Supervisors info:
Παπαδόπουλος Τριαντάφυλλος, Καθηγητής, Τμήμα Οδοντιατρικής, Σχολή Επιστημών Υγείας, ΕΚΠΑ.
Καρκαζής Ηρακλής, Καθηγητής, Τμήμα Οδοντιατρικής, Σχολή Επιστημών Υγείας, ΕΚΠΑ.
Σαραφιανού Ασπασία, Επίκουρη Καθηγήτρια, Τμήμα Οδοντιατρικής, Σχολή Επιστημών Υγείας, ΕΚΠΑ.
Summary:
Introduction
For implant supported prostheses passive fit is considered an ideal goal, preventing biological and mechanical implications in the future. However, passive fit and zero marginal discrepancy are technically almost impossible to achieve. Additionally, the correlation between the degree of marginal gap and the incidence of clinical implications is yet to be defined. Nonetheless, it is clear that the various clinical and laboratory procedures introduce errors affecting the passivity of fit. These steps include impression techniques, definitive cast production and prosthesis manufacturing.
Introduction of intraoral digital impression systems, enabling direct digitization of the oral environment without impression materials, as well as laboratory scanners, digitizing the definitive casts, affected multiple areas of dentistry including implantology. A fully digital approach in prosthetic dentistry is nowadays possible, given the fact that Computer Added Design and Computer Added Manufacturing (CAD-CAM) procedures are widely acceptable over dental laboratories.
Several studies have compared the accuracy of intraoral digital systems for crowns and short span prostheses; there is not enough knowledge, however, of the effect of intraoral digital systems on the marginal fit of long span implant supported prostheses.
Aim
The aim of the current study was to investigate the effect of a conventional and an intraoral digital impression technique, as well as the effect of screw tightening sequence on the marginal fit of screw retained implant supported maxillary half arch prostheses on parallel implants.
Materials and Methods
This laboratory study was conducted on a simulation cast based on a real patient case. Two impression techniques were compared: The closed tray technique with Monophase Vinyl Polysiloxane from an automix device (Variotime Dynamix Monophase, Heraeus Kulzer GmbH, Germany) utilizing perforated commercially available trays (CTM) and the intraoral digital impression technique with the I-Tero™ system (I-tero™, CADENT® Ltd., Israel) (IOS).
For every impression technique were produced three metallic frames of screw retained restorations supported by implants at the locations of the maxillary right central incisor (11), first right premolar (14) and second right molar (17). The marginal adaptation of the metallic frames was examined with non destructive methods implementing negative replicas, which were sectioned and studied under light microscope. 24 replicas were created. There were 2 subgroups of samples for each impression technique (CTM, IOS) depending on the screw tightening sequence (A11: 11, 17, 14 and A17: 17, 11, 14). In total, there were 4 groups with 6 samples each (CTM A11, CTM A17, IOS A11, IOS A17). The marginal adaptation of the frames was quantitatively evaluated with 3 indices: Horizontal Discrepancy Title (FDH), Vertical Discrepancy Title (FDV), Conical Discrepancy Title (FDC). These were calculated on the means of the measurements of the horizontal, the vertical and the conical marginal discrepancy respectively. The conical marginal discrepancy was geometrically defined at the conical part of the internal hexagon of the implant system (Seven™, MIS®) that was used. Data were statistically at the SPSS software, with one-way ANOVA (a=.05) and post-hoc Tukey’s tests.
Results
There was a significant effect of the impression technique combined with the screw tightening sequence on the FDH: F(3,20)=5.558, p<.01, ω=.60, on the FDV: F(3,20)=3.299, p<.05, ω=.15 and on the FDC: F(3,20)=4.996, p<.05, ω=.58. The post-hoc Tukey’s tests revealed significant differences only for the FDH (p<.05) between the groups CTM A11– IOS A11, CTM A11-IOS A17, as well as CTM A17 – IOS A11 and CTM A17-IOS A17.
Conclusions
Within the limitations of this study it was concluded that all the studied combinations of impression techniques and screw tightening sequences resulted in marginal discrepancies. The closed tray impression technique with addition silicone gave better results, while the screw tightening sequence does not seem to affect the framework adaptation on the implants.
Clinical relevance
The digital intraoral scanning systems have undoubtedly a lot of advantages; however, regarding implementation of such systems in implant dentistry one should proceed with caution as not acceptable fit levels might result.
Keywords:
Intraoral Digital Scanning, PVS, Negative Replica, Implant Supported Bridge, Dental Osseointegrated Implants, Screw Retained Prosthesis, Passive Fit, Marginal Gap.
