RESUMEN
BACKGROUND: A study is made of posterior crossbite in deciduous dentition and its possible association to extrinsic factors (bad oral habits). METHODS: A total of 1168 Spanish children between 3 and 6 years of age were included in the study. Exploration of the oral cavity was performed to assess the presence of crossbite (uni- or bilateral and/or functional), and a questionnaire was administered to the parents or caregivers to determine the presence of bad oral habits and their duration. RESULTS: In occlusion, 19.7% of the cases (n = 230) presented uni- or bilateral posterior crossbite. On adopting centric relation confronting the midlines, crossbite persisted in 165 children, indicating that 65 cases were due to premature contacts (functional crossbite). The identified favoring factors were pacifier use, thumb sucking, oral breathing and tongue thrusting or immature swallowing. DISCUSSION: Most studies in the literature report a relationship between posterior crossbite and bad oral habits. The proportion of posterior crossbites identified in our study (16.6%) is consistent with the data published by authors such as Kobayashi, Limeira or Paolantonio, among others, but differs from the results of Zhifei Zhou, Peres or Germa. In coincidence with most studies, we recorded a statistically significant association between posterior crossbite and bad oral habits. CONCLUSIONS: Bad oral habits favor the appearance of posterior crossbite, and the duration of the habit, its intensity (in the case of thumb sucking) and type (in the case of pacifier use) act as influencing factors. Functional study characterized the types of posterior crossbites and identified those attributable to premature contacts. This aspect has not been addressed by previous studies, and we consider the findings to be very interesting for analyzing and identifying the features of true crossbites.