Analysis of sutural strain in maxillary protraction therapy

The goal of the study was to examine the strain in the sutures of the midface and the cranial base with maxillary protraction therapy and to clarify whether such stretching suggests a skeletal effect of the apparatus employed for that purpose.

Using a finite elements model, a maxillary protraction therapy was simulated with various force levels and vectors, and the strains appearing at the sutures (in microstrain) were measured at the midface and the cranial base. The simulation model we employed consisted of 53,555 individual elements; the simulated forces were 2 x 3 N and 2 x 5 N, while the vectors of the applied forces were in the anterior and anterior caudal direction.

The maximum measured strains were on average below 10 microstrain, while higher values were measured only at the nasal bone and at the cranial base at the oval and spinous foramina with anterior directed force vectors (26.4 microstrain). With an anterior-caudal force vector, the measured values were usually lower.

The measured strains were on average about hundredfold lower than the Frost thresholds (2000 microstrain). It does not seem probable that the strains occurring upon maxillary protraction therapy suffice to stimulate any additional bone growth.

The good clinical efficacy of maxillary protraction therapy is apparently based, for the most part, on dental effects, while its skeletal effects still remain doubtful.