The Effects Of Molar Distalization By Using Clear Aligners

Objective:To evaluate the efficiency of molar distalization in different skeletal types by using clear aligners and analyse the influence factors of the efficiency.Methods:Three cases of adult Class I,Class II and Class III malocclusion with different Sagittal Facial Types were selected,and maxillary or mandibular molars were distalized by applying Clear Aligners to solve the crowding dentition,correct the occlusal relationship and improve facial profile.Three-dimensional measurement by CBCT,the superimposition and analysis of digital models and lateral cephalometric data and superimposition were used to evaluate the efficiency of molar distalization by using clear aligners,to discuss the change of the dentition,the skeleton and the facial profileCase 1: A 20-year-old female presented with a chief complaint of irregular dental alignment,skeletal Class Ⅲ malocclusion with a average GoGn-SN angle,slight mandibular protrusion,mild lip incompleteness,and gummy smile.Bilateral molars were Angle’s Class III malocclusion,and bilateral canines were Angle’s Class I malocclusion.Dentitions were moderate crowding,and archs were narrow.Lateral cephalometric film showed the lingual inclination of the lower anterior teeth,and CBCT images showed that the labiolingual bone plate of the lower anterior teeth was thin.Extracting the third molars and applying clear aligners combined with microscrews to distalize molars providing space for aligning dentition,retracting anterior teeth and correcting occlusal relationship.Controling lower anterior teeth torque to avoid fenestration.Designing mesial inclination to improve the stability of treatment result.Case 2: A 23-year-old male presented with a chief complaint of convex profile,skeletal Class Ⅱ malocclusion with a average GoGn-SN angle,retrusive chin lead to convex profile with a deep chin groove.Maxillary midline was deviated 1 mm accompanying facial asymmetry.Bilateral molars were Angle’s Class Ⅱ malocclusion,and bilateral canines were Angle’s Class Ⅱ malocclusion.Anterior overjet was three degree.Some space in the maxillary dentition,and Spee curve was deep.Extracting themaxillary third molars and applying clear aligners combined with intermaxillary traction to distalize maxillary molars providing space for retracting anterior teeth and correcting occlusal relationship.Designing Power Ridge to express lingual-root torque and move bodily.Designing interproximal enamel reduction in mandibular anterior teeth to solve Bolton index discrepancy,arrange and level dentition.Case 3: A 28-year-old female presented with a chief of irregular dental alignment,skeletal Class Ⅰ malocclusion with a average GoGn-SN angle.Bilateral molars were Angle’s Class Ⅰ malocclusion,and bilateral canines were Angle’s Class Ⅱmalocclusion.Anterior overjet was two degree.Dentitions were moderate crowding.Extracting the third molars and applying clear aligners combined with microscrews to distalize molars providing space for aligning dentition,retracting anterior teeth and correcting occlusal relationship.Mandibular anterior teeth were intruded step by step to solve anterior teeth overbite.Results:Case 1:Molars were distalized significantly after phase 1 treatment.The CBCT measurement results indicated that the mean efficiency of the maxillary molars was77%,while the measurement results of model superimposition was 76.3%。The second maxillary molars occurred mesial inclination and expressed root buccal torque.The treatment achieve dentition alignment,retraction of anterior teeth and improvement of facial profile.The final adjustment for the occlusion is under way.Case 2: Molars were distalized significantly after treatment.The measurement results of model superimposition indicated that the mean efficiency of the maxillary molars was 64.7%.All space was closed,and the torque of anterior teeth were controlled well.Dentition was leveled as the mandibular anterior teeth were intruded abviously.As the inclination of posterior occlusial plane was descreased and the width of the maxillary arch was increased,the position of mandible was forward and the facial profile was improved.Case 3 : Molars were distalized significantly after phase 1 treatment.The measurement results of model superimposition indicated that the mean efficiency of themaxillary molars was 42.6%,while the mandibular molars was 66.1%.The dentition crowding was solved well.The maxillary anterior teeth were retracted,the mandibular anterior teeth were intruded and the anterior overbite was corrected slightly.Further molars distalization is being conducted to correct the canine relationship and the anterior teeth overbite.Conclusions:The efficiency of molars distalization by using clear aligners is pretty good,and the highest and lowest accuracy in the three cases were 96.0% and 42.9% respectively.The accuracy is related to the type of anchorage,the location of anchorage traction point,patient compliance,and the design of treatment perscription including the position of teeth,staging of movement,attachment and IER.