Influence of intraoral scanning distance on marginal adaptation of milled structures: an in vitro laboratory study

Abstract

The development of the CAI/CAD/CAM (Computer Aided Impression/Computer Aided Design/Computer Aided Manufacturing) system in dentistry has provided dentists with rapid and effective solutions for various rehabilitations. When scanning implants and/or abutments, the aim is to transfer the three-dimensional positioning of the implants from the mouth to the virtual model. For this purpose, Intraoral Scanbodies (ISBs) are used. The objective of the study was to determine whether the distance between the ISBs influences the marginal fit of milled structures obtained through a digital clinical-laboratory workflow. To this end, three lower models missing the left posterior elements were prepared. Initially, two implants (Helix GM 3.5 x 11.5, Neodent, Straumann) were installed in each model with distances of 7, 14, and 21mm between them, measured from the central axis of the implants. Then, multi units (GM Conical MultiUnit 2.5, Neodent, Straumann) and compatible ISBs were installed. In the next phase, scans were first performed by using a laboratory scanner (inEos X5 dental laboratory scanner, Dentsply Sirona) for the control group. Subsequent scans for the test groups were performed using the Virtuo Vivo intraoral camera (Straumann). The partial scanning files in the .STL (Standard Tessellation Language) extension were sent to an image software (Geomagic Control X, 3D Systems, Version 2018.1.1) where intraoral scans were compared with the control group, in the condition of mesh overlap. Then, the .STL files were sent to D-Lab – Digital Laboratory, and a total of 5 structures with 3 elements each were milled in a Cobalt-Chrome (Co-Cr) alloy for each group. Each multi unit-structure junction was evaluated using Scanning Electron Microscopy (Scanning Electron Microscope, Zeiss EVO MA10) and the horizontal misfits of the mesial and distal faces of each junction were identified. Standardized digital periapical radiographs were taken of all structures screwed onto the multi units, allowing for a comparison between the level of misfit visible on the radiographs and the results found in SEM. The radiographs were taken with the Portable Digital X-Ray (Diox, Micro Image), following the manufacturer's instructions. Data were analyzed using Rstudio (RStudio Team, 2024). Shapiro-Wilk and ANOVA tests followed by Tukey's test were applied, with α=0.05 for group comparisons. No statistically significant differences were found between the groups studied. Within the limitations of the study, it was concluded that regardless of the tested distances, the virtual models were accurate, the milled structures fit the implant abutments, and digital radiography can be a reliable method for analyzing structure fit.