Biomechanical In Vitro Study on the Stability of Patient-Specific CAD/CAM Mandibular Reconstruction Plates: A Comparison Between Selective Laser Melted, Milled, and Hand-Bent Plates

Abstract

Study design: An experimental in vitro study.

Objective: Plate fractures are a recurrent problem in alloplastic mandibular reconstruction. Hypothetically it can be assumed that computer-aided design (CAD)/computer-aided manufacturing (CAM) reconstruction plates have a higher stability than conventional hand-bent plates. The aim of the study was to compare additive and subtractive fabricated CAD/CAM mandibular reconstruction plates as well as conventional plates with regard to their biomechanical properties.

Methods: In a chewing simulator, plates of 2 conventional locking plate systems and 2 CAD/CAM-fabricated plate systems were compared. The plates were loaded in a fatigue test. The maximum number of cycles until plate fracture and the plate stiffness were compared.

Results: While all conventional plates fractured at a maximum load between 150 and 210 N (Newton) after a number of cycles between 40 000 and 643 000, none of the CAD/CAM plates broke despite a nearly doubled load of 330 N and 2 million cycles. Both CAD/CAM systems proved to be significantly superior to the hand-bent plates. There was no difference between the 2 CAD/CAM systems.

Conclusions: Concerning the risk of plate fracture, patient-specific CAD/CAM reconstruction plates appear to have a significant advantage over conventional hand-bent plates in alloplastic mandibular reconstruction.

Keywords: CAD-CAM; biomechanics; mandibular reconstruction; patient-specific implants.

Figure 1.

Prepared experimental models of the tested plate systems: (A) DePuy Synthes MatrixMANDIBLE, (B) KLS Martin ThreadLock, (C) DePuy Synthes TruMatch, and (D) KLS Martin UNIQOS (N = 10 each).

Figure 2.

Labeling of the plate sections using a DePuy Synthes MatrixMANDIBLE plate (group A) as an example. The dotted lines mark the shortening points and the crosses the removed plate sections. The holes were numbered starting from the shortened ramus segment. The KLS Martin ThreadLock plates (group B) have 6 holes in the ramus segment and 20 in the corpus segment and have been shortened and labeled analogously to 4 holes in the ramus and 19 holes in the corpus segment. The screws were numbered in the same way as the holes.

Figure 3.

A, Schematic picture of the experimental setup with (not yet resected) jaw model. B, Finished trial setup.

Figure 4.

Fracture of a DePuy Synthes MatrixMANDIBLE plate (group A). The picture shows a typical fracture location proximate to the resection margin (between screw holes 18 and 19).

Figure 5.

The 3 determined straight lines are shown. They visualize the elastic deformation behavior of the plate systems, that is, the deformation in mm (maximum vertical displacement) as a function of the maximum load in Newton (N). As explained in the text, no straight-line equation could be determined for group B (KLS Martin ThreadLock). Thus, for the complete picture the mean value of the first force level (150 N) of group B is displayed.