Accuracy of digital versus conventional implant impressions

Abstract

The accuracy of digital impressions greatly influences the clinical viability in implant restorations. The aim of this study is to compare the accuracy of gypsum models acquired from the conventional implant impression to digitally milled models created from direct digitalization by three-dimensional analysis. Thirty gypsum and 30 digitally milled models impressed directly from a reference model were prepared. The models were scanned by a laboratory scanner and 30 STL datasets from each group were imported to an inspection software. The datasets were aligned to the reference dataset by a repeated best fit algorithm and 10 specified contact locations of interest were measured in mean volumetric deviations. The areas were pooled by cusps, fossae, interproximal contacts, horizontal and vertical axes of implant position and angulation. The pooled areas were statistically analysed by comparing each group to the reference model to investigate the mean volumetric deviations accounting for accuracy and standard deviations for precision. Milled models from digital impressions had comparable accuracy to gypsum models from conventional impressions. However, differences in fossae and vertical displacement of the implant position from the gypsum and digitally milled models compared to the reference model, exhibited statistical significance (p<0.001, p=0.020 respectively).

Evaluation of the Accuracy of Conventional and Digital Impression Techniques for Implant Restorations

“…Accuracy consists of precision and trueness (ISO 5725‐1) . Precision represents the degree of reproducibility between repeated measurements.…”

“…As the precision increases, the predictability of the measurement increases. Trueness describes the closeness to the actual dimensions of the object, which is defined by a comparison between the measurement control and a test object …”

“…To date, several implant impression techniques, such as the open tray and closed tray, and different impression transfers and materials have been investigated regarding their accuracy …”

“…Bench scanners are becoming more frequently used because they combine the advantages of a CAD/CAM prosthesis and decreased laboratory cost; therefore, digital impression techniques at the implant level play an important role in the development of a fully digital workflow for implant restorations . CAD/CAM‐fabricated restorations with indirect data capturing require precise casts, making precise impressions indispensable, and this technology increases the potential for the implant‐supported prosthesis to have a better passive fit, which is considered an essential prerequisite for maintaining osseointegration …”

Soft tissue replication in single unit implant impressions—A three dimensional clinical study

“…Digital impressions can minimize inaccuracies such as impression material strain, displacement of implant impression components and gypsum expansion, eliminating the need for conventional impression materials and making it faster and more comfortable for patients, although the high cost of investment is still a barrier to become a standard of care . The use of IOS allows for the immediate determination of the quality of the impression, with described values of trueness ranging from 44 to 64 microns (μm) and of precision from 16 to 27 μm, depending on the IOS used but well below the currently accepted threshold of 100‐120 μm of clinical deviation, being described as a comparable alternative to conventional impression methods …”