Background: Orthodontic treatment need has commonly been assessed using treatment need indices during clinical examinations or using photographs in combination with plaster casts. Recently, the use of intraoral photographs alone to screen malocclusions has increased.

Objective: This study aimed to validate intraoral photographs for the assessment of orthodontic treatment need.

Materials and methods: The study sample consisted of case files from 30 pre-orthodontic patients aged 12-19 years. Each case file included intraoral photographs and casts. The cases were consecutively recruited from two orthodontic treatment waiting lists: 15 from the Department of Orthodontics at Folktandvården Eastmaninstitutet, Stockholm, Sweden and 15 from the Center for Orthodontics and Pediatric Dentistry, Norrköping, Public Dental Service Östergötland. Their orthodontic treatment need was assessed by four raters (calibrated orthodontists) using the indices IOTN-AC, IOTN-DHC, ICON, and DAI. The four raters individually assessed the 30 cases on three occasions: (1) photos only, (2) photos and casts, and (3) photos only. Finally, the four raters jointly made a consensus assessment using both photos and casts. For IOTN-AC and IOTN-DHC, interrater agreement was assessed with Fleiss' kappa, and validity with the Wilcoxon signed-rank test. For ICON and DAI, interrater agreement was assessed with Intra Class Correlation (ICC) (1, 2) and validity with a paired t-test.

Results: Interrater agreement for IOTN-AC was slight (0.14-0.18) and moderate for IOTN-DHC (0.51-0.57), regardless of whether photographs were used alone or combined with casts. ICON demonstrated moderate interrater agreement (0.57-0.72), while DAI showed moderate to excellent (0.70-0.91), similarly unaffected by the use of photographs alone or in combination with casts. The validity analysis, which compared the individual assessments to the consensus one, revealed equivalent differences whether the assessment involved intraoral photographs alone or in combination with casts.

Conclusion: Intraoral photographs are sufficient for assessing orthodontic treatment need because interrater agreement and validity are similar whether photos are used alone or with casts. However, interrater variability was substantial for both assessment methods.

Trial registration: ClinicalTrial.gov. identifier: NCT05038865.