Validation of a patient-specific system for mandible-first bimaxillary surgery: ramus and implant positioning precision assessment and guide design comparison

Abstract

In orthognathic surgery, the use of patient-specific osteosynthesis devices is a novel approach used to transfer the virtual surgical plan to the patient. The aim of this study is to analyse the quality of mandibular anatomy reproduction using a mandible-first mandibular-PSI guided procedure on 22 patients. Three different positioning guide designs were compared in terms of osteosynthesis plate positioning and mandibular anatomical outcome. PSIs and positioning guides were designed according to virtual surgical plan and 3D printed using biocompatible materials. A CBCT scan was performed 1 month after surgery and postoperative mandibular models were segmented for comparison against the surgical plan. A precision comparison was carried out among the three groups. Correlations between obtained rami and plates discrepancies and between planned rami displacements and obtained rami discrepancies were calculated. Intraoperatively, all PSIs were successfully applied. The procedure was found to be accurate in planned mandibular anatomy reproduction. Different guide designs did not differ in mandibular outcome precision. Plate positional discrepancies influenced the corresponding ramus position, mainly in roll angle and vertical translation. Ramus planned displacement was found to be a further potential source of inaccuracy, possibly due to osteosynthesis surface interference. Computer-assisted designed and manufactured (CAD/CAM) devices-widely known as Patient Specific Implants (PSIs)-have been increasingly adopted for orthognathic surgery, as per recent evidence in Literature of gaining better accuracy for virtual planning transfer to the patient (

PSI-Guided Mandible-First Orthognathic Surgery: Maxillo-Mandibular Position Accuracy and Vertical Dimension Adjustability.

“…The present protocol was approved by the Sant'Orsola-Malpighi University Hospital ethics committee (approval number 238/2012/0/Disp PL02, amended 18/10/2016); the study conformed to the principles of the Declaration of Helsinki. Written informed consent was obtained from all the patients upon enrollment in the trial 2 .…”

“…1B). Three guide types were used throughout the trial and were compared in our previous work on this cohort of patients 2 . The custom 3D-printed titanium alloy (Ti6Al4V) plates were designed to fixate the proximal and distal mandibular fragments in their planned positions using the screw fixation holes, drilled according to the positioning guides, as reference.…”

“…These movements were determined aligning the planned model to the post-operative result via ICP alignment and colorimetric map inspection (Fig. 3B, C), then evaluating the translational shift and the rotation of the model according to Euler angles convention 2 . The signed discrepancies were tabulated applying conventional signs.…”

“…While part of the advantages has not been demonstrated, the increased intraoperative flexibility offered by this approach in terms of vertical correction is counterbalanced by its reliance on the exactness of the post-osteosynthesis spatial relationship between proximal and distal mandibular segments. In the pursuit of a solution to such issue, we combined the mandible-first approach with a PSI-guided mandibular procedure and demonstrated that it leads to a satisfactory reproduction of the planned mandibular anatomy 2 . Current literature on mandibular and bimaxillary PSI-guided orthognathic surgery is still poor, and the potential failure due to dental interferences caused by combined maxillary and mandibular inaccuracies beyond the surgeon's level of control, has been reported but has not been extensively investigated yet 3,4 .…”

PSI-Guided Mandible-First Orthognathic Surgery: Maxillo-Mandibular Position Accuracy and Vertical Dimension Adjustability

“…In the pursuit of a technique which could reliably reproduce the digitally planned spatial relationship between the mandibular condyle-bearing segments and teeth-bearing segment, we combined the mandible-first approach with a PSI-guided mandibular procedure and demonstrated that it leads to a satisfactory reproduction of the planned mandibular anatomy [2].…”