Holberg Christof, Mahaini Luai, Rudzki Ingrid
Department of Orthodontics, University of Munich, Munich, Germany.
Angle Orthod. 2007 Jul;77(4):586-94. doi: 10.2319/090505-312.
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.
本研究的目的是通过上颌前牵引治疗来检测中面部和颅底缝线处的应变，并阐明这种拉伸是否表明用于该目的的矫治器具有骨骼效应。
使用有限元模型，模拟不同力水平和方向的上颌前牵引治疗，并测量中面部和颅底缝线处出现的应变（以微应变计）。我们使用的模拟模型由53555个独立单元组成；模拟力为2×3 N和2×5 N，施加力的方向为前方和前尾向。
测得的最大应变平均低于10微应变，仅在鼻骨以及颅底的椭圆形孔和棘孔处，当力的方向为前方时测得较高值（26.4微应变）。当力的方向为前尾向时，测得的值通常较低。
测得的应变平均比弗罗斯特阈值（2000微应变）低约百倍。上颌前牵引治疗时出现的应变似乎不足以刺激任何额外的骨生长。
上颌前牵引治疗良好的临床疗效显然在很大程度上基于牙齿效应，而其骨骼效应仍存疑问。
