The key to accuracy of zygoma repositioning: Suitability of the SynpliciTi customized guide-plates

Stability of maxillary expansion osteotomy using patient-specific fixation implants without necessitating removable appliances: a retrospective analysis

OBJECTIVE

This study aimed to evaluate the long-term stability of surgical maxillary expansion using patient-specific fixation implants (PSFIs) without intraoral retention.

MATERIALS AND METHODS

Fifteen patients who had undergone segmented Le Fort I osteotomy and PSFIs with available preoperative (t0) early (t1) and 1-year follow-up computed tomography (CT) scans (t2) were evaluated. The early and 1-year 3D models were superimposed to transfer the bony landmarks; the distances between each pair of landmarks at the different time points were then measured. The distances between the canines and second molars were also measured directly on the CT scans.

RESULTS

The achieved maxillary expansions ranged from a median of 4.39 (2.00-6.27) mm at the greater palatine foramina to a median of 2.14 (1.56-2 > 83) mm at the canine level of the palatal bone. One year postoperatively, the changes in skeletal diameters ranged from a median of - 0.53 (- 1.65 to 0.41) mm at the greater palatine foramina (p = 0.12) to 0.17 (- 0.09 to 0.32) mm at the canine level of the palatal bone (p = 0.56). Changes in dental arch diameters ranged from a median of - 0.6 (- 2 to 0.00) mm between the second molars to - 1.3 (- 1.8 to - 0.25) mm between the canines (P < 0.05).

CONCLUSION

This study showed the stability of maxillary expansion osteotomy using PSFIs, even without postoperative intraoral retention.

CLINICAL RELEVANCE

PSFIs are a reliable method for the surgical treatment of transverse maxillary discrepancy. PFSIs are easy-to-use and improve surgical accuracy.

Digital planning and individual implants for secondary reconstruction of midfacial deformities: A pilot study

Objective

To evaluate the feasibility and accuracy of implementing three‐dimensional virtual surgical planning (VSP) and subsequent transfer by additive manufactured tools in the secondary reconstruction of residual post‐traumatic deformities in the midface.

Methods

Patients after secondary reconstruction of post‐traumatic midfacial deformities were included in this case series. The metrical deviation between the virtually planned and postoperative position of patient‐specific implants (PSI) and bone segments was measured at corresponding reference points. Further information collected included demographic data, post‐traumatic symptoms, and type of transfer tools.

Results

Eight consecutive patients were enrolled in the study. In five patients, VSP with subsequent manufacturing of combined predrilling/osteotomy guides and PSI was performed. In three patients, osteotomy guides, repositioning guides, and individually prebent plates were used following VSP. The median distances between the virtually planned and the postoperative position of the PSI were 2.01 mm (n = 18) compared to a median distance concerning the bone segments of 3.05 mm (n = 12). In patients where PSI were used, the median displacement of the bone segments was lower (n = 7, median 2.77 mm) than in the group with prebent plates (n = 5, 3.28 mm).

Conclusion

This study demonstrated the feasibility of VSP and transfer by additive manufactured tools for the secondary reconstruction of complex residual post‐traumatic deformities in the midface. However, the median deviations observed in this case series were unexpectedly high. The use of navigational systems may further improve the level of accuracy.

To evaluate the feasibility and accuracy of implementing three‐dimensional virtual surgical planning (VSP) and subsequent transfer by additive manufactured tools in the secondary reconstruction of residual post‐traumatic deformities in the midface. This study demonstrated the feasibility of VSP and transfer by additive manufactured tools for the secondary reconstruction of complex residual post‐traumatic deformities in the midface. However, the median deviations observed in this case series were unexpectedly high. The use of navigational systems may further improve the level of accuracy.

Three-Dimensional Cephalometric Landmarking and Frankfort Horizontal Plane Construction: Reproducibility of Conventional and Novel Landmarks

