Stress distribution in the temporomandibular joint after mandibular protraction: a 3-dimensional finite element study. Part 2.

INTRODUCTION: Patterns of stress generation in the temporomandibular joint (TMJ) after mandibular protraction with a construction bite of 5 mm advancement and 4 mm opening were investigated by using a 3-dimensional finite element method; the results were reported in Part 1. In Part 2, the effects of varying the construction bite are reported.

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). Sagittal advancement was 5 mm, as in Part 1; however, the vertical openings of the construction bite were changed from 4 mm to 2 and 6 mm. The stresses thus obtained were compared for differences in magnitude and pattern.

RESULTS: Tensile stresses migrated more posteriorly on the condylar head with increased bite height. The locations of the tensile stresses in the glenoid fossa were similar in all simulations. The TMJ as a whole showed increased loading with the increasing vertical openings.

CONCLUSIONS: This study indicates that increasing the construction bite height might give more favorable stress patterns in the TMJ, thereby improving the condylar response to functional appliances. The findings of this preliminary study need to be investigated in an animal model and in humans before deriving clinical implications.