title: Comparison of Stresses Generated within the Supporting Structures of Mandibular Second Molars Restored with Different Crown Materials: 3-D Finite Element Analysis (FEA).
abstract: OBJECTIVE
  This study compares the FEA-calculated stresses generated within the supporting periodontal structure of a mandibular second molar restored with a full ceramic crown and with a porcelain-fused-to-metal (PFM) crown, each resisting occlusal forces acting at different inclinations.
  
  
  METHODS
  Three-dimensional finite element models representing the crown of an unrestored mandibular second molar and two relevant restoration designs were constructed. Two designs represented the molar restored with a full ceramic crown and with a PFM crown, each cemented with the same resin cement. Occlusion was assumed at three contact areas, which equally shared a 100 N force. The analysis was carried out for forces located in the bucco-axial-lingual plane at five inclinations, 0, 22.5°, 45°, 67.5°, and 90°, measured from the axial direction of the tooth. The magnitudes and sites of the maximum equivalent stress (MES) generated within the supporting periodontium of each analyzed model were collected.
  
  
  RESULTS
  Generally, there were no significant differences in the site and magnitude of MES in the regions of the supporting structure for the analyzed models. The MES was located at the tooth periodontal ligament (PDL) bifurcation area and distal root apex, crestal bone at the junction between cortical and cancellous bone, and the distal wall of the mesial root socket of cancellous bone. The highest stresses corresponded to a horizontal load, followed by the axial load in the PDL and cortical zones. The results show opposite observations for the cancellous bone. The lowest stresses were generated under a load inclination between 22.5° and 45°.
  
  
  CONCLUSIONS
  Considering the stresses generated within the supporting structures, the present work validates, by calculation, the proposed clinical use of either a full ceramic crown or a PFM crown as a restoration for mandibular second molars.
authors.affiliation: Conservative Dental Sciences Department, Faculty of Dentistry, King Abdulaziz University, Jeddah, Kingdom of Saudi Arabia.
authors.forename: Dalia A
authors.initials: DA
authors.lastname: Abuelenain
authors.affiliation: Conservative Dental Sciences Department, Faculty of Dentistry, King Abdulaziz University, Jeddah, Kingdom of Saudi Arabia.
authors.forename: Reem
authors.initials: R
authors.lastname: Ajaj
authors.affiliation: Conservative Dental Sciences Department, Faculty of Dentistry, King Abdulaziz University, Jeddah, Kingdom of Saudi Arabia.
authors.forename: Eman I M Fath
authors.initials: EI
authors.lastname: El-Bab
authors.affiliation: Mechanical Engineering Department, Al Azhar University, Cairo, Egypt.
authors.forename: Mohammad M I
authors.initials: MM
authors.lastname: Hammouda
mesh_terms: D001732:Bite Force; D002516:Ceramics / Q000737:chemistry*; D003442:Crowns / Q000706:statistics & numerical data; D003764:Dental Materials / Q000737:chemistry*; D003793:Dental Restoration, Permanent; D003799:Dental Stress Analysis / Q000379:methods; D020342:Finite Element Analysis; D006801:Humans; D008670:Metals / Q000737:chemistry*; D003765:Models, Dental; D008963:Molar / Q000502:physiology*; D013314:Stress, Mechanical
chemical_list: D003764:Dental Materials; D008670:Metals
keywords: 3-D finite element analysis; Mandibular second molar; PFM restoration; full ceramic restoration; supporting structure; von Mises equivalent stress