To evaluate and understand the impact of dental treatment on oral health-related quality of life (OHRQoL) of adolescents.A sequential explanatory mixed-methods design was performed. A sample of 182 adolescents, aged 10 and 15 years old who had finished their dental treatment at adolescent dental clinic of Federal University of Santa Maria from 2010 to 2016, were included. Participants answered the short form of Child Perceptions Questionnaire (CPQ prior to their dental treatment and 1 month after concluding the treatment. The effect size was calculated to assess magnitude of change. In qualitative phase, semi-structured interviews took place at the end of the dental treatment. Interviews were audio-recorded and analyzed according to thematic analysis following Braun and Clarke.The effect sizes ranged from 0.35 to 1.00, and the oral symptom domain presented the greatest effect. Sixteen interviews were conducted and five themes emerged: concept of quality of life, oral health influenced by oral conditions, oral health symptoms influencing seeking care behavior, personal and subjective experiences, and dental educational environment.Dental treatment has an uncountable meaning for adolescents because it has a psychosocial meaning in this phase of life and it is able to improve their OHRQoL.