Comparative biomechanical and photoelastic evaluation of different fixation techniques of sagittal split ramus...

The aim of the present study was to comparatively evaluate the resistance and tension areas created after load incidence in different varieties of sagittal split ramus osteotomy fixation techniques.

Fifty synthetic polyurethane hemimandible replicas were subjected to linear loading tests to evaluate 4 fixation techniques of the sagittal split ramus osteotomy using 2-mm system plates and screws. The hemimandibles were fixed with three 90 degrees linear screws, three 60 degrees linear screws, 3 screws in a reversed L arrangement, and one titanium miniplate. Each group was subjected to linear loading using an Instron 4411 servohydraulic mechanical testing unit. The load peak value and peak displacement were measured. Another 4 hemimandible replicas were made of photoelastic resin and subjected to photoelastic analysis after linear loading with a 3-mm displacement.

The results of the mechanical tests showed statistically significant differences between the fixation groups. The linear 90 degrees fixation and the reversed L arrangement presented with greater loading resistance, followed by the linear 60 degrees fixation and miniplates. In relation to the stress distribution in the photoelastic analysis, the fringes were concentrated near the osteotomy and to the lower part of the mandible in the linear 90 degrees -screw system and reversed L arrangement. In the case of the linear 60 degrees screws, most fringes were located around and between the screws. In the case of the miniplates, the fringes were concentrated around the screws near the osteotomy and more distally.

Under the conditions tested, the linear 90 degrees and reversed L arrangements provided the most favorable behavior.