Stress distribution in the temporomandibular joint after mandibular protraction: a 3-dimensional finite element method study. Part 1.

INTRODUCTION: This study was designed to evaluate patterns of stress generation in the temporomandibular joint after mandibular protraction, by using a 3-dimensional finite element method. The results of the initial investigation are reported here in Part 1. The effects of varying the construction bite are reported in Part 2.

METHODS: A 3-dimensional computer-aided design model was developed from the magnetic resonance images of a growing boy (age, 12 years), by using I-DEAS NX (version 11.0, Siemens PLM Software, Plano, Tex). The model simulated mandibular protraction, with 5 mm of sagittal advancement and 4 mm of vertical opening. Stress distributions on the condylar neck, the glenoid fossa, and the articular disc in the anteroposterior and mediolateral directions were assessed.

RESULTS: Tensile stresses were located on the posterosuperior aspects and compressive stresses on the anterior and anterosuperior aspects of the condylar head. Tensile stresses were found in the posterior region of the glenoid fossa near the attachment of the posterior connective tissues.

CONCLUSIONS: These results suggest that, on mandibular protraction, the mandibular condyle experiences tensile stresses in the posterosuperior aspect that might help explain condylar growth in this direction. Similarly, on the glenoid fossa, tensile stresses are created in the region of posterior connective tissues; this might be correlated with the increased cellular activity in this region. Further study with variable vertical heights of the construction bites is needed.