Abstract
Preload loss can favor the occurrence of implant-abutment interface misfit, and bacterial colonization at this interface may lead to implant failure. The aim of this study was to evaluate the preload loss and bacterial penetration through the implant-abutment interface of conical and external hexagon connection systems subjected to thermal cycling and mechanical fatigue (TM). Four different implant-abutment connection systems were evaluated (n=6): external hexagon with universal post, Morse taper with universal post, Morse taper with universal post through bolt, and locking taper with standard abutment. The assemblies (implant-abutment) were subjected to a thermal cycling regimen (1,000 cycles of 5 degrees C and 55 degrees C) and to mechanical fatigue (1.0 million cycles, 1.0 Hz, 120 N). The assemblies were immersed in Tryptic Soy + Yeast Extract broth containing Streptococcus sanguinis and incubated at 37 degrees C and 10% CO(2) for 72 h. Detorque values were recorded. The bacterial penetration was assessed and the abutments were observed by scanning electron microscopy. The preload data were analyzed statistically by two-way ANOVA and Tukey's test at 5% significance level. All screw abutment systems showed significantly higher (p<0.05) detorque values when subjected to TM and all conical systems presented bacterial penetration. The results show no relationship between the preload loss and the bacterial penetration.
Highlights
Implant dentistry has become one of the most successful rehabilitation technique among medical and dental specialties
The abutment could not be totally immersed in the broth because the screw hole on the top of two systems, external hexagon and Morse taper with universal post through bolt, could act as a second way for bacterial penetration
It was hypothesized that thermal cycling and mechanical fatigue could favor preload loss and facilitate bacterial penetration in the external hexagon and conical junction systems
Summary
Implant dentistry has become one of the most successful rehabilitation technique among medical and dental specialties. Over the last 30 years, clinical evidence has shown excellent long-term results for osseointegrated implants with success rate above 90% [1,2]. This predictable treatment requires a dynamic equilibrium between mechanical and biological factors. Mechanical factors, such as the implant-abutment precise fit and the abutment screw preload, are involved in the success of implant rehabilitation. The preload loss during the occlusal load with the prosthesis in function favors the misfit of the implant-abutment connection and this can result in stress increase in the implant and connection components, and in the surrounding bone [3,4,5]. The stress at connection components could cause screw fracture and loss, abutment and prosthesis damage, requiring the repair or replacement of the prosthesis and its components
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