Abstract
Statement of problem
Screw loosening is the most common mechanical complication with implant prostheses.
How the alteration of implant-to-abutment connection surfaces that occurs during laboratory
procedures affects screw loosening is unclear.
Purpose
The purpose of this in vitro study was to compare the reverse tightening value (RTV)
differences between custom castable abutments before casting, after casting in a conventional
manner, and after casting with custom protector caps and pegs.
Material and methods
Thirty implants with a standard-diameter conical connection (NobelReplace Conical
Connection 4.3×13 mm; Nobel Biocare AG) and 30 premachined 4.3-mm GoldAdapt abutments
(GoldAdapt; Nobel Biocare AG) were selected for this study. Specimens were divided
into 3 groups (n=10): the uncast custom castable abutment group (UCCA) in which abutments
were new and not cast; the unprotected custom castable abutment group (UPCCA) in which
abutments were cast and devested with airborne-particle abrasion; and the protected
custom castable abutment group (PCCA) in which abutments were cast by using protector
caps and pegs made by milling zirconia and then devested with airborne-particle abrasion.
All abutments in each group were tightened to 35 Ncm with a calibrated digital tightening
device. After 10 minutes, all screws were retightened to 35 Ncm. At 3 hours, each
screw was loosened, and the value at which the initial loosening occurred was documented
as the RTV. The results were statistically analyzed with 1-way ANOVA to explore differences,
and post hoc tests with Tukey adjustment were used for multiple comparisons.
Results
Among the tested groups, the mean RTV ranged from 19.89 Ncm to 27.19 Ncm: UCCA 27.19
Ncm, UPCCA 19.89 Ncm, and PCCA 24.24 Ncm. A significant difference was found among
the tested groups (P<.05).
Conclusions
Casting procedures, especially devestment with airborne-particle abrasion, affected
implant-abutment connections and the seat site of the screw. Protecting the implant
connection site and the seat site of the abutment screw with protector caps and pegs
prevented a significant loss of the RTV.
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Article info
Publication history
Published online: November 17, 2022
Publication stage
In Press Corrected ProofIdentification
Copyright
© 2022 by the Editorial Council for The Journal of Prosthetic Dentistry.
