title: Effect of increased crown height on stress distribution in short dental implant components and their surrounding bone: A finite element analysis.
abstract: BACKGROUND
  Implants in posterior regions of the jaw require short dental implants with long crown heights, leading to increased crown-to-implant ratios and mechanical stress. This can lead to fracture and screw loosening.
  
  
  OBJECTIVE
  The purpose of this study was to investigate the dynamic nature and behavior of prosthetic components and preimplant bone and evaluate the effect of increased crown height space (CHS) and crown-to-implant ratio on stress concentrations under external oblique forces.
  
  
  METHODS
  The severely resorbed bone of a posterior mandible site was modeled with Mimics and Catia software. A second mandibular premolar tooth was modeled with CHS values of 8.8, 11.2, 13.6, and 16 mm. A Straumann implant (4.1×8 mm), a directly attached crown, and an abutment screw were modeled with geometric data and designed by using SolidWorks software. Abaqus software was used for the dynamic simulation of screw tightening and the application of an external load to the buccal cusp at a 75.8-degree angle with the occlusal plane. The distribution of screw load and member load at each step was compared, and the stress values were calculated within the dental implant complex and surrounding bone.
  
  
  RESULTS
  During tightening, the magnitude and distribution of the preload and clamp load were uniform and equal at the cross section of all CHSs. Under an external load, the screw load decreased and member load increased. An increase in the CHS caused the corresponding distribution to become more nonuniform and increased the maximum compressive and tensile stresses in the preimplant bone. Additionally, the von Mises stress decreased at the abutment screw and increased at the abutment and fixture.
  
  
  CONCLUSIONS
  Under nonaxial forces, increased CHS does not influence the decrease in screw load or increase in member load. However, it contributes to screw loosening and fatigue fracture by skewing the stress distribution to the transverse section of the implant.
authors: Graduate student, Department of Mechanical Engineering, School of Mechanics, University of Tehran, Tehran, Iran.
authors: Haddad Arabi
authors: HA
authors: Bulaqi
authors: Professor, Department of Mechanical Engineering, School of Mechanics, University of Tehran, Tehran, Iran.
authors: Mahmoud
authors: M
authors: Mousavi Mashhadi
authors: Assistant Professor, Department of Periodontics, School of Dentistry, Qom University of Medical Sciences, Qom, Iran.
authors: Hamed
authors: H
authors: Safari
authors: Associate Professor, Implant Research Center, Department of Mechanical Engineering, School of Mechanics, University of Tehran, Tehran, Iran.
authors: Mohammad Mahdi
authors: MM
authors: Samandari
authors: Graduate student, Department of Mechanical Engineering, School of Mechanics, University of Tehran, Tehran, Iran. Electronic address: geramipa@tums.ac.ir.
authors: Farideh
authors: F
authors: Geramipanah
mesh_terms: D000465:Algorithms; D001696:Biomechanical Phenomena; D001862:Bone Resorption / Q000503:physiopathology; D003188:Composite Resins / Q000737:chemistry; D017076:Computer-Aided Design; D054893:Cone-Beam Computed Tomography / Q000379:methods; D003442:Crowns; D059605:Dental Implant-Abutment Design; D015921:Dental Implants; D003764:Dental Materials / Q000737:chemistry; D003776:Dental Porcelain / Q000737:chemistry; D017267:Dental Prosthesis Design; D019094:Dental Prosthesis, Implant-Supported; D019232:Dental Restoration Failure; D020342:Finite Element Analysis; D006047:Gold Alloys / Q000737:chemistry; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008334:Mandible / Q000503:physiopathology; D008336:Mandibular Diseases / Q000503:physiopathology; D013314:Stress, Mechanical; D014025:Titanium / Q000737:chemistry
chemical_list: D003188:Composite Resins; D015921:Dental Implants; D003764:Dental Materials; D006047:Gold Alloys; D003776:Dental Porcelain; D014025:Titanium