Soft tissue index of orthodontic treatment need (STIOTN): Development and validation

Background: Index of Orthodontic Treatment Need (IOTN) emphasizes occlusal discrepancies.Facial aesthetics index (FAI) although soft-tissue-oriented, serves only as a complement rather than a standalone tool.This study thus aimed to develop and validate a Soft Tissue Index of Orthodontic Treatment Need (STIOTN) to address the limitations of existing indices that focus primarily on dental and occlusal parameters.Materials and Methods: A two-phase cross-sectional study was conducted involving index development and validation.Six key soft-tissue parametersfacial profile, nasolabial angle, lip competence, lip relation to the E-line, chin prominence, and mandibular plane angle-were defined based on clinical relevance and existing literature.Expert orthodontists (n=14) evaluated the proposed index to establish content validity, followed by application to a diverse clinical (n=310) and community (n=326) population.Reliability was assessed using Cohen's Kappa, test-retest statistics, and intraclass correlation coefficients (ICC).Results: The STIOTN demonstrated excellent content validity (S-CVI/Ave=0.96)and strong inter-rater reliability across parameters (κ=0.69-0.93,p