Presentation and Evaluation of a Modified Wax-Bite Dental Splint for Surgical Navigation in Craniomaxillofacial Surgery

The effect on the performance of a dynamic navigation system of superimposing a standard tessellation language (STL) file obtained with an intraoral scan on a cone beam computer tomograph (CBCT). An experimental in vitro study

OBJECTIVES

To compare the accuracy and operative time of implant placement using a dynamic computer assisted implant surgery (dCAIS) system based on a cone beam computer tomography (CBCT) image, with and without superimposing a standard tessellation language (STL) file of an intraoral scan of the patient.

METHODS

Ten identical resin models simulating an upper maxilla with posterior edentulism were assigned to two groups. In the CBCT+STL group, a CBCT file and an intraoral STL file were superimposed and used for registration; in the CBCT group, registration was performed using CBCT images. Six implants were placed in each model using the Navident® dynamic navigation system. Anatomy registration was performed by tracing fiducial points on the CBCT or STL image, depending on the group. Preoperative and postoperative CBCT images were overlaid to assess implant placement accuracy.

RESULTS

Sixty implants were analyzed (30 implants in each group). 3D platform deviation was significantly lower (mean difference (MD): 0.17 mm; 95 % confidence interval (CI): 0.01 to 0.23; P = 0.039) in the CBCT+STL group (mean: 0.71 mm; standard deviation (SD): 0.29) than in the CBCT group (mean: 0.88 mm; SD: 0.39). The remaining accuracy outcome variables (angular deviation MD: -0.01; platform lateral deviation MD: 0.08 mm; apex global MD: 0.01 mm; apex depth MD: 0.33 mm) and surgery time (MD: 3.383 min.) were similar in both groups (p > 0.05).

CONCLUSIONS

The introduction of an intraoral scan (STL) seems to reduce deviations slightly in dental implant placement with dCAIS systems. However, the clinical repercussion of this improvement is questionable.

CLINICAL SIGNIFICANCE

Superimposing an intraoral scan on the CBCT image does not seem to increase the accuracy of dCAIS systems but can be useful when radiographic artifacts are present.

A New Technology Using Mixed Reality Surgical Navigation with the Unlocking Closed Reduction Technique Frame to Assist Pelvic Fracture Reduction and Fixation: Technical Note

BACKGROUND

Pelvic ring disruption (PRD) is a serious trauma associated with high mortality and disability rates. Poor reduction can lead to complications such as pelvic deformity and delayed fracture healing. Here, we introduce a new technology using mixed reality surgical navigation (MRSN) with an unlocking closed reduction technique (UCRT) frame to assist pelvic fracture reduction and fixation.

METHODS

Thirty patients with PRD were enrolled in this study. All of the patients underwent preoperative CT scans, with the pelvis and tracker segmented into three-dimensional models. Under MRSN guidance, auxiliary reduction screws were inserted to grasp the pelvic bone. An ideal trajectory for closed reduction was planned, and suitable CS screws were used for stable fixation after good reduction. Operation time, fluoroscopy frequency, and both Matta and Majeed scores were analyzed.

RESULTS

The mean follow-up period was 10.8 months (7.5, 12.25 months) (range 6-24 months). The average duration of operation was 212.5 min (187.5, 272.8 min) (range 133-562 min), and the average reduction time was 23.0 min (15.0, 42.5 min) (range 10-70). The average fluoroscopy frequency was 34.0 times (31.5, 52.5 times) (range 23-68 times). One hundred and fifty screws were successfully inserted on the first attempt. All the fractures healed well with no complications. Excellent reduction quality (Matta score ≤4 mm) was achieved in 29/30 cases, and good reduction quality (Matta score between 4 and 10 mm) was achieved in 1/30 cases. All patients achieved bone healing after an average of 4.0 months (3.5, 5.9 months) (range 3-6), as well as good function recovery with an average Majeed score of 91.0 (87.8, 95.0) (range 71-100).

CONCLUSION

The MRSN technique described improved reduction accuracy and radiation exposure without considerable extension of operation time.

