A Cone-beam CT Study On The Position Changes Of Posterior Teeth Treated With The Cast Splint Herbst Appliance

Objectives: To access the three-dimensional changes of maxillary and mandibular posterior teeth in patients who were treated with the cast splint Herbst appliance in the early permanent dentition with Class II malocclusion characterized by mandibular retrognathia and to provide clinical reference for the control of posterior teeth in the second phase of fixed appliance therapy.Methods: This study selected 21 patients with Class II malocclusion characterized by mandibular retrognathia in the early permanent dentition.The treatment group consisted 11 patients(male 6,female 5,average ages 12.3 years)who were treated with the cast splint Herbst appliance.And the control group consisted 10 patients(male 5,female 5,average ages 12.6 years)who were untreated but observed.Cone-beam computed tomography(CBCT) images were taken before Herbst treatment, immediately after Herbst treatment, before observation and after observation.The 3D reconstructions of each patient were evaluated using the In Vivo5 software packages, and the relevant parameters of maxillary and mandibular posterior teeth in the mesiodistal,vertical and buccolingual direction were measured.In addition, the cephalometric variables were evaluated.The acquired data were then statistically analyzed.Results: 1.Changes of linear measurements in the mesiodistal and vertical direction:the maxillary posterior teeth moved backward,the mandibular posterior teeth moved forward,the maxillary second molars were intruded and the mandibular posterior teeth were extruded at stage T2 than stage T1 in the treatment group,and they all had statistical significance(P<0.05).Though the maxillary first premolars, second premolars and first molars were also intruded, they had no significant differences(P>0.05);The maxillary and mandibular posterior teeth also moved forward andextruded(P>0.05)at stage t2 than stage t1 in the control group(P>0.05).Between the two groups,the maxillary posterior teeth moved backward and were intruded,the mandibular posterior teeth moved forward and were extruded in the treatment group than control group,and they all had statistical significances(P<0.05). 2. Changes of angular measurements in the mesiodistal direction:the distal inclination of the maxillary second molars increased(P<0.05), Though the distal inclination of the other maxillary posterior teeth and the mesial inclination of the mandibular posterior teeth increased at stage T2 than stage T1 in the treatment group, the differences had no statistical significance;the mesiodistal inclination of maxillary and mandibular posterior teeth had no obvious changs(P>0.05) at stage t2 than stage t1 in the control group.Between the two groups,only the distal inclination of the maxillary second molars increased(P<0.05). 3.Changes of angular measurements in the buccolingual direction:the buccal inclination of the maxillary and mandibular posterior teeth increased(P>0.05) at stage T2 than stage T1 in the treatment group;the lingual inclination of the maxillary posterior teeth and the buccal inclination of the mandibular posterior teeth increased(P>0.05) at stage t2 than staget1 in the control group.Between the two groups,the buccolingual inclination of the maxillary and mandibular posterior teeth had no obvious changs(P>0.05). 4.Changes of cephalometric measurements :at stage T2 than stage T1 in the treatment group,A-RL and SNA increased(P>0.05),B-RL,Pog-RL,Go-Pog,Co-Pog, N-Me,ANS-Me,S-Go and OP/SN increased(P<0.05),the wits and ANB decreased(P>0.05);changes of the linear measurements all had statistic differences,but changes of the angular measurements all had no statistic differences at stage t2 than stage t1 in the control group. Between the two groups, the linear measurements increased more(P<0.05) except A-RL(P>0.05) and Wits(P<0.05) in the treatment group than the control group,the angular measurements such as SNA,ANB decreased more(P<0.05),but SNB,OP/SN(P<0.05) incrased more in the treatment group than the control group.Conclusions: The three-dimensional changes of maxillary and mandibular posterior teeth inpatients with Class II malocclusion characterized by mandibular retrognathia treated with the cast splint Herbst appliance were as follows: 1.The mandibular posterior teeth moved forward bodily. The maxillary posterior teeth moved backward bodily, except the maxillary second molars moved backward tiltly. 2.the maxillary molars were intruded and the mandibular posterior teeth were extruded. 3.the buccolingual inclination of the maxillary and mandibular posterior teeth had no obvious changs.