In some dentofacial deformity patients, especially patients undergoing surgical orthodontic treatments, Computed Tomography (CT) scans are useful to assess complex asymmetry or to plan orthognathic surgery. This assessment would be made easier for orthodontists and surgeons with a three-dimensional (3D) cephalometric analysis, which would require the localization of landmarks and the construction of reference planes. The objectives of this study were to assess manual landmarking repeatability and reproducibility (R&R) of a set of 3D landmarks and to evaluate R&R of vertical cephalometric measurements using two Frankfort Horizontal (FH) planes as references for horizontal 3D imaging reorientation. Thirty-three landmarks, divided into “conventional”, “foraminal” and “dental”, were manually located twice by three experienced operators on 20 randomly-selected CT scans of orthognathic surgery patients. R&R confidence intervals (CI) of each landmark in the -x, -y and -z directions were computed according to the ISO 5725 standard. These landmarks were then used to construct 2 FH planes: a conventional FH plane (orbitale left, porion right and left) and a newly proposed FH plane (midinternal acoustic foramen, orbitale right and left). R&R of vertical cephalometric measurements were computed using these 2 FH planes as horizontal references for CT reorientation. Landmarks showing a 95% CI of repeatability and/or reproducibility > 2 mm were found exclusively in the “conventional” landmarks group. Vertical measurements showed excellent R&R (95% CI < 1 mm) with either FH plane as horizontal reference. However, the 2 FH planes were not found to be parallel (absolute angular difference of 2.41°, SD 1.27°). Overall, “dental” and “foraminal” landmarks were more reliable than the “conventional” landmarks. Despite the poor reliability of the landmarks orbitale and porion, the construction of the conventional FH plane provided a reliable horizontal reference for 3D craniofacial CT scan reorientation.

Three-Dimensional Custom-Made Surgical Guides in Facial Feminization Surgery: Prospective Study on Safety and Accuracy

BACKGROUND

Facial feminization surgery (FFS) includes several osseous modifications of the forehead, mandible, and chin, procedures that require precision to provide the patient with a satisfactory result. Mispositioned osteotomies can lead to serious complications and poor aesthetic outcomes. Surgical cutting guides are commonly employed in plastic and maxillofacial surgery to improve safety and accuracy. Yet, to our knowledge, there is no report in the literature on the clinical application of cutting guides in FFS.

OBJECTIVES

The authors sought to assess the safety and accuracy of custom surgical cutting guides in FFS procedures.

METHODS

A prospective follow-up of 45 patients regarding FFS with preoperative virtual planning and 3-dimensional custom-made surgical guides for anterior frontal sinus wall setback, mandibular angle reduction, and/or osseous genioplasty was conducted. Accuracy (superimposing preoperative data on postoperative data by global registration with a 1-mm margin of error), safety (intradural intrusion for the forehead procedures and injury of the infra alveolar nerve for chin and mandibular angles), and patient satisfaction were assessed.

RESULTS

A total 133 procedures were documented. There was no cerebrospinal fluid leak on the forehead procedures or any infra alveolar nerve or tooth root injury on both chin and mandibular angle operations (safety, 100%). Accuracy was 90.80% on the forehead (n = 25), 85.72% on the mandibular angles (n = 44), and 96.20% on the chin (n = 26). Overall satisfaction was 94.40%.

CONCLUSIONS

Custom-made surgical cutting guides could be a safe and accurate tool for forehead, mandibular angles, and chin procedures for FFS.

LEVEL OF EVIDENCE: 4

Time-dependent in silico modelling of orthognathic surgery to support the design of biodegradable bone plates

Orthognathic surgery is performed to realign the jaws of a patient through several osteotomies. The state-of-the-art bone plates used to maintain the bone fragments in place are made of titanium. The presence of these non-degradable plates can have unwanted side effects on the long term (e.g. higher infection risk) if they are not removed. Using a biodegradable material such as magnesium may be a possible solution to this problem. However, biodegradation leads to a decrease of mechanical strength, therefore a time-dependent computational approach can help to evaluate the performance of such plates. In the present work, a computational framework has been developed to include biodegradation and bone healing algorithms in a finite element model. It includes bone plates and the mandible, which are submitted to masticatory loads during the early healing period (two months following the surgery). Two different bone plate designs with different stiffnesses have been tested. The stiff design exhibited good mechanical stability, with maximum Von Mises stress being less than 40% of the yield strength throughout the simulation. The flexible design shows high stresses when the bone healing has not started in the fracture gaps, indicating possible failure of the plate. However, this design leads to a higher bone healing quality after two months, as more cartilage is formed due to higher strains exerted in fracture gaps. We therefore conclude that in silico modelling can support tuning of the design parameters to ensure mechanical stability and while promoting bone healing.

Standard and Customized Alloplastic Facial Implants Refining Orthognathic Surgery: Outcome Evaluation

PURPOSE

Conventional orthognathic osteotomies provide appropriate functional outcomes but might be unable to correct midface deficiency, achieve a satisfactory outcome in asymmetrical cases, or allow sufficient chin advancement. We evaluated the outcome of both standard and customized facial high-density porous polyethylene implants used to refine the cosmetic outcome of orthognathic surgery.

PATIENTS AND METHODS

We implemented a retrospective study. The sample was composed of all patients who underwent facial alloplastic augmentation between June 2011 and October 2018 in our department. The complication rate was recorded after a mean follow-up period of 41 months postoperatively, and patient satisfaction was assessed through a qualitative evaluation based on an 11-item questionnaire.

