PSI OGS

When asked what is the breakthrough of the decade in orthognathic surgery, perhaps most surgeons would agree that it is the development of virtual surgical planning (VSP) combined with personalized cutting guides and fixation plates, known in the field as patient-specific implants (PSI).

Errors in clinical and radiographic assessment

Errors in facebow transfer

Errors in mounting of dental casts

Alternatively, VSP and fabrication of PSI can be performed in a surgeon-oriented approach. The main advantages of this approach are that the surgeon would have total control of the whole process and that the time from surgical planning to having the PSI ready for surgery is much faster, because the whole process from planning to product delivery would only take 5–7 days from our experience.6,7

The main reason for advancing from the conventional method to the use of PSI for osteosynthesis in orthognathic surgery is the expected benefit of increased accuracy that (supposedly) matches the plan.

A systematic review concluded that a linear deviation within 2 mm for all three axes, and an angular deviation within 2.7o in pitch, roll, or jaw were considered to be accurate in a virtually planned orthognathic surgery that is positioned with an occlusal wafer.17

Knowing the benefits, it is important to understand the limitations of PSI for orthognathic surgery. The following limitations/disadvantages should be considered: (1) high cost; (2) turnaround time; (3) possibility of ill-fitting surgical guide or PSI; (4) inability to perform intraoperative adjustment; and (5) bony interferences are not easily noticeable.

The concept of surgeon-designed PSI may help to reduce the costs; however, the regulations of many countries only allow approved commercial implant products for surgical use.6

For the turnaround time, it was reported a range of 15 days– 42 days from planning to product delivery would be required depending on the companies’ support.

Occasionally, the surgical guide or PSI is found to be ill-fitting on the bony architecture during the surgery. It could be a production error or distortion of the printed titanium framework, or more frequently it could be the irregularities of thin bone or teeth roots on the surface of the maxilla that cause interferences to the adaption of the surgical guide or PSI.

From our experience, it is particularly challenging for an impaction and setback movement of the Le Fort I osteotomy, where the posterior and superior bony interferences at the pterygoid plates are difficult to be noticed but yet hinder a passive fitting of the PSI.

It is expected the costs will lower in the future when more companies are providing the service. With the development of open-source computer planning and PSI design software programs, surgeons/medical technicians can plan and design PSI in their offices, which can then be exported for production. Some centers have pioneered in this field of designing PSI in-house.6,24

In principle, degradable biomaterials with the incorporation of growth factors to induce bone formation could also be printed and used for bone fixation.27,28

Although it is without a doubt that the popularity of PSI will continue to increase in the future, as the technology becomes more accessible and the cost of 3D printing becomes lower, there will still be times when the hardware fails to fit or produce the desired repositioning, or when intraoperative alterations of the planned movements are desired. Therefore, it is still important for young surgeons to go through training in the conventional approach before advancing to orthognathic surgery with PSI.

https://pubmed.ncbi.nlm.nih.gov/36336593/

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