Comparison of the accuracy of digital and conventional impression techniques in multiple implants with different angulations

Çopuroğlu, A. (2024). Comparison of the accuracy of digital and conventional impression techniques in multiple implants with different angulations. Yeditepe University, Institute of Health Sciences, Department of Prosthodontics, Ph.D, Thesis. Istanbul. The purpose of this study is to evaluate the effect of digital impression technique and conventional impression technique with different materials on the accuracy of impression in fully edentulous jaws with multiple implants placed at various angles. The current study evaluated two different fully edentulous upper jaw master models in which four internally connected implants were placed parallelly and angled to each other. In the first master model, four implants were positioned at a 90° angle to the occlusal plane and parallel to each other. In the second master model, two implants were placed in the anterior region in the canine areas at a 90° angle to the occlusal plane and parallel to each other, while the other two implants were placed in the posterior region at a 30° distal angle according to the all-on-4 protocol. Stock open trays with window space corresponding to the implant site were used for the conventional groups. Impressions were taken from the models using three different conventional impression materials; polyvinylsiloxane (PVS), polyether (PE), polyvinyl siloxane ether (PVSE), and digital impression method (3Shape TRIOS 3). As the sample size for each group was determined to be 10 based on the results of the power analysis, the impression process was repeated 10 times for each group. Cast models were produced from the conventional impressions, and all samples were scanned with an extraoral scanner (3Shape Lab Scanner 1E) and stored as STL files. The STL files of the obtained 8 groups were evaluated for accuracy using the Geomagic Control X program. In the evaluation of the findings of the study, IBM SPSS Statistics 22 software was used for statistical analysis. The normal distribution of parameters was assessed using the Kolmogorov-Smirnov and Shapiro-Wilk tests, and it was determined that the parameters were normally distributed. For assessing the amount of deviation in the study data, a two-way ANOVA test was used, along with post hoc Tukey test. Significance was evaluated at p<0.05 level. In the parallel model; the deviation amount of the digital impression group was significantly higher than the PE group (p:0.016; p<0.05), and there was no statistically significant difference among the other groups (p>0.05). In the angulated model; the deviation amount of PE group was significantly lower than the PVSE group (p:0.007; p<0.05), and the digital impression group (p:0.016; p<0.05); and there was no statistically significant difference among the other groups (p>0.05). When parallel model and angulated model was compared, the deviation amount increased in each group, and statistically significant results were found in PVS, PE, and digital impression groups (p<0.05). The angulation of implants had a negative effect on the accuracy of the impression. Polyether impression material provided more accurate results in both parallel and angulated cases. Keywords: impression accuracy, parallel implant, angulated implant, polyvinylsiloxane, polyether, polyvinyl siloxane ether