Referencing for intraoperative navigation: Evaluation of human bias

Navigation-assisted surgery is the gold standard for complex reconstructive procedures of the midface and facial skeleton, and artificial and anatomical landmarks are often used for reference. The correct identification of these landmarks before surgery is crucial for the accuracy of the navigation system. This study aimed to investigate the human errors in reference point placement. This retrospective study investigated 228 reference-point positions in 51 cases where navigation was utilized. The discrepancies between the actual reference point-position and manually planned preoperative reference points were quantified using Brainlab iPlanCMF 3.0.6. The referencing methods used in these cases included dental registration splints, osteosynthesis materials, anatomical landmarks, and combinations of these methods. The average discrepancy in the actual and manually planned reference points was 0.29 ± 0.41 mm. The use of anatomical landmarks demonstrated a significantly lower deviation (p < 0.05), although the differences between the errors in reference-point placement using dental registration splints, osteosynthesis materials, or combinations of these methods were not statistically significant. The frequency of misplacement of reference points was significantly higher than expected. These errors might have been caused by human bias during manual placement of the points or intraoperative difficulties caused by extensive metal artifacts. Thus, we postulate that the surgical personnel involved in planning navigation-assisted surgery should undergo intensive training. The development of new referencing methods that are less susceptible to these causes of error might help overcome human bias.

Registration-free workflow for electromagnetic and optical navigation in orbital and craniofacial surgery

The accuracy of intra-operative navigation is largely dependent on the intra-operative registration procedure. Next to accuracy, important factors to consider for the registration procedure are invasiveness, time consumption, logistical demands, user-dependency, compatibility and radiation exposure. In this study, a workflow is presented that eliminates the need for a registration procedure altogether: registration-free navigation. In the workflow, the maxillary dental model is fused to the pre-operative imaging data using commercially available virtual planning software. A virtual Dynamic Reference Frame on a splint is designed on the patient’s fused maxillary dentition: during surgery, the splint containing the reference frame is positioned on the patient’s dentition. This alleviates the need for any registration procedure, since the position of the reference frame is known from the design. The accuracy of the workflow was evaluated in a cadaver set-up, and compared to bone-anchored fiducial, virtual splint and surface-based registration. The results showed that accuracy of the workflow was greatly dependent on tracking technique used: the workflow was the most accurate with electromagnetic tracking, but the least accurate with optical tracking. Although this method offers a time-efficient, non-invasive, radiation-free automatic alternative for registration, clinical implementation is hampered by the unexplained differences in accuracy between tracking techniques.

Virtual splint registration for electromagnetic and optical navigation in orbital and craniofacial surgery

In intra-operative navigation, a registration procedure is performed to register the patient's position to the pre-operative imaging data. The registration process is the main factor that determines accuracy of the navigation feedback. In this study, a novel registration protocol for craniofacial surgery is presented, that utilizes a virtual splint with marker points. The accuracy of the proposed method was evaluated by two observers in five human cadaver heads, for optical and electromagnetic navigation, and compared to maxillary bone-anchored fiducial registration (optical and electromagnetic) and surface-based registration (electromagnetic). The results showed minimal differences in accuracy compared to bone-anchored fiducials at the level of the infra-orbital rim. Both point-based techniques had lower error estimates at the infraorbital rim than surface-based registration, but surface-based registration had the lowest loss of accuracy over target distance. An advantage over existing point-based registration methods (bone-anchored fiducials, existing splint techniques) is that radiological imaging does not need to be repeated, since the need for physical fiducials to be present in the image volume is eradicated. Other advantages include reduction of invasiveness compared to bone-achnored fiducials and a possible reduction of human error in the registration process.

A Splint-to-CT Data Registration Strategy for Maxillary Navigation Surgery

Computer-assisted navigation plays an important role in modern craniomaxillofacial surgery. Although headpins and skull posts are widely used for the fixation of the reference frame, they require the use of invasive procedures. Headbands are easily displaced intraoperatively, thus reducing the accuracy of the surgical outcome. This study reported the utility of a novel splint integrated with a reference frame and registration markers for maxillary navigation surgery. A maxillary splint with a 10 cm resin handle was fabricated before surgery, to fix the reference frame to the splint. The splint was set after the incorporation of fiducial gutta-percha markers into both the splint and resin handle for marker-based pair-point registration. A computed tomography (CT) scan was acquired for preoperative CT-based planning. A marker-based pair-point registration procedure can be completed easily and noninvasively using this custom-made integrated splint, and maxillary navigation surgery can be performed with high accuracy. This method also provides maximum convenience for the surgeon, as the splint does not require reregistration, and can be removed temporarily when required. The splint-to-CT data registration strategy has potential applicability not only for maxillary surgery but also for otolaryngologic surgery, neurosurgery, and surgical repair after craniofacial trauma.

Image-guided cochlear access by non-invasive registration: a cadaveric feasibility study

Image-guided cochlear implant surgery is expected to reduce volume of mastoidectomy, accelerate recovery, and improve safety. The purpose of this study was to investigate the safety and effectiveness of image-guided cochlear implant surgery by a non-invasive registration method, in a cadaveric study. We developed a visual positioning frame that can utilize the maxillary dentition as a registration tool and completed the tunnels experiment on 5 cadaver specimens (8 cases in total). The accuracy of the entry point and the target point were 0.471 ± 0.276 mm and 0.671 ± 0.268 mm, respectively. The shortest distance from the margin of the tunnel to the facial nerve and the ossicular chain were 0.790 ± 0.709 mm and 1.960 ± 0.630 mm, respectively. All facial nerves, tympanic membranes, and ossicular chains were completely preserved. Using this approach, high accuracy was achieved in this preliminary study, suggesting that the non-invasive registration method can meet the accuracy requirements for cochlear implant surgery. Based on the above accuracy, we speculate that our method can also be applied to neurosurgery, orbitofacial surgery, lateral skull base surgery, and anterior skull base surgery with satisfactory accuracy.

Intraoperative Navigation and Cone Beam Computed Tomography for Restoring Orbital Dimensions: A Single-Center Experience

Background

Correction of post-traumatic orbital defects remains a challenge for the maxillofacial surgeon. We examined the added value of combined intraoperative (IO) navigation and IO cone beam computed tomography (CBCT).

Materials and Methods

A retrospective cohort study was performed in all consecutive patients requiring unilateral post-traumatic orbital surgery between January 2012 and December 2018. Patients were divided into 3 groups: IO navigation (NAV), IO-CBCT (CBCT), and IO navigation with IO-CBCT (NAV-CBCT). A detailed description of our workflow is provided. Volumetric comparison of the operated orbit to the contralateral orbit was made with Brainlab.

Results

Of the 81 cases, 22 patients were included (12 males/10 females) with a mean age of 51 years. Three patients were assigned to NAV, 6 to CBCT, and 13 to NAV-CBCT. The reconstructed orbital volume did not significantly differ from the contralateral orbital volume within the 3 groups. The mean difference between the contralateral and the operated orbit was 3.05 cm³, 3.72 cm³, and 1.47 cm³ for NAV, CBCT, and NAV-CBCT, respectively, where only NAV-CBCT showed a significant smaller volumetric difference in comparison to CBCT alone. Gender or age did not correlate with difference in orbital volume. Normal function and aesthetics was seen at 6 weeks postoperative in 0 of 3, 6of 6, and 6 of 13 patients of the NAV, CBCT, and NAV-CBCT, respectively.

Conclusion

Orbital defects can be treated effectively using IO navigation. Although our data could not demonstrate a significant added value of IO-CBCT in cases where IO navigation was used based on volumetric difference alone, the combination of IO-CBCT and IO navigation seems to give the best results considering both volumetric difference and postoperative function and aesthetics. Confirmation in a prospective, randomized trial with a larger sample size is required.

Application of an open position splint integrated with a reference frame and registration markers for mandibular navigation surgery

Navigation surgery plays an important role in modern craniomaxillofacial surgery, but it is difficult to apply navigation surgery to the mandible, due to its mobility. At present, headbands or headpins are widely used for fixation of the reference frame, and three strategies are generally used for the application of navigation surgery to the mandible. This article reports the application of a novel open position splint integrated with a reference frame and registration markers for mandibular navigation surgery as a fourth strategy. Using this custom-made integrated splint, a marker-based pair-point registration procedure was completed easily and non-invasively. Furthermore, the neurovascular canal tract could be easily identified, and the cyst, as well as the surrounding daughter cysts, could be removed with high accuracy. This strategy has potential for widespread clinical application in mandibular navigation surgery.

Application of a non-invasive reference headband and a surgical splint for intraoperative paediatric navigation

The key to the success of surgical navigation based on computer-aided design and computer-aided manufacturing (CAD/CAM) planning is the registration process. This has to be precise and adapted to the surgical needs. However, the application of a conventional rigid skull-fixed navigation star for accurate registration is limited for use in the paediatric population, because of the risk of unstable fixation, dural perforation, and intracranial bleeding. The authors describe their experience with a non-invasive reference headband that was used in combination with a custom-made acrylic resin dental registration splint for resection of a rare infraorbital zygomatic desmoplastic fibroma in a 2-year old patient. This approach appears not to have been reported in the literature to date.