## 2 Materials and Methods  
Ethics approval for this study was received from the Maria Sklodowska-Curie Memorial Cancer Center Ethics Committee in Gliwice (KB 430-15/17). Patients and their legal guardians provided informed consent. A total of 14 patients (10 male/4 female) aged 8-17 years old, treated at our institution between 2015 and 2019 due to malignant/benign tumors or congenital deformities affecting the mandible and TMJ, were enrolled in the study. The protocol for TMJ reconstruction assumed the following: preoperative examination and imaging (orthopantomogram, head and neck, abdomen, pelvis, and lower limb CT scans with contrast), virtual imaging (Figure 1), stereolithographic models, production of 3D custom-made resection templates (Figure 1b,c and Figure 2), and temporomandibular joint implants designed for graft fixation (Figures 1d and 2d) (ChM, Poland, EC Certificate, NO:60099942 0001; ISO 9001:2015, ISO 3485:2016.3).  
Resection of the mandible ramus within the affected TMJ with/without the body of the mandible was performed through the conventional submandibular approach, and exposure of the TMJ was performed through the conventional preauricular approach. Facial nerve branches were identified and preserved using intraoperative neuromonitoring. Prior to resection osteotomy, customized surgical templates were applied in order to ensure a precise cut and adjust the osteotomy line to the graft (Figure 2a). The microvascularized bone graft was harvested either from the fibula (fibula free flap (FFF)) or iliac crest (iliac crest free flap (ICFF)) with use of customized resection templates to obtain the desired amount and shape of the graft (Figure 2b,c). After resection, the microvascularized graft was conventionally connected to the facial and/or temporal vessels in order to provide sufficient blood supply, connected to the 3D customized TMJ prosthesis and stabilized by the titanium reconstruction plate 2.0 (ChM, Bialystok, Poland) (Figure 2d).  
Figure 1: Virtual imaging and planning, with: (**a**) planning of the resection area; (**b**) surgical guideway for resection osteotomies; (**c**) surgical guideway for graft harvesting osteotomies; and (**d**) microvascularized graft supported with customized temporomandibular joint (TMJ) prosthesis consisting of polymeric glenoid fossa and titanium, and osteosynthesis trauma plate 2.0 (ChM, Bialystok, Poland).  
After the surgery, a control orthopantomogram and CT scan were performed in order to confirm the proper positioning of the graft and prosthesis. During the postoperative period the viability of the osteecutaneous free flaps was assessed via clinical monitoring (Doppler imaging and physical examination): the flap was inspected every hour on the first day and every 3-5 h for the next 4 days. Mean postoperative downtime was 10-14 days. All patients were referred to physiotherapy shortly after the surgery. During the preoperative and follow-up periods, maximal interincisal opening (MIO), lateral deflation on the reconstructed side, asymmetry, and growth of the operated and contralateral sides were measured (orthopantomogram, cephalometric X-ray superimposition, CT scans). The patients were functionally assessed by examining masticatory function, speech, and aesthetic appearance. Microplates were removed 3-6 months after the surgery in order to allow further sufficient growth of the mandible. Statgraphics Centurion XVI, StarPoint Technologies INC., The Plains, VA, USA, was used for statistical analyses. Linear regression analysis and one-way analysis of variance were used to evaluate the clinical material. Statistical significance was established at \(p<0.05\).