Bacterial penetration through screw access hole in screw-retained monolithic zirconia implant crowns
Dr. Pauliina Moilanen1, Prof. Timo Närhi1, Dr. Jenni Hjerppe2, Vuokko Loimaranta3
1 Department of Prosthetic Dentistry and Stomatognathic Physiology, University of Turku, Turku, Finland,
2 Clinic of Reconstructive Dentistry, Center for Dental Medicine, University of Zürich, Zürich, Switzerland,
3 Institute of Dentistry, University of Turku, Turku, Finland
Objectives
The aim of this study was to test the bacterial penetration of screw access holes in monolithic zirconia implant crowns sealed using different methods.
Materials and Methods
24 monolithic premolar zirconia (IPS e.max ZirCAD) crowns were divided into four groups (n=6) according to screw access hole sealing method: unbonded composite (UBC), bonded composite (BC), airborne-particle abrasion and bonded composite (ABC), negative control without screw access hole. The test system consisted of upper and lower chamber. Crowns with filled screw access hole were fixed in plastic upper chambers, occlusal part of the crown being inside of the chamber while apical part was outside. Polytetrafluoroethylene tapes were placed inside the apical parts of the crowns and freshly prepared S.mutans bacterial suspension was poured into the upper chambers. The lower chambers were filled with bacteria culture media up to the apical parts of the crowns. Bacterial penetration through the model system was assessed by visual inspection of the turbidity of the lower chamber. S.mutans identity was confirmed on agar plate culture. After 28 days the PTFE tapes were removed and transferred to nutritious medium, vortexed and sonicated before an aliquot of 50µl was plated on agar plates. After incubation at 37°C, the amount of bacterial growth was evaluated. The statistical analysis was performed using Fisher-Freeman-Halton exact test and pairwise comparison with z-test.
Results
In all the test groups bacterial penetration was noticed by the eight days (BC (1/6), ABC (3/6), UBC (6/6)), whereas control group stayed bacteria free. Bacteria penetrated through the screw access hole of all the specimens in UBC group within 24 hours, being significantly faster than in other groups (p=0.011).
Conclusions
The sealing method of the screw access hole affects the bacterial penetration. Using a resin bonding significantly reduces S. mutans penetration but it does not prevent it completely.