title: Effects of abutment screw coating on implant preload.
abstract: OBJECTIVE
  The aim of the present study was to investigate the effects of tungsten carbide carbon (WC/CTa) screw surface coating on abutment screw preload in three implant connection systems in comparison to noncoated titanium alloy (Ta) screws.
  
  
  METHODS
  Preload of WC/CTa abutment screws was compared to noncoated Ta screws in three implant connection systems. The differences in preloads were measured in tightening rotational angle, compression force, initial screw removal torque, and postload screw removal torque after 1 million cyclic loads. Preload loss percent was calculated to determine the efficacy of maintaining the preload of two abutment screw types in relation to implant connection systems.
  
  
  RESULTS
  WC/CTa screws provided 10 degrees higher tightening rotational angle than Ta screws in all three connection systems. This difference was statistically significant (p < 0.05). External-hex butt joint implant connections had a higher compression force than the two internal conical implant connections. WC/CTa screws provided a statistically significantly higher compression force than Ta screws in all three implant connections (p < 0.05). Ta screws required statistically higher removal torque than WC/CTa screws in all three implant connections (p < 0.05); however, Ta screws needed statistically lower postload removal torque than WC/CTa screws in all three implant connections (p < 0.05). Ta screws had a statistically higher preload loss percent than WC/CTa screws in all three implant connections (p < 0.05), indicating that WC/CTa screws were superior in maintaining the preload than Ta screws.
  
  
  CONCLUSIONS
  Within the limits of present study, the following conclusions were made: (1) WC/CTa screws provided higher preload than noncoated Ta screws in all three implant connection systems. (2) The initial removal torque for Ta screws required higher force than WC/CTa screws, whereas postload removal torque for Ta screws was lower than WC/CTa screws. Calculated Ta screw preload loss percent was higher than for WC/CTa screws, suggesting that WC/CTa screws were more effective in maintaining the preload than Ta screws. (3) Internal conical connections were more effective in maintaining the screw preload in cyclic loads than external-hex butt joint connections.
authors.affiliation: Department of Prosthodontics, School of Dentistry, Pusan National University, Busan, South Korea.
authors.forename: Jae-Kyoung
authors.initials: JK
authors.lastname: Park
authors.forename: Jin-Uk
authors.initials: JU
authors.lastname: Choi
authors.forename: Young-Chan
authors.initials: YC
authors.lastname: Jeon
authors.forename: Kyung-Soo
authors.initials: KS
authors.lastname: Choi
authors.forename: Chang-Mo
authors.initials: CM
authors.lastname: Jeong
mesh_terms: D002244:Carbon / Q000737:chemistry; D020099:Coated Materials, Biocompatible / Q000737:chemistry*; D000044:Dental Abutments; D003722:Dental Alloys / Q000737:chemistry; D015921:Dental Implants; D003764:Dental Materials / Q000737:chemistry*; D017267:Dental Prosthesis Design; D003799:Dental Stress Analysis / Q000295:instrumentation; D006801:Humans; D008422:Materials Testing; D012399:Rotation; D013314:Stress, Mechanical; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry; D019415:Torque; D017973:Tungsten Compounds / Q000737:chemistry
chemical_list: D020099:Coated Materials, Biocompatible; D003722:Dental Alloys; D015921:Dental Implants; D003764:Dental Materials; D017973:Tungsten Compounds; C002802:tungsten carbide; D002244:Carbon; D014025:Titanium