Introduction: Oral habits interfere in the development of the functions of the stomatognathic system; there- fore, they are an etiological factor in the development of malocclusions.   Aim: To compare the frequency of oral habits and its relationship with malocclusion in children aged 4-12 in San Luis Potosí-Mexico and Medellín-Colombia.   Materials and methods: Cross-sectional, descriptive study. Convenience sample of 598 children from 4 to 12 years old (299 children per city). For data analysis, a contingency table with chi-square was prepared using spss v. 21.   Results: The most frequent oral habit for the total sample was onychophagy. When comparing the sample in both cities, onychophagy was highly frequent in San Luis Potosí, while mouth breathing was more com- mon in Medellín. In San Luis Potosí, most children with some habit had a class i molar ratio, except those with atypical swallowing, who exhibited class iii malocclusion. From the statistical point of view, atypical swallowing was the habit with the highest significance in relation to the presence of malocclusions in the total sample. A direct relationship between the presence of posterior cross bite and digit sucking in San Luis Potosí (p ≤ 0.05) was also found.   Conclusions: Atypical swallowing and open bite are directly related, which suggests that the swallowing function can be a causal factor of malocclusion; moreover, a direct relationship between digit sucking and posterior cross bite was found

Introduction: malocclusions are a series of disorders in which the anatomic phy-siologic controls of the stomatognathic system are in disharmony with the dental segments. Epidemiological studies show that malocclusion have high prevalence rates of over 60% in the studied populations. The malocclusion research in populations of 4 to 5 years old report prevalence of 70 to 80%, which evolve to 96,4% in teenagers. Dacosta and Onyeaso report that the prevalence of dental malocclusions worldwide ranges from 65 to 89%. Objective: compare the type of malocclusion that is most frequently presented in odontopediatric clinics of the Autonomous University of San Luis Potosi and the University of Antioquia. Methodology: an observational study was conducted of transversal and comparative type with a convenience sample; a higher frequency of class i type 1 was seen in group 1, with a percen-tage of 52,7%, while in group 2, the predominant malocclusions where class ii div. 1, with a percentage of 23,6% and class iii with 22,5%. Conclusion: the results in each population were different. The diagnosis of occlusal alterations is recommended to be performed in a timely manner to allow the implementation of assistance programs that include therapy and functional orthopedics of the jawbone for an early rehabilitation of the stomatognathic system.