that there is too little bone.
This situation is due to the presence of the maxillary sinus, an air-filled cavity. Fitting implants in this area therefore sometimes requires elevating the sinus membrane.
Elevating the sinus membrane entails covering the sinus floor with a bone graft.
Types of bone graft
In most cases we use synthetic bone grafts. This removes the need to harvest bone.
The grafting technique
To fit the graft, access to the sinus must be opened. There are two main ways to do this:
Lateral access or Cadwell-Luc procedure
This allows us to graft large areas of bone. A small area is opened in the external wall of the sinus, giving ample access to and excellent visibility of the area to be operated on.
Anaesthesia must be applied deep into the vestibule to make sure that it correctly reaches all of the maxillary sinus. Being the sinus floor, the palate too must be anaesthetised.
To do this, the dentist must find the mound of the zygomatic process above the first superior molar, lifting the gum upwards to reveal the area. It is from here that we will access the maxillary sinus. The trap-door must be ovoid in shape rather than rectangular to prevent the appearance of cutting edges, and its lower part must be just over the palate. This height is measured by observing the line of the palate on the panoramic X-ray or scan. The lower part of the trap-door must be 1 or 2 mm from the palate line so that we can properly remove the Schneider membrane.
The trap-door must very gently drilled due to being a very fine cortical layer, often similar to an eggshell. A worn tungsten or diamond drill must therefore be used, drilling carefully so as not to scratch the mucous membrane coating the inside face of the maxillary sinus or Schneider membrane. While the thickness of both the cortical sheet and the Schneider membrane changes from one person to another, it is always very delicate.
Once the trap-door has been drilled, an ovoid layer of bone is left in the middle which moves inwards when pushed gently, indicating that this central layer is now isolated from the rest of the cortical bone and that we have successfully open the trap-door. We will then start to remove the membrane gently, from below, using a special blunt instrument similar to a composite spatula. The membrane is removed all along the bottom of the maxillary sinus until coming to the internal wall, next to the ascending nasal pits. A little of the anterior and superior membrane must also be removed to make sure that the membrane is not in tension and that it won’t rip when removed.
Once the Schneider membrane has been freed, it is folded upwards, proceeding with the filling process which will form the bone to which the implants will be fixed. We start by introducing a membrane of growth factors to protect the Schneider membrane. This is followed by the pellet of activated factors and filling biomaterial such as Bio-Oss or Apatos by OsteoBiol, to which autologous bone can be added, taken from other parts of the mouth or the drilling of other implants, from the upper jaw tuberosity, or from the ascending branch of the mandible. Finally, from outside the trap-door and to protect it, a membrane of fibrin in turn obtained from the growth factors is added. The process is completed by sewing the gum over the space.
Waiting time for fitting implants after the lifting process.
This depends on the thickness of the alveolar bone to which the maxillary sinus floor lifting process is applied. It also depends on the kind of filling used:
- If the bone is 3 or 4 mm long and the filling used is only biomaterial: 6 months.
- If it is only autologous bone: 3 months.
- And if it is a combination of the two the waiting time will depend on the proportion of each one used.
If the bone measures 1 mm, the waiting time is 9 months-1 year depending on the filling material used.
If the bone measures 5 mm or more, the implants can be fitted during the lifting process. In this case, once the trap-door has been opened, we can sometimes start by fitting the implants and then the filling. At others, we start with the filling followed by the implants.
Ridge access with osteotomes
This technique is only suitable for small grafts. Here the material is pushed to the bottom of the sinus, through the space opened by the implant perforation. Depending on the situation, it may be possible to fit the implants at the same time as the bone graft.
The bone must have 5 mm or more for the sinus lift to be effective.
If a lift is only 2 or 3 mm, the introduction of biomaterial may not be necessary. Bone would seem to form in any case.
If we want to raise it more than 3 mm, we must fit, by crestal approach, a membrane of growth factors, or a ‘pellet’ of growth factors mixed with a biomaterial and autologous bone if we have been able to obtain it.
This technique offers better post-operatory response than the Cadwell-luc lateral trap-door, although we do not have as good a view of what we are doing as we do with the lateral trap-door in the maxillary sinus. Today the lateral trap-door is reserved for cases that require a great deal of filling.
Sinus lift contraindications
While contraindications are rare, as in all surgical operations, the patient’s health must be checked before proceeding.
The state of the sinus must be carefully studied and, if in any doubt, the opinion of an ear, nose and throat specialist requested.
Effects of the operation
The effects of a sinus lift are simple and rather painless.
Like in all surgical operations, a bone graft can be followed by the appearance of an oedema, light haemorrhaging or bruising. Whatever the case, it is essential to observe your surgeon’s medical prescription and advice.
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