Since the first description of zygoma implant’s (ZI) surgical technique in 1998 by Brånemark, clinicians have presented several modifications to this original implant dentistry technique. What are the 5 ZI placement surgical techniques you should know about and what are the differences among them?
1. The classical approach
The classical approach was first introduced by Brånemark in 1998 and begins with a maxillary vestibular incision similar Le Fort I. This incision is made between the first molar regions from side to side. Anteriorly, the nasal mucosa is dissected to increase visibility of the local anatomy. The dissection progresses along the infra-zygomatic crest towards the zygomatic bone. The infraorbital nerve is localised and protected. At this point the zygomatic region is fully exposed. In addition, the palatal flap is reflected to entirely expose the alveolar ridge and the hard palate. At this stage, an oval shape window is opened on the upper-lateral aspect of the maxillary sinus wall in the extension of the infra-zygomatic crest. The maxillary sinus mucosa is then reflected. The window is used to provide direct vision of the maxillary sinus roof allowing the direct control during the zygomatic bone drilling phase. The drilling phase includes several steps:
- A Ø 2.9 mm round bur is used to penetrate the crest and mark the entrance in the roof of the sinus
- The entire site in the zygoma is then prepared with a Ø 2.9 mm twist drill
- A 3.5-mm pilot drill is employed to enlarge the site
- To ensure a better accuracy, the wider drill is provided with a non-cutting tip Ø 2.8 mm
- Once the surgical site is patent the preparation continues with a Ø 3.5-mm twist drill that has got a cutting tip
- A depth indicator is used to decide the correct length of the ZI
- A 4-mm countersink drill might be used in case the palatal cortical bone is very dense to avoid the risk of excessive widening of the palatal entrance.
At this point, the ZI is inserted manually and slowly until adequate depth is reached and soft tissues are sutured.
To use this technique, enough bone volume must be present in the anterior maxilla to allow the placement of two to four conventional implants combined with the ZI.
2. The sinus slot approach
The sinus slot method was first introduced by Stella and Warner in 2000. The surgical approach starts with a crestal incision extending from one maxillary tuberosity to the contralateral one. Vertical releasing incisions are made bilaterally at the maxillary tuberosity level. Thus, a similar Le Fort I exposure is accomplished. This will extend around the base of the piriform rim, up to inferior aspect of the infraorbital nerves and around the body of the zygoma bilaterally. At this point the palatal mucosa is reflected only to expose the crest of the alveolar ridge. A fissure bur is then used to make a hole through the bone and into the sinus cavity at the superior extent of the contour of the zygomatic buttress. The depth gauge is positioned in the bur hole and placed to simulate the degree of approach of the ZI twist drill. A second bur hole is made on this line 5 mm above the alveolar crest. A slot is then created to connect the two bur holes. The superior part of the slot extends to the zygoma bone base, while the inferior part approaches the floor of the maxillary sinus. In this way the slot results in a smaller antrostomy that will help to orient the twist drills for placement.
The drilling phase includes these steps:
- With a round bur, a small notch is made at the ideal location on the maxillary alveolar ridge, which lines up with the sinus slot
- Ø 2.9 mm zygomatic twist drill is placed in the notch point, directly over the crest of the ridge, and the drill is directed such that it extents directly through the sinus slot that was previously fabricated
- The tip of the drill is guided through the centre of the slot under direct visualisation. The drill is advanced superiorly toward the junction of the lateral orbital rim and zygomatic arch
- Ø 3.5-mm pilot drill and 3.5-mm twist drill are then used in the same way, being directed through the centre of the sinus slot
- The depth of preparation is checked with the depth gauge, and the appropriate length implant is chosen
- The ZI is placed in direct vision
Once the ZI is inserted manually and slowly the soft tissue are sutured.
3. The extra-sinus zygomatic implants approach
This approach was first introduced by Migliorança et al. in 2006 and is also called “extra-maxillary implants” or “extra-sinus zygomatic implants”. The surgical incision begins with maxillary alveolar crest incision joining both maxillary tuberosities, along with two vertical releasing incisions in the zygomatic pillar area. A full thickness mucoperiosteal flap is reflected. The ZIs are placed externally to the maxillary antrum, in close contact to the lateral wall of the maxillary sinus. Ideally the position of the ZIs should aim to be as distal as possible, preferably in the second premolar or first molar region. With this particular approach, it is not necessary perform any maxillary antrostomy. The drilling phase include the below steps:
- With a round bur a small pierces of the residual ridge near to the top of the crest, from palatal to buccal side is made. The aim is to emerge in the buccal aspect of the ridge, external to the maxillary sinus
- The drilling continues toward the zygomatic bone along the external aspect of the lateral wall of the maxillary sinus until it reaches the zygomatic bone. At this stage the zygomatic bone is perforated up to the bone cancellous layer
- The depth gauge is then used to control the measurement of the ZIs, which are defined as 2 mm less than the obtained measurement
- The osteotomy is progressively widened using these drills in sequence: Ø 2.9 mm twist drill; Ø 2.9/3.5 mm pilot drill; and Ø 3.5 mm twist drill.
- The ZIs are placed with an initial insertion torque of 40 Ncm and completed manually
Ideally, the ZIs platform should emerge over or close to the alveolar ridge.
4. The minimally invasive approach
In the minimally invasive approach, the preoperative surgical plan is realised by transferring computer tomography (CT) information to a stereolithography custom-made drill surgical stent. CT data for each patient are imported to a planning software which allows a virtual simulation of the ZI placement on the 3D model. Once the planning is finished, the treatment plan is then used to fabricate a surgical drill stent with skeletal support. The goal is to create an individualised surgical drill stent that matches the patient’s bone profile. The drill guide is then created by stereolithography. The surgical drill stent contains cylindrical openings into which stainless steel tubes can be fixed. Each cylinder’s position corresponds to the position of the planned implants.
This surgical procedure involves a mucoperiostal incision as described in the classical or extra-sinusal approach. After the surgical drill stent is fitted onto the maxilla with osteosynthesis screws, the drilling sequence is performed with the use of appropriate drills.
5. The computer-aided surgical navigation system approach
Another potential approach is represented by using a computer-generated tracking technology, which continuously registers the position of patient and surgical tools (computer-aided navigation). The ZI placements by using of a computer-aided surgical navigation system was first introduced by Schramm et al. 2000. This particular approach is centered on computed tomography (CT) data, a navigation system for the preoperative planning and intra-operative control system. The preoperative planning is supported by 3D visualisation, which calculates an accurate conversion that carries the coordinate system of the CT scan to the patient, an LED emitter array can be attached to the skull or directly to the maxilla of the patient. Continuous visualisation of the drill sequence is displayed in real time on the computer screen. By controlling the drill in the planned direction, the ZI placement can be carried out with precision.
According to my experience, “open flap” techniques represent the gold standard due to accuracy issues related to the use of software-guided surgery / surgical stents.
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Below a ZI clinical case performed by Mr Andrea Tedesco