BACKGROUND:Many clinical cases show that micro-implant teeth in the orthodontic treatment are effective with strong resistance.OBJECTIVE:To compare the effectiveness of micro-implant headgear and mouth external devices as a strong orthodontic treatment for front teeth with Angle class Ⅱ and Ⅰmalocclusion.DESIGN,TIME AND SETTING:Case comparative analysis by X-ray was performed at Department of Orthodontics,Hospital of Guilin Medical College from June 2003 to October 2007.PARTICIPANTS:Thirty bimaxillary protrusion patients were divided into two groups:16 cases were treated with micro-implant and the others with extraoral J hook.METHODS:In the anti-implant support group,between the alveolar attack of the upper bilateral first permanent molars and premolars second intervals,micro-titanium alloy implant was implanted as anchorage off space.The implants were early used to do canine backward ligation,after the entire arch-lateral incisor teeth in the upper far in the hook traction devices,space between the implants and hook was closed using a flexible traction.In extraoral J-hook group,J-hook-class Ⅱ traction and headgear extraoral J hook slide were used to strengthen posterior teeth anchorage and close space.The traditional method was used to strengthen support on the lower first and second permanent molars on the upper band combined with support on face-bow lips and lower-profile.Preoperative and postoperative cranial lateral films were taken.MAIN OUTCOME MEASURES:To compare the line of cephalometric X-ray in two groups before and after treatment to observe the change in the location of the first molar.The relation changes of anterior teeth review of coverage and class Ⅱ molar,and improvement of facial convex were observed after treatment.RESULTS:Tissues around the implant were normal,and two cases of micro-implant loosed,which were fixed following re-implantation.Orthodontic treatment of the two groups established the normal relation between over bite and overjet of the front teeth,and corrected class Ⅱmolar relations,with stable location of the first molar,endoduction of upper front teeth and decrease in facial convex.Cephalometric X-ray results showed that in the implant group,the upper first molar advanced,whose crown was forward 0.86 mm,margin of incisors to 6.17 mm;while in the extraoral J hook group,the molars advanced 2.36 mm,and margin of incisors to 4.51 mm.The differences between two groups were significant(P

F0.01(1,5)=16. 30,P0. 05). Conclusion Laboratory results thus suggest that infection intensity is related to snail size per se, whereas prevalence in the field is related to snail size only through the correlation between size and age. In addition, under these experimental conditions, infected snails were no larger than uninfected snails, so the gigantism snails observed in the field might not be attributable to Trichobilharzia-induced effect.