Nose-breathing children have more tongue strenght than children who breathe through their mouth. In addition, their tongue pressure increases with age, while mouth-breathing children do not. These are some results from research by the federal university Minas Gerais in Brazil.
The study has been conducted by researchers Azevedo, Lima, Furlan and Motta. Because the tongue plays a decisive role in oral functions, they wanted to know which factors affect the tongue strenght. Structural breathing through the mouth or through the nose appears to have a major influence, according to their study.
The study measured upward tongue pressure in children with mouth breathing (identified by open mouth behavior) and children with nasal breathing (recognized by closed lips). Forty children aged 5 to 12 years took part. The Iowa Oral Performance Instrument (IOPI) was used to measure the upward tongue pressure.
The mean upward tongue pressure of the group of children with a mouth breathing pattern was lower than that of the nose-breathing group of children. There was no difference in tongue pressure between boys and girls. There was, however, a strong and direct correlation between tongue pressure and the age of children with a nasal breathing pattern. In this group, tongue pressure increased with age. A difference in tongue pressure in children of a different age was not observed in the mouth-breathing group. The findings thus suggest that the mode of breathing (through the nose or through the mouth) plays an important role in developing tongue strength and thus oral functions.
The summary of the research can be read in this pdf.