Clinical Resarch On Segmental Invisible Technique With Mini-implant For En-masse Retraction Of Maxillary Anterior Teeth

Objective To evaluate the clinical efficiency of segmental invisible technique with mini-implant for en-masse retraction of maxillary anterior teeth on the aspect of vertical and sagittal as well as torque in the treatment of bimaxillary protrusion.Methods Twelve subjects with upper dental alveolar bone protrusion were selected for this study,with the average age of 25.2±5.2 years old,and all required to extract two maxillary premolars and have strong anchorage control.The first treatment stage was conducted with segmental invisible technique:segmental invisible applance in the maxillary arch combined with fixed labial brace in the mandible arch.Maxillary anterior teeth were retracted in the early stage by elastics from the hook on the labial segmental of the canine to the micro-implant between the the second premolar and the first molar maxillary.All were required to take X-ray and plaster casts.Arch-dimension variables including sagittal and vertical varibles were evaluated by cephalometric and plaster casts before and after the first treatment.All data were analyzed by SPSS 20.0 software.Results After an average of 11.6 months’ treatment in the first stage,the profles of the 12 cases changed significantly.(1)For vertical control,U1AP-RL was decreased by 0.80 mm,U1CP-RL was decreased by 1.85 mm,U1E-RL was decreased by 4.54 mm,all the values showed a statistically significant difference.(2)For vertical control,U1E-PP was decreased by 0.78 mm,U1AP-PP was decreased by 0.29 mm,while U1CR-PP was showed no significant difference(P>0.05).(3)Torque values of all the anterior teeth showed a statistically significant decrease.Each change was 8.34° by maxillary incisor,6.05° by maxillary lateral incisor and 5.86° by maxillary canine,respectively.All of the anterior teeth were showed a decreased torque with canine displayed uprighting and central incisor changed the most.Torque of maxillary incisor kept within the normal range,while the canine appeared to be too straight.Conclusion(1)Generally,segmental invisible technique with mini-implant can achieve a good therapeutic effect in early improving the patient’s profile,providing an invisible and aesthetic process meanwhile.(2)Segmental invisible technique produced controlled tipping movement as well as a slight bodily movement.Extrusion of maxillary incisors went with the retraction.However,anterior bite was simply deepened by 0.78mm alone with a slight intrusion in the apical area,and the center of resistance remained unchanged.Therefore,segmental invisible technique is efficient in the vertical control of anterior teeth in the treatment of bimaxillary protrusion.(3)All the anterior teeth showed a decrease in torque values,with maxillary incisors changed greatest and maxillary canines appeared to be straight or even lingual inclined.Segmental invisible technique inevitably led to certain torque loss of the anterior teeth.