Mandibular Reconstruction after Resection of Ameloblastoma by Custom-Made CAD/CAM Mandibular Titanium Prosthesis: Two Case Reports, Finite Element Analysis and Discussion of the Technique

Abstract

Virtual surgical planning for CAD/CAM mandibular reconstruction by titanium prosthesis was recently reported for resected cases. Even if some advantages are evident, difficulties that may arise for TMJ function after reconstruction originate from prosthesis contamination through oral mucosa dehiscence. In these two cases reported of mandibular reconstruction after resection of ameloblastoma by custom-made CAD/CAM titanium prosthesis, the procedures were aimed to preserve the TMJ glenoid cavity and articular disc avoiding functional problems for hemi-mandibular resections that included the condyle (as in case #1) or with condylar preservation (as in case #2) and avoiding intraoral incisions in both cases. The entire surgical planning and prosthetic fabrication were explained with specifications and the sequence of the surgical procedure. Finite elements analysis (FEA) was performed to check the force distribution and efficacy of the prosthetic device (case 1 with hemi-mandibular resection and rehabilitation). Although successful in these two cases, surgical reconstruction of the mandibular defect after resection by a CAD-CAM custom-made prosthesis still shows some drawbacks and failure risks. Several advantages of this technique and the surgical success in these two cases were presented, but limitations and side effects must be considered when cases are selected.

Keywords: CAD-CAM; ameloblastoma; mandible; prosthesis; reconstruction; titanium.

Figure 1

Pre-surgical frontal clinical view of the extraoral asymmetry of the lower third of the face.

Figure 2

Pre-surgery panoramic X-ray showing a wide radiolucent lesion extending from dental elements 4.5 to the entire right mandible ramus involving the right mandibular body.

Figure 3

CT scan 3D reconstruction showing the huge lesion extending from dental elements and 5 to the entire right mandible ramus involving the right mandibular body and the alveolar nerve canal, with perforations of the cortical bone wall on both buccal and lingual sides.

Figure 4

Simulation of the general shape of the mandibular prosthesis delineated from the mirrored image of the unaffected side on 3D models. (a) inferior view; (b) frontal view.

Figure 5

CAD-CAM custom-made hemi-mandibular prosthesis.

Figure 6

Finite element analysis (FEA) showing von Mises stress concentration on the prosthesis on the conjunction margin of the plate with the first lower right screw (the peak stress was 50 MPa) and on the interior surface of the condylar portion of the plate (the peak stress was 50 MPa). FEA was conducted assuming a static load of 600 N on the central incisors (purple arrows) also resulting in an upward load on both condylar surfaces for elevator muscles action (orange arrows).

Figure 7

Intra-operative sequence: (a) intra-operative view: trans-cutaneous access in the submandibular area. (b) Positioning of the custom-made surgical guide. (c) Preservation of the articular disc. (d) Positioning of the custom-made mandibular prosthesis.

Figure 8

(a) Post-surgical frontal clinical view of the restored symmetry of the lower third of the face. (b) Post-surgery panoramic X-ray of the mandibular prosthesis positioning.

Figure 9

Pre-surgery panoramic X-ray showing a wide radiolucent lesion involving the body and ramus of the right mandible.

Figure 10

CT scan 3D reconstruction showing the ameloblastoma lesion involving the body and ramus of the right mandible.

Figure 11

(a) Simulation of the general shape of the mandibular prosthesis delineated from the mirrored image of the unaffected side on 3D models in frontal view; (b) CAD-CAM custom-made mandibular prosthesis.

Figure 12

(a) Post-surgery view of intraoral rehabilitation. (b) Post-surgery panoramic X-ray of the positioned mandibular prosthesis.