Fig.1
The cost of each iOS is important and must be considered before buying one.

Fig.2
Macro-anatomical limitations
Anatomical structure like the mouth opening, the coronoid process, tongue and chicks, can limit the possibility to use the iOS.

Fig.3
Micro-anatomic information: texture of the abutments.
The texture of the abutment is more evident when a traditional impression with light material is taken and then scanned in the lab than an intraoral digital impression. Also a difficulty in scanning the inter proximal sub gingival margin is noted.
IOS – orange; Traditional impression– blue.

Fig.4
Teeth proximity (How close is too close?)
The finishing lines can not be detected when a confounder is closer than 0.5 mm.

Fig.5
0.5 mm is the distance needed between the marginal preparation of the abutment and the adjacent proximal tooth.

Fig.6
When there is contact between two teeth surfaces

Fig.7
The STL file can not detect the borders in between.

Fig.8
Difficulty in scanning sub gingival margins.
In this paper the technical reasons way the software ‘smooths’ the horizontal margin, due to the missing data in the scan, are clearly explained.(1,2).

Fig.9
Anytime the gingival margin is closer than 0.5 mm to the margin’s abutment, the STL file will show distortion of finishing line (1,2).

Fig.10
If the finishing line is placed into the sulcus, a certain amount of the final preparation (related with the depth of the prep itself) will be lost (3).

Fig.11
Many different iOS are available in the market and are mainly based on the same optical technology but the ‘game’ is played by the software of the system and consequently they work differently (4).

Fig.12
Comparison of scanning shots made with different iOS and compared to traditional impression.

Fig.13
A) Global and positive mean of each scanner. The line indicate mean value, the box upper and lower quartile, while the whites show overall distribution. Outliers are indicated with a diamond.
B) Median of greatest 1%. Distance in mm. The line indicates mean value, the box upper and lower quartile, while the whiskers show overall distribution. Outliers are in dictated with a diamond. All distances in mm.

Conclusions

It can be concluded that iOS can be a useful tool in dentistry but same limitations are still present and must be well known by the dentist that want to approach the market and buy one device.
Clinical procedures should be adapted to iOS and behavior of practitioners as well.

Bibliography

1. Keeling A, Wu J, Ferrari M.
Confounding factors affecting the marginal quality of an intra-oral scan.
J Dent. 2017 Apr;59:33-40. doi: 10.1016/j.jdent.2017.02.003. Epub 2017 Feb 9.
2. Ferrari M, Keeling A, Mandelli F, Lo Giudice G, Garcia-Godoy F, Joda T.
The ability of marginal detection using different intraoral scanning systems: A pilot randomized controlled trial.
Am J Dent. 2018 Oct;31(5):272-276.
3. Mandelli F, Ferrini F, Gastaldi G, Gherlone E, Ferrari M.
Improvement of a Digital Impression with Conventional Materials: Overcoming Intraoral Scanner Limitations.
Int J Prosthodont. 2017 Jul/Aug;30(4):373-376. doi: 10.11607/ijp.5138.
4. Osnes CA, Wu JH, Venezia P, Ferrari M, Keeling AJ.
Full arch precision of six intraoral scanners in vitro.
J Prosthodont Res. 2020 Jan;64(1):6-11. doi: 10.1016/j.jpor.2019.05.005. Epub 2019 Jun 18.