title: Does matching relation exist between the length and the tilting angle of terminal implants in the all-on-four protocol? stress distributions by 3D finite element analysis.
abstract: OBJECTIVE
  To explore whether there is matching relation between the length and the tilting angle of terminal implants in the All-on-Four protocol by studying the effects of different implant configurations on stress distributions of implant, bone, and framework.
  
  
  METHODS
  Four implants were employed to support a full-arch fixed prosthesis and five three-dimensional finite element models were established with CT images, based on the length (S and L) and distal tilt angle (0°, 30° and 45°) of terminal implants for an edentulous mandible, which named: Tilt0-S, Tilt30-S, Tilt30-L, Tilt45-S and Tilt45-L. An oblique 240 N was loaded at second molar. The von Mises Stresses were analyzed. The implants were consecutively named #1 to #4 from the loading point.
  
  
  RESULTS
  1) Tilt0-S had the greatest stress on the implants, with the other groups exhibiting variable reductions; the four implants of Tilt45-L demonstrated the greatest reduction in stress. 2) Tilt0-S had the greatest stress at bone around #1 implant neck, and Tilt45-L exhibited the least stress, which was a 36.3% reduction compared to Tilt0-S. 3) The greatest stress in the framework was found on the cantilevers distal to #1 implant. Tilt45-S exhibited the least stress.
  
  
  CONCLUSIONS
  Matching different length and tilting angle of the terminal implants led to variable stress reductions on implants, bone and the superstructure. By optimizing implant configuration, the reduction of stress on implants and surrounding bone could be maximized. Under the present condition, Tilt45-L was the preferred configuration. Further clinical testings are required.
authors.affiliation: Department of Stomatology, Changhai Hospital, Shanghai, China.
authors.forename: Xiaomei
authors.initials: X
authors.lastname: Li
authors.affiliation: Department of Stomatology, Changhai Hospital, Shanghai, China.
authors.forename: Zhizhong
authors.initials: Z
authors.lastname: Cao
authors.affiliation: Department of Stomatology, Changhai Hospital, Shanghai, China.
authors.forename: Xiaoqian
authors.initials: X
authors.lastname: Qiu
authors.affiliation: Department of Stomatology, Changhai Hospital, Shanghai, China.
authors.forename: Zhen
authors.initials: Z
authors.lastname: Tang
authors.affiliation: School of Life Sciences and Technology, Tongji University, Shanghai, China.
authors.forename: Lulu
authors.initials: L
authors.lastname: Gong
authors.affiliation: Department of Stomatology, Changhai Hospital, Shanghai, China.
authors.forename: Dalin
authors.initials: D
authors.lastname: Wang
keywords: All-on-Four; Edentulous mandibles; Finite element analysis; Fixed prosthesis; Implant; Stress