1. 在螺纹材料、尺寸、载荷都相同的情况下,三角形螺纹牙所受的剪应力最小,断裂载荷也比梯形螺纹和矩形螺纹高。
In the same material, dimension and load circumstance, the cut stress of the triangle thread is smallest. Its rupture load is higher than the echelon and rectangle.

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2. 结果:发现7~8岁组患儿上磨远移的距离大于10~11岁组的患儿,7~ 8岁组患儿上颌骨向前生长抑制较10~ 11岁组明显,7~ 8岁组患儿替期选用口外弓的治疗效果较10~ 11岁组为好。
Results: The more distance of maxillary molar and more obvious inhibition of maxilla bone growth forward in group of 7~8 year old children were detected than those in group of 10~11 year old children.

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3. 结果:发现7~8岁组患儿上磨远移的距离大于10~11岁组的患儿,7~ 8岁组患儿上颌骨向前生长抑制较10~ 11岁组明显,7~ 8岁组患儿替期选用口外弓的治疗效果较10~ 11岁组为好。
Results: The more distance of maxillary molar and more obvious inhibition of maxilla bone growth forward in group of 7~8 year old children were detected than those in group of 10~11 year old children.

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