Objective To analyze the effects of different traction sites and directions on the maxilla and upper dentition when using clear aligners combined with protraction for the treatment of maxillary deficiency.Methods A three-dimensional(3D)finite element model including the zygomaticomaxillary complex,maxillary dentition,and clear aligners was constructed.The models were divided into Group 1(traction hook at the distal of the lateral incisor)and Group 2(traction hook at the distal of the canine).Each group was analyzed under four loading conditions with protraction angles of 0°,10°,20°,and 30° relative to the occlusal plane.A unilateral protraction force of 500 g was applied.The differences in stress distribution and displacement of the maxillary bone and dentition under different loading conditions were analyzed.Results When the protraction angle was 30°,both groups showed forward and downward displacement of the maxilla,while other angles resulted in counterclockwise rotation.Under the same protraction direction,the total displacement of the maxilla and displacements in all directions in Group 2 were greater than those in Group 1.The upper central incisors in Group 1 showed lingual displacement,which increased with the protraction angle.The maxillary dentition in Group 2 showed forward displacement,with the minimum total and sagittal displacements at a protraction angle of 30°.Stress concentration was mainly observed in the zygomaticomaxillary suture and anterior alveolar bone regions in both groups,decreasing as the protraction angle increased.Conclusions Clear aligners combined with protraction can be applied to skeletal Class Ⅲ patients with mild maxillary deficiency.When the protraction site is located at the distal of the canine with a 30° downward and forward angle to the occlusal plane,the maxilla can achieve ideal forward and downward displacement with the minimum labial movement of the upper anterior teeth.

Objective To analyze the effects of different traction sites and directions on the maxilla and upper dentition when using clear aligners combined with protraction for the treatment of maxillary deficiency.Methods A three-dimensional(3D)finite element model including the zygomaticomaxillary complex,maxillary dentition,and clear aligners was constructed.The models were divided into Group 1(traction hook at the distal of the lateral incisor)and Group 2(traction hook at the distal of the canine).Each group was analyzed under four loading conditions with protraction angles of 0°,10°,20°,and 30° relative to the occlusal plane.A unilateral protraction force of 500 g was applied.The differences in stress distribution and displacement of the maxillary bone and dentition under different loading conditions were analyzed.Results When the protraction angle was 30°,both groups showed forward and downward displacement of the maxilla,while other angles resulted in counterclockwise rotation.Under the same protraction direction,the total displacement of the maxilla and displacements in all directions in Group 2 were greater than those in Group 1.The upper central incisors in Group 1 showed lingual displacement,which increased with the protraction angle.The maxillary dentition in Group 2 showed forward displacement,with the minimum total and sagittal displacements at a protraction angle of 30°.Stress concentration was mainly observed in the zygomaticomaxillary suture and anterior alveolar bone regions in both groups,decreasing as the protraction angle increased.Conclusions Clear aligners combined with protraction can be applied to skeletal Class Ⅲ patients with mild maxillary deficiency.When the protraction site is located at the distal of the canine with a 30° downward and forward angle to the occlusal plane,the maxilla can achieve ideal forward and downward displacement with the minimum labial movement of the upper anterior teeth.