24 November 2020

---

How accurate is a digital impression?

Co-author: F. Florenzano

Lorenzo Breschi

---

Today, the use of digital workflows for the fabrication of indirect restorations is constantly increasing thanks to the evolution of computer-aided design and computer-aided manufacturing-based processes in dentistry.

Some authors claimed that digital intraoral impressions are superior than conventional impression techniques with elastomeric materials, as they are safer in terms of cross-contamination, more comfortable for the patients, time-saving for the operator, require only data storage, and can be transferred digitally to the dental technician.

However, indirect restorative workflow, whether conventional or digital, risks to include errors at each step to minimize the cumulative error through the whole process. 

Intraoral scanning serves as the basis for the digital workflow and thus, its accuracy is crucial for a successful restorative treatment and progress in hardware and software aimed to improve the process. 

Recently, a new Cerec system, Primescan AC(Sirona, Bensheim, Germany), has been launched and the research group of Jae-Hoon Kim et al. from Pusan National University, Korea conducted a study  to evaluate the influence of tooth location and inlay cavity type on the accuracy of the digital intraoral impression using comparative 3D analysis.

Material and methods 

To conduct the research the Korean group performed Class II inlay preparation on anatomical models of maxillary ( tooth 1.6) and mandibular ( tooth 4.6) first molars. Mesio- occlusal and disto-occlusal cavities were prepared by authors. The axial wall of the proximal box measured 1 mm or 2 mm in height. Thus, four types of inlay cavities were prepared in 1.6 and 4.6, respectively and ten digital impressions of each cavity were obtained using Cerec Primescan (Sirona). In this study, the researcher acquired intraoral digital impressions on the phantom head. Reference scans were obtained with a laboratory scanner (E3, 3Shape). 

Finally, Jae-Hoon Kim et al. exported all obtained data for comparative analysis of the three-dimensional models. 

Results 

The results obtained by the authors showed that the trueness obtained for 1.6 was higher than that for 4.6 (p < 0.05), while the precision was similar between 1.6  and 4.6. The cavity type affected the accuracy of the digital impressions . Indeed, the researchers obtained higher deviations at the margins of the proximal boxes regardless of the cavity type.

Conclusions
The Korean authors, concluded that, within the limitations their study, tooth location and inlaycavity type affected the accuracy of the intraoral digital impression. The overall accuracy of digital impressions for inlay preparations was found to be clinically acceptable, but positive deviations were observed by authors at the margins of the proximal boxes.