Three-dimensional Cone-beam Computed Tomography Analysis Of Dental And Skeletal Transverse Changes With The Technology Of Mandibular Expansion

Lateral expansion of the mandible is an important way that we obtain arch space.The technology of rapid expansion in the maxillary arch has been widely used at home and abroad.When we grasp appropriate timing of arch expansion in the pure maxillary transverse hypoplasia,treatment effect is often ideal.Different from expanding midpalatal suture in the maxillary,The lower jaw median joint cartilage has begined into a single entity with bone tissue after the birth of 1-1.5 years and can not expand it in puberty.For this reason,mandibular arch expansion has been highly questioned for a long time.However,nowadays mandibular arch expansion technology begin to be widely used in clinical practice,such as the Schwarz appliance,and several studies have reported good clinical results with the technique.Mandibular traditional fixed appliances was modified by professor Zhao guizhi and over hundreds cases has been successfully treated.Currently most scholars believe that the width of the mandibular arch expansion is the effect of buccal inclination of tooth.Would mandibular arch expansion can effect alveolar bone,root and jaw,the stability of treatment and the amount of arch expansion,it has been the focus of attention of orthodontist.In recent years,cone-beam CT and three-dimensional analysis software have enabled us accurately analysis of three-dimensional computer model and become possible for us to accurately evaluate the mandibular arch expansion on the teeth and jaw,which provides an effective means.Three-dimensional model can not only comprehensively and multi-angle observe model but also the accuracy and precision of the measurement is much more higher.Research PurposesThe aim of this study is to evaluate the transverse changes of the crown,CEJ,alveolar proces,root,mandibular body,condylar head and antegonial notch before and after mandibular arch expansion with three-dimensional computer model.From the research,some references are provide for the clinical plan of orthodontic treatment.Research MethodsTwenty-nine young patients with arch narrow and crowding(17 men,12 women,mean age: 10~14 years)treated by the technology of mandibular expansion were selected.CBCT images were made before and after mandibular expansion.All CBCT images were reconstructed and segmented by MIMICS 15.0 image processing software and Geomagic Studio 12 image processing software.We measured the distance between crowns,CEJs,lingual surfaces of the alveolar processes,buccal surfaces of the alveolar processes,inner surface of the mandibular bodies,outer surface of the mandibular bodies,the outermost part of the condylar heads and antegonial notches at the mandibular right and left first molar,second premolar,first premolar and canine.In addition,we assessed the distance between roots in the two-dimensional CBCT.Paired T tests were used to evaluate the changes during mandibular expansion.Results1.The distance between crowns and CEJs showed significant increase after expansion(P<0.05).Mandibular arch width were significantly increased by using mandibular expansion.The range of augment of premolar area is the largest,followed by the molar area,canine area.2.The interbuccal dentoalveolar width and interlingual dentoalveolar width had significant increase as measured from a point 3 mm below the cementoenamel junction(P<0.05).Alveolar bone expansion is similar to the way the expansion of the dental arch.The range of augment of the inter-width of lingual dentoalveolar was greater than the inter-width of lingual dentoalveolar.3.The distance between roots showed a slight increase(P<0.05).The range of augment of inter-width of roots is the least.4.No significant(P>0.05)differences were observed in the inter-widths of the mandibular body.5.No significant(P>0.05)differences were observed in the inter-width of condylar heads,or mandibular antegonial notches.Conclusion1.The mandibular expansion can effectively open space and solve mandibular transverse deficiency and crowding for adolescents.2.The modified mandibular arch expander not only expands the mandibular arch by inclination movement of tooth,but also expands the alveolar process and the root tip.Mandibular body,condylar heads,and mandibular antegonial notches are not significantly affected by the modified expander.3.Useing CBCT and to reconstruct mandibular three-dimensional model show precise changes in internal structures and can not only comprehensively and multi-angle observe model but also the accuracy and precision of the measurement is much more higher.