ABSTRACT
Objective To evaluate the influence of stress distributions on bone-anchored maxillary protraction at different protraction sites, so as to guide patients to choose an optimal protraction site in clinic. Methods A three-dimensional (3D) finite element model of child head with implant anchorages was establised. Four protraction sites were set according to the position of implant installation. Working condition 1: the alveolar bone at the intersection of distal 2 mm of primary lateral incisor crown distal surface and gingival cervical margin to 5 mm. Working condition 2: the alveolar bone at the intersection of mesial 2 mm of maxillary first primary molar crown mesial surface and gingival cervical margin to 5 mm. Working condition 3: the alveolar bone at the intersection of mesial 2 mm of maxillary first molar crown mesial surface and gingival cervical margin to 5 mm. Working condition 4: the alveolar bone at the intersection of distal 2 mm of maxillary first molar crown distal surface and gingival cervical margin to 5 mm. The finite element models were loaded with 500 g protraction force at each side with 30° forward direction to the occlusal plane. Stress distributions on each suture were analysed. Results The maximum stress of frontomaxillary suture was in working condition 2 (1 477-28 190 Pa). The maximum stress of nasomaxillary suture was in working condition 1 (5.296-924 Pa). The maximum stress of zygomaticomaxillary suture was in working condition 4(394.7-13 130 Pa). The maximum stress of zygomaticofrontalis suture was in working condition 4 (495.2-31 690 Pa). The maximum stress of zygomaticotemporal suture was in working condition 3 (1 148-15 870 Pa). The maximum stress of medianpalatine suture was in working condition I (6.479-730 Pa). Conclusions When the protraction sites are set in distal maxillary primary lateral incisor and mesial maxillary first primary molar, it is of positive significance to improve the concave profile, especially in nose root. When the protraction sites are set in mesial or distal maxillary first molar, it is of positive significance to improve the concave profile, especially in maxillary basal bone of the midface.
ABSTRACT
Objective To explore the relationship between the volume and function of the heart and the pathogenesis of vasovagol syncope (VVS) through the detection of the left atrial volume index(LAVI).Methods The 68 cases in the observation group were diagnosed as VVS and hospitalized in the First Hospital of Jilin University from Jan.1 to Dec.31 in 2012.The 60 cases in the control group were children and adolescents receiving healthy physical examinations during the same period.All the patients were given the examination of heart color Doppler ultrasound,head up tilt test(HUT),body height,body mass,chest X-ray and accounted the LAVI and cardiothoracic ratio was accounted.Results The average age in the observation group and the control group was(12.19 ± 2.01) and(12.15 ± 2.00) years old,respectively.And there was no statistically significant difference in age between these two groups (t =0.10,P ＞0.05).There were 23 boys and 45 girls in the observation group,and 31 boys and 29 girls in the control group.There was statistically significant difference in the ratio of gender composition between these two groups (x2 =4.16,P ＜ 0.05).The LAVI values in these two groups were (21.23 ± 2.04) mL/m2 and (23.45 ± 3.01) mL/m2,respectively.There was statistically significant difference between two groups(t =4.29,P ＜ 0.05).The LAVI values in VVS mixed inhibition (VVS-MI),VVS vascular inhibition (VVS-VI) and VVS cardiac inhibition (VVS-CI) were (21.41 ± 2.98) mL/m2,(21.06 ± 2.59) mL/m2 and(21.23 ± 3.22) mL/m2,respectively.There were statistically significant differences between VVS-MI or VVS-VI and the control groups(t =3.27,3.36,all P ＜ 0.05),but there was no statistically significant difference between VVS-CI and control groups(t =1.61,P ＞ 0.05).The cardiothoracic ratio were 0.43 ± 0.07 and 0.46 ± 0.06 in the observation group and the control group,respectively,and there was statistically significant difference between these two groups(t =3.05,P ＜0.05).Conclusions The pathogenesis of VVS is related to the size and function of left heart.The children and adolescents with smaller LAVI and cardiothoracic ratio are more susceptible to VVS.