Biomechanical evaluation of internal and external hexagon platform switched implant-abutment connections: An in vitro laboratory and three-dimensional finite element analysis.
OBJECTIVE
The aim of this study was to assess the effect of abutment's diameter shifting on reliability and stress distribution within the implant-abutment connection for internal and external hexagon implants. The postulated hypothesis was that platform-switched implants would result in increased stress concentration within the implant-abutment connection, leading to the systems' lower reliability.


METHODS
Eighty-four implants were divided in four groups (n=21): REG-EH and SWT-EH (regular and switched-platform implants with external connection, respectively); REG-IH and SWT-IH (regular and switched-platform implants with internal connection, respectively). The corresponding abutments were screwed to the implants and standardized maxillary central incisor metal crowns were cemented and subjected to step-stress accelerated life testing. Use-level probability Weibull curves and reliability were calculated. Four finite element models reproducing the characteristics of specimens used in laboratory testing were created. The models were full constrained on the bottom and lateral surface of the cylinder of acrylic resin and one 30° off-axis load (300N) was applied on the lingual side of the crown (close to the incisal edge) in order to evaluate the stress distribution (s(vM)) within the implant-abutment complex.


RESULTS
The Beta values for groups SWT-EH (1.31), REG-EH (1.55), SWT-IH (1.83) and REG-IH (1.82) indicated that fatigue accelerated the failure of all groups. The higher levels of σ(vM) within the implant-abutment connection observed for platform-switched implants (groups SWT-EH and SWT-IH) were in agreement with the lower reliability observed for the external hex implants, but not for the internal hex implants. The reliability 90% confidence intervals (50,000 cycles at 300N) were 0.53(0.33-0.70), 0.93(0.80-0.97), 0.99(0.93-0.99) and 0.99(0.99-1.00), for the SWT-EH, REG-EH, SWT-IH, and REH-IH, respectively.


CONCLUSIONS
The postulated hypothesis was partially accepted. The higher levels of stress observed within implant-abutment connection when reducing abutment diameter (cross-sectional area) resulted in lower reliability for external hex implants, but not for internal hex implants.
Department of Biomaterials and Biomimetics, New York University College of Dentistry, New York, NY 10010, USA. ac.freitas.jr@gmail.com
Amilcar C
AC
Freitas-Júnior
Eduardo P
EP
Rocha
Estevam A
EA
Bonfante
Erika O
EO
Almeida
Rodolfo B
RB
Anchieta
Ana P
AP
Martini
Wirley G
WG
Assunção
Nelson R F A
NR
Silva
Paulo G
PG
Coelho
D001696:Biomechanical Phenomena; D059605:Dental Implant-Abutment Design / Q000379:methods*; D015921:Dental Implants; D003799:Dental Stress Analysis; D020342:Finite Element Analysis; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning
D015921:Dental Implants