title: Effect of cyclic loading on the vertical microgap of long-span zirconia frameworks supported by 4 or 6 implants.
abstract: BACKGROUND
  Few studies have investigated the microgap of long-span complete-arch fixed dental prosthesis zirconia frameworks.
  
  
  OBJECTIVE
  The purpose of this study was to evaluate the effects of cyclic loading on the vertical microgap of maxillary 12-unit prostheses supported by 4 implants and on 14-unit prostheses supported by 6 implants.
  
  
  METHODS
  One-piece zirconia frameworks were fabricated with a computer-aided design/computer-aided manufacturing technique and divided into 2 groups (n=5): a group of 12-unit prostheses and a group of 14-unit prostheses. The vertical microgap between the frameworks and prosthetic abutments was measured with an optical microscope (80×) under 2 reading conditions. Condition 1 (1-screw test): 1A, the screw on implant 1 was tightened and readings were made on all implants; 1B, the screw was changed to implant 4 (implant 6 for the 14-unit group) and readings were made on all implants. Condition 2: the microgap was measured with all screws tightened before cyclic loading (2A). Specimens were submitted to 200 N underwater (37°C) cyclic loading at a 2-Hz frequency for 1×10(6) cycles. Microgap reading condition 2 was repeated after cyclic loading (2B). The data were submitted to a linear mixed-effects model for statistical comparison (α=.05).
  
  
  RESULTS
  A lower (P<.05) vertical microgap (μm) was found for the 12-unit group (reading conditions: 1A, 47.93; 1B, 43.83; 2A, 11.77; and 2B, 11.25) compared to the 14-unit group (1A, 94.87; 1B, 112.56; 2A, 21.28; and 2B, 16.90). No differences were found when each group was compared before and after cyclic loading (P>.05).
  
  
  CONCLUSIONS
  The vertical microgap was significantly reduced after tightening all the screws in the framework, possibly leading to a nonpassive situation. Longer-span frameworks showed an increased microgap. Cyclic loading had no influence on the vertical microgap within each group.
authors.affiliation: Assistant Professor, Department of Prosthodontics, School of Dentistry, Fluminense Federal University, Niterói, Rio de Janeiro, Brazil. Electronic address: rtiossi@yahoo.com.
authors.forename: Rodrigo
authors.initials: R
authors.lastname: Tiossi
authors.affiliation: Postdoctoral Research Associate, Department of Dental Materials and Prosthodontics, University of São Paulo Ribeirão Preto School of Dentistry, Ribeirão Preto, São Paulo, Brazil.
authors.forename: Erica Alves
authors.initials: EA
authors.lastname: Gomes
authors.affiliation: Laboratory Specialist, Department of Dental Materials and Prosthodontics, University of São Paulo Ribeirão Preto School of Dentistry, Ribeirão Preto, São Paulo, Brazil.
authors.forename: Adriana Cláudia
authors.initials: AC
authors.lastname: Lapria Faria
authors.affiliation: Assistant Professor, Department of Dental Materials and Prosthodontics, University of São Paulo Ribeirão Preto School of Dentistry, Ribeirão Preto, São Paulo, Brazil.
authors.forename: Renata Cristina
authors.initials: RC
authors.lastname: Silveira Rodrigues
authors.affiliation: Full Professor, Department of Dental Materials and Prosthodontics, University of São Paulo Ribeirão Preto School of Dentistry, Ribeirão Preto, São Paulo, Brazil.
authors.forename: Ricardo Faria
authors.initials: RF
authors.lastname: Ribeiro
mesh_terms: D017076:Computer-Aided Design; D000044:Dental Abutments; D059605:Dental Implant-Abutment Design / Q000145:classification; D015921:Dental Implants; D018772:Dental Marginal Adaptation / Q000145:classification*; D003764:Dental Materials / Q000737:chemistry*; D019094:Dental Prosthesis, Implant-Supported; D003779:Denture Design; D003827:Denture, Complete, Upper; D006801:Humans; D008422:Materials Testing; D008437:Maxilla / Q000033:anatomy & histology; D008953:Models, Anatomic; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D014584:User-Computer Interface; D014867:Water / Q000737:chemistry; D015040:Zirconium / Q000737:chemistry*
chemical_list: D015921:Dental Implants; D003764:Dental Materials; D014867:Water; D015040:Zirconium; C028541:zirconium oxide