title: The Effect of Tissue Entrapment on Screw Loosening at the Implant/Abutment Interface of External- and Internal-Connection Implants: An In Vitro Study.
abstract: OBJECTIVE
  To compare the removal of torque values of machined implant abutment connections (internal and external) with and without soft tissue entrapment using an in vitro model.
  
  
  METHODS
  Thirty external- and 30 internal-connection implants were embedded in urethane dimethacrylate. Porcine tissue was prepared and measured to thicknesses of 0.5 and 1.0 mm. Six groups (n = 10) were studied: External- and internal-connection implants with no tissue (control), 0.5, and 1.0 mm of tissue were entrapped at the implant/abutment interface. Abutments were inserted to 20 Ncm for all six groups. Insertion torque values were recorded using a digital torque gauge. All groups were then immersed in 1 M NaOH for 48 hours to dissolve tissue. Subsequent reverse torque measurements were recorded. Mean and standard deviation were determined for each group, and one-way ANOVA and Bonferroni test were used for statistical analysis.
  
  
  RESULTS
  All 60 specimens achieved a 20-Ncm insertion torque, despite tissue entrapment. Reverse torque measurements for external connection displayed a statistically significant difference (p < 0.05) between all groups with mean reverse torque values for the control (13.71 ± 1.4 Ncm), 0.5 mm (7.83 ± 2.4 Ncm), and 1.0 mm tissue entrapment (2.29 ± 1.4 Ncm) groups. Some statistically significant differences (p < 0.05) were found between internal-connection groups. In all specimens, tissue did not completely dissolve after 48 hours.
  
  
  CONCLUSIONS
  External-connection implants were significantly affected by tissue entrapment; the thicker the tissue, the lower the reverse torque values noted. Internal-connection implants were less affected by tissue entrapment.
authors.affiliation: Department of Graduate Prosthodontics, New York Presbyterian, Queens, NY.
authors.forename: Helios A
authors.initials: HA
authors.lastname: Zeno
authors.affiliation: Department of Graduate Prosthodontics, New York Presbyterian, Queens, NY.
authors.forename: Renan L
authors.initials: RL
authors.lastname: Buitrago
authors.affiliation: Department of Graduate Prosthodontics, New York Presbyterian, Queens, NY.
authors.forename: Sidney S
authors.initials: SS
authors.lastname: Sternberger
authors.affiliation: Department of Graduate Prosthodontics, New York Presbyterian, Queens, NY.
authors.forename: Marisa E
authors.initials: ME
authors.lastname: Patt
authors.affiliation: Department of Biomaterials and Biomimetics, New York University College of Dentistry, New York, NY.
authors.forename: Nick
authors.initials: N
authors.lastname: Tovar
authors.affiliation: Department of Biomaterials and Biomimetics, New York University College of Dentistry, New York, NY.
authors.forename: Paulo
authors.initials: P
authors.lastname: Coelho
authors.affiliation: Department of Graduate Prosthodontics, New York Presbyterian, Queens, NY.|Department of Graduate Prosthodontics, New York University College of Dentistry, New York, NY.
authors.forename: Kenneth S
authors.initials: KS
authors.lastname: Kurtz
authors.affiliation: Director of Graduate Prosthodontics, New York Presbyterian, Queens, NY.
authors.forename: Frank J
authors.initials: FJ
authors.lastname: Tuminelli
mesh_terms: D000818:Animals; D001863:Bone Screws; D000044:Dental Abutments; D015921:Dental Implants; D003799:Dental Stress Analysis; D013552:Swine; D019415:Torque
chemical_list: D015921:Dental Implants
keywords: Tissue entrapment; gingival entrapment; preload; screw loosening