Image-guided surgery in oral cancer:toward improved margin control

Purpose of review The aim of this review is to discuss recent studies on the assessment of tumor extension and resection margins by different intraoperative techniques allowing for image-guided surgery of oral cancer. Recent findings There are different in-vivo and ex-vivo intraoperative techniques to improve margin control of which intraoperative ultrasound and targeted fluorescence-guided resections have high potential clinical value and are closest to clinical implementation. In oral cancer surgery, resection margins, particularly deep margins, are often inadequate. Intraoperative frozen section does not improve resection margin control sufficiently. Specimen-driven intraoperative assessment for gross analysis of suspected margins reduces the amount of positive resection margins substantially but leaves still room for improvement. Mucosal staining methods, optical coherence tomography and narrow band imaging can only be used for superficial (mucosal) resection margin control. Spectroscopy is under investigation, but clinical data are scarce. Intraoperative ex-vivo imaging of the resection specimen by magnetic resonance and PET/computed tomography may be used to assess resection margins but needs more research. Intraoperative in-vivo ad ex-vivo ultrasound and targeted fluorescence imaging have high potential clinical value to guide oral cancer resections and are closest to clinical implementation for improved margin control

A Contemporary Approach to Non-Invasive 3D Determination of Individual Masticatory Muscle Forces:A Proof of Concept

Over the past decade, the demand for three-dimensional (3D) patient-specific (PS) modelling and simulations has increased considerably; they are now widely available and generally accepted as part of patient care. However, the patient specificity of current PS designs is often limited to this patient-matched fit and lacks individual mechanical aspects, or parameters, that conform to the specific patient’s needs in terms of biomechanical acceptance. Most biomechanical models of the mandible, e.g., finite element analyses (FEA), often used to design reconstructive implants or total joint replacement devices for the temporomandibular joint (TMJ), make use of a literature-based (mean) simplified muscular model of the masticatory muscles. A muscle’s cross-section seems proportionally related to its maximum contractile force and can be multiplied by an intrinsic strength constant, which previously has been calculated to be a constant of 37 [N/cm2]. Here, we propose a contemporary method to determine the patient-specific intrinsic strength value of the elevator mouth-closing muscles. The hypothesis is that patient-specific individual mandible elevator muscle forces can be approximated in a non-invasive manner. MRI muscle delineation was combined with bite force measurements and 3D-FEA to determine PS intrinsic strength values. The subject-specific intrinsic strength values were 40.6 [N/cm2] and 25.6 [N/cm2] for the 29- and 56-year-old subjects, respectively. Despite using a small cohort in this proof of concept study, we show that there is great variation between our subjects’ individual muscular intrinsic strength. This variation, together with the difference between our individual results and those presented in the literature, emphasises the value of our patient-specific muscle modelling and intrinsic strength determination protocol to ensure accurate biomechanical analyses and simulations. Furthermore, it suggests that average muscular models may only be sufficiently accurate for biomechanical analyses at a macro-scale level. A future larger cohort study will put the patient-specific intrinsic strength values in perspective

Mandibular dental implant placement immediately after teeth removal in head and neck cancer patients

BACKGROUND: Little is known about immediate implant placement in head and neck cancer patients. We studied implant survival and functional outcomes of overdentures fabricated on implants placed immediately after removal of the lower dentition during ablative surgery or preceding primary radiotherapy (RT). METHODS: Inclusion criteria were primary head and neck cancer, dentate lower jaw, and indication for removal of remaining teeth. Two implants to support a mandibular overdenture were placed immediately after extraction of the dentition during ablative surgery, or prior to starting primary radiotherapy. Standardized questionnaires and clinical assessments were conducted (median follow-up 18.5 months, IQR 13.3). RESULTS: Fifty-eight implants were placed in 29 patients. Four implants were lost (implant survival rate 93.1%). In 9 patients, no functional overdenture could be made. All patients were satisfied with their dentures. CONCLUSIONS: Combining dental implant placement with removal of remaining teeth preceding head neck oncology treatment results in a favorable treatment outcome

Prosthodontic rehabilitation of head and neck cancer patients-Challenges and new developments

Head and neck cancer treatment can severely alter oral function and aesthetics, and reduce quality of life. The role of maxillofacial prosthodontists in multidisciplinary treatment of head and neck cancer patients is essential when it comes to oral rehabilitation and its planning. This role should preferably start on the day of first intake. Maxillofacial prosthodontists should be involved in the care pathway to shape and outline the prosthetic and dental rehabilitation in line with the reconstructive surgical options. With the progress of three-dimensional technology, the pretreatment insight in overall prognosis and possibilities of surgical and/or prosthetic rehabilitation has tremendously increased. This increased insight has helped to improve quality of cancer care. This expert review addresses the involvement of maxillofacial prosthodontists in treatment planning, highlighting prosthodontic rehabilitation of head and neck cancer patients from start to finish

Three-Dimensional Guided Zygomatic Implant Placement after Maxillectomy

Zygomatic implants are used in patients with maxillary defects to improve the retention and stability of obturator prostheses, thereby securing good oral function. Prosthetic-driven placement of zygomatic implants is even difficult for experienced surgeons, and with a free-hand approach, deviation from the preplanned implant positions is inevitable, thereby impeding immediate implant-retained obturation. A novel, digitalized workflow of surgical planning was used in 10 patients. Maxillectomy was performed with 3D-printed cutting, and drill guides were used for subsequent placement of zygomatic implants with immediate placement of implant-retained obturator prosthesis. The outcome parameters were the accuracy of implant positioning and the prosthetic fit of the obturator prosthesis in this one-stage procedure. Zygomatic implants (n = 28) were placed with good accuracy (mean deviation 1.73 ± 0.57 mm and 2.97 ± 1.38° 3D angle deviation), and in all cases, the obturator prosthesis fitted as pre-operatively planned. The 3D accuracy of the abutment positions was 1.58 ± 1.66 mm. The accuracy of the abutment position in the occlusal plane was 2.21 ± 1.33 mm, with a height accuracy of 1.32 ± 1.57 mm. This feasibility study shows that the application of these novel designed 3D-printed surgical guides results in predictable zygomatic implant placement and provides the possibility of immediate prosthetic rehabilitation in head and neck oncology patients after maxillectomy

Accuracy Assessment of Pedicle and Lateral Mass Screw Insertion Assisted by Customized 3D-Printed Drill Guides:A Human Cadaver Study

BACKGROUND: Accurate cervical screw insertion is of paramount importance considering the risk of damage to adjacent vital structures. Recent research in 3-dimensional (3D) technology describes the advantage of patient-specific drill guides for accurate screw positioning, but consensus about the optimal guide design and the accuracy is lacking. OBJECTIVE: To find the optimal design and to evaluate the accuracy of individualized 3D-printed drill guides for lateral mass and pedicle screw placement in the cervical and upper thoracic spine. METHODS: Five Thiel-embalmed human cadavers were used for individualized drill-guide planning of 86 screw trajectories in the cervical and upper thoracic spine. Using 3D bone models reconstructed from acquired computed tomography scans, the drill guides were produced for both pedicle and lateral mass screw trajectories. During the study, the initial minimalistic design was refined, resulting in the advanced guide design. Screw trajectories were drilled and the realized trajectories were compared to the planned trajectories using 3D deviation analysis. RESULTS: The overall entry point and 3D angular accuracy were 0.76 +/- 0.52 mm and 3.22 +/- 2.34 degrees, respectively. Average measurements for the minimalistic guides were 1.20 mm for entry points, 5.61 degrees for the 3D angulation, 2.38 degrees for the 2D axial angulation, and 4.80 degrees for the 2D sagittal angulation. For the advanced guides, the respective measurements were 0.66 mm, 2.72 degrees, 1.26 degrees, and 2.12 degrees, respectively. CONCLUSION: The study ultimately resulted in an advanced guide design including caudally positioned hooks, crosslink support structure, and metal inlays. The novel advanced drill guide design yields excellent drilling accuracy