Objective: The aim of this study was to evaluate the initial reaction of nasomaxillary complex to protraction force using electronic speckle pattern interferometry (ESPI). Materials and methods:The experiment was done on a dry human skull. Orthopedic protraction forces were applied bilaterally at two different levels; one at the occlusal level and the other at about 15 mm above the occlusal plane and the bone response was studied at two different parameters for each point of force application, namely reactions at 0° angulation and 20° downward to the occlusal plane and to two different force magnitudes of 10 ounces (280 gm) and 16 ounces (453.6 gm). The tests were repeated after expansion and the bone response patterns were compared with preexpansion patterns. Results:The results showed that when a protraction force was applied at the occlusal level, maxilla underwent anterior displacement and counterclockwise rotation. Maxilla underwent pure translation without rotational component when the protraction force was applied at 15 mm above the occlusal plane at an angle of 20° downward to the occlusal plane with activation of the rapid expansion screw by quarter turn. The image obtained during translation was used to locate the center of resistance of nasomaxillary complex. Conclusion:The study highlighted the importance of expanding the maxilla prior to or during the application of protraction force. ESPI is a valuable tool in the evaluation of initial bone response following orthopedic traction in orthodontics.

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