Effects of maxillary second molar eruption on first molar distalization

Objectives: To investigate the effects of the maxillary second molar eruption on the first molar distalization by pendulum appliance and facebow.Methods: 19 dental Class III cases were divided into two groups (group 1, 9 cases, second molars had not erupted, mean starting age of 11.2; group 2, 10 cases, second molars had erupted, mean starting age of 12.3), and all the first molars were distalized with the pendulum appliance and facebow. Pre- and postdistalization cephalometric radiographs of two groups were analyzed according to Friedrich methods.Results: The first molars were all distalized effectively. In group 1,on average, the distance of the first molars distalizing (4.3mm) was larger than group 2 (3.5mm) (P<0.05), the distalizing speed (1.4 mm per month) was quicker than group 2 (1.1mm per month) (P<0.05), and distal tipping (5.3°) was more than twice that in group 2 (2.4°) (P<0.01).However the crowns mesially tipping of the first premolar and proclining of the maxillary incisors were all slight and there was no obvious differernce between the two groups.Conclusion: During distalizing the first molar with the pendulum appliance and facebow, the eruption state of the second molar has an obvious influence on the first molar distalization but not on the anchorage loss of premolar and incisors.