[The effect of maxillary and mandibular lip bumper on teeth and dental arch in late mixed dentition].

PURPOSE: To study the effect of maxillary and mandibular lip bumper on tooth and dental arch in late mixed dentition. METHODS: Twelve subjects with mild or moderate crowding were selected. They were treated with maxillary and mandibular lip bumper for eight months. Analysis of cephalometrics and model measurements were done before and after treatment and paired t test were performed respectively for their changes. RESULTS: After treatment, SNA and SNB increased by 1.02 degrees and 0.97 degrees (P<0.05). Upper and lower incisor both had controlled tipping movement. The crown of incisor moved mesially and had root apex were fixed relatively. The center of rotation was close to root apex. The upper and lower molar moved differently. Upper molar was upright distally and the center of rotation was close to the crown. However, the lower molar tipped distally and the center of rotation was close to the center of resistance.The width between the first molars and length of maxillary dental arch increased by 4.12 mm and 5.09 mm (P<0.01). The width between the first molars and length of mandibular dental arch increased by 4.07 mm and 6.86 mm (P<0.01) CONCLUSION: Clinical application of lip bumper could cause transverse and vertical changes in dental arch ,which help to decrease or remove crowding.