This study aimed to evaluate the accuracy of in-house surgeon-design PSIs and cutting guides for wafer-less positioning of the maxilla in Le Fort I osteotomy. The key findings of this study were 1) the median deviations of the actual maxilla when compared to the planned position in the x, y and z axes, and the inter-canine and inter-molar lines were less than 1mm, which indicate an accurate positioning of the maxilla by the cutting guides and PSIs ; 2) the deviations of the principal axes in pitch, yaw and roll were 1.40o, 0.90o and 0.600, respectively, with pitch significantly less accurate than the other two orientations; 3) there were no difference in accuracy of using PSIs in Le Fort I osteotomy in one-piece or two-piece; and 4) there were no post-operative complications of the PSIs for the Le Fort I osteotomy during the 6-months review period.
Traditional orthognathic surgery planning and execution relies on facebow transfer, stone model surgery, and laboratory-made wafers for positioning of the osteotomized jaws. The inevitable errors of manual record taking and transfer as well as the inadequacy of the articulator to simulate the mandibular movement have proved to be the causes of inaccurate surgical execution [6, 18]. The advancement in virtual planning is a significant breakthrough in orthognathic surgery as it allows surgeons to visualise the bony structure pre-operatively and to plan the surgical movement with precision. Combined with 3D printing, surgical wafers can now be constructed without the need of laboratory transfer of records, thus reducing the potential errors during the process [8]. However, these 3D-printed wafers still led to discrepancies from planned movement due to their reliance on the mandible for the fixation of the maxillary segment. [19]. Imperfect fitting of the surgical wafer to the occlusion, or the difference in the condyle position during the scanning process are also possible errors of a wafer-guided orthognathic surgery [20, 21].
In order to avoid the errors from using a surgical wafer, the concept of wafer-less orthognathic surgery has blossomed. Wafer-less surgery with PSI enables accurate placement of the maxilla independent of the condyle or mandible, and without the need for extraoral reference points. [22]. Several studies on commercial company-designed and fabricated PSIs have demonstrated great potentials. It was shown that these PSIs enabled precise positioning and fixation in maxillary osteotomy [13] with adequate strength and stability [23]. Furthermore, wafer-less PSIs improved the accuracy, predictability and surgical time of orthognathic surgery [24].
However, there are drawbacks of PSI made by commercial companies: 1) the high cost, 2) the long turnaround time that spans from 4 to 6 weeks; and 3) and the surgeon’s lack of control in designing the implant. We discovered that by having our surgeons design the PSI in-house, the disadvantages of contracting commercial PSI can be overcome.
The accuracy of PSIs is one of the most important factors in determining their adoption. Accuracy is measured by comparing the difference between the planned model and the actual postoperative jaw position in linear and angular dimensions. In a systematic review on the accuracy of VSP in orthognathic surgery, it was agreed that linear deviations of less than 2 mm (xyz-axis) between the planned and actual post-operative models were considered acceptable. [24]. It was also stated in the review that the angular accuracy of pitch, yaw and roll of VSP were up to 2.75°, 1.7° and 1.1°, respectively [24]. Previous studies on the accuracy of commercial PSIs showed the difference between planned and actual models were around 1mm [12]. In this study, it is shown that in-house surgeon-designed PSIs could match commercial PSIs in terms of accuracy in the linear angulations. In addition, the deviations of the median angular measurements in pitch, roll and yaw were extremely low (0.6o – 1.4o); indicating the execution of the orthognathic planning was precise.
Another novel finding of this study was that there were no differences in accuracy of PSIs in one-piece or two-piece Le Fort I osteotomy. The cases that require multiple segmentation of Le Fort I (3 or 4 pieces) were not analysed as these procedures are not common in many centres around the world. Moreover, multi-segmentation of Le Fort I may be better fixed with the use of a surgical wafer and customised arch bar, instead of the sole application of PSIs.
One major advantage of designing PSIs in-house is the time saved. In our centre, surgeons receive trainings to design PSIs. On average, a trained surgeon requires only 3 to 4 hours to conduct VSP and design the surgical guides and PSIs for a case. The designs are then sent out for printing, and the products are typically ready in 7 working days. This in-house process is significantly more time-efficient than outsourcing the PSIs to be designed and made. With less time required to prepare for surgery, patient waiting time for operation is shortened and a turnover of cases is higher. Another advantage of designing in-house is that the surgeons can implement specific design features into the PSIs and surgical guides according to their personal preferences. It is also particularly beneficial for junior surgeons to understand the challenges of a case through the planning and designing process.
Safety, as reflected in the incidence of surgical complications, is an important factor to consider when implementing a new treatment modality. Rückschloß et al. suggested that VSP using PSIs can help reduce the risk of post-operative complications such as nerve injury or damaged dental roots because surgeons are able to mark out these structures and plan for the depth of penetration into bone [25]. In this study, there were no cases that presented with infection or exposure of the PSIs, loosening of screws, or incidences that led to removal of the PSIs in the early postoperative period. It proves that the in-house surgeon-designed PSIs are safe for use. An extended follow-up is required to observe if there are any long-term complications.
In conclusion, this study shows that in-house surgeon-designed 3D-printed PSIs for wafer-less Le Fort I osteotomy are accurate in the execution of VSP, with minimal discrepancies in all linear and angular measurements. The pitch is relatively less accurate when compared to the yaw and the roll. There were no complications observed in the early post-operative period. In-house surgeon-designed 3D-printed PSIs can be an alternative to commercial PSIs for wafer-less Le Fort I osteotomy as it shortens the preparation time of surgery, and potentially reduces the surgical cost of the patient or the institute.