Figure 3. Lip pressure on the upper central incisors and peri-oral muscle activity (both recorded in the resting position of the lips) in the Class I group (n = 21) and the Class II, Division 2 group (n = 21). (A) Resting lip pressure in the incisal and cervical areas, as well as the weighted average of incisal and cervical pressures. The latter parameter represents the lingual tipping effect on the upper centrals. All values are mean values of the right and left upper central incisors. (B) Resting activity of the orbicularis oris superior muscle (OOS), the orbicularis oris inferior muscle (OOI), the depressor labii inferioris muscle (DLI), and the mentalis muscle (MEN). ^*Differences to the corresponding values of the Class I group were statistically significant (Mann-Whitney U test, p < 0.01).