Abstract: Abstract Objective: To study the 3D direction movement and the expression efficiency of molar distalizaiton with bracketless invisible appliance. Methods: Adult patients of Angle Class I and Angle Class II were selected to use bracketless invisible appliance for molar distalization. Among them, group Angle Class I (9 cases), with the average age of 23 years old, make maxillary and mandibular molar distal movements. Group Angle Class II (10 cases), with the average age of 24 years old, make maxillary molar distal movement. The lateral cephalometric radiographs were taken before and after the treatment of molars, and calculate movement distance, angle, movement effciency, anchorage loss of anterior teeth in three dimensional direction. Statistical analysis of all data.Results: Angle Class II: the distal maxillary expression rate of the first molar and second molar were 65.86% and 71.68%. Angle Class I: the distal maxillary expression rate of the first molar and second molar were 73.88%and 77.73%. The distal mandibular expression rate of the first molar and second molar were 69.1% and 75.03%. There is a certain degree of molar distal titl and vertical upward intruding. There was no significant loss of anchorage in anterior teeth. Conclusion: The use of the bracketless invisible appliance is effective in molar distalizatioin, but with a certain degree of molar distal tilt, vertical upward intruding; the anchorage of anterior teeth is basically intact.

Key words: clear aligners, molar distal movement, lateral cranial radiograph, cephalometric measurement, expression efficiency