Assessing the Influence of Implant Scanning Techniques on the Accuracy of Maxillary Complete-Arch Digital Scans for Implant Overdentures: A Comparative Clinical Study

Overview

Recently different protocols have been developed for the implementation of intraoral scanning in full-arch implant workflows, as horizontal scan body scanning, 1 reverse scanning 2 and scan body systems with an integrated verification jig 3 . The aforementioned approaches are aiming to reduce the inaccuracies related with the implementation of intraoral scanners in full-arch implant cases and to improve the efficiency of the whole digital workflow. However the efficiency of these methods and the parameters that can influence their accuracy, as the design of the scan body have not been investigated. The purpose of the present in vivo study is to compare the trueness and the precision of the recorded implant's position, between conventional and novel implant acquisition protocols.

The collection of the clinical data for the present research is going to be performed in a private dental clinic.A single patient presenting with an edentulous maxillary arch will be enrolled in the present study. The patient has to be treated with the placement of four implants and to be planned to be restored with an implant-supported overdenture.In total 3 different scan body systems are going to be evaluated in the present research: conventional scan-bodies (Cares Mono Scan body, Straumann), scan-bodies designed for a horizontal intraoral scanning (Apollo and Reference Scan body, Dynamic abutment), reverse scan bodies (ReveX, Straumann; Scanalog, Dynamic abutment) The scan-bodies will be hand-tightening over the multi-units, which previously will be fixed on 4 implants in patient's maxilla. Each one of the evaluated scan bodies is going to be scanned using an intraoral scanner Trios 5 (3Shape). The verified dentate scan path recommended by the manufacturer is going to be followed, to scan the reference cast 10 times, for each one of the evaluated scan body systems. The digital scans for each group are going to be performed without removing the scan-bodies in order to eliminate the effect of scan body fit. Finally, an analog impression of splinted impression posts is going to be taken in order to serve as a reference. Based to the analog impression a reference cast is going to be fabricated using a plaster (Type 3, Moldano, Kulzer) and be scanned by a desktop scanner (T710, Medit) using laboratory scan bodies to serve as a reference.The STL files for each evaluated group along with the scans from the industrial scanner will be imported in a metrology software (Geomagic, control X). The digital model derived from each evaluated group is going to be superimposed with the model obtained from the industrial scanner respectively. In order to achieve an accurate superimposition, first "align between measured data" function will be utilized, followed by "best-fit alignment". During the alignment, the area of the scan bodies will be excluded, in order to prevent them from influencing the alignment and the subsequent evaluation. This will be accomplished by using the "use select data only" function. In order to standardize the aforementioned procedure, all superimposed models will be cut simultaneously in the same region. Afterwards, the overall deviation will be calculated, by using "3D compare" function on Geomagic software, by creating a color map in superimposed digital models to qualitative analyze any 3D deviation. The color map is going to be ranged from -0.5mm to +0.5mm. Mean discrepancy is going to be measured in root mean square RMS, which is a mathematical measure of magnitude of a set of numbers. Trueness will be defined in terms of the mean discrepancy on the positions of the implant abutments, between the digitized by the industrial scanner reference cast and each evaluated group. Precision will be described as the standard deviation of the mean absolute discrepancies computed between the digitized by the industrial scanner reference cast and each evaluated group. A smaller SD indicates that measurements are more precise and consistent, while larger SD will imply greater variability.A power analysis was performed utilizing the G\*Power software (G\*Power, Heinrich- Heine-Universität Düsseldorf, Germany). The total sample size was calculated based on an effect size of 0.4, an alpha error probability of 0.05, a power of 0.8 and an estimated correlation between measurements of 0.5. The power analysis revealed that a minimum of 10 data sets per evaluated group is required to perform the present study. Statistical analysis will be performed using SPSS statistics software (version 29, IBM software). Descriptive statistics will be calculated for each evaluated group. The Shapiro-Wilk test will be performed in order to test if the data are normally distributed (P\<0.05). For the trueness and the precision, post-hoc analysis (Tukey, Scheffe) will be conducted to assess which evaluated implant acquisition technique will be statistically significantly different. Fisher's exact test will be used to assess the association between the implant acquisition method and the accuracy of the fit. The level of significance will be set at 0.05. The agreement of fit assessment between the two experienced clinicians will be tested with κ statistics (Cohen's k-score).