Ahlgren J, Bendéus M
Swed Dent J Suppl. 1982;15:27-35.
The purpose of this study was to measure cephalometrically the change in muscle length and torque of the masticatory muscles produced by an activator appliance. The study was based on 10 orthodontic cases with distoclusion. Muscle length and force arm (leverage) were measured on two lateral cephalometric roentgenograms of each subject, one with the teeth in centric occlusion and one with an activator between the teeth. The construction bite of the activator was taken with the mandible repositioned 2-3 mm below and 5-6 mm ahead of resting position. It was found that the temporal masseter and medial pterygoid muscles increased 5-15% in length whereas the lateral pterygoid decreased 25% in length with the activator in place. The effect on the force arm on the temporal muscle was small, a decrease of 3-6%, but that on the masseter was much more dramatic, a decrease of 21-22%. Thus, as far as the torque of the temporal muscle is concerned, the small decrease in force arm is well compensated for by the increased muscle tension due to the stretching by the activator. The clinical significance of the findings for obtaining the best construction bite of the activator is discussed.
本研究的目的是通过头影测量法测定功能性矫治器所引起的咀嚼肌长度和扭矩的变化。该研究基于10例远中错（牙合）的正畸病例。在每位受试者的两张头颅侧位X线片上测量肌肉长度和力臂（杠杆），一张是牙齿处于正中咬合位时拍摄的，另一张是牙齿间戴有功能性矫治器时拍摄的。功能性矫治器的建（牙合）咬合是在下颌重新定位到比休息位低2 - 3mm且前方5 - 6mm的位置时取得的。结果发现，当戴用功能性矫治器时，颞肌、咬肌和翼内肌长度增加5% - 15%，而翼外肌长度减少25%。功能性矫治器对颞肌力臂的影响较小，减少了3% - 6%，但对咬肌力臂的影响更为显著，减少了21% - 22%。因此，就颞肌扭矩而言，力臂的小幅减小被功能性矫治器拉伸引起的肌肉张力增加所充分补偿。文中讨论了这些研究结果对于获得功能性矫治器最佳建（牙合）咬合的临床意义。