RESULTS

The sample was composed of 24 implants placed in 14 patients: 13 mandibular angle implants, among which 4 were customized; 8 malar implants; and 3 chin implants. No physical complications such as hematoma, infection, migration, or hypoesthesia were observed. Two implants had to be removed because of early unsatisfactory esthetic outcomes. Of 14 patients, 11 answered our questionnaire. Eighty-two percent strongly agreed that the overall outcome was satisfactory.

CONCLUSIONS

The results of this study confirm the low physical complication rate described in the literature, and the esthetic complication rate remains lower than the rates observed in previous reports. A high satisfaction rate was found among patients. The lowest mean satisfaction score was noted for appropriate implant symmetry (3.5), whereas the highest mean satisfaction score (3.8) was achieved when using customized implants. If standard high-density porous polyethylene implants appear to be relevant adjuncts to orthognathic surgery, customized implants seem to achieve higher satisfaction, although their prohibitive cost should be considered.

Development of a novel anatomical thin titanium mesh plate with reduction guidance and fixation function for Asian zygomatic-orbitomaxillary complex fracture

For this study we developed an anatomical thin titanium mesh (ATTM) plate for Asian zygomaticomaxillary complex (ZMC) fracture repair with reduction guidance and fixation function. The ATTM plate profile was designed as an L-shape to fix at the anterior maxilla and lateral buttress of the ZMC. Computer-aided stamping analysis was performed on four screw-hole patterns in the ATTM plate - a control without screw-holes, square screw-holes, double screw-holes, and large-diameter, double screw-holes - using upper/lower dies of averaged ZMC reconstruction models. A regular ATTM plate of 0.6 mm thickness was manufactured and pre-bent using a patient-matched stamping process to verify its feasibility on three ZMC fracture models with one, two, and three fracture segments. The stamping analysis found that the double screw-holes design resulted in the most favorable performance among all the designs because of maximum von Mises stress (408 MPa) under the ultimate tensile strength. Positioning practice showed that the stamped, pre-bent ATTM plate can be used as a reduction guide to provide precise ZMC segment fixation in a completely passive fashion while limiting redundant rotation/micromovement between the separate bones in all directions. This study concluded that the ATTM plate with double screw-hole pattern design, using a patient-matched, pre-bent technique, can fit the ATTM plate/ZMC interface well, decrease mobility of unstable fracture segments, and provide good original facial contour recovery, while improving reduction efficiency.

Customized surgical template fabrication under biomechanical consideration by integrating CBCT image, CAD system and finite element analysis

This study developed a customized surgical template under mechanical consideration for molar intrusion. Two finite element (FE) models were analyzed for the primary stability under 100 gf traction forces with one mini-screw inserted at the buccal side in horizontal and another in palatal side with two optional positions at 60° (P60) or 15° (P15) angles with inclination toward the molar occlusal surface. The surgical template was generated using rapid prototyping (RP) printing for the clinical application based on improved primarily stability model. The surrounding bone strains for models P15 and P60 were far lower than the bone remodeling critical value. Model P60 presented much lower micro-motion in the screw/bone interface and the screw head displacement than those values in model P15. Using FE analysis for biomechanical evaluation and combining with CT image, image superimposed method and CAD technique can fabricate accuracy/security customized surgical template for mini-screws with better primary stability.

Use of the 3D surgical modelling technique with open-source software for mandibular fibula free flap reconstruction and its surgical guides

INTRODUCTION

Tridimensional (3D) surgical modelling is a necessary step to create 3D-printed surgical tools, and expensive professional software is generally needed. Open-source software are functional, reliable, updated, may be downloaded for free and used to produce 3D models. Few surgical teams have used free solutions for mastering 3D surgical modelling for reconstructive surgery with osseous free flaps. We described an Open-source software 3D surgical modelling protocol to perform a fast and nearly free mandibular reconstruction with microvascular fibula free flap and its surgical guides, with no need for engineering support.

PROCEDURE

Four successive specialised Open-source software were used to perform our 3D modelling: OsiriX^®, Meshlab^®, Netfabb^® and Blender^®. Digital Imaging and Communications in Medicine (DICOM) data on patient skull and fibula, obtained with a computerised tomography (CT) scan, were needed. The 3D modelling of the reconstructed mandible and its surgical guides were created.

CONCLUSIONS

This new strategy may improve surgical management in Oral and Craniomaxillofacial surgery. Further clinical studies are needed to demonstrate the feasibility, reproducibility, transfer of know how and benefits of this technique.