title: Experimental in vivo acute and chronic biomechanical and histomorphometrical comparison of self-drilling and self-tapping anterior cervical screws.
abstract: OBJECTIVE
  Self-drilling screws (SDS) and self-tapping screws (STS) allow for quicker bone insertion and are associated with increased anchorage. This is an experimental in vivo comparison of anterior cervical SDS and STS in the post-insertion acute and chronic phases.
  
  
  METHODS
  Thirty C2-C6 vertebrae from six Santa Inês hair sheep were used. Each screw design was randomly assigned to five of each spinal level. Insertion torque was measured using a torque device. Three animals were killed in each phase. Vertebrae were randomly assigned to pullout tests and histomorphometrical bone-screw interface evaluation (percent screw-bone contact and bone density inside and outside the threaded area). Statistical significance was set at P < 0.05.
  
  
  RESULTS
  SDS insertion torque was greater than STS (P = 0.0001). SDS pullout strength was significantly greater than STS in the acute and chronic phases (P = 0.0001, 0.0003, respectively). SDS percent screw-bone contact and inside area bone density were significantly greater in both phases. No outside area bone density differences were observed in either phase.
  
  
  CONCLUSIONS
  SDS had higher insertion torque and better anchorage than STS in both phases. SDS percent bone-screw contact and inside area bone density were higher in both phases.
authors.affiliation: Faculty of Medicine of Ribeirão Preto, Department of Biomechanics, Medicine and Rehabilitation of the Locomotor System, University Hospital, Av. Bandeirantes, 3900, 11º andar, Ribeirao Preto (São Paulo), 14048-900, Brazil, maximilianoporto@ymail.com.
authors.forename: Maximiliano Aguiar
authors.initials: MA
authors.lastname: Porto
authors.forename: Patrícia
authors.initials: P
authors.lastname: Silva
authors.forename: Rodrigo
authors.initials: R
authors.lastname: Rosa
authors.forename: José Batista
authors.initials: JB
authors.lastname: Volpon
authors.forename: Antônio Carlos
authors.initials: AC
authors.lastname: Shimano
authors.forename: Francisco José Albuquerque
authors.initials: FJ
authors.lastname: de Paula
authors.forename: Helton Luiz Aparecido
authors.initials: HL
authors.lastname: Defino
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D015519:Bone Density; D001860:Bone Plates; D001863:Bone Screws; D002574:Cervical Vertebrae / Q000473:pathology / Q000601:surgery*; D016268:Internal Fixators; D008297:Male; D023421:Models, Animal; D012756:Sheep; D013314:Stress, Mechanical; D019415:Torque