Theory of quasi-circular-arc gear's shaping is discussed in this paper, and its common tooth-surface equation is developed.

叙述了准端面双圆弧齿轮的形成原理，推导了这种齿轮的通用齿面方程。

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Tooth decay is a leading chronic childhood disease -- more common than asthma -- and it's almost entirely preventable, according to the Centers for Disease Control and Prevention.

CNN: Baby's teeth: What you should know