title: BIOMECHANICAL EVALUATION OF THE INFLUENCE OF CERVICAL SCREWS TAPPING AND DESIGN.
abstract: OBJECTIVE
  To assess if the screw design (self-drilling/self-tapping) and the pilot hole tapping could affect the insertion torque and screw pullout strength of the screw used in anterior fixation of the cervical spine.
  
  
  METHODS
  Forty self-tapping screws and 20 self-drilling screws were inserted into 10 models of artificial bone and 10 cervical vertebrae of sheep. The studied parameters were the insertion torque and pullout strength. The following groups were created: Group I-self-tapping screw insertion after pilot hole drilling and tapping; Group II-self-tapping screw insertion after pilot hole drilling without tapping; Group III-self-drilling screw insertion without drilling and tapping. In Groups I and II, the pilot hole had 14.0 mm in depth and was made with a 3mmn drill, while tapping was made with a 4mm tap. The insertion torque was measured and the pullout test was performed. The comparison between groups was made considering the mean insertion torque and the maximum mean pullout strength with the variance analysis (ANOVA; p≤ 0.05).
  
  
  RESULTS
  Previous drilling and tapping of pilot hole significantly decreased the insertion torque and the pullout strength.
  
  
  CONCLUSIONS
  The insertion torque and pullout strength of self-drilling screws were significantly higher when compared to self-tapping screws inserted after pilot hole tapping.
authors.affiliation: Post-graduate Student, School of Medicine, Universidade de São Paulo (USP), Ribeirão Preto, SP, Brazil.
authors.forename: Patricia
authors.initials: P
authors.lastname: Silva
authors.affiliation: Post-graduate Student, School of Medicine, Universidade de São Paulo (USP), Ribeirão Preto, SP, Brazil.
authors.forename: Rodrigo César
authors.initials: RC
authors.lastname: Rosa
authors.affiliation: Professor, Department of Biomechanics, Medicine and Rehabilitation of the Locomotor Apparatus, School of Medicine, Universidade de São Paulo (USP), Ribeirão Preto, SP, Brazil.
authors.forename: Antonio Carlos
authors.initials: AC
authors.lastname: Shimano
authors.affiliation: Professor, Department of Internal Medicine, School of Medicine, Universidade de São Paulo (USP), Ribeirão Preto, SP, Brazil.
authors.forename: Francisco José
authors.initials: FJ
authors.lastname: Albuquerque de Paula
authors.affiliation: Professor, Department of Biomechanics, Medicine and Rehabilitation of the Locomotor Apparatus, School of Medicine, Universidade de São Paulo (USP), Ribeirão Preto, SP, Brazil.
authors.forename: José Batista
authors.initials: JB
authors.lastname: Volpon
authors.affiliation: Professor, Department of Biomechanics, Medicine and Rehabilitation of the Locomotor Apparatus, School of Medicine, Universidade de São Paulo (USP), Ribeirão Preto, SP, Brazil.
authors.forename: Helton Luiz
authors.initials: HL
authors.lastname: Aparecido Defino
keywords: Biomechanics; Bone screw; Orthopedic fixation devices; Spine