The occlusal conditions among global populations deviate from the criteria for normal occlusion. Without appropriate guidelines, it is difficult to assess the defects for which treatment is absolutely indicated objectively. Currently, the Index of Orthodontic Treatment Need (IOTN) is the most commonly used by clinicians.

Aim

This paper aimed to analyse the studies conducted on the IOTN and to explain its applications.

Material and methods

A review of the literature from 2015–2020 using the Dentistry & Oral Sciences Source database at ebscohost.com with the keyword of IOTN.

Results

Individual criteria of both IOTN components, index applications and modifications have been presented. Advantages and clinical situations in which its use may belimited have been discussed. The Easy IOTN application can help make the IOTN popular among clinicians and make it easier to qualify a patient for the appropriate IOTN grade. The results of papers investigating the index validity have been analysed. Various indices of orthodontic treatment needs have been compared.

Conclusions

The combination of the AC and DHC components of the IOTN is the main index of treatment needs used by both clinicians and researchers as the index of choice for assessing masticatory organ function and aesthetics. Attempts have been made to develop new methods of measuring treatment needs that would be even more precise and allow to estimate the complexity of the necessary treatment and assess its effectiveness. The ICON, which is partially based on the universal assumptions of the IOTN, is a viable candidate to replace the gold standard, the IOTN.