目的：对外伤引起的年轻恒前牙冠折露髓行活髓切断术，并于2年以上追踪观察其根管、根尖孔发育情况。

Objective:To treatment the young permanent incisors with exposed pulps in crown by pulpotomy and observe the growth of root canals and apexogenesis following up over 2 years.

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恒昌行第一部货车。

Hang Cheung Hong's first lorry.

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铺轨机走行液压系统控制重点在于行走恒速控制和行走同步性控制。

The emphases of the running hydraulic system in track-laying machine are the constant speed control and running synchronization control.

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