Development of a mandibular motion simulator for total joint replacement

Abstract

Purpose: The purpose of this study was to develop a motion simulator capable of recreating and recording the full range of mandibular motions in a cadaveric preparation for an intact temporomandibular joint (TMJ) and after total joint replacement.

Material and methods: A human cadaver head was used. Two sets of tracking balls were attached to the forehead and mandible, respectively. Computed tomographic (CT) scan was performed and 3-dimensional CT models of the skull were generated. The cadaver head was then dissected to attach the muscle activation cables and mounted onto the TMJ simulator. Realistic jaw motions were generated through the application of the following muscle forces: lateral pterygoid muscle, suprahyoid depressors (geniohyoid, mylohyoid, and digastric muscles), and elevator muscles. To simulate muscle contraction, cables were inserted into the mandible at the center area of each muscle's attachment. To provide a minimum mouth closing force at the initial position, the elevator muscles were combined at the anterior mandible. During mandibular movement, each motion was recorded using a high-resolution laser scanner. The right TMJ of the same head was reconstructed with a total TMJ prosthesis. The same forces were applied and the jaw motions were recorded again. CT scan was performed and 3-dimensional CT models of the skull with TMJ prosthesis were generated.

Results: Mandibular motions, before and after TMJ replacement, with and without lateral pterygoid muscle reattachment, were re-created in a cadaveric preparation. The laser-scanned data during the mandibular motion were used to drive 3-dimensional CT models. A movie for each mandibular motion was subsequently created for motion path analysis. Compared with mandibular motion before TMJ replacement, mandibular lateral and protrusive motions after TMJ replacement, with and without lateral pterygoid muscle reattachment, were greatly limited. The jaw motion recorded before total joint replacement was applied to the mandibular and prostheses models after total TMJ replacement. The condylar component was observed sinking into the fossa during jaw motion.

Conclusion: A motion simulator capable of re-creating and recording full range of mandibular motions in a cadaveric preparation has been developed. It can be used to simulate mandibular motions for the intact TMJ and total joint prosthesis, and to re-create and record their full range of mandibular motions. In addition, the full range of the recorded motion can be re-created as motion images in a computer. These images can be used for motion path analysis and to study the causation of limited range of motion after total joint replacement and strategies for improvement.

FIGURE 1

Temporomandibular joint motion simulator. A, Hardware for temporomandibular joint motion simulator. B, Mounted surrogate skull with an artificial hyoid bone.

FIGURE 2

Lateral pterygoid muscle vector was redirected out of the skull.

FIGURE 3

Vertexes of lateral pterygoid muscles were redirected out of the skull through copper pipes placed on the cranial base above infratemporal fossa. The 3 threaded bars were used to mount the skull onto the simulator.

FIGURE 4

Vectors of suprahyoid muscles were directed to an artificial hyoid bone.

FIGURE 5

Cables were attached to anatomic locations of the suprahyoid muscles.

FIGURE 6

The cadaveric head was prepared and mounted on the temporomandibular joint simulator. The simulator was placed on a fluoroscopic radiographic machine.

FIGURE 7

A handheld high-resolution laser scanner was used to scan the fiducial tracking balls at each interval. The mouth in this figure was in the closed position.

FIGURE 8

The right temporomandibular joint of the same cadaver head was replaced with a total temporomandibular joint prosthesis. A, Fossa component. B, Condyle component.

FIGURE 9

Three-dimensional computer models for studying mandibular motion (A) before and (B) after total temporomandibular joint replacement.

FIGURE 10

Mandibular motion in millimeters (mm) at lower incisor tip before total temporomandibular joint replacement. A, Opening movement (right view). B, Lateral movement (frontal view). C, Protrusive movement (right view).

FIGURE 11

Mandibular motion in millimeters (mm) after right total temporomandibular joint replacement without lateral pterygoid muscle reattachment. A, Opening movement (right view). B, Lateral movement (frontal view). C, Protrusive movement (right view).

FIGURE 12

Mandibular motion in millimeters (mm) after right total temporomandibular joint replacement with lateral pterygoid muscle reattachment. A, Opening movement (right view). B, Lateral movement (frontal view). C, Protrusive movement (right view).

FIGURE 13

Movies of re-created jaw motions of computer models (click each image to activate the movies, available in the online version of the article).

FIGURE 14

Motion recorded before total joint replacement was applied to the mandibular and prosthesis model after total joint replacement. The right figure showed the same motion on an enlarged view with only the top inner half of the fossa and condyle. The condyle sank (penetrated) into the fossa during the jaw motion following the normal path (click each image to activate the movies, available in the online version of the article).