RESEARCH AND EDUCATION Effect of bone quality and bone loss level around internal and external connection implants: A finite element analysis study Cleidiel Aparecido Araujo Lemos, DDS, MS, PhD, a Fellippo Ramos Verri, DDS, MS, PhD, b Pedro Yoshito Noritomi, Eng, MS, PhD, c Daniel Takanori Kemmoku, Eng, d Victor Eduardo de Souza Batista, DDS, MS, PhD, e Ronaldo Silva Cruz, DDS, MS, f Jessica Marcela de Luna Gomes, DDS, MS, g and Eduardo Piza Pellizzer, DDS, MS, PhD h Dental implants have been considered a predictable treatment for the rehabilitation of edentulous patients. 1,2 However, maintaining bone around dental implants is of concern because the amount of marginal bone loss around the implant is directly related to delayed implant failures. 3,4 The biomechanical effects of different variables on dental implants are important because the intimate contact between the implant and the bone transfers occlusal loads directly to the bone. 5 In some situations, this occlusal load may exceed the physiological limit of bone, accelerating bone resorption. 6 Among the different factors that contribute to stress con- centration in bone, implants, and prosthetic components, This study was supported by Scholarship of São Paulo State Research FoundationdFAPESP: #2015/24442-8; #2009/16164-7; and CNPq: 306288/2016-8. a Adjunct Professor, Division of Prosthodontics, Department of Dentistry, Federal University of Juiz de Fora (UFJF-GV), Governador Valadares, Minas Gerais, Brazil. b Associate Professor, Department of Dental Materials and Prosthodontics, Araçatuba Dental School, Universidade Estadual Paulista (UNESP), Araçatuba, Sao Paulo, Brazil. c Researcher, Tridimensional Technology Division, Renato Archer’s Information Technology Center, Campinas, São Paulo, Brazil. d Researcher, Tridimensional Technology Division, Renato Archer’s Information Technology Center, Campinas, São Paulo, Brazil. e Professor, Department Prosthodontics, Presidente Prudente Dental School, University of the West of São Paulo (UNOESTE), Presidente Prudente, Brazil. f PhD student, Department of Dental Materials and Prosthodontics, Araçatuba Dental School, Universidade Estadual Paulista (UNESP), Araçatuba, Sao Paulo, Brazil. g PhD student, Department of Dental Materials and Prosthodontics, Araçatuba Dental School, Universidade Estadual Paulista (UNESP), Araçatuba, Sao Paulo, Brazil. h Titular Professor, Department of Dental Materials and Prosthodontics, Araçatuba Dental School, Universidade Estadual Paulista (UNESP), Araçatuba, Sao Paulo, Brazil. ABSTRACT Statement of problem. A consensus regarding the biomechanical effects of vertical bone loss in normal and osteoporotic bone tissue according to different implant-abutment interfaces is lacking. Purpose. The purpose of this finite element analysis study was to evaluate the effect of vertical bone loss (without bone loss; with 1.5-mm bone loss; with 3-mm bone loss; and with 4.5-mm bone loss) in normal and osteoporotic bone that received a Ø4×10-mm implant with different implant-abutment connections (external connection [external hexagon] and internal connection [Morse taper]) by using 3D finite element analysis. Material and methods. Sixteen 3D models were simulated. Axial and oblique forces of 200 N and 100 N, respectively, were applied on the occlusal surfaces of the prostheses. Maximum principal stress and microstrain were determined from the bone tissue of each model. von Mises stress analysis was used to evaluate the stress distribution in implants and prosthetic components (fixation screws, abutment, and crown). Results. The results showed higher stress concentrations in models with bone loss as increased vertical bone loss contributed to higher stress and microstrain in the bone tissue, regardless of the quality of bone and implant-abutment connection. Osteoporotic bone contributed to increase in microstrain in the trabecular bone. The internal connection showed lower stress than the external connection implants only in models without marginal bone loss. Furthermore, higher stress concentrations were observed in the implants and fixation screws in models with increased bone loss and external connection implants, mainly under oblique loading. Osteoporotic bone did not affect stress distribution in the implants and prosthetic components. Conclusions. Progressive bone loss contributed to higher stress in the bone tissue, implants, and prosthetic components. The osteoporotic bone affects only the microstrain in the trabecular bone, but not the stress in the implants and prosthetic components. The internal connection implants showed lower stress in the cortical bone only in models without bone loss, while external connection implants exhibited higher stress in the implants and screws under oblique loading. (J Prosthet Dent 2020; -: ---) THE JOURNAL OF PROSTHETIC DENTISTRY 1