The phenomenon of bone dehiscences Definitionanterior tooth movement exceeds bony apposition can lead to resorption of the cortical bone and exposure of the root High-risk populationmandible & maxilla protrusion expansion of the maxillary arch Example 1Location of bone-thickness measurements before and after retractionS1S2S3Example 2rotated canines and crowding of the incisors are found in the pretherapeutic mandibular situationcorresponding pretreatment CT examination：3D-reconstructionnarrow frontal mandibular alveolarprocess with thin facial bone platesClinical situation after two years of orthodontic treatmentCorresponding CT examination： 3D-reconstruction extensive facial dehiscences above the roots of the incisors and caninesDental anatomy Alveolar bone proper Supporting alveolar bone Cortical plate Spongy bone bone traces tooth movement?A basic axiom in orthodontics is whenever orthodontic tooth movement occurs, bone around the alveolar socket will remodel to the same extent The truth is In the vertical dimension: during orthodontic tooth extrusion, bone increase is usually less than the dental displacement, leading to an increase in the clinical crown. In the transverse dimension: bone remodeling/tooth movement ratio of tooth retraction with tip and with torque is 1:2 and 1:2.35 respectivelyRepair of the perforation site bone dehiscences were partly repaired in the retention period, but it was insufficient to cover the root completely Repair of the perforation site will lead to relapse of the teethconclusion retraction of the incisors is limited forcing the tooth against the cortical bone may cause adverse sequelae surgical orthodontic treatment should be taked when tooth movement exceed “bone wall”anterior maxillary subapical osteotomyinitial examinationbefore surgery：maxillary first premolars and left mandibular central incisor were extracted. All residual third molars were also extractedafter surgery：anterior maxillary dentoalveolar segment repositioned 4mm posteriorly and 3.5 mm upward.after 2 years of retention：referenceAlexander D. Vardimon, Eyal Oren. Cortical bone remodeling/tooth movement ratio during maxillary incisor retraction with tip versus torque movements. American Journal of Orthodontics and Dentofacial Orthopedics, Volume 114, Number 5 Simten Sarikaya, Bulent Haydar. Changes in alveolar bone thickness due to retraction of anterior teeth. American Journal of Orthodontics and Dentofacial Orthopedics. July 2002 Heinrich Wehrbein, Priv Doz Dr med. Human histologic tissue response after long-term orthodontic tooth movement. American Journal of Orthodontics and Dentofacial Orthopedics, Volume 107, No. 4 Javad Hazrati Marangalou, Farzan Ghalichi. Numerical simulation of orthodontic bone remodeling. orthodontic waves. (2009):64-71 Manabu Miyamoto, Takashi Yamashiro. Surgical orthodontic treatment for severe maxillary protrusion with aggressive periodontitis. orthodontic waves.(2008):171-178Thank you!