title: Periodontal effects of rapid maxillary expansion with tooth-tissue-borne and tooth-borne expanders: a computed tomography evaluation.
abstract: BACKGROUND
  The force delivered during rapid maxillary expansion (RME) produces areas of compression on the periodontal ligament of the supporting teeth. The resulting alveolar bone resorption can lead to unwanted tooth movement in the same direction. The purpose of this study was to evaluate periodontal changes by means of computed tomography after RME with tooth-tissue-borne and tooth-borne expanders.
  
  
  METHODS
  The sample comprised 8 girls, 11 to 14 years old, with Class I or II malocclusions with unilateral or bilateral posterior crossbites Four girls were treated with tooth-tissue-borne Haas-type expanders, and 4 were treated with tooth-borne Hyrax expanders. The appliances were activated up to the full 7-mm capacity of the expansion screw. Spiral CT scans were taken before expansion and after the 3-month retention period when the expander was removed. One-millimeter thick axial sections were exposed parallel to the palatal plane, comprising the dentoalveolar area and the base of the maxilla up to the inferior third of the nasal cavity. Multiplanar reconstruction was used to measure buccal and lingual bone plate thickness and buccal alveolar bone crest level by means of the computerized method.
  
  
  CONCLUSIONS
  RME reduced the buccal bone plate thickness of supporting teeth 0.6 to 0.9 mm and increased the lingual bone plate thickness 0.8 to 1.3 mm. The increase in lingual bone plate thickness of the maxillary posterior teeth was greater in the tooth-borne expansion group than in the tooth-tissue-borne group. RME induced bone dehiscences on the anchorage teeth's buccal aspect (7.1 +/- 4.6 mm at the first premolars and 3.8 +/- 4.4 mm at the mesiobuccal area of the first molars), especially in subjects with thinner buccal bone plates. The tooth-borne expander produced greater reduction of first premolar buccal alveolar bone crest level than did the tooth-tissue-borne expander.
authors.affiliation: Department of Orthodontics, University of São Paulo, Brazil. dgarib@uol.com.br
authors.forename: Daniela Gamba
authors.initials: DG
authors.lastname: Garib
authors.forename: José Fernando Castanha
authors.initials: JF
authors.lastname: Henriques
authors.forename: Guilherme
authors.initials: G
authors.lastname: Janson
authors.forename: Marcos Roberto
authors.initials: MR
authors.lastname: de Freitas
authors.forename: Adriano Yacubian
authors.initials: AY
authors.lastname: Fernandes
mesh_terms: D000293:Adolescent; D016301:Alveolar Bone Loss / Q000000981:diagnostic imaging / Q000209:etiology*; D002508:Cephalometry; D002648:Child; D003799:Dental Stress Analysis; D005260:Female; D006801:Humans; D052280:Orthodontic Anchorage Procedures / Q000009:adverse effects*; D010155:Palatal Expansion Technique / Q000009:adverse effects* / Q000295:instrumentation*; D010513:Periodontal Ligament / Q000503:physiopathology; D036542:Tomography, Spiral Computed