Lip sucking habit and associated craniofacial differences in a set of monozygotic twins.

Objective: The objective of this study was to evaluate the influence of lip sucking on dentofacial development in a pair of 6.5-year-old monozygotic twins.
Background: Lip sucking, which causes an imbalance in splanchnocraniums soft tissues pressures, can influence the hard tissues development, and contribute to orthodontic anomalies.
Methods: Analysis of lateral cephalometric X-rays was performed by 9 orthodontists. Data were compared using the Mann-Whitney and Kruskal-Wallis tests. Statistical significance was defined as p<0.05.
Results: SNA, A-NPog, and Cond-A values suggested an anterior shift of the maxilla. The 1u to SN, 1u to A-Pog, 1u to A-Pog angle, and 1u-Avert values indicated an upper incisor protrusion. While the 1l to A-Pog, 1l to A-Pog angle and 1l to Go-Me values showed a retrusion of the lower incisors, the NL-NSL implied a hard palate rotation counterclockwise. The SNA-Me indicated that the mandible of the lip-sucking patient was in a more inferior position.
Conclusion: Lip sucking can influence the skeletal development of maxilla, the position of upper and lower incisors and the position of mandible. Skeletal development of mandible seems to be unaffected (Tab. 3, Fig. 1, Ref. 26).