Rapid progress of digital technologies in the field of measurement, recognition and manufacturing has led to innovations in medical care systems. In dentistry, digital technologies such as optical scanning, CAD/CAM, and digital imaging simulation have been widely used in the workflow of prosthodontics and dental implant treatment. The application of digital technology to maxillofacial reconstructive treatment is expected to bring great benefits and effectiveness.
Maxillofacial reconstructive treatment needs a multi-disciplinary approach with seamless collaboration among various specialists from medical and dental fields. Digital workflows and digital platforms are effective and essential tools for providing the patients’ information and fixed images of the treatments and their outcomes to all participating staff, in addition to morphological image visualization, prosthetic and surgical simulation, manufacturing of prostheses and surgical operation tools, and data accumulation. Tohoku University Hospital has already set up a team-approach system based on such a digital workflow and platform, which is accelerating close cooperation in maxillofacial reconstructive treatment.
Currently, the accuracy and precision of digital scanning and manufacturing of dental devices are not enough and need to be improved, but are acceptable for maxillofacial reconstruction.
Therefore, the introduction and deployment of a digital workflow and platform in maxillofacial reconstruction is an urgent and important task.

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The primary goal of mandibular reconstruction is to restore function and esthetics. Reconstruction with free fibular flaps following segmental mandibulectomy is the gold standard because of its high success rate, however, it requires a long and complex procedure. It has recently been reported that digital technologies and virtual simulations using computer-aided design （CAD） and computer-aided manufacturing （CAM） have improved the outcomes. Here, we report the procedure for mandibular reconstruction using three-dimensional （3D） models and an alignment tray manufactured in-house.
In patients with mandibular gingival cancer who needed to undergo segmental resection and reconstruction with free fibular flaps, the surgery was performed with virtual planning using resection guides and the alignment tray. These devices are superior in terms of cost performance, and can simplify each procedure, facilitating positioning of the donor bone with plate fixation and reproduction of the mandible. In conclusion, the technique using the alignment tray is simple, and has the potential to offer more predictable outcomes for esthetics.

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Maxillofacial reconstruction after tumor resection has become challenging due to patients’ demand for restoration of esthetics and oro-pharyngeal functions. It requires radical resection of the tumor, stable bone fixation, well-vascularized soft tissue coverage, and minimized postoperative deviation of the mandible. To achieve these goals, specialists in various fields should work together and create multidisciplinary treatment plans for patients. Especially, surgeons and maxillofacial prosthodontists must discuss the design of the reconstructive surgery with the desired prosthetics in mind because surgical results greatly affect maxillofacial prosthodontics rehabilitation. Advances in digital technology, such as surgical simulation and 3D printing, have improved understanding of the surgical process and prediction of postoperative conditions. In our hospital, a digital workflow has been introduced to maxillofacial reconstruction in order to facilitate surgical planning and postoperative rehabilitation.
This article describes a multidisciplinary approach to maxillofacial reconstruction using a digital workflow and reports the role of the maxillofacial prosthodontist in the approach.

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There are various types of medical digital support systems such as CAD/CAM devices, 3D printers and intraoral scanners. Especially in the field of dental prosthesis, it is possible to produce prostheses using only a digital system without using impression materials or plaster models.
In maxillofacial prosthetics, 3D printer modeling models have been used for preoperative simulation and patient explanation. Especially in preoperative simulations of surgical procedures, medical support based on visualization models using CT images is increasing year by year. In addition to visualization support, it is possible to use digital technologies in a wide range such as for performing surgical procedures using a surgical guide designed after digital simulation. However, there are many unsettled approaches and utilization methods, and further possibilities and developments are expected. In this paper, from the viewpoint of a dental technician, we explain how digital technology is actually used in maxillofacial reconstruction medicine.

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Nasal air leakage during pronunciation and eating in maxillectomy patients reduces their quality of life. However, an objective evaluation of the sealing effect of wearing an obturator prosthesis has yet to be established. We aimed to verify the sealing effect of obturators by comparing intraoral air pressure （IAP） and sound pressure （SP） between with and without obturators as well as with healthy people.
The participants were seven maxillectomy patients with obturators and 15 healthy young volunteers. IAP was measured by miniature digital atmospheric pressure sensors placed on their palates with denture adhesive. SP was measured using a voice-level meter. Each subject was asked to pronounce the plosive sound /pa/ 10 times. The mean maximal IAP in maxillectomy patients with obturators was significantly higher than that without obturators. Wearing obturators significantly increased IAP. No differences in mean maximal SP were observed among the three groups, i.e. with/without obturators and healthy volunteers. Positive, moderate to strong correlations between IAP and SP were found in the healthy participants and maxillectomy patients without obturators, indicating that IAP was affected by SP. From these results, it was suggested that the sealing effect of obturators could be inferred from the relationship between IAP and SP.

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The purpose of this study is to evaluate the effects of different types of direct retainers on the strain around the abutment teeth in a maxillectomy model using strain gauge measurements.
A simulated unilateral left-side maxillectomy model and prosthesis were fabricated. A triaxial strain gauge on #11 and uniaxial strain gauges on #14, #15, #16 and #17 were fixed on the model to determine the deformation under two conditions: a dislodgement force and a vertical occlusal load. A 0.9 mm wire clasp （WC）, an O-ring attachment （OP） and a magnetic attachment （MA） were applied as a direct retainer on #11. The magnitudes of each strain, the maximum principle strains （MPSs） and their directions were statistically analyzed by one-way ANOVA with a post hoc Bonferroni test.
In the dislodgement test, the MPSs of the OP were significantly smaller than those of the WC and MA in almost all tested conditions. Both the MPS and direction of the WC model were found to be the smallest in the occlusal load test. The results suggest that the design of an anterior direct retainer would directly affect prosthesis movement and the associated stress distribution to the area around the abutment teeth in the model.

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It is important for head and neck tumor patients to maintain their quality of life after tumor resection. These patients may suffer from speech disability, chewing disability, swallowing dysfunction due to mandibular defect, and limited tongue movement and mass after subtotal glossectomy and flap reconstruction. This report describes a preprosthetic surgical treatment including digital surgical simulation and a multidisciplinary approach. Three-dimensional surgical simulation was performed using digitalized CT and study cast images. The combination of skeletal and soft tissue images enables us to predetermine the tissue margin and shape for a mandibular alveoplasty. This method was applied to a 65-year-old male patient who underwent marginal mandibulectomy and rectus abdominal muscle reconstruction, who had limited tongue movement and no space for a prosthesis. Through collaboration among a plastic surgeon, oral surgeon and maxillofacial prosthodontist, a surgical guide was produced from the simulation by a 3D printer, and the mandibular prosthesis was delivered after the alveoplasty. It is suggested that digital simulation and a multidisciplinary approach are effective for installing dentures for patients with head and neck tumors.